extend.texi (PowerPC AltiVec/VSX Built-in Functions): Document new power8 builtins.

[thirdparty/gcc.git] / gcc / doc / extend.texi

@c Copyright (C) 1988-2013 Free Software Foundation, Inc.

@c This is part of the GCC manual.
@c For copying conditions, see the file gcc.texi.

@node C Extensions
@chapter Extensions to the C Language Family
@cindex extensions, C language
@cindex C language extensions

@opindex pedantic
GNU C provides several language features not found in ISO standard C@.
(The @option{-pedantic} option directs GCC to print a warning message if
any of these features is used.)  To test for the availability of these
features in conditional compilation, check for a predefined macro
@code{__GNUC__}, which is always defined under GCC@.

These extensions are available in C and Objective-C@.  Most of them are
also available in C++.  @xref{C++ Extensions,,Extensions to the
C++ Language}, for extensions that apply @emph{only} to C++.

Some features that are in ISO C99 but not C90 or C++ are also, as
extensions, accepted by GCC in C90 mode and in C++.

@menu
* Statement Exprs::     Putting statements and declarations inside expressions.
* Local Labels::        Labels local to a block.
* Labels as Values::    Getting pointers to labels, and computed gotos.
* Nested Functions::    As in Algol and Pascal, lexical scoping of functions.
* Constructing Calls::  Dispatching a call to another function.
* Typeof::              @code{typeof}: referring to the type of an expression.
* Conditionals::        Omitting the middle operand of a @samp{?:} expression.
* __int128::                    128-bit integers---@code{__int128}.
* Long Long::           Double-word integers---@code{long long int}.
* Complex::             Data types for complex numbers.
* Floating Types::      Additional Floating Types.
* Half-Precision::      Half-Precision Floating Point.
* Decimal Float::       Decimal Floating Types.
* Hex Floats::          Hexadecimal floating-point constants.
* Fixed-Point::         Fixed-Point Types.
* Named Address Spaces::Named address spaces.
* Zero Length::         Zero-length arrays.
* Empty Structures::    Structures with no members.
* Variable Length::     Arrays whose length is computed at run time.
* Variadic Macros::     Macros with a variable number of arguments.
* Escaped Newlines::    Slightly looser rules for escaped newlines.
* Subscripting::        Any array can be subscripted, even if not an lvalue.
* Pointer Arith::       Arithmetic on @code{void}-pointers and function pointers.
* Initializers::        Non-constant initializers.
* Compound Literals::   Compound literals give structures, unions
                        or arrays as values.
* Designated Inits::    Labeling elements of initializers.
* Case Ranges::         `case 1 ... 9' and such.
* Cast to Union::       Casting to union type from any member of the union.
* Mixed Declarations::  Mixing declarations and code.
* Function Attributes:: Declaring that functions have no side effects,
                        or that they can never return.
* Attribute Syntax::    Formal syntax for attributes.
* Function Prototypes:: Prototype declarations and old-style definitions.
* C++ Comments::        C++ comments are recognized.
* Dollar Signs::        Dollar sign is allowed in identifiers.
* Character Escapes::   @samp{\e} stands for the character @key{ESC}.
* Variable Attributes:: Specifying attributes of variables.
* Type Attributes::     Specifying attributes of types.
* Alignment::           Inquiring about the alignment of a type or variable.
* Inline::              Defining inline functions (as fast as macros).
* Volatiles::           What constitutes an access to a volatile object.
* Extended Asm::        Assembler instructions with C expressions as operands.
                        (With them you can define ``built-in'' functions.)
* Constraints::         Constraints for asm operands
* Asm Labels::          Specifying the assembler name to use for a C symbol.
* Explicit Reg Vars::   Defining variables residing in specified registers.
* Alternate Keywords::  @code{__const__}, @code{__asm__}, etc., for header files.
* Incomplete Enums::    @code{enum foo;}, with details to follow.
* Function Names::      Printable strings which are the name of the current
                        function.
* Return Address::      Getting the return or frame address of a function.
* Vector Extensions::   Using vector instructions through built-in functions.
* Offsetof::            Special syntax for implementing @code{offsetof}.
* __sync Builtins::     Legacy built-in functions for atomic memory access.
* __atomic Builtins::   Atomic built-in functions with memory model.
* x86 specific memory model extensions for transactional memory:: x86 memory models.
* Object Size Checking:: Built-in functions for limited buffer overflow
                        checking.
* Cilk Plus Builtins::  Built-in functions for the Cilk Plus language extension.
* Other Builtins::      Other built-in functions.
* Target Builtins::     Built-in functions specific to particular targets.
* Target Format Checks:: Format checks specific to particular targets.
* Pragmas::             Pragmas accepted by GCC.
* Unnamed Fields::      Unnamed struct/union fields within structs/unions.
* Thread-Local::        Per-thread variables.
* Binary constants::    Binary constants using the @samp{0b} prefix.
@end menu

@node Statement Exprs
@section Statements and Declarations in Expressions
@cindex statements inside expressions
@cindex declarations inside expressions
@cindex expressions containing statements
@cindex macros, statements in expressions

@c the above section title wrapped and causes an underfull hbox.. i
@c changed it from "within" to "in". --mew 4feb93
A compound statement enclosed in parentheses may appear as an expression
in GNU C@.  This allows you to use loops, switches, and local variables
within an expression.

Recall that a compound statement is a sequence of statements surrounded
by braces; in this construct, parentheses go around the braces.  For
example:

@smallexample
(@{ int y = foo (); int z;
   if (y > 0) z = y;
   else z = - y;
   z; @})
@end smallexample

@noindent
is a valid (though slightly more complex than necessary) expression
for the absolute value of @code{foo ()}.

The last thing in the compound statement should be an expression
followed by a semicolon; the value of this subexpression serves as the
value of the entire construct.  (If you use some other kind of statement
last within the braces, the construct has type @code{void}, and thus
effectively no value.)

This feature is especially useful in making macro definitions ``safe'' (so
that they evaluate each operand exactly once).  For example, the
``maximum'' function is commonly defined as a macro in standard C as
follows:

@smallexample
#define max(a,b) ((a) > (b) ? (a) : (b))
@end smallexample

@noindent
@cindex side effects, macro argument
But this definition computes either @var{a} or @var{b} twice, with bad
results if the operand has side effects.  In GNU C, if you know the
type of the operands (here taken as @code{int}), you can define
the macro safely as follows:

@smallexample
#define maxint(a,b) \
  (@{int _a = (a), _b = (b); _a > _b ? _a : _b; @})
@end smallexample

Embedded statements are not allowed in constant expressions, such as
the value of an enumeration constant, the width of a bit-field, or
the initial value of a static variable.

If you don't know the type of the operand, you can still do this, but you
must use @code{typeof} (@pxref{Typeof}).

In G++, the result value of a statement expression undergoes array and
function pointer decay, and is returned by value to the enclosing
expression.  For instance, if @code{A} is a class, then

@smallexample
        A a;

        (@{a;@}).Foo ()
@end smallexample

@noindent
constructs a temporary @code{A} object to hold the result of the
statement expression, and that is used to invoke @code{Foo}.
Therefore the @code{this} pointer observed by @code{Foo} is not the
address of @code{a}.

In a statement expression, any temporaries created within a statement
are destroyed at that statement's end.  This makes statement
expressions inside macros slightly different from function calls.  In
the latter case temporaries introduced during argument evaluation are
destroyed at the end of the statement that includes the function
call.  In the statement expression case they are destroyed during
the statement expression.  For instance,

@smallexample
#define macro(a)  (@{__typeof__(a) b = (a); b + 3; @})
template<typename T> T function(T a) @{ T b = a; return b + 3; @}

void foo ()
@{
  macro (X ());
  function (X ());
@}
@end smallexample

@noindent
has different places where temporaries are destroyed.  For the
@code{macro} case, the temporary @code{X} is destroyed just after
the initialization of @code{b}.  In the @code{function} case that
temporary is destroyed when the function returns.

These considerations mean that it is probably a bad idea to use
statement expressions of this form in header files that are designed to
work with C++.  (Note that some versions of the GNU C Library contained
header files using statement expressions that lead to precisely this
bug.)

Jumping into a statement expression with @code{goto} or using a
@code{switch} statement outside the statement expression with a
@code{case} or @code{default} label inside the statement expression is
not permitted.  Jumping into a statement expression with a computed
@code{goto} (@pxref{Labels as Values}) has undefined behavior.
Jumping out of a statement expression is permitted, but if the
statement expression is part of a larger expression then it is
unspecified which other subexpressions of that expression have been
evaluated except where the language definition requires certain
subexpressions to be evaluated before or after the statement
expression.  In any case, as with a function call, the evaluation of a
statement expression is not interleaved with the evaluation of other
parts of the containing expression.  For example,

@smallexample
  foo (), ((@{ bar1 (); goto a; 0; @}) + bar2 ()), baz();
@end smallexample

@noindent
calls @code{foo} and @code{bar1} and does not call @code{baz} but
may or may not call @code{bar2}.  If @code{bar2} is called, it is
called after @code{foo} and before @code{bar1}.

@node Local Labels
@section Locally Declared Labels
@cindex local labels
@cindex macros, local labels

GCC allows you to declare @dfn{local labels} in any nested block
scope.  A local label is just like an ordinary label, but you can
only reference it (with a @code{goto} statement, or by taking its
address) within the block in which it is declared.

A local label declaration looks like this:

@smallexample
__label__ @var{label};
@end smallexample

@noindent
or

@smallexample
__label__ @var{label1}, @var{label2}, /* @r{@dots{}} */;
@end smallexample

Local label declarations must come at the beginning of the block,
before any ordinary declarations or statements.

The label declaration defines the label @emph{name}, but does not define
the label itself.  You must do this in the usual way, with
@code{@var{label}:}, within the statements of the statement expression.

The local label feature is useful for complex macros.  If a macro
contains nested loops, a @code{goto} can be useful for breaking out of
them.  However, an ordinary label whose scope is the whole function
cannot be used: if the macro can be expanded several times in one
function, the label is multiply defined in that function.  A
local label avoids this problem.  For example:

@smallexample
#define SEARCH(value, array, target)              \
do @{                                              \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i < max; i++)                       \
    for (j = 0; j < max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        @{ (value) = i; goto found; @}              \
  (value) = -1;                                   \
 found:;                                          \
@} while (0)
@end smallexample

This could also be written using a statement expression:

@smallexample
#define SEARCH(array, target)                     \
(@{                                                \
  __label__ found;                                \
  typeof (target) _SEARCH_target = (target);      \
  typeof (*(array)) *_SEARCH_array = (array);     \
  int i, j;                                       \
  int value;                                      \
  for (i = 0; i < max; i++)                       \
    for (j = 0; j < max; j++)                     \
      if (_SEARCH_array[i][j] == _SEARCH_target)  \
        @{ value = i; goto found; @}                \
  value = -1;                                     \
 found:                                           \
  value;                                          \
@})
@end smallexample

Local label declarations also make the labels they declare visible to
nested functions, if there are any.  @xref{Nested Functions}, for details.

@node Labels as Values
@section Labels as Values
@cindex labels as values
@cindex computed gotos
@cindex goto with computed label
@cindex address of a label

You can get the address of a label defined in the current function
(or a containing function) with the unary operator @samp{&&}.  The
value has type @code{void *}.  This value is a constant and can be used
wherever a constant of that type is valid.  For example:

@smallexample
void *ptr;
/* @r{@dots{}} */
ptr = &&foo;
@end smallexample

To use these values, you need to be able to jump to one.  This is done
with the computed goto statement@footnote{The analogous feature in
Fortran is called an assigned goto, but that name seems inappropriate in
C, where one can do more than simply store label addresses in label
variables.}, @code{goto *@var{exp};}.  For example,

@smallexample
goto *ptr;
@end smallexample

@noindent
Any expression of type @code{void *} is allowed.

One way of using these constants is in initializing a static array that
serves as a jump table:

@smallexample
static void *array[] = @{ &&foo, &&bar, &&hack @};
@end smallexample

@noindent
Then you can select a label with indexing, like this:

@smallexample
goto *array[i];
@end smallexample

@noindent
Note that this does not check whether the subscript is in bounds---array
indexing in C never does that.

Such an array of label values serves a purpose much like that of the
@code{switch} statement.  The @code{switch} statement is cleaner, so
use that rather than an array unless the problem does not fit a
@code{switch} statement very well.

Another use of label values is in an interpreter for threaded code.
The labels within the interpreter function can be stored in the
threaded code for super-fast dispatching.

You may not use this mechanism to jump to code in a different function.
If you do that, totally unpredictable things happen.  The best way to
avoid this is to store the label address only in automatic variables and
never pass it as an argument.

An alternate way to write the above example is

@smallexample
static const int array[] = @{ &&foo - &&foo, &&bar - &&foo,
                             &&hack - &&foo @};
goto *(&&foo + array[i]);
@end smallexample

@noindent
This is more friendly to code living in shared libraries, as it reduces
the number of dynamic relocations that are needed, and by consequence,
allows the data to be read-only.

The @code{&&foo} expressions for the same label might have different
values if the containing function is inlined or cloned.  If a program
relies on them being always the same,
@code{__attribute__((__noinline__,__noclone__))} should be used to
prevent inlining and cloning.  If @code{&&foo} is used in a static
variable initializer, inlining and cloning is forbidden.

@node Nested Functions
@section Nested Functions
@cindex nested functions
@cindex downward funargs
@cindex thunks

A @dfn{nested function} is a function defined inside another function.
Nested functions are supported as an extension in GNU C, but are not
supported by GNU C++.

The nested function's name is local to the block where it is defined.
For example, here we define a nested function named @code{square}, and
call it twice:

@smallexample
@group
foo (double a, double b)
@{
  double square (double z) @{ return z * z; @}

  return square (a) + square (b);
@}
@end group
@end smallexample

The nested function can access all the variables of the containing
function that are visible at the point of its definition.  This is
called @dfn{lexical scoping}.  For example, here we show a nested
function which uses an inherited variable named @code{offset}:

@smallexample
@group
bar (int *array, int offset, int size)
@{
  int access (int *array, int index)
    @{ return array[index + offset]; @}
  int i;
  /* @r{@dots{}} */
  for (i = 0; i < size; i++)
    /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */
@}
@end group
@end smallexample

Nested function definitions are permitted within functions in the places
where variable definitions are allowed; that is, in any block, mixed
with the other declarations and statements in the block.

It is possible to call the nested function from outside the scope of its
name by storing its address or passing the address to another function:

@smallexample
hack (int *array, int size)
@{
  void store (int index, int value)
    @{ array[index] = value; @}

  intermediate (store, size);
@}
@end smallexample

Here, the function @code{intermediate} receives the address of
@code{store} as an argument.  If @code{intermediate} calls @code{store},
the arguments given to @code{store} are used to store into @code{array}.
But this technique works only so long as the containing function
(@code{hack}, in this example) does not exit.

If you try to call the nested function through its address after the
containing function exits, all hell breaks loose.  If you try
to call it after a containing scope level exits, and if it refers
to some of the variables that are no longer in scope, you may be lucky,
but it's not wise to take the risk.  If, however, the nested function
does not refer to anything that has gone out of scope, you should be
safe.

GCC implements taking the address of a nested function using a technique
called @dfn{trampolines}.  This technique was described in
@cite{Lexical Closures for C++} (Thomas M. Breuel, USENIX
C++ Conference Proceedings, October 17-21, 1988).

A nested function can jump to a label inherited from a containing
function, provided the label is explicitly declared in the containing
function (@pxref{Local Labels}).  Such a jump returns instantly to the
containing function, exiting the nested function that did the
@code{goto} and any intermediate functions as well.  Here is an example:

@smallexample
@group
bar (int *array, int offset, int size)
@{
  __label__ failure;
  int access (int *array, int index)
    @{
      if (index > size)
        goto failure;
      return array[index + offset];
    @}
  int i;
  /* @r{@dots{}} */
  for (i = 0; i < size; i++)
    /* @r{@dots{}} */ access (array, i) /* @r{@dots{}} */
  /* @r{@dots{}} */
  return 0;

 /* @r{Control comes here from @code{access}
    if it detects an error.}  */
 failure:
  return -1;
@}
@end group
@end smallexample

A nested function always has no linkage.  Declaring one with
@code{extern} or @code{static} is erroneous.  If you need to declare the nested function
before its definition, use @code{auto} (which is otherwise meaningless
for function declarations).

@smallexample
bar (int *array, int offset, int size)
@{
  __label__ failure;
  auto int access (int *, int);
  /* @r{@dots{}} */
  int access (int *array, int index)
    @{
      if (index > size)
        goto failure;
      return array[index + offset];
    @}
  /* @r{@dots{}} */
@}
@end smallexample

@node Constructing Calls
@section Constructing Function Calls
@cindex constructing calls
@cindex forwarding calls

Using the built-in functions described below, you can record
the arguments a function received, and call another function
with the same arguments, without knowing the number or types
of the arguments.

You can also record the return value of that function call,
and later return that value, without knowing what data type
the function tried to return (as long as your caller expects
that data type).

However, these built-in functions may interact badly with some
sophisticated features or other extensions of the language.  It
is, therefore, not recommended to use them outside very simple
functions acting as mere forwarders for their arguments.

@deftypefn {Built-in Function} {void *} __builtin_apply_args ()
This built-in function returns a pointer to data
describing how to perform a call with the same arguments as are passed
to the current function.

The function saves the arg pointer register, structure value address,
and all registers that might be used to pass arguments to a function
into a block of memory allocated on the stack.  Then it returns the
address of that block.
@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_apply (void (*@var{function})(), void *@var{arguments}, size_t @var{size})
This built-in function invokes @var{function}
with a copy of the parameters described by @var{arguments}
and @var{size}.

The value of @var{arguments} should be the value returned by
@code{__builtin_apply_args}.  The argument @var{size} specifies the size
of the stack argument data, in bytes.

This function returns a pointer to data describing
how to return whatever value is returned by @var{function}.  The data
is saved in a block of memory allocated on the stack.

It is not always simple to compute the proper value for @var{size}.  The
value is used by @code{__builtin_apply} to compute the amount of data
that should be pushed on the stack and copied from the incoming argument
area.
@end deftypefn

@deftypefn {Built-in Function} {void} __builtin_return (void *@var{result})
This built-in function returns the value described by @var{result} from
the containing function.  You should specify, for @var{result}, a value
returned by @code{__builtin_apply}.
@end deftypefn

@deftypefn {Built-in Function} {} __builtin_va_arg_pack ()
This built-in function represents all anonymous arguments of an inline
function.  It can be used only in inline functions that are always
inlined, never compiled as a separate function, such as those using
@code{__attribute__ ((__always_inline__))} or
@code{__attribute__ ((__gnu_inline__))} extern inline functions.
It must be only passed as last argument to some other function
with variable arguments.  This is useful for writing small wrapper
inlines for variable argument functions, when using preprocessor
macros is undesirable.  For example:
@smallexample
extern int myprintf (FILE *f, const char *format, ...);
extern inline __attribute__ ((__gnu_inline__)) int
myprintf (FILE *f, const char *format, ...)
@{
  int r = fprintf (f, "myprintf: ");
  if (r < 0)
    return r;
  int s = fprintf (f, format, __builtin_va_arg_pack ());
  if (s < 0)
    return s;
  return r + s;
@}
@end smallexample
@end deftypefn

@deftypefn {Built-in Function} {size_t} __builtin_va_arg_pack_len ()
This built-in function returns the number of anonymous arguments of
an inline function.  It can be used only in inline functions that
are always inlined, never compiled as a separate function, such
as those using @code{__attribute__ ((__always_inline__))} or
@code{__attribute__ ((__gnu_inline__))} extern inline functions.
For example following does link- or run-time checking of open
arguments for optimized code:
@smallexample
#ifdef __OPTIMIZE__
extern inline __attribute__((__gnu_inline__)) int
myopen (const char *path, int oflag, ...)
@{
  if (__builtin_va_arg_pack_len () > 1)
    warn_open_too_many_arguments ();

  if (__builtin_constant_p (oflag))
    @{
      if ((oflag & O_CREAT) != 0 && __builtin_va_arg_pack_len () < 1)
        @{
          warn_open_missing_mode ();
          return __open_2 (path, oflag);
        @}
      return open (path, oflag, __builtin_va_arg_pack ());
    @}

  if (__builtin_va_arg_pack_len () < 1)
    return __open_2 (path, oflag);

  return open (path, oflag, __builtin_va_arg_pack ());
@}
#endif
@end smallexample
@end deftypefn

@node Typeof
@section Referring to a Type with @code{typeof}
@findex typeof
@findex sizeof
@cindex macros, types of arguments

Another way to refer to the type of an expression is with @code{typeof}.
The syntax of using of this keyword looks like @code{sizeof}, but the
construct acts semantically like a type name defined with @code{typedef}.

There are two ways of writing the argument to @code{typeof}: with an
expression or with a type.  Here is an example with an expression:

@smallexample
typeof (x[0](1))
@end smallexample

@noindent
This assumes that @code{x} is an array of pointers to functions;
the type described is that of the values of the functions.

Here is an example with a typename as the argument:

@smallexample
typeof (int *)
@end smallexample

@noindent
Here the type described is that of pointers to @code{int}.

If you are writing a header file that must work when included in ISO C
programs, write @code{__typeof__} instead of @code{typeof}.
@xref{Alternate Keywords}.

A @code{typeof} construct can be used anywhere a typedef name can be
used.  For example, you can use it in a declaration, in a cast, or inside
of @code{sizeof} or @code{typeof}.

The operand of @code{typeof} is evaluated for its side effects if and
only if it is an expression of variably modified type or the name of
such a type.

@code{typeof} is often useful in conjunction with
statement expressions (@pxref{Statement Exprs}).
Here is how the two together can
be used to define a safe ``maximum'' macro which operates on any
arithmetic type and evaluates each of its arguments exactly once:

@smallexample
#define max(a,b) \
  (@{ typeof (a) _a = (a); \
      typeof (b) _b = (b); \
    _a > _b ? _a : _b; @})
@end smallexample

@cindex underscores in variables in macros
@cindex @samp{_} in variables in macros
@cindex local variables in macros
@cindex variables, local, in macros
@cindex macros, local variables in

The reason for using names that start with underscores for the local
variables is to avoid conflicts with variable names that occur within the
expressions that are substituted for @code{a} and @code{b}.  Eventually we
hope to design a new form of declaration syntax that allows you to declare
variables whose scopes start only after their initializers; this will be a
more reliable way to prevent such conflicts.

@noindent
Some more examples of the use of @code{typeof}:

@itemize @bullet
@item
This declares @code{y} with the type of what @code{x} points to.

@smallexample
typeof (*x) y;
@end smallexample

@item
This declares @code{y} as an array of such values.

@smallexample
typeof (*x) y[4];
@end smallexample

@item
This declares @code{y} as an array of pointers to characters:

@smallexample
typeof (typeof (char *)[4]) y;
@end smallexample

@noindent
It is equivalent to the following traditional C declaration:

@smallexample
char *y[4];
@end smallexample

To see the meaning of the declaration using @code{typeof}, and why it
might be a useful way to write, rewrite it with these macros:

@smallexample
#define pointer(T)  typeof(T *)
#define array(T, N) typeof(T [N])
@end smallexample

@noindent
Now the declaration can be rewritten this way:

@smallexample
array (pointer (char), 4) y;
@end smallexample

@noindent
Thus, @code{array (pointer (char), 4)} is the type of arrays of 4
pointers to @code{char}.
@end itemize

@emph{Compatibility Note:} In addition to @code{typeof}, GCC 2 supported
a more limited extension that permitted one to write

@smallexample
typedef @var{T} = @var{expr};
@end smallexample

@noindent
with the effect of declaring @var{T} to have the type of the expression
@var{expr}.  This extension does not work with GCC 3 (versions between
3.0 and 3.2 crash; 3.2.1 and later give an error).  Code that
relies on it should be rewritten to use @code{typeof}:

@smallexample
typedef typeof(@var{expr}) @var{T};
@end smallexample

@noindent
This works with all versions of GCC@.

@node Conditionals
@section Conditionals with Omitted Operands
@cindex conditional expressions, extensions
@cindex omitted middle-operands
@cindex middle-operands, omitted
@cindex extensions, @code{?:}
@cindex @code{?:} extensions

The middle operand in a conditional expression may be omitted.  Then
if the first operand is nonzero, its value is the value of the conditional
expression.

Therefore, the expression

@smallexample
x ? : y
@end smallexample

@noindent
has the value of @code{x} if that is nonzero; otherwise, the value of
@code{y}.

This example is perfectly equivalent to

@smallexample
x ? x : y
@end smallexample

@cindex side effect in @code{?:}
@cindex @code{?:} side effect
@noindent
In this simple case, the ability to omit the middle operand is not
especially useful.  When it becomes useful is when the first operand does,
or may (if it is a macro argument), contain a side effect.  Then repeating
the operand in the middle would perform the side effect twice.  Omitting
the middle operand uses the value already computed without the undesirable
effects of recomputing it.

@node __int128
@section 128-bit integers
@cindex @code{__int128} data types

As an extension the integer scalar type @code{__int128} is supported for
targets which have an integer mode wide enough to hold 128 bits.
Simply write @code{__int128} for a signed 128-bit integer, or
@code{unsigned __int128} for an unsigned 128-bit integer.  There is no
support in GCC for expressing an integer constant of type @code{__int128}
for targets with @code{long long} integer less than 128 bits wide.

@node Long Long
@section Double-Word Integers
@cindex @code{long long} data types
@cindex double-word arithmetic
@cindex multiprecision arithmetic
@cindex @code{LL} integer suffix
@cindex @code{ULL} integer suffix

ISO C99 supports data types for integers that are at least 64 bits wide,
and as an extension GCC supports them in C90 mode and in C++.
Simply write @code{long long int} for a signed integer, or
@code{unsigned long long int} for an unsigned integer.  To make an
integer constant of type @code{long long int}, add the suffix @samp{LL}
to the integer.  To make an integer constant of type @code{unsigned long
long int}, add the suffix @samp{ULL} to the integer.

You can use these types in arithmetic like any other integer types.
Addition, subtraction, and bitwise boolean operations on these types
are open-coded on all types of machines.  Multiplication is open-coded
if the machine supports a fullword-to-doubleword widening multiply
instruction.  Division and shifts are open-coded only on machines that
provide special support.  The operations that are not open-coded use
special library routines that come with GCC@.

There may be pitfalls when you use @code{long long} types for function
arguments without function prototypes.  If a function
expects type @code{int} for its argument, and you pass a value of type
@code{long long int}, confusion results because the caller and the
subroutine disagree about the number of bytes for the argument.
Likewise, if the function expects @code{long long int} and you pass
@code{int}.  The best way to avoid such problems is to use prototypes.

@node Complex
@section Complex Numbers
@cindex complex numbers
@cindex @code{_Complex} keyword
@cindex @code{__complex__} keyword

ISO C99 supports complex floating data types, and as an extension GCC
supports them in C90 mode and in C++.  GCC also supports complex integer data
types which are not part of ISO C99.  You can declare complex types
using the keyword @code{_Complex}.  As an extension, the older GNU
keyword @code{__complex__} is also supported.

For example, @samp{_Complex double x;} declares @code{x} as a
variable whose real part and imaginary part are both of type
@code{double}.  @samp{_Complex short int y;} declares @code{y} to
have real and imaginary parts of type @code{short int}; this is not
likely to be useful, but it shows that the set of complex types is
complete.

To write a constant with a complex data type, use the suffix @samp{i} or
@samp{j} (either one; they are equivalent).  For example, @code{2.5fi}
has type @code{_Complex float} and @code{3i} has type
@code{_Complex int}.  Such a constant always has a pure imaginary
value, but you can form any complex value you like by adding one to a
real constant.  This is a GNU extension; if you have an ISO C99
conforming C library (such as the GNU C Library), and want to construct complex
constants of floating type, you should include @code{<complex.h>} and
use the macros @code{I} or @code{_Complex_I} instead.

@cindex @code{__real__} keyword
@cindex @code{__imag__} keyword
To extract the real part of a complex-valued expression @var{exp}, write
@code{__real__ @var{exp}}.  Likewise, use @code{__imag__} to
extract the imaginary part.  This is a GNU extension; for values of
floating type, you should use the ISO C99 functions @code{crealf},
@code{creal}, @code{creall}, @code{cimagf}, @code{cimag} and
@code{cimagl}, declared in @code{<complex.h>} and also provided as
built-in functions by GCC@.

@cindex complex conjugation
The operator @samp{~} performs complex conjugation when used on a value
with a complex type.  This is a GNU extension; for values of
floating type, you should use the ISO C99 functions @code{conjf},
@code{conj} and @code{conjl}, declared in @code{<complex.h>} and also
provided as built-in functions by GCC@.

GCC can allocate complex automatic variables in a noncontiguous
fashion; it's even possible for the real part to be in a register while
the imaginary part is on the stack (or vice versa).  Only the DWARF 2
debug info format can represent this, so use of DWARF 2 is recommended.
If you are using the stabs debug info format, GCC describes a noncontiguous
complex variable as if it were two separate variables of noncomplex type.
If the variable's actual name is @code{foo}, the two fictitious
variables are named @code{foo$real} and @code{foo$imag}.  You can
examine and set these two fictitious variables with your debugger.

@node Floating Types
@section Additional Floating Types
@cindex additional floating types
@cindex @code{__float80} data type
@cindex @code{__float128} data type
@cindex @code{w} floating point suffix
@cindex @code{q} floating point suffix
@cindex @code{W} floating point suffix
@cindex @code{Q} floating point suffix

As an extension, GNU C supports additional floating
types, @code{__float80} and @code{__float128} to support 80-bit
(@code{XFmode}) and 128-bit (@code{TFmode}) floating types.
Support for additional types includes the arithmetic operators:
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types.  Use a suffix @samp{w} or @samp{W}
in a literal constant of type @code{__float80} and @samp{q} or @samp{Q}
for @code{_float128}.  You can declare complex types using the
corresponding internal complex type, @code{XCmode} for @code{__float80}
type and @code{TCmode} for @code{__float128} type:

@smallexample
typedef _Complex float __attribute__((mode(TC))) _Complex128;
typedef _Complex float __attribute__((mode(XC))) _Complex80;
@end smallexample

Not all targets support additional floating-point types.  @code{__float80}
and @code{__float128} types are supported on i386, x86_64 and IA-64 targets.
The @code{__float128} type is supported on hppa HP-UX targets.

@node Half-Precision
@section Half-Precision Floating Point
@cindex half-precision floating point
@cindex @code{__fp16} data type

On ARM targets, GCC supports half-precision (16-bit) floating point via
the @code{__fp16} type.  You must enable this type explicitly
with the @option{-mfp16-format} command-line option in order to use it.

ARM supports two incompatible representations for half-precision
floating-point values.  You must choose one of the representations and
use it consistently in your program.

Specifying @option{-mfp16-format=ieee} selects the IEEE 754-2008 format.
This format can represent normalized values in the range of @math{2^{-14}} to 65504.
There are 11 bits of significand precision, approximately 3
decimal digits.

Specifying @option{-mfp16-format=alternative} selects the ARM
alternative format.  This representation is similar to the IEEE
format, but does not support infinities or NaNs.  Instead, the range
of exponents is extended, so that this format can represent normalized
values in the range of @math{2^{-14}} to 131008.

The @code{__fp16} type is a storage format only.  For purposes
of arithmetic and other operations, @code{__fp16} values in C or C++
expressions are automatically promoted to @code{float}.  In addition,
you cannot declare a function with a return value or parameters
of type @code{__fp16}.

Note that conversions from @code{double} to @code{__fp16}
involve an intermediate conversion to @code{float}.  Because
of rounding, this can sometimes produce a different result than a
direct conversion.

ARM provides hardware support for conversions between
@code{__fp16} and @code{float} values
as an extension to VFP and NEON (Advanced SIMD).  GCC generates
code using these hardware instructions if you compile with
options to select an FPU that provides them;
for example, @option{-mfpu=neon-fp16 -mfloat-abi=softfp},
in addition to the @option{-mfp16-format} option to select
a half-precision format.

Language-level support for the @code{__fp16} data type is
independent of whether GCC generates code using hardware floating-point
instructions.  In cases where hardware support is not specified, GCC
implements conversions between @code{__fp16} and @code{float} values
as library calls.

@node Decimal Float
@section Decimal Floating Types
@cindex decimal floating types
@cindex @code{_Decimal32} data type
@cindex @code{_Decimal64} data type
@cindex @code{_Decimal128} data type
@cindex @code{df} integer suffix
@cindex @code{dd} integer suffix
@cindex @code{dl} integer suffix
@cindex @code{DF} integer suffix
@cindex @code{DD} integer suffix
@cindex @code{DL} integer suffix

As an extension, GNU C supports decimal floating types as
defined in the N1312 draft of ISO/IEC WDTR24732.  Support for decimal
floating types in GCC will evolve as the draft technical report changes.
Calling conventions for any target might also change.  Not all targets
support decimal floating types.

The decimal floating types are @code{_Decimal32}, @code{_Decimal64}, and
@code{_Decimal128}.  They use a radix of ten, unlike the floating types
@code{float}, @code{double}, and @code{long double} whose radix is not
specified by the C standard but is usually two.

Support for decimal floating types includes the arithmetic operators
add, subtract, multiply, divide; unary arithmetic operators;
relational operators; equality operators; and conversions to and from
integer and other floating types.  Use a suffix @samp{df} or
@samp{DF} in a literal constant of type @code{_Decimal32}, @samp{dd}
or @samp{DD} for @code{_Decimal64}, and @samp{dl} or @samp{DL} for
@code{_Decimal128}.

GCC support of decimal float as specified by the draft technical report
is incomplete:

@itemize @bullet
@item
When the value of a decimal floating type cannot be represented in the
integer type to which it is being converted, the result is undefined
rather than the result value specified by the draft technical report.

@item
GCC does not provide the C library functionality associated with
@file{math.h}, @file{fenv.h}, @file{stdio.h}, @file{stdlib.h}, and
@file{wchar.h}, which must come from a separate C library implementation.
Because of this the GNU C compiler does not define macro
@code{__STDC_DEC_FP__} to indicate that the implementation conforms to
the technical report.
@end itemize

Types @code{_Decimal32}, @code{_Decimal64}, and @code{_Decimal128}
are supported by the DWARF 2 debug information format.

@node Hex Floats
@section Hex Floats
@cindex hex floats

ISO C99 supports floating-point numbers written not only in the usual
decimal notation, such as @code{1.55e1}, but also numbers such as
@code{0x1.fp3} written in hexadecimal format.  As a GNU extension, GCC
supports this in C90 mode (except in some cases when strictly
conforming) and in C++.  In that format the
@samp{0x} hex introducer and the @samp{p} or @samp{P} exponent field are
mandatory.  The exponent is a decimal number that indicates the power of
2 by which the significant part is multiplied.  Thus @samp{0x1.f} is
@tex
$1 {15\over16}$,
@end tex
@ifnottex
1 15/16,
@end ifnottex
@samp{p3} multiplies it by 8, and the value of @code{0x1.fp3}
is the same as @code{1.55e1}.

Unlike for floating-point numbers in the decimal notation the exponent
is always required in the hexadecimal notation.  Otherwise the compiler
would not be able to resolve the ambiguity of, e.g., @code{0x1.f}.  This
could mean @code{1.0f} or @code{1.9375} since @samp{f} is also the
extension for floating-point constants of type @code{float}.

@node Fixed-Point
@section Fixed-Point Types
@cindex fixed-point types
@cindex @code{_Fract} data type
@cindex @code{_Accum} data type
@cindex @code{_Sat} data type
@cindex @code{hr} fixed-suffix
@cindex @code{r} fixed-suffix
@cindex @code{lr} fixed-suffix
@cindex @code{llr} fixed-suffix
@cindex @code{uhr} fixed-suffix
@cindex @code{ur} fixed-suffix
@cindex @code{ulr} fixed-suffix
@cindex @code{ullr} fixed-suffix
@cindex @code{hk} fixed-suffix
@cindex @code{k} fixed-suffix
@cindex @code{lk} fixed-suffix
@cindex @code{llk} fixed-suffix
@cindex @code{uhk} fixed-suffix
@cindex @code{uk} fixed-suffix
@cindex @code{ulk} fixed-suffix
@cindex @code{ullk} fixed-suffix
@cindex @code{HR} fixed-suffix
@cindex @code{R} fixed-suffix
@cindex @code{LR} fixed-suffix
@cindex @code{LLR} fixed-suffix
@cindex @code{UHR} fixed-suffix
@cindex @code{UR} fixed-suffix
@cindex @code{ULR} fixed-suffix
@cindex @code{ULLR} fixed-suffix
@cindex @code{HK} fixed-suffix
@cindex @code{K} fixed-suffix
@cindex @code{LK} fixed-suffix
@cindex @code{LLK} fixed-suffix
@cindex @code{UHK} fixed-suffix
@cindex @code{UK} fixed-suffix
@cindex @code{ULK} fixed-suffix
@cindex @code{ULLK} fixed-suffix

As an extension, GNU C supports fixed-point types as
defined in the N1169 draft of ISO/IEC DTR 18037.  Support for fixed-point
types in GCC will evolve as the draft technical report changes.
Calling conventions for any target might also change.  Not all targets
support fixed-point types.

The fixed-point types are
@code{short _Fract},
@code{_Fract},
@code{long _Fract},
@code{long long _Fract},
@code{unsigned short _Fract},
@code{unsigned _Fract},
@code{unsigned long _Fract},
@code{unsigned long long _Fract},
@code{_Sat short _Fract},
@code{_Sat _Fract},
@code{_Sat long _Fract},
@code{_Sat long long _Fract},
@code{_Sat unsigned short _Fract},
@code{_Sat unsigned _Fract},
@code{_Sat unsigned long _Fract},
@code{_Sat unsigned long long _Fract},
@code{short _Accum},
@code{_Accum},
@code{long _Accum},
@code{long long _Accum},
@code{unsigned short _Accum},
@code{unsigned _Accum},
@code{unsigned long _Accum},
@code{unsigned long long _Accum},
@code{_Sat short _Accum},
@code{_Sat _Accum},
@code{_Sat long _Accum},
@code{_Sat long long _Accum},
@code{_Sat unsigned short _Accum},
@code{_Sat unsigned _Accum},
@code{_Sat unsigned long _Accum},
@code{_Sat unsigned long long _Accum}.

Fixed-point data values contain fractional and optional integral parts.
The format of fixed-point data varies and depends on the target machine.

Support for fixed-point types includes:
@itemize @bullet
@item
prefix and postfix increment and decrement operators (@code{++}, @code{--})
@item
unary arithmetic operators (@code{+}, @code{-}, @code{!})
@item
binary arithmetic operators (@code{+}, @code{-}, @code{*}, @code{/})
@item
binary shift operators (@code{<<}, @code{>>})
@item
relational operators (@code{<}, @code{<=}, @code{>=}, @code{>})
@item
equality operators (@code{==}, @code{!=})
@item
assignment operators (@code{+=}, @code{-=}, @code{*=}, @code{/=},
@code{<<=}, @code{>>=})
@item
conversions to and from integer, floating-point, or fixed-point types
@end itemize

Use a suffix in a fixed-point literal constant:
@itemize
@item @samp{hr} or @samp{HR} for @code{short _Fract} and
@code{_Sat short _Fract}
@item @samp{r} or @samp{R} for @code{_Fract} and @code{_Sat _Fract}
@item @samp{lr} or @samp{LR} for @code{long _Fract} and
@code{_Sat long _Fract}
@item @samp{llr} or @samp{LLR} for @code{long long _Fract} and
@code{_Sat long long _Fract}
@item @samp{uhr} or @samp{UHR} for @code{unsigned short _Fract} and
@code{_Sat unsigned short _Fract}
@item @samp{ur} or @samp{UR} for @code{unsigned _Fract} and
@code{_Sat unsigned _Fract}
@item @samp{ulr} or @samp{ULR} for @code{unsigned long _Fract} and
@code{_Sat unsigned long _Fract}
@item @samp{ullr} or @samp{ULLR} for @code{unsigned long long _Fract}
and @code{_Sat unsigned long long _Fract}
@item @samp{hk} or @samp{HK} for @code{short _Accum} and
@code{_Sat short _Accum}
@item @samp{k} or @samp{K} for @code{_Accum} and @code{_Sat _Accum}
@item @samp{lk} or @samp{LK} for @code{long _Accum} and
@code{_Sat long _Accum}
@item @samp{llk} or @samp{LLK} for @code{long long _Accum} and
@code{_Sat long long _Accum}
@item @samp{uhk} or @samp{UHK} for @code{unsigned short _Accum} and
@code{_Sat unsigned short _Accum}
@item @samp{uk} or @samp{UK} for @code{unsigned _Accum} and
@code{_Sat unsigned _Accum}
@item @samp{ulk} or @samp{ULK} for @code{unsigned long _Accum} and
@code{_Sat unsigned long _Accum}
@item @samp{ullk} or @samp{ULLK} for @code{unsigned long long _Accum}
and @code{_Sat unsigned long long _Accum}
@end itemize

GCC support of fixed-point types as specified by the draft technical report
is incomplete:

@itemize @bullet
@item
Pragmas to control overflow and rounding behaviors are not implemented.
@end itemize

Fixed-point types are supported by the DWARF 2 debug information format.

@node Named Address Spaces
@section Named Address Spaces
@cindex Named Address Spaces

As an extension, GNU C supports named address spaces as
defined in the N1275 draft of ISO/IEC DTR 18037.  Support for named
address spaces in GCC will evolve as the draft technical report
changes.  Calling conventions for any target might also change.  At
present, only the AVR, SPU, M32C, and RL78 targets support address
spaces other than the generic address space.

Address space identifiers may be used exactly like any other C type
qualifier (e.g., @code{const} or @code{volatile}).  See the N1275
document for more details.

@anchor{AVR Named Address Spaces}
@subsection AVR Named Address Spaces

On the AVR target, there are several address spaces that can be used
in order to put read-only data into the flash memory and access that
data by means of the special instructions @code{LPM} or @code{ELPM}
needed to read from flash.

Per default, any data including read-only data is located in RAM
(the generic address space) so that non-generic address spaces are
needed to locate read-only data in flash memory
@emph{and} to generate the right instructions to access this data
without using (inline) assembler code.

@table @code
@item __flash
@cindex @code{__flash} AVR Named Address Spaces
The @code{__flash} qualifier locates data in the
@code{.progmem.data} section. Data is read using the @code{LPM}
instruction. Pointers to this address space are 16 bits wide.

@item __flash1
@itemx __flash2
@itemx __flash3
@itemx __flash4
@itemx __flash5
@cindex @code{__flash1} AVR Named Address Spaces
@cindex @code{__flash2} AVR Named Address Spaces
@cindex @code{__flash3} AVR Named Address Spaces
@cindex @code{__flash4} AVR Named Address Spaces
@cindex @code{__flash5} AVR Named Address Spaces
These are 16-bit address spaces locating data in section
@code{.progmem@var{N}.data} where @var{N} refers to
address space @code{__flash@var{N}}.
The compiler sets the @code{RAMPZ} segment register appropriately 
before reading data by means of the @code{ELPM} instruction.

@item __memx
@cindex @code{__memx} AVR Named Address Spaces
This is a 24-bit address space that linearizes flash and RAM:
If the high bit of the address is set, data is read from
RAM using the lower two bytes as RAM address.
If the high bit of the address is clear, data is read from flash
with @code{RAMPZ} set according to the high byte of the address.
@xref{AVR Built-in Functions,,@code{__builtin_avr_flash_segment}}.

Objects in this address space are located in @code{.progmemx.data}.
@end table

@b{Example}

@smallexample
char my_read (const __flash char ** p)
@{
    /* p is a pointer to RAM that points to a pointer to flash.
       The first indirection of p reads that flash pointer
       from RAM and the second indirection reads a char from this
       flash address.  */

    return **p;
@}

/* Locate array[] in flash memory */
const __flash int array[] = @{ 3, 5, 7, 11, 13, 17, 19 @};

int i = 1;

int main (void)
@{
   /* Return 17 by reading from flash memory */
   return array[array[i]];
@}
@end smallexample

@noindent
For each named address space supported by avr-gcc there is an equally
named but uppercase built-in macro defined. 
The purpose is to facilitate testing if respective address space
support is available or not:

@smallexample
#ifdef __FLASH
const __flash int var = 1;

int read_var (void)
@{
    return var;
@}
#else
#include <avr/pgmspace.h> /* From AVR-LibC */

const int var PROGMEM = 1;

int read_var (void)
@{
    return (int) pgm_read_word (&var);
@}
#endif /* __FLASH */
@end smallexample

@noindent
Notice that attribute @ref{AVR Variable Attributes,,@code{progmem}}
locates data in flash but
accesses to these data read from generic address space, i.e.@:
from RAM,
so that you need special accessors like @code{pgm_read_byte}
from @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC}}
together with attribute @code{progmem}.

@noindent
@b{Limitations and caveats}

@itemize
@item
Reading across the 64@tie{}KiB section boundary of
the @code{__flash} or @code{__flash@var{N}} address spaces
shows undefined behavior. The only address space that
supports reading across the 64@tie{}KiB flash segment boundaries is
@code{__memx}.

@item
If you use one of the @code{__flash@var{N}} address spaces
you must arrange your linker script to locate the
@code{.progmem@var{N}.data} sections according to your needs.

@item
Any data or pointers to the non-generic address spaces must
be qualified as @code{const}, i.e.@: as read-only data.
This still applies if the data in one of these address
spaces like software version number or calibration lookup table are intended to
be changed after load time by, say, a boot loader. In this case
the right qualification is @code{const} @code{volatile} so that the compiler
must not optimize away known values or insert them
as immediates into operands of instructions.

@item
The following code initializes a variable @code{pfoo}
located in static storage with a 24-bit address:
@smallexample
extern const __memx char foo;
const __memx void *pfoo = &foo;
@end smallexample

@noindent
Such code requires at least binutils 2.23, see
@w{@uref{http://sourceware.org/PR13503,PR13503}}.

@end itemize

@subsection M32C Named Address Spaces
@cindex @code{__far} M32C Named Address Spaces

On the M32C target, with the R8C and M16C CPU variants, variables
qualified with @code{__far} are accessed using 32-bit addresses in
order to access memory beyond the first 64@tie{}Ki bytes.  If
@code{__far} is used with the M32CM or M32C CPU variants, it has no
effect.

@subsection RL78 Named Address Spaces
@cindex @code{__far} RL78 Named Address Spaces

On the RL78 target, variables qualified with @code{__far} are accessed
with 32-bit pointers (20-bit addresses) rather than the default 16-bit
addresses.  Non-far variables are assumed to appear in the topmost
64@tie{}KiB of the address space.

@subsection SPU Named Address Spaces
@cindex @code{__ea} SPU Named Address Spaces

On the SPU target variables may be declared as
belonging to another address space by qualifying the type with the
@code{__ea} address space identifier:

@smallexample
extern int __ea i;
@end smallexample

@noindent 
The compiler generates special code to access the variable @code{i}.
It may use runtime library
support, or generate special machine instructions to access that address
space.

@node Zero Length
@section Arrays of Length Zero
@cindex arrays of length zero
@cindex zero-length arrays
@cindex length-zero arrays
@cindex flexible array members

Zero-length arrays are allowed in GNU C@.  They are very useful as the
last element of a structure that is really a header for a variable-length
object:

@smallexample
struct line @{
  int length;
  char contents[0];
@};

struct line *thisline = (struct line *)
  malloc (sizeof (struct line) + this_length);
thisline->length = this_length;
@end smallexample

In ISO C90, you would have to give @code{contents} a length of 1, which
means either you waste space or complicate the argument to @code{malloc}.

In ISO C99, you would use a @dfn{flexible array member}, which is
slightly different in syntax and semantics:

@itemize @bullet
@item
Flexible array members are written as @code{contents[]} without
the @code{0}.

@item
Flexible array members have incomplete type, and so the @code{sizeof}
operator may not be applied.  As a quirk of the original implementation
of zero-length arrays, @code{sizeof} evaluates to zero.

@item
Flexible array members may only appear as the last member of a
@code{struct} that is otherwise non-empty.

@item
A structure containing a flexible array member, or a union containing
such a structure (possibly recursively), may not be a member of a
structure or an element of an array.  (However, these uses are
permitted by GCC as extensions.)
@end itemize

GCC versions before 3.0 allowed zero-length arrays to be statically
initialized, as if they were flexible arrays.  In addition to those
cases that were useful, it also allowed initializations in situations
that would corrupt later data.  Non-empty initialization of zero-length
arrays is now treated like any case where there are more initializer
elements than the array holds, in that a suitable warning about ``excess
elements in array'' is given, and the excess elements (all of them, in
this case) are ignored.

Instead GCC allows static initialization of flexible array members.
This is equivalent to defining a new structure containing the original
structure followed by an array of sufficient size to contain the data.
E.g.@: in the following, @code{f1} is constructed as if it were declared
like @code{f2}.

@smallexample
struct f1 @{
  int x; int y[];
@} f1 = @{ 1, @{ 2, 3, 4 @} @};

struct f2 @{
  struct f1 f1; int data[3];
@} f2 = @{ @{ 1 @}, @{ 2, 3, 4 @} @};
@end smallexample

@noindent
The convenience of this extension is that @code{f1} has the desired
type, eliminating the need to consistently refer to @code{f2.f1}.

This has symmetry with normal static arrays, in that an array of
unknown size is also written with @code{[]}.

Of course, this extension only makes sense if the extra data comes at
the end of a top-level object, as otherwise we would be overwriting
data at subsequent offsets.  To avoid undue complication and confusion
with initialization of deeply nested arrays, we simply disallow any
non-empty initialization except when the structure is the top-level
object.  For example:

@smallexample
struct foo @{ int x; int y[]; @};
struct bar @{ struct foo z; @};

struct foo a = @{ 1, @{ 2, 3, 4 @} @};        // @r{Valid.}
struct bar b = @{ @{ 1, @{ 2, 3, 4 @} @} @};    // @r{Invalid.}
struct bar c = @{ @{ 1, @{ @} @} @};            // @r{Valid.}
struct foo d[1] = @{ @{ 1 @{ 2, 3, 4 @} @} @};  // @r{Invalid.}
@end smallexample

@node Empty Structures
@section Structures With No Members
@cindex empty structures
@cindex zero-size structures

GCC permits a C structure to have no members:

@smallexample
struct empty @{
@};
@end smallexample

The structure has size zero.  In C++, empty structures are part
of the language.  G++ treats empty structures as if they had a single
member of type @code{char}.

@node Variable Length
@section Arrays of Variable Length
@cindex variable-length arrays
@cindex arrays of variable length
@cindex VLAs

Variable-length automatic arrays are allowed in ISO C99, and as an
extension GCC accepts them in C90 mode and in C++.  These arrays are
declared like any other automatic arrays, but with a length that is not
a constant expression.  The storage is allocated at the point of
declaration and deallocated when the block scope containing the declaration
exits.  For
example:

@smallexample
FILE *
concat_fopen (char *s1, char *s2, char *mode)
@{
  char str[strlen (s1) + strlen (s2) + 1];
  strcpy (str, s1);
  strcat (str, s2);
  return fopen (str, mode);
@}
@end smallexample

@cindex scope of a variable length array
@cindex variable-length array scope
@cindex deallocating variable length arrays
Jumping or breaking out of the scope of the array name deallocates the
storage.  Jumping into the scope is not allowed; you get an error
message for it.

@cindex @code{alloca} vs variable-length arrays
You can use the function @code{alloca} to get an effect much like
variable-length arrays.  The function @code{alloca} is available in
many other C implementations (but not in all).  On the other hand,
variable-length arrays are more elegant.

There are other differences between these two methods.  Space allocated
with @code{alloca} exists until the containing @emph{function} returns.
The space for a variable-length array is deallocated as soon as the array
name's scope ends.  (If you use both variable-length arrays and
@code{alloca} in the same function, deallocation of a variable-length array
also deallocates anything more recently allocated with @code{alloca}.)

You can also use variable-length arrays as arguments to functions:

@smallexample
struct entry
tester (int len, char data[len][len])
@{
  /* @r{@dots{}} */
@}
@end smallexample

The length of an array is computed once when the storage is allocated
and is remembered for the scope of the array in case you access it with
@code{sizeof}.

If you want to pass the array first and the length afterward, you can
use a forward declaration in the parameter list---another GNU extension.

@smallexample
struct entry
tester (int len; char data[len][len], int len)
@{
  /* @r{@dots{}} */
@}
@end smallexample

@cindex parameter forward declaration
The @samp{int len} before the semicolon is a @dfn{parameter forward
declaration}, and it serves the purpose of making the name @code{len}
known when the declaration of @code{data} is parsed.

You can write any number of such parameter forward declarations in the
parameter list.  They can be separated by commas or semicolons, but the
last one must end with a semicolon, which is followed by the ``real''
parameter declarations.  Each forward declaration must match a ``real''
declaration in parameter name and data type.  ISO C99 does not support
parameter forward declarations.

@node Variadic Macros
@section Macros with a Variable Number of Arguments.
@cindex variable number of arguments
@cindex macro with variable arguments
@cindex rest argument (in macro)
@cindex variadic macros

In the ISO C standard of 1999, a macro can be declared to accept a
variable number of arguments much as a function can.  The syntax for
defining the macro is similar to that of a function.  Here is an
example:

@smallexample
#define debug(format, ...) fprintf (stderr, format, __VA_ARGS__)
@end smallexample

@noindent
Here @samp{@dots{}} is a @dfn{variable argument}.  In the invocation of
such a macro, it represents the zero or more tokens until the closing
parenthesis that ends the invocation, including any commas.  This set of
tokens replaces the identifier @code{__VA_ARGS__} in the macro body
wherever it appears.  See the CPP manual for more information.

GCC has long supported variadic macros, and used a different syntax that
allowed you to give a name to the variable arguments just like any other
argument.  Here is an example:

@smallexample
#define debug(format, args...) fprintf (stderr, format, args)
@end smallexample

@noindent
This is in all ways equivalent to the ISO C example above, but arguably
more readable and descriptive.

GNU CPP has two further variadic macro extensions, and permits them to
be used with either of the above forms of macro definition.

In standard C, you are not allowed to leave the variable argument out
entirely; but you are allowed to pass an empty argument.  For example,
this invocation is invalid in ISO C, because there is no comma after
the string:

@smallexample
debug ("A message")
@end smallexample

GNU CPP permits you to completely omit the variable arguments in this
way.  In the above examples, the compiler would complain, though since
the expansion of the macro still has the extra comma after the format
string.

To help solve this problem, CPP behaves specially for variable arguments
used with the token paste operator, @samp{##}.  If instead you write

@smallexample
#define debug(format, ...) fprintf (stderr, format, ## __VA_ARGS__)
@end smallexample

@noindent
and if the variable arguments are omitted or empty, the @samp{##}
operator causes the preprocessor to remove the comma before it.  If you
do provide some variable arguments in your macro invocation, GNU CPP
does not complain about the paste operation and instead places the
variable arguments after the comma.  Just like any other pasted macro
argument, these arguments are not macro expanded.

@node Escaped Newlines
@section Slightly Looser Rules for Escaped Newlines
@cindex escaped newlines
@cindex newlines (escaped)

Recently, the preprocessor has relaxed its treatment of escaped
newlines.  Previously, the newline had to immediately follow a
backslash.  The current implementation allows whitespace in the form
of spaces, horizontal and vertical tabs, and form feeds between the
backslash and the subsequent newline.  The preprocessor issues a
warning, but treats it as a valid escaped newline and combines the two
lines to form a single logical line.  This works within comments and
tokens, as well as between tokens.  Comments are @emph{not} treated as
whitespace for the purposes of this relaxation, since they have not
yet been replaced with spaces.

@node Subscripting
@section Non-Lvalue Arrays May Have Subscripts
@cindex subscripting
@cindex arrays, non-lvalue

@cindex subscripting and function values
In ISO C99, arrays that are not lvalues still decay to pointers, and
may be subscripted, although they may not be modified or used after
the next sequence point and the unary @samp{&} operator may not be
applied to them.  As an extension, GNU C allows such arrays to be
subscripted in C90 mode, though otherwise they do not decay to
pointers outside C99 mode.  For example,
this is valid in GNU C though not valid in C90:

@smallexample
@group
struct foo @{int a[4];@};

struct foo f();

bar (int index)
@{
  return f().a[index];
@}
@end group
@end smallexample

@node Pointer Arith
@section Arithmetic on @code{void}- and Function-Pointers
@cindex void pointers, arithmetic
@cindex void, size of pointer to
@cindex function pointers, arithmetic
@cindex function, size of pointer to

In GNU C, addition and subtraction operations are supported on pointers to
@code{void} and on pointers to functions.  This is done by treating the
size of a @code{void} or of a function as 1.

A consequence of this is that @code{sizeof} is also allowed on @code{void}
and on function types, and returns 1.

@opindex Wpointer-arith
The option @option{-Wpointer-arith} requests a warning if these extensions
are used.

@node Initializers
@section Non-Constant Initializers
@cindex initializers, non-constant
@cindex non-constant initializers

As in standard C++ and ISO C99, the elements of an aggregate initializer for an
automatic variable are not required to be constant expressions in GNU C@.
Here is an example of an initializer with run-time varying elements:

@smallexample
foo (float f, float g)
@{
  float beat_freqs[2] = @{ f-g, f+g @};
  /* @r{@dots{}} */
@}
@end smallexample

@node Compound Literals
@section Compound Literals
@cindex constructor expressions
@cindex initializations in expressions
@cindex structures, constructor expression
@cindex expressions, constructor
@cindex compound literals
@c The GNU C name for what C99 calls compound literals was "constructor expressions".

ISO C99 supports compound literals.  A compound literal looks like
a cast containing an initializer.  Its value is an object of the
type specified in the cast, containing the elements specified in
the initializer; it is an lvalue.  As an extension, GCC supports
compound literals in C90 mode and in C++, though the semantics are
somewhat different in C++.

Usually, the specified type is a structure.  Assume that
@code{struct foo} and @code{structure} are declared as shown:

@smallexample
struct foo @{int a; char b[2];@} structure;
@end smallexample

@noindent
Here is an example of constructing a @code{struct foo} with a compound literal:

@smallexample
structure = ((struct foo) @{x + y, 'a', 0@});
@end smallexample

@noindent
This is equivalent to writing the following:

@smallexample
@{
  struct foo temp = @{x + y, 'a', 0@};
  structure = temp;
@}
@end smallexample

You can also construct an array, though this is dangerous in C++, as
explained below.  If all the elements of the compound literal are
(made up of) simple constant expressions, suitable for use in
initializers of objects of static storage duration, then the compound
literal can be coerced to a pointer to its first element and used in
such an initializer, as shown here:

@smallexample
char **foo = (char *[]) @{ "x", "y", "z" @};
@end smallexample

Compound literals for scalar types and union types are
also allowed, but then the compound literal is equivalent
to a cast.

As a GNU extension, GCC allows initialization of objects with static storage
duration by compound literals (which is not possible in ISO C99, because
the initializer is not a constant).
It is handled as if the object is initialized only with the bracket
enclosed list if the types of the compound literal and the object match.
The initializer list of the compound literal must be constant.
If the object being initialized has array type of unknown size, the size is
determined by compound literal size.

@smallexample
static struct foo x = (struct foo) @{1, 'a', 'b'@};
static int y[] = (int []) @{1, 2, 3@};
static int z[] = (int [3]) @{1@};
@end smallexample

@noindent
The above lines are equivalent to the following:
@smallexample
static struct foo x = @{1, 'a', 'b'@};
static int y[] = @{1, 2, 3@};
static int z[] = @{1, 0, 0@};
@end smallexample

In C, a compound literal designates an unnamed object with static or
automatic storage duration.  In C++, a compound literal designates a
temporary object, which only lives until the end of its
full-expression.  As a result, well-defined C code that takes the
address of a subobject of a compound literal can be undefined in C++.
For instance, if the array compound literal example above appeared
inside a function, any subsequent use of @samp{foo} in C++ has
undefined behavior because the lifetime of the array ends after the
declaration of @samp{foo}.  As a result, the C++ compiler now rejects
the conversion of a temporary array to a pointer.

As an optimization, the C++ compiler sometimes gives array compound
literals longer lifetimes: when the array either appears outside a
function or has const-qualified type.  If @samp{foo} and its
initializer had elements of @samp{char *const} type rather than
@samp{char *}, or if @samp{foo} were a global variable, the array
would have static storage duration.  But it is probably safest just to
avoid the use of array compound literals in code compiled as C++.

@node Designated Inits
@section Designated Initializers
@cindex initializers with labeled elements
@cindex labeled elements in initializers
@cindex case labels in initializers
@cindex designated initializers

Standard C90 requires the elements of an initializer to appear in a fixed
order, the same as the order of the elements in the array or structure
being initialized.

In ISO C99 you can give the elements in any order, specifying the array
indices or structure field names they apply to, and GNU C allows this as
an extension in C90 mode as well.  This extension is not
implemented in GNU C++.

To specify an array index, write
@samp{[@var{index}] =} before the element value.  For example,

@smallexample
int a[6] = @{ [4] = 29, [2] = 15 @};
@end smallexample

@noindent
is equivalent to

@smallexample
int a[6] = @{ 0, 0, 15, 0, 29, 0 @};
@end smallexample

@noindent
The index values must be constant expressions, even if the array being
initialized is automatic.

An alternative syntax for this that has been obsolete since GCC 2.5 but
GCC still accepts is to write @samp{[@var{index}]} before the element
value, with no @samp{=}.

To initialize a range of elements to the same value, write
@samp{[@var{first} ... @var{last}] = @var{value}}.  This is a GNU
extension.  For example,

@smallexample
int widths[] = @{ [0 ... 9] = 1, [10 ... 99] = 2, [100] = 3 @};
@end smallexample

@noindent
If the value in it has side-effects, the side-effects happen only once,
not for each initialized field by the range initializer.

@noindent
Note that the length of the array is the highest value specified
plus one.

In a structure initializer, specify the name of a field to initialize
with @samp{.@var{fieldname} =} before the element value.  For example,
given the following structure,

@smallexample
struct point @{ int x, y; @};
@end smallexample

@noindent
the following initialization

@smallexample
struct point p = @{ .y = yvalue, .x = xvalue @};
@end smallexample

@noindent
is equivalent to

@smallexample
struct point p = @{ xvalue, yvalue @};
@end smallexample

Another syntax that has the same meaning, obsolete since GCC 2.5, is
@samp{@var{fieldname}:}, as shown here:

@smallexample
struct point p = @{ y: yvalue, x: xvalue @};
@end smallexample

@cindex designators
The @samp{[@var{index}]} or @samp{.@var{fieldname}} is known as a
@dfn{designator}.  You can also use a designator (or the obsolete colon
syntax) when initializing a union, to specify which element of the union
should be used.  For example,

@smallexample
union foo @{ int i; double d; @};

union foo f = @{ .d = 4 @};
@end smallexample

@noindent
converts 4 to a @code{double} to store it in the union using
the second element.  By contrast, casting 4 to type @code{union foo}
stores it into the union as the integer @code{i}, since it is
an integer.  (@xref{Cast to Union}.)

You can combine this technique of naming elements with ordinary C
initialization of successive elements.  Each initializer element that
does not have a designator applies to the next consecutive element of the
array or structure.  For example,

@smallexample
int a[6] = @{ [1] = v1, v2, [4] = v4 @};
@end smallexample

@noindent
is equivalent to

@smallexample
int a[6] = @{ 0, v1, v2, 0, v4, 0 @};
@end smallexample

Labeling the elements of an array initializer is especially useful
when the indices are characters or belong to an @code{enum} type.
For example:

@smallexample
int whitespace[256]
  = @{ [' '] = 1, ['\t'] = 1, ['\h'] = 1,
      ['\f'] = 1, ['\n'] = 1, ['\r'] = 1 @};
@end smallexample

@cindex designator lists
You can also write a series of @samp{.@var{fieldname}} and
@samp{[@var{index}]} designators before an @samp{=} to specify a
nested subobject to initialize; the list is taken relative to the
subobject corresponding to the closest surrounding brace pair.  For
example, with the @samp{struct point} declaration above:

@smallexample
struct point ptarray[10] = @{ [2].y = yv2, [2].x = xv2, [0].x = xv0 @};
@end smallexample

@noindent
If the same field is initialized multiple times, it has the value from
the last initialization.  If any such overridden initialization has
side-effect, it is unspecified whether the side-effect happens or not.
Currently, GCC discards them and issues a warning.

@node Case Ranges
@section Case Ranges
@cindex case ranges
@cindex ranges in case statements

You can specify a range of consecutive values in a single @code{case} label,
like this:

@smallexample
case @var{low} ... @var{high}:
@end smallexample

@noindent
This has the same effect as the proper number of individual @code{case}
labels, one for each integer value from @var{low} to @var{high}, inclusive.

This feature is especially useful for ranges of ASCII character codes:

@smallexample
case 'A' ... 'Z':
@end smallexample

@strong{Be careful:} Write spaces around the @code{...}, for otherwise
it may be parsed wrong when you use it with integer values.  For example,
write this:

@smallexample
case 1 ... 5:
@end smallexample

@noindent
rather than this:

@smallexample
case 1...5:
@end smallexample

@node Cast to Union
@section Cast to a Union Type
@cindex cast to a union
@cindex union, casting to a

A cast to union type is similar to other casts, except that the type
specified is a union type.  You can specify the type either with
@code{union @var{tag}} or with a typedef name.  A cast to union is actually
a constructor, not a cast, and hence does not yield an lvalue like
normal casts.  (@xref{Compound Literals}.)

The types that may be cast to the union type are those of the members
of the union.  Thus, given the following union and variables:

@smallexample
union foo @{ int i; double d; @};
int x;
double y;
@end smallexample

@noindent
both @code{x} and @code{y} can be cast to type @code{union foo}.

Using the cast as the right-hand side of an assignment to a variable of
union type is equivalent to storing in a member of the union:

@smallexample
union foo u;
/* @r{@dots{}} */
u = (union foo) x  @equiv{}  u.i = x
u = (union foo) y  @equiv{}  u.d = y
@end smallexample

You can also use the union cast as a function argument:

@smallexample
void hack (union foo);
/* @r{@dots{}} */
hack ((union foo) x);
@end smallexample

@node Mixed Declarations
@section Mixed Declarations and Code
@cindex mixed declarations and code
@cindex declarations, mixed with code
@cindex code, mixed with declarations

ISO C99 and ISO C++ allow declarations and code to be freely mixed
within compound statements.  As an extension, GNU C also allows this in
C90 mode.  For example, you could do:

@smallexample
int i;
/* @r{@dots{}} */
i++;
int j = i + 2;
@end smallexample

Each identifier is visible from where it is declared until the end of
the enclosing block.

@node Function Attributes
@section Declaring Attributes of Functions
@cindex function attributes
@cindex declaring attributes of functions
@cindex functions that never return
@cindex functions that return more than once
@cindex functions that have no side effects
@cindex functions in arbitrary sections
@cindex functions that behave like malloc
@cindex @code{volatile} applied to function
@cindex @code{const} applied to function
@cindex functions with @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style arguments
@cindex functions with non-null pointer arguments
@cindex functions that are passed arguments in registers on the 386
@cindex functions that pop the argument stack on the 386
@cindex functions that do not pop the argument stack on the 386
@cindex functions that have different compilation options on the 386
@cindex functions that have different optimization options
@cindex functions that are dynamically resolved

In GNU C, you declare certain things about functions called in your program
which help the compiler optimize function calls and check your code more
carefully.

The keyword @code{__attribute__} allows you to specify special
attributes when making a declaration.  This keyword is followed by an
attribute specification inside double parentheses.  The following
attributes are currently defined for functions on all targets:
@code{aligned}, @code{alloc_size}, @code{noreturn},
@code{returns_twice}, @code{noinline}, @code{noclone},
@code{always_inline}, @code{flatten}, @code{pure}, @code{const},
@code{nothrow}, @code{sentinel}, @code{format}, @code{format_arg},
@code{no_instrument_function}, @code{no_split_stack},
@code{section}, @code{constructor},
@code{destructor}, @code{used}, @code{unused}, @code{deprecated},
@code{weak}, @code{malloc}, @code{alias}, @code{ifunc},
@code{warn_unused_result}, @code{nonnull}, @code{gnu_inline},
@code{externally_visible}, @code{hot}, @code{cold}, @code{artificial},
@code{no_sanitize_address}, @code{no_address_safety_analysis},
@code{error} and @code{warning}.
Several other attributes are defined for functions on particular
target systems.  Other attributes, including @code{section} are
supported for variables declarations (@pxref{Variable Attributes})
and for types (@pxref{Type Attributes}).

GCC plugins may provide their own attributes.

You may also specify attributes with @samp{__} preceding and following
each keyword.  This allows you to use them in header files without
being concerned about a possible macro of the same name.  For example,
you may use @code{__noreturn__} instead of @code{noreturn}.

@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.

@table @code
@c Keep this table alphabetized by attribute name.  Treat _ as space.

@item alias ("@var{target}")
@cindex @code{alias} attribute
The @code{alias} attribute causes the declaration to be emitted as an
alias for another symbol, which must be specified.  For instance,

@smallexample
void __f () @{ /* @r{Do something.} */; @}
void f () __attribute__ ((weak, alias ("__f")));
@end smallexample

@noindent
defines @samp{f} to be a weak alias for @samp{__f}.  In C++, the
mangled name for the target must be used.  It is an error if @samp{__f}
is not defined in the same translation unit.

Not all target machines support this attribute.

@item aligned (@var{alignment})
@cindex @code{aligned} attribute
This attribute specifies a minimum alignment for the function,
measured in bytes.

You cannot use this attribute to decrease the alignment of a function,
only to increase it.  However, when you explicitly specify a function
alignment this overrides the effect of the
@option{-falign-functions} (@pxref{Optimize Options}) option for this
function.

Note that the effectiveness of @code{aligned} attributes may be
limited by inherent limitations in your linker.  On many systems, the
linker is only able to arrange for functions to be aligned up to a
certain maximum alignment.  (For some linkers, the maximum supported
alignment may be very very small.)  See your linker documentation for
further information.

The @code{aligned} attribute can also be used for variables and fields
(@pxref{Variable Attributes}.)

@item alloc_size
@cindex @code{alloc_size} attribute
The @code{alloc_size} attribute is used to tell the compiler that the
function return value points to memory, where the size is given by
one or two of the functions parameters.  GCC uses this
information to improve the correctness of @code{__builtin_object_size}.

The function parameter(s) denoting the allocated size are specified by
one or two integer arguments supplied to the attribute.  The allocated size
is either the value of the single function argument specified or the product
of the two function arguments specified.  Argument numbering starts at
one.

For instance,

@smallexample
void* my_calloc(size_t, size_t) __attribute__((alloc_size(1,2)))
void my_realloc(void*, size_t) __attribute__((alloc_size(2)))
@end smallexample

@noindent
declares that @code{my_calloc} returns memory of the size given by
the product of parameter 1 and 2 and that @code{my_realloc} returns memory
of the size given by parameter 2.

@item always_inline
@cindex @code{always_inline} function attribute
Generally, functions are not inlined unless optimization is specified.
For functions declared inline, this attribute inlines the function even
if no optimization level is specified.

@item gnu_inline
@cindex @code{gnu_inline} function attribute
This attribute should be used with a function that is also declared
with the @code{inline} keyword.  It directs GCC to treat the function
as if it were defined in gnu90 mode even when compiling in C99 or
gnu99 mode.

If the function is declared @code{extern}, then this definition of the
function is used only for inlining.  In no case is the function
compiled as a standalone function, not even if you take its address
explicitly.  Such an address becomes an external reference, as if you
had only declared the function, and had not defined it.  This has
almost the effect of a macro.  The way to use this is to put a
function definition in a header file with this attribute, and put
another copy of the function, without @code{extern}, in a library
file.  The definition in the header file causes most calls to the
function to be inlined.  If any uses of the function remain, they
refer to the single copy in the library.  Note that the two
definitions of the functions need not be precisely the same, although
if they do not have the same effect your program may behave oddly.

In C, if the function is neither @code{extern} nor @code{static}, then
the function is compiled as a standalone function, as well as being
inlined where possible.

This is how GCC traditionally handled functions declared
@code{inline}.  Since ISO C99 specifies a different semantics for
@code{inline}, this function attribute is provided as a transition
measure and as a useful feature in its own right.  This attribute is
available in GCC 4.1.3 and later.  It is available if either of the
preprocessor macros @code{__GNUC_GNU_INLINE__} or
@code{__GNUC_STDC_INLINE__} are defined.  @xref{Inline,,An Inline
Function is As Fast As a Macro}.

In C++, this attribute does not depend on @code{extern} in any way,
but it still requires the @code{inline} keyword to enable its special
behavior.

@item artificial
@cindex @code{artificial} function attribute
This attribute is useful for small inline wrappers that if possible
should appear during debugging as a unit.  Depending on the debug
info format it either means marking the function as artificial
or using the caller location for all instructions within the inlined
body.

@item bank_switch
@cindex interrupt handler functions
When added to an interrupt handler with the M32C port, causes the
prologue and epilogue to use bank switching to preserve the registers
rather than saving them on the stack.

@item flatten
@cindex @code{flatten} function attribute
Generally, inlining into a function is limited.  For a function marked with
this attribute, every call inside this function is inlined, if possible.
Whether the function itself is considered for inlining depends on its size and
the current inlining parameters.

@item error ("@var{message}")
@cindex @code{error} function attribute
If this attribute is used on a function declaration and a call to such a function
is not eliminated through dead code elimination or other optimizations, an error
that includes @var{message} is diagnosed.  This is useful
for compile-time checking, especially together with @code{__builtin_constant_p}
and inline functions where checking the inline function arguments is not
possible through @code{extern char [(condition) ? 1 : -1];} tricks.
While it is possible to leave the function undefined and thus invoke
a link failure, when using this attribute the problem is diagnosed
earlier and with exact location of the call even in presence of inline
functions or when not emitting debugging information.

@item warning ("@var{message}")
@cindex @code{warning} function attribute
If this attribute is used on a function declaration and a call to such a function
is not eliminated through dead code elimination or other optimizations, a warning
that includes @var{message} is diagnosed.  This is useful
for compile-time checking, especially together with @code{__builtin_constant_p}
and inline functions.  While it is possible to define the function with
a message in @code{.gnu.warning*} section, when using this attribute the problem
is diagnosed earlier and with exact location of the call even in presence
of inline functions or when not emitting debugging information.

@item cdecl
@cindex functions that do pop the argument stack on the 386
@opindex mrtd
On the Intel 386, the @code{cdecl} attribute causes the compiler to
assume that the calling function pops off the stack space used to
pass arguments.  This is
useful to override the effects of the @option{-mrtd} switch.

@item const
@cindex @code{const} function attribute
Many functions do not examine any values except their arguments, and
have no effects except the return value.  Basically this is just slightly
more strict class than the @code{pure} attribute below, since function is not
allowed to read global memory.

@cindex pointer arguments
Note that a function that has pointer arguments and examines the data
pointed to must @emph{not} be declared @code{const}.  Likewise, a
function that calls a non-@code{const} function usually must not be
@code{const}.  It does not make sense for a @code{const} function to
return @code{void}.

The attribute @code{const} is not implemented in GCC versions earlier
than 2.5.  An alternative way to declare that a function has no side
effects, which works in the current version and in some older versions,
is as follows:

@smallexample
typedef int intfn ();

extern const intfn square;
@end smallexample

@noindent
This approach does not work in GNU C++ from 2.6.0 on, since the language
specifies that the @samp{const} must be attached to the return value.

@item constructor
@itemx destructor
@itemx constructor (@var{priority})
@itemx destructor (@var{priority})
@cindex @code{constructor} function attribute
@cindex @code{destructor} function attribute
The @code{constructor} attribute causes the function to be called
automatically before execution enters @code{main ()}.  Similarly, the
@code{destructor} attribute causes the function to be called
automatically after @code{main ()} completes or @code{exit ()} is
called.  Functions with these attributes are useful for
initializing data that is used implicitly during the execution of
the program.

You may provide an optional integer priority to control the order in
which constructor and destructor functions are run.  A constructor
with a smaller priority number runs before a constructor with a larger
priority number; the opposite relationship holds for destructors.  So,
if you have a constructor that allocates a resource and a destructor
that deallocates the same resource, both functions typically have the
same priority.  The priorities for constructor and destructor
functions are the same as those specified for namespace-scope C++
objects (@pxref{C++ Attributes}).

These attributes are not currently implemented for Objective-C@.

@item deprecated
@itemx deprecated (@var{msg})
@cindex @code{deprecated} attribute.
The @code{deprecated} attribute results in a warning if the function
is used anywhere in the source file.  This is useful when identifying
functions that are expected to be removed in a future version of a
program.  The warning also includes the location of the declaration
of the deprecated function, to enable users to easily find further
information about why the function is deprecated, or what they should
do instead.  Note that the warnings only occurs for uses:

@smallexample
int old_fn () __attribute__ ((deprecated));
int old_fn ();
int (*fn_ptr)() = old_fn;
@end smallexample

@noindent
results in a warning on line 3 but not line 2.  The optional @var{msg}
argument, which must be a string, is printed in the warning if
present.

The @code{deprecated} attribute can also be used for variables and
types (@pxref{Variable Attributes}, @pxref{Type Attributes}.)

@item disinterrupt
@cindex @code{disinterrupt} attribute
On Epiphany and MeP targets, this attribute causes the compiler to emit
instructions to disable interrupts for the duration of the given
function.

@item dllexport
@cindex @code{__declspec(dllexport)}
On Microsoft Windows targets and Symbian OS targets the
@code{dllexport} attribute causes the compiler to provide a global
pointer to a pointer in a DLL, so that it can be referenced with the
@code{dllimport} attribute.  On Microsoft Windows targets, the pointer
name is formed by combining @code{_imp__} and the function or variable
name.

You can use @code{__declspec(dllexport)} as a synonym for
@code{__attribute__ ((dllexport))} for compatibility with other
compilers.

On systems that support the @code{visibility} attribute, this
attribute also implies ``default'' visibility.  It is an error to
explicitly specify any other visibility.

In previous versions of GCC, the @code{dllexport} attribute was ignored
for inlined functions, unless the @option{-fkeep-inline-functions} flag
had been used.  The default behavior now is to emit all dllexported
inline functions; however, this can cause object file-size bloat, in
which case the old behavior can be restored by using
@option{-fno-keep-inline-dllexport}.

The attribute is also ignored for undefined symbols.

When applied to C++ classes, the attribute marks defined non-inlined
member functions and static data members as exports.  Static consts
initialized in-class are not marked unless they are also defined
out-of-class.

For Microsoft Windows targets there are alternative methods for
including the symbol in the DLL's export table such as using a
@file{.def} file with an @code{EXPORTS} section or, with GNU ld, using
the @option{--export-all} linker flag.

@item dllimport
@cindex @code{__declspec(dllimport)}
On Microsoft Windows and Symbian OS targets, the @code{dllimport}
attribute causes the compiler to reference a function or variable via
a global pointer to a pointer that is set up by the DLL exporting the
symbol.  The attribute implies @code{extern}.  On Microsoft Windows
targets, the pointer name is formed by combining @code{_imp__} and the
function or variable name.

You can use @code{__declspec(dllimport)} as a synonym for
@code{__attribute__ ((dllimport))} for compatibility with other
compilers.

On systems that support the @code{visibility} attribute, this
attribute also implies ``default'' visibility.  It is an error to
explicitly specify any other visibility.

Currently, the attribute is ignored for inlined functions.  If the
attribute is applied to a symbol @emph{definition}, an error is reported.
If a symbol previously declared @code{dllimport} is later defined, the
attribute is ignored in subsequent references, and a warning is emitted.
The attribute is also overridden by a subsequent declaration as
@code{dllexport}.

When applied to C++ classes, the attribute marks non-inlined
member functions and static data members as imports.  However, the
attribute is ignored for virtual methods to allow creation of vtables
using thunks.

On the SH Symbian OS target the @code{dllimport} attribute also has
another affect---it can cause the vtable and run-time type information
for a class to be exported.  This happens when the class has a
dllimported constructor or a non-inline, non-pure virtual function
and, for either of those two conditions, the class also has an inline
constructor or destructor and has a key function that is defined in
the current translation unit.

For Microsoft Windows targets the use of the @code{dllimport}
attribute on functions is not necessary, but provides a small
performance benefit by eliminating a thunk in the DLL@.  The use of the
@code{dllimport} attribute on imported variables was required on older
versions of the GNU linker, but can now be avoided by passing the
@option{--enable-auto-import} switch to the GNU linker.  As with
functions, using the attribute for a variable eliminates a thunk in
the DLL@.

One drawback to using this attribute is that a pointer to a
@emph{variable} marked as @code{dllimport} cannot be used as a constant
address. However, a pointer to a @emph{function} with the
@code{dllimport} attribute can be used as a constant initializer; in
this case, the address of a stub function in the import lib is
referenced.  On Microsoft Windows targets, the attribute can be disabled
for functions by setting the @option{-mnop-fun-dllimport} flag.

@item eightbit_data
@cindex eight-bit data on the H8/300, H8/300H, and H8S
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified
variable should be placed into the eight-bit data section.
The compiler generates more efficient code for certain operations
on data in the eight-bit data area.  Note the eight-bit data area is limited to
256 bytes of data.

You must use GAS and GLD from GNU binutils version 2.7 or later for
this attribute to work correctly.

@item exception_handler
@cindex exception handler functions on the Blackfin processor
Use this attribute on the Blackfin to indicate that the specified function
is an exception handler.  The compiler generates function entry and
exit sequences suitable for use in an exception handler when this
attribute is present.

@item externally_visible
@cindex @code{externally_visible} attribute.
This attribute, attached to a global variable or function, nullifies
the effect of the @option{-fwhole-program} command-line option, so the
object remains visible outside the current compilation unit.

If @option{-fwhole-program} is used together with @option{-flto} and 
@command{gold} is used as the linker plugin, 
@code{externally_visible} attributes are automatically added to functions 
(not variable yet due to a current @command{gold} issue) 
that are accessed outside of LTO objects according to resolution file
produced by @command{gold}.
For other linkers that cannot generate resolution file,
explicit @code{externally_visible} attributes are still necessary.

@item far
@cindex functions that handle memory bank switching
On 68HC11 and 68HC12 the @code{far} attribute causes the compiler to
use a calling convention that takes care of switching memory banks when
entering and leaving a function.  This calling convention is also the
default when using the @option{-mlong-calls} option.

On 68HC12 the compiler uses the @code{call} and @code{rtc} instructions
to call and return from a function.

On 68HC11 the compiler generates a sequence of instructions
to invoke a board-specific routine to switch the memory bank and call the
real function.  The board-specific routine simulates a @code{call}.
At the end of a function, it jumps to a board-specific routine
instead of using @code{rts}.  The board-specific return routine simulates
the @code{rtc}.

On MeP targets this causes the compiler to use a calling convention
that assumes the called function is too far away for the built-in
addressing modes.

@item fast_interrupt
@cindex interrupt handler functions
Use this attribute on the M32C and RX ports to indicate that the specified
function is a fast interrupt handler.  This is just like the
@code{interrupt} attribute, except that @code{freit} is used to return
instead of @code{reit}.

@item fastcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{fastcall} attribute causes the compiler to
pass the first argument (if of integral type) in the register ECX and
the second argument (if of integral type) in the register EDX@.  Subsequent
and other typed arguments are passed on the stack.  The called function
pops the arguments off the stack.  If the number of arguments is variable all
arguments are pushed on the stack.

@item thiscall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{thiscall} attribute causes the compiler to
pass the first argument (if of integral type) in the register ECX.
Subsequent and other typed arguments are passed on the stack. The called
function pops the arguments off the stack.
If the number of arguments is variable all arguments are pushed on the
stack.
The @code{thiscall} attribute is intended for C++ non-static member functions.
As a GCC extension, this calling convention can be used for C functions
and for static member methods.

@item format (@var{archetype}, @var{string-index}, @var{first-to-check})
@cindex @code{format} function attribute
@opindex Wformat
The @code{format} attribute specifies that a function takes @code{printf},
@code{scanf}, @code{strftime} or @code{strfmon} style arguments that
should be type-checked against a format string.  For example, the
declaration:

@smallexample
extern int
my_printf (void *my_object, const char *my_format, ...)
      __attribute__ ((format (printf, 2, 3)));
@end smallexample

@noindent
causes the compiler to check the arguments in calls to @code{my_printf}
for consistency with the @code{printf} style format string argument
@code{my_format}.

The parameter @var{archetype} determines how the format string is
interpreted, and should be @code{printf}, @code{scanf}, @code{strftime},
@code{gnu_printf}, @code{gnu_scanf}, @code{gnu_strftime} or
@code{strfmon}.  (You can also use @code{__printf__},
@code{__scanf__}, @code{__strftime__} or @code{__strfmon__}.)  On
MinGW targets, @code{ms_printf}, @code{ms_scanf}, and
@code{ms_strftime} are also present.
@var{archetype} values such as @code{printf} refer to the formats accepted
by the system's C runtime library,
while values prefixed with @samp{gnu_} always refer
to the formats accepted by the GNU C Library.  On Microsoft Windows
targets, values prefixed with @samp{ms_} refer to the formats accepted by the
@file{msvcrt.dll} library.
The parameter @var{string-index}
specifies which argument is the format string argument (starting
from 1), while @var{first-to-check} is the number of the first
argument to check against the format string.  For functions
where the arguments are not available to be checked (such as
@code{vprintf}), specify the third parameter as zero.  In this case the
compiler only checks the format string for consistency.  For
@code{strftime} formats, the third parameter is required to be zero.
Since non-static C++ methods have an implicit @code{this} argument, the
arguments of such methods should be counted from two, not one, when
giving values for @var{string-index} and @var{first-to-check}.

In the example above, the format string (@code{my_format}) is the second
argument of the function @code{my_print}, and the arguments to check
start with the third argument, so the correct parameters for the format
attribute are 2 and 3.

@opindex ffreestanding
@opindex fno-builtin
The @code{format} attribute allows you to identify your own functions
that take format strings as arguments, so that GCC can check the
calls to these functions for errors.  The compiler always (unless
@option{-ffreestanding} or @option{-fno-builtin} is used) checks formats
for the standard library functions @code{printf}, @code{fprintf},
@code{sprintf}, @code{scanf}, @code{fscanf}, @code{sscanf}, @code{strftime},
@code{vprintf}, @code{vfprintf} and @code{vsprintf} whenever such
warnings are requested (using @option{-Wformat}), so there is no need to
modify the header file @file{stdio.h}.  In C99 mode, the functions
@code{snprintf}, @code{vsnprintf}, @code{vscanf}, @code{vfscanf} and
@code{vsscanf} are also checked.  Except in strictly conforming C
standard modes, the X/Open function @code{strfmon} is also checked as
are @code{printf_unlocked} and @code{fprintf_unlocked}.
@xref{C Dialect Options,,Options Controlling C Dialect}.

For Objective-C dialects, @code{NSString} (or @code{__NSString__}) is
recognized in the same context.  Declarations including these format attributes
are parsed for correct syntax, however the result of checking of such format
strings is not yet defined, and is not carried out by this version of the
compiler.

The target may also provide additional types of format checks.
@xref{Target Format Checks,,Format Checks Specific to Particular
Target Machines}.

@item format_arg (@var{string-index})
@cindex @code{format_arg} function attribute
@opindex Wformat-nonliteral
The @code{format_arg} attribute specifies that a function takes a format
string for a @code{printf}, @code{scanf}, @code{strftime} or
@code{strfmon} style function and modifies it (for example, to translate
it into another language), so the result can be passed to a
@code{printf}, @code{scanf}, @code{strftime} or @code{strfmon} style
function (with the remaining arguments to the format function the same
as they would have been for the unmodified string).  For example, the
declaration:

@smallexample
extern char *
my_dgettext (char *my_domain, const char *my_format)
      __attribute__ ((format_arg (2)));
@end smallexample

@noindent
causes the compiler to check the arguments in calls to a @code{printf},
@code{scanf}, @code{strftime} or @code{strfmon} type function, whose
format string argument is a call to the @code{my_dgettext} function, for
consistency with the format string argument @code{my_format}.  If the
@code{format_arg} attribute had not been specified, all the compiler
could tell in such calls to format functions would be that the format
string argument is not constant; this would generate a warning when
@option{-Wformat-nonliteral} is used, but the calls could not be checked
without the attribute.

The parameter @var{string-index} specifies which argument is the format
string argument (starting from one).  Since non-static C++ methods have
an implicit @code{this} argument, the arguments of such methods should
be counted from two.

The @code{format_arg} attribute allows you to identify your own
functions that modify format strings, so that GCC can check the
calls to @code{printf}, @code{scanf}, @code{strftime} or @code{strfmon}
type function whose operands are a call to one of your own function.
The compiler always treats @code{gettext}, @code{dgettext}, and
@code{dcgettext} in this manner except when strict ISO C support is
requested by @option{-ansi} or an appropriate @option{-std} option, or
@option{-ffreestanding} or @option{-fno-builtin}
is used.  @xref{C Dialect Options,,Options
Controlling C Dialect}.

For Objective-C dialects, the @code{format-arg} attribute may refer to an
@code{NSString} reference for compatibility with the @code{format} attribute
above.

The target may also allow additional types in @code{format-arg} attributes.
@xref{Target Format Checks,,Format Checks Specific to Particular
Target Machines}.

@item function_vector
@cindex calling functions through the function vector on H8/300, M16C, M32C and SH2A processors
Use this attribute on the H8/300, H8/300H, and H8S to indicate that the specified
function should be called through the function vector.  Calling a
function through the function vector reduces code size, however;
the function vector has a limited size (maximum 128 entries on the H8/300
and 64 entries on the H8/300H and H8S) and shares space with the interrupt vector.

On SH2A targets, this attribute declares a function to be called using the
TBR relative addressing mode.  The argument to this attribute is the entry
number of the same function in a vector table containing all the TBR
relative addressable functions.  For correct operation the TBR must be setup
accordingly to point to the start of the vector table before any functions with
this attribute are invoked.  Usually a good place to do the initialization is
the startup routine.  The TBR relative vector table can have at max 256 function
entries.  The jumps to these functions are generated using a SH2A specific,
non delayed branch instruction JSR/N @@(disp8,TBR).  You must use GAS and GLD
from GNU binutils version 2.7 or later for this attribute to work correctly.

Please refer the example of M16C target, to see the use of this
attribute while declaring a function,

In an application, for a function being called once, this attribute
saves at least 8 bytes of code; and if other successive calls are being
made to the same function, it saves 2 bytes of code per each of these
calls.

On M16C/M32C targets, the @code{function_vector} attribute declares a
special page subroutine call function. Use of this attribute reduces
the code size by 2 bytes for each call generated to the
subroutine. The argument to the attribute is the vector number entry
from the special page vector table which contains the 16 low-order
bits of the subroutine's entry address. Each vector table has special
page number (18 to 255) that is used in @code{jsrs} instructions.
Jump addresses of the routines are generated by adding 0x0F0000 (in
case of M16C targets) or 0xFF0000 (in case of M32C targets), to the
2-byte addresses set in the vector table. Therefore you need to ensure
that all the special page vector routines should get mapped within the
address range 0x0F0000 to 0x0FFFFF (for M16C) and 0xFF0000 to 0xFFFFFF
(for M32C).

In the following example 2 bytes are saved for each call to
function @code{foo}.

@smallexample
void foo (void) __attribute__((function_vector(0x18)));
void foo (void)
@{
@}

void bar (void)
@{
    foo();
@}
@end smallexample

If functions are defined in one file and are called in another file,
then be sure to write this declaration in both files.

This attribute is ignored for R8C target.

@item ifunc ("@var{resolver}")
@cindex @code{ifunc} attribute
The @code{ifunc} attribute is used to mark a function as an indirect
function using the STT_GNU_IFUNC symbol type extension to the ELF
standard.  This allows the resolution of the symbol value to be
determined dynamically at load time, and an optimized version of the
routine can be selected for the particular processor or other system
characteristics determined then.  To use this attribute, first define
the implementation functions available, and a resolver function that
returns a pointer to the selected implementation function.  The
implementation functions' declarations must match the API of the
function being implemented, the resolver's declaration is be a
function returning pointer to void function returning void:

@smallexample
void *my_memcpy (void *dst, const void *src, size_t len)
@{
  @dots{}
@}

static void (*resolve_memcpy (void)) (void)
@{
  return my_memcpy; // we'll just always select this routine
@}
@end smallexample

@noindent
The exported header file declaring the function the user calls would
contain:

@smallexample
extern void *memcpy (void *, const void *, size_t);
@end smallexample

@noindent
allowing the user to call this as a regular function, unaware of the
implementation.  Finally, the indirect function needs to be defined in
the same translation unit as the resolver function:

@smallexample
void *memcpy (void *, const void *, size_t)
     __attribute__ ((ifunc ("resolve_memcpy")));
@end smallexample

Indirect functions cannot be weak, and require a recent binutils (at
least version 2.20.1), and GNU C library (at least version 2.11.1).

@item interrupt
@cindex interrupt handler functions
Use this attribute on the ARM, AVR, CR16, Epiphany, M32C, M32R/D, m68k, MeP, MIPS,
RL78, RX and Xstormy16 ports to indicate that the specified function is an
interrupt handler.  The compiler generates function entry and exit
sequences suitable for use in an interrupt handler when this attribute
is present.  With Epiphany targets it may also generate a special section with
code to initialize the interrupt vector table.

Note, interrupt handlers for the Blackfin, H8/300, H8/300H, H8S, MicroBlaze,
and SH processors can be specified via the @code{interrupt_handler} attribute.

Note, on the AVR, the hardware globally disables interrupts when an
interrupt is executed.  The first instruction of an interrupt handler
declared with this attribute is a @code{SEI} instruction to
re-enable interrupts.  See also the @code{signal} function attribute
that does not insert a @code{SEI} instruction.  If both @code{signal} and
@code{interrupt} are specified for the same function, @code{signal}
is silently ignored.

Note, for the ARM, you can specify the kind of interrupt to be handled by
adding an optional parameter to the interrupt attribute like this:

@smallexample
void f () __attribute__ ((interrupt ("IRQ")));
@end smallexample

@noindent
Permissible values for this parameter are: @code{IRQ}, @code{FIQ},
@code{SWI}, @code{ABORT} and @code{UNDEF}.

On ARMv7-M the interrupt type is ignored, and the attribute means the function
may be called with a word-aligned stack pointer.

On Epiphany targets one or more optional parameters can be added like this:

@smallexample
void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();
@end smallexample

Permissible values for these parameters are: @w{@code{reset}},
@w{@code{software_exception}}, @w{@code{page_miss}},
@w{@code{timer0}}, @w{@code{timer1}}, @w{@code{message}},
@w{@code{dma0}}, @w{@code{dma1}}, @w{@code{wand}} and @w{@code{swi}}.
Multiple parameters indicate that multiple entries in the interrupt
vector table should be initialized for this function, i.e.@: for each
parameter @w{@var{name}}, a jump to the function is emitted in
the section @w{ivt_entry_@var{name}}.  The parameter(s) may be omitted
entirely, in which case no interrupt vector table entry is provided.

Note, on Epiphany targets, interrupts are enabled inside the function
unless the @code{disinterrupt} attribute is also specified.

On Epiphany targets, you can also use the following attribute to
modify the behavior of an interrupt handler:
@table @code
@item forwarder_section
@cindex @code{forwarder_section} attribute
The interrupt handler may be in external memory which cannot be
reached by a branch instruction, so generate a local memory trampoline
to transfer control.  The single parameter identifies the section where
the trampoline is placed.
@end table

The following examples are all valid uses of these attributes on
Epiphany targets:
@smallexample
void __attribute__ ((interrupt)) universal_handler ();
void __attribute__ ((interrupt ("dma1"))) dma1_handler ();
void __attribute__ ((interrupt ("dma0, dma1"))) universal_dma_handler ();
void __attribute__ ((interrupt ("timer0"), disinterrupt))
  fast_timer_handler ();
void __attribute__ ((interrupt ("dma0, dma1"), forwarder_section ("tramp")))
  external_dma_handler ();
@end smallexample

On MIPS targets, you can use the following attributes to modify the behavior
of an interrupt handler:
@table @code
@item use_shadow_register_set
@cindex @code{use_shadow_register_set} attribute
Assume that the handler uses a shadow register set, instead of
the main general-purpose registers.

@item keep_interrupts_masked
@cindex @code{keep_interrupts_masked} attribute
Keep interrupts masked for the whole function.  Without this attribute,
GCC tries to reenable interrupts for as much of the function as it can.

@item use_debug_exception_return
@cindex @code{use_debug_exception_return} attribute
Return using the @code{deret} instruction.  Interrupt handlers that don't
have this attribute return using @code{eret} instead.
@end table

You can use any combination of these attributes, as shown below:
@smallexample
void __attribute__ ((interrupt)) v0 ();
void __attribute__ ((interrupt, use_shadow_register_set)) v1 ();
void __attribute__ ((interrupt, keep_interrupts_masked)) v2 ();
void __attribute__ ((interrupt, use_debug_exception_return)) v3 ();
void __attribute__ ((interrupt, use_shadow_register_set,
                     keep_interrupts_masked)) v4 ();
void __attribute__ ((interrupt, use_shadow_register_set,
                     use_debug_exception_return)) v5 ();
void __attribute__ ((interrupt, keep_interrupts_masked,
                     use_debug_exception_return)) v6 ();
void __attribute__ ((interrupt, use_shadow_register_set,
                     keep_interrupts_masked,
                     use_debug_exception_return)) v7 ();
@end smallexample

On RL78, use @code{brk_interrupt} instead of @code{interrupt} for
handlers intended to be used with the @code{BRK} opcode (i.e.@: those
that must end with @code{RETB} instead of @code{RETI}).

@item interrupt_handler
@cindex interrupt handler functions on the Blackfin, m68k, H8/300 and SH processors
Use this attribute on the Blackfin, m68k, H8/300, H8/300H, H8S, and SH to
indicate that the specified function is an interrupt handler.  The compiler
generates function entry and exit sequences suitable for use in an
interrupt handler when this attribute is present.

@item interrupt_thread
@cindex interrupt thread functions on fido
Use this attribute on fido, a subarchitecture of the m68k, to indicate
that the specified function is an interrupt handler that is designed
to run as a thread.  The compiler omits generate prologue/epilogue
sequences and replaces the return instruction with a @code{sleep}
instruction.  This attribute is available only on fido.

@item isr
@cindex interrupt service routines on ARM
Use this attribute on ARM to write Interrupt Service Routines. This is an
alias to the @code{interrupt} attribute above.

@item kspisusp
@cindex User stack pointer in interrupts on the Blackfin
When used together with @code{interrupt_handler}, @code{exception_handler}
or @code{nmi_handler}, code is generated to load the stack pointer
from the USP register in the function prologue.

@item l1_text
@cindex @code{l1_text} function attribute
This attribute specifies a function to be placed into L1 Instruction
SRAM@. The function is put into a specific section named @code{.l1.text}.
With @option{-mfdpic}, function calls with a such function as the callee
or caller uses inlined PLT.

@item l2
@cindex @code{l2} function attribute
On the Blackfin, this attribute specifies a function to be placed into L2
SRAM. The function is put into a specific section named
@code{.l1.text}. With @option{-mfdpic}, callers of such functions use
an inlined PLT.

@item leaf
@cindex @code{leaf} function attribute
Calls to external functions with this attribute must return to the current
compilation unit only by return or by exception handling.  In particular, leaf
functions are not allowed to call callback function passed to it from the current
compilation unit or directly call functions exported by the unit or longjmp
into the unit.  Leaf function might still call functions from other compilation
units and thus they are not necessarily leaf in the sense that they contain no
function calls at all.

The attribute is intended for library functions to improve dataflow analysis.
The compiler takes the hint that any data not escaping the current compilation unit can
not be used or modified by the leaf function.  For example, the @code{sin} function
is a leaf function, but @code{qsort} is not.

Note that leaf functions might invoke signals and signal handlers might be
defined in the current compilation unit and use static variables.  The only
compliant way to write such a signal handler is to declare such variables
@code{volatile}.

The attribute has no effect on functions defined within the current compilation
unit.  This is to allow easy merging of multiple compilation units into one,
for example, by using the link-time optimization.  For this reason the
attribute is not allowed on types to annotate indirect calls.

@item long_call/short_call
@cindex indirect calls on ARM
This attribute specifies how a particular function is called on
ARM and Epiphany.  Both attributes override the
@option{-mlong-calls} (@pxref{ARM Options})
command-line switch and @code{#pragma long_calls} settings.  The
@code{long_call} attribute indicates that the function might be far
away from the call site and require a different (more expensive)
calling sequence.   The @code{short_call} attribute always places
the offset to the function from the call site into the @samp{BL}
instruction directly.

@item longcall/shortcall
@cindex functions called via pointer on the RS/6000 and PowerPC
On the Blackfin, RS/6000 and PowerPC, the @code{longcall} attribute
indicates that the function might be far away from the call site and
require a different (more expensive) calling sequence.  The
@code{shortcall} attribute indicates that the function is always close
enough for the shorter calling sequence to be used.  These attributes
override both the @option{-mlongcall} switch and, on the RS/6000 and
PowerPC, the @code{#pragma longcall} setting.

@xref{RS/6000 and PowerPC Options}, for more information on whether long
calls are necessary.

@item long_call/near/far
@cindex indirect calls on MIPS
These attributes specify how a particular function is called on MIPS@.
The attributes override the @option{-mlong-calls} (@pxref{MIPS Options})
command-line switch.  The @code{long_call} and @code{far} attributes are
synonyms, and cause the compiler to always call
the function by first loading its address into a register, and then using
the contents of that register.  The @code{near} attribute has the opposite
effect; it specifies that non-PIC calls should be made using the more
efficient @code{jal} instruction.

@item malloc
@cindex @code{malloc} attribute
The @code{malloc} attribute is used to tell the compiler that a function
may be treated as if any non-@code{NULL} pointer it returns cannot
alias any other pointer valid when the function returns and that the memory
has undefined content.
This often improves optimization.
Standard functions with this property include @code{malloc} and
@code{calloc}.  @code{realloc}-like functions do not have this
property as the memory pointed to does not have undefined content.

@item mips16/nomips16
@cindex @code{mips16} attribute
@cindex @code{nomips16} attribute

On MIPS targets, you can use the @code{mips16} and @code{nomips16}
function attributes to locally select or turn off MIPS16 code generation.
A function with the @code{mips16} attribute is emitted as MIPS16 code,
while MIPS16 code generation is disabled for functions with the
@code{nomips16} attribute.  These attributes override the
@option{-mips16} and @option{-mno-mips16} options on the command line
(@pxref{MIPS Options}).

When compiling files containing mixed MIPS16 and non-MIPS16 code, the
preprocessor symbol @code{__mips16} reflects the setting on the command line,
not that within individual functions.  Mixed MIPS16 and non-MIPS16 code
may interact badly with some GCC extensions such as @code{__builtin_apply}
(@pxref{Constructing Calls}).

@item micromips/nomicromips
@cindex @code{micromips} attribute
@cindex @code{nomicromips} attribute

On MIPS targets, you can use the @code{micromips} and @code{nomicromips}
function attributes to locally select or turn off microMIPS code generation.
A function with the @code{micromips} attribute is emitted as microMIPS code,
while microMIPS code generation is disabled for functions with the
@code{nomicromips} attribute.  These attributes override the
@option{-mmicromips} and @option{-mno-micromips} options on the command line
(@pxref{MIPS Options}).

When compiling files containing mixed microMIPS and non-microMIPS code, the
preprocessor symbol @code{__mips_micromips} reflects the setting on the
command line,
not that within individual functions.  Mixed microMIPS and non-microMIPS code
may interact badly with some GCC extensions such as @code{__builtin_apply}
(@pxref{Constructing Calls}).

@item model (@var{model-name})
@cindex function addressability on the M32R/D
@cindex variable addressability on the IA-64

On the M32R/D, use this attribute to set the addressability of an
object, and of the code generated for a function.  The identifier
@var{model-name} is one of @code{small}, @code{medium}, or
@code{large}, representing each of the code models.

Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the @code{ld24} instruction), and are
callable with the @code{bl} instruction.

Medium model objects may live anywhere in the 32-bit address space (the
compiler generates @code{seth/add3} instructions to load their addresses),
and are callable with the @code{bl} instruction.

Large model objects may live anywhere in the 32-bit address space (the
compiler generates @code{seth/add3} instructions to load their addresses),
and may not be reachable with the @code{bl} instruction (the compiler
generates the much slower @code{seth/add3/jl} instruction sequence).

On IA-64, use this attribute to set the addressability of an object.
At present, the only supported identifier for @var{model-name} is
@code{small}, indicating addressability via ``small'' (22-bit)
addresses (so that their addresses can be loaded with the @code{addl}
instruction).  Caveat: such addressing is by definition not position
independent and hence this attribute must not be used for objects
defined by shared libraries.

@item ms_abi/sysv_abi
@cindex @code{ms_abi} attribute
@cindex @code{sysv_abi} attribute

On 32-bit and 64-bit (i?86|x86_64)-*-* targets, you can use an ABI attribute
to indicate which calling convention should be used for a function.  The
@code{ms_abi} attribute tells the compiler to use the Microsoft ABI,
while the @code{sysv_abi} attribute tells the compiler to use the ABI
used on GNU/Linux and other systems.  The default is to use the Microsoft ABI
when targeting Windows.  On all other systems, the default is the x86/AMD ABI.

Note, the @code{ms_abi} attribute for Microsoft Windows 64-bit targets currently
requires the @option{-maccumulate-outgoing-args} option.

@item callee_pop_aggregate_return (@var{number})
@cindex @code{callee_pop_aggregate_return} attribute

On 32-bit i?86-*-* targets, you can use this attribute to control how
aggregates are returned in memory.  If the caller is responsible for
popping the hidden pointer together with the rest of the arguments, specify
@var{number} equal to zero.  If callee is responsible for popping the
hidden pointer, specify @var{number} equal to one.  

The default i386 ABI assumes that the callee pops the
stack for hidden pointer.  However, on 32-bit i386 Microsoft Windows targets,
the compiler assumes that the
caller pops the stack for hidden pointer.

@item ms_hook_prologue
@cindex @code{ms_hook_prologue} attribute

On 32-bit i[34567]86-*-* targets and 64-bit x86_64-*-* targets, you can use
this function attribute to make GCC generate the ``hot-patching'' function
prologue used in Win32 API functions in Microsoft Windows XP Service Pack 2
and newer.

@item naked
@cindex function without a prologue/epilogue code
Use this attribute on the ARM, AVR, MCORE, RL78, RX and SPU ports to indicate that
the specified function does not need prologue/epilogue sequences generated by
the compiler.  It is up to the programmer to provide these sequences. The
only statements that can be safely included in naked functions are
@code{asm} statements that do not have operands.  All other statements,
including declarations of local variables, @code{if} statements, and so
forth, should be avoided.  Naked functions should be used to implement the
body of an assembly function, while allowing the compiler to construct
the requisite function declaration for the assembler.

@item near
@cindex functions that do not handle memory bank switching on 68HC11/68HC12
On 68HC11 and 68HC12 the @code{near} attribute causes the compiler to
use the normal calling convention based on @code{jsr} and @code{rts}.
This attribute can be used to cancel the effect of the @option{-mlong-calls}
option.

On MeP targets this attribute causes the compiler to assume the called
function is close enough to use the normal calling convention,
overriding the @option{-mtf} command-line option.

@item nesting
@cindex Allow nesting in an interrupt handler on the Blackfin processor.
Use this attribute together with @code{interrupt_handler},
@code{exception_handler} or @code{nmi_handler} to indicate that the function
entry code should enable nested interrupts or exceptions.

@item nmi_handler
@cindex NMI handler functions on the Blackfin processor
Use this attribute on the Blackfin to indicate that the specified function
is an NMI handler.  The compiler generates function entry and
exit sequences suitable for use in an NMI handler when this
attribute is present.

@item nocompression
@cindex @code{nocompression} attribute
On MIPS targets, you can use the @code{nocompression} function attribute
to locally turn off MIPS16 and microMIPS code generation.  This attribute
overrides the @option{-mips16} and @option{-mmicromips} options on the
command line (@pxref{MIPS Options}).

@item no_instrument_function
@cindex @code{no_instrument_function} function attribute
@opindex finstrument-functions
If @option{-finstrument-functions} is given, profiling function calls are
generated at entry and exit of most user-compiled functions.
Functions with this attribute are not so instrumented.

@item no_split_stack
@cindex @code{no_split_stack} function attribute
@opindex fsplit-stack
If @option{-fsplit-stack} is given, functions have a small
prologue which decides whether to split the stack.  Functions with the
@code{no_split_stack} attribute do not have that prologue, and thus
may run with only a small amount of stack space available.

@item noinline
@cindex @code{noinline} function attribute
This function attribute prevents a function from being considered for
inlining.
@c Don't enumerate the optimizations by name here; we try to be
@c future-compatible with this mechanism.
If the function does not have side-effects, there are optimizations
other than inlining that cause function calls to be optimized away,
although the function call is live.  To keep such calls from being
optimized away, put
@smallexample
asm ("");
@end smallexample

@noindent
(@pxref{Extended Asm}) in the called function, to serve as a special
side-effect.

@item noclone
@cindex @code{noclone} function attribute
This function attribute prevents a function from being considered for
cloning---a mechanism that produces specialized copies of functions
and which is (currently) performed by interprocedural constant
propagation.

@item nonnull (@var{arg-index}, @dots{})
@cindex @code{nonnull} function attribute
The @code{nonnull} attribute specifies that some function parameters should
be non-null pointers.  For instance, the declaration:

@smallexample
extern void *
my_memcpy (void *dest, const void *src, size_t len)
        __attribute__((nonnull (1, 2)));
@end smallexample

@noindent
causes the compiler to check that, in calls to @code{my_memcpy},
arguments @var{dest} and @var{src} are non-null.  If the compiler
determines that a null pointer is passed in an argument slot marked
as non-null, and the @option{-Wnonnull} option is enabled, a warning
is issued.  The compiler may also choose to make optimizations based
on the knowledge that certain function arguments will never be null.

If no argument index list is given to the @code{nonnull} attribute,
all pointer arguments are marked as non-null.  To illustrate, the
following declaration is equivalent to the previous example:

@smallexample
extern void *
my_memcpy (void *dest, const void *src, size_t len)
        __attribute__((nonnull));
@end smallexample

@item noreturn
@cindex @code{noreturn} function attribute
A few standard library functions, such as @code{abort} and @code{exit},
cannot return.  GCC knows this automatically.  Some programs define
their own functions that never return.  You can declare them
@code{noreturn} to tell the compiler this fact.  For example,

@smallexample
@group
void fatal () __attribute__ ((noreturn));

void
fatal (/* @r{@dots{}} */)
@{
  /* @r{@dots{}} */ /* @r{Print error message.} */ /* @r{@dots{}} */
  exit (1);
@}
@end group
@end smallexample

The @code{noreturn} keyword tells the compiler to assume that
@code{fatal} cannot return.  It can then optimize without regard to what
would happen if @code{fatal} ever did return.  This makes slightly
better code.  More importantly, it helps avoid spurious warnings of
uninitialized variables.

The @code{noreturn} keyword does not affect the exceptional path when that
applies: a @code{noreturn}-marked function may still return to the caller
by throwing an exception or calling @code{longjmp}.

Do not assume that registers saved by the calling function are
restored before calling the @code{noreturn} function.

It does not make sense for a @code{noreturn} function to have a return
type other than @code{void}.

The attribute @code{noreturn} is not implemented in GCC versions
earlier than 2.5.  An alternative way to declare that a function does
not return, which works in the current version and in some older
versions, is as follows:

@smallexample
typedef void voidfn ();

volatile voidfn fatal;
@end smallexample

@noindent
This approach does not work in GNU C++.

@item nothrow
@cindex @code{nothrow} function attribute
The @code{nothrow} attribute is used to inform the compiler that a
function cannot throw an exception.  For example, most functions in
the standard C library can be guaranteed not to throw an exception
with the notable exceptions of @code{qsort} and @code{bsearch} that
take function pointer arguments.  The @code{nothrow} attribute is not
implemented in GCC versions earlier than 3.3.

@item nosave_low_regs
@cindex @code{nosave_low_regs} attribute
Use this attribute on SH targets to indicate that an @code{interrupt_handler}
function should not save and restore registers R0..R7.  This can be used on SH3*
and SH4* targets that have a second R0..R7 register bank for non-reentrant
interrupt handlers.

@item optimize
@cindex @code{optimize} function attribute
The @code{optimize} attribute is used to specify that a function is to
be compiled with different optimization options than specified on the
command line.  Arguments can either be numbers or strings.  Numbers
are assumed to be an optimization level.  Strings that begin with
@code{O} are assumed to be an optimization option, while other options
are assumed to be used with a @code{-f} prefix.  You can also use the
@samp{#pragma GCC optimize} pragma to set the optimization options
that affect more than one function.
@xref{Function Specific Option Pragmas}, for details about the
@samp{#pragma GCC optimize} pragma.

This can be used for instance to have frequently-executed functions
compiled with more aggressive optimization options that produce faster
and larger code, while other functions can be compiled with less
aggressive options.

@item OS_main/OS_task
@cindex @code{OS_main} AVR function attribute
@cindex @code{OS_task} AVR function attribute
On AVR, functions with the @code{OS_main} or @code{OS_task} attribute
do not save/restore any call-saved register in their prologue/epilogue.

The @code{OS_main} attribute can be used when there @emph{is
guarantee} that interrupts are disabled at the time when the function
is entered.  This saves resources when the stack pointer has to be
changed to set up a frame for local variables.

The @code{OS_task} attribute can be used when there is @emph{no
guarantee} that interrupts are disabled at that time when the function
is entered like for, e@.g@. task functions in a multi-threading operating
system. In that case, changing the stack pointer register is
guarded by save/clear/restore of the global interrupt enable flag.

The differences to the @code{naked} function attribute are:
@itemize @bullet
@item @code{naked} functions do not have a return instruction whereas 
@code{OS_main} and @code{OS_task} functions have a @code{RET} or
@code{RETI} return instruction.
@item @code{naked} functions do not set up a frame for local variables
or a frame pointer whereas @code{OS_main} and @code{OS_task} do this
as needed.
@end itemize

@item pcs
@cindex @code{pcs} function attribute

The @code{pcs} attribute can be used to control the calling convention
used for a function on ARM.  The attribute takes an argument that specifies
the calling convention to use.

When compiling using the AAPCS ABI (or a variant of it) then valid
values for the argument are @code{"aapcs"} and @code{"aapcs-vfp"}.  In
order to use a variant other than @code{"aapcs"} then the compiler must
be permitted to use the appropriate co-processor registers (i.e., the
VFP registers must be available in order to use @code{"aapcs-vfp"}).
For example,

@smallexample
/* Argument passed in r0, and result returned in r0+r1.  */
double f2d (float) __attribute__((pcs("aapcs")));
@end smallexample

Variadic functions always use the @code{"aapcs"} calling convention and
the compiler rejects attempts to specify an alternative.

@item pure
@cindex @code{pure} function attribute
Many functions have no effects except the return value and their
return value depends only on the parameters and/or global variables.
Such a function can be subject
to common subexpression elimination and loop optimization just as an
arithmetic operator would be.  These functions should be declared
with the attribute @code{pure}.  For example,

@smallexample
int square (int) __attribute__ ((pure));
@end smallexample

@noindent
says that the hypothetical function @code{square} is safe to call
fewer times than the program says.

Some of common examples of pure functions are @code{strlen} or @code{memcmp}.
Interesting non-pure functions are functions with infinite loops or those
depending on volatile memory or other system resource, that may change between
two consecutive calls (such as @code{feof} in a multithreading environment).

The attribute @code{pure} is not implemented in GCC versions earlier
than 2.96.

@item hot
@cindex @code{hot} function attribute
The @code{hot} attribute on a function is used to inform the compiler that
the function is a hot spot of the compiled program.  The function is
optimized more aggressively and on many target it is placed into special
subsection of the text section so all hot functions appears close together
improving locality.

When profile feedback is available, via @option{-fprofile-use}, hot functions
are automatically detected and this attribute is ignored.

The @code{hot} attribute on functions is not implemented in GCC versions
earlier than 4.3.

@cindex @code{hot} label attribute
The @code{hot} attribute on a label is used to inform the compiler that
path following the label are more likely than paths that are not so
annotated.  This attribute is used in cases where @code{__builtin_expect}
cannot be used, for instance with computed goto or @code{asm goto}.

The @code{hot} attribute on labels is not implemented in GCC versions
earlier than 4.8.

@item cold
@cindex @code{cold} function attribute
The @code{cold} attribute on functions is used to inform the compiler that
the function is unlikely to be executed.  The function is optimized for
size rather than speed and on many targets it is placed into special
subsection of the text section so all cold functions appears close together
improving code locality of non-cold parts of program.  The paths leading
to call of cold functions within code are marked as unlikely by the branch
prediction mechanism.  It is thus useful to mark functions used to handle
unlikely conditions, such as @code{perror}, as cold to improve optimization
of hot functions that do call marked functions in rare occasions.

When profile feedback is available, via @option{-fprofile-use}, cold functions
are automatically detected and this attribute is ignored.

The @code{cold} attribute on functions is not implemented in GCC versions
earlier than 4.3.

@cindex @code{cold} label attribute
The @code{cold} attribute on labels is used to inform the compiler that
the path following the label is unlikely to be executed.  This attribute
is used in cases where @code{__builtin_expect} cannot be used, for instance
with computed goto or @code{asm goto}.

The @code{cold} attribute on labels is not implemented in GCC versions
earlier than 4.8.

@item no_sanitize_address
@itemx no_address_safety_analysis
@cindex @code{no_sanitize_address} function attribute
The @code{no_sanitize_address} attribute on functions is used
to inform the compiler that it should not instrument memory accesses
in the function when compiling with the @option{-fsanitize=address} option.
The @code{no_address_safety_analysis} is a deprecated alias of the
@code{no_sanitize_address} attribute, new code should use
@code{no_sanitize_address}.

@item regparm (@var{number})
@cindex @code{regparm} attribute
@cindex functions that are passed arguments in registers on the 386
On the Intel 386, the @code{regparm} attribute causes the compiler to
pass arguments number one to @var{number} if they are of integral type
in registers EAX, EDX, and ECX instead of on the stack.  Functions that
take a variable number of arguments continue to be passed all of their
arguments on the stack.

Beware that on some ELF systems this attribute is unsuitable for
global functions in shared libraries with lazy binding (which is the
default).  Lazy binding sends the first call via resolving code in
the loader, which might assume EAX, EDX and ECX can be clobbered, as
per the standard calling conventions.  Solaris 8 is affected by this.
Systems with the GNU C Library version 2.1 or higher
and FreeBSD are believed to be
safe since the loaders there save EAX, EDX and ECX.  (Lazy binding can be
disabled with the linker or the loader if desired, to avoid the
problem.)

@item sseregparm
@cindex @code{sseregparm} attribute
On the Intel 386 with SSE support, the @code{sseregparm} attribute
causes the compiler to pass up to 3 floating-point arguments in
SSE registers instead of on the stack.  Functions that take a
variable number of arguments continue to pass all of their
floating-point arguments on the stack.

@item force_align_arg_pointer
@cindex @code{force_align_arg_pointer} attribute
On the Intel x86, the @code{force_align_arg_pointer} attribute may be
applied to individual function definitions, generating an alternate
prologue and epilogue that realigns the run-time stack if necessary.
This supports mixing legacy codes that run with a 4-byte aligned stack
with modern codes that keep a 16-byte stack for SSE compatibility.

@item renesas
@cindex @code{renesas} attribute
On SH targets this attribute specifies that the function or struct follows the
Renesas ABI.

@item resbank
@cindex @code{resbank} attribute
On the SH2A target, this attribute enables the high-speed register
saving and restoration using a register bank for @code{interrupt_handler}
routines.  Saving to the bank is performed automatically after the CPU
accepts an interrupt that uses a register bank.

The nineteen 32-bit registers comprising general register R0 to R14,
control register GBR, and system registers MACH, MACL, and PR and the
vector table address offset are saved into a register bank.  Register
banks are stacked in first-in last-out (FILO) sequence.  Restoration
from the bank is executed by issuing a RESBANK instruction.

@item returns_twice
@cindex @code{returns_twice} attribute
The @code{returns_twice} attribute tells the compiler that a function may
return more than one time.  The compiler ensures that all registers
are dead before calling such a function and emits a warning about
the variables that may be clobbered after the second return from the
function.  Examples of such functions are @code{setjmp} and @code{vfork}.
The @code{longjmp}-like counterpart of such function, if any, might need
to be marked with the @code{noreturn} attribute.

@item saveall
@cindex save all registers on the Blackfin, H8/300, H8/300H, and H8S
Use this attribute on the Blackfin, H8/300, H8/300H, and H8S to indicate that
all registers except the stack pointer should be saved in the prologue
regardless of whether they are used or not.

@item save_volatiles
@cindex save volatile registers on the MicroBlaze
Use this attribute on the MicroBlaze to indicate that the function is
an interrupt handler.  All volatile registers (in addition to non-volatile
registers) are saved in the function prologue.  If the function is a leaf
function, only volatiles used by the function are saved.  A normal function
return is generated instead of a return from interrupt.

@item section ("@var{section-name}")
@cindex @code{section} function attribute
Normally, the compiler places the code it generates in the @code{text} section.
Sometimes, however, you need additional sections, or you need certain
particular functions to appear in special sections.  The @code{section}
attribute specifies that a function lives in a particular section.
For example, the declaration:

@smallexample
extern void foobar (void) __attribute__ ((section ("bar")));
@end smallexample

@noindent
puts the function @code{foobar} in the @code{bar} section.

Some file formats do not support arbitrary sections so the @code{section}
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.

@item sentinel
@cindex @code{sentinel} function attribute
This function attribute ensures that a parameter in a function call is
an explicit @code{NULL}.  The attribute is only valid on variadic
functions.  By default, the sentinel is located at position zero, the
last parameter of the function call.  If an optional integer position
argument P is supplied to the attribute, the sentinel must be located at
position P counting backwards from the end of the argument list.

@smallexample
__attribute__ ((sentinel))
is equivalent to
__attribute__ ((sentinel(0)))
@end smallexample

The attribute is automatically set with a position of 0 for the built-in
functions @code{execl} and @code{execlp}.  The built-in function
@code{execle} has the attribute set with a position of 1.

A valid @code{NULL} in this context is defined as zero with any pointer
type.  If your system defines the @code{NULL} macro with an integer type
then you need to add an explicit cast.  GCC replaces @code{stddef.h}
with a copy that redefines NULL appropriately.

The warnings for missing or incorrect sentinels are enabled with
@option{-Wformat}.

@item short_call
See @code{long_call/short_call}.

@item shortcall
See @code{longcall/shortcall}.

@item signal
@cindex interrupt handler functions on the AVR processors
Use this attribute on the AVR to indicate that the specified
function is an interrupt handler.  The compiler generates function
entry and exit sequences suitable for use in an interrupt handler when this
attribute is present.

See also the @code{interrupt} function attribute. 

The AVR hardware globally disables interrupts when an interrupt is executed.
Interrupt handler functions defined with the @code{signal} attribute
do not re-enable interrupts.  It is save to enable interrupts in a
@code{signal} handler.  This ``save'' only applies to the code
generated by the compiler and not to the IRQ layout of the
application which is responsibility of the application.

If both @code{signal} and @code{interrupt} are specified for the same
function, @code{signal} is silently ignored.

@item sp_switch
@cindex @code{sp_switch} attribute
Use this attribute on the SH to indicate an @code{interrupt_handler}
function should switch to an alternate stack.  It expects a string
argument that names a global variable holding the address of the
alternate stack.

@smallexample
void *alt_stack;
void f () __attribute__ ((interrupt_handler,
                          sp_switch ("alt_stack")));
@end smallexample

@item stdcall
@cindex functions that pop the argument stack on the 386
On the Intel 386, the @code{stdcall} attribute causes the compiler to
assume that the called function pops off the stack space used to
pass arguments, unless it takes a variable number of arguments.

@item syscall_linkage
@cindex @code{syscall_linkage} attribute
This attribute is used to modify the IA-64 calling convention by marking
all input registers as live at all function exits.  This makes it possible
to restart a system call after an interrupt without having to save/restore
the input registers.  This also prevents kernel data from leaking into
application code.

@item target
@cindex @code{target} function attribute
The @code{target} attribute is used to specify that a function is to
be compiled with different target options than specified on the
command line.  This can be used for instance to have functions
compiled with a different ISA (instruction set architecture) than the
default.  You can also use the @samp{#pragma GCC target} pragma to set
more than one function to be compiled with specific target options.
@xref{Function Specific Option Pragmas}, for details about the
@samp{#pragma GCC target} pragma.

For instance on a 386, you could compile one function with
@code{target("sse4.1,arch=core2")} and another with
@code{target("sse4a,arch=amdfam10")}.  This is equivalent to
compiling the first function with @option{-msse4.1} and
@option{-march=core2} options, and the second function with
@option{-msse4a} and @option{-march=amdfam10} options.  It is up to the
user to make sure that a function is only invoked on a machine that
supports the particular ISA it is compiled for (for example by using
@code{cpuid} on 386 to determine what feature bits and architecture
family are used).

@smallexample
int core2_func (void) __attribute__ ((__target__ ("arch=core2")));
int sse3_func (void) __attribute__ ((__target__ ("sse3")));
@end smallexample

On the 386, the following options are allowed:

@table @samp
@item abm
@itemx no-abm
@cindex @code{target("abm")} attribute
Enable/disable the generation of the advanced bit instructions.

@item aes
@itemx no-aes
@cindex @code{target("aes")} attribute
Enable/disable the generation of the AES instructions.

@item default
@cindex @code{target("default")} attribute
@xref{Function Multiversioning}, where it is used to specify the
default function version.

@item mmx
@itemx no-mmx
@cindex @code{target("mmx")} attribute
Enable/disable the generation of the MMX instructions.

@item pclmul
@itemx no-pclmul
@cindex @code{target("pclmul")} attribute
Enable/disable the generation of the PCLMUL instructions.

@item popcnt
@itemx no-popcnt
@cindex @code{target("popcnt")} attribute
Enable/disable the generation of the POPCNT instruction.

@item sse
@itemx no-sse
@cindex @code{target("sse")} attribute
Enable/disable the generation of the SSE instructions.

@item sse2
@itemx no-sse2
@cindex @code{target("sse2")} attribute
Enable/disable the generation of the SSE2 instructions.

@item sse3
@itemx no-sse3
@cindex @code{target("sse3")} attribute
Enable/disable the generation of the SSE3 instructions.

@item sse4
@itemx no-sse4
@cindex @code{target("sse4")} attribute
Enable/disable the generation of the SSE4 instructions (both SSE4.1
and SSE4.2).

@item sse4.1
@itemx no-sse4.1
@cindex @code{target("sse4.1")} attribute
Enable/disable the generation of the sse4.1 instructions.

@item sse4.2
@itemx no-sse4.2
@cindex @code{target("sse4.2")} attribute
Enable/disable the generation of the sse4.2 instructions.

@item sse4a
@itemx no-sse4a
@cindex @code{target("sse4a")} attribute
Enable/disable the generation of the SSE4A instructions.

@item fma4
@itemx no-fma4
@cindex @code{target("fma4")} attribute
Enable/disable the generation of the FMA4 instructions.

@item xop
@itemx no-xop
@cindex @code{target("xop")} attribute
Enable/disable the generation of the XOP instructions.

@item lwp
@itemx no-lwp
@cindex @code{target("lwp")} attribute
Enable/disable the generation of the LWP instructions.

@item ssse3
@itemx no-ssse3
@cindex @code{target("ssse3")} attribute
Enable/disable the generation of the SSSE3 instructions.

@item cld
@itemx no-cld
@cindex @code{target("cld")} attribute
Enable/disable the generation of the CLD before string moves.

@item fancy-math-387
@itemx no-fancy-math-387
@cindex @code{target("fancy-math-387")} attribute
Enable/disable the generation of the @code{sin}, @code{cos}, and
@code{sqrt} instructions on the 387 floating-point unit.

@item fused-madd
@itemx no-fused-madd
@cindex @code{target("fused-madd")} attribute
Enable/disable the generation of the fused multiply/add instructions.

@item ieee-fp
@itemx no-ieee-fp
@cindex @code{target("ieee-fp")} attribute
Enable/disable the generation of floating point that depends on IEEE arithmetic.

@item inline-all-stringops
@itemx no-inline-all-stringops
@cindex @code{target("inline-all-stringops")} attribute
Enable/disable inlining of string operations.

@item inline-stringops-dynamically
@itemx no-inline-stringops-dynamically
@cindex @code{target("inline-stringops-dynamically")} attribute
Enable/disable the generation of the inline code to do small string
operations and calling the library routines for large operations.

@item align-stringops
@itemx no-align-stringops
@cindex @code{target("align-stringops")} attribute
Do/do not align destination of inlined string operations.

@item recip
@itemx no-recip
@cindex @code{target("recip")} attribute
Enable/disable the generation of RCPSS, RCPPS, RSQRTSS and RSQRTPS
instructions followed an additional Newton-Raphson step instead of
doing a floating-point division.

@item arch=@var{ARCH}
@cindex @code{target("arch=@var{ARCH}")} attribute
Specify the architecture to generate code for in compiling the function.

@item tune=@var{TUNE}
@cindex @code{target("tune=@var{TUNE}")} attribute
Specify the architecture to tune for in compiling the function.

@item fpmath=@var{FPMATH}
@cindex @code{target("fpmath=@var{FPMATH}")} attribute
Specify which floating-point unit to use.  The
@code{target("fpmath=sse,387")} option must be specified as
@code{target("fpmath=sse+387")} because the comma would separate
different options.
@end table

On the PowerPC, the following options are allowed:

@table @samp
@item altivec
@itemx no-altivec
@cindex @code{target("altivec")} attribute
Generate code that uses (does not use) AltiVec instructions.  In
32-bit code, you cannot enable AltiVec instructions unless
@option{-mabi=altivec} is used on the command line.

@item cmpb
@itemx no-cmpb
@cindex @code{target("cmpb")} attribute
Generate code that uses (does not use) the compare bytes instruction
implemented on the POWER6 processor and other processors that support
the PowerPC V2.05 architecture.

@item dlmzb
@itemx no-dlmzb
@cindex @code{target("dlmzb")} attribute
Generate code that uses (does not use) the string-search @samp{dlmzb}
instruction on the IBM 405, 440, 464 and 476 processors.  This instruction is
generated by default when targeting those processors.

@item fprnd
@itemx no-fprnd
@cindex @code{target("fprnd")} attribute
Generate code that uses (does not use) the FP round to integer
instructions implemented on the POWER5+ processor and other processors
that support the PowerPC V2.03 architecture.

@item hard-dfp
@itemx no-hard-dfp
@cindex @code{target("hard-dfp")} attribute
Generate code that uses (does not use) the decimal floating-point
instructions implemented on some POWER processors.

@item isel
@itemx no-isel
@cindex @code{target("isel")} attribute
Generate code that uses (does not use) ISEL instruction.

@item mfcrf
@itemx no-mfcrf
@cindex @code{target("mfcrf")} attribute
Generate code that uses (does not use) the move from condition
register field instruction implemented on the POWER4 processor and
other processors that support the PowerPC V2.01 architecture.

@item mfpgpr
@itemx no-mfpgpr
@cindex @code{target("mfpgpr")} attribute
Generate code that uses (does not use) the FP move to/from general
purpose register instructions implemented on the POWER6X processor and
other processors that support the extended PowerPC V2.05 architecture.

@item mulhw
@itemx no-mulhw
@cindex @code{target("mulhw")} attribute
Generate code that uses (does not use) the half-word multiply and
multiply-accumulate instructions on the IBM 405, 440, 464 and 476 processors.
These instructions are generated by default when targeting those
processors.

@item multiple
@itemx no-multiple
@cindex @code{target("multiple")} attribute
Generate code that uses (does not use) the load multiple word
instructions and the store multiple word instructions.

@item update
@itemx no-update
@cindex @code{target("update")} attribute
Generate code that uses (does not use) the load or store instructions
that update the base register to the address of the calculated memory
location.

@item popcntb
@itemx no-popcntb
@cindex @code{target("popcntb")} attribute
Generate code that uses (does not use) the popcount and double-precision
FP reciprocal estimate instruction implemented on the POWER5
processor and other processors that support the PowerPC V2.02
architecture.

@item popcntd
@itemx no-popcntd
@cindex @code{target("popcntd")} attribute
Generate code that uses (does not use) the popcount instruction
implemented on the POWER7 processor and other processors that support
the PowerPC V2.06 architecture.

@item powerpc-gfxopt
@itemx no-powerpc-gfxopt
@cindex @code{target("powerpc-gfxopt")} attribute
Generate code that uses (does not use) the optional PowerPC
architecture instructions in the Graphics group, including
floating-point select.

@item powerpc-gpopt
@itemx no-powerpc-gpopt
@cindex @code{target("powerpc-gpopt")} attribute
Generate code that uses (does not use) the optional PowerPC
architecture instructions in the General Purpose group, including
floating-point square root.

@item recip-precision
@itemx no-recip-precision
@cindex @code{target("recip-precision")} attribute
Assume (do not assume) that the reciprocal estimate instructions
provide higher-precision estimates than is mandated by the powerpc
ABI.

@item string
@itemx no-string
@cindex @code{target("string")} attribute
Generate code that uses (does not use) the load string instructions
and the store string word instructions to save multiple registers and
do small block moves.

@item vsx
@itemx no-vsx
@cindex @code{target("vsx")} attribute
Generate code that uses (does not use) vector/scalar (VSX)
instructions, and also enable the use of built-in functions that allow
more direct access to the VSX instruction set.  In 32-bit code, you
cannot enable VSX or AltiVec instructions unless
@option{-mabi=altivec} is used on the command line.

@item friz
@itemx no-friz
@cindex @code{target("friz")} attribute
Generate (do not generate) the @code{friz} instruction when the
@option{-funsafe-math-optimizations} option is used to optimize
rounding a floating-point value to 64-bit integer and back to floating
point.  The @code{friz} instruction does not return the same value if
the floating-point number is too large to fit in an integer.

@item avoid-indexed-addresses
@itemx no-avoid-indexed-addresses
@cindex @code{target("avoid-indexed-addresses")} attribute
Generate code that tries to avoid (not avoid) the use of indexed load
or store instructions.

@item paired
@itemx no-paired
@cindex @code{target("paired")} attribute
Generate code that uses (does not use) the generation of PAIRED simd
instructions.

@item longcall
@itemx no-longcall
@cindex @code{target("longcall")} attribute
Generate code that assumes (does not assume) that all calls are far
away so that a longer more expensive calling sequence is required.

@item cpu=@var{CPU}
@cindex @code{target("cpu=@var{CPU}")} attribute
Specify the architecture to generate code for when compiling the
function.  If you select the @code{target("cpu=power7")} attribute when
generating 32-bit code, VSX and AltiVec instructions are not generated
unless you use the @option{-mabi=altivec} option on the command line.

@item tune=@var{TUNE}
@cindex @code{target("tune=@var{TUNE}")} attribute
Specify the architecture to tune for when compiling the function.  If
you do not specify the @code{target("tune=@var{TUNE}")} attribute and
you do specify the @code{target("cpu=@var{CPU}")} attribute,
compilation tunes for the @var{CPU} architecture, and not the
default tuning specified on the command line.
@end table

On the 386/x86_64 and PowerPC back ends, you can use either multiple
strings to specify multiple options, or you can separate the option
with a comma (@code{,}).

On the 386/x86_64 and PowerPC back ends, the inliner does not inline a
function that has different target options than the caller, unless the
callee has a subset of the target options of the caller.  For example
a function declared with @code{target("sse3")} can inline a function
with @code{target("sse2")}, since @code{-msse3} implies @code{-msse2}.

The @code{target} attribute is not implemented in GCC versions earlier
than 4.4 for the i386/x86_64 and 4.6 for the PowerPC back ends.  It is
not currently implemented for other back ends.

@item tiny_data
@cindex tiny data section on the H8/300H and H8S
Use this attribute on the H8/300H and H8S to indicate that the specified
variable should be placed into the tiny data section.
The compiler generates more efficient code for loads and stores
on data in the tiny data section.  Note the tiny data area is limited to
slightly under 32KB of data.

@item trap_exit
@cindex @code{trap_exit} attribute
Use this attribute on the SH for an @code{interrupt_handler} to return using
@code{trapa} instead of @code{rte}.  This attribute expects an integer
argument specifying the trap number to be used.

@item trapa_handler
@cindex @code{trapa_handler} attribute
On SH targets this function attribute is similar to @code{interrupt_handler}
but it does not save and restore all registers.

@item unused
@cindex @code{unused} attribute.
This attribute, attached to a function, means that the function is meant
to be possibly unused.  GCC does not produce a warning for this
function.

@item used
@cindex @code{used} attribute.
This attribute, attached to a function, means that code must be emitted
for the function even if it appears that the function is not referenced.
This is useful, for example, when the function is referenced only in
inline assembly.

When applied to a member function of a C++ class template, the
attribute also means that the function is instantiated if the
class itself is instantiated.

@item version_id
@cindex @code{version_id} attribute
This IA-64 HP-UX attribute, attached to a global variable or function, renames a
symbol to contain a version string, thus allowing for function level
versioning.  HP-UX system header files may use function level versioning
for some system calls.

@smallexample
extern int foo () __attribute__((version_id ("20040821")));
@end smallexample

@noindent
Calls to @var{foo} are mapped to calls to @var{foo@{20040821@}}.

@item visibility ("@var{visibility_type}")
@cindex @code{visibility} attribute
This attribute affects the linkage of the declaration to which it is attached.
There are four supported @var{visibility_type} values: default,
hidden, protected or internal visibility.

@smallexample
void __attribute__ ((visibility ("protected")))
f () @{ /* @r{Do something.} */; @}
int i __attribute__ ((visibility ("hidden")));
@end smallexample

The possible values of @var{visibility_type} correspond to the
visibility settings in the ELF gABI.

@table @dfn
@c keep this list of visibilities in alphabetical order.

@item default
Default visibility is the normal case for the object file format.
This value is available for the visibility attribute to override other
options that may change the assumed visibility of entities.

On ELF, default visibility means that the declaration is visible to other
modules and, in shared libraries, means that the declared entity may be
overridden.

On Darwin, default visibility means that the declaration is visible to
other modules.

Default visibility corresponds to ``external linkage'' in the language.

@item hidden
Hidden visibility indicates that the entity declared has a new
form of linkage, which we call ``hidden linkage''.  Two
declarations of an object with hidden linkage refer to the same object
if they are in the same shared object.

@item internal
Internal visibility is like hidden visibility, but with additional
processor specific semantics.  Unless otherwise specified by the
psABI, GCC defines internal visibility to mean that a function is
@emph{never} called from another module.  Compare this with hidden
functions which, while they cannot be referenced directly by other
modules, can be referenced indirectly via function pointers.  By
indicating that a function cannot be called from outside the module,
GCC may for instance omit the load of a PIC register since it is known
that the calling function loaded the correct value.

@item protected
Protected visibility is like default visibility except that it
indicates that references within the defining module bind to the
definition in that module.  That is, the declared entity cannot be
overridden by another module.

@end table

All visibilities are supported on many, but not all, ELF targets
(supported when the assembler supports the @samp{.visibility}
pseudo-op).  Default visibility is supported everywhere.  Hidden
visibility is supported on Darwin targets.

The visibility attribute should be applied only to declarations that
would otherwise have external linkage.  The attribute should be applied
consistently, so that the same entity should not be declared with
different settings of the attribute.

In C++, the visibility attribute applies to types as well as functions
and objects, because in C++ types have linkage.  A class must not have
greater visibility than its non-static data member types and bases,
and class members default to the visibility of their class.  Also, a
declaration without explicit visibility is limited to the visibility
of its type.

In C++, you can mark member functions and static member variables of a
class with the visibility attribute.  This is useful if you know a
particular method or static member variable should only be used from
one shared object; then you can mark it hidden while the rest of the
class has default visibility.  Care must be taken to avoid breaking
the One Definition Rule; for example, it is usually not useful to mark
an inline method as hidden without marking the whole class as hidden.

A C++ namespace declaration can also have the visibility attribute.
This attribute applies only to the particular namespace body, not to
other definitions of the same namespace; it is equivalent to using
@samp{#pragma GCC visibility} before and after the namespace
definition (@pxref{Visibility Pragmas}).

In C++, if a template argument has limited visibility, this
restriction is implicitly propagated to the template instantiation.
Otherwise, template instantiations and specializations default to the
visibility of their template.

If both the template and enclosing class have explicit visibility, the
visibility from the template is used.

@item vliw
@cindex @code{vliw} attribute
On MeP, the @code{vliw} attribute tells the compiler to emit
instructions in VLIW mode instead of core mode.  Note that this
attribute is not allowed unless a VLIW coprocessor has been configured
and enabled through command-line options.

@item warn_unused_result
@cindex @code{warn_unused_result} attribute
The @code{warn_unused_result} attribute causes a warning to be emitted
if a caller of the function with this attribute does not use its
return value.  This is useful for functions where not checking
the result is either a security problem or always a bug, such as
@code{realloc}.

@smallexample
int fn () __attribute__ ((warn_unused_result));
int foo ()
@{
  if (fn () < 0) return -1;
  fn ();
  return 0;
@}
@end smallexample

@noindent
results in warning on line 5.

@item weak
@cindex @code{weak} attribute
The @code{weak} attribute causes the declaration to be emitted as a weak
symbol rather than a global.  This is primarily useful in defining
library functions that can be overridden in user code, though it can
also be used with non-function declarations.  Weak symbols are supported
for ELF targets, and also for a.out targets when using the GNU assembler
and linker.

@item weakref
@itemx weakref ("@var{target}")
@cindex @code{weakref} attribute
The @code{weakref} attribute marks a declaration as a weak reference.
Without arguments, it should be accompanied by an @code{alias} attribute
naming the target symbol.  Optionally, the @var{target} may be given as
an argument to @code{weakref} itself.  In either case, @code{weakref}
implicitly marks the declaration as @code{weak}.  Without a
@var{target}, given as an argument to @code{weakref} or to @code{alias},
@code{weakref} is equivalent to @code{weak}.

@smallexample
static int x() __attribute__ ((weakref ("y")));
/* is equivalent to... */
static int x() __attribute__ ((weak, weakref, alias ("y")));
/* and to... */
static int x() __attribute__ ((weakref));
static int x() __attribute__ ((alias ("y")));
@end smallexample

A weak reference is an alias that does not by itself require a
definition to be given for the target symbol.  If the target symbol is
only referenced through weak references, then it becomes a @code{weak}
undefined symbol.  If it is directly referenced, however, then such
strong references prevail, and a definition is required for the
symbol, not necessarily in the same translation unit.

The effect is equivalent to moving all references to the alias to a
separate translation unit, renaming the alias to the aliased symbol,
declaring it as weak, compiling the two separate translation units and
performing a reloadable link on them.

At present, a declaration to which @code{weakref} is attached can
only be @code{static}.

@end table

You can specify multiple attributes in a declaration by separating them
by commas within the double parentheses or by immediately following an
attribute declaration with another attribute declaration.

@cindex @code{#pragma}, reason for not using
@cindex pragma, reason for not using
Some people object to the @code{__attribute__} feature, suggesting that
ISO C's @code{#pragma} should be used instead.  At the time
@code{__attribute__} was designed, there were two reasons for not doing
this.

@enumerate
@item
It is impossible to generate @code{#pragma} commands from a macro.

@item
There is no telling what the same @code{#pragma} might mean in another
compiler.
@end enumerate

These two reasons applied to almost any application that might have been
proposed for @code{#pragma}.  It was basically a mistake to use
@code{#pragma} for @emph{anything}.

The ISO C99 standard includes @code{_Pragma}, which now allows pragmas
to be generated from macros.  In addition, a @code{#pragma GCC}
namespace is now in use for GCC-specific pragmas.  However, it has been
found convenient to use @code{__attribute__} to achieve a natural
attachment of attributes to their corresponding declarations, whereas
@code{#pragma GCC} is of use for constructs that do not naturally form
part of the grammar.  @xref{Pragmas,,Pragmas Accepted by GCC}.

@node Attribute Syntax
@section Attribute Syntax
@cindex attribute syntax

This section describes the syntax with which @code{__attribute__} may be
used, and the constructs to which attribute specifiers bind, for the C
language.  Some details may vary for C++ and Objective-C@.  Because of
infelicities in the grammar for attributes, some forms described here
may not be successfully parsed in all cases.

There are some problems with the semantics of attributes in C++.  For
example, there are no manglings for attributes, although they may affect
code generation, so problems may arise when attributed types are used in
conjunction with templates or overloading.  Similarly, @code{typeid}
does not distinguish between types with different attributes.  Support
for attributes in C++ may be restricted in future to attributes on
declarations only, but not on nested declarators.

@xref{Function Attributes}, for details of the semantics of attributes
applying to functions.  @xref{Variable Attributes}, for details of the
semantics of attributes applying to variables.  @xref{Type Attributes},
for details of the semantics of attributes applying to structure, union
and enumerated types.

An @dfn{attribute specifier} is of the form
@code{__attribute__ ((@var{attribute-list}))}.  An @dfn{attribute list}
is a possibly empty comma-separated sequence of @dfn{attributes}, where
each attribute is one of the following:

@itemize @bullet
@item
Empty.  Empty attributes are ignored.

@item
A word (which may be an identifier such as @code{unused}, or a reserved
word such as @code{const}).

@item
A word, followed by, in parentheses, parameters for the attribute.
These parameters take one of the following forms:

@itemize @bullet
@item
An identifier.  For example, @code{mode} attributes use this form.

@item
An identifier followed by a comma and a non-empty comma-separated list
of expressions.  For example, @code{format} attributes use this form.

@item
A possibly empty comma-separated list of expressions.  For example,
@code{format_arg} attributes use this form with the list being a single
integer constant expression, and @code{alias} attributes use this form
with the list being a single string constant.
@end itemize
@end itemize

An @dfn{attribute specifier list} is a sequence of one or more attribute
specifiers, not separated by any other tokens.

In GNU C, an attribute specifier list may appear after the colon following a
label, other than a @code{case} or @code{default} label.  The only
attribute it makes sense to use after a label is @code{unused}.  This
feature is intended for program-generated code that may contain unused labels,
but which is compiled with @option{-Wall}.  It is
not normally appropriate to use in it human-written code, though it
could be useful in cases where the code that jumps to the label is
contained within an @code{#ifdef} conditional.  GNU C++ only permits
attributes on labels if the attribute specifier is immediately
followed by a semicolon (i.e., the label applies to an empty
statement).  If the semicolon is missing, C++ label attributes are
ambiguous, as it is permissible for a declaration, which could begin
with an attribute list, to be labelled in C++.  Declarations cannot be
labelled in C90 or C99, so the ambiguity does not arise there.

An attribute specifier list may appear as part of a @code{struct},
@code{union} or @code{enum} specifier.  It may go either immediately
after the @code{struct}, @code{union} or @code{enum} keyword, or after
the closing brace.  The former syntax is preferred.
Where attribute specifiers follow the closing brace, they are considered
to relate to the structure, union or enumerated type defined, not to any
enclosing declaration the type specifier appears in, and the type
defined is not complete until after the attribute specifiers.
@c Otherwise, there would be the following problems: a shift/reduce
@c conflict between attributes binding the struct/union/enum and
@c binding to the list of specifiers/qualifiers; and "aligned"
@c attributes could use sizeof for the structure, but the size could be
@c changed later by "packed" attributes.

Otherwise, an attribute specifier appears as part of a declaration,
counting declarations of unnamed parameters and type names, and relates
to that declaration (which may be nested in another declaration, for
example in the case of a parameter declaration), or to a particular declarator
within a declaration.  Where an
attribute specifier is applied to a parameter declared as a function or
an array, it should apply to the function or array rather than the
pointer to which the parameter is implicitly converted, but this is not
yet correctly implemented.

Any list of specifiers and qualifiers at the start of a declaration may
contain attribute specifiers, whether or not such a list may in that
context contain storage class specifiers.  (Some attributes, however,
are essentially in the nature of storage class specifiers, and only make
sense where storage class specifiers may be used; for example,
@code{section}.)  There is one necessary limitation to this syntax: the
first old-style parameter declaration in a function definition cannot
begin with an attribute specifier, because such an attribute applies to
the function instead by syntax described below (which, however, is not
yet implemented in this case).  In some other cases, attribute
specifiers are permitted by this grammar but not yet supported by the
compiler.  All attribute specifiers in this place relate to the
declaration as a whole.  In the obsolescent usage where a type of
@code{int} is implied by the absence of type specifiers, such a list of
specifiers and qualifiers may be an attribute specifier list with no
other specifiers or qualifiers.

At present, the first parameter in a function prototype must have some
type specifier that is not an attribute specifier; this resolves an
ambiguity in the interpretation of @code{void f(int
(__attribute__((foo)) x))}, but is subject to change.  At present, if
the parentheses of a function declarator contain only attributes then
those attributes are ignored, rather than yielding an error or warning
or implying a single parameter of type int, but this is subject to
change.

An attribute specifier list may appear immediately before a declarator
(other than the first) in a comma-separated list of declarators in a
declaration of more than one identifier using a single list of
specifiers and qualifiers.  Such attribute specifiers apply
only to the identifier before whose declarator they appear.  For
example, in

@smallexample
__attribute__((noreturn)) void d0 (void),
    __attribute__((format(printf, 1, 2))) d1 (const char *, ...),
     d2 (void)
@end smallexample

@noindent
the @code{noreturn} attribute applies to all the functions
declared; the @code{format} attribute only applies to @code{d1}.

An attribute specifier list may appear immediately before the comma,
@code{=} or semicolon terminating the declaration of an identifier other
than a function definition.  Such attribute specifiers apply
to the declared object or function.  Where an
assembler name for an object or function is specified (@pxref{Asm
Labels}), the attribute must follow the @code{asm}
specification.

An attribute specifier list may, in future, be permitted to appear after
the declarator in a function definition (before any old-style parameter
declarations or the function body).

Attribute specifiers may be mixed with type qualifiers appearing inside
the @code{[]} of a parameter array declarator, in the C99 construct by
which such qualifiers are applied to the pointer to which the array is
implicitly converted.  Such attribute specifiers apply to the pointer,
not to the array, but at present this is not implemented and they are
ignored.

An attribute specifier list may appear at the start of a nested
declarator.  At present, there are some limitations in this usage: the
attributes correctly apply to the declarator, but for most individual
attributes the semantics this implies are not implemented.
When attribute specifiers follow the @code{*} of a pointer
declarator, they may be mixed with any type qualifiers present.
The following describes the formal semantics of this syntax.  It makes the
most sense if you are familiar with the formal specification of
declarators in the ISO C standard.

Consider (as in C99 subclause 6.7.5 paragraph 4) a declaration @code{T
D1}, where @code{T} contains declaration specifiers that specify a type
@var{Type} (such as @code{int}) and @code{D1} is a declarator that
contains an identifier @var{ident}.  The type specified for @var{ident}
for derived declarators whose type does not include an attribute
specifier is as in the ISO C standard.

If @code{D1} has the form @code{( @var{attribute-specifier-list} D )},
and the declaration @code{T D} specifies the type
``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then
@code{T D1} specifies the type ``@var{derived-declarator-type-list}
@var{attribute-specifier-list} @var{Type}'' for @var{ident}.

If @code{D1} has the form @code{*
@var{type-qualifier-and-attribute-specifier-list} D}, and the
declaration @code{T D} specifies the type
``@var{derived-declarator-type-list} @var{Type}'' for @var{ident}, then
@code{T D1} specifies the type ``@var{derived-declarator-type-list}
@var{type-qualifier-and-attribute-specifier-list} pointer to @var{Type}'' for
@var{ident}.

For example,

@smallexample
void (__attribute__((noreturn)) ****f) (void);
@end smallexample

@noindent
specifies the type ``pointer to pointer to pointer to pointer to
non-returning function returning @code{void}''.  As another example,

@smallexample
char *__attribute__((aligned(8))) *f;
@end smallexample

@noindent
specifies the type ``pointer to 8-byte-aligned pointer to @code{char}''.
Note again that this does not work with most attributes; for example,
the usage of @samp{aligned} and @samp{noreturn} attributes given above
is not yet supported.

For compatibility with existing code written for compiler versions that
did not implement attributes on nested declarators, some laxity is
allowed in the placing of attributes.  If an attribute that only applies
to types is applied to a declaration, it is treated as applying to
the type of that declaration.  If an attribute that only applies to
declarations is applied to the type of a declaration, it is treated
as applying to that declaration; and, for compatibility with code
placing the attributes immediately before the identifier declared, such
an attribute applied to a function return type is treated as
applying to the function type, and such an attribute applied to an array
element type is treated as applying to the array type.  If an
attribute that only applies to function types is applied to a
pointer-to-function type, it is treated as applying to the pointer
target type; if such an attribute is applied to a function return type
that is not a pointer-to-function type, it is treated as applying
to the function type.

@node Function Prototypes
@section Prototypes and Old-Style Function Definitions
@cindex function prototype declarations
@cindex old-style function definitions
@cindex promotion of formal parameters

GNU C extends ISO C to allow a function prototype to override a later
old-style non-prototype definition.  Consider the following example:

@smallexample
/* @r{Use prototypes unless the compiler is old-fashioned.}  */
#ifdef __STDC__
#define P(x) x
#else
#define P(x) ()
#endif

/* @r{Prototype function declaration.}  */
int isroot P((uid_t));

/* @r{Old-style function definition.}  */
int
isroot (x)   /* @r{??? lossage here ???} */
     uid_t x;
@{
  return x == 0;
@}
@end smallexample

Suppose the type @code{uid_t} happens to be @code{short}.  ISO C does
not allow this example, because subword arguments in old-style
non-prototype definitions are promoted.  Therefore in this example the
function definition's argument is really an @code{int}, which does not
match the prototype argument type of @code{short}.

This restriction of ISO C makes it hard to write code that is portable
to traditional C compilers, because the programmer does not know
whether the @code{uid_t} type is @code{short}, @code{int}, or
@code{long}.  Therefore, in cases like these GNU C allows a prototype
to override a later old-style definition.  More precisely, in GNU C, a
function prototype argument type overrides the argument type specified
by a later old-style definition if the former type is the same as the
latter type before promotion.  Thus in GNU C the above example is
equivalent to the following:

@smallexample
int isroot (uid_t);

int
isroot (uid_t x)
@{
  return x == 0;
@}
@end smallexample

@noindent
GNU C++ does not support old-style function definitions, so this
extension is irrelevant.

@node C++ Comments
@section C++ Style Comments
@cindex @code{//}
@cindex C++ comments
@cindex comments, C++ style

In GNU C, you may use C++ style comments, which start with @samp{//} and
continue until the end of the line.  Many other C implementations allow
such comments, and they are included in the 1999 C standard.  However,
C++ style comments are not recognized if you specify an @option{-std}
option specifying a version of ISO C before C99, or @option{-ansi}
(equivalent to @option{-std=c90}).

@node Dollar Signs
@section Dollar Signs in Identifier Names
@cindex $
@cindex dollar signs in identifier names
@cindex identifier names, dollar signs in

In GNU C, you may normally use dollar signs in identifier names.
This is because many traditional C implementations allow such identifiers.
However, dollar signs in identifiers are not supported on a few target
machines, typically because the target assembler does not allow them.

@node Character Escapes
@section The Character @key{ESC} in Constants

You can use the sequence @samp{\e} in a string or character constant to
stand for the ASCII character @key{ESC}.

@node Variable Attributes
@section Specifying Attributes of Variables
@cindex attribute of variables
@cindex variable attributes

The keyword @code{__attribute__} allows you to specify special
attributes of variables or structure fields.  This keyword is followed
by an attribute specification inside double parentheses.  Some
attributes are currently defined generically for variables.
Other attributes are defined for variables on particular target
systems.  Other attributes are available for functions
(@pxref{Function Attributes}) and for types (@pxref{Type Attributes}).
Other front ends might define more attributes
(@pxref{C++ Extensions,,Extensions to the C++ Language}).

You may also specify attributes with @samp{__} preceding and following
each keyword.  This allows you to use them in header files without
being concerned about a possible macro of the same name.  For example,
you may use @code{__aligned__} instead of @code{aligned}.

@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.

@table @code
@cindex @code{aligned} attribute
@item aligned (@var{alignment})
This attribute specifies a minimum alignment for the variable or
structure field, measured in bytes.  For example, the declaration:

@smallexample
int x __attribute__ ((aligned (16))) = 0;
@end smallexample

@noindent
causes the compiler to allocate the global variable @code{x} on a
16-byte boundary.  On a 68040, this could be used in conjunction with
an @code{asm} expression to access the @code{move16} instruction which
requires 16-byte aligned operands.

You can also specify the alignment of structure fields.  For example, to
create a double-word aligned @code{int} pair, you could write:

@smallexample
struct foo @{ int x[2] __attribute__ ((aligned (8))); @};
@end smallexample

@noindent
This is an alternative to creating a union with a @code{double} member,
which forces the union to be double-word aligned.

As in the preceding examples, you can explicitly specify the alignment
(in bytes) that you wish the compiler to use for a given variable or
structure field.  Alternatively, you can leave out the alignment factor
and just ask the compiler to align a variable or field to the
default alignment for the target architecture you are compiling for.
The default alignment is sufficient for all scalar types, but may not be
enough for all vector types on a target that supports vector operations.
The default alignment is fixed for a particular target ABI.

GCC also provides a target specific macro @code{__BIGGEST_ALIGNMENT__},
which is the largest alignment ever used for any data type on the
target machine you are compiling for.  For example, you could write:

@smallexample
short array[3] __attribute__ ((aligned (__BIGGEST_ALIGNMENT__)));
@end smallexample

The compiler automatically sets the alignment for the declared
variable or field to @code{__BIGGEST_ALIGNMENT__}.  Doing this can
often make copy operations more efficient, because the compiler can
use whatever instructions copy the biggest chunks of memory when
performing copies to or from the variables or fields that you have
aligned this way.  Note that the value of @code{__BIGGEST_ALIGNMENT__}
may change depending on command-line options.

When used on a struct, or struct member, the @code{aligned} attribute can
only increase the alignment; in order to decrease it, the @code{packed}
attribute must be specified as well.  When used as part of a typedef, the
@code{aligned} attribute can both increase and decrease alignment, and
specifying the @code{packed} attribute generates a warning.

Note that the effectiveness of @code{aligned} attributes may be limited
by inherent limitations in your linker.  On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment.  (For some linkers, the maximum supported alignment may
be very very small.)  If your linker is only able to align variables
up to a maximum of 8-byte alignment, then specifying @code{aligned(16)}
in an @code{__attribute__} still only provides you with 8-byte
alignment.  See your linker documentation for further information.

The @code{aligned} attribute can also be used for functions
(@pxref{Function Attributes}.)

@item cleanup (@var{cleanup_function})
@cindex @code{cleanup} attribute
The @code{cleanup} attribute runs a function when the variable goes
out of scope.  This attribute can only be applied to auto function
scope variables; it may not be applied to parameters or variables
with static storage duration.  The function must take one parameter,
a pointer to a type compatible with the variable.  The return value
of the function (if any) is ignored.

If @option{-fexceptions} is enabled, then @var{cleanup_function}
is run during the stack unwinding that happens during the
processing of the exception.  Note that the @code{cleanup} attribute
does not allow the exception to be caught, only to perform an action.
It is undefined what happens if @var{cleanup_function} does not
return normally.

@item common
@itemx nocommon
@cindex @code{common} attribute
@cindex @code{nocommon} attribute
@opindex fcommon
@opindex fno-common
The @code{common} attribute requests GCC to place a variable in
``common'' storage.  The @code{nocommon} attribute requests the
opposite---to allocate space for it directly.

These attributes override the default chosen by the
@option{-fno-common} and @option{-fcommon} flags respectively.

@item deprecated
@itemx deprecated (@var{msg})
@cindex @code{deprecated} attribute
The @code{deprecated} attribute results in a warning if the variable
is used anywhere in the source file.  This is useful when identifying
variables that are expected to be removed in a future version of a
program.  The warning also includes the location of the declaration
of the deprecated variable, to enable users to easily find further
information about why the variable is deprecated, or what they should
do instead.  Note that the warning only occurs for uses:

@smallexample
extern int old_var __attribute__ ((deprecated));
extern int old_var;
int new_fn () @{ return old_var; @}
@end smallexample

@noindent
results in a warning on line 3 but not line 2.  The optional @var{msg}
argument, which must be a string, is printed in the warning if
present.

The @code{deprecated} attribute can also be used for functions and
types (@pxref{Function Attributes}, @pxref{Type Attributes}.)

@item mode (@var{mode})
@cindex @code{mode} attribute
This attribute specifies the data type for the declaration---whichever
type corresponds to the mode @var{mode}.  This in effect lets you
request an integer or floating-point type according to its width.

You may also specify a mode of @code{byte} or @code{__byte__} to
indicate the mode corresponding to a one-byte integer, @code{word} or
@code{__word__} for the mode of a one-word integer, and @code{pointer}
or @code{__pointer__} for the mode used to represent pointers.

@item packed
@cindex @code{packed} attribute
The @code{packed} attribute specifies that a variable or structure field
should have the smallest possible alignment---one byte for a variable,
and one bit for a field, unless you specify a larger value with the
@code{aligned} attribute.

Here is a structure in which the field @code{x} is packed, so that it
immediately follows @code{a}:

@smallexample
struct foo
@{
  char a;
  int x[2] __attribute__ ((packed));
@};
@end smallexample

@emph{Note:} The 4.1, 4.2 and 4.3 series of GCC ignore the
@code{packed} attribute on bit-fields of type @code{char}.  This has
been fixed in GCC 4.4 but the change can lead to differences in the
structure layout.  See the documentation of
@option{-Wpacked-bitfield-compat} for more information.

@item section ("@var{section-name}")
@cindex @code{section} variable attribute
Normally, the compiler places the objects it generates in sections like
@code{data} and @code{bss}.  Sometimes, however, you need additional sections,
or you need certain particular variables to appear in special sections,
for example to map to special hardware.  The @code{section}
attribute specifies that a variable (or function) lives in a particular
section.  For example, this small program uses several specific section names:

@smallexample
struct duart a __attribute__ ((section ("DUART_A"))) = @{ 0 @};
struct duart b __attribute__ ((section ("DUART_B"))) = @{ 0 @};
char stack[10000] __attribute__ ((section ("STACK"))) = @{ 0 @};
int init_data __attribute__ ((section ("INITDATA")));

main()
@{
  /* @r{Initialize stack pointer} */
  init_sp (stack + sizeof (stack));

  /* @r{Initialize initialized data} */
  memcpy (&init_data, &data, &edata - &data);

  /* @r{Turn on the serial ports} */
  init_duart (&a);
  init_duart (&b);
@}
@end smallexample

@noindent
Use the @code{section} attribute with
@emph{global} variables and not @emph{local} variables,
as shown in the example.

You may use the @code{section} attribute with initialized or
uninitialized global variables but the linker requires
each object be defined once, with the exception that uninitialized
variables tentatively go in the @code{common} (or @code{bss}) section
and can be multiply ``defined''.  Using the @code{section} attribute
changes what section the variable goes into and may cause the
linker to issue an error if an uninitialized variable has multiple
definitions.  You can force a variable to be initialized with the
@option{-fno-common} flag or the @code{nocommon} attribute.

Some file formats do not support arbitrary sections so the @code{section}
attribute is not available on all platforms.
If you need to map the entire contents of a module to a particular
section, consider using the facilities of the linker instead.

@item shared
@cindex @code{shared} variable attribute
On Microsoft Windows, in addition to putting variable definitions in a named
section, the section can also be shared among all running copies of an
executable or DLL@.  For example, this small program defines shared data
by putting it in a named section @code{shared} and marking the section
shareable:

@smallexample
int foo __attribute__((section ("shared"), shared)) = 0;

int
main()
@{
  /* @r{Read and write foo.  All running
     copies see the same value.}  */
  return 0;
@}
@end smallexample

@noindent
You may only use the @code{shared} attribute along with @code{section}
attribute with a fully-initialized global definition because of the way
linkers work.  See @code{section} attribute for more information.

The @code{shared} attribute is only available on Microsoft Windows@.

@item tls_model ("@var{tls_model}")
@cindex @code{tls_model} attribute
The @code{tls_model} attribute sets thread-local storage model
(@pxref{Thread-Local}) of a particular @code{__thread} variable,
overriding @option{-ftls-model=} command-line switch on a per-variable
basis.
The @var{tls_model} argument should be one of @code{global-dynamic},
@code{local-dynamic}, @code{initial-exec} or @code{local-exec}.

Not all targets support this attribute.

@item unused
This attribute, attached to a variable, means that the variable is meant
to be possibly unused.  GCC does not produce a warning for this
variable.

@item used
This attribute, attached to a variable, means that the variable must be
emitted even if it appears that the variable is not referenced.

When applied to a static data member of a C++ class template, the
attribute also means that the member is instantiated if the
class itself is instantiated.

@item vector_size (@var{bytes})
This attribute specifies the vector size for the variable, measured in
bytes.  For example, the declaration:

@smallexample
int foo __attribute__ ((vector_size (16)));
@end smallexample

@noindent
causes the compiler to set the mode for @code{foo}, to be 16 bytes,
divided into @code{int} sized units.  Assuming a 32-bit int (a vector of
4 units of 4 bytes), the corresponding mode of @code{foo} is V4SI@.

This attribute is only applicable to integral and float scalars,
although arrays, pointers, and function return values are allowed in
conjunction with this construct.

Aggregates with this attribute are invalid, even if they are of the same
size as a corresponding scalar.  For example, the declaration:

@smallexample
struct S @{ int a; @};
struct S  __attribute__ ((vector_size (16))) foo;
@end smallexample

@noindent
is invalid even if the size of the structure is the same as the size of
the @code{int}.

@item selectany
The @code{selectany} attribute causes an initialized global variable to
have link-once semantics.  When multiple definitions of the variable are
encountered by the linker, the first is selected and the remainder are
discarded.  Following usage by the Microsoft compiler, the linker is told
@emph{not} to warn about size or content differences of the multiple
definitions.

Although the primary usage of this attribute is for POD types, the
attribute can also be applied to global C++ objects that are initialized
by a constructor.  In this case, the static initialization and destruction
code for the object is emitted in each translation defining the object,
but the calls to the constructor and destructor are protected by a
link-once guard variable.

The @code{selectany} attribute is only available on Microsoft Windows
targets.  You can use @code{__declspec (selectany)} as a synonym for
@code{__attribute__ ((selectany))} for compatibility with other
compilers.

@item weak
The @code{weak} attribute is described in @ref{Function Attributes}.

@item dllimport
The @code{dllimport} attribute is described in @ref{Function Attributes}.

@item dllexport
The @code{dllexport} attribute is described in @ref{Function Attributes}.

@end table

@anchor{AVR Variable Attributes}
@subsection AVR Variable Attributes

@table @code
@item progmem
@cindex @code{progmem} AVR variable attribute
The @code{progmem} attribute is used on the AVR to place read-only
data in the non-volatile program memory (flash). The @code{progmem}
attribute accomplishes this by putting respective variables into a
section whose name starts with @code{.progmem}.

This attribute works similar to the @code{section} attribute
but adds additional checking. Notice that just like the
@code{section} attribute, @code{progmem} affects the location
of the data but not how this data is accessed.

In order to read data located with the @code{progmem} attribute
(inline) assembler must be used.
@smallexample
/* Use custom macros from @w{@uref{http://nongnu.org/avr-libc/user-manual/,AVR-LibC}} */
#include <avr/pgmspace.h> 

/* Locate var in flash memory */
const int var[2] PROGMEM = @{ 1, 2 @};

int read_var (int i)
@{
    /* Access var[] by accessor macro from avr/pgmspace.h */
    return (int) pgm_read_word (& var[i]);
@}
@end smallexample

AVR is a Harvard architecture processor and data and read-only data
normally resides in the data memory (RAM).

See also the @ref{AVR Named Address Spaces} section for
an alternate way to locate and access data in flash memory.
@end table

@subsection Blackfin Variable Attributes

Three attributes are currently defined for the Blackfin.

@table @code
@item l1_data
@itemx l1_data_A
@itemx l1_data_B
@cindex @code{l1_data} variable attribute
@cindex @code{l1_data_A} variable attribute
@cindex @code{l1_data_B} variable attribute
Use these attributes on the Blackfin to place the variable into L1 Data SRAM.
Variables with @code{l1_data} attribute are put into the specific section
named @code{.l1.data}. Those with @code{l1_data_A} attribute are put into
the specific section named @code{.l1.data.A}. Those with @code{l1_data_B}
attribute are put into the specific section named @code{.l1.data.B}.

@item l2
@cindex @code{l2} variable attribute
Use this attribute on the Blackfin to place the variable into L2 SRAM.
Variables with @code{l2} attribute are put into the specific section
named @code{.l2.data}.
@end table

@subsection M32R/D Variable Attributes

One attribute is currently defined for the M32R/D@.

@table @code
@item model (@var{model-name})
@cindex variable addressability on the M32R/D
Use this attribute on the M32R/D to set the addressability of an object.
The identifier @var{model-name} is one of @code{small}, @code{medium},
or @code{large}, representing each of the code models.

Small model objects live in the lower 16MB of memory (so that their
addresses can be loaded with the @code{ld24} instruction).

Medium and large model objects may live anywhere in the 32-bit address space
(the compiler generates @code{seth/add3} instructions to load their
addresses).
@end table

@anchor{MeP Variable Attributes}
@subsection MeP Variable Attributes

The MeP target has a number of addressing modes and busses.  The
@code{near} space spans the standard memory space's first 16 megabytes
(24 bits).  The @code{far} space spans the entire 32-bit memory space.
The @code{based} space is a 128-byte region in the memory space that
is addressed relative to the @code{$tp} register.  The @code{tiny}
space is a 65536-byte region relative to the @code{$gp} register.  In
addition to these memory regions, the MeP target has a separate 16-bit
control bus which is specified with @code{cb} attributes.

@table @code

@item based
Any variable with the @code{based} attribute is assigned to the
@code{.based} section, and is accessed with relative to the
@code{$tp} register.

@item tiny
Likewise, the @code{tiny} attribute assigned variables to the
@code{.tiny} section, relative to the @code{$gp} register.

@item near
Variables with the @code{near} attribute are assumed to have addresses
that fit in a 24-bit addressing mode.  This is the default for large
variables (@code{-mtiny=4} is the default) but this attribute can
override @code{-mtiny=} for small variables, or override @code{-ml}.

@item far
Variables with the @code{far} attribute are addressed using a full
32-bit address.  Since this covers the entire memory space, this
allows modules to make no assumptions about where variables might be
stored.

@item io
@itemx io (@var{addr})
Variables with the @code{io} attribute are used to address
memory-mapped peripherals.  If an address is specified, the variable
is assigned that address, else it is not assigned an address (it is
assumed some other module assigns an address).  Example:

@smallexample
int timer_count __attribute__((io(0x123)));
@end smallexample

@item cb
@itemx cb (@var{addr})
Variables with the @code{cb} attribute are used to access the control
bus, using special instructions.  @code{addr} indicates the control bus
address.  Example:

@smallexample
int cpu_clock __attribute__((cb(0x123)));
@end smallexample

@end table

@anchor{i386 Variable Attributes}
@subsection i386 Variable Attributes

Two attributes are currently defined for i386 configurations:
@code{ms_struct} and @code{gcc_struct}

@table @code
@item ms_struct
@itemx gcc_struct
@cindex @code{ms_struct} attribute
@cindex @code{gcc_struct} attribute

If @code{packed} is used on a structure, or if bit-fields are used,
it may be that the Microsoft ABI lays out the structure differently
than the way GCC normally does.  Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.

Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.

The Microsoft structure layout algorithm is fairly simple with the exception
of the bit-field packing.  
The padding and alignment of members of structures and whether a bit-field 
can straddle a storage-unit boundary are determine by these rules:

@enumerate
@item Structure members are stored sequentially in the order in which they are
declared: the first member has the lowest memory address and the last member
the highest.

@item Every data object has an alignment requirement.  The alignment requirement
for all data except structures, unions, and arrays is either the size of the
object or the current packing size (specified with either the
@code{aligned} attribute or the @code{pack} pragma),
whichever is less.  For structures, unions, and arrays,
the alignment requirement is the largest alignment requirement of its members.
Every object is allocated an offset so that:

@smallexample
offset % alignment_requirement == 0
@end smallexample

@item Adjacent bit-fields are packed into the same 1-, 2-, or 4-byte allocation
unit if the integral types are the same size and if the next bit-field fits
into the current allocation unit without crossing the boundary imposed by the
common alignment requirements of the bit-fields.
@end enumerate

MSVC interprets zero-length bit-fields in the following ways:

@enumerate
@item If a zero-length bit-field is inserted between two bit-fields that
are normally coalesced, the bit-fields are not coalesced.

For example:

@smallexample
struct
 @{
   unsigned long bf_1 : 12;
   unsigned long : 0;
   unsigned long bf_2 : 12;
 @} t1;
@end smallexample

@noindent
The size of @code{t1} is 8 bytes with the zero-length bit-field.  If the
zero-length bit-field were removed, @code{t1}'s size would be 4 bytes.

@item If a zero-length bit-field is inserted after a bit-field, @code{foo}, and the
alignment of the zero-length bit-field is greater than the member that follows it,
@code{bar}, @code{bar} is aligned as the type of the zero-length bit-field.

For example:

@smallexample
struct
 @{
   char foo : 4;
   short : 0;
   char bar;
 @} t2;

struct
 @{
   char foo : 4;
   short : 0;
   double bar;
 @} t3;
@end smallexample

@noindent
For @code{t2}, @code{bar} is placed at offset 2, rather than offset 1.
Accordingly, the size of @code{t2} is 4.  For @code{t3}, the zero-length
bit-field does not affect the alignment of @code{bar} or, as a result, the size
of the structure.

Taking this into account, it is important to note the following:

@enumerate
@item If a zero-length bit-field follows a normal bit-field, the type of the
zero-length bit-field may affect the alignment of the structure as whole. For
example, @code{t2} has a size of 4 bytes, since the zero-length bit-field follows a
normal bit-field, and is of type short.

@item Even if a zero-length bit-field is not followed by a normal bit-field, it may
still affect the alignment of the structure:

@smallexample
struct
 @{
   char foo : 6;
   long : 0;
 @} t4;
@end smallexample

@noindent
Here, @code{t4} takes up 4 bytes.
@end enumerate

@item Zero-length bit-fields following non-bit-field members are ignored:

@smallexample
struct
 @{
   char foo;
   long : 0;
   char bar;
 @} t5;
@end smallexample

@noindent
Here, @code{t5} takes up 2 bytes.
@end enumerate
@end table

@subsection PowerPC Variable Attributes

Three attributes currently are defined for PowerPC configurations:
@code{altivec}, @code{ms_struct} and @code{gcc_struct}.

For full documentation of the struct attributes please see the
documentation in @ref{i386 Variable Attributes}.

For documentation of @code{altivec} attribute please see the
documentation in @ref{PowerPC Type Attributes}.

@subsection SPU Variable Attributes

The SPU supports the @code{spu_vector} attribute for variables.  For
documentation of this attribute please see the documentation in
@ref{SPU Type Attributes}.

@subsection Xstormy16 Variable Attributes

One attribute is currently defined for xstormy16 configurations:
@code{below100}.

@table @code
@item below100
@cindex @code{below100} attribute

If a variable has the @code{below100} attribute (@code{BELOW100} is
allowed also), GCC places the variable in the first 0x100 bytes of
memory and use special opcodes to access it.  Such variables are
placed in either the @code{.bss_below100} section or the
@code{.data_below100} section.

@end table

@node Type Attributes
@section Specifying Attributes of Types
@cindex attribute of types
@cindex type attributes

The keyword @code{__attribute__} allows you to specify special
attributes of @code{struct} and @code{union} types when you define
such types.  This keyword is followed by an attribute specification
inside double parentheses.  Seven attributes are currently defined for
types: @code{aligned}, @code{packed}, @code{transparent_union},
@code{unused}, @code{deprecated}, @code{visibility}, and
@code{may_alias}.  Other attributes are defined for functions
(@pxref{Function Attributes}) and for variables (@pxref{Variable
Attributes}).

You may also specify any one of these attributes with @samp{__}
preceding and following its keyword.  This allows you to use these
attributes in header files without being concerned about a possible
macro of the same name.  For example, you may use @code{__aligned__}
instead of @code{aligned}.

You may specify type attributes in an enum, struct or union type
declaration or definition, or for other types in a @code{typedef}
declaration.

For an enum, struct or union type, you may specify attributes either
between the enum, struct or union tag and the name of the type, or
just past the closing curly brace of the @emph{definition}.  The
former syntax is preferred.

@xref{Attribute Syntax}, for details of the exact syntax for using
attributes.

@table @code
@cindex @code{aligned} attribute
@item aligned (@var{alignment})
This attribute specifies a minimum alignment (in bytes) for variables
of the specified type.  For example, the declarations:

@smallexample
struct S @{ short f[3]; @} __attribute__ ((aligned (8)));
typedef int more_aligned_int __attribute__ ((aligned (8)));
@end smallexample

@noindent
force the compiler to ensure (as far as it can) that each variable whose
type is @code{struct S} or @code{more_aligned_int} is allocated and
aligned @emph{at least} on a 8-byte boundary.  On a SPARC, having all
variables of type @code{struct S} aligned to 8-byte boundaries allows
the compiler to use the @code{ldd} and @code{std} (doubleword load and
store) instructions when copying one variable of type @code{struct S} to
another, thus improving run-time efficiency.

Note that the alignment of any given @code{struct} or @code{union} type
is required by the ISO C standard to be at least a perfect multiple of
the lowest common multiple of the alignments of all of the members of
the @code{struct} or @code{union} in question.  This means that you @emph{can}
effectively adjust the alignment of a @code{struct} or @code{union}
type by attaching an @code{aligned} attribute to any one of the members
of such a type, but the notation illustrated in the example above is a
more obvious, intuitive, and readable way to request the compiler to
adjust the alignment of an entire @code{struct} or @code{union} type.

As in the preceding example, you can explicitly specify the alignment
(in bytes) that you wish the compiler to use for a given @code{struct}
or @code{union} type.  Alternatively, you can leave out the alignment factor
and just ask the compiler to align a type to the maximum
useful alignment for the target machine you are compiling for.  For
example, you could write:

@smallexample
struct S @{ short f[3]; @} __attribute__ ((aligned));
@end smallexample

Whenever you leave out the alignment factor in an @code{aligned}
attribute specification, the compiler automatically sets the alignment
for the type to the largest alignment that is ever used for any data
type on the target machine you are compiling for.  Doing this can often
make copy operations more efficient, because the compiler can use
whatever instructions copy the biggest chunks of memory when performing
copies to or from the variables that have types that you have aligned
this way.

In the example above, if the size of each @code{short} is 2 bytes, then
the size of the entire @code{struct S} type is 6 bytes.  The smallest
power of two that is greater than or equal to that is 8, so the
compiler sets the alignment for the entire @code{struct S} type to 8
bytes.

Note that although you can ask the compiler to select a time-efficient
alignment for a given type and then declare only individual stand-alone
objects of that type, the compiler's ability to select a time-efficient
alignment is primarily useful only when you plan to create arrays of
variables having the relevant (efficiently aligned) type.  If you
declare or use arrays of variables of an efficiently-aligned type, then
it is likely that your program also does pointer arithmetic (or
subscripting, which amounts to the same thing) on pointers to the
relevant type, and the code that the compiler generates for these
pointer arithmetic operations is often more efficient for
efficiently-aligned types than for other types.

The @code{aligned} attribute can only increase the alignment; but you
can decrease it by specifying @code{packed} as well.  See below.

Note that the effectiveness of @code{aligned} attributes may be limited
by inherent limitations in your linker.  On many systems, the linker is
only able to arrange for variables to be aligned up to a certain maximum
alignment.  (For some linkers, the maximum supported alignment may
be very very small.)  If your linker is only able to align variables
up to a maximum of 8-byte alignment, then specifying @code{aligned(16)}
in an @code{__attribute__} still only provides you with 8-byte
alignment.  See your linker documentation for further information.

@item packed
This attribute, attached to @code{struct} or @code{union} type
definition, specifies that each member (other than zero-width bit-fields)
of the structure or union is placed to minimize the memory required.  When
attached to an @code{enum} definition, it indicates that the smallest
integral type should be used.

@opindex fshort-enums
Specifying this attribute for @code{struct} and @code{union} types is
equivalent to specifying the @code{packed} attribute on each of the
structure or union members.  Specifying the @option{-fshort-enums}
flag on the line is equivalent to specifying the @code{packed}
attribute on all @code{enum} definitions.

In the following example @code{struct my_packed_struct}'s members are
packed closely together, but the internal layout of its @code{s} member
is not packed---to do that, @code{struct my_unpacked_struct} needs to
be packed too.

@smallexample
struct my_unpacked_struct
 @{
    char c;
    int i;
 @};

struct __attribute__ ((__packed__)) my_packed_struct
  @{
     char c;
     int  i;
     struct my_unpacked_struct s;
  @};
@end smallexample

You may only specify this attribute on the definition of an @code{enum},
@code{struct} or @code{union}, not on a @code{typedef} that does not
also define the enumerated type, structure or union.

@item transparent_union
This attribute, attached to a @code{union} type definition, indicates
that any function parameter having that union type causes calls to that
function to be treated in a special way.

First, the argument corresponding to a transparent union type can be of
any type in the union; no cast is required.  Also, if the union contains
a pointer type, the corresponding argument can be a null pointer
constant or a void pointer expression; and if the union contains a void
pointer type, the corresponding argument can be any pointer expression.
If the union member type is a pointer, qualifiers like @code{const} on
the referenced type must be respected, just as with normal pointer
conversions.

Second, the argument is passed to the function using the calling
conventions of the first member of the transparent union, not the calling
conventions of the union itself.  All members of the union must have the
same machine representation; this is necessary for this argument passing
to work properly.

Transparent unions are designed for library functions that have multiple
interfaces for compatibility reasons.  For example, suppose the
@code{wait} function must accept either a value of type @code{int *} to
comply with POSIX, or a value of type @code{union wait *} to comply with
the 4.1BSD interface.  If @code{wait}'s parameter were @code{void *},
@code{wait} would accept both kinds of arguments, but it would also
accept any other pointer type and this would make argument type checking
less useful.  Instead, @code{<sys/wait.h>} might define the interface
as follows:

@smallexample
typedef union __attribute__ ((__transparent_union__))
  @{
    int *__ip;
    union wait *__up;
  @} wait_status_ptr_t;

pid_t wait (wait_status_ptr_t);
@end smallexample

@noindent
This interface allows either @code{int *} or @code{union wait *}
arguments to be passed, using the @code{int *} calling convention.
The program can call @code{wait} with arguments of either type:

@smallexample
int w1 () @{ int w; return wait (&w); @}
int w2 () @{ union wait w; return wait (&w); @}
@end smallexample

@noindent
With this interface, @code{wait}'s implementation might look like this:

@smallexample
pid_t wait (wait_status_ptr_t p)
@{
  return waitpid (-1, p.__ip, 0);
@}
@end smallexample

@item unused
When attached to a type (including a @code{union} or a @code{struct}),
this attribute means that variables of that type are meant to appear
possibly unused.  GCC does not produce a warning for any variables of
that type, even if the variable appears to do nothing.  This is often
the case with lock or thread classes, which are usually defined and then
not referenced, but contain constructors and destructors that have
nontrivial bookkeeping functions.

@item deprecated
@itemx deprecated (@var{msg})
The @code{deprecated} attribute results in a warning if the type
is used anywhere in the source file.  This is useful when identifying
types that are expected to be removed in a future version of a program.
If possible, the warning also includes the location of the declaration
of the deprecated type, to enable users to easily find further
information about why the type is deprecated, or what they should do
instead.  Note that the warnings only occur for uses and then only
if the type is being applied to an identifier that itself is not being
declared as deprecated.

@smallexample
typedef int T1 __attribute__ ((deprecated));
T1 x;
typedef T1 T2;
T2 y;
typedef T1 T3 __attribute__ ((deprecated));
T3 z __attribute__ ((deprecated));
@end smallexample

@noindent
results in a warning on line 2 and 3 but not lines 4, 5, or 6.  No
warning is issued for line 4 because T2 is not explicitly
deprecated.  Line 5 has no warning because T3 is explicitly
deprecated.  Similarly for line 6.  The optional @var{msg}
argument, which must be a string, is printed in the warning if
present.

The @code{deprecated} attribute can also be used for functions and
variables (@pxref{Function Attributes}, @pxref{Variable Attributes}.)

@item may_alias
Accesses through pointers to types with this attribute are not subject
to type-based alias analysis, but are instead assumed to be able to alias
any other type of objects.
In the context of section 6.5 paragraph 7 of the C99 standard,
an lvalue expression
dereferencing such a pointer is treated like having a character type.
See @option{-fstrict-aliasing} for more information on aliasing issues.
This extension exists to support some vector APIs, in which pointers to
one vector type are permitted to alias pointers to a different vector type.

Note that an object of a type with this attribute does not have any
special semantics.

Example of use:

@smallexample
typedef short __attribute__((__may_alias__)) short_a;

int
main (void)
@{
  int a = 0x12345678;
  short_a *b = (short_a *) &a;

  b[1] = 0;

  if (a == 0x12345678)
    abort();

  exit(0);
@}
@end smallexample

@noindent
If you replaced @code{short_a} with @code{short} in the variable
declaration, the above program would abort when compiled with
@option{-fstrict-aliasing}, which is on by default at @option{-O2} or
above in recent GCC versions.

@item visibility
In C++, attribute visibility (@pxref{Function Attributes}) can also be
applied to class, struct, union and enum types.  Unlike other type
attributes, the attribute must appear between the initial keyword and
the name of the type; it cannot appear after the body of the type.

Note that the type visibility is applied to vague linkage entities
associated with the class (vtable, typeinfo node, etc.).  In
particular, if a class is thrown as an exception in one shared object
and caught in another, the class must have default visibility.
Otherwise the two shared objects are unable to use the same
typeinfo node and exception handling will break.

@end table

To specify multiple attributes, separate them by commas within the
double parentheses: for example, @samp{__attribute__ ((aligned (16),
packed))}.

@subsection ARM Type Attributes

On those ARM targets that support @code{dllimport} (such as Symbian
OS), you can use the @code{notshared} attribute to indicate that the
virtual table and other similar data for a class should not be
exported from a DLL@.  For example:

@smallexample
class __declspec(notshared) C @{
public:
  __declspec(dllimport) C();
  virtual void f();
@}

__declspec(dllexport)
C::C() @{@}
@end smallexample

@noindent
In this code, @code{C::C} is exported from the current DLL, but the
virtual table for @code{C} is not exported.  (You can use
@code{__attribute__} instead of @code{__declspec} if you prefer, but
most Symbian OS code uses @code{__declspec}.)

@anchor{MeP Type Attributes}
@subsection MeP Type Attributes

Many of the MeP variable attributes may be applied to types as well.
Specifically, the @code{based}, @code{tiny}, @code{near}, and
@code{far} attributes may be applied to either.  The @code{io} and
@code{cb} attributes may not be applied to types.

@anchor{i386 Type Attributes}
@subsection i386 Type Attributes

Two attributes are currently defined for i386 configurations:
@code{ms_struct} and @code{gcc_struct}.

@table @code

@item ms_struct
@itemx gcc_struct
@cindex @code{ms_struct}
@cindex @code{gcc_struct}

If @code{packed} is used on a structure, or if bit-fields are used
it may be that the Microsoft ABI packs them differently
than GCC normally packs them.  Particularly when moving packed
data between functions compiled with GCC and the native Microsoft compiler
(either via function call or as data in a file), it may be necessary to access
either format.

Currently @option{-m[no-]ms-bitfields} is provided for the Microsoft Windows X86
compilers to match the native Microsoft compiler.
@end table

@anchor{PowerPC Type Attributes}
@subsection PowerPC Type Attributes

Three attributes currently are defined for PowerPC configurations:
@code{altivec}, @code{ms_struct} and @code{gcc_struct}.

For full documentation of the @code{ms_struct} and @code{gcc_struct}
attributes please see the documentation in @ref{i386 Type Attributes}.

The @code{altivec} attribute allows one to declare AltiVec vector data
types supported by the AltiVec Programming Interface Manual.  The
attribute requires an argument to specify one of three vector types:
@code{vector__}, @code{pixel__} (always followed by unsigned short),
and @code{bool__} (always followed by unsigned).

@smallexample
__attribute__((altivec(vector__)))
__attribute__((altivec(pixel__))) unsigned short
__attribute__((altivec(bool__))) unsigned
@end smallexample

These attributes mainly are intended to support the @code{__vector},
@code{__pixel}, and @code{__bool} AltiVec keywords.

@anchor{SPU Type Attributes}
@subsection SPU Type Attributes

The SPU supports the @code{spu_vector} attribute for types.  This attribute
allows one to declare vector data types supported by the Sony/Toshiba/IBM SPU
Language Extensions Specification.  It is intended to support the
@code{__vector} keyword.

@node Alignment
@section Inquiring on Alignment of Types or Variables
@cindex alignment
@cindex type alignment
@cindex variable alignment

The keyword @code{__alignof__} allows you to inquire about how an object
is aligned, or the minimum alignment usually required by a type.  Its
syntax is just like @code{sizeof}.

For example, if the target machine requires a @code{double} value to be
aligned on an 8-byte boundary, then @code{__alignof__ (double)} is 8.
This is true on many RISC machines.  On more traditional machine
designs, @code{__alignof__ (double)} is 4 or even 2.

Some machines never actually require alignment; they allow reference to any
data type even at an odd address.  For these machines, @code{__alignof__}
reports the smallest alignment that GCC gives the data type, usually as
mandated by the target ABI.

If the operand of @code{__alignof__} is an lvalue rather than a type,
its value is the required alignment for its type, taking into account
any minimum alignment specified with GCC's @code{__attribute__}
extension (@pxref{Variable Attributes}).  For example, after this
declaration:

@smallexample
struct foo @{ int x; char y; @} foo1;
@end smallexample

@noindent
the value of @code{__alignof__ (foo1.y)} is 1, even though its actual
alignment is probably 2 or 4, the same as @code{__alignof__ (int)}.

It is an error to ask for the alignment of an incomplete type.


@node Inline
@section An Inline Function is As Fast As a Macro
@cindex inline functions
@cindex integrating function code
@cindex open coding
@cindex macros, inline alternative

By declaring a function inline, you can direct GCC to make
calls to that function faster.  One way GCC can achieve this is to
integrate that function's code into the code for its callers.  This
makes execution faster by eliminating the function-call overhead; in
addition, if any of the actual argument values are constant, their
known values may permit simplifications at compile time so that not
all of the inline function's code needs to be included.  The effect on
code size is less predictable; object code may be larger or smaller
with function inlining, depending on the particular case.  You can
also direct GCC to try to integrate all ``simple enough'' functions
into their callers with the option @option{-finline-functions}.

GCC implements three different semantics of declaring a function
inline.  One is available with @option{-std=gnu89} or
@option{-fgnu89-inline} or when @code{gnu_inline} attribute is present
on all inline declarations, another when
@option{-std=c99}, @option{-std=c11},
@option{-std=gnu99} or @option{-std=gnu11}
(without @option{-fgnu89-inline}), and the third
is used when compiling C++.

To declare a function inline, use the @code{inline} keyword in its
declaration, like this:

@smallexample
static inline int
inc (int *a)
@{
  return (*a)++;
@}
@end smallexample

If you are writing a header file to be included in ISO C90 programs, write
@code{__inline__} instead of @code{inline}.  @xref{Alternate Keywords}.

The three types of inlining behave similarly in two important cases:
when the @code{inline} keyword is used on a @code{static} function,
like the example above, and when a function is first declared without
using the @code{inline} keyword and then is defined with
@code{inline}, like this:

@smallexample
extern int inc (int *a);
inline int
inc (int *a)
@{
  return (*a)++;
@}
@end smallexample

In both of these common cases, the program behaves the same as if you
had not used the @code{inline} keyword, except for its speed.

@cindex inline functions, omission of
@opindex fkeep-inline-functions
When a function is both inline and @code{static}, if all calls to the
function are integrated into the caller, and the function's address is
never used, then the function's own assembler code is never referenced.
In this case, GCC does not actually output assembler code for the
function, unless you specify the option @option{-fkeep-inline-functions}.
Some calls cannot be integrated for various reasons (in particular,
calls that precede the function's definition cannot be integrated, and
neither can recursive calls within the definition).  If there is a
nonintegrated call, then the function is compiled to assembler code as
usual.  The function must also be compiled as usual if the program
refers to its address, because that can't be inlined.

@opindex Winline
Note that certain usages in a function definition can make it unsuitable
for inline substitution.  Among these usages are: variadic functions, use of
@code{alloca}, use of variable-length data types (@pxref{Variable Length}),
use of computed goto (@pxref{Labels as Values}), use of nonlocal goto,
and nested functions (@pxref{Nested Functions}).  Using @option{-Winline}
warns when a function marked @code{inline} could not be substituted,
and gives the reason for the failure.

@cindex automatic @code{inline} for C++ member fns
@cindex @code{inline} automatic for C++ member fns
@cindex member fns, automatically @code{inline}
@cindex C++ member fns, automatically @code{inline}
@opindex fno-default-inline
As required by ISO C++, GCC considers member functions defined within
the body of a class to be marked inline even if they are
not explicitly declared with the @code{inline} keyword.  You can
override this with @option{-fno-default-inline}; @pxref{C++ Dialect
Options,,Options Controlling C++ Dialect}.

GCC does not inline any functions when not optimizing unless you specify
the @samp{always_inline} attribute for the function, like this:

@smallexample
/* @r{Prototype.}  */
inline void foo (const char) __attribute__((always_inline));
@end smallexample

The remainder of this section is specific to GNU C90 inlining.

@cindex non-static inline function
When an inline function is not @code{static}, then the compiler must assume
that there may be calls from other source files; since a global symbol can
be defined only once in any program, the function must not be defined in
the other source files, so the calls therein cannot be integrated.
Therefore, a non-@code{static} inline function is always compiled on its
own in the usual fashion.

If you specify both @code{inline} and @code{extern} in the function
definition, then the definition is used only for inlining.  In no case
is the function compiled on its own, not even if you refer to its
address explicitly.  Such an address becomes an external reference, as
if you had only declared the function, and had not defined it.

This combination of @code{inline} and @code{extern} has almost the
effect of a macro.  The way to use it is to put a function definition in
a header file with these keywords, and put another copy of the
definition (lacking @code{inline} and @code{extern}) in a library file.
The definition in the header file causes most calls to the function
to be inlined.  If any uses of the function remain, they refer to
the single copy in the library.

@node Volatiles
@section When is a Volatile Object Accessed?
@cindex accessing volatiles
@cindex volatile read
@cindex volatile write
@cindex volatile access

C has the concept of volatile objects.  These are normally accessed by
pointers and used for accessing hardware or inter-thread
communication.  The standard encourages compilers to refrain from
optimizations concerning accesses to volatile objects, but leaves it
implementation defined as to what constitutes a volatile access.  The
minimum requirement is that at a sequence point all previous accesses
to volatile objects have stabilized and no subsequent accesses have
occurred.  Thus an implementation is free to reorder and combine
volatile accesses that occur between sequence points, but cannot do
so for accesses across a sequence point.  The use of volatile does
not allow you to violate the restriction on updating objects multiple
times between two sequence points.

Accesses to non-volatile objects are not ordered with respect to
volatile accesses.  You cannot use a volatile object as a memory
barrier to order a sequence of writes to non-volatile memory.  For
instance:

@smallexample
int *ptr = @var{something};
volatile int vobj;
*ptr = @var{something};
vobj = 1;
@end smallexample

@noindent
Unless @var{*ptr} and @var{vobj} can be aliased, it is not guaranteed
that the write to @var{*ptr} occurs by the time the update
of @var{vobj} happens.  If you need this guarantee, you must use
a stronger memory barrier such as:

@smallexample
int *ptr = @var{something};
volatile int vobj;
*ptr = @var{something};
asm volatile ("" : : : "memory");
vobj = 1;
@end smallexample

A scalar volatile object is read when it is accessed in a void context:

@smallexample
volatile int *src = @var{somevalue};
*src;
@end smallexample

Such expressions are rvalues, and GCC implements this as a
read of the volatile object being pointed to.

Assignments are also expressions and have an rvalue.  However when
assigning to a scalar volatile, the volatile object is not reread,
regardless of whether the assignment expression's rvalue is used or
not.  If the assignment's rvalue is used, the value is that assigned
to the volatile object.  For instance, there is no read of @var{vobj}
in all the following cases:

@smallexample
int obj;
volatile int vobj;
vobj = @var{something};
obj = vobj = @var{something};
obj ? vobj = @var{onething} : vobj = @var{anotherthing};
obj = (@var{something}, vobj = @var{anotherthing});
@end smallexample

If you need to read the volatile object after an assignment has
occurred, you must use a separate expression with an intervening
sequence point.

As bit-fields are not individually addressable, volatile bit-fields may
be implicitly read when written to, or when adjacent bit-fields are
accessed.  Bit-field operations may be optimized such that adjacent
bit-fields are only partially accessed, if they straddle a storage unit
boundary.  For these reasons it is unwise to use volatile bit-fields to
access hardware.

@node Extended Asm
@section Assembler Instructions with C Expression Operands
@cindex extended @code{asm}
@cindex @code{asm} expressions
@cindex assembler instructions
@cindex registers

In an assembler instruction using @code{asm}, you can specify the
operands of the instruction using C expressions.  This means you need not
guess which registers or memory locations contain the data you want
to use.

You must specify an assembler instruction template much like what
appears in a machine description, plus an operand constraint string for
each operand.

For example, here is how to use the 68881's @code{fsinx} instruction:

@smallexample
asm ("fsinx %1,%0" : "=f" (result) : "f" (angle));
@end smallexample

@noindent
Here @code{angle} is the C expression for the input operand while
@code{result} is that of the output operand.  Each has @samp{"f"} as its
operand constraint, saying that a floating-point register is required.
The @samp{=} in @samp{=f} indicates that the operand is an output; all
output operands' constraints must use @samp{=}.  The constraints use the
same language used in the machine description (@pxref{Constraints}).

Each operand is described by an operand-constraint string followed by
the C expression in parentheses.  A colon separates the assembler
template from the first output operand and another separates the last
output operand from the first input, if any.  Commas separate the
operands within each group.  The total number of operands is currently
limited to 30; this limitation may be lifted in some future version of
GCC@.

If there are no output operands but there are input operands, you must
place two consecutive colons surrounding the place where the output
operands would go.

As of GCC version 3.1, it is also possible to specify input and output
operands using symbolic names which can be referenced within the
assembler code.  These names are specified inside square brackets
preceding the constraint string, and can be referenced inside the
assembler code using @code{%[@var{name}]} instead of a percentage sign
followed by the operand number.  Using named operands the above example
could look like:

@smallexample
asm ("fsinx %[angle],%[output]"
     : [output] "=f" (result)
     : [angle] "f" (angle));
@end smallexample

@noindent
Note that the symbolic operand names have no relation whatsoever to
other C identifiers.  You may use any name you like, even those of
existing C symbols, but you must ensure that no two operands within the same
assembler construct use the same symbolic name.

Output operand expressions must be lvalues; the compiler can check this.
The input operands need not be lvalues.  The compiler cannot check
whether the operands have data types that are reasonable for the
instruction being executed.  It does not parse the assembler instruction
template and does not know what it means or even whether it is valid
assembler input.  The extended @code{asm} feature is most often used for
machine instructions the compiler itself does not know exist.  If
the output expression cannot be directly addressed (for example, it is a
bit-field), your constraint must allow a register.  In that case, GCC
uses the register as the output of the @code{asm}, and then stores
that register into the output.

The ordinary output operands must be write-only; GCC assumes that
the values in these operands before the instruction are dead and need
not be generated.  Extended asm supports input-output or read-write
operands.  Use the constraint character @samp{+} to indicate such an
operand and list it with the output operands.

You may, as an alternative, logically split its function into two
separate operands, one input operand and one write-only output
operand.  The connection between them is expressed by constraints
that say they need to be in the same location when the instruction
executes.  You can use the same C expression for both operands, or
different expressions.  For example, here we write the (fictitious)
@samp{combine} instruction with @code{bar} as its read-only source
operand and @code{foo} as its read-write destination:

@smallexample
asm ("combine %2,%0" : "=r" (foo) : "0" (foo), "g" (bar));
@end smallexample

@noindent
The constraint @samp{"0"} for operand 1 says that it must occupy the
same location as operand 0.  A number in constraint is allowed only in
an input operand and it must refer to an output operand.

Only a number in the constraint can guarantee that one operand is in
the same place as another.  The mere fact that @code{foo} is the value
of both operands is not enough to guarantee that they are in the
same place in the generated assembler code.  The following does not
work reliably:

@smallexample
asm ("combine %2,%0" : "=r" (foo) : "r" (foo), "g" (bar));
@end smallexample

Various optimizations or reloading could cause operands 0 and 1 to be in
different registers; GCC knows no reason not to do so.  For example, the
compiler might find a copy of the value of @code{foo} in one register and
use it for operand 1, but generate the output operand 0 in a different
register (copying it afterward to @code{foo}'s own address).  Of course,
since the register for operand 1 is not even mentioned in the assembler
code, the result will not work, but GCC can't tell that.

As of GCC version 3.1, one may write @code{[@var{name}]} instead of
the operand number for a matching constraint.  For example:

@smallexample
asm ("cmoveq %1,%2,%[result]"
     : [result] "=r"(result)
     : "r" (test), "r"(new), "[result]"(old));
@end smallexample

Sometimes you need to make an @code{asm} operand be a specific register,
but there's no matching constraint letter for that register @emph{by
itself}.  To force the operand into that register, use a local variable
for the operand and specify the register in the variable declaration.
@xref{Explicit Reg Vars}.  Then for the @code{asm} operand, use any
register constraint letter that matches the register:

@smallexample
register int *p1 asm ("r0") = @dots{};
register int *p2 asm ("r1") = @dots{};
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
@end smallexample

@anchor{Example of asm with clobbered asm reg}
In the above example, beware that a register that is call-clobbered by
the target ABI will be overwritten by any function call in the
assignment, including library calls for arithmetic operators.
Also a register may be clobbered when generating some operations,
like variable shift, memory copy or memory move on x86.
Assuming it is a call-clobbered register, this may happen to @code{r0}
above by the assignment to @code{p2}.  If you have to use such a
register, use temporary variables for expressions between the register
assignment and use:

@smallexample
int t1 = @dots{};
register int *p1 asm ("r0") = @dots{};
register int *p2 asm ("r1") = t1;
register int *result asm ("r0");
asm ("sysint" : "=r" (result) : "0" (p1), "r" (p2));
@end smallexample

Some instructions clobber specific hard registers.  To describe this,
write a third colon after the input operands, followed by the names of
the clobbered hard registers (given as strings).  Here is a realistic
example for the VAX:

@smallexample
asm volatile ("movc3 %0,%1,%2"
              : /* @r{no outputs} */
              : "g" (from), "g" (to), "g" (count)
              : "r0", "r1", "r2", "r3", "r4", "r5");
@end smallexample

You may not write a clobber description in a way that overlaps with an
input or output operand.  For example, you may not have an operand
describing a register class with one member if you mention that register
in the clobber list.  Variables declared to live in specific registers
(@pxref{Explicit Reg Vars}), and used as asm input or output operands must
have no part mentioned in the clobber description.
There is no way for you to specify that an input
operand is modified without also specifying it as an output
operand.  Note that if all the output operands you specify are for this
purpose (and hence unused), you then also need to specify
@code{volatile} for the @code{asm} construct, as described below, to
prevent GCC from deleting the @code{asm} statement as unused.

If you refer to a particular hardware register from the assembler code,
you probably have to list the register after the third colon to
tell the compiler the register's value is modified.  In some assemblers,
the register names begin with @samp{%}; to produce one @samp{%} in the
assembler code, you must write @samp{%%} in the input.

If your assembler instruction can alter the condition code register, add
@samp{cc} to the list of clobbered registers.  GCC on some machines
represents the condition codes as a specific hardware register;
@samp{cc} serves to name this register.  On other machines, the
condition code is handled differently, and specifying @samp{cc} has no
effect.  But it is valid no matter what the machine.

If your assembler instructions access memory in an unpredictable
fashion, add @samp{memory} to the list of clobbered registers.  This
causes GCC to not keep memory values cached in registers across the
assembler instruction and not optimize stores or loads to that memory.
You also should add the @code{volatile} keyword if the memory
affected is not listed in the inputs or outputs of the @code{asm}, as
the @samp{memory} clobber does not count as a side-effect of the
@code{asm}.  If you know how large the accessed memory is, you can add
it as input or output but if this is not known, you should add
@samp{memory}.  As an example, if you access ten bytes of a string, you
can use a memory input like:

@smallexample
@{"m"( (@{ struct @{ char x[10]; @} *p = (void *)ptr ; *p; @}) )@}.
@end smallexample

Note that in the following example the memory input is necessary,
otherwise GCC might optimize the store to @code{x} away:
@smallexample
int foo ()
@{
  int x = 42;
  int *y = &x;
  int result;
  asm ("magic stuff accessing an 'int' pointed to by '%1'"
       : "=&d" (r) : "a" (y), "m" (*y));
  return result;
@}
@end smallexample

You can put multiple assembler instructions together in a single
@code{asm} template, separated by the characters normally used in assembly
code for the system.  A combination that works in most places is a newline
to break the line, plus a tab character to move to the instruction field
(written as @samp{\n\t}).  Sometimes semicolons can be used, if the
assembler allows semicolons as a line-breaking character.  Note that some
assembler dialects use semicolons to start a comment.
The input operands are guaranteed not to use any of the clobbered
registers, and neither do the output operands' addresses, so you can
read and write the clobbered registers as many times as you like.  Here
is an example of multiple instructions in a template; it assumes the
subroutine @code{_foo} accepts arguments in registers 9 and 10:

@smallexample
asm ("movl %0,r9\n\tmovl %1,r10\n\tcall _foo"
     : /* no outputs */
     : "g" (from), "g" (to)
     : "r9", "r10");
@end smallexample

Unless an output operand has the @samp{&} constraint modifier, GCC
may allocate it in the same register as an unrelated input operand, on
the assumption the inputs are consumed before the outputs are produced.
This assumption may be false if the assembler code actually consists of
more than one instruction.  In such a case, use @samp{&} for each output
operand that may not overlap an input.  @xref{Modifiers}.

If you want to test the condition code produced by an assembler
instruction, you must include a branch and a label in the @code{asm}
construct, as follows:

@smallexample
asm ("clr %0\n\tfrob %1\n\tbeq 0f\n\tmov #1,%0\n0:"
     : "g" (result)
     : "g" (input));
@end smallexample

@noindent
This assumes your assembler supports local labels, as the GNU assembler
and most Unix assemblers do.

Speaking of labels, jumps from one @code{asm} to another are not
supported.  The compiler's optimizers do not know about these jumps, and
therefore they cannot take account of them when deciding how to
optimize.  @xref{Extended asm with goto}.

@cindex macros containing @code{asm}
Usually the most convenient way to use these @code{asm} instructions is to
encapsulate them in macros that look like functions.  For example,

@smallexample
#define sin(x)       \
(@{ double __value, __arg = (x);   \
   asm ("fsinx %1,%0": "=f" (__value): "f" (__arg));  \
   __value; @})
@end smallexample

@noindent
Here the variable @code{__arg} is used to make sure that the instruction
operates on a proper @code{double} value, and to accept only those
arguments @code{x} that can convert automatically to a @code{double}.

Another way to make sure the instruction operates on the correct data
type is to use a cast in the @code{asm}.  This is different from using a
variable @code{__arg} in that it converts more different types.  For
example, if the desired type is @code{int}, casting the argument to
@code{int} accepts a pointer with no complaint, while assigning the
argument to an @code{int} variable named @code{__arg} warns about
using a pointer unless the caller explicitly casts it.

If an @code{asm} has output operands, GCC assumes for optimization
purposes the instruction has no side effects except to change the output
operands.  This does not mean instructions with a side effect cannot be
used, but you must be careful, because the compiler may eliminate them
if the output operands aren't used, or move them out of loops, or
replace two with one if they constitute a common subexpression.  Also,
if your instruction does have a side effect on a variable that otherwise
appears not to change, the old value of the variable may be reused later
if it happens to be found in a register.

You can prevent an @code{asm} instruction from being deleted
by writing the keyword @code{volatile} after
the @code{asm}.  For example:

@smallexample
#define get_and_set_priority(new)              \
(@{ int __old;                                  \
   asm volatile ("get_and_set_priority %0, %1" \
                 : "=g" (__old) : "g" (new));  \
   __old; @})
@end smallexample

@noindent
The @code{volatile} keyword indicates that the instruction has
important side-effects.  GCC does not delete a volatile @code{asm} if
it is reachable.  (The instruction can still be deleted if GCC can
prove that control flow never reaches the location of the
instruction.)  Note that even a volatile @code{asm} instruction
can be moved relative to other code, including across jump
instructions.  For example, on many targets there is a system
register that can be set to control the rounding mode of
floating-point operations.  You might try
setting it with a volatile @code{asm}, like this PowerPC example:

@smallexample
       asm volatile("mtfsf 255,%0" : : "f" (fpenv));
       sum = x + y;
@end smallexample

@noindent
This does not work reliably, as the compiler may move the addition back
before the volatile @code{asm}.  To make it work you need to add an
artificial dependency to the @code{asm} referencing a variable in the code
you don't want moved, for example:

@smallexample
    asm volatile ("mtfsf 255,%1" : "=X"(sum): "f"(fpenv));
    sum = x + y;
@end smallexample

Similarly, you can't expect a
sequence of volatile @code{asm} instructions to remain perfectly
consecutive.  If you want consecutive output, use a single @code{asm}.
Also, GCC performs some optimizations across a volatile @code{asm}
instruction; GCC does not ``forget everything'' when it encounters
a volatile @code{asm} instruction the way some other compilers do.

An @code{asm} instruction without any output operands is treated
identically to a volatile @code{asm} instruction.

It is a natural idea to look for a way to give access to the condition
code left by the assembler instruction.  However, when we attempted to
implement this, we found no way to make it work reliably.  The problem
is that output operands might need reloading, which result in
additional following ``store'' instructions.  On most machines, these
instructions alter the condition code before there is time to
test it.  This problem doesn't arise for ordinary ``test'' and
``compare'' instructions because they don't have any output operands.

For reasons similar to those described above, it is not possible to give
an assembler instruction access to the condition code left by previous
instructions.

@anchor{Extended asm with goto}
As of GCC version 4.5, @code{asm goto} may be used to have the assembly
jump to one or more C labels.  In this form, a fifth section after the
clobber list contains a list of all C labels to which the assembly may jump.
Each label operand is implicitly self-named.  The @code{asm} is also assumed
to fall through to the next statement.

This form of @code{asm} is restricted to not have outputs.  This is due
to a internal restriction in the compiler that control transfer instructions
cannot have outputs.  This restriction on @code{asm goto} may be lifted
in some future version of the compiler.  In the meantime, @code{asm goto}
may include a memory clobber, and so leave outputs in memory.

@smallexample
int frob(int x)
@{
  int y;
  asm goto ("frob %%r5, %1; jc %l[error]; mov (%2), %%r5"
            : : "r"(x), "r"(&y) : "r5", "memory" : error);
  return y;
 error:
  return -1;
@}
@end smallexample

@noindent
In this (inefficient) example, the @code{frob} instruction sets the
carry bit to indicate an error.  The @code{jc} instruction detects
this and branches to the @code{error} label.  Finally, the output
of the @code{frob} instruction (@code{%r5}) is stored into the memory
for variable @code{y}, which is later read by the @code{return} statement.

@smallexample
void doit(void)
@{
  int i = 0;
  asm goto ("mfsr %%r1, 123; jmp %%r1;"
            ".pushsection doit_table;"
            ".long %l0, %l1, %l2, %l3;"
            ".popsection"
            : : : "r1" : label1, label2, label3, label4);
  __builtin_unreachable ();

 label1:
  f1();
  return;
 label2:
  f2();
  return;
 label3:
  i = 1;
 label4:
  f3(i);
@}
@end smallexample

@noindent
In this (also inefficient) example, the @code{mfsr} instruction reads
an address from some out-of-band machine register, and the following
@code{jmp} instruction branches to that address.  The address read by
the @code{mfsr} instruction is assumed to have been previously set via
some application-specific mechanism to be one of the four values stored
in the @code{doit_table} section.  Finally, the @code{asm} is followed
by a call to @code{__builtin_unreachable} to indicate that the @code{asm}
does not in fact fall through.

@smallexample
#define TRACE1(NUM)                         \
  do @{                                      \
    asm goto ("0: nop;"                     \
              ".pushsection trace_table;"   \
              ".long 0b, %l0;"              \
              ".popsection"                 \
              : : : : trace#NUM);           \
    if (0) @{ trace#NUM: trace(); @}          \
  @} while (0)
#define TRACE  TRACE1(__COUNTER__)
@end smallexample

@noindent
In this example (which in fact inspired the @code{asm goto} feature)
we want on rare occasions to call the @code{trace} function; on other
occasions we'd like to keep the overhead to the absolute minimum.
The normal code path consists of a single @code{nop} instruction.
However, we record the address of this @code{nop} together with the
address of a label that calls the @code{trace} function.  This allows
the @code{nop} instruction to be patched at run time to be an
unconditional branch to the stored label.  It is assumed that an
optimizing compiler moves the labeled block out of line, to
optimize the fall through path from the @code{asm}.

If you are writing a header file that should be includable in ISO C
programs, write @code{__asm__} instead of @code{asm}.  @xref{Alternate
Keywords}.

@subsection Size of an @code{asm}

Some targets require that GCC track the size of each instruction used in
order to generate correct code.  Because the final length of an
@code{asm} is only known by the assembler, GCC must make an estimate as
to how big it will be.  The estimate is formed by counting the number of
statements in the pattern of the @code{asm} and multiplying that by the
length of the longest instruction on that processor.  Statements in the
@code{asm} are identified by newline characters and whatever statement
separator characters are supported by the assembler; on most processors
this is the @samp{;} character.

Normally, GCC's estimate is perfectly adequate to ensure that correct
code is generated, but it is possible to confuse the compiler if you use
pseudo instructions or assembler macros that expand into multiple real
instructions or if you use assembler directives that expand to more
space in the object file than is needed for a single instruction.
If this happens then the assembler produces a diagnostic saying that
a label is unreachable.

@subsection i386 floating-point asm operands

On i386 targets, there are several rules on the usage of stack-like registers
in the operands of an @code{asm}.  These rules apply only to the operands
that are stack-like registers:

@enumerate
@item
Given a set of input registers that die in an @code{asm}, it is
necessary to know which are implicitly popped by the @code{asm}, and
which must be explicitly popped by GCC@.

An input register that is implicitly popped by the @code{asm} must be
explicitly clobbered, unless it is constrained to match an
output operand.

@item
For any input register that is implicitly popped by an @code{asm}, it is
necessary to know how to adjust the stack to compensate for the pop.
If any non-popped input is closer to the top of the reg-stack than
the implicitly popped register, it would not be possible to know what the
stack looked like---it's not clear how the rest of the stack ``slides
up''.

All implicitly popped input registers must be closer to the top of
the reg-stack than any input that is not implicitly popped.

It is possible that if an input dies in an @code{asm}, the compiler might
use the input register for an output reload.  Consider this example:

@smallexample
asm ("foo" : "=t" (a) : "f" (b));
@end smallexample

@noindent
This code says that input @code{b} is not popped by the @code{asm}, and that
the @code{asm} pushes a result onto the reg-stack, i.e., the stack is one
deeper after the @code{asm} than it was before.  But, it is possible that
reload may think that it can use the same register for both the input and
the output.

To prevent this from happening,
if any input operand uses the @code{f} constraint, all output register
constraints must use the @code{&} early-clobber modifier.

The example above would be correctly written as:

@smallexample
asm ("foo" : "=&t" (a) : "f" (b));
@end smallexample

@item
Some operands need to be in particular places on the stack.  All
output operands fall in this category---GCC has no other way to
know which registers the outputs appear in unless you indicate
this in the constraints.

Output operands must specifically indicate which register an output
appears in after an @code{asm}.  @code{=f} is not allowed: the operand
constraints must select a class with a single register.

@item
Output operands may not be ``inserted'' between existing stack registers.
Since no 387 opcode uses a read/write operand, all output operands
are dead before the @code{asm}, and are pushed by the @code{asm}.
It makes no sense to push anywhere but the top of the reg-stack.

Output operands must start at the top of the reg-stack: output
operands may not ``skip'' a register.

@item
Some @code{asm} statements may need extra stack space for internal
calculations.  This can be guaranteed by clobbering stack registers
unrelated to the inputs and outputs.

@end enumerate

Here are a couple of reasonable @code{asm}s to want to write.  This
@code{asm}
takes one input, which is internally popped, and produces two outputs.

@smallexample
asm ("fsincos" : "=t" (cos), "=u" (sin) : "0" (inp));
@end smallexample

@noindent
This @code{asm} takes two inputs, which are popped by the @code{fyl2xp1} opcode,
and replaces them with one output.  The @code{st(1)} clobber is necessary 
for the compiler to know that @code{fyl2xp1} pops both inputs.

@smallexample
asm ("fyl2xp1" : "=t" (result) : "0" (x), "u" (y) : "st(1)");
@end smallexample

@include md.texi

@node Asm Labels
@section Controlling Names Used in Assembler Code
@cindex assembler names for identifiers
@cindex names used in assembler code
@cindex identifiers, names in assembler code

You can specify the name to be used in the assembler code for a C
function or variable by writing the @code{asm} (or @code{__asm__})
keyword after the declarator as follows:

@smallexample
int foo asm ("myfoo") = 2;
@end smallexample

@noindent
This specifies that the name to be used for the variable @code{foo} in
the assembler code should be @samp{myfoo} rather than the usual
@samp{_foo}.

On systems where an underscore is normally prepended to the name of a C
function or variable, this feature allows you to define names for the
linker that do not start with an underscore.

It does not make sense to use this feature with a non-static local
variable since such variables do not have assembler names.  If you are
trying to put the variable in a particular register, see @ref{Explicit
Reg Vars}.  GCC presently accepts such code with a warning, but will
probably be changed to issue an error, rather than a warning, in the
future.

You cannot use @code{asm} in this way in a function @emph{definition}; but
you can get the same effect by writing a declaration for the function
before its definition and putting @code{asm} there, like this:

@smallexample
extern func () asm ("FUNC");

func (x, y)
     int x, y;
/* @r{@dots{}} */
@end smallexample

It is up to you to make sure that the assembler names you choose do not
conflict with any other assembler symbols.  Also, you must not use a
register name; that would produce completely invalid assembler code.  GCC
does not as yet have the ability to store static variables in registers.
Perhaps that will be added.

@node Explicit Reg Vars
@section Variables in Specified Registers
@cindex explicit register variables
@cindex variables in specified registers
@cindex specified registers
@cindex registers, global allocation

GNU C allows you to put a few global variables into specified hardware
registers.  You can also specify the register in which an ordinary
register variable should be allocated.

@itemize @bullet
@item
Global register variables reserve registers throughout the program.
This may be useful in programs such as programming language
interpreters that have a couple of global variables that are accessed
very often.

@item
Local register variables in specific registers do not reserve the
registers, except at the point where they are used as input or output
operands in an @code{asm} statement and the @code{asm} statement itself is
not deleted.  The compiler's data flow analysis is capable of determining
where the specified registers contain live values, and where they are
available for other uses.  Stores into local register variables may be deleted
when they appear to be dead according to dataflow analysis.  References
to local register variables may be deleted or moved or simplified.

These local variables are sometimes convenient for use with the extended
@code{asm} feature (@pxref{Extended Asm}), if you want to write one
output of the assembler instruction directly into a particular register.
(This works provided the register you specify fits the constraints
specified for that operand in the @code{asm}.)
@end itemize

@menu
* Global Reg Vars::
* Local Reg Vars::
@end menu

@node Global Reg Vars
@subsection Defining Global Register Variables
@cindex global register variables
@cindex registers, global variables in

You can define a global register variable in GNU C like this:

@smallexample
register int *foo asm ("a5");
@end smallexample

@noindent
Here @code{a5} is the name of the register that should be used.  Choose a
register that is normally saved and restored by function calls on your
machine, so that library routines will not clobber it.

Naturally the register name is cpu-dependent, so you need to
conditionalize your program according to cpu type.  The register
@code{a5} is a good choice on a 68000 for a variable of pointer
type.  On machines with register windows, be sure to choose a ``global''
register that is not affected magically by the function call mechanism.

In addition, different operating systems on the same CPU may differ in how they
name the registers; then you need additional conditionals.  For
example, some 68000 operating systems call this register @code{%a5}.

Eventually there may be a way of asking the compiler to choose a register
automatically, but first we need to figure out how it should choose and
how to enable you to guide the choice.  No solution is evident.

Defining a global register variable in a certain register reserves that
register entirely for this use, at least within the current compilation.
The register is not allocated for any other purpose in the functions
in the current compilation, and is not saved and restored by
these functions.  Stores into this register are never deleted even if they
appear to be dead, but references may be deleted or moved or
simplified.

It is not safe to access the global register variables from signal
handlers, or from more than one thread of control, because the system
library routines may temporarily use the register for other things (unless
you recompile them specially for the task at hand).

@cindex @code{qsort}, and global register variables
It is not safe for one function that uses a global register variable to
call another such function @code{foo} by way of a third function
@code{lose} that is compiled without knowledge of this variable (i.e.@: in a
different source file in which the variable isn't declared).  This is
because @code{lose} might save the register and put some other value there.
For example, you can't expect a global register variable to be available in
the comparison-function that you pass to @code{qsort}, since @code{qsort}
might have put something else in that register.  (If you are prepared to
recompile @code{qsort} with the same global register variable, you can
solve this problem.)

If you want to recompile @code{qsort} or other source files that do not
actually use your global register variable, so that they do not use that
register for any other purpose, then it suffices to specify the compiler
option @option{-ffixed-@var{reg}}.  You need not actually add a global
register declaration to their source code.

A function that can alter the value of a global register variable cannot
safely be called from a function compiled without this variable, because it
could clobber the value the caller expects to find there on return.
Therefore, the function that is the entry point into the part of the
program that uses the global register variable must explicitly save and
restore the value that belongs to its caller.

@cindex register variable after @code{longjmp}
@cindex global register after @code{longjmp}
@cindex value after @code{longjmp}
@findex longjmp
@findex setjmp
On most machines, @code{longjmp} restores to each global register
variable the value it had at the time of the @code{setjmp}.  On some
machines, however, @code{longjmp} does not change the value of global
register variables.  To be portable, the function that called @code{setjmp}
should make other arrangements to save the values of the global register
variables, and to restore them in a @code{longjmp}.  This way, the same
thing happens regardless of what @code{longjmp} does.

All global register variable declarations must precede all function
definitions.  If such a declaration could appear after function
definitions, the declaration would be too late to prevent the register from
being used for other purposes in the preceding functions.

Global register variables may not have initial values, because an
executable file has no means to supply initial contents for a register.

On the SPARC, there are reports that g3 @dots{} g7 are suitable
registers, but certain library functions, such as @code{getwd}, as well
as the subroutines for division and remainder, modify g3 and g4.  g1 and
g2 are local temporaries.

On the 68000, a2 @dots{} a5 should be suitable, as should d2 @dots{} d7.
Of course, it does not do to use more than a few of those.

@node Local Reg Vars
@subsection Specifying Registers for Local Variables
@cindex local variables, specifying registers
@cindex specifying registers for local variables
@cindex registers for local variables

You can define a local register variable with a specified register
like this:

@smallexample
register int *foo asm ("a5");
@end smallexample

@noindent
Here @code{a5} is the name of the register that should be used.  Note
that this is the same syntax used for defining global register
variables, but for a local variable it appears within a function.

Naturally the register name is cpu-dependent, but this is not a
problem, since specific registers are most often useful with explicit
assembler instructions (@pxref{Extended Asm}).  Both of these things
generally require that you conditionalize your program according to
cpu type.

In addition, operating systems on one type of cpu may differ in how they
name the registers; then you need additional conditionals.  For
example, some 68000 operating systems call this register @code{%a5}.

Defining such a register variable does not reserve the register; it
remains available for other uses in places where flow control determines
the variable's value is not live.

This option does not guarantee that GCC generates code that has
this variable in the register you specify at all times.  You may not
code an explicit reference to this register in the @emph{assembler
instruction template} part of an @code{asm} statement and assume it
always refers to this variable.  However, using the variable as an
@code{asm} @emph{operand} guarantees that the specified register is used
for the operand.

Stores into local register variables may be deleted when they appear to be dead
according to dataflow analysis.  References to local register variables may
be deleted or moved or simplified.

As for global register variables, it's recommended that you choose a
register that is normally saved and restored by function calls on
your machine, so that library routines will not clobber it.  A common
pitfall is to initialize multiple call-clobbered registers with
arbitrary expressions, where a function call or library call for an
arithmetic operator overwrites a register value from a previous
assignment, for example @code{r0} below:
@smallexample
register int *p1 asm ("r0") = @dots{};
register int *p2 asm ("r1") = @dots{};
@end smallexample

@noindent
In those cases, a solution is to use a temporary variable for
each arbitrary expression.   @xref{Example of asm with clobbered asm reg}.

@node Alternate Keywords
@section Alternate Keywords
@cindex alternate keywords
@cindex keywords, alternate

@option{-ansi} and the various @option{-std} options disable certain
keywords.  This causes trouble when you want to use GNU C extensions, or
a general-purpose header file that should be usable by all programs,
including ISO C programs.  The keywords @code{asm}, @code{typeof} and
@code{inline} are not available in programs compiled with
@option{-ansi} or @option{-std} (although @code{inline} can be used in a
program compiled with @option{-std=c99} or @option{-std=c11}).  The
ISO C99 keyword
@code{restrict} is only available when @option{-std=gnu99} (which will
eventually be the default) or @option{-std=c99} (or the equivalent
@option{-std=iso9899:1999}), or an option for a later standard
version, is used.

The way to solve these problems is to put @samp{__} at the beginning and
end of each problematical keyword.  For example, use @code{__asm__}
instead of @code{asm}, and @code{__inline__} instead of @code{inline}.

Other C compilers won't accept these alternative keywords; if you want to
compile with another compiler, you can define the alternate keywords as
macros to replace them with the customary keywords.  It looks like this:

@smallexample
#ifndef __GNUC__
#define __asm__ asm
#endif
@end smallexample

@findex __extension__
@opindex pedantic
@option{-pedantic} and other options cause warnings for many GNU C extensions.
You can
prevent such warnings within one expression by writing
@code{__extension__} before the expression.  @code{__extension__} has no
effect aside from this.

@node Incomplete Enums
@section Incomplete @code{enum} Types

You can define an @code{enum} tag without specifying its possible values.
This results in an incomplete type, much like what you get if you write
@code{struct foo} without describing the elements.  A later declaration
that does specify the possible values completes the type.

You can't allocate variables or storage using the type while it is
incomplete.  However, you can work with pointers to that type.

This extension may not be very useful, but it makes the handling of
@code{enum} more consistent with the way @code{struct} and @code{union}
are handled.

This extension is not supported by GNU C++.

@node Function Names
@section Function Names as Strings
@cindex @code{__func__} identifier
@cindex @code{__FUNCTION__} identifier
@cindex @code{__PRETTY_FUNCTION__} identifier

GCC provides three magic variables that hold the name of the current
function, as a string.  The first of these is @code{__func__}, which
is part of the C99 standard:

The identifier @code{__func__} is implicitly declared by the translator
as if, immediately following the opening brace of each function
definition, the declaration

@smallexample
static const char __func__[] = "function-name";
@end smallexample

@noindent
appeared, where function-name is the name of the lexically-enclosing
function.  This name is the unadorned name of the function.

@code{__FUNCTION__} is another name for @code{__func__}.  Older
versions of GCC recognize only this name.  However, it is not
standardized.  For maximum portability, we recommend you use
@code{__func__}, but provide a fallback definition with the
preprocessor:

@smallexample
#if __STDC_VERSION__ < 199901L
# if __GNUC__ >= 2
#  define __func__ __FUNCTION__
# else
#  define __func__ "<unknown>"
# endif
#endif
@end smallexample

In C, @code{__PRETTY_FUNCTION__} is yet another name for
@code{__func__}.  However, in C++, @code{__PRETTY_FUNCTION__} contains
the type signature of the function as well as its bare name.  For
example, this program:

@smallexample
extern "C" @{
extern int printf (char *, ...);
@}

class a @{
 public:
  void sub (int i)
    @{
      printf ("__FUNCTION__ = %s\n", __FUNCTION__);
      printf ("__PRETTY_FUNCTION__ = %s\n", __PRETTY_FUNCTION__);
    @}
@};

int
main (void)
@{
  a ax;
  ax.sub (0);
  return 0;
@}
@end smallexample

@noindent
gives this output:

@smallexample
__FUNCTION__ = sub
__PRETTY_FUNCTION__ = void a::sub(int)
@end smallexample

These identifiers are not preprocessor macros.  In GCC 3.3 and
earlier, in C only, @code{__FUNCTION__} and @code{__PRETTY_FUNCTION__}
were treated as string literals; they could be used to initialize
@code{char} arrays, and they could be concatenated with other string
literals.  GCC 3.4 and later treat them as variables, like
@code{__func__}.  In C++, @code{__FUNCTION__} and
@code{__PRETTY_FUNCTION__} have always been variables.

@node Return Address
@section Getting the Return or Frame Address of a Function

These functions may be used to get information about the callers of a
function.

@deftypefn {Built-in Function} {void *} __builtin_return_address (unsigned int @var{level})
This function returns the return address of the current function, or of
one of its callers.  The @var{level} argument is number of frames to
scan up the call stack.  A value of @code{0} yields the return address
of the current function, a value of @code{1} yields the return address
of the caller of the current function, and so forth.  When inlining
the expected behavior is that the function returns the address of
the function that is returned to.  To work around this behavior use
the @code{noinline} function attribute.

The @var{level} argument must be a constant integer.

On some machines it may be impossible to determine the return address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function returns @code{0} or a
random value.  In addition, @code{__builtin_frame_address} may be used
to determine if the top of the stack has been reached.

Additional post-processing of the returned value may be needed, see
@code{__builtin_extract_return_addr}.

This function should only be used with a nonzero argument for debugging
purposes.
@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_extract_return_addr (void *@var{addr})
The address as returned by @code{__builtin_return_address} may have to be fed
through this function to get the actual encoded address.  For example, on the
31-bit S/390 platform the highest bit has to be masked out, or on SPARC
platforms an offset has to be added for the true next instruction to be
executed.

If no fixup is needed, this function simply passes through @var{addr}.
@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_frob_return_address (void *@var{addr})
This function does the reverse of @code{__builtin_extract_return_addr}.
@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_frame_address (unsigned int @var{level})
This function is similar to @code{__builtin_return_address}, but it
returns the address of the function frame rather than the return address
of the function.  Calling @code{__builtin_frame_address} with a value of
@code{0} yields the frame address of the current function, a value of
@code{1} yields the frame address of the caller of the current function,
and so forth.

The frame is the area on the stack that holds local variables and saved
registers.  The frame address is normally the address of the first word
pushed on to the stack by the function.  However, the exact definition
depends upon the processor and the calling convention.  If the processor
has a dedicated frame pointer register, and the function has a frame,
then @code{__builtin_frame_address} returns the value of the frame
pointer register.

On some machines it may be impossible to determine the frame address of
any function other than the current one; in such cases, or when the top
of the stack has been reached, this function returns @code{0} if
the first frame pointer is properly initialized by the startup code.

This function should only be used with a nonzero argument for debugging
purposes.
@end deftypefn

@node Vector Extensions
@section Using Vector Instructions through Built-in Functions

On some targets, the instruction set contains SIMD vector instructions which
operate on multiple values contained in one large register at the same time.
For example, on the i386 the MMX, 3DNow!@: and SSE extensions can be used
this way.

The first step in using these extensions is to provide the necessary data
types.  This should be done using an appropriate @code{typedef}:

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));
@end smallexample

@noindent
The @code{int} type specifies the base type, while the attribute specifies
the vector size for the variable, measured in bytes.  For example, the
declaration above causes the compiler to set the mode for the @code{v4si}
type to be 16 bytes wide and divided into @code{int} sized units.  For
a 32-bit @code{int} this means a vector of 4 units of 4 bytes, and the
corresponding mode of @code{foo} is @acronym{V4SI}.

The @code{vector_size} attribute is only applicable to integral and
float scalars, although arrays, pointers, and function return values
are allowed in conjunction with this construct. Only sizes that are
a power of two are currently allowed.

All the basic integer types can be used as base types, both as signed
and as unsigned: @code{char}, @code{short}, @code{int}, @code{long},
@code{long long}.  In addition, @code{float} and @code{double} can be
used to build floating-point vector types.

Specifying a combination that is not valid for the current architecture
causes GCC to synthesize the instructions using a narrower mode.
For example, if you specify a variable of type @code{V4SI} and your
architecture does not allow for this specific SIMD type, GCC
produces code that uses 4 @code{SIs}.

The types defined in this manner can be used with a subset of normal C
operations.  Currently, GCC allows using the following operators
on these types: @code{+, -, *, /, unary minus, ^, |, &, ~, %}@.

The operations behave like C++ @code{valarrays}.  Addition is defined as
the addition of the corresponding elements of the operands.  For
example, in the code below, each of the 4 elements in @var{a} is
added to the corresponding 4 elements in @var{b} and the resulting
vector is stored in @var{c}.

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));

v4si a, b, c;

c = a + b;
@end smallexample

Subtraction, multiplication, division, and the logical operations
operate in a similar manner.  Likewise, the result of using the unary
minus or complement operators on a vector type is a vector whose
elements are the negative or complemented values of the corresponding
elements in the operand.

It is possible to use shifting operators @code{<<}, @code{>>} on
integer-type vectors. The operation is defined as following: @code{@{a0,
a1, @dots{}, an@} >> @{b0, b1, @dots{}, bn@} == @{a0 >> b0, a1 >> b1,
@dots{}, an >> bn@}}@. Vector operands must have the same number of
elements. 

For convenience, it is allowed to use a binary vector operation
where one operand is a scalar. In that case the compiler transforms
the scalar operand into a vector where each element is the scalar from
the operation. The transformation happens only if the scalar could be
safely converted to the vector-element type.
Consider the following code.

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));

v4si a, b, c;
long l;

a = b + 1;    /* a = b + @{1,1,1,1@}; */
a = 2 * b;    /* a = @{2,2,2,2@} * b; */

a = l + a;    /* Error, cannot convert long to int. */
@end smallexample

Vectors can be subscripted as if the vector were an array with
the same number of elements and base type.  Out of bound accesses
invoke undefined behavior at run time.  Warnings for out of bound
accesses for vector subscription can be enabled with
@option{-Warray-bounds}.

Vector comparison is supported with standard comparison
operators: @code{==, !=, <, <=, >, >=}. Comparison operands can be
vector expressions of integer-type or real-type. Comparison between
integer-type vectors and real-type vectors are not supported.  The
result of the comparison is a vector of the same width and number of
elements as the comparison operands with a signed integral element
type.

Vectors are compared element-wise producing 0 when comparison is false
and -1 (constant of the appropriate type where all bits are set)
otherwise. Consider the following example.

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));

v4si a = @{1,2,3,4@};
v4si b = @{3,2,1,4@};
v4si c;

c = a >  b;     /* The result would be @{0, 0,-1, 0@}  */
c = a == b;     /* The result would be @{0,-1, 0,-1@}  */
@end smallexample

Vector shuffling is available using functions
@code{__builtin_shuffle (vec, mask)} and
@code{__builtin_shuffle (vec0, vec1, mask)}.
Both functions construct a permutation of elements from one or two
vectors and return a vector of the same type as the input vector(s).
The @var{mask} is an integral vector with the same width (@var{W})
and element count (@var{N}) as the output vector.

The elements of the input vectors are numbered in memory ordering of
@var{vec0} beginning at 0 and @var{vec1} beginning at @var{N}.  The
elements of @var{mask} are considered modulo @var{N} in the single-operand
case and modulo @math{2*@var{N}} in the two-operand case.

Consider the following example,

@smallexample
typedef int v4si __attribute__ ((vector_size (16)));

v4si a = @{1,2,3,4@};
v4si b = @{5,6,7,8@};
v4si mask1 = @{0,1,1,3@};
v4si mask2 = @{0,4,2,5@};
v4si res;

res = __builtin_shuffle (a, mask1);       /* res is @{1,2,2,4@}  */
res = __builtin_shuffle (a, b, mask2);    /* res is @{1,5,3,6@}  */
@end smallexample

Note that @code{__builtin_shuffle} is intentionally semantically
compatible with the OpenCL @code{shuffle} and @code{shuffle2} functions.

You can declare variables and use them in function calls and returns, as
well as in assignments and some casts.  You can specify a vector type as
a return type for a function.  Vector types can also be used as function
arguments.  It is possible to cast from one vector type to another,
provided they are of the same size (in fact, you can also cast vectors
to and from other datatypes of the same size).

You cannot operate between vectors of different lengths or different
signedness without a cast.

@node Offsetof
@section Offsetof
@findex __builtin_offsetof

GCC implements for both C and C++ a syntactic extension to implement
the @code{offsetof} macro.

@smallexample
primary:
        "__builtin_offsetof" "(" @code{typename} "," offsetof_member_designator ")"

offsetof_member_designator:
          @code{identifier}
        | offsetof_member_designator "." @code{identifier}
        | offsetof_member_designator "[" @code{expr} "]"
@end smallexample

This extension is sufficient such that

@smallexample
#define offsetof(@var{type}, @var{member})  __builtin_offsetof (@var{type}, @var{member})
@end smallexample

@noindent
is a suitable definition of the @code{offsetof} macro.  In C++, @var{type}
may be dependent.  In either case, @var{member} may consist of a single
identifier, or a sequence of member accesses and array references.

@node __sync Builtins
@section Legacy __sync Built-in Functions for Atomic Memory Access

The following built-in functions
are intended to be compatible with those described
in the @cite{Intel Itanium Processor-specific Application Binary Interface},
section 7.4.  As such, they depart from the normal GCC practice of using
the @samp{__builtin_} prefix, and further that they are overloaded such that
they work on multiple types.

The definition given in the Intel documentation allows only for the use of
the types @code{int}, @code{long}, @code{long long} as well as their unsigned
counterparts.  GCC allows any integral scalar or pointer type that is
1, 2, 4 or 8 bytes in length.

Not all operations are supported by all target processors.  If a particular
operation cannot be implemented on the target processor, a warning is
generated and a call an external function is generated.  The external
function carries the same name as the built-in version,
with an additional suffix
@samp{_@var{n}} where @var{n} is the size of the data type.

@c ??? Should we have a mechanism to suppress this warning?  This is almost
@c useful for implementing the operation under the control of an external
@c mutex.

In most cases, these built-in functions are considered a @dfn{full barrier}.
That is,
no memory operand is moved across the operation, either forward or
backward.  Further, instructions are issued as necessary to prevent the
processor from speculating loads across the operation and from queuing stores
after the operation.

All of the routines are described in the Intel documentation to take
``an optional list of variables protected by the memory barrier''.  It's
not clear what is meant by that; it could mean that @emph{only} the
following variables are protected, or it could mean that these variables
should in addition be protected.  At present GCC ignores this list and
protects all variables that are globally accessible.  If in the future
we make some use of this list, an empty list will continue to mean all
globally accessible variables.

@table @code
@item @var{type} __sync_fetch_and_add (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_sub (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_or (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_and (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_xor (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_fetch_and_nand (@var{type} *ptr, @var{type} value, ...)
@findex __sync_fetch_and_add
@findex __sync_fetch_and_sub
@findex __sync_fetch_and_or
@findex __sync_fetch_and_and
@findex __sync_fetch_and_xor
@findex __sync_fetch_and_nand
These built-in functions perform the operation suggested by the name, and
returns the value that had previously been in memory.  That is,

@smallexample
@{ tmp = *ptr; *ptr @var{op}= value; return tmp; @}
@{ tmp = *ptr; *ptr = ~(tmp & value); return tmp; @}   // nand
@end smallexample

@emph{Note:} GCC 4.4 and later implement @code{__sync_fetch_and_nand}
as @code{*ptr = ~(tmp & value)} instead of @code{*ptr = ~tmp & value}.

@item @var{type} __sync_add_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_sub_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_or_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_and_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_xor_and_fetch (@var{type} *ptr, @var{type} value, ...)
@itemx @var{type} __sync_nand_and_fetch (@var{type} *ptr, @var{type} value, ...)
@findex __sync_add_and_fetch
@findex __sync_sub_and_fetch
@findex __sync_or_and_fetch
@findex __sync_and_and_fetch
@findex __sync_xor_and_fetch
@findex __sync_nand_and_fetch
These built-in functions perform the operation suggested by the name, and
return the new value.  That is,

@smallexample
@{ *ptr @var{op}= value; return *ptr; @}
@{ *ptr = ~(*ptr & value); return *ptr; @}   // nand
@end smallexample

@emph{Note:} GCC 4.4 and later implement @code{__sync_nand_and_fetch}
as @code{*ptr = ~(*ptr & value)} instead of
@code{*ptr = ~*ptr & value}.

@item bool __sync_bool_compare_and_swap (@var{type} *ptr, @var{type} oldval, @var{type} newval, ...)
@itemx @var{type} __sync_val_compare_and_swap (@var{type} *ptr, @var{type} oldval, @var{type} newval, ...)
@findex __sync_bool_compare_and_swap
@findex __sync_val_compare_and_swap
These built-in functions perform an atomic compare and swap.
That is, if the current
value of @code{*@var{ptr}} is @var{oldval}, then write @var{newval} into
@code{*@var{ptr}}.

The ``bool'' version returns true if the comparison is successful and
@var{newval} is written.  The ``val'' version returns the contents
of @code{*@var{ptr}} before the operation.

@item __sync_synchronize (...)
@findex __sync_synchronize
This built-in function issues a full memory barrier.

@item @var{type} __sync_lock_test_and_set (@var{type} *ptr, @var{type} value, ...)
@findex __sync_lock_test_and_set
This built-in function, as described by Intel, is not a traditional test-and-set
operation, but rather an atomic exchange operation.  It writes @var{value}
into @code{*@var{ptr}}, and returns the previous contents of
@code{*@var{ptr}}.

Many targets have only minimal support for such locks, and do not support
a full exchange operation.  In this case, a target may support reduced
functionality here by which the @emph{only} valid value to store is the
immediate constant 1.  The exact value actually stored in @code{*@var{ptr}}
is implementation defined.

This built-in function is not a full barrier,
but rather an @dfn{acquire barrier}.
This means that references after the operation cannot move to (or be
speculated to) before the operation, but previous memory stores may not
be globally visible yet, and previous memory loads may not yet be
satisfied.

@item void __sync_lock_release (@var{type} *ptr, ...)
@findex __sync_lock_release
This built-in function releases the lock acquired by
@code{__sync_lock_test_and_set}.
Normally this means writing the constant 0 to @code{*@var{ptr}}.

This built-in function is not a full barrier,
but rather a @dfn{release barrier}.
This means that all previous memory stores are globally visible, and all
previous memory loads have been satisfied, but following memory reads
are not prevented from being speculated to before the barrier.
@end table

@node __atomic Builtins
@section Built-in functions for memory model aware atomic operations

The following built-in functions approximately match the requirements for
C++11 memory model. Many are similar to the @samp{__sync} prefixed built-in
functions, but all also have a memory model parameter.  These are all
identified by being prefixed with @samp{__atomic}, and most are overloaded
such that they work with multiple types.

GCC allows any integral scalar or pointer type that is 1, 2, 4, or 8
bytes in length. 16-byte integral types are also allowed if
@samp{__int128} (@pxref{__int128}) is supported by the architecture.

Target architectures are encouraged to provide their own patterns for
each of these built-in functions.  If no target is provided, the original 
non-memory model set of @samp{__sync} atomic built-in functions are
utilized, along with any required synchronization fences surrounding it in
order to achieve the proper behavior.  Execution in this case is subject
to the same restrictions as those built-in functions.

If there is no pattern or mechanism to provide a lock free instruction
sequence, a call is made to an external routine with the same parameters
to be resolved at run time.

The four non-arithmetic functions (load, store, exchange, and 
compare_exchange) all have a generic version as well.  This generic
version works on any data type.  If the data type size maps to one
of the integral sizes that may have lock free support, the generic
version utilizes the lock free built-in function.  Otherwise an
external call is left to be resolved at run time.  This external call is
the same format with the addition of a @samp{size_t} parameter inserted
as the first parameter indicating the size of the object being pointed to.
All objects must be the same size.

There are 6 different memory models that can be specified.  These map
to the same names in the C++11 standard.  Refer there or to the
@uref{http://gcc.gnu.org/wiki/Atomic/GCCMM/AtomicSync,GCC wiki on
atomic synchronization} for more detailed definitions.  These memory
models integrate both barriers to code motion as well as synchronization
requirements with other threads. These are listed in approximately
ascending order of strength. It is also possible to use target specific
flags for memory model flags, like Hardware Lock Elision.

@table  @code
@item __ATOMIC_RELAXED
No barriers or synchronization.
@item __ATOMIC_CONSUME
Data dependency only for both barrier and synchronization with another
thread.
@item __ATOMIC_ACQUIRE
Barrier to hoisting of code and synchronizes with release (or stronger)
semantic stores from another thread.
@item __ATOMIC_RELEASE
Barrier to sinking of code and synchronizes with acquire (or stronger)
semantic loads from another thread.
@item __ATOMIC_ACQ_REL
Full barrier in both directions and synchronizes with acquire loads and
release stores in another thread.
@item __ATOMIC_SEQ_CST
Full barrier in both directions and synchronizes with acquire loads and
release stores in all threads.
@end table

When implementing patterns for these built-in functions, the memory model
parameter can be ignored as long as the pattern implements the most
restrictive @code{__ATOMIC_SEQ_CST} model.  Any of the other memory models
execute correctly with this memory model but they may not execute as
efficiently as they could with a more appropriate implementation of the
relaxed requirements.

Note that the C++11 standard allows for the memory model parameter to be
determined at run time rather than at compile time.  These built-in
functions map any run-time value to @code{__ATOMIC_SEQ_CST} rather
than invoke a runtime library call or inline a switch statement.  This is
standard compliant, safe, and the simplest approach for now.

The memory model parameter is a signed int, but only the lower 8 bits are
reserved for the memory model.  The remainder of the signed int is reserved
for future use and should be 0.  Use of the predefined atomic values
ensures proper usage.

@deftypefn {Built-in Function} @var{type} __atomic_load_n (@var{type} *ptr, int memmodel)
This built-in function implements an atomic load operation.  It returns the
contents of @code{*@var{ptr}}.

The valid memory model variants are
@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, @code{__ATOMIC_ACQUIRE},
and @code{__ATOMIC_CONSUME}.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_load (@var{type} *ptr, @var{type} *ret, int memmodel)
This is the generic version of an atomic load.  It returns the
contents of @code{*@var{ptr}} in @code{*@var{ret}}.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_store_n (@var{type} *ptr, @var{type} val, int memmodel)
This built-in function implements an atomic store operation.  It writes 
@code{@var{val}} into @code{*@var{ptr}}.  

The valid memory model variants are
@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, and @code{__ATOMIC_RELEASE}.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_store (@var{type} *ptr, @var{type} *val, int memmodel)
This is the generic version of an atomic store.  It stores the value
of @code{*@var{val}} into @code{*@var{ptr}}.

@end deftypefn

@deftypefn {Built-in Function} @var{type} __atomic_exchange_n (@var{type} *ptr, @var{type} val, int memmodel)
This built-in function implements an atomic exchange operation.  It writes
@var{val} into @code{*@var{ptr}}, and returns the previous contents of
@code{*@var{ptr}}.

The valid memory model variants are
@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, @code{__ATOMIC_ACQUIRE},
@code{__ATOMIC_RELEASE}, and @code{__ATOMIC_ACQ_REL}.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_exchange (@var{type} *ptr, @var{type} *val, @var{type} *ret, int memmodel)
This is the generic version of an atomic exchange.  It stores the
contents of @code{*@var{val}} into @code{*@var{ptr}}. The original value
of @code{*@var{ptr}} is copied into @code{*@var{ret}}.

@end deftypefn

@deftypefn {Built-in Function} bool __atomic_compare_exchange_n (@var{type} *ptr, @var{type} *expected, @var{type} desired, bool weak, int success_memmodel, int failure_memmodel)
This built-in function implements an atomic compare and exchange operation.
This compares the contents of @code{*@var{ptr}} with the contents of
@code{*@var{expected}} and if equal, writes @var{desired} into
@code{*@var{ptr}}.  If they are not equal, the current contents of
@code{*@var{ptr}} is written into @code{*@var{expected}}.  @var{weak} is true
for weak compare_exchange, and false for the strong variation.  Many targets 
only offer the strong variation and ignore the parameter.  When in doubt, use
the strong variation.

True is returned if @var{desired} is written into
@code{*@var{ptr}} and the execution is considered to conform to the
memory model specified by @var{success_memmodel}.  There are no
restrictions on what memory model can be used here.

False is returned otherwise, and the execution is considered to conform
to @var{failure_memmodel}. This memory model cannot be
@code{__ATOMIC_RELEASE} nor @code{__ATOMIC_ACQ_REL}.  It also cannot be a
stronger model than that specified by @var{success_memmodel}.

@end deftypefn

@deftypefn {Built-in Function} bool __atomic_compare_exchange (@var{type} *ptr, @var{type} *expected, @var{type} *desired, bool weak, int success_memmodel, int failure_memmodel)
This built-in function implements the generic version of
@code{__atomic_compare_exchange}.  The function is virtually identical to
@code{__atomic_compare_exchange_n}, except the desired value is also a
pointer.

@end deftypefn

@deftypefn {Built-in Function} @var{type} __atomic_add_fetch (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_sub_fetch (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_and_fetch (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_xor_fetch (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_or_fetch (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_nand_fetch (@var{type} *ptr, @var{type} val, int memmodel)
These built-in functions perform the operation suggested by the name, and
return the result of the operation. That is,

@smallexample
@{ *ptr @var{op}= val; return *ptr; @}
@end smallexample

All memory models are valid.

@end deftypefn

@deftypefn {Built-in Function} @var{type} __atomic_fetch_add (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_sub (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_and (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_xor (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_or (@var{type} *ptr, @var{type} val, int memmodel)
@deftypefnx {Built-in Function} @var{type} __atomic_fetch_nand (@var{type} *ptr, @var{type} val, int memmodel)
These built-in functions perform the operation suggested by the name, and
return the value that had previously been in @code{*@var{ptr}}.  That is,

@smallexample
@{ tmp = *ptr; *ptr @var{op}= val; return tmp; @}
@end smallexample

All memory models are valid.

@end deftypefn

@deftypefn {Built-in Function} bool __atomic_test_and_set (void *ptr, int memmodel)

This built-in function performs an atomic test-and-set operation on
the byte at @code{*@var{ptr}}.  The byte is set to some implementation
defined nonzero ``set'' value and the return value is @code{true} if and only
if the previous contents were ``set''.

All memory models are valid.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_clear (bool *ptr, int memmodel)

This built-in function performs an atomic clear operation on
@code{*@var{ptr}}.  After the operation, @code{*@var{ptr}} contains 0.

The valid memory model variants are
@code{__ATOMIC_RELAXED}, @code{__ATOMIC_SEQ_CST}, and
@code{__ATOMIC_RELEASE}.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_thread_fence (int memmodel)

This built-in function acts as a synchronization fence between threads
based on the specified memory model.

All memory orders are valid.

@end deftypefn

@deftypefn {Built-in Function} void __atomic_signal_fence (int memmodel)

This built-in function acts as a synchronization fence between a thread
and signal handlers based in the same thread.

All memory orders are valid.

@end deftypefn

@deftypefn {Built-in Function} bool __atomic_always_lock_free (size_t size,  void *ptr)

This built-in function returns true if objects of @var{size} bytes always
generate lock free atomic instructions for the target architecture.  
@var{size} must resolve to a compile-time constant and the result also
resolves to a compile-time constant.

@var{ptr} is an optional pointer to the object that may be used to determine
alignment.  A value of 0 indicates typical alignment should be used.  The 
compiler may also ignore this parameter.

@smallexample
if (_atomic_always_lock_free (sizeof (long long), 0))
@end smallexample

@end deftypefn

@deftypefn {Built-in Function} bool __atomic_is_lock_free (size_t size, void *ptr)

This built-in function returns true if objects of @var{size} bytes always
generate lock free atomic instructions for the target architecture.  If
it is not known to be lock free a call is made to a runtime routine named
@code{__atomic_is_lock_free}.

@var{ptr} is an optional pointer to the object that may be used to determine
alignment.  A value of 0 indicates typical alignment should be used.  The 
compiler may also ignore this parameter.
@end deftypefn

@node x86 specific memory model extensions for transactional memory
@section x86 specific memory model extensions for transactional memory

The i386 architecture supports additional memory ordering flags
to mark lock critical sections for hardware lock elision. 
These must be specified in addition to an existing memory model to 
atomic intrinsics.

@table @code
@item __ATOMIC_HLE_ACQUIRE
Start lock elision on a lock variable.
Memory model must be @code{__ATOMIC_ACQUIRE} or stronger.
@item __ATOMIC_HLE_RELEASE
End lock elision on a lock variable.
Memory model must be @code{__ATOMIC_RELEASE} or stronger.
@end table

When a lock acquire fails it's required for good performance to abort
the transaction quickly. This can be done with a @code{_mm_pause}

@smallexample
#include <immintrin.h> // For _mm_pause

/* Acquire lock with lock elision */
while (__atomic_exchange_n(&lockvar, 1, __ATOMIC_ACQUIRE|__ATOMIC_HLE_ACQUIRE))
    _mm_pause(); /* Abort failed transaction */
...
/* Free lock with lock elision */
__atomic_clear(&lockvar, __ATOMIC_RELEASE|__ATOMIC_HLE_RELEASE);
@end smallexample

@node Object Size Checking
@section Object Size Checking Built-in Functions
@findex __builtin_object_size
@findex __builtin___memcpy_chk
@findex __builtin___mempcpy_chk
@findex __builtin___memmove_chk
@findex __builtin___memset_chk
@findex __builtin___strcpy_chk
@findex __builtin___stpcpy_chk
@findex __builtin___strncpy_chk
@findex __builtin___strcat_chk
@findex __builtin___strncat_chk
@findex __builtin___sprintf_chk
@findex __builtin___snprintf_chk
@findex __builtin___vsprintf_chk
@findex __builtin___vsnprintf_chk
@findex __builtin___printf_chk
@findex __builtin___vprintf_chk
@findex __builtin___fprintf_chk
@findex __builtin___vfprintf_chk

GCC implements a limited buffer overflow protection mechanism
that can prevent some buffer overflow attacks.

@deftypefn {Built-in Function} {size_t} __builtin_object_size (void * @var{ptr}, int @var{type})
is a built-in construct that returns a constant number of bytes from
@var{ptr} to the end of the object @var{ptr} pointer points to
(if known at compile time).  @code{__builtin_object_size} never evaluates
its arguments for side-effects.  If there are any side-effects in them, it
returns @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0}
for @var{type} 2 or 3.  If there are multiple objects @var{ptr} can
point to and all of them are known at compile time, the returned number
is the maximum of remaining byte counts in those objects if @var{type} & 2 is
0 and minimum if nonzero.  If it is not possible to determine which objects
@var{ptr} points to at compile time, @code{__builtin_object_size} should
return @code{(size_t) -1} for @var{type} 0 or 1 and @code{(size_t) 0}
for @var{type} 2 or 3.

@var{type} is an integer constant from 0 to 3.  If the least significant
bit is clear, objects are whole variables, if it is set, a closest
surrounding subobject is considered the object a pointer points to.
The second bit determines if maximum or minimum of remaining bytes
is computed.

@smallexample
struct V @{ char buf1[10]; int b; char buf2[10]; @} var;
char *p = &var.buf1[1], *q = &var.b;

/* Here the object p points to is var.  */
assert (__builtin_object_size (p, 0) == sizeof (var) - 1);
/* The subobject p points to is var.buf1.  */
assert (__builtin_object_size (p, 1) == sizeof (var.buf1) - 1);
/* The object q points to is var.  */
assert (__builtin_object_size (q, 0)
        == (char *) (&var + 1) - (char *) &var.b);
/* The subobject q points to is var.b.  */
assert (__builtin_object_size (q, 1) == sizeof (var.b));
@end smallexample
@end deftypefn

There are built-in functions added for many common string operation
functions, e.g., for @code{memcpy} @code{__builtin___memcpy_chk}
built-in is provided.  This built-in has an additional last argument,
which is the number of bytes remaining in object the @var{dest}
argument points to or @code{(size_t) -1} if the size is not known.

The built-in functions are optimized into the normal string functions
like @code{memcpy} if the last argument is @code{(size_t) -1} or if
it is known at compile time that the destination object will not
be overflown.  If the compiler can determine at compile time the
object will be always overflown, it issues a warning.

The intended use can be e.g.@:

@smallexample
#undef memcpy
#define bos0(dest) __builtin_object_size (dest, 0)
#define memcpy(dest, src, n) \
  __builtin___memcpy_chk (dest, src, n, bos0 (dest))

char *volatile p;
char buf[10];
/* It is unknown what object p points to, so this is optimized
   into plain memcpy - no checking is possible.  */
memcpy (p, "abcde", n);
/* Destination is known and length too.  It is known at compile
   time there will be no overflow.  */
memcpy (&buf[5], "abcde", 5);
/* Destination is known, but the length is not known at compile time.
   This will result in __memcpy_chk call that can check for overflow
   at run time.  */
memcpy (&buf[5], "abcde", n);
/* Destination is known and it is known at compile time there will
   be overflow.  There will be a warning and __memcpy_chk call that
   will abort the program at run time.  */
memcpy (&buf[6], "abcde", 5);
@end smallexample

Such built-in functions are provided for @code{memcpy}, @code{mempcpy},
@code{memmove}, @code{memset}, @code{strcpy}, @code{stpcpy}, @code{strncpy},
@code{strcat} and @code{strncat}.

There are also checking built-in functions for formatted output functions.
@smallexample
int __builtin___sprintf_chk (char *s, int flag, size_t os, const char *fmt, ...);
int __builtin___snprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                              const char *fmt, ...);
int __builtin___vsprintf_chk (char *s, int flag, size_t os, const char *fmt,
                              va_list ap);
int __builtin___vsnprintf_chk (char *s, size_t maxlen, int flag, size_t os,
                               const char *fmt, va_list ap);
@end smallexample

The added @var{flag} argument is passed unchanged to @code{__sprintf_chk}
etc.@: functions and can contain implementation specific flags on what
additional security measures the checking function might take, such as
handling @code{%n} differently.

The @var{os} argument is the object size @var{s} points to, like in the
other built-in functions.  There is a small difference in the behavior
though, if @var{os} is @code{(size_t) -1}, the built-in functions are
optimized into the non-checking functions only if @var{flag} is 0, otherwise
the checking function is called with @var{os} argument set to
@code{(size_t) -1}.

In addition to this, there are checking built-in functions
@code{__builtin___printf_chk}, @code{__builtin___vprintf_chk},
@code{__builtin___fprintf_chk} and @code{__builtin___vfprintf_chk}.
These have just one additional argument, @var{flag}, right before
format string @var{fmt}.  If the compiler is able to optimize them to
@code{fputc} etc.@: functions, it does, otherwise the checking function
is called and the @var{flag} argument passed to it.

@node Other Builtins
@section Other Built-in Functions Provided by GCC
@cindex built-in functions
@findex __builtin_fpclassify
@findex __builtin_isfinite
@findex __builtin_isnormal
@findex __builtin_isgreater
@findex __builtin_isgreaterequal
@findex __builtin_isinf_sign
@findex __builtin_isless
@findex __builtin_islessequal
@findex __builtin_islessgreater
@findex __builtin_isunordered
@findex __builtin_powi
@findex __builtin_powif
@findex __builtin_powil
@findex _Exit
@findex _exit
@findex abort
@findex abs
@findex acos
@findex acosf
@findex acosh
@findex acoshf
@findex acoshl
@findex acosl
@findex alloca
@findex asin
@findex asinf
@findex asinh
@findex asinhf
@findex asinhl
@findex asinl
@findex atan
@findex atan2
@findex atan2f
@findex atan2l
@findex atanf
@findex atanh
@findex atanhf
@findex atanhl
@findex atanl
@findex bcmp
@findex bzero
@findex cabs
@findex cabsf
@findex cabsl
@findex cacos
@findex cacosf
@findex cacosh
@findex cacoshf
@findex cacoshl
@findex cacosl
@findex calloc
@findex carg
@findex cargf
@findex cargl
@findex casin
@findex casinf
@findex casinh
@findex casinhf
@findex casinhl
@findex casinl
@findex catan
@findex catanf
@findex catanh
@findex catanhf
@findex catanhl
@findex catanl
@findex cbrt
@findex cbrtf
@findex cbrtl
@findex ccos
@findex ccosf
@findex ccosh
@findex ccoshf
@findex ccoshl
@findex ccosl
@findex ceil
@findex ceilf
@findex ceill
@findex cexp
@findex cexpf
@findex cexpl
@findex cimag
@findex cimagf
@findex cimagl
@findex clog
@findex clogf
@findex clogl
@findex conj
@findex conjf
@findex conjl
@findex copysign
@findex copysignf
@findex copysignl
@findex cos
@findex cosf
@findex cosh
@findex coshf
@findex coshl
@findex cosl
@findex cpow
@findex cpowf
@findex cpowl
@findex cproj
@findex cprojf
@findex cprojl
@findex creal
@findex crealf
@findex creall
@findex csin
@findex csinf
@findex csinh
@findex csinhf
@findex csinhl
@findex csinl
@findex csqrt
@findex csqrtf
@findex csqrtl
@findex ctan
@findex ctanf
@findex ctanh
@findex ctanhf
@findex ctanhl
@findex ctanl
@findex dcgettext
@findex dgettext
@findex drem
@findex dremf
@findex dreml
@findex erf
@findex erfc
@findex erfcf
@findex erfcl
@findex erff
@findex erfl
@findex exit
@findex exp
@findex exp10
@findex exp10f
@findex exp10l
@findex exp2
@findex exp2f
@findex exp2l
@findex expf
@findex expl
@findex expm1
@findex expm1f
@findex expm1l
@findex fabs
@findex fabsf
@findex fabsl
@findex fdim
@findex fdimf
@findex fdiml
@findex ffs
@findex floor
@findex floorf
@findex floorl
@findex fma
@findex fmaf
@findex fmal
@findex fmax
@findex fmaxf
@findex fmaxl
@findex fmin
@findex fminf
@findex fminl
@findex fmod
@findex fmodf
@findex fmodl
@findex fprintf
@findex fprintf_unlocked
@findex fputs
@findex fputs_unlocked
@findex frexp
@findex frexpf
@findex frexpl
@findex fscanf
@findex gamma
@findex gammaf
@findex gammal
@findex gamma_r
@findex gammaf_r
@findex gammal_r
@findex gettext
@findex hypot
@findex hypotf
@findex hypotl
@findex ilogb
@findex ilogbf
@findex ilogbl
@findex imaxabs
@findex index
@findex isalnum
@findex isalpha
@findex isascii
@findex isblank
@findex iscntrl
@findex isdigit
@findex isgraph
@findex islower
@findex isprint
@findex ispunct
@findex isspace
@findex isupper
@findex iswalnum
@findex iswalpha
@findex iswblank
@findex iswcntrl
@findex iswdigit
@findex iswgraph
@findex iswlower
@findex iswprint
@findex iswpunct
@findex iswspace
@findex iswupper
@findex iswxdigit
@findex isxdigit
@findex j0
@findex j0f
@findex j0l
@findex j1
@findex j1f
@findex j1l
@findex jn
@findex jnf
@findex jnl
@findex labs
@findex ldexp
@findex ldexpf
@findex ldexpl
@findex lgamma
@findex lgammaf
@findex lgammal
@findex lgamma_r
@findex lgammaf_r
@findex lgammal_r
@findex llabs
@findex llrint
@findex llrintf
@findex llrintl
@findex llround
@findex llroundf
@findex llroundl
@findex log
@findex log10
@findex log10f
@findex log10l
@findex log1p
@findex log1pf
@findex log1pl
@findex log2
@findex log2f
@findex log2l
@findex logb
@findex logbf
@findex logbl
@findex logf
@findex logl
@findex lrint
@findex lrintf
@findex lrintl
@findex lround
@findex lroundf
@findex lroundl
@findex malloc
@findex memchr
@findex memcmp
@findex memcpy
@findex mempcpy
@findex memset
@findex modf
@findex modff
@findex modfl
@findex nearbyint
@findex nearbyintf
@findex nearbyintl
@findex nextafter
@findex nextafterf
@findex nextafterl
@findex nexttoward
@findex nexttowardf
@findex nexttowardl
@findex pow
@findex pow10
@findex pow10f
@findex pow10l
@findex powf
@findex powl
@findex printf
@findex printf_unlocked
@findex putchar
@findex puts
@findex remainder
@findex remainderf
@findex remainderl
@findex remquo
@findex remquof
@findex remquol
@findex rindex
@findex rint
@findex rintf
@findex rintl
@findex round
@findex roundf
@findex roundl
@findex scalb
@findex scalbf
@findex scalbl
@findex scalbln
@findex scalblnf
@findex scalblnf
@findex scalbn
@findex scalbnf
@findex scanfnl
@findex signbit
@findex signbitf
@findex signbitl
@findex signbitd32
@findex signbitd64
@findex signbitd128
@findex significand
@findex significandf
@findex significandl
@findex sin
@findex sincos
@findex sincosf
@findex sincosl
@findex sinf
@findex sinh
@findex sinhf
@findex sinhl
@findex sinl
@findex snprintf
@findex sprintf
@findex sqrt
@findex sqrtf
@findex sqrtl
@findex sscanf
@findex stpcpy
@findex stpncpy
@findex strcasecmp
@findex strcat
@findex strchr
@findex strcmp
@findex strcpy
@findex strcspn
@findex strdup
@findex strfmon
@findex strftime
@findex strlen
@findex strncasecmp
@findex strncat
@findex strncmp
@findex strncpy
@findex strndup
@findex strpbrk
@findex strrchr
@findex strspn
@findex strstr
@findex tan
@findex tanf
@findex tanh
@findex tanhf
@findex tanhl
@findex tanl
@findex tgamma
@findex tgammaf
@findex tgammal
@findex toascii
@findex tolower
@findex toupper
@findex towlower
@findex towupper
@findex trunc
@findex truncf
@findex truncl
@findex vfprintf
@findex vfscanf
@findex vprintf
@findex vscanf
@findex vsnprintf
@findex vsprintf
@findex vsscanf
@findex y0
@findex y0f
@findex y0l
@findex y1
@findex y1f
@findex y1l
@findex yn
@findex ynf
@findex ynl

GCC provides a large number of built-in functions other than the ones
mentioned above.  Some of these are for internal use in the processing
of exceptions or variable-length argument lists and are not
documented here because they may change from time to time; we do not
recommend general use of these functions.

The remaining functions are provided for optimization purposes.

@opindex fno-builtin
GCC includes built-in versions of many of the functions in the standard
C library.  The versions prefixed with @code{__builtin_} are always
treated as having the same meaning as the C library function even if you
specify the @option{-fno-builtin} option.  (@pxref{C Dialect Options})
Many of these functions are only optimized in certain cases; if they are
not optimized in a particular case, a call to the library function is
emitted.

@opindex ansi
@opindex std
Outside strict ISO C mode (@option{-ansi}, @option{-std=c90},
@option{-std=c99} or @option{-std=c11}), the functions
@code{_exit}, @code{alloca}, @code{bcmp}, @code{bzero},
@code{dcgettext}, @code{dgettext}, @code{dremf}, @code{dreml},
@code{drem}, @code{exp10f}, @code{exp10l}, @code{exp10}, @code{ffsll},
@code{ffsl}, @code{ffs}, @code{fprintf_unlocked},
@code{fputs_unlocked}, @code{gammaf}, @code{gammal}, @code{gamma},
@code{gammaf_r}, @code{gammal_r}, @code{gamma_r}, @code{gettext},
@code{index}, @code{isascii}, @code{j0f}, @code{j0l}, @code{j0},
@code{j1f}, @code{j1l}, @code{j1}, @code{jnf}, @code{jnl}, @code{jn},
@code{lgammaf_r}, @code{lgammal_r}, @code{lgamma_r}, @code{mempcpy},
@code{pow10f}, @code{pow10l}, @code{pow10}, @code{printf_unlocked},
@code{rindex}, @code{scalbf}, @code{scalbl}, @code{scalb},
@code{signbit}, @code{signbitf}, @code{signbitl}, @code{signbitd32},
@code{signbitd64}, @code{signbitd128}, @code{significandf},
@code{significandl}, @code{significand}, @code{sincosf},
@code{sincosl}, @code{sincos}, @code{stpcpy}, @code{stpncpy},
@code{strcasecmp}, @code{strdup}, @code{strfmon}, @code{strncasecmp},
@code{strndup}, @code{toascii}, @code{y0f}, @code{y0l}, @code{y0},
@code{y1f}, @code{y1l}, @code{y1}, @code{ynf}, @code{ynl} and
@code{yn}
may be handled as built-in functions.
All these functions have corresponding versions
prefixed with @code{__builtin_}, which may be used even in strict C90
mode.

The ISO C99 functions
@code{_Exit}, @code{acoshf}, @code{acoshl}, @code{acosh}, @code{asinhf},
@code{asinhl}, @code{asinh}, @code{atanhf}, @code{atanhl}, @code{atanh},
@code{cabsf}, @code{cabsl}, @code{cabs}, @code{cacosf}, @code{cacoshf},
@code{cacoshl}, @code{cacosh}, @code{cacosl}, @code{cacos},
@code{cargf}, @code{cargl}, @code{carg}, @code{casinf}, @code{casinhf},
@code{casinhl}, @code{casinh}, @code{casinl}, @code{casin},
@code{catanf}, @code{catanhf}, @code{catanhl}, @code{catanh},
@code{catanl}, @code{catan}, @code{cbrtf}, @code{cbrtl}, @code{cbrt},
@code{ccosf}, @code{ccoshf}, @code{ccoshl}, @code{ccosh}, @code{ccosl},
@code{ccos}, @code{cexpf}, @code{cexpl}, @code{cexp}, @code{cimagf},
@code{cimagl}, @code{cimag}, @code{clogf}, @code{clogl}, @code{clog},
@code{conjf}, @code{conjl}, @code{conj}, @code{copysignf}, @code{copysignl},
@code{copysign}, @code{cpowf}, @code{cpowl}, @code{cpow}, @code{cprojf},
@code{cprojl}, @code{cproj}, @code{crealf}, @code{creall}, @code{creal},
@code{csinf}, @code{csinhf}, @code{csinhl}, @code{csinh}, @code{csinl},
@code{csin}, @code{csqrtf}, @code{csqrtl}, @code{csqrt}, @code{ctanf},
@code{ctanhf}, @code{ctanhl}, @code{ctanh}, @code{ctanl}, @code{ctan},
@code{erfcf}, @code{erfcl}, @code{erfc}, @code{erff}, @code{erfl},
@code{erf}, @code{exp2f}, @code{exp2l}, @code{exp2}, @code{expm1f},
@code{expm1l}, @code{expm1}, @code{fdimf}, @code{fdiml}, @code{fdim},
@code{fmaf}, @code{fmal}, @code{fmaxf}, @code{fmaxl}, @code{fmax},
@code{fma}, @code{fminf}, @code{fminl}, @code{fmin}, @code{hypotf},
@code{hypotl}, @code{hypot}, @code{ilogbf}, @code{ilogbl}, @code{ilogb},
@code{imaxabs}, @code{isblank}, @code{iswblank}, @code{lgammaf},
@code{lgammal}, @code{lgamma}, @code{llabs}, @code{llrintf}, @code{llrintl},
@code{llrint}, @code{llroundf}, @code{llroundl}, @code{llround},
@code{log1pf}, @code{log1pl}, @code{log1p}, @code{log2f}, @code{log2l},
@code{log2}, @code{logbf}, @code{logbl}, @code{logb}, @code{lrintf},
@code{lrintl}, @code{lrint}, @code{lroundf}, @code{lroundl},
@code{lround}, @code{nearbyintf}, @code{nearbyintl}, @code{nearbyint},
@code{nextafterf}, @code{nextafterl}, @code{nextafter},
@code{nexttowardf}, @code{nexttowardl}, @code{nexttoward},
@code{remainderf}, @code{remainderl}, @code{remainder}, @code{remquof},
@code{remquol}, @code{remquo}, @code{rintf}, @code{rintl}, @code{rint},
@code{roundf}, @code{roundl}, @code{round}, @code{scalblnf},
@code{scalblnl}, @code{scalbln}, @code{scalbnf}, @code{scalbnl},
@code{scalbn}, @code{snprintf}, @code{tgammaf}, @code{tgammal},
@code{tgamma}, @code{truncf}, @code{truncl}, @code{trunc},
@code{vfscanf}, @code{vscanf}, @code{vsnprintf} and @code{vsscanf}
are handled as built-in functions
except in strict ISO C90 mode (@option{-ansi} or @option{-std=c90}).

There are also built-in versions of the ISO C99 functions
@code{acosf}, @code{acosl}, @code{asinf}, @code{asinl}, @code{atan2f},
@code{atan2l}, @code{atanf}, @code{atanl}, @code{ceilf}, @code{ceill},
@code{cosf}, @code{coshf}, @code{coshl}, @code{cosl}, @code{expf},
@code{expl}, @code{fabsf}, @code{fabsl}, @code{floorf}, @code{floorl},
@code{fmodf}, @code{fmodl}, @code{frexpf}, @code{frexpl}, @code{ldexpf},
@code{ldexpl}, @code{log10f}, @code{log10l}, @code{logf}, @code{logl},
@code{modfl}, @code{modf}, @code{powf}, @code{powl}, @code{sinf},
@code{sinhf}, @code{sinhl}, @code{sinl}, @code{sqrtf}, @code{sqrtl},
@code{tanf}, @code{tanhf}, @code{tanhl} and @code{tanl}
that are recognized in any mode since ISO C90 reserves these names for
the purpose to which ISO C99 puts them.  All these functions have
corresponding versions prefixed with @code{__builtin_}.

The ISO C94 functions
@code{iswalnum}, @code{iswalpha}, @code{iswcntrl}, @code{iswdigit},
@code{iswgraph}, @code{iswlower}, @code{iswprint}, @code{iswpunct},
@code{iswspace}, @code{iswupper}, @code{iswxdigit}, @code{towlower} and
@code{towupper}
are handled as built-in functions
except in strict ISO C90 mode (@option{-ansi} or @option{-std=c90}).

The ISO C90 functions
@code{abort}, @code{abs}, @code{acos}, @code{asin}, @code{atan2},
@code{atan}, @code{calloc}, @code{ceil}, @code{cosh}, @code{cos},
@code{exit}, @code{exp}, @code{fabs}, @code{floor}, @code{fmod},
@code{fprintf}, @code{fputs}, @code{frexp}, @code{fscanf},
@code{isalnum}, @code{isalpha}, @code{iscntrl}, @code{isdigit},
@code{isgraph}, @code{islower}, @code{isprint}, @code{ispunct},
@code{isspace}, @code{isupper}, @code{isxdigit}, @code{tolower},
@code{toupper}, @code{labs}, @code{ldexp}, @code{log10}, @code{log},
@code{malloc}, @code{memchr}, @code{memcmp}, @code{memcpy},
@code{memset}, @code{modf}, @code{pow}, @code{printf}, @code{putchar},
@code{puts}, @code{scanf}, @code{sinh}, @code{sin}, @code{snprintf},
@code{sprintf}, @code{sqrt}, @code{sscanf}, @code{strcat},
@code{strchr}, @code{strcmp}, @code{strcpy}, @code{strcspn},
@code{strlen}, @code{strncat}, @code{strncmp}, @code{strncpy},
@code{strpbrk}, @code{strrchr}, @code{strspn}, @code{strstr},
@code{tanh}, @code{tan}, @code{vfprintf}, @code{vprintf} and @code{vsprintf}
are all recognized as built-in functions unless
@option{-fno-builtin} is specified (or @option{-fno-builtin-@var{function}}
is specified for an individual function).  All of these functions have
corresponding versions prefixed with @code{__builtin_}.

GCC provides built-in versions of the ISO C99 floating-point comparison
macros that avoid raising exceptions for unordered operands.  They have
the same names as the standard macros ( @code{isgreater},
@code{isgreaterequal}, @code{isless}, @code{islessequal},
@code{islessgreater}, and @code{isunordered}) , with @code{__builtin_}
prefixed.  We intend for a library implementor to be able to simply
@code{#define} each standard macro to its built-in equivalent.
In the same fashion, GCC provides @code{fpclassify}, @code{isfinite},
@code{isinf_sign} and @code{isnormal} built-ins used with
@code{__builtin_} prefixed.  The @code{isinf} and @code{isnan}
built-in functions appear both with and without the @code{__builtin_} prefix.

@deftypefn {Built-in Function} int __builtin_types_compatible_p (@var{type1}, @var{type2})

You can use the built-in function @code{__builtin_types_compatible_p} to
determine whether two types are the same.

This built-in function returns 1 if the unqualified versions of the
types @var{type1} and @var{type2} (which are types, not expressions) are
compatible, 0 otherwise.  The result of this built-in function can be
used in integer constant expressions.

This built-in function ignores top level qualifiers (e.g., @code{const},
@code{volatile}).  For example, @code{int} is equivalent to @code{const
int}.

The type @code{int[]} and @code{int[5]} are compatible.  On the other
hand, @code{int} and @code{char *} are not compatible, even if the size
of their types, on the particular architecture are the same.  Also, the
amount of pointer indirection is taken into account when determining
similarity.  Consequently, @code{short *} is not similar to
@code{short **}.  Furthermore, two types that are typedefed are
considered compatible if their underlying types are compatible.

An @code{enum} type is not considered to be compatible with another
@code{enum} type even if both are compatible with the same integer
type; this is what the C standard specifies.
For example, @code{enum @{foo, bar@}} is not similar to
@code{enum @{hot, dog@}}.

You typically use this function in code whose execution varies
depending on the arguments' types.  For example:

@smallexample
#define foo(x)                                                  \
  (@{                                                           \
    typeof (x) tmp = (x);                                       \
    if (__builtin_types_compatible_p (typeof (x), long double)) \
      tmp = foo_long_double (tmp);                              \
    else if (__builtin_types_compatible_p (typeof (x), double)) \
      tmp = foo_double (tmp);                                   \
    else if (__builtin_types_compatible_p (typeof (x), float))  \
      tmp = foo_float (tmp);                                    \
    else                                                        \
      abort ();                                                 \
    tmp;                                                        \
  @})
@end smallexample

@emph{Note:} This construct is only available for C@.

@end deftypefn

@deftypefn {Built-in Function} @var{type} __builtin_choose_expr (@var{const_exp}, @var{exp1}, @var{exp2})

You can use the built-in function @code{__builtin_choose_expr} to
evaluate code depending on the value of a constant expression.  This
built-in function returns @var{exp1} if @var{const_exp}, which is an
integer constant expression, is nonzero.  Otherwise it returns @var{exp2}.

This built-in function is analogous to the @samp{? :} operator in C,
except that the expression returned has its type unaltered by promotion
rules.  Also, the built-in function does not evaluate the expression
that is not chosen.  For example, if @var{const_exp} evaluates to true,
@var{exp2} is not evaluated even if it has side-effects.

This built-in function can return an lvalue if the chosen argument is an
lvalue.

If @var{exp1} is returned, the return type is the same as @var{exp1}'s
type.  Similarly, if @var{exp2} is returned, its return type is the same
as @var{exp2}.

Example:

@smallexample
#define foo(x)                                                    \
  __builtin_choose_expr (                                         \
    __builtin_types_compatible_p (typeof (x), double),            \
    foo_double (x),                                               \
    __builtin_choose_expr (                                       \
      __builtin_types_compatible_p (typeof (x), float),           \
      foo_float (x),                                              \
      /* @r{The void expression results in a compile-time error}  \
         @r{when assigning the result to something.}  */          \
      (void)0))
@end smallexample

@emph{Note:} This construct is only available for C@.  Furthermore, the
unused expression (@var{exp1} or @var{exp2} depending on the value of
@var{const_exp}) may still generate syntax errors.  This may change in
future revisions.

@end deftypefn

@deftypefn {Built-in Function} @var{type} __builtin_complex (@var{real}, @var{imag})

The built-in function @code{__builtin_complex} is provided for use in
implementing the ISO C11 macros @code{CMPLXF}, @code{CMPLX} and
@code{CMPLXL}.  @var{real} and @var{imag} must have the same type, a
real binary floating-point type, and the result has the corresponding
complex type with real and imaginary parts @var{real} and @var{imag}.
Unlike @samp{@var{real} + I * @var{imag}}, this works even when
infinities, NaNs and negative zeros are involved.

@end deftypefn

@deftypefn {Built-in Function} int __builtin_constant_p (@var{exp})
You can use the built-in function @code{__builtin_constant_p} to
determine if a value is known to be constant at compile time and hence
that GCC can perform constant-folding on expressions involving that
value.  The argument of the function is the value to test.  The function
returns the integer 1 if the argument is known to be a compile-time
constant and 0 if it is not known to be a compile-time constant.  A
return of 0 does not indicate that the value is @emph{not} a constant,
but merely that GCC cannot prove it is a constant with the specified
value of the @option{-O} option.

You typically use this function in an embedded application where
memory is a critical resource.  If you have some complex calculation,
you may want it to be folded if it involves constants, but need to call
a function if it does not.  For example:

@smallexample
#define Scale_Value(X)      \
  (__builtin_constant_p (X) \
  ? ((X) * SCALE + OFFSET) : Scale (X))
@end smallexample

You may use this built-in function in either a macro or an inline
function.  However, if you use it in an inlined function and pass an
argument of the function as the argument to the built-in, GCC 
never returns 1 when you call the inline function with a string constant
or compound literal (@pxref{Compound Literals}) and does not return 1
when you pass a constant numeric value to the inline function unless you
specify the @option{-O} option.

You may also use @code{__builtin_constant_p} in initializers for static
data.  For instance, you can write

@smallexample
static const int table[] = @{
   __builtin_constant_p (EXPRESSION) ? (EXPRESSION) : -1,
   /* @r{@dots{}} */
@};
@end smallexample

@noindent
This is an acceptable initializer even if @var{EXPRESSION} is not a
constant expression, including the case where
@code{__builtin_constant_p} returns 1 because @var{EXPRESSION} can be
folded to a constant but @var{EXPRESSION} contains operands that are
not otherwise permitted in a static initializer (for example,
@code{0 && foo ()}).  GCC must be more conservative about evaluating the
built-in in this case, because it has no opportunity to perform
optimization.

Previous versions of GCC did not accept this built-in in data
initializers.  The earliest version where it is completely safe is
3.0.1.
@end deftypefn

@deftypefn {Built-in Function} long __builtin_expect (long @var{exp}, long @var{c})
@opindex fprofile-arcs
You may use @code{__builtin_expect} to provide the compiler with
branch prediction information.  In general, you should prefer to
use actual profile feedback for this (@option{-fprofile-arcs}), as
programmers are notoriously bad at predicting how their programs
actually perform.  However, there are applications in which this
data is hard to collect.

The return value is the value of @var{exp}, which should be an integral
expression.  The semantics of the built-in are that it is expected that
@var{exp} == @var{c}.  For example:

@smallexample
if (__builtin_expect (x, 0))
  foo ();
@end smallexample

@noindent
indicates that we do not expect to call @code{foo}, since
we expect @code{x} to be zero.  Since you are limited to integral
expressions for @var{exp}, you should use constructions such as

@smallexample
if (__builtin_expect (ptr != NULL, 1))
  foo (*ptr);
@end smallexample

@noindent
when testing pointer or floating-point values.
@end deftypefn

@deftypefn {Built-in Function} void __builtin_trap (void)
This function causes the program to exit abnormally.  GCC implements
this function by using a target-dependent mechanism (such as
intentionally executing an illegal instruction) or by calling
@code{abort}.  The mechanism used may vary from release to release so
you should not rely on any particular implementation.
@end deftypefn

@deftypefn {Built-in Function} void __builtin_unreachable (void)
If control flow reaches the point of the @code{__builtin_unreachable},
the program is undefined.  It is useful in situations where the
compiler cannot deduce the unreachability of the code.

One such case is immediately following an @code{asm} statement that
either never terminates, or one that transfers control elsewhere
and never returns.  In this example, without the
@code{__builtin_unreachable}, GCC issues a warning that control
reaches the end of a non-void function.  It also generates code
to return after the @code{asm}.

@smallexample
int f (int c, int v)
@{
  if (c)
    @{
      return v;
    @}
  else
    @{
      asm("jmp error_handler");
      __builtin_unreachable ();
    @}
@}
@end smallexample

@noindent
Because the @code{asm} statement unconditionally transfers control out
of the function, control never reaches the end of the function
body.  The @code{__builtin_unreachable} is in fact unreachable and
communicates this fact to the compiler.

Another use for @code{__builtin_unreachable} is following a call a
function that never returns but that is not declared
@code{__attribute__((noreturn))}, as in this example:

@smallexample
void function_that_never_returns (void);

int g (int c)
@{
  if (c)
    @{
      return 1;
    @}
  else
    @{
      function_that_never_returns ();
      __builtin_unreachable ();
    @}
@}
@end smallexample

@end deftypefn

@deftypefn {Built-in Function} void *__builtin_assume_aligned (const void *@var{exp}, size_t @var{align}, ...)
This function returns its first argument, and allows the compiler
to assume that the returned pointer is at least @var{align} bytes
aligned.  This built-in can have either two or three arguments,
if it has three, the third argument should have integer type, and
if it is nonzero means misalignment offset.  For example:

@smallexample
void *x = __builtin_assume_aligned (arg, 16);
@end smallexample

@noindent
means that the compiler can assume @code{x}, set to @code{arg}, is at least
16-byte aligned, while:

@smallexample
void *x = __builtin_assume_aligned (arg, 32, 8);
@end smallexample

@noindent
means that the compiler can assume for @code{x}, set to @code{arg}, that
@code{(char *) x - 8} is 32-byte aligned.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_LINE ()
This function is the equivalent to the preprocessor @code{__LINE__}
macro and returns the line number of the invocation of the built-in.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_FUNCTION ()
This function is the equivalent to the preprocessor @code{__FUNCTION__}
macro and returns the function name the invocation of the built-in is in.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_FILE ()
This function is the equivalent to the preprocessor @code{__FILE__}
macro and returns the file name the invocation of the built-in is in.
@end deftypefn

@deftypefn {Built-in Function} void __builtin___clear_cache (char *@var{begin}, char *@var{end})
This function is used to flush the processor's instruction cache for
the region of memory between @var{begin} inclusive and @var{end}
exclusive.  Some targets require that the instruction cache be
flushed, after modifying memory containing code, in order to obtain
deterministic behavior.

If the target does not require instruction cache flushes,
@code{__builtin___clear_cache} has no effect.  Otherwise either
instructions are emitted in-line to clear the instruction cache or a
call to the @code{__clear_cache} function in libgcc is made.
@end deftypefn

@deftypefn {Built-in Function} void __builtin_prefetch (const void *@var{addr}, ...)
This function is used to minimize cache-miss latency by moving data into
a cache before it is accessed.
You can insert calls to @code{__builtin_prefetch} into code for which
you know addresses of data in memory that is likely to be accessed soon.
If the target supports them, data prefetch instructions are generated.
If the prefetch is done early enough before the access then the data will
be in the cache by the time it is accessed.

The value of @var{addr} is the address of the memory to prefetch.
There are two optional arguments, @var{rw} and @var{locality}.
The value of @var{rw} is a compile-time constant one or zero; one
means that the prefetch is preparing for a write to the memory address
and zero, the default, means that the prefetch is preparing for a read.
The value @var{locality} must be a compile-time constant integer between
zero and three.  A value of zero means that the data has no temporal
locality, so it need not be left in the cache after the access.  A value
of three means that the data has a high degree of temporal locality and
should be left in all levels of cache possible.  Values of one and two
mean, respectively, a low or moderate degree of temporal locality.  The
default is three.

@smallexample
for (i = 0; i < n; i++)
  @{
    a[i] = a[i] + b[i];
    __builtin_prefetch (&a[i+j], 1, 1);
    __builtin_prefetch (&b[i+j], 0, 1);
    /* @r{@dots{}} */
  @}
@end smallexample

Data prefetch does not generate faults if @var{addr} is invalid, but
the address expression itself must be valid.  For example, a prefetch
of @code{p->next} does not fault if @code{p->next} is not a valid
address, but evaluation faults if @code{p} is not a valid address.

If the target does not support data prefetch, the address expression
is evaluated if it includes side effects but no other code is generated
and GCC does not issue a warning.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_huge_val (void)
Returns a positive infinity, if supported by the floating-point format,
else @code{DBL_MAX}.  This function is suitable for implementing the
ISO C macro @code{HUGE_VAL}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_huge_valf (void)
Similar to @code{__builtin_huge_val}, except the return type is @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_huge_vall (void)
Similar to @code{__builtin_huge_val}, except the return
type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_fpclassify (int, int, int, int, int, ...)
This built-in implements the C99 fpclassify functionality.  The first
five int arguments should be the target library's notion of the
possible FP classes and are used for return values.  They must be
constant values and they must appear in this order: @code{FP_NAN},
@code{FP_INFINITE}, @code{FP_NORMAL}, @code{FP_SUBNORMAL} and
@code{FP_ZERO}.  The ellipsis is for exactly one floating-point value
to classify.  GCC treats the last argument as type-generic, which
means it does not do default promotion from float to double.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_inf (void)
Similar to @code{__builtin_huge_val}, except a warning is generated
if the target floating-point format does not support infinities.
@end deftypefn

@deftypefn {Built-in Function} _Decimal32 __builtin_infd32 (void)
Similar to @code{__builtin_inf}, except the return type is @code{_Decimal32}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal64 __builtin_infd64 (void)
Similar to @code{__builtin_inf}, except the return type is @code{_Decimal64}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal128 __builtin_infd128 (void)
Similar to @code{__builtin_inf}, except the return type is @code{_Decimal128}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_inff (void)
Similar to @code{__builtin_inf}, except the return type is @code{float}.
This function is suitable for implementing the ISO C99 macro @code{INFINITY}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_infl (void)
Similar to @code{__builtin_inf}, except the return
type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_isinf_sign (...)
Similar to @code{isinf}, except the return value is negative for
an argument of @code{-Inf}.  Note while the parameter list is an
ellipsis, this function only accepts exactly one floating-point
argument.  GCC treats this parameter as type-generic, which means it
does not do default promotion from float to double.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_nan (const char *str)
This is an implementation of the ISO C99 function @code{nan}.

Since ISO C99 defines this function in terms of @code{strtod}, which we
do not implement, a description of the parsing is in order.  The string
is parsed as by @code{strtol}; that is, the base is recognized by
leading @samp{0} or @samp{0x} prefixes.  The number parsed is placed
in the significand such that the least significant bit of the number
is at the least significant bit of the significand.  The number is
truncated to fit the significand field provided.  The significand is
forced to be a quiet NaN@.

This function, if given a string literal all of which would have been
consumed by @code{strtol}, is evaluated early enough that it is considered a
compile-time constant.
@end deftypefn

@deftypefn {Built-in Function} _Decimal32 __builtin_nand32 (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{_Decimal32}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal64 __builtin_nand64 (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{_Decimal64}.
@end deftypefn

@deftypefn {Built-in Function} _Decimal128 __builtin_nand128 (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{_Decimal128}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_nanf (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_nanl (const char *str)
Similar to @code{__builtin_nan}, except the return type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_nans (const char *str)
Similar to @code{__builtin_nan}, except the significand is forced
to be a signaling NaN@.  The @code{nans} function is proposed by
@uref{http://www.open-std.org/jtc1/sc22/wg14/www/docs/n965.htm,,WG14 N965}.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_nansf (const char *str)
Similar to @code{__builtin_nans}, except the return type is @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_nansl (const char *str)
Similar to @code{__builtin_nans}, except the return type is @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ffs (unsigned int x)
Returns one plus the index of the least significant 1-bit of @var{x}, or
if @var{x} is zero, returns zero.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clz (unsigned int x)
Returns the number of leading 0-bits in @var{x}, starting at the most
significant bit position.  If @var{x} is 0, the result is undefined.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ctz (unsigned int x)
Returns the number of trailing 0-bits in @var{x}, starting at the least
significant bit position.  If @var{x} is 0, the result is undefined.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clrsb (int x)
Returns the number of leading redundant sign bits in @var{x}, i.e.@: the
number of bits following the most significant bit that are identical
to it.  There are no special cases for 0 or other values. 
@end deftypefn

@deftypefn {Built-in Function} int __builtin_popcount (unsigned int x)
Returns the number of 1-bits in @var{x}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_parity (unsigned int x)
Returns the parity of @var{x}, i.e.@: the number of 1-bits in @var{x}
modulo 2.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ffsl (unsigned long)
Similar to @code{__builtin_ffs}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clzl (unsigned long)
Similar to @code{__builtin_clz}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ctzl (unsigned long)
Similar to @code{__builtin_ctz}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clrsbl (long)
Similar to @code{__builtin_clrsb}, except the argument type is
@code{long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_popcountl (unsigned long)
Similar to @code{__builtin_popcount}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_parityl (unsigned long)
Similar to @code{__builtin_parity}, except the argument type is
@code{unsigned long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ffsll (unsigned long long)
Similar to @code{__builtin_ffs}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clzll (unsigned long long)
Similar to @code{__builtin_clz}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_ctzll (unsigned long long)
Similar to @code{__builtin_ctz}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_clrsbll (long long)
Similar to @code{__builtin_clrsb}, except the argument type is
@code{long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_popcountll (unsigned long long)
Similar to @code{__builtin_popcount}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} int __builtin_parityll (unsigned long long)
Similar to @code{__builtin_parity}, except the argument type is
@code{unsigned long long}.
@end deftypefn

@deftypefn {Built-in Function} double __builtin_powi (double, int)
Returns the first argument raised to the power of the second.  Unlike the
@code{pow} function no guarantees about precision and rounding are made.
@end deftypefn

@deftypefn {Built-in Function} float __builtin_powif (float, int)
Similar to @code{__builtin_powi}, except the argument and return types
are @code{float}.
@end deftypefn

@deftypefn {Built-in Function} {long double} __builtin_powil (long double, int)
Similar to @code{__builtin_powi}, except the argument and return types
are @code{long double}.
@end deftypefn

@deftypefn {Built-in Function} uint16_t __builtin_bswap16 (uint16_t x)
Returns @var{x} with the order of the bytes reversed; for example,
@code{0xaabb} becomes @code{0xbbaa}.  Byte here always means
exactly 8 bits.
@end deftypefn

@deftypefn {Built-in Function} uint32_t __builtin_bswap32 (uint32_t x)
Similar to @code{__builtin_bswap16}, except the argument and return types
are 32 bit.
@end deftypefn

@deftypefn {Built-in Function} uint64_t __builtin_bswap64 (uint64_t x)
Similar to @code{__builtin_bswap32}, except the argument and return types
are 64 bit.
@end deftypefn

@node Cilk Plus Builtins
@section Cilk Plus C/C++ language extension Built-in Functions.

GCC provides support for the following built-in reduction funtions if Cilk Plus
is enabled. Cilk Plus can be enabled using the @option{-fcilkplus} flag.

@itemize @bullet
@item __sec_implicit_index
@item __sec_reduce
@item __sec_reduce_add
@item __sec_reduce_all_nonzero
@item __sec_reduce_all_zero
@item __sec_reduce_any_nonzero
@item __sec_reduce_any_zero
@item __sec_reduce_max
@item __sec_reduce_min
@item __sec_reduce_max_ind
@item __sec_reduce_min_ind
@item __sec_reduce_mul
@item __sec_reduce_mutating
@end itemize

Further details and examples about these built-in functions are described 
in the Cilk Plus language manual which can be found at 
@uref{http://www.cilkplus.org}.

@node Target Builtins
@section Built-in Functions Specific to Particular Target Machines

On some target machines, GCC supports many built-in functions specific
to those machines.  Generally these generate calls to specific machine
instructions, but allow the compiler to schedule those calls.

@menu
* Alpha Built-in Functions::
* ARM iWMMXt Built-in Functions::
* ARM NEON Intrinsics::
* AVR Built-in Functions::
* Blackfin Built-in Functions::
* FR-V Built-in Functions::
* X86 Built-in Functions::
* X86 transactional memory intrinsics::
* MIPS DSP Built-in Functions::
* MIPS Paired-Single Support::
* MIPS Loongson Built-in Functions::
* Other MIPS Built-in Functions::
* picoChip Built-in Functions::
* PowerPC Built-in Functions::
* PowerPC AltiVec/VSX Built-in Functions::
* RX Built-in Functions::
* SH Built-in Functions::
* SPARC VIS Built-in Functions::
* SPU Built-in Functions::
* TI C6X Built-in Functions::
* TILE-Gx Built-in Functions::
* TILEPro Built-in Functions::
@end menu

@node Alpha Built-in Functions
@subsection Alpha Built-in Functions

These built-in functions are available for the Alpha family of
processors, depending on the command-line switches used.

The following built-in functions are always available.  They
all generate the machine instruction that is part of the name.

@smallexample
long __builtin_alpha_implver (void)
long __builtin_alpha_rpcc (void)
long __builtin_alpha_amask (long)
long __builtin_alpha_cmpbge (long, long)
long __builtin_alpha_extbl (long, long)
long __builtin_alpha_extwl (long, long)
long __builtin_alpha_extll (long, long)
long __builtin_alpha_extql (long, long)
long __builtin_alpha_extwh (long, long)
long __builtin_alpha_extlh (long, long)
long __builtin_alpha_extqh (long, long)
long __builtin_alpha_insbl (long, long)
long __builtin_alpha_inswl (long, long)
long __builtin_alpha_insll (long, long)
long __builtin_alpha_insql (long, long)
long __builtin_alpha_inswh (long, long)
long __builtin_alpha_inslh (long, long)
long __builtin_alpha_insqh (long, long)
long __builtin_alpha_mskbl (long, long)
long __builtin_alpha_mskwl (long, long)
long __builtin_alpha_mskll (long, long)
long __builtin_alpha_mskql (long, long)
long __builtin_alpha_mskwh (long, long)
long __builtin_alpha_msklh (long, long)
long __builtin_alpha_mskqh (long, long)
long __builtin_alpha_umulh (long, long)
long __builtin_alpha_zap (long, long)
long __builtin_alpha_zapnot (long, long)
@end smallexample

The following built-in functions are always with @option{-mmax}
or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{pca56} or
later.  They all generate the machine instruction that is part
of the name.

@smallexample
long __builtin_alpha_pklb (long)
long __builtin_alpha_pkwb (long)
long __builtin_alpha_unpkbl (long)
long __builtin_alpha_unpkbw (long)
long __builtin_alpha_minub8 (long, long)
long __builtin_alpha_minsb8 (long, long)
long __builtin_alpha_minuw4 (long, long)
long __builtin_alpha_minsw4 (long, long)
long __builtin_alpha_maxub8 (long, long)
long __builtin_alpha_maxsb8 (long, long)
long __builtin_alpha_maxuw4 (long, long)
long __builtin_alpha_maxsw4 (long, long)
long __builtin_alpha_perr (long, long)
@end smallexample

The following built-in functions are always with @option{-mcix}
or @option{-mcpu=@var{cpu}} where @var{cpu} is @code{ev67} or
later.  They all generate the machine instruction that is part
of the name.

@smallexample
long __builtin_alpha_cttz (long)
long __builtin_alpha_ctlz (long)
long __builtin_alpha_ctpop (long)
@end smallexample

The following built-in functions are available on systems that use the OSF/1
PALcode.  Normally they invoke the @code{rduniq} and @code{wruniq}
PAL calls, but when invoked with @option{-mtls-kernel}, they invoke
@code{rdval} and @code{wrval}.

@smallexample
void *__builtin_thread_pointer (void)
void __builtin_set_thread_pointer (void *)
@end smallexample

@node ARM iWMMXt Built-in Functions
@subsection ARM iWMMXt Built-in Functions

These built-in functions are available for the ARM family of
processors when the @option{-mcpu=iwmmxt} switch is used:

@smallexample
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef char v8qi __attribute__ ((vector_size (8)));

int __builtin_arm_getwcgr0 (void)
void __builtin_arm_setwcgr0 (int)
int __builtin_arm_getwcgr1 (void)
void __builtin_arm_setwcgr1 (int)
int __builtin_arm_getwcgr2 (void)
void __builtin_arm_setwcgr2 (int)
int __builtin_arm_getwcgr3 (void)
void __builtin_arm_setwcgr3 (int)
int __builtin_arm_textrmsb (v8qi, int)
int __builtin_arm_textrmsh (v4hi, int)
int __builtin_arm_textrmsw (v2si, int)
int __builtin_arm_textrmub (v8qi, int)
int __builtin_arm_textrmuh (v4hi, int)
int __builtin_arm_textrmuw (v2si, int)
v8qi __builtin_arm_tinsrb (v8qi, int, int)
v4hi __builtin_arm_tinsrh (v4hi, int, int)
v2si __builtin_arm_tinsrw (v2si, int, int)
long long __builtin_arm_tmia (long long, int, int)
long long __builtin_arm_tmiabb (long long, int, int)
long long __builtin_arm_tmiabt (long long, int, int)
long long __builtin_arm_tmiaph (long long, int, int)
long long __builtin_arm_tmiatb (long long, int, int)
long long __builtin_arm_tmiatt (long long, int, int)
int __builtin_arm_tmovmskb (v8qi)
int __builtin_arm_tmovmskh (v4hi)
int __builtin_arm_tmovmskw (v2si)
long long __builtin_arm_waccb (v8qi)
long long __builtin_arm_wacch (v4hi)
long long __builtin_arm_waccw (v2si)
v8qi __builtin_arm_waddb (v8qi, v8qi)
v8qi __builtin_arm_waddbss (v8qi, v8qi)
v8qi __builtin_arm_waddbus (v8qi, v8qi)
v4hi __builtin_arm_waddh (v4hi, v4hi)
v4hi __builtin_arm_waddhss (v4hi, v4hi)
v4hi __builtin_arm_waddhus (v4hi, v4hi)
v2si __builtin_arm_waddw (v2si, v2si)
v2si __builtin_arm_waddwss (v2si, v2si)
v2si __builtin_arm_waddwus (v2si, v2si)
v8qi __builtin_arm_walign (v8qi, v8qi, int)
long long __builtin_arm_wand(long long, long long)
long long __builtin_arm_wandn (long long, long long)
v8qi __builtin_arm_wavg2b (v8qi, v8qi)
v8qi __builtin_arm_wavg2br (v8qi, v8qi)
v4hi __builtin_arm_wavg2h (v4hi, v4hi)
v4hi __builtin_arm_wavg2hr (v4hi, v4hi)
v8qi __builtin_arm_wcmpeqb (v8qi, v8qi)
v4hi __builtin_arm_wcmpeqh (v4hi, v4hi)
v2si __builtin_arm_wcmpeqw (v2si, v2si)
v8qi __builtin_arm_wcmpgtsb (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtsh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtsw (v2si, v2si)
v8qi __builtin_arm_wcmpgtub (v8qi, v8qi)
v4hi __builtin_arm_wcmpgtuh (v4hi, v4hi)
v2si __builtin_arm_wcmpgtuw (v2si, v2si)
long long __builtin_arm_wmacs (long long, v4hi, v4hi)
long long __builtin_arm_wmacsz (v4hi, v4hi)
long long __builtin_arm_wmacu (long long, v4hi, v4hi)
long long __builtin_arm_wmacuz (v4hi, v4hi)
v4hi __builtin_arm_wmadds (v4hi, v4hi)
v4hi __builtin_arm_wmaddu (v4hi, v4hi)
v8qi __builtin_arm_wmaxsb (v8qi, v8qi)
v4hi __builtin_arm_wmaxsh (v4hi, v4hi)
v2si __builtin_arm_wmaxsw (v2si, v2si)
v8qi __builtin_arm_wmaxub (v8qi, v8qi)
v4hi __builtin_arm_wmaxuh (v4hi, v4hi)
v2si __builtin_arm_wmaxuw (v2si, v2si)
v8qi __builtin_arm_wminsb (v8qi, v8qi)
v4hi __builtin_arm_wminsh (v4hi, v4hi)
v2si __builtin_arm_wminsw (v2si, v2si)
v8qi __builtin_arm_wminub (v8qi, v8qi)
v4hi __builtin_arm_wminuh (v4hi, v4hi)
v2si __builtin_arm_wminuw (v2si, v2si)
v4hi __builtin_arm_wmulsm (v4hi, v4hi)
v4hi __builtin_arm_wmulul (v4hi, v4hi)
v4hi __builtin_arm_wmulum (v4hi, v4hi)
long long __builtin_arm_wor (long long, long long)
v2si __builtin_arm_wpackdss (long long, long long)
v2si __builtin_arm_wpackdus (long long, long long)
v8qi __builtin_arm_wpackhss (v4hi, v4hi)
v8qi __builtin_arm_wpackhus (v4hi, v4hi)
v4hi __builtin_arm_wpackwss (v2si, v2si)
v4hi __builtin_arm_wpackwus (v2si, v2si)
long long __builtin_arm_wrord (long long, long long)
long long __builtin_arm_wrordi (long long, int)
v4hi __builtin_arm_wrorh (v4hi, long long)
v4hi __builtin_arm_wrorhi (v4hi, int)
v2si __builtin_arm_wrorw (v2si, long long)
v2si __builtin_arm_wrorwi (v2si, int)
v2si __builtin_arm_wsadb (v2si, v8qi, v8qi)
v2si __builtin_arm_wsadbz (v8qi, v8qi)
v2si __builtin_arm_wsadh (v2si, v4hi, v4hi)
v2si __builtin_arm_wsadhz (v4hi, v4hi)
v4hi __builtin_arm_wshufh (v4hi, int)
long long __builtin_arm_wslld (long long, long long)
long long __builtin_arm_wslldi (long long, int)
v4hi __builtin_arm_wsllh (v4hi, long long)
v4hi __builtin_arm_wsllhi (v4hi, int)
v2si __builtin_arm_wsllw (v2si, long long)
v2si __builtin_arm_wsllwi (v2si, int)
long long __builtin_arm_wsrad (long long, long long)
long long __builtin_arm_wsradi (long long, int)
v4hi __builtin_arm_wsrah (v4hi, long long)
v4hi __builtin_arm_wsrahi (v4hi, int)
v2si __builtin_arm_wsraw (v2si, long long)
v2si __builtin_arm_wsrawi (v2si, int)
long long __builtin_arm_wsrld (long long, long long)
long long __builtin_arm_wsrldi (long long, int)
v4hi __builtin_arm_wsrlh (v4hi, long long)
v4hi __builtin_arm_wsrlhi (v4hi, int)
v2si __builtin_arm_wsrlw (v2si, long long)
v2si __builtin_arm_wsrlwi (v2si, int)
v8qi __builtin_arm_wsubb (v8qi, v8qi)
v8qi __builtin_arm_wsubbss (v8qi, v8qi)
v8qi __builtin_arm_wsubbus (v8qi, v8qi)
v4hi __builtin_arm_wsubh (v4hi, v4hi)
v4hi __builtin_arm_wsubhss (v4hi, v4hi)
v4hi __builtin_arm_wsubhus (v4hi, v4hi)
v2si __builtin_arm_wsubw (v2si, v2si)
v2si __builtin_arm_wsubwss (v2si, v2si)
v2si __builtin_arm_wsubwus (v2si, v2si)
v4hi __builtin_arm_wunpckehsb (v8qi)
v2si __builtin_arm_wunpckehsh (v4hi)
long long __builtin_arm_wunpckehsw (v2si)
v4hi __builtin_arm_wunpckehub (v8qi)
v2si __builtin_arm_wunpckehuh (v4hi)
long long __builtin_arm_wunpckehuw (v2si)
v4hi __builtin_arm_wunpckelsb (v8qi)
v2si __builtin_arm_wunpckelsh (v4hi)
long long __builtin_arm_wunpckelsw (v2si)
v4hi __builtin_arm_wunpckelub (v8qi)
v2si __builtin_arm_wunpckeluh (v4hi)
long long __builtin_arm_wunpckeluw (v2si)
v8qi __builtin_arm_wunpckihb (v8qi, v8qi)
v4hi __builtin_arm_wunpckihh (v4hi, v4hi)
v2si __builtin_arm_wunpckihw (v2si, v2si)
v8qi __builtin_arm_wunpckilb (v8qi, v8qi)
v4hi __builtin_arm_wunpckilh (v4hi, v4hi)
v2si __builtin_arm_wunpckilw (v2si, v2si)
long long __builtin_arm_wxor (long long, long long)
long long __builtin_arm_wzero ()
@end smallexample

@node ARM NEON Intrinsics
@subsection ARM NEON Intrinsics

These built-in intrinsics for the ARM Advanced SIMD extension are available
when the @option{-mfpu=neon} switch is used:

@include arm-neon-intrinsics.texi

@node AVR Built-in Functions
@subsection AVR Built-in Functions

For each built-in function for AVR, there is an equally named,
uppercase built-in macro defined. That way users can easily query if
or if not a specific built-in is implemented or not. For example, if
@code{__builtin_avr_nop} is available the macro
@code{__BUILTIN_AVR_NOP} is defined to @code{1} and undefined otherwise.

The following built-in functions map to the respective machine
instruction, i.e.@: @code{nop}, @code{sei}, @code{cli}, @code{sleep},
@code{wdr}, @code{swap}, @code{fmul}, @code{fmuls}
resp. @code{fmulsu}. The three @code{fmul*} built-ins are implemented
as library call if no hardware multiplier is available.

@smallexample
void __builtin_avr_nop (void)
void __builtin_avr_sei (void)
void __builtin_avr_cli (void)
void __builtin_avr_sleep (void)
void __builtin_avr_wdr (void)
unsigned char __builtin_avr_swap (unsigned char)
unsigned int __builtin_avr_fmul (unsigned char, unsigned char)
int __builtin_avr_fmuls (char, char)
int __builtin_avr_fmulsu (char, unsigned char)
@end smallexample

In order to delay execution for a specific number of cycles, GCC
implements
@smallexample
void __builtin_avr_delay_cycles (unsigned long ticks)
@end smallexample

@noindent
@code{ticks} is the number of ticks to delay execution. Note that this
built-in does not take into account the effect of interrupts that
might increase delay time. @code{ticks} must be a compile-time
integer constant; delays with a variable number of cycles are not supported.

@smallexample
char __builtin_avr_flash_segment (const __memx void*)
@end smallexample

@noindent
This built-in takes a byte address to the 24-bit
@ref{AVR Named Address Spaces,address space} @code{__memx} and returns
the number of the flash segment (the 64 KiB chunk) where the address
points to.  Counting starts at @code{0}.
If the address does not point to flash memory, return @code{-1}.

@smallexample
unsigned char __builtin_avr_insert_bits (unsigned long map, unsigned char bits, unsigned char val)
@end smallexample

@noindent
Insert bits from @var{bits} into @var{val} and return the resulting
value. The nibbles of @var{map} determine how the insertion is
performed: Let @var{X} be the @var{n}-th nibble of @var{map}
@enumerate
@item If @var{X} is @code{0xf},
then the @var{n}-th bit of @var{val} is returned unaltered.

@item If X is in the range 0@dots{}7,
then the @var{n}-th result bit is set to the @var{X}-th bit of @var{bits}

@item If X is in the range 8@dots{}@code{0xe},
then the @var{n}-th result bit is undefined.
@end enumerate

@noindent
One typical use case for this built-in is adjusting input and
output values to non-contiguous port layouts. Some examples:

@smallexample
// same as val, bits is unused
__builtin_avr_insert_bits (0xffffffff, bits, val)
@end smallexample

@smallexample
// same as bits, val is unused
__builtin_avr_insert_bits (0x76543210, bits, val)
@end smallexample

@smallexample
// same as rotating bits by 4
__builtin_avr_insert_bits (0x32107654, bits, 0)
@end smallexample

@smallexample
// high nibble of result is the high nibble of val
// low nibble of result is the low nibble of bits
__builtin_avr_insert_bits (0xffff3210, bits, val)
@end smallexample

@smallexample
// reverse the bit order of bits
__builtin_avr_insert_bits (0x01234567, bits, 0)
@end smallexample

@node Blackfin Built-in Functions
@subsection Blackfin Built-in Functions

Currently, there are two Blackfin-specific built-in functions.  These are
used for generating @code{CSYNC} and @code{SSYNC} machine insns without
using inline assembly; by using these built-in functions the compiler can
automatically add workarounds for hardware errata involving these
instructions.  These functions are named as follows:

@smallexample
void __builtin_bfin_csync (void)
void __builtin_bfin_ssync (void)
@end smallexample

@node FR-V Built-in Functions
@subsection FR-V Built-in Functions

GCC provides many FR-V-specific built-in functions.  In general,
these functions are intended to be compatible with those described
by @cite{FR-V Family, Softune C/C++ Compiler Manual (V6), Fujitsu
Semiconductor}.  The two exceptions are @code{__MDUNPACKH} and
@code{__MBTOHE}, the GCC forms of which pass 128-bit values by
pointer rather than by value.

Most of the functions are named after specific FR-V instructions.
Such functions are said to be ``directly mapped'' and are summarized
here in tabular form.

@menu
* Argument Types::
* Directly-mapped Integer Functions::
* Directly-mapped Media Functions::
* Raw read/write Functions::
* Other Built-in Functions::
@end menu

@node Argument Types
@subsubsection Argument Types

The arguments to the built-in functions can be divided into three groups:
register numbers, compile-time constants and run-time values.  In order
to make this classification clear at a glance, the arguments and return
values are given the following pseudo types:

@multitable @columnfractions .20 .30 .15 .35
@item Pseudo type @tab Real C type @tab Constant? @tab Description
@item @code{uh} @tab @code{unsigned short} @tab No @tab an unsigned halfword
@item @code{uw1} @tab @code{unsigned int} @tab No @tab an unsigned word
@item @code{sw1} @tab @code{int} @tab No @tab a signed word
@item @code{uw2} @tab @code{unsigned long long} @tab No
@tab an unsigned doubleword
@item @code{sw2} @tab @code{long long} @tab No @tab a signed doubleword
@item @code{const} @tab @code{int} @tab Yes @tab an integer constant
@item @code{acc} @tab @code{int} @tab Yes @tab an ACC register number
@item @code{iacc} @tab @code{int} @tab Yes @tab an IACC register number
@end multitable

These pseudo types are not defined by GCC, they are simply a notational
convenience used in this manual.

Arguments of type @code{uh}, @code{uw1}, @code{sw1}, @code{uw2}
and @code{sw2} are evaluated at run time.  They correspond to
register operands in the underlying FR-V instructions.

@code{const} arguments represent immediate operands in the underlying
FR-V instructions.  They must be compile-time constants.

@code{acc} arguments are evaluated at compile time and specify the number
of an accumulator register.  For example, an @code{acc} argument of 2
selects the ACC2 register.

@code{iacc} arguments are similar to @code{acc} arguments but specify the
number of an IACC register.  See @pxref{Other Built-in Functions}
for more details.

@node Directly-mapped Integer Functions
@subsubsection Directly-mapped Integer Functions

The functions listed below map directly to FR-V I-type instructions.

@multitable @columnfractions .45 .32 .23
@item Function prototype @tab Example usage @tab Assembly output
@item @code{sw1 __ADDSS (sw1, sw1)}
@tab @code{@var{c} = __ADDSS (@var{a}, @var{b})}
@tab @code{ADDSS @var{a},@var{b},@var{c}}
@item @code{sw1 __SCAN (sw1, sw1)}
@tab @code{@var{c} = __SCAN (@var{a}, @var{b})}
@tab @code{SCAN @var{a},@var{b},@var{c}}
@item @code{sw1 __SCUTSS (sw1)}
@tab @code{@var{b} = __SCUTSS (@var{a})}
@tab @code{SCUTSS @var{a},@var{b}}
@item @code{sw1 __SLASS (sw1, sw1)}
@tab @code{@var{c} = __SLASS (@var{a}, @var{b})}
@tab @code{SLASS @var{a},@var{b},@var{c}}
@item @code{void __SMASS (sw1, sw1)}
@tab @code{__SMASS (@var{a}, @var{b})}
@tab @code{SMASS @var{a},@var{b}}
@item @code{void __SMSSS (sw1, sw1)}
@tab @code{__SMSSS (@var{a}, @var{b})}
@tab @code{SMSSS @var{a},@var{b}}
@item @code{void __SMU (sw1, sw1)}
@tab @code{__SMU (@var{a}, @var{b})}
@tab @code{SMU @var{a},@var{b}}
@item @code{sw2 __SMUL (sw1, sw1)}
@tab @code{@var{c} = __SMUL (@var{a}, @var{b})}
@tab @code{SMUL @var{a},@var{b},@var{c}}
@item @code{sw1 __SUBSS (sw1, sw1)}
@tab @code{@var{c} = __SUBSS (@var{a}, @var{b})}
@tab @code{SUBSS @var{a},@var{b},@var{c}}
@item @code{uw2 __UMUL (uw1, uw1)}
@tab @code{@var{c} = __UMUL (@var{a}, @var{b})}
@tab @code{UMUL @var{a},@var{b},@var{c}}
@end multitable

@node Directly-mapped Media Functions
@subsubsection Directly-mapped Media Functions

The functions listed below map directly to FR-V M-type instructions.

@multitable @columnfractions .45 .32 .23
@item Function prototype @tab Example usage @tab Assembly output
@item @code{uw1 __MABSHS (sw1)}
@tab @code{@var{b} = __MABSHS (@var{a})}
@tab @code{MABSHS @var{a},@var{b}}
@item @code{void __MADDACCS (acc, acc)}
@tab @code{__MADDACCS (@var{b}, @var{a})}
@tab @code{MADDACCS @var{a},@var{b}}
@item @code{sw1 __MADDHSS (sw1, sw1)}
@tab @code{@var{c} = __MADDHSS (@var{a}, @var{b})}
@tab @code{MADDHSS @var{a},@var{b},@var{c}}
@item @code{uw1 __MADDHUS (uw1, uw1)}
@tab @code{@var{c} = __MADDHUS (@var{a}, @var{b})}
@tab @code{MADDHUS @var{a},@var{b},@var{c}}
@item @code{uw1 __MAND (uw1, uw1)}
@tab @code{@var{c} = __MAND (@var{a}, @var{b})}
@tab @code{MAND @var{a},@var{b},@var{c}}
@item @code{void __MASACCS (acc, acc)}
@tab @code{__MASACCS (@var{b}, @var{a})}
@tab @code{MASACCS @var{a},@var{b}}
@item @code{uw1 __MAVEH (uw1, uw1)}
@tab @code{@var{c} = __MAVEH (@var{a}, @var{b})}
@tab @code{MAVEH @var{a},@var{b},@var{c}}
@item @code{uw2 __MBTOH (uw1)}
@tab @code{@var{b} = __MBTOH (@var{a})}
@tab @code{MBTOH @var{a},@var{b}}
@item @code{void __MBTOHE (uw1 *, uw1)}
@tab @code{__MBTOHE (&@var{b}, @var{a})}
@tab @code{MBTOHE @var{a},@var{b}}
@item @code{void __MCLRACC (acc)}
@tab @code{__MCLRACC (@var{a})}
@tab @code{MCLRACC @var{a}}
@item @code{void __MCLRACCA (void)}
@tab @code{__MCLRACCA ()}
@tab @code{MCLRACCA}
@item @code{uw1 __Mcop1 (uw1, uw1)}
@tab @code{@var{c} = __Mcop1 (@var{a}, @var{b})}
@tab @code{Mcop1 @var{a},@var{b},@var{c}}
@item @code{uw1 __Mcop2 (uw1, uw1)}
@tab @code{@var{c} = __Mcop2 (@var{a}, @var{b})}
@tab @code{Mcop2 @var{a},@var{b},@var{c}}
@item @code{uw1 __MCPLHI (uw2, const)}
@tab @code{@var{c} = __MCPLHI (@var{a}, @var{b})}
@tab @code{MCPLHI @var{a},#@var{b},@var{c}}
@item @code{uw1 __MCPLI (uw2, const)}
@tab @code{@var{c} = __MCPLI (@var{a}, @var{b})}
@tab @code{MCPLI @var{a},#@var{b},@var{c}}
@item @code{void __MCPXIS (acc, sw1, sw1)}
@tab @code{__MCPXIS (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXIS @var{a},@var{b},@var{c}}
@item @code{void __MCPXIU (acc, uw1, uw1)}
@tab @code{__MCPXIU (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXIU @var{a},@var{b},@var{c}}
@item @code{void __MCPXRS (acc, sw1, sw1)}
@tab @code{__MCPXRS (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXRS @var{a},@var{b},@var{c}}
@item @code{void __MCPXRU (acc, uw1, uw1)}
@tab @code{__MCPXRU (@var{c}, @var{a}, @var{b})}
@tab @code{MCPXRU @var{a},@var{b},@var{c}}
@item @code{uw1 __MCUT (acc, uw1)}
@tab @code{@var{c} = __MCUT (@var{a}, @var{b})}
@tab @code{MCUT @var{a},@var{b},@var{c}}
@item @code{uw1 __MCUTSS (acc, sw1)}
@tab @code{@var{c} = __MCUTSS (@var{a}, @var{b})}
@tab @code{MCUTSS @var{a},@var{b},@var{c}}
@item @code{void __MDADDACCS (acc, acc)}
@tab @code{__MDADDACCS (@var{b}, @var{a})}
@tab @code{MDADDACCS @var{a},@var{b}}
@item @code{void __MDASACCS (acc, acc)}
@tab @code{__MDASACCS (@var{b}, @var{a})}
@tab @code{MDASACCS @var{a},@var{b}}
@item @code{uw2 __MDCUTSSI (acc, const)}
@tab @code{@var{c} = __MDCUTSSI (@var{a}, @var{b})}
@tab @code{MDCUTSSI @var{a},#@var{b},@var{c}}
@item @code{uw2 __MDPACKH (uw2, uw2)}
@tab @code{@var{c} = __MDPACKH (@var{a}, @var{b})}
@tab @code{MDPACKH @var{a},@var{b},@var{c}}
@item @code{uw2 __MDROTLI (uw2, const)}
@tab @code{@var{c} = __MDROTLI (@var{a}, @var{b})}
@tab @code{MDROTLI @var{a},#@var{b},@var{c}}
@item @code{void __MDSUBACCS (acc, acc)}
@tab @code{__MDSUBACCS (@var{b}, @var{a})}
@tab @code{MDSUBACCS @var{a},@var{b}}
@item @code{void __MDUNPACKH (uw1 *, uw2)}
@tab @code{__MDUNPACKH (&@var{b}, @var{a})}
@tab @code{MDUNPACKH @var{a},@var{b}}
@item @code{uw2 __MEXPDHD (uw1, const)}
@tab @code{@var{c} = __MEXPDHD (@var{a}, @var{b})}
@tab @code{MEXPDHD @var{a},#@var{b},@var{c}}
@item @code{uw1 __MEXPDHW (uw1, const)}
@tab @code{@var{c} = __MEXPDHW (@var{a}, @var{b})}
@tab @code{MEXPDHW @var{a},#@var{b},@var{c}}
@item @code{uw1 __MHDSETH (uw1, const)}
@tab @code{@var{c} = __MHDSETH (@var{a}, @var{b})}
@tab @code{MHDSETH @var{a},#@var{b},@var{c}}
@item @code{sw1 __MHDSETS (const)}
@tab @code{@var{b} = __MHDSETS (@var{a})}
@tab @code{MHDSETS #@var{a},@var{b}}
@item @code{uw1 __MHSETHIH (uw1, const)}
@tab @code{@var{b} = __MHSETHIH (@var{b}, @var{a})}
@tab @code{MHSETHIH #@var{a},@var{b}}
@item @code{sw1 __MHSETHIS (sw1, const)}
@tab @code{@var{b} = __MHSETHIS (@var{b}, @var{a})}
@tab @code{MHSETHIS #@var{a},@var{b}}
@item @code{uw1 __MHSETLOH (uw1, const)}
@tab @code{@var{b} = __MHSETLOH (@var{b}, @var{a})}
@tab @code{MHSETLOH #@var{a},@var{b}}
@item @code{sw1 __MHSETLOS (sw1, const)}
@tab @code{@var{b} = __MHSETLOS (@var{b}, @var{a})}
@tab @code{MHSETLOS #@var{a},@var{b}}
@item @code{uw1 __MHTOB (uw2)}
@tab @code{@var{b} = __MHTOB (@var{a})}
@tab @code{MHTOB @var{a},@var{b}}
@item @code{void __MMACHS (acc, sw1, sw1)}
@tab @code{__MMACHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMACHS @var{a},@var{b},@var{c}}
@item @code{void __MMACHU (acc, uw1, uw1)}
@tab @code{__MMACHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMACHU @var{a},@var{b},@var{c}}
@item @code{void __MMRDHS (acc, sw1, sw1)}
@tab @code{__MMRDHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMRDHS @var{a},@var{b},@var{c}}
@item @code{void __MMRDHU (acc, uw1, uw1)}
@tab @code{__MMRDHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMRDHU @var{a},@var{b},@var{c}}
@item @code{void __MMULHS (acc, sw1, sw1)}
@tab @code{__MMULHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMULHS @var{a},@var{b},@var{c}}
@item @code{void __MMULHU (acc, uw1, uw1)}
@tab @code{__MMULHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMULHU @var{a},@var{b},@var{c}}
@item @code{void __MMULXHS (acc, sw1, sw1)}
@tab @code{__MMULXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MMULXHS @var{a},@var{b},@var{c}}
@item @code{void __MMULXHU (acc, uw1, uw1)}
@tab @code{__MMULXHU (@var{c}, @var{a}, @var{b})}
@tab @code{MMULXHU @var{a},@var{b},@var{c}}
@item @code{uw1 __MNOT (uw1)}
@tab @code{@var{b} = __MNOT (@var{a})}
@tab @code{MNOT @var{a},@var{b}}
@item @code{uw1 __MOR (uw1, uw1)}
@tab @code{@var{c} = __MOR (@var{a}, @var{b})}
@tab @code{MOR @var{a},@var{b},@var{c}}
@item @code{uw1 __MPACKH (uh, uh)}
@tab @code{@var{c} = __MPACKH (@var{a}, @var{b})}
@tab @code{MPACKH @var{a},@var{b},@var{c}}
@item @code{sw2 __MQADDHSS (sw2, sw2)}
@tab @code{@var{c} = __MQADDHSS (@var{a}, @var{b})}
@tab @code{MQADDHSS @var{a},@var{b},@var{c}}
@item @code{uw2 __MQADDHUS (uw2, uw2)}
@tab @code{@var{c} = __MQADDHUS (@var{a}, @var{b})}
@tab @code{MQADDHUS @var{a},@var{b},@var{c}}
@item @code{void __MQCPXIS (acc, sw2, sw2)}
@tab @code{__MQCPXIS (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXIS @var{a},@var{b},@var{c}}
@item @code{void __MQCPXIU (acc, uw2, uw2)}
@tab @code{__MQCPXIU (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXIU @var{a},@var{b},@var{c}}
@item @code{void __MQCPXRS (acc, sw2, sw2)}
@tab @code{__MQCPXRS (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXRS @var{a},@var{b},@var{c}}
@item @code{void __MQCPXRU (acc, uw2, uw2)}
@tab @code{__MQCPXRU (@var{c}, @var{a}, @var{b})}
@tab @code{MQCPXRU @var{a},@var{b},@var{c}}
@item @code{sw2 __MQLCLRHS (sw2, sw2)}
@tab @code{@var{c} = __MQLCLRHS (@var{a}, @var{b})}
@tab @code{MQLCLRHS @var{a},@var{b},@var{c}}
@item @code{sw2 __MQLMTHS (sw2, sw2)}
@tab @code{@var{c} = __MQLMTHS (@var{a}, @var{b})}
@tab @code{MQLMTHS @var{a},@var{b},@var{c}}
@item @code{void __MQMACHS (acc, sw2, sw2)}
@tab @code{__MQMACHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMACHS @var{a},@var{b},@var{c}}
@item @code{void __MQMACHU (acc, uw2, uw2)}
@tab @code{__MQMACHU (@var{c}, @var{a}, @var{b})}
@tab @code{MQMACHU @var{a},@var{b},@var{c}}
@item @code{void __MQMACXHS (acc, sw2, sw2)}
@tab @code{__MQMACXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMACXHS @var{a},@var{b},@var{c}}
@item @code{void __MQMULHS (acc, sw2, sw2)}
@tab @code{__MQMULHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULHS @var{a},@var{b},@var{c}}
@item @code{void __MQMULHU (acc, uw2, uw2)}
@tab @code{__MQMULHU (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULHU @var{a},@var{b},@var{c}}
@item @code{void __MQMULXHS (acc, sw2, sw2)}
@tab @code{__MQMULXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULXHS @var{a},@var{b},@var{c}}
@item @code{void __MQMULXHU (acc, uw2, uw2)}
@tab @code{__MQMULXHU (@var{c}, @var{a}, @var{b})}
@tab @code{MQMULXHU @var{a},@var{b},@var{c}}
@item @code{sw2 __MQSATHS (sw2, sw2)}
@tab @code{@var{c} = __MQSATHS (@var{a}, @var{b})}
@tab @code{MQSATHS @var{a},@var{b},@var{c}}
@item @code{uw2 __MQSLLHI (uw2, int)}
@tab @code{@var{c} = __MQSLLHI (@var{a}, @var{b})}
@tab @code{MQSLLHI @var{a},@var{b},@var{c}}
@item @code{sw2 __MQSRAHI (sw2, int)}
@tab @code{@var{c} = __MQSRAHI (@var{a}, @var{b})}
@tab @code{MQSRAHI @var{a},@var{b},@var{c}}
@item @code{sw2 __MQSUBHSS (sw2, sw2)}
@tab @code{@var{c} = __MQSUBHSS (@var{a}, @var{b})}
@tab @code{MQSUBHSS @var{a},@var{b},@var{c}}
@item @code{uw2 __MQSUBHUS (uw2, uw2)}
@tab @code{@var{c} = __MQSUBHUS (@var{a}, @var{b})}
@tab @code{MQSUBHUS @var{a},@var{b},@var{c}}
@item @code{void __MQXMACHS (acc, sw2, sw2)}
@tab @code{__MQXMACHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQXMACHS @var{a},@var{b},@var{c}}
@item @code{void __MQXMACXHS (acc, sw2, sw2)}
@tab @code{__MQXMACXHS (@var{c}, @var{a}, @var{b})}
@tab @code{MQXMACXHS @var{a},@var{b},@var{c}}
@item @code{uw1 __MRDACC (acc)}
@tab @code{@var{b} = __MRDACC (@var{a})}
@tab @code{MRDACC @var{a},@var{b}}
@item @code{uw1 __MRDACCG (acc)}
@tab @code{@var{b} = __MRDACCG (@var{a})}
@tab @code{MRDACCG @var{a},@var{b}}
@item @code{uw1 __MROTLI (uw1, const)}
@tab @code{@var{c} = __MROTLI (@var{a}, @var{b})}
@tab @code{MROTLI @var{a},#@var{b},@var{c}}
@item @code{uw1 __MROTRI (uw1, const)}
@tab @code{@var{c} = __MROTRI (@var{a}, @var{b})}
@tab @code{MROTRI @var{a},#@var{b},@var{c}}
@item @code{sw1 __MSATHS (sw1, sw1)}
@tab @code{@var{c} = __MSATHS (@var{a}, @var{b})}
@tab @code{MSATHS @var{a},@var{b},@var{c}}
@item @code{uw1 __MSATHU (uw1, uw1)}
@tab @code{@var{c} = __MSATHU (@var{a}, @var{b})}
@tab @code{MSATHU @var{a},@var{b},@var{c}}
@item @code{uw1 __MSLLHI (uw1, const)}
@tab @code{@var{c} = __MSLLHI (@var{a}, @var{b})}
@tab @code{MSLLHI @var{a},#@var{b},@var{c}}
@item @code{sw1 __MSRAHI (sw1, const)}
@tab @code{@var{c} = __MSRAHI (@var{a}, @var{b})}
@tab @code{MSRAHI @var{a},#@var{b},@var{c}}
@item @code{uw1 __MSRLHI (uw1, const)}
@tab @code{@var{c} = __MSRLHI (@var{a}, @var{b})}
@tab @code{MSRLHI @var{a},#@var{b},@var{c}}
@item @code{void __MSUBACCS (acc, acc)}
@tab @code{__MSUBACCS (@var{b}, @var{a})}
@tab @code{MSUBACCS @var{a},@var{b}}
@item @code{sw1 __MSUBHSS (sw1, sw1)}
@tab @code{@var{c} = __MSUBHSS (@var{a}, @var{b})}
@tab @code{MSUBHSS @var{a},@var{b},@var{c}}
@item @code{uw1 __MSUBHUS (uw1, uw1)}
@tab @code{@var{c} = __MSUBHUS (@var{a}, @var{b})}
@tab @code{MSUBHUS @var{a},@var{b},@var{c}}
@item @code{void __MTRAP (void)}
@tab @code{__MTRAP ()}
@tab @code{MTRAP}
@item @code{uw2 __MUNPACKH (uw1)}
@tab @code{@var{b} = __MUNPACKH (@var{a})}
@tab @code{MUNPACKH @var{a},@var{b}}
@item @code{uw1 __MWCUT (uw2, uw1)}
@tab @code{@var{c} = __MWCUT (@var{a}, @var{b})}
@tab @code{MWCUT @var{a},@var{b},@var{c}}
@item @code{void __MWTACC (acc, uw1)}
@tab @code{__MWTACC (@var{b}, @var{a})}
@tab @code{MWTACC @var{a},@var{b}}
@item @code{void __MWTACCG (acc, uw1)}
@tab @code{__MWTACCG (@var{b}, @var{a})}
@tab @code{MWTACCG @var{a},@var{b}}
@item @code{uw1 __MXOR (uw1, uw1)}
@tab @code{@var{c} = __MXOR (@var{a}, @var{b})}
@tab @code{MXOR @var{a},@var{b},@var{c}}
@end multitable

@node Raw read/write Functions
@subsubsection Raw read/write Functions

This sections describes built-in functions related to read and write
instructions to access memory.  These functions generate
@code{membar} instructions to flush the I/O load and stores where
appropriate, as described in Fujitsu's manual described above.

@table @code

@item unsigned char __builtin_read8 (void *@var{data})
@item unsigned short __builtin_read16 (void *@var{data})
@item unsigned long __builtin_read32 (void *@var{data})
@item unsigned long long __builtin_read64 (void *@var{data})

@item void __builtin_write8 (void *@var{data}, unsigned char @var{datum})
@item void __builtin_write16 (void *@var{data}, unsigned short @var{datum})
@item void __builtin_write32 (void *@var{data}, unsigned long @var{datum})
@item void __builtin_write64 (void *@var{data}, unsigned long long @var{datum})
@end table

@node Other Built-in Functions
@subsubsection Other Built-in Functions

This section describes built-in functions that are not named after
a specific FR-V instruction.

@table @code
@item sw2 __IACCreadll (iacc @var{reg})
Return the full 64-bit value of IACC0@.  The @var{reg} argument is reserved
for future expansion and must be 0.

@item sw1 __IACCreadl (iacc @var{reg})
Return the value of IACC0H if @var{reg} is 0 and IACC0L if @var{reg} is 1.
Other values of @var{reg} are rejected as invalid.

@item void __IACCsetll (iacc @var{reg}, sw2 @var{x})
Set the full 64-bit value of IACC0 to @var{x}.  The @var{reg} argument
is reserved for future expansion and must be 0.

@item void __IACCsetl (iacc @var{reg}, sw1 @var{x})
Set IACC0H to @var{x} if @var{reg} is 0 and IACC0L to @var{x} if @var{reg}
is 1.  Other values of @var{reg} are rejected as invalid.

@item void __data_prefetch0 (const void *@var{x})
Use the @code{dcpl} instruction to load the contents of address @var{x}
into the data cache.

@item void __data_prefetch (const void *@var{x})
Use the @code{nldub} instruction to load the contents of address @var{x}
into the data cache.  The instruction is issued in slot I1@.
@end table

@node X86 Built-in Functions
@subsection X86 Built-in Functions

These built-in functions are available for the i386 and x86-64 family
of computers, depending on the command-line switches used.

If you specify command-line switches such as @option{-msse},
the compiler could use the extended instruction sets even if the built-ins
are not used explicitly in the program.  For this reason, applications
that perform run-time CPU detection must compile separate files for each
supported architecture, using the appropriate flags.  In particular,
the file containing the CPU detection code should be compiled without
these options.

The following machine modes are available for use with MMX built-in functions
(@pxref{Vector Extensions}): @code{V2SI} for a vector of two 32-bit integers,
@code{V4HI} for a vector of four 16-bit integers, and @code{V8QI} for a
vector of eight 8-bit integers.  Some of the built-in functions operate on
MMX registers as a whole 64-bit entity, these use @code{V1DI} as their mode.

If 3DNow!@: extensions are enabled, @code{V2SF} is used as a mode for a vector
of two 32-bit floating-point values.

If SSE extensions are enabled, @code{V4SF} is used for a vector of four 32-bit
floating-point values.  Some instructions use a vector of four 32-bit
integers, these use @code{V4SI}.  Finally, some instructions operate on an
entire vector register, interpreting it as a 128-bit integer, these use mode
@code{TI}.

In 64-bit mode, the x86-64 family of processors uses additional built-in
functions for efficient use of @code{TF} (@code{__float128}) 128-bit
floating point and @code{TC} 128-bit complex floating-point values.

The following floating-point built-in functions are available in 64-bit
mode.  All of them implement the function that is part of the name.

@smallexample
__float128 __builtin_fabsq (__float128)
__float128 __builtin_copysignq (__float128, __float128)
@end smallexample

The following built-in function is always available.

@table @code
@item void __builtin_ia32_pause (void)
Generates the @code{pause} machine instruction with a compiler memory
barrier.
@end table

The following floating-point built-in functions are made available in the
64-bit mode.

@table @code
@item __float128 __builtin_infq (void)
Similar to @code{__builtin_inf}, except the return type is @code{__float128}.
@findex __builtin_infq

@item __float128 __builtin_huge_valq (void)
Similar to @code{__builtin_huge_val}, except the return type is @code{__float128}.
@findex __builtin_huge_valq
@end table

The following built-in functions are always available and can be used to
check the target platform type.

@deftypefn {Built-in Function} void __builtin_cpu_init (void)
This function runs the CPU detection code to check the type of CPU and the
features supported.  This built-in function needs to be invoked along with the built-in functions
to check CPU type and features, @code{__builtin_cpu_is} and
@code{__builtin_cpu_supports}, only when used in a function that is
executed before any constructors are called.  The CPU detection code is
automatically executed in a very high priority constructor.

For example, this function has to be used in @code{ifunc} resolvers that
check for CPU type using the built-in functions @code{__builtin_cpu_is}
and @code{__builtin_cpu_supports}, or in constructors on targets that
don't support constructor priority.
@smallexample

static void (*resolve_memcpy (void)) (void)
@{
  // ifunc resolvers fire before constructors, explicitly call the init
  // function.
  __builtin_cpu_init ();
  if (__builtin_cpu_supports ("ssse3"))
    return ssse3_memcpy; // super fast memcpy with ssse3 instructions.
  else
    return default_memcpy;
@}

void *memcpy (void *, const void *, size_t)
     __attribute__ ((ifunc ("resolve_memcpy")));
@end smallexample

@end deftypefn

@deftypefn {Built-in Function} int __builtin_cpu_is (const char *@var{cpuname})
This function returns a positive integer if the run-time CPU
is of type @var{cpuname}
and returns @code{0} otherwise. The following CPU names can be detected:

@table @samp
@item intel
Intel CPU.

@item atom
Intel Atom CPU.

@item core2
Intel Core 2 CPU.

@item corei7
Intel Core i7 CPU.

@item nehalem
Intel Core i7 Nehalem CPU.

@item westmere
Intel Core i7 Westmere CPU.

@item sandybridge
Intel Core i7 Sandy Bridge CPU.

@item amd
AMD CPU.

@item amdfam10h
AMD Family 10h CPU.

@item barcelona
AMD Family 10h Barcelona CPU.

@item shanghai
AMD Family 10h Shanghai CPU.

@item istanbul
AMD Family 10h Istanbul CPU.

@item btver1
AMD Family 14h CPU.

@item amdfam15h
AMD Family 15h CPU.

@item bdver1
AMD Family 15h Bulldozer version 1.

@item bdver2
AMD Family 15h Bulldozer version 2.

@item bdver3
AMD Family 15h Bulldozer version 3.

@item btver2
AMD Family 16h CPU.
@end table

Here is an example:
@smallexample
if (__builtin_cpu_is ("corei7"))
  @{
     do_corei7 (); // Core i7 specific implementation.
  @}
else
  @{
     do_generic (); // Generic implementation.
  @}
@end smallexample
@end deftypefn

@deftypefn {Built-in Function} int __builtin_cpu_supports (const char *@var{feature})
This function returns a positive integer if the run-time CPU
supports @var{feature}
and returns @code{0} otherwise. The following features can be detected:

@table @samp
@item cmov
CMOV instruction.
@item mmx
MMX instructions.
@item popcnt
POPCNT instruction.
@item sse
SSE instructions.
@item sse2
SSE2 instructions.
@item sse3
SSE3 instructions.
@item ssse3
SSSE3 instructions.
@item sse4.1
SSE4.1 instructions.
@item sse4.2
SSE4.2 instructions.
@item avx
AVX instructions.
@item avx2
AVX2 instructions.
@end table

Here is an example:
@smallexample
if (__builtin_cpu_supports ("popcnt"))
  @{
     asm("popcnt %1,%0" : "=r"(count) : "rm"(n) : "cc");
  @}
else
  @{
     count = generic_countbits (n); //generic implementation.
  @}
@end smallexample
@end deftypefn


The following built-in functions are made available by @option{-mmmx}.
All of them generate the machine instruction that is part of the name.

@smallexample
v8qi __builtin_ia32_paddb (v8qi, v8qi)
v4hi __builtin_ia32_paddw (v4hi, v4hi)
v2si __builtin_ia32_paddd (v2si, v2si)
v8qi __builtin_ia32_psubb (v8qi, v8qi)
v4hi __builtin_ia32_psubw (v4hi, v4hi)
v2si __builtin_ia32_psubd (v2si, v2si)
v8qi __builtin_ia32_paddsb (v8qi, v8qi)
v4hi __builtin_ia32_paddsw (v4hi, v4hi)
v8qi __builtin_ia32_psubsb (v8qi, v8qi)
v4hi __builtin_ia32_psubsw (v4hi, v4hi)
v8qi __builtin_ia32_paddusb (v8qi, v8qi)
v4hi __builtin_ia32_paddusw (v4hi, v4hi)
v8qi __builtin_ia32_psubusb (v8qi, v8qi)
v4hi __builtin_ia32_psubusw (v4hi, v4hi)
v4hi __builtin_ia32_pmullw (v4hi, v4hi)
v4hi __builtin_ia32_pmulhw (v4hi, v4hi)
di __builtin_ia32_pand (di, di)
di __builtin_ia32_pandn (di,di)
di __builtin_ia32_por (di, di)
di __builtin_ia32_pxor (di, di)
v8qi __builtin_ia32_pcmpeqb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpeqw (v4hi, v4hi)
v2si __builtin_ia32_pcmpeqd (v2si, v2si)
v8qi __builtin_ia32_pcmpgtb (v8qi, v8qi)
v4hi __builtin_ia32_pcmpgtw (v4hi, v4hi)
v2si __builtin_ia32_pcmpgtd (v2si, v2si)
v8qi __builtin_ia32_punpckhbw (v8qi, v8qi)
v4hi __builtin_ia32_punpckhwd (v4hi, v4hi)
v2si __builtin_ia32_punpckhdq (v2si, v2si)
v8qi __builtin_ia32_punpcklbw (v8qi, v8qi)
v4hi __builtin_ia32_punpcklwd (v4hi, v4hi)
v2si __builtin_ia32_punpckldq (v2si, v2si)
v8qi __builtin_ia32_packsswb (v4hi, v4hi)
v4hi __builtin_ia32_packssdw (v2si, v2si)
v8qi __builtin_ia32_packuswb (v4hi, v4hi)

v4hi __builtin_ia32_psllw (v4hi, v4hi)
v2si __builtin_ia32_pslld (v2si, v2si)
v1di __builtin_ia32_psllq (v1di, v1di)
v4hi __builtin_ia32_psrlw (v4hi, v4hi)
v2si __builtin_ia32_psrld (v2si, v2si)
v1di __builtin_ia32_psrlq (v1di, v1di)
v4hi __builtin_ia32_psraw (v4hi, v4hi)
v2si __builtin_ia32_psrad (v2si, v2si)
v4hi __builtin_ia32_psllwi (v4hi, int)
v2si __builtin_ia32_pslldi (v2si, int)
v1di __builtin_ia32_psllqi (v1di, int)
v4hi __builtin_ia32_psrlwi (v4hi, int)
v2si __builtin_ia32_psrldi (v2si, int)
v1di __builtin_ia32_psrlqi (v1di, int)
v4hi __builtin_ia32_psrawi (v4hi, int)
v2si __builtin_ia32_psradi (v2si, int)

@end smallexample

The following built-in functions are made available either with
@option{-msse}, or with a combination of @option{-m3dnow} and
@option{-march=athlon}.  All of them generate the machine
instruction that is part of the name.

@smallexample
v4hi __builtin_ia32_pmulhuw (v4hi, v4hi)
v8qi __builtin_ia32_pavgb (v8qi, v8qi)
v4hi __builtin_ia32_pavgw (v4hi, v4hi)
v1di __builtin_ia32_psadbw (v8qi, v8qi)
v8qi __builtin_ia32_pmaxub (v8qi, v8qi)
v4hi __builtin_ia32_pmaxsw (v4hi, v4hi)
v8qi __builtin_ia32_pminub (v8qi, v8qi)
v4hi __builtin_ia32_pminsw (v4hi, v4hi)
int __builtin_ia32_pextrw (v4hi, int)
v4hi __builtin_ia32_pinsrw (v4hi, int, int)
int __builtin_ia32_pmovmskb (v8qi)
void __builtin_ia32_maskmovq (v8qi, v8qi, char *)
void __builtin_ia32_movntq (di *, di)
void __builtin_ia32_sfence (void)
@end smallexample

The following built-in functions are available when @option{-msse} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
int __builtin_ia32_comieq (v4sf, v4sf)
int __builtin_ia32_comineq (v4sf, v4sf)
int __builtin_ia32_comilt (v4sf, v4sf)
int __builtin_ia32_comile (v4sf, v4sf)
int __builtin_ia32_comigt (v4sf, v4sf)
int __builtin_ia32_comige (v4sf, v4sf)
int __builtin_ia32_ucomieq (v4sf, v4sf)
int __builtin_ia32_ucomineq (v4sf, v4sf)
int __builtin_ia32_ucomilt (v4sf, v4sf)
int __builtin_ia32_ucomile (v4sf, v4sf)
int __builtin_ia32_ucomigt (v4sf, v4sf)
int __builtin_ia32_ucomige (v4sf, v4sf)
v4sf __builtin_ia32_addps (v4sf, v4sf)
v4sf __builtin_ia32_subps (v4sf, v4sf)
v4sf __builtin_ia32_mulps (v4sf, v4sf)
v4sf __builtin_ia32_divps (v4sf, v4sf)
v4sf __builtin_ia32_addss (v4sf, v4sf)
v4sf __builtin_ia32_subss (v4sf, v4sf)
v4sf __builtin_ia32_mulss (v4sf, v4sf)
v4sf __builtin_ia32_divss (v4sf, v4sf)
v4si __builtin_ia32_cmpeqps (v4sf, v4sf)
v4si __builtin_ia32_cmpltps (v4sf, v4sf)
v4si __builtin_ia32_cmpleps (v4sf, v4sf)
v4si __builtin_ia32_cmpgtps (v4sf, v4sf)
v4si __builtin_ia32_cmpgeps (v4sf, v4sf)
v4si __builtin_ia32_cmpunordps (v4sf, v4sf)
v4si __builtin_ia32_cmpneqps (v4sf, v4sf)
v4si __builtin_ia32_cmpnltps (v4sf, v4sf)
v4si __builtin_ia32_cmpnleps (v4sf, v4sf)
v4si __builtin_ia32_cmpngtps (v4sf, v4sf)
v4si __builtin_ia32_cmpngeps (v4sf, v4sf)
v4si __builtin_ia32_cmpordps (v4sf, v4sf)
v4si __builtin_ia32_cmpeqss (v4sf, v4sf)
v4si __builtin_ia32_cmpltss (v4sf, v4sf)
v4si __builtin_ia32_cmpless (v4sf, v4sf)
v4si __builtin_ia32_cmpunordss (v4sf, v4sf)
v4si __builtin_ia32_cmpneqss (v4sf, v4sf)
v4si __builtin_ia32_cmpnlts (v4sf, v4sf)
v4si __builtin_ia32_cmpnless (v4sf, v4sf)
v4si __builtin_ia32_cmpordss (v4sf, v4sf)
v4sf __builtin_ia32_maxps (v4sf, v4sf)
v4sf __builtin_ia32_maxss (v4sf, v4sf)
v4sf __builtin_ia32_minps (v4sf, v4sf)
v4sf __builtin_ia32_minss (v4sf, v4sf)
v4sf __builtin_ia32_andps (v4sf, v4sf)
v4sf __builtin_ia32_andnps (v4sf, v4sf)
v4sf __builtin_ia32_orps (v4sf, v4sf)
v4sf __builtin_ia32_xorps (v4sf, v4sf)
v4sf __builtin_ia32_movss (v4sf, v4sf)
v4sf __builtin_ia32_movhlps (v4sf, v4sf)
v4sf __builtin_ia32_movlhps (v4sf, v4sf)
v4sf __builtin_ia32_unpckhps (v4sf, v4sf)
v4sf __builtin_ia32_unpcklps (v4sf, v4sf)
v4sf __builtin_ia32_cvtpi2ps (v4sf, v2si)
v4sf __builtin_ia32_cvtsi2ss (v4sf, int)
v2si __builtin_ia32_cvtps2pi (v4sf)
int __builtin_ia32_cvtss2si (v4sf)
v2si __builtin_ia32_cvttps2pi (v4sf)
int __builtin_ia32_cvttss2si (v4sf)
v4sf __builtin_ia32_rcpps (v4sf)
v4sf __builtin_ia32_rsqrtps (v4sf)
v4sf __builtin_ia32_sqrtps (v4sf)
v4sf __builtin_ia32_rcpss (v4sf)
v4sf __builtin_ia32_rsqrtss (v4sf)
v4sf __builtin_ia32_sqrtss (v4sf)
v4sf __builtin_ia32_shufps (v4sf, v4sf, int)
void __builtin_ia32_movntps (float *, v4sf)
int __builtin_ia32_movmskps (v4sf)
@end smallexample

The following built-in functions are available when @option{-msse} is used.

@table @code
@item v4sf __builtin_ia32_loadaps (float *)
Generates the @code{movaps} machine instruction as a load from memory.
@item void __builtin_ia32_storeaps (float *, v4sf)
Generates the @code{movaps} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadups (float *)
Generates the @code{movups} machine instruction as a load from memory.
@item void __builtin_ia32_storeups (float *, v4sf)
Generates the @code{movups} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadsss (float *)
Generates the @code{movss} machine instruction as a load from memory.
@item void __builtin_ia32_storess (float *, v4sf)
Generates the @code{movss} machine instruction as a store to memory.
@item v4sf __builtin_ia32_loadhps (v4sf, const v2sf *)
Generates the @code{movhps} machine instruction as a load from memory.
@item v4sf __builtin_ia32_loadlps (v4sf, const v2sf *)
Generates the @code{movlps} machine instruction as a load from memory
@item void __builtin_ia32_storehps (v2sf *, v4sf)
Generates the @code{movhps} machine instruction as a store to memory.
@item void __builtin_ia32_storelps (v2sf *, v4sf)
Generates the @code{movlps} machine instruction as a store to memory.
@end table

The following built-in functions are available when @option{-msse2} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
int __builtin_ia32_comisdeq (v2df, v2df)
int __builtin_ia32_comisdlt (v2df, v2df)
int __builtin_ia32_comisdle (v2df, v2df)
int __builtin_ia32_comisdgt (v2df, v2df)
int __builtin_ia32_comisdge (v2df, v2df)
int __builtin_ia32_comisdneq (v2df, v2df)
int __builtin_ia32_ucomisdeq (v2df, v2df)
int __builtin_ia32_ucomisdlt (v2df, v2df)
int __builtin_ia32_ucomisdle (v2df, v2df)
int __builtin_ia32_ucomisdgt (v2df, v2df)
int __builtin_ia32_ucomisdge (v2df, v2df)
int __builtin_ia32_ucomisdneq (v2df, v2df)
v2df __builtin_ia32_cmpeqpd (v2df, v2df)
v2df __builtin_ia32_cmpltpd (v2df, v2df)
v2df __builtin_ia32_cmplepd (v2df, v2df)
v2df __builtin_ia32_cmpgtpd (v2df, v2df)
v2df __builtin_ia32_cmpgepd (v2df, v2df)
v2df __builtin_ia32_cmpunordpd (v2df, v2df)
v2df __builtin_ia32_cmpneqpd (v2df, v2df)
v2df __builtin_ia32_cmpnltpd (v2df, v2df)
v2df __builtin_ia32_cmpnlepd (v2df, v2df)
v2df __builtin_ia32_cmpngtpd (v2df, v2df)
v2df __builtin_ia32_cmpngepd (v2df, v2df)
v2df __builtin_ia32_cmpordpd (v2df, v2df)
v2df __builtin_ia32_cmpeqsd (v2df, v2df)
v2df __builtin_ia32_cmpltsd (v2df, v2df)
v2df __builtin_ia32_cmplesd (v2df, v2df)
v2df __builtin_ia32_cmpunordsd (v2df, v2df)
v2df __builtin_ia32_cmpneqsd (v2df, v2df)
v2df __builtin_ia32_cmpnltsd (v2df, v2df)
v2df __builtin_ia32_cmpnlesd (v2df, v2df)
v2df __builtin_ia32_cmpordsd (v2df, v2df)
v2di __builtin_ia32_paddq (v2di, v2di)
v2di __builtin_ia32_psubq (v2di, v2di)
v2df __builtin_ia32_addpd (v2df, v2df)
v2df __builtin_ia32_subpd (v2df, v2df)
v2df __builtin_ia32_mulpd (v2df, v2df)
v2df __builtin_ia32_divpd (v2df, v2df)
v2df __builtin_ia32_addsd (v2df, v2df)
v2df __builtin_ia32_subsd (v2df, v2df)
v2df __builtin_ia32_mulsd (v2df, v2df)
v2df __builtin_ia32_divsd (v2df, v2df)
v2df __builtin_ia32_minpd (v2df, v2df)
v2df __builtin_ia32_maxpd (v2df, v2df)
v2df __builtin_ia32_minsd (v2df, v2df)
v2df __builtin_ia32_maxsd (v2df, v2df)
v2df __builtin_ia32_andpd (v2df, v2df)
v2df __builtin_ia32_andnpd (v2df, v2df)
v2df __builtin_ia32_orpd (v2df, v2df)
v2df __builtin_ia32_xorpd (v2df, v2df)
v2df __builtin_ia32_movsd (v2df, v2df)
v2df __builtin_ia32_unpckhpd (v2df, v2df)
v2df __builtin_ia32_unpcklpd (v2df, v2df)
v16qi __builtin_ia32_paddb128 (v16qi, v16qi)
v8hi __builtin_ia32_paddw128 (v8hi, v8hi)
v4si __builtin_ia32_paddd128 (v4si, v4si)
v2di __builtin_ia32_paddq128 (v2di, v2di)
v16qi __builtin_ia32_psubb128 (v16qi, v16qi)
v8hi __builtin_ia32_psubw128 (v8hi, v8hi)
v4si __builtin_ia32_psubd128 (v4si, v4si)
v2di __builtin_ia32_psubq128 (v2di, v2di)
v8hi __builtin_ia32_pmullw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhw128 (v8hi, v8hi)
v2di __builtin_ia32_pand128 (v2di, v2di)
v2di __builtin_ia32_pandn128 (v2di, v2di)
v2di __builtin_ia32_por128 (v2di, v2di)
v2di __builtin_ia32_pxor128 (v2di, v2di)
v16qi __builtin_ia32_pavgb128 (v16qi, v16qi)
v8hi __builtin_ia32_pavgw128 (v8hi, v8hi)
v16qi __builtin_ia32_pcmpeqb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpeqw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpeqd128 (v4si, v4si)
v16qi __builtin_ia32_pcmpgtb128 (v16qi, v16qi)
v8hi __builtin_ia32_pcmpgtw128 (v8hi, v8hi)
v4si __builtin_ia32_pcmpgtd128 (v4si, v4si)
v16qi __builtin_ia32_pmaxub128 (v16qi, v16qi)
v8hi __builtin_ia32_pmaxsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminub128 (v16qi, v16qi)
v8hi __builtin_ia32_pminsw128 (v8hi, v8hi)
v16qi __builtin_ia32_punpckhbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpckhwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckhdq128 (v4si, v4si)
v2di __builtin_ia32_punpckhqdq128 (v2di, v2di)
v16qi __builtin_ia32_punpcklbw128 (v16qi, v16qi)
v8hi __builtin_ia32_punpcklwd128 (v8hi, v8hi)
v4si __builtin_ia32_punpckldq128 (v4si, v4si)
v2di __builtin_ia32_punpcklqdq128 (v2di, v2di)
v16qi __builtin_ia32_packsswb128 (v8hi, v8hi)
v8hi __builtin_ia32_packssdw128 (v4si, v4si)
v16qi __builtin_ia32_packuswb128 (v8hi, v8hi)
v8hi __builtin_ia32_pmulhuw128 (v8hi, v8hi)
void __builtin_ia32_maskmovdqu (v16qi, v16qi)
v2df __builtin_ia32_loadupd (double *)
void __builtin_ia32_storeupd (double *, v2df)
v2df __builtin_ia32_loadhpd (v2df, double const *)
v2df __builtin_ia32_loadlpd (v2df, double const *)
int __builtin_ia32_movmskpd (v2df)
int __builtin_ia32_pmovmskb128 (v16qi)
void __builtin_ia32_movnti (int *, int)
void __builtin_ia32_movnti64 (long long int *, long long int)
void __builtin_ia32_movntpd (double *, v2df)
void __builtin_ia32_movntdq (v2df *, v2df)
v4si __builtin_ia32_pshufd (v4si, int)
v8hi __builtin_ia32_pshuflw (v8hi, int)
v8hi __builtin_ia32_pshufhw (v8hi, int)
v2di __builtin_ia32_psadbw128 (v16qi, v16qi)
v2df __builtin_ia32_sqrtpd (v2df)
v2df __builtin_ia32_sqrtsd (v2df)
v2df __builtin_ia32_shufpd (v2df, v2df, int)
v2df __builtin_ia32_cvtdq2pd (v4si)
v4sf __builtin_ia32_cvtdq2ps (v4si)
v4si __builtin_ia32_cvtpd2dq (v2df)
v2si __builtin_ia32_cvtpd2pi (v2df)
v4sf __builtin_ia32_cvtpd2ps (v2df)
v4si __builtin_ia32_cvttpd2dq (v2df)
v2si __builtin_ia32_cvttpd2pi (v2df)
v2df __builtin_ia32_cvtpi2pd (v2si)
int __builtin_ia32_cvtsd2si (v2df)
int __builtin_ia32_cvttsd2si (v2df)
long long __builtin_ia32_cvtsd2si64 (v2df)
long long __builtin_ia32_cvttsd2si64 (v2df)
v4si __builtin_ia32_cvtps2dq (v4sf)
v2df __builtin_ia32_cvtps2pd (v4sf)
v4si __builtin_ia32_cvttps2dq (v4sf)
v2df __builtin_ia32_cvtsi2sd (v2df, int)
v2df __builtin_ia32_cvtsi642sd (v2df, long long)
v4sf __builtin_ia32_cvtsd2ss (v4sf, v2df)
v2df __builtin_ia32_cvtss2sd (v2df, v4sf)
void __builtin_ia32_clflush (const void *)
void __builtin_ia32_lfence (void)
void __builtin_ia32_mfence (void)
v16qi __builtin_ia32_loaddqu (const char *)
void __builtin_ia32_storedqu (char *, v16qi)
v1di __builtin_ia32_pmuludq (v2si, v2si)
v2di __builtin_ia32_pmuludq128 (v4si, v4si)
v8hi __builtin_ia32_psllw128 (v8hi, v8hi)
v4si __builtin_ia32_pslld128 (v4si, v4si)
v2di __builtin_ia32_psllq128 (v2di, v2di)
v8hi __builtin_ia32_psrlw128 (v8hi, v8hi)
v4si __builtin_ia32_psrld128 (v4si, v4si)
v2di __builtin_ia32_psrlq128 (v2di, v2di)
v8hi __builtin_ia32_psraw128 (v8hi, v8hi)
v4si __builtin_ia32_psrad128 (v4si, v4si)
v2di __builtin_ia32_pslldqi128 (v2di, int)
v8hi __builtin_ia32_psllwi128 (v8hi, int)
v4si __builtin_ia32_pslldi128 (v4si, int)
v2di __builtin_ia32_psllqi128 (v2di, int)
v2di __builtin_ia32_psrldqi128 (v2di, int)
v8hi __builtin_ia32_psrlwi128 (v8hi, int)
v4si __builtin_ia32_psrldi128 (v4si, int)
v2di __builtin_ia32_psrlqi128 (v2di, int)
v8hi __builtin_ia32_psrawi128 (v8hi, int)
v4si __builtin_ia32_psradi128 (v4si, int)
v4si __builtin_ia32_pmaddwd128 (v8hi, v8hi)
v2di __builtin_ia32_movq128 (v2di)
@end smallexample

The following built-in functions are available when @option{-msse3} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
v2df __builtin_ia32_addsubpd (v2df, v2df)
v4sf __builtin_ia32_addsubps (v4sf, v4sf)
v2df __builtin_ia32_haddpd (v2df, v2df)
v4sf __builtin_ia32_haddps (v4sf, v4sf)
v2df __builtin_ia32_hsubpd (v2df, v2df)
v4sf __builtin_ia32_hsubps (v4sf, v4sf)
v16qi __builtin_ia32_lddqu (char const *)
void __builtin_ia32_monitor (void *, unsigned int, unsigned int)
v2df __builtin_ia32_movddup (v2df)
v4sf __builtin_ia32_movshdup (v4sf)
v4sf __builtin_ia32_movsldup (v4sf)
void __builtin_ia32_mwait (unsigned int, unsigned int)
@end smallexample

The following built-in functions are available when @option{-msse3} is used.

@table @code
@item v2df __builtin_ia32_loadddup (double const *)
Generates the @code{movddup} machine instruction as a load from memory.
@end table

The following built-in functions are available when @option{-mssse3} is used.
All of them generate the machine instruction that is part of the name
with MMX registers.

@smallexample
v2si __builtin_ia32_phaddd (v2si, v2si)
v4hi __builtin_ia32_phaddw (v4hi, v4hi)
v4hi __builtin_ia32_phaddsw (v4hi, v4hi)
v2si __builtin_ia32_phsubd (v2si, v2si)
v4hi __builtin_ia32_phsubw (v4hi, v4hi)
v4hi __builtin_ia32_phsubsw (v4hi, v4hi)
v4hi __builtin_ia32_pmaddubsw (v8qi, v8qi)
v4hi __builtin_ia32_pmulhrsw (v4hi, v4hi)
v8qi __builtin_ia32_pshufb (v8qi, v8qi)
v8qi __builtin_ia32_psignb (v8qi, v8qi)
v2si __builtin_ia32_psignd (v2si, v2si)
v4hi __builtin_ia32_psignw (v4hi, v4hi)
v1di __builtin_ia32_palignr (v1di, v1di, int)
v8qi __builtin_ia32_pabsb (v8qi)
v2si __builtin_ia32_pabsd (v2si)
v4hi __builtin_ia32_pabsw (v4hi)
@end smallexample

The following built-in functions are available when @option{-mssse3} is used.
All of them generate the machine instruction that is part of the name
with SSE registers.

@smallexample
v4si __builtin_ia32_phaddd128 (v4si, v4si)
v8hi __builtin_ia32_phaddw128 (v8hi, v8hi)
v8hi __builtin_ia32_phaddsw128 (v8hi, v8hi)
v4si __builtin_ia32_phsubd128 (v4si, v4si)
v8hi __builtin_ia32_phsubw128 (v8hi, v8hi)
v8hi __builtin_ia32_phsubsw128 (v8hi, v8hi)
v8hi __builtin_ia32_pmaddubsw128 (v16qi, v16qi)
v8hi __builtin_ia32_pmulhrsw128 (v8hi, v8hi)
v16qi __builtin_ia32_pshufb128 (v16qi, v16qi)
v16qi __builtin_ia32_psignb128 (v16qi, v16qi)
v4si __builtin_ia32_psignd128 (v4si, v4si)
v8hi __builtin_ia32_psignw128 (v8hi, v8hi)
v2di __builtin_ia32_palignr128 (v2di, v2di, int)
v16qi __builtin_ia32_pabsb128 (v16qi)
v4si __builtin_ia32_pabsd128 (v4si)
v8hi __builtin_ia32_pabsw128 (v8hi)
@end smallexample

The following built-in functions are available when @option{-msse4.1} is
used.  All of them generate the machine instruction that is part of the
name.

@smallexample
v2df __builtin_ia32_blendpd (v2df, v2df, const int)
v4sf __builtin_ia32_blendps (v4sf, v4sf, const int)
v2df __builtin_ia32_blendvpd (v2df, v2df, v2df)
v4sf __builtin_ia32_blendvps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_dppd (v2df, v2df, const int)
v4sf __builtin_ia32_dpps (v4sf, v4sf, const int)
v4sf __builtin_ia32_insertps128 (v4sf, v4sf, const int)
v2di __builtin_ia32_movntdqa (v2di *);
v16qi __builtin_ia32_mpsadbw128 (v16qi, v16qi, const int)
v8hi __builtin_ia32_packusdw128 (v4si, v4si)
v16qi __builtin_ia32_pblendvb128 (v16qi, v16qi, v16qi)
v8hi __builtin_ia32_pblendw128 (v8hi, v8hi, const int)
v2di __builtin_ia32_pcmpeqq (v2di, v2di)
v8hi __builtin_ia32_phminposuw128 (v8hi)
v16qi __builtin_ia32_pmaxsb128 (v16qi, v16qi)
v4si __builtin_ia32_pmaxsd128 (v4si, v4si)
v4si __builtin_ia32_pmaxud128 (v4si, v4si)
v8hi __builtin_ia32_pmaxuw128 (v8hi, v8hi)
v16qi __builtin_ia32_pminsb128 (v16qi, v16qi)
v4si __builtin_ia32_pminsd128 (v4si, v4si)
v4si __builtin_ia32_pminud128 (v4si, v4si)
v8hi __builtin_ia32_pminuw128 (v8hi, v8hi)
v4si __builtin_ia32_pmovsxbd128 (v16qi)
v2di __builtin_ia32_pmovsxbq128 (v16qi)
v8hi __builtin_ia32_pmovsxbw128 (v16qi)
v2di __builtin_ia32_pmovsxdq128 (v4si)
v4si __builtin_ia32_pmovsxwd128 (v8hi)
v2di __builtin_ia32_pmovsxwq128 (v8hi)
v4si __builtin_ia32_pmovzxbd128 (v16qi)
v2di __builtin_ia32_pmovzxbq128 (v16qi)
v8hi __builtin_ia32_pmovzxbw128 (v16qi)
v2di __builtin_ia32_pmovzxdq128 (v4si)
v4si __builtin_ia32_pmovzxwd128 (v8hi)
v2di __builtin_ia32_pmovzxwq128 (v8hi)
v2di __builtin_ia32_pmuldq128 (v4si, v4si)
v4si __builtin_ia32_pmulld128 (v4si, v4si)
int __builtin_ia32_ptestc128 (v2di, v2di)
int __builtin_ia32_ptestnzc128 (v2di, v2di)
int __builtin_ia32_ptestz128 (v2di, v2di)
v2df __builtin_ia32_roundpd (v2df, const int)
v4sf __builtin_ia32_roundps (v4sf, const int)
v2df __builtin_ia32_roundsd (v2df, v2df, const int)
v4sf __builtin_ia32_roundss (v4sf, v4sf, const int)
@end smallexample

The following built-in functions are available when @option{-msse4.1} is
used.

@table @code
@item v4sf __builtin_ia32_vec_set_v4sf (v4sf, float, const int)
Generates the @code{insertps} machine instruction.
@item int __builtin_ia32_vec_ext_v16qi (v16qi, const int)
Generates the @code{pextrb} machine instruction.
@item v16qi __builtin_ia32_vec_set_v16qi (v16qi, int, const int)
Generates the @code{pinsrb} machine instruction.
@item v4si __builtin_ia32_vec_set_v4si (v4si, int, const int)
Generates the @code{pinsrd} machine instruction.
@item v2di __builtin_ia32_vec_set_v2di (v2di, long long, const int)
Generates the @code{pinsrq} machine instruction in 64bit mode.
@end table

The following built-in functions are changed to generate new SSE4.1
instructions when @option{-msse4.1} is used.

@table @code
@item float __builtin_ia32_vec_ext_v4sf (v4sf, const int)
Generates the @code{extractps} machine instruction.
@item int __builtin_ia32_vec_ext_v4si (v4si, const int)
Generates the @code{pextrd} machine instruction.
@item long long __builtin_ia32_vec_ext_v2di (v2di, const int)
Generates the @code{pextrq} machine instruction in 64bit mode.
@end table

The following built-in functions are available when @option{-msse4.2} is
used.  All of them generate the machine instruction that is part of the
name.

@smallexample
v16qi __builtin_ia32_pcmpestrm128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestri128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestria128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestric128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestrio128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestris128 (v16qi, int, v16qi, int, const int)
int __builtin_ia32_pcmpestriz128 (v16qi, int, v16qi, int, const int)
v16qi __builtin_ia32_pcmpistrm128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistri128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistria128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistric128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistrio128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistris128 (v16qi, v16qi, const int)
int __builtin_ia32_pcmpistriz128 (v16qi, v16qi, const int)
v2di __builtin_ia32_pcmpgtq (v2di, v2di)
@end smallexample

The following built-in functions are available when @option{-msse4.2} is
used.

@table @code
@item unsigned int __builtin_ia32_crc32qi (unsigned int, unsigned char)
Generates the @code{crc32b} machine instruction.
@item unsigned int __builtin_ia32_crc32hi (unsigned int, unsigned short)
Generates the @code{crc32w} machine instruction.
@item unsigned int __builtin_ia32_crc32si (unsigned int, unsigned int)
Generates the @code{crc32l} machine instruction.
@item unsigned long long __builtin_ia32_crc32di (unsigned long long, unsigned long long)
Generates the @code{crc32q} machine instruction.
@end table

The following built-in functions are changed to generate new SSE4.2
instructions when @option{-msse4.2} is used.

@table @code
@item int __builtin_popcount (unsigned int)
Generates the @code{popcntl} machine instruction.
@item int __builtin_popcountl (unsigned long)
Generates the @code{popcntl} or @code{popcntq} machine instruction,
depending on the size of @code{unsigned long}.
@item int __builtin_popcountll (unsigned long long)
Generates the @code{popcntq} machine instruction.
@end table

The following built-in functions are available when @option{-mavx} is
used. All of them generate the machine instruction that is part of the
name.

@smallexample
v4df __builtin_ia32_addpd256 (v4df,v4df)
v8sf __builtin_ia32_addps256 (v8sf,v8sf)
v4df __builtin_ia32_addsubpd256 (v4df,v4df)
v8sf __builtin_ia32_addsubps256 (v8sf,v8sf)
v4df __builtin_ia32_andnpd256 (v4df,v4df)
v8sf __builtin_ia32_andnps256 (v8sf,v8sf)
v4df __builtin_ia32_andpd256 (v4df,v4df)
v8sf __builtin_ia32_andps256 (v8sf,v8sf)
v4df __builtin_ia32_blendpd256 (v4df,v4df,int)
v8sf __builtin_ia32_blendps256 (v8sf,v8sf,int)
v4df __builtin_ia32_blendvpd256 (v4df,v4df,v4df)
v8sf __builtin_ia32_blendvps256 (v8sf,v8sf,v8sf)
v2df __builtin_ia32_cmppd (v2df,v2df,int)
v4df __builtin_ia32_cmppd256 (v4df,v4df,int)
v4sf __builtin_ia32_cmpps (v4sf,v4sf,int)
v8sf __builtin_ia32_cmpps256 (v8sf,v8sf,int)
v2df __builtin_ia32_cmpsd (v2df,v2df,int)
v4sf __builtin_ia32_cmpss (v4sf,v4sf,int)
v4df __builtin_ia32_cvtdq2pd256 (v4si)
v8sf __builtin_ia32_cvtdq2ps256 (v8si)
v4si __builtin_ia32_cvtpd2dq256 (v4df)
v4sf __builtin_ia32_cvtpd2ps256 (v4df)
v8si __builtin_ia32_cvtps2dq256 (v8sf)
v4df __builtin_ia32_cvtps2pd256 (v4sf)
v4si __builtin_ia32_cvttpd2dq256 (v4df)
v8si __builtin_ia32_cvttps2dq256 (v8sf)
v4df __builtin_ia32_divpd256 (v4df,v4df)
v8sf __builtin_ia32_divps256 (v8sf,v8sf)
v8sf __builtin_ia32_dpps256 (v8sf,v8sf,int)
v4df __builtin_ia32_haddpd256 (v4df,v4df)
v8sf __builtin_ia32_haddps256 (v8sf,v8sf)
v4df __builtin_ia32_hsubpd256 (v4df,v4df)
v8sf __builtin_ia32_hsubps256 (v8sf,v8sf)
v32qi __builtin_ia32_lddqu256 (pcchar)
v32qi __builtin_ia32_loaddqu256 (pcchar)
v4df __builtin_ia32_loadupd256 (pcdouble)
v8sf __builtin_ia32_loadups256 (pcfloat)
v2df __builtin_ia32_maskloadpd (pcv2df,v2df)
v4df __builtin_ia32_maskloadpd256 (pcv4df,v4df)
v4sf __builtin_ia32_maskloadps (pcv4sf,v4sf)
v8sf __builtin_ia32_maskloadps256 (pcv8sf,v8sf)
void __builtin_ia32_maskstorepd (pv2df,v2df,v2df)
void __builtin_ia32_maskstorepd256 (pv4df,v4df,v4df)
void __builtin_ia32_maskstoreps (pv4sf,v4sf,v4sf)
void __builtin_ia32_maskstoreps256 (pv8sf,v8sf,v8sf)
v4df __builtin_ia32_maxpd256 (v4df,v4df)
v8sf __builtin_ia32_maxps256 (v8sf,v8sf)
v4df __builtin_ia32_minpd256 (v4df,v4df)
v8sf __builtin_ia32_minps256 (v8sf,v8sf)
v4df __builtin_ia32_movddup256 (v4df)
int __builtin_ia32_movmskpd256 (v4df)
int __builtin_ia32_movmskps256 (v8sf)
v8sf __builtin_ia32_movshdup256 (v8sf)
v8sf __builtin_ia32_movsldup256 (v8sf)
v4df __builtin_ia32_mulpd256 (v4df,v4df)
v8sf __builtin_ia32_mulps256 (v8sf,v8sf)
v4df __builtin_ia32_orpd256 (v4df,v4df)
v8sf __builtin_ia32_orps256 (v8sf,v8sf)
v2df __builtin_ia32_pd_pd256 (v4df)
v4df __builtin_ia32_pd256_pd (v2df)
v4sf __builtin_ia32_ps_ps256 (v8sf)
v8sf __builtin_ia32_ps256_ps (v4sf)
int __builtin_ia32_ptestc256 (v4di,v4di,ptest)
int __builtin_ia32_ptestnzc256 (v4di,v4di,ptest)
int __builtin_ia32_ptestz256 (v4di,v4di,ptest)
v8sf __builtin_ia32_rcpps256 (v8sf)
v4df __builtin_ia32_roundpd256 (v4df,int)
v8sf __builtin_ia32_roundps256 (v8sf,int)
v8sf __builtin_ia32_rsqrtps_nr256 (v8sf)
v8sf __builtin_ia32_rsqrtps256 (v8sf)
v4df __builtin_ia32_shufpd256 (v4df,v4df,int)
v8sf __builtin_ia32_shufps256 (v8sf,v8sf,int)
v4si __builtin_ia32_si_si256 (v8si)
v8si __builtin_ia32_si256_si (v4si)
v4df __builtin_ia32_sqrtpd256 (v4df)
v8sf __builtin_ia32_sqrtps_nr256 (v8sf)
v8sf __builtin_ia32_sqrtps256 (v8sf)
void __builtin_ia32_storedqu256 (pchar,v32qi)
void __builtin_ia32_storeupd256 (pdouble,v4df)
void __builtin_ia32_storeups256 (pfloat,v8sf)
v4df __builtin_ia32_subpd256 (v4df,v4df)
v8sf __builtin_ia32_subps256 (v8sf,v8sf)
v4df __builtin_ia32_unpckhpd256 (v4df,v4df)
v8sf __builtin_ia32_unpckhps256 (v8sf,v8sf)
v4df __builtin_ia32_unpcklpd256 (v4df,v4df)
v8sf __builtin_ia32_unpcklps256 (v8sf,v8sf)
v4df __builtin_ia32_vbroadcastf128_pd256 (pcv2df)
v8sf __builtin_ia32_vbroadcastf128_ps256 (pcv4sf)
v4df __builtin_ia32_vbroadcastsd256 (pcdouble)
v4sf __builtin_ia32_vbroadcastss (pcfloat)
v8sf __builtin_ia32_vbroadcastss256 (pcfloat)
v2df __builtin_ia32_vextractf128_pd256 (v4df,int)
v4sf __builtin_ia32_vextractf128_ps256 (v8sf,int)
v4si __builtin_ia32_vextractf128_si256 (v8si,int)
v4df __builtin_ia32_vinsertf128_pd256 (v4df,v2df,int)
v8sf __builtin_ia32_vinsertf128_ps256 (v8sf,v4sf,int)
v8si __builtin_ia32_vinsertf128_si256 (v8si,v4si,int)
v4df __builtin_ia32_vperm2f128_pd256 (v4df,v4df,int)
v8sf __builtin_ia32_vperm2f128_ps256 (v8sf,v8sf,int)
v8si __builtin_ia32_vperm2f128_si256 (v8si,v8si,int)
v2df __builtin_ia32_vpermil2pd (v2df,v2df,v2di,int)
v4df __builtin_ia32_vpermil2pd256 (v4df,v4df,v4di,int)
v4sf __builtin_ia32_vpermil2ps (v4sf,v4sf,v4si,int)
v8sf __builtin_ia32_vpermil2ps256 (v8sf,v8sf,v8si,int)
v2df __builtin_ia32_vpermilpd (v2df,int)
v4df __builtin_ia32_vpermilpd256 (v4df,int)
v4sf __builtin_ia32_vpermilps (v4sf,int)
v8sf __builtin_ia32_vpermilps256 (v8sf,int)
v2df __builtin_ia32_vpermilvarpd (v2df,v2di)
v4df __builtin_ia32_vpermilvarpd256 (v4df,v4di)
v4sf __builtin_ia32_vpermilvarps (v4sf,v4si)
v8sf __builtin_ia32_vpermilvarps256 (v8sf,v8si)
int __builtin_ia32_vtestcpd (v2df,v2df,ptest)
int __builtin_ia32_vtestcpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestcps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestcps256 (v8sf,v8sf,ptest)
int __builtin_ia32_vtestnzcpd (v2df,v2df,ptest)
int __builtin_ia32_vtestnzcpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestnzcps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestnzcps256 (v8sf,v8sf,ptest)
int __builtin_ia32_vtestzpd (v2df,v2df,ptest)
int __builtin_ia32_vtestzpd256 (v4df,v4df,ptest)
int __builtin_ia32_vtestzps (v4sf,v4sf,ptest)
int __builtin_ia32_vtestzps256 (v8sf,v8sf,ptest)
void __builtin_ia32_vzeroall (void)
void __builtin_ia32_vzeroupper (void)
v4df __builtin_ia32_xorpd256 (v4df,v4df)
v8sf __builtin_ia32_xorps256 (v8sf,v8sf)
@end smallexample

The following built-in functions are available when @option{-mavx2} is
used. All of them generate the machine instruction that is part of the
name.

@smallexample
v32qi __builtin_ia32_mpsadbw256 (v32qi,v32qi,v32qi,int)
v32qi __builtin_ia32_pabsb256 (v32qi)
v16hi __builtin_ia32_pabsw256 (v16hi)
v8si __builtin_ia32_pabsd256 (v8si)
v16hi __builtin_ia32_packssdw256 (v8si,v8si)
v32qi __builtin_ia32_packsswb256 (v16hi,v16hi)
v16hi __builtin_ia32_packusdw256 (v8si,v8si)
v32qi __builtin_ia32_packuswb256 (v16hi,v16hi)
v32qi __builtin_ia32_paddb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddw256 (v16hi,v16hi)
v8si __builtin_ia32_paddd256 (v8si,v8si)
v4di __builtin_ia32_paddq256 (v4di,v4di)
v32qi __builtin_ia32_paddsb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddsw256 (v16hi,v16hi)
v32qi __builtin_ia32_paddusb256 (v32qi,v32qi)
v16hi __builtin_ia32_paddusw256 (v16hi,v16hi)
v4di __builtin_ia32_palignr256 (v4di,v4di,int)
v4di __builtin_ia32_andsi256 (v4di,v4di)
v4di __builtin_ia32_andnotsi256 (v4di,v4di)
v32qi __builtin_ia32_pavgb256 (v32qi,v32qi)
v16hi __builtin_ia32_pavgw256 (v16hi,v16hi)
v32qi __builtin_ia32_pblendvb256 (v32qi,v32qi,v32qi)
v16hi __builtin_ia32_pblendw256 (v16hi,v16hi,int)
v32qi __builtin_ia32_pcmpeqb256 (v32qi,v32qi)
v16hi __builtin_ia32_pcmpeqw256 (v16hi,v16hi)
v8si __builtin_ia32_pcmpeqd256 (c8si,v8si)
v4di __builtin_ia32_pcmpeqq256 (v4di,v4di)
v32qi __builtin_ia32_pcmpgtb256 (v32qi,v32qi)
v16hi __builtin_ia32_pcmpgtw256 (16hi,v16hi)
v8si __builtin_ia32_pcmpgtd256 (v8si,v8si)
v4di __builtin_ia32_pcmpgtq256 (v4di,v4di)
v16hi __builtin_ia32_phaddw256 (v16hi,v16hi)
v8si __builtin_ia32_phaddd256 (v8si,v8si)
v16hi __builtin_ia32_phaddsw256 (v16hi,v16hi)
v16hi __builtin_ia32_phsubw256 (v16hi,v16hi)
v8si __builtin_ia32_phsubd256 (v8si,v8si)
v16hi __builtin_ia32_phsubsw256 (v16hi,v16hi)
v32qi __builtin_ia32_pmaddubsw256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaddwd256 (v16hi,v16hi)
v32qi __builtin_ia32_pmaxsb256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaxsw256 (v16hi,v16hi)
v8si __builtin_ia32_pmaxsd256 (v8si,v8si)
v32qi __builtin_ia32_pmaxub256 (v32qi,v32qi)
v16hi __builtin_ia32_pmaxuw256 (v16hi,v16hi)
v8si __builtin_ia32_pmaxud256 (v8si,v8si)
v32qi __builtin_ia32_pminsb256 (v32qi,v32qi)
v16hi __builtin_ia32_pminsw256 (v16hi,v16hi)
v8si __builtin_ia32_pminsd256 (v8si,v8si)
v32qi __builtin_ia32_pminub256 (v32qi,v32qi)
v16hi __builtin_ia32_pminuw256 (v16hi,v16hi)
v8si __builtin_ia32_pminud256 (v8si,v8si)
int __builtin_ia32_pmovmskb256 (v32qi)
v16hi __builtin_ia32_pmovsxbw256 (v16qi)
v8si __builtin_ia32_pmovsxbd256 (v16qi)
v4di __builtin_ia32_pmovsxbq256 (v16qi)
v8si __builtin_ia32_pmovsxwd256 (v8hi)
v4di __builtin_ia32_pmovsxwq256 (v8hi)
v4di __builtin_ia32_pmovsxdq256 (v4si)
v16hi __builtin_ia32_pmovzxbw256 (v16qi)
v8si __builtin_ia32_pmovzxbd256 (v16qi)
v4di __builtin_ia32_pmovzxbq256 (v16qi)
v8si __builtin_ia32_pmovzxwd256 (v8hi)
v4di __builtin_ia32_pmovzxwq256 (v8hi)
v4di __builtin_ia32_pmovzxdq256 (v4si)
v4di __builtin_ia32_pmuldq256 (v8si,v8si)
v16hi __builtin_ia32_pmulhrsw256 (v16hi, v16hi)
v16hi __builtin_ia32_pmulhuw256 (v16hi,v16hi)
v16hi __builtin_ia32_pmulhw256 (v16hi,v16hi)
v16hi __builtin_ia32_pmullw256 (v16hi,v16hi)
v8si __builtin_ia32_pmulld256 (v8si,v8si)
v4di __builtin_ia32_pmuludq256 (v8si,v8si)
v4di __builtin_ia32_por256 (v4di,v4di)
v16hi __builtin_ia32_psadbw256 (v32qi,v32qi)
v32qi __builtin_ia32_pshufb256 (v32qi,v32qi)
v8si __builtin_ia32_pshufd256 (v8si,int)
v16hi __builtin_ia32_pshufhw256 (v16hi,int)
v16hi __builtin_ia32_pshuflw256 (v16hi,int)
v32qi __builtin_ia32_psignb256 (v32qi,v32qi)
v16hi __builtin_ia32_psignw256 (v16hi,v16hi)
v8si __builtin_ia32_psignd256 (v8si,v8si)
v4di __builtin_ia32_pslldqi256 (v4di,int)
v16hi __builtin_ia32_psllwi256 (16hi,int)
v16hi __builtin_ia32_psllw256(v16hi,v8hi)
v8si __builtin_ia32_pslldi256 (v8si,int)
v8si __builtin_ia32_pslld256(v8si,v4si)
v4di __builtin_ia32_psllqi256 (v4di,int)
v4di __builtin_ia32_psllq256(v4di,v2di)
v16hi __builtin_ia32_psrawi256 (v16hi,int)
v16hi __builtin_ia32_psraw256 (v16hi,v8hi)
v8si __builtin_ia32_psradi256 (v8si,int)
v8si __builtin_ia32_psrad256 (v8si,v4si)
v4di __builtin_ia32_psrldqi256 (v4di, int)
v16hi __builtin_ia32_psrlwi256 (v16hi,int)
v16hi __builtin_ia32_psrlw256 (v16hi,v8hi)
v8si __builtin_ia32_psrldi256 (v8si,int)
v8si __builtin_ia32_psrld256 (v8si,v4si)
v4di __builtin_ia32_psrlqi256 (v4di,int)
v4di __builtin_ia32_psrlq256(v4di,v2di)
v32qi __builtin_ia32_psubb256 (v32qi,v32qi)
v32hi __builtin_ia32_psubw256 (v16hi,v16hi)
v8si __builtin_ia32_psubd256 (v8si,v8si)
v4di __builtin_ia32_psubq256 (v4di,v4di)
v32qi __builtin_ia32_psubsb256 (v32qi,v32qi)
v16hi __builtin_ia32_psubsw256 (v16hi,v16hi)
v32qi __builtin_ia32_psubusb256 (v32qi,v32qi)
v16hi __builtin_ia32_psubusw256 (v16hi,v16hi)
v32qi __builtin_ia32_punpckhbw256 (v32qi,v32qi)
v16hi __builtin_ia32_punpckhwd256 (v16hi,v16hi)
v8si __builtin_ia32_punpckhdq256 (v8si,v8si)
v4di __builtin_ia32_punpckhqdq256 (v4di,v4di)
v32qi __builtin_ia32_punpcklbw256 (v32qi,v32qi)
v16hi __builtin_ia32_punpcklwd256 (v16hi,v16hi)
v8si __builtin_ia32_punpckldq256 (v8si,v8si)
v4di __builtin_ia32_punpcklqdq256 (v4di,v4di)
v4di __builtin_ia32_pxor256 (v4di,v4di)
v4di __builtin_ia32_movntdqa256 (pv4di)
v4sf __builtin_ia32_vbroadcastss_ps (v4sf)
v8sf __builtin_ia32_vbroadcastss_ps256 (v4sf)
v4df __builtin_ia32_vbroadcastsd_pd256 (v2df)
v4di __builtin_ia32_vbroadcastsi256 (v2di)
v4si __builtin_ia32_pblendd128 (v4si,v4si)
v8si __builtin_ia32_pblendd256 (v8si,v8si)
v32qi __builtin_ia32_pbroadcastb256 (v16qi)
v16hi __builtin_ia32_pbroadcastw256 (v8hi)
v8si __builtin_ia32_pbroadcastd256 (v4si)
v4di __builtin_ia32_pbroadcastq256 (v2di)
v16qi __builtin_ia32_pbroadcastb128 (v16qi)
v8hi __builtin_ia32_pbroadcastw128 (v8hi)
v4si __builtin_ia32_pbroadcastd128 (v4si)
v2di __builtin_ia32_pbroadcastq128 (v2di)
v8si __builtin_ia32_permvarsi256 (v8si,v8si)
v4df __builtin_ia32_permdf256 (v4df,int)
v8sf __builtin_ia32_permvarsf256 (v8sf,v8sf)
v4di __builtin_ia32_permdi256 (v4di,int)
v4di __builtin_ia32_permti256 (v4di,v4di,int)
v4di __builtin_ia32_extract128i256 (v4di,int)
v4di __builtin_ia32_insert128i256 (v4di,v2di,int)
v8si __builtin_ia32_maskloadd256 (pcv8si,v8si)
v4di __builtin_ia32_maskloadq256 (pcv4di,v4di)
v4si __builtin_ia32_maskloadd (pcv4si,v4si)
v2di __builtin_ia32_maskloadq (pcv2di,v2di)
void __builtin_ia32_maskstored256 (pv8si,v8si,v8si)
void __builtin_ia32_maskstoreq256 (pv4di,v4di,v4di)
void __builtin_ia32_maskstored (pv4si,v4si,v4si)
void __builtin_ia32_maskstoreq (pv2di,v2di,v2di)
v8si __builtin_ia32_psllv8si (v8si,v8si)
v4si __builtin_ia32_psllv4si (v4si,v4si)
v4di __builtin_ia32_psllv4di (v4di,v4di)
v2di __builtin_ia32_psllv2di (v2di,v2di)
v8si __builtin_ia32_psrav8si (v8si,v8si)
v4si __builtin_ia32_psrav4si (v4si,v4si)
v8si __builtin_ia32_psrlv8si (v8si,v8si)
v4si __builtin_ia32_psrlv4si (v4si,v4si)
v4di __builtin_ia32_psrlv4di (v4di,v4di)
v2di __builtin_ia32_psrlv2di (v2di,v2di)
v2df __builtin_ia32_gathersiv2df (v2df, pcdouble,v4si,v2df,int)
v4df __builtin_ia32_gathersiv4df (v4df, pcdouble,v4si,v4df,int)
v2df __builtin_ia32_gatherdiv2df (v2df, pcdouble,v2di,v2df,int)
v4df __builtin_ia32_gatherdiv4df (v4df, pcdouble,v4di,v4df,int)
v4sf __builtin_ia32_gathersiv4sf (v4sf, pcfloat,v4si,v4sf,int)
v8sf __builtin_ia32_gathersiv8sf (v8sf, pcfloat,v8si,v8sf,int)
v4sf __builtin_ia32_gatherdiv4sf (v4sf, pcfloat,v2di,v4sf,int)
v4sf __builtin_ia32_gatherdiv4sf256 (v4sf, pcfloat,v4di,v4sf,int)
v2di __builtin_ia32_gathersiv2di (v2di, pcint64,v4si,v2di,int)
v4di __builtin_ia32_gathersiv4di (v4di, pcint64,v4si,v4di,int)
v2di __builtin_ia32_gatherdiv2di (v2di, pcint64,v2di,v2di,int)
v4di __builtin_ia32_gatherdiv4di (v4di, pcint64,v4di,v4di,int)
v4si __builtin_ia32_gathersiv4si (v4si, pcint,v4si,v4si,int)
v8si __builtin_ia32_gathersiv8si (v8si, pcint,v8si,v8si,int)
v4si __builtin_ia32_gatherdiv4si (v4si, pcint,v2di,v4si,int)
v4si __builtin_ia32_gatherdiv4si256 (v4si, pcint,v4di,v4si,int)
@end smallexample

The following built-in functions are available when @option{-maes} is
used.  All of them generate the machine instruction that is part of the
name.

@smallexample
v2di __builtin_ia32_aesenc128 (v2di, v2di)
v2di __builtin_ia32_aesenclast128 (v2di, v2di)
v2di __builtin_ia32_aesdec128 (v2di, v2di)
v2di __builtin_ia32_aesdeclast128 (v2di, v2di)
v2di __builtin_ia32_aeskeygenassist128 (v2di, const int)
v2di __builtin_ia32_aesimc128 (v2di)
@end smallexample

The following built-in function is available when @option{-mpclmul} is
used.

@table @code
@item v2di __builtin_ia32_pclmulqdq128 (v2di, v2di, const int)
Generates the @code{pclmulqdq} machine instruction.
@end table

The following built-in function is available when @option{-mfsgsbase} is
used.  All of them generate the machine instruction that is part of the
name.

@smallexample
unsigned int __builtin_ia32_rdfsbase32 (void)
unsigned long long __builtin_ia32_rdfsbase64 (void)
unsigned int __builtin_ia32_rdgsbase32 (void)
unsigned long long __builtin_ia32_rdgsbase64 (void)
void _writefsbase_u32 (unsigned int)
void _writefsbase_u64 (unsigned long long)
void _writegsbase_u32 (unsigned int)
void _writegsbase_u64 (unsigned long long)
@end smallexample

The following built-in function is available when @option{-mrdrnd} is
used.  All of them generate the machine instruction that is part of the
name.

@smallexample
unsigned int __builtin_ia32_rdrand16_step (unsigned short *)
unsigned int __builtin_ia32_rdrand32_step (unsigned int *)
unsigned int __builtin_ia32_rdrand64_step (unsigned long long *)
@end smallexample

The following built-in functions are available when @option{-msse4a} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
void __builtin_ia32_movntsd (double *, v2df)
void __builtin_ia32_movntss (float *, v4sf)
v2di __builtin_ia32_extrq  (v2di, v16qi)
v2di __builtin_ia32_extrqi (v2di, const unsigned int, const unsigned int)
v2di __builtin_ia32_insertq (v2di, v2di)
v2di __builtin_ia32_insertqi (v2di, v2di, const unsigned int, const unsigned int)
@end smallexample

The following built-in functions are available when @option{-mxop} is used.
@smallexample
v2df __builtin_ia32_vfrczpd (v2df)
v4sf __builtin_ia32_vfrczps (v4sf)
v2df __builtin_ia32_vfrczsd (v2df, v2df)
v4sf __builtin_ia32_vfrczss (v4sf, v4sf)
v4df __builtin_ia32_vfrczpd256 (v4df)
v8sf __builtin_ia32_vfrczps256 (v8sf)
v2di __builtin_ia32_vpcmov (v2di, v2di, v2di)
v2di __builtin_ia32_vpcmov_v2di (v2di, v2di, v2di)
v4si __builtin_ia32_vpcmov_v4si (v4si, v4si, v4si)
v8hi __builtin_ia32_vpcmov_v8hi (v8hi, v8hi, v8hi)
v16qi __builtin_ia32_vpcmov_v16qi (v16qi, v16qi, v16qi)
v2df __builtin_ia32_vpcmov_v2df (v2df, v2df, v2df)
v4sf __builtin_ia32_vpcmov_v4sf (v4sf, v4sf, v4sf)
v4di __builtin_ia32_vpcmov_v4di256 (v4di, v4di, v4di)
v8si __builtin_ia32_vpcmov_v8si256 (v8si, v8si, v8si)
v16hi __builtin_ia32_vpcmov_v16hi256 (v16hi, v16hi, v16hi)
v32qi __builtin_ia32_vpcmov_v32qi256 (v32qi, v32qi, v32qi)
v4df __builtin_ia32_vpcmov_v4df256 (v4df, v4df, v4df)
v8sf __builtin_ia32_vpcmov_v8sf256 (v8sf, v8sf, v8sf)
v16qi __builtin_ia32_vpcomeqb (v16qi, v16qi)
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
v4si __builtin_ia32_vpcomeqd (v4si, v4si)
v2di __builtin_ia32_vpcomeqq (v2di, v2di)
v16qi __builtin_ia32_vpcomequb (v16qi, v16qi)
v4si __builtin_ia32_vpcomequd (v4si, v4si)
v2di __builtin_ia32_vpcomequq (v2di, v2di)
v8hi __builtin_ia32_vpcomequw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomeqw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomfalseb (v16qi, v16qi)
v4si __builtin_ia32_vpcomfalsed (v4si, v4si)
v2di __builtin_ia32_vpcomfalseq (v2di, v2di)
v16qi __builtin_ia32_vpcomfalseub (v16qi, v16qi)
v4si __builtin_ia32_vpcomfalseud (v4si, v4si)
v2di __builtin_ia32_vpcomfalseuq (v2di, v2di)
v8hi __builtin_ia32_vpcomfalseuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomfalsew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomgeb (v16qi, v16qi)
v4si __builtin_ia32_vpcomged (v4si, v4si)
v2di __builtin_ia32_vpcomgeq (v2di, v2di)
v16qi __builtin_ia32_vpcomgeub (v16qi, v16qi)
v4si __builtin_ia32_vpcomgeud (v4si, v4si)
v2di __builtin_ia32_vpcomgeuq (v2di, v2di)
v8hi __builtin_ia32_vpcomgeuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomgew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomgtb (v16qi, v16qi)
v4si __builtin_ia32_vpcomgtd (v4si, v4si)
v2di __builtin_ia32_vpcomgtq (v2di, v2di)
v16qi __builtin_ia32_vpcomgtub (v16qi, v16qi)
v4si __builtin_ia32_vpcomgtud (v4si, v4si)
v2di __builtin_ia32_vpcomgtuq (v2di, v2di)
v8hi __builtin_ia32_vpcomgtuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomgtw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomleb (v16qi, v16qi)
v4si __builtin_ia32_vpcomled (v4si, v4si)
v2di __builtin_ia32_vpcomleq (v2di, v2di)
v16qi __builtin_ia32_vpcomleub (v16qi, v16qi)
v4si __builtin_ia32_vpcomleud (v4si, v4si)
v2di __builtin_ia32_vpcomleuq (v2di, v2di)
v8hi __builtin_ia32_vpcomleuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomlew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomltb (v16qi, v16qi)
v4si __builtin_ia32_vpcomltd (v4si, v4si)
v2di __builtin_ia32_vpcomltq (v2di, v2di)
v16qi __builtin_ia32_vpcomltub (v16qi, v16qi)
v4si __builtin_ia32_vpcomltud (v4si, v4si)
v2di __builtin_ia32_vpcomltuq (v2di, v2di)
v8hi __builtin_ia32_vpcomltuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomltw (v8hi, v8hi)
v16qi __builtin_ia32_vpcomneb (v16qi, v16qi)
v4si __builtin_ia32_vpcomned (v4si, v4si)
v2di __builtin_ia32_vpcomneq (v2di, v2di)
v16qi __builtin_ia32_vpcomneub (v16qi, v16qi)
v4si __builtin_ia32_vpcomneud (v4si, v4si)
v2di __builtin_ia32_vpcomneuq (v2di, v2di)
v8hi __builtin_ia32_vpcomneuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomnew (v8hi, v8hi)
v16qi __builtin_ia32_vpcomtrueb (v16qi, v16qi)
v4si __builtin_ia32_vpcomtrued (v4si, v4si)
v2di __builtin_ia32_vpcomtrueq (v2di, v2di)
v16qi __builtin_ia32_vpcomtrueub (v16qi, v16qi)
v4si __builtin_ia32_vpcomtrueud (v4si, v4si)
v2di __builtin_ia32_vpcomtrueuq (v2di, v2di)
v8hi __builtin_ia32_vpcomtrueuw (v8hi, v8hi)
v8hi __builtin_ia32_vpcomtruew (v8hi, v8hi)
v4si __builtin_ia32_vphaddbd (v16qi)
v2di __builtin_ia32_vphaddbq (v16qi)
v8hi __builtin_ia32_vphaddbw (v16qi)
v2di __builtin_ia32_vphadddq (v4si)
v4si __builtin_ia32_vphaddubd (v16qi)
v2di __builtin_ia32_vphaddubq (v16qi)
v8hi __builtin_ia32_vphaddubw (v16qi)
v2di __builtin_ia32_vphaddudq (v4si)
v4si __builtin_ia32_vphadduwd (v8hi)
v2di __builtin_ia32_vphadduwq (v8hi)
v4si __builtin_ia32_vphaddwd (v8hi)
v2di __builtin_ia32_vphaddwq (v8hi)
v8hi __builtin_ia32_vphsubbw (v16qi)
v2di __builtin_ia32_vphsubdq (v4si)
v4si __builtin_ia32_vphsubwd (v8hi)
v4si __builtin_ia32_vpmacsdd (v4si, v4si, v4si)
v2di __builtin_ia32_vpmacsdqh (v4si, v4si, v2di)
v2di __builtin_ia32_vpmacsdql (v4si, v4si, v2di)
v4si __builtin_ia32_vpmacssdd (v4si, v4si, v4si)
v2di __builtin_ia32_vpmacssdqh (v4si, v4si, v2di)
v2di __builtin_ia32_vpmacssdql (v4si, v4si, v2di)
v4si __builtin_ia32_vpmacsswd (v8hi, v8hi, v4si)
v8hi __builtin_ia32_vpmacssww (v8hi, v8hi, v8hi)
v4si __builtin_ia32_vpmacswd (v8hi, v8hi, v4si)
v8hi __builtin_ia32_vpmacsww (v8hi, v8hi, v8hi)
v4si __builtin_ia32_vpmadcsswd (v8hi, v8hi, v4si)
v4si __builtin_ia32_vpmadcswd (v8hi, v8hi, v4si)
v16qi __builtin_ia32_vpperm (v16qi, v16qi, v16qi)
v16qi __builtin_ia32_vprotb (v16qi, v16qi)
v4si __builtin_ia32_vprotd (v4si, v4si)
v2di __builtin_ia32_vprotq (v2di, v2di)
v8hi __builtin_ia32_vprotw (v8hi, v8hi)
v16qi __builtin_ia32_vpshab (v16qi, v16qi)
v4si __builtin_ia32_vpshad (v4si, v4si)
v2di __builtin_ia32_vpshaq (v2di, v2di)
v8hi __builtin_ia32_vpshaw (v8hi, v8hi)
v16qi __builtin_ia32_vpshlb (v16qi, v16qi)
v4si __builtin_ia32_vpshld (v4si, v4si)
v2di __builtin_ia32_vpshlq (v2di, v2di)
v8hi __builtin_ia32_vpshlw (v8hi, v8hi)
@end smallexample

The following built-in functions are available when @option{-mfma4} is used.
All of them generate the machine instruction that is part of the name
with MMX registers.

@smallexample
v2df __builtin_ia32_fmaddpd (v2df, v2df, v2df)
v4sf __builtin_ia32_fmaddps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fmaddsd (v2df, v2df, v2df)
v4sf __builtin_ia32_fmaddss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fmsubpd (v2df, v2df, v2df)
v4sf __builtin_ia32_fmsubps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fmsubsd (v2df, v2df, v2df)
v4sf __builtin_ia32_fmsubss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fnmaddpd (v2df, v2df, v2df)
v4sf __builtin_ia32_fnmaddps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fnmaddsd (v2df, v2df, v2df)
v4sf __builtin_ia32_fnmaddss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fnmsubpd (v2df, v2df, v2df)
v4sf __builtin_ia32_fnmsubps (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fnmsubsd (v2df, v2df, v2df)
v4sf __builtin_ia32_fnmsubss (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fmaddsubpd  (v2df, v2df, v2df)
v4sf __builtin_ia32_fmaddsubps  (v4sf, v4sf, v4sf)
v2df __builtin_ia32_fmsubaddpd  (v2df, v2df, v2df)
v4sf __builtin_ia32_fmsubaddps  (v4sf, v4sf, v4sf)
v4df __builtin_ia32_fmaddpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_fmaddps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_fmsubpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_fmsubps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_fnmaddpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_fnmaddps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_fnmsubpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_fnmsubps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_fmaddsubpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_fmaddsubps256 (v8sf, v8sf, v8sf)
v4df __builtin_ia32_fmsubaddpd256 (v4df, v4df, v4df)
v8sf __builtin_ia32_fmsubaddps256 (v8sf, v8sf, v8sf)

@end smallexample

The following built-in functions are available when @option{-mlwp} is used.

@smallexample
void __builtin_ia32_llwpcb16 (void *);
void __builtin_ia32_llwpcb32 (void *);
void __builtin_ia32_llwpcb64 (void *);
void * __builtin_ia32_llwpcb16 (void);
void * __builtin_ia32_llwpcb32 (void);
void * __builtin_ia32_llwpcb64 (void);
void __builtin_ia32_lwpval16 (unsigned short, unsigned int, unsigned short)
void __builtin_ia32_lwpval32 (unsigned int, unsigned int, unsigned int)
void __builtin_ia32_lwpval64 (unsigned __int64, unsigned int, unsigned int)
unsigned char __builtin_ia32_lwpins16 (unsigned short, unsigned int, unsigned short)
unsigned char __builtin_ia32_lwpins32 (unsigned int, unsigned int, unsigned int)
unsigned char __builtin_ia32_lwpins64 (unsigned __int64, unsigned int, unsigned int)
@end smallexample

The following built-in functions are available when @option{-mbmi} is used.
All of them generate the machine instruction that is part of the name.
@smallexample
unsigned int __builtin_ia32_bextr_u32(unsigned int, unsigned int);
unsigned long long __builtin_ia32_bextr_u64 (unsigned long long, unsigned long long);
@end smallexample

The following built-in functions are available when @option{-mbmi2} is used.
All of them generate the machine instruction that is part of the name.
@smallexample
unsigned int _bzhi_u32 (unsigned int, unsigned int)
unsigned int _pdep_u32 (unsigned int, unsigned int)
unsigned int _pext_u32 (unsigned int, unsigned int)
unsigned long long _bzhi_u64 (unsigned long long, unsigned long long)
unsigned long long _pdep_u64 (unsigned long long, unsigned long long)
unsigned long long _pext_u64 (unsigned long long, unsigned long long)
@end smallexample

The following built-in functions are available when @option{-mlzcnt} is used.
All of them generate the machine instruction that is part of the name.
@smallexample
unsigned short __builtin_ia32_lzcnt_16(unsigned short);
unsigned int __builtin_ia32_lzcnt_u32(unsigned int);
unsigned long long __builtin_ia32_lzcnt_u64 (unsigned long long);
@end smallexample

The following built-in functions are available when @option{-mtbm} is used.
Both of them generate the immediate form of the bextr machine instruction.
@smallexample
unsigned int __builtin_ia32_bextri_u32 (unsigned int, const unsigned int);
unsigned long long __builtin_ia32_bextri_u64 (unsigned long long, const unsigned long long);
@end smallexample


The following built-in functions are available when @option{-m3dnow} is used.
All of them generate the machine instruction that is part of the name.

@smallexample
void __builtin_ia32_femms (void)
v8qi __builtin_ia32_pavgusb (v8qi, v8qi)
v2si __builtin_ia32_pf2id (v2sf)
v2sf __builtin_ia32_pfacc (v2sf, v2sf)
v2sf __builtin_ia32_pfadd (v2sf, v2sf)
v2si __builtin_ia32_pfcmpeq (v2sf, v2sf)
v2si __builtin_ia32_pfcmpge (v2sf, v2sf)
v2si __builtin_ia32_pfcmpgt (v2sf, v2sf)
v2sf __builtin_ia32_pfmax (v2sf, v2sf)
v2sf __builtin_ia32_pfmin (v2sf, v2sf)
v2sf __builtin_ia32_pfmul (v2sf, v2sf)
v2sf __builtin_ia32_pfrcp (v2sf)
v2sf __builtin_ia32_pfrcpit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfrcpit2 (v2sf, v2sf)
v2sf __builtin_ia32_pfrsqrt (v2sf)
v2sf __builtin_ia32_pfrsqrtit1 (v2sf, v2sf)
v2sf __builtin_ia32_pfsub (v2sf, v2sf)
v2sf __builtin_ia32_pfsubr (v2sf, v2sf)
v2sf __builtin_ia32_pi2fd (v2si)
v4hi __builtin_ia32_pmulhrw (v4hi, v4hi)
@end smallexample

The following built-in functions are available when both @option{-m3dnow}
and @option{-march=athlon} are used.  All of them generate the machine
instruction that is part of the name.

@smallexample
v2si __builtin_ia32_pf2iw (v2sf)
v2sf __builtin_ia32_pfnacc (v2sf, v2sf)
v2sf __builtin_ia32_pfpnacc (v2sf, v2sf)
v2sf __builtin_ia32_pi2fw (v2si)
v2sf __builtin_ia32_pswapdsf (v2sf)
v2si __builtin_ia32_pswapdsi (v2si)
@end smallexample

The following built-in functions are available when @option{-mrtm} is used
They are used for restricted transactional memory. These are the internal
low level functions. Normally the functions in 
@ref{X86 transactional memory intrinsics} should be used instead.

@smallexample
int __builtin_ia32_xbegin ()
void __builtin_ia32_xend ()
void __builtin_ia32_xabort (status)
int __builtin_ia32_xtest ()
@end smallexample

@node X86 transactional memory intrinsics
@subsection X86 transaction memory intrinsics

Hardware transactional memory intrinsics for i386. These allow to use
memory transactions with RTM (Restricted Transactional Memory).
For using HLE (Hardware Lock Elision) see @ref{x86 specific memory model extensions for transactional memory} instead.
This support is enabled with the @option{-mrtm} option.

A memory transaction commits all changes to memory in an atomic way,
as visible to other threads. If the transaction fails it is rolled back
and all side effects discarded.

Generally there is no guarantee that a memory transaction ever suceeds
and suitable fallback code always needs to be supplied.

@deftypefn {RTM Function} {unsigned} _xbegin ()
Start a RTM (Restricted Transactional Memory) transaction. 
Returns _XBEGIN_STARTED when the transaction
started successfully (note this is not 0, so the constant has to be 
explicitely tested). When the transaction aborts all side effects
are undone and an abort code is returned. There is no guarantee
any transaction ever succeeds, so there always needs to be a valid
tested fallback path.
@end deftypefn

@smallexample
#include <immintrin.h>

if ((status = _xbegin ()) == _XBEGIN_STARTED) @{
    ... transaction code...
    _xend ();
@} else @{
    ... non transactional fallback path...
@}
@end smallexample

Valid abort status bits (when the value is not @code{_XBEGIN_STARTED}) are:

@table @code
@item _XABORT_EXPLICIT
Transaction explicitely aborted with @code{_xabort}. The parameter passed
to @code{_xabort} is available with @code{_XABORT_CODE(status)}
@item _XABORT_RETRY
Transaction retry is possible.
@item _XABORT_CONFLICT
Transaction abort due to a memory conflict with another thread
@item _XABORT_CAPACITY
Transaction abort due to the transaction using too much memory
@item _XABORT_DEBUG
Transaction abort due to a debug trap
@item _XABORT_NESTED
Transaction abort in a inner nested transaction
@end table

@deftypefn {RTM Function} {void} _xend ()
Commit the current transaction. When no transaction is active this will
fault. All memory side effects of the transactions will become visible
to other threads in an atomic matter.
@end deftypefn

@deftypefn {RTM Function} {int} _xtest ()
Return a value not zero when a transaction is currently active, otherwise 0.
@end deftypefn

@deftypefn {RTM Function} {void} _xabort (status)
Abort the current transaction. When no transaction is active this is a no-op.
status must be a 8bit constant, that is included in the status code returned
by @code{_xbegin}
@end deftypefn

@node MIPS DSP Built-in Functions
@subsection MIPS DSP Built-in Functions

The MIPS DSP Application-Specific Extension (ASE) includes new
instructions that are designed to improve the performance of DSP and
media applications.  It provides instructions that operate on packed
8-bit/16-bit integer data, Q7, Q15 and Q31 fractional data.

GCC supports MIPS DSP operations using both the generic
vector extensions (@pxref{Vector Extensions}) and a collection of
MIPS-specific built-in functions.  Both kinds of support are
enabled by the @option{-mdsp} command-line option.

Revision 2 of the ASE was introduced in the second half of 2006.
This revision adds extra instructions to the original ASE, but is
otherwise backwards-compatible with it.  You can select revision 2
using the command-line option @option{-mdspr2}; this option implies
@option{-mdsp}.

The SCOUNT and POS bits of the DSP control register are global.  The
WRDSP, EXTPDP, EXTPDPV and MTHLIP instructions modify the SCOUNT and
POS bits.  During optimization, the compiler does not delete these
instructions and it does not delete calls to functions containing
these instructions.

At present, GCC only provides support for operations on 32-bit
vectors.  The vector type associated with 8-bit integer data is
usually called @code{v4i8}, the vector type associated with Q7
is usually called @code{v4q7}, the vector type associated with 16-bit
integer data is usually called @code{v2i16}, and the vector type
associated with Q15 is usually called @code{v2q15}.  They can be
defined in C as follows:

@smallexample
typedef signed char v4i8 __attribute__ ((vector_size(4)));
typedef signed char v4q7 __attribute__ ((vector_size(4)));
typedef short v2i16 __attribute__ ((vector_size(4)));
typedef short v2q15 __attribute__ ((vector_size(4)));
@end smallexample

@code{v4i8}, @code{v4q7}, @code{v2i16} and @code{v2q15} values are
initialized in the same way as aggregates.  For example:

@smallexample
v4i8 a = @{1, 2, 3, 4@};
v4i8 b;
b = (v4i8) @{5, 6, 7, 8@};

v2q15 c = @{0x0fcb, 0x3a75@};
v2q15 d;
d = (v2q15) @{0.1234 * 0x1.0p15, 0.4567 * 0x1.0p15@};
@end smallexample

@emph{Note:} The CPU's endianness determines the order in which values
are packed.  On little-endian targets, the first value is the least
significant and the last value is the most significant.  The opposite
order applies to big-endian targets.  For example, the code above
sets the lowest byte of @code{a} to @code{1} on little-endian targets
and @code{4} on big-endian targets.

@emph{Note:} Q7, Q15 and Q31 values must be initialized with their integer
representation.  As shown in this example, the integer representation
of a Q7 value can be obtained by multiplying the fractional value by
@code{0x1.0p7}.  The equivalent for Q15 values is to multiply by
@code{0x1.0p15}.  The equivalent for Q31 values is to multiply by
@code{0x1.0p31}.

The table below lists the @code{v4i8} and @code{v2q15} operations for which
hardware support exists.  @code{a} and @code{b} are @code{v4i8} values,
and @code{c} and @code{d} are @code{v2q15} values.

@multitable @columnfractions .50 .50
@item C code @tab MIPS instruction
@item @code{a + b} @tab @code{addu.qb}
@item @code{c + d} @tab @code{addq.ph}
@item @code{a - b} @tab @code{subu.qb}
@item @code{c - d} @tab @code{subq.ph}
@end multitable

The table below lists the @code{v2i16} operation for which
hardware support exists for the DSP ASE REV 2.  @code{e} and @code{f} are
@code{v2i16} values.

@multitable @columnfractions .50 .50
@item C code @tab MIPS instruction
@item @code{e * f} @tab @code{mul.ph}
@end multitable

It is easier to describe the DSP built-in functions if we first define
the following types:

@smallexample
typedef int q31;
typedef int i32;
typedef unsigned int ui32;
typedef long long a64;
@end smallexample

@code{q31} and @code{i32} are actually the same as @code{int}, but we
use @code{q31} to indicate a Q31 fractional value and @code{i32} to
indicate a 32-bit integer value.  Similarly, @code{a64} is the same as
@code{long long}, but we use @code{a64} to indicate values that are
placed in one of the four DSP accumulators (@code{$ac0},
@code{$ac1}, @code{$ac2} or @code{$ac3}).

Also, some built-in functions prefer or require immediate numbers as
parameters, because the corresponding DSP instructions accept both immediate
numbers and register operands, or accept immediate numbers only.  The
immediate parameters are listed as follows.

@smallexample
imm0_3: 0 to 3.
imm0_7: 0 to 7.
imm0_15: 0 to 15.
imm0_31: 0 to 31.
imm0_63: 0 to 63.
imm0_255: 0 to 255.
imm_n32_31: -32 to 31.
imm_n512_511: -512 to 511.
@end smallexample

The following built-in functions map directly to a particular MIPS DSP
instruction.  Please refer to the architecture specification
for details on what each instruction does.

@smallexample
v2q15 __builtin_mips_addq_ph (v2q15, v2q15)
v2q15 __builtin_mips_addq_s_ph (v2q15, v2q15)
q31 __builtin_mips_addq_s_w (q31, q31)
v4i8 __builtin_mips_addu_qb (v4i8, v4i8)
v4i8 __builtin_mips_addu_s_qb (v4i8, v4i8)
v2q15 __builtin_mips_subq_ph (v2q15, v2q15)
v2q15 __builtin_mips_subq_s_ph (v2q15, v2q15)
q31 __builtin_mips_subq_s_w (q31, q31)
v4i8 __builtin_mips_subu_qb (v4i8, v4i8)
v4i8 __builtin_mips_subu_s_qb (v4i8, v4i8)
i32 __builtin_mips_addsc (i32, i32)
i32 __builtin_mips_addwc (i32, i32)
i32 __builtin_mips_modsub (i32, i32)
i32 __builtin_mips_raddu_w_qb (v4i8)
v2q15 __builtin_mips_absq_s_ph (v2q15)
q31 __builtin_mips_absq_s_w (q31)
v4i8 __builtin_mips_precrq_qb_ph (v2q15, v2q15)
v2q15 __builtin_mips_precrq_ph_w (q31, q31)
v2q15 __builtin_mips_precrq_rs_ph_w (q31, q31)
v4i8 __builtin_mips_precrqu_s_qb_ph (v2q15, v2q15)
q31 __builtin_mips_preceq_w_phl (v2q15)
q31 __builtin_mips_preceq_w_phr (v2q15)
v2q15 __builtin_mips_precequ_ph_qbl (v4i8)
v2q15 __builtin_mips_precequ_ph_qbr (v4i8)
v2q15 __builtin_mips_precequ_ph_qbla (v4i8)
v2q15 __builtin_mips_precequ_ph_qbra (v4i8)
v2q15 __builtin_mips_preceu_ph_qbl (v4i8)
v2q15 __builtin_mips_preceu_ph_qbr (v4i8)
v2q15 __builtin_mips_preceu_ph_qbla (v4i8)
v2q15 __builtin_mips_preceu_ph_qbra (v4i8)
v4i8 __builtin_mips_shll_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shll_qb (v4i8, i32)
v2q15 __builtin_mips_shll_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_ph (v2q15, i32)
v2q15 __builtin_mips_shll_s_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shll_s_ph (v2q15, i32)
q31 __builtin_mips_shll_s_w (q31, imm0_31)
q31 __builtin_mips_shll_s_w (q31, i32)
v4i8 __builtin_mips_shrl_qb (v4i8, imm0_7)
v4i8 __builtin_mips_shrl_qb (v4i8, i32)
v2q15 __builtin_mips_shra_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_ph (v2q15, i32)
v2q15 __builtin_mips_shra_r_ph (v2q15, imm0_15)
v2q15 __builtin_mips_shra_r_ph (v2q15, i32)
q31 __builtin_mips_shra_r_w (q31, imm0_31)
q31 __builtin_mips_shra_r_w (q31, i32)
v2q15 __builtin_mips_muleu_s_ph_qbl (v4i8, v2q15)
v2q15 __builtin_mips_muleu_s_ph_qbr (v4i8, v2q15)
v2q15 __builtin_mips_mulq_rs_ph (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phl (v2q15, v2q15)
q31 __builtin_mips_muleq_s_w_phr (v2q15, v2q15)
a64 __builtin_mips_dpau_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpau_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbl (a64, v4i8, v4i8)
a64 __builtin_mips_dpsu_h_qbr (a64, v4i8, v4i8)
a64 __builtin_mips_dpaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpaq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_dpsq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_dpsq_sa_l_w (a64, q31, q31)
a64 __builtin_mips_mulsaq_s_w_ph (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_s_w_phr (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phl (a64, v2q15, v2q15)
a64 __builtin_mips_maq_sa_w_phr (a64, v2q15, v2q15)
i32 __builtin_mips_bitrev (i32)
i32 __builtin_mips_insv (i32, i32)
v4i8 __builtin_mips_repl_qb (imm0_255)
v4i8 __builtin_mips_repl_qb (i32)
v2q15 __builtin_mips_repl_ph (imm_n512_511)
v2q15 __builtin_mips_repl_ph (i32)
void __builtin_mips_cmpu_eq_qb (v4i8, v4i8)
void __builtin_mips_cmpu_lt_qb (v4i8, v4i8)
void __builtin_mips_cmpu_le_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_eq_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_lt_qb (v4i8, v4i8)
i32 __builtin_mips_cmpgu_le_qb (v4i8, v4i8)
void __builtin_mips_cmp_eq_ph (v2q15, v2q15)
void __builtin_mips_cmp_lt_ph (v2q15, v2q15)
void __builtin_mips_cmp_le_ph (v2q15, v2q15)
v4i8 __builtin_mips_pick_qb (v4i8, v4i8)
v2q15 __builtin_mips_pick_ph (v2q15, v2q15)
v2q15 __builtin_mips_packrl_ph (v2q15, v2q15)
i32 __builtin_mips_extr_w (a64, imm0_31)
i32 __builtin_mips_extr_w (a64, i32)
i32 __builtin_mips_extr_r_w (a64, imm0_31)
i32 __builtin_mips_extr_s_h (a64, i32)
i32 __builtin_mips_extr_rs_w (a64, imm0_31)
i32 __builtin_mips_extr_rs_w (a64, i32)
i32 __builtin_mips_extr_s_h (a64, imm0_31)
i32 __builtin_mips_extr_r_w (a64, i32)
i32 __builtin_mips_extp (a64, imm0_31)
i32 __builtin_mips_extp (a64, i32)
i32 __builtin_mips_extpdp (a64, imm0_31)
i32 __builtin_mips_extpdp (a64, i32)
a64 __builtin_mips_shilo (a64, imm_n32_31)
a64 __builtin_mips_shilo (a64, i32)
a64 __builtin_mips_mthlip (a64, i32)
void __builtin_mips_wrdsp (i32, imm0_63)
i32 __builtin_mips_rddsp (imm0_63)
i32 __builtin_mips_lbux (void *, i32)
i32 __builtin_mips_lhx (void *, i32)
i32 __builtin_mips_lwx (void *, i32)
a64 __builtin_mips_ldx (void *, i32) [MIPS64 only]
i32 __builtin_mips_bposge32 (void)
a64 __builtin_mips_madd (a64, i32, i32);
a64 __builtin_mips_maddu (a64, ui32, ui32);
a64 __builtin_mips_msub (a64, i32, i32);
a64 __builtin_mips_msubu (a64, ui32, ui32);
a64 __builtin_mips_mult (i32, i32);
a64 __builtin_mips_multu (ui32, ui32);
@end smallexample

The following built-in functions map directly to a particular MIPS DSP REV 2
instruction.  Please refer to the architecture specification
for details on what each instruction does.

@smallexample
v4q7 __builtin_mips_absq_s_qb (v4q7);
v2i16 __builtin_mips_addu_ph (v2i16, v2i16);
v2i16 __builtin_mips_addu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_adduh_qb (v4i8, v4i8);
v4i8 __builtin_mips_adduh_r_qb (v4i8, v4i8);
i32 __builtin_mips_append (i32, i32, imm0_31);
i32 __builtin_mips_balign (i32, i32, imm0_3);
i32 __builtin_mips_cmpgdu_eq_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_lt_qb (v4i8, v4i8);
i32 __builtin_mips_cmpgdu_le_qb (v4i8, v4i8);
a64 __builtin_mips_dpa_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dps_w_ph (a64, v2i16, v2i16);
v2i16 __builtin_mips_mul_ph (v2i16, v2i16);
v2i16 __builtin_mips_mul_s_ph (v2i16, v2i16);
q31 __builtin_mips_mulq_rs_w (q31, q31);
v2q15 __builtin_mips_mulq_s_ph (v2q15, v2q15);
q31 __builtin_mips_mulq_s_w (q31, q31);
a64 __builtin_mips_mulsa_w_ph (a64, v2i16, v2i16);
v4i8 __builtin_mips_precr_qb_ph (v2i16, v2i16);
v2i16 __builtin_mips_precr_sra_ph_w (i32, i32, imm0_31);
v2i16 __builtin_mips_precr_sra_r_ph_w (i32, i32, imm0_31);
i32 __builtin_mips_prepend (i32, i32, imm0_31);
v4i8 __builtin_mips_shra_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_r_qb (v4i8, imm0_7);
v4i8 __builtin_mips_shra_qb (v4i8, i32);
v4i8 __builtin_mips_shra_r_qb (v4i8, i32);
v2i16 __builtin_mips_shrl_ph (v2i16, imm0_15);
v2i16 __builtin_mips_shrl_ph (v2i16, i32);
v2i16 __builtin_mips_subu_ph (v2i16, v2i16);
v2i16 __builtin_mips_subu_s_ph (v2i16, v2i16);
v4i8 __builtin_mips_subuh_qb (v4i8, v4i8);
v4i8 __builtin_mips_subuh_r_qb (v4i8, v4i8);
v2q15 __builtin_mips_addqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_addqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_addqh_w (q31, q31);
q31 __builtin_mips_addqh_r_w (q31, q31);
v2q15 __builtin_mips_subqh_ph (v2q15, v2q15);
v2q15 __builtin_mips_subqh_r_ph (v2q15, v2q15);
q31 __builtin_mips_subqh_w (q31, q31);
q31 __builtin_mips_subqh_r_w (q31, q31);
a64 __builtin_mips_dpax_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpsx_w_ph (a64, v2i16, v2i16);
a64 __builtin_mips_dpaqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpaqx_sa_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_s_w_ph (a64, v2q15, v2q15);
a64 __builtin_mips_dpsqx_sa_w_ph (a64, v2q15, v2q15);
@end smallexample


@node MIPS Paired-Single Support
@subsection MIPS Paired-Single Support

The MIPS64 architecture includes a number of instructions that
operate on pairs of single-precision floating-point values.
Each pair is packed into a 64-bit floating-point register,
with one element being designated the ``upper half'' and
the other being designated the ``lower half''.

GCC supports paired-single operations using both the generic
vector extensions (@pxref{Vector Extensions}) and a collection of
MIPS-specific built-in functions.  Both kinds of support are
enabled by the @option{-mpaired-single} command-line option.

The vector type associated with paired-single values is usually
called @code{v2sf}.  It can be defined in C as follows:

@smallexample
typedef float v2sf __attribute__ ((vector_size (8)));
@end smallexample

@code{v2sf} values are initialized in the same way as aggregates.
For example:

@smallexample
v2sf a = @{1.5, 9.1@};
v2sf b;
float e, f;
b = (v2sf) @{e, f@};
@end smallexample

@emph{Note:} The CPU's endianness determines which value is stored in
the upper half of a register and which value is stored in the lower half.
On little-endian targets, the first value is the lower one and the second
value is the upper one.  The opposite order applies to big-endian targets.
For example, the code above sets the lower half of @code{a} to
@code{1.5} on little-endian targets and @code{9.1} on big-endian targets.

@node MIPS Loongson Built-in Functions
@subsection MIPS Loongson Built-in Functions

GCC provides intrinsics to access the SIMD instructions provided by the
ST Microelectronics Loongson-2E and -2F processors.  These intrinsics,
available after inclusion of the @code{loongson.h} header file,
operate on the following 64-bit vector types:

@itemize
@item @code{uint8x8_t}, a vector of eight unsigned 8-bit integers;
@item @code{uint16x4_t}, a vector of four unsigned 16-bit integers;
@item @code{uint32x2_t}, a vector of two unsigned 32-bit integers;
@item @code{int8x8_t}, a vector of eight signed 8-bit integers;
@item @code{int16x4_t}, a vector of four signed 16-bit integers;
@item @code{int32x2_t}, a vector of two signed 32-bit integers.
@end itemize

The intrinsics provided are listed below; each is named after the
machine instruction to which it corresponds, with suffixes added as
appropriate to distinguish intrinsics that expand to the same machine
instruction yet have different argument types.  Refer to the architecture
documentation for a description of the functionality of each
instruction.

@smallexample
int16x4_t packsswh (int32x2_t s, int32x2_t t);
int8x8_t packsshb (int16x4_t s, int16x4_t t);
uint8x8_t packushb (uint16x4_t s, uint16x4_t t);
uint32x2_t paddw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t paddh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t paddb_u (uint8x8_t s, uint8x8_t t);
int32x2_t paddw_s (int32x2_t s, int32x2_t t);
int16x4_t paddh_s (int16x4_t s, int16x4_t t);
int8x8_t paddb_s (int8x8_t s, int8x8_t t);
uint64_t paddd_u (uint64_t s, uint64_t t);
int64_t paddd_s (int64_t s, int64_t t);
int16x4_t paddsh (int16x4_t s, int16x4_t t);
int8x8_t paddsb (int8x8_t s, int8x8_t t);
uint16x4_t paddush (uint16x4_t s, uint16x4_t t);
uint8x8_t paddusb (uint8x8_t s, uint8x8_t t);
uint64_t pandn_ud (uint64_t s, uint64_t t);
uint32x2_t pandn_uw (uint32x2_t s, uint32x2_t t);
uint16x4_t pandn_uh (uint16x4_t s, uint16x4_t t);
uint8x8_t pandn_ub (uint8x8_t s, uint8x8_t t);
int64_t pandn_sd (int64_t s, int64_t t);
int32x2_t pandn_sw (int32x2_t s, int32x2_t t);
int16x4_t pandn_sh (int16x4_t s, int16x4_t t);
int8x8_t pandn_sb (int8x8_t s, int8x8_t t);
uint16x4_t pavgh (uint16x4_t s, uint16x4_t t);
uint8x8_t pavgb (uint8x8_t s, uint8x8_t t);
uint32x2_t pcmpeqw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpeqh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpeqb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpeqw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpeqh_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpeqb_s (int8x8_t s, int8x8_t t);
uint32x2_t pcmpgtw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t pcmpgth_u (uint16x4_t s, uint16x4_t t);
uint8x8_t pcmpgtb_u (uint8x8_t s, uint8x8_t t);
int32x2_t pcmpgtw_s (int32x2_t s, int32x2_t t);
int16x4_t pcmpgth_s (int16x4_t s, int16x4_t t);
int8x8_t pcmpgtb_s (int8x8_t s, int8x8_t t);
uint16x4_t pextrh_u (uint16x4_t s, int field);
int16x4_t pextrh_s (int16x4_t s, int field);
uint16x4_t pinsrh_0_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_1_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_2_u (uint16x4_t s, uint16x4_t t);
uint16x4_t pinsrh_3_u (uint16x4_t s, uint16x4_t t);
int16x4_t pinsrh_0_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_1_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_2_s (int16x4_t s, int16x4_t t);
int16x4_t pinsrh_3_s (int16x4_t s, int16x4_t t);
int32x2_t pmaddhw (int16x4_t s, int16x4_t t);
int16x4_t pmaxsh (int16x4_t s, int16x4_t t);
uint8x8_t pmaxub (uint8x8_t s, uint8x8_t t);
int16x4_t pminsh (int16x4_t s, int16x4_t t);
uint8x8_t pminub (uint8x8_t s, uint8x8_t t);
uint8x8_t pmovmskb_u (uint8x8_t s);
int8x8_t pmovmskb_s (int8x8_t s);
uint16x4_t pmulhuh (uint16x4_t s, uint16x4_t t);
int16x4_t pmulhh (int16x4_t s, int16x4_t t);
int16x4_t pmullh (int16x4_t s, int16x4_t t);
int64_t pmuluw (uint32x2_t s, uint32x2_t t);
uint8x8_t pasubub (uint8x8_t s, uint8x8_t t);
uint16x4_t biadd (uint8x8_t s);
uint16x4_t psadbh (uint8x8_t s, uint8x8_t t);
uint16x4_t pshufh_u (uint16x4_t dest, uint16x4_t s, uint8_t order);
int16x4_t pshufh_s (int16x4_t dest, int16x4_t s, uint8_t order);
uint16x4_t psllh_u (uint16x4_t s, uint8_t amount);
int16x4_t psllh_s (int16x4_t s, uint8_t amount);
uint32x2_t psllw_u (uint32x2_t s, uint8_t amount);
int32x2_t psllw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrlh_u (uint16x4_t s, uint8_t amount);
int16x4_t psrlh_s (int16x4_t s, uint8_t amount);
uint32x2_t psrlw_u (uint32x2_t s, uint8_t amount);
int32x2_t psrlw_s (int32x2_t s, uint8_t amount);
uint16x4_t psrah_u (uint16x4_t s, uint8_t amount);
int16x4_t psrah_s (int16x4_t s, uint8_t amount);
uint32x2_t psraw_u (uint32x2_t s, uint8_t amount);
int32x2_t psraw_s (int32x2_t s, uint8_t amount);
uint32x2_t psubw_u (uint32x2_t s, uint32x2_t t);
uint16x4_t psubh_u (uint16x4_t s, uint16x4_t t);
uint8x8_t psubb_u (uint8x8_t s, uint8x8_t t);
int32x2_t psubw_s (int32x2_t s, int32x2_t t);
int16x4_t psubh_s (int16x4_t s, int16x4_t t);
int8x8_t psubb_s (int8x8_t s, int8x8_t t);
uint64_t psubd_u (uint64_t s, uint64_t t);
int64_t psubd_s (int64_t s, int64_t t);
int16x4_t psubsh (int16x4_t s, int16x4_t t);
int8x8_t psubsb (int8x8_t s, int8x8_t t);
uint16x4_t psubush (uint16x4_t s, uint16x4_t t);
uint8x8_t psubusb (uint8x8_t s, uint8x8_t t);
uint32x2_t punpckhwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpckhhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpckhbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpckhwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpckhhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpckhbh_s (int8x8_t s, int8x8_t t);
uint32x2_t punpcklwd_u (uint32x2_t s, uint32x2_t t);
uint16x4_t punpcklhw_u (uint16x4_t s, uint16x4_t t);
uint8x8_t punpcklbh_u (uint8x8_t s, uint8x8_t t);
int32x2_t punpcklwd_s (int32x2_t s, int32x2_t t);
int16x4_t punpcklhw_s (int16x4_t s, int16x4_t t);
int8x8_t punpcklbh_s (int8x8_t s, int8x8_t t);
@end smallexample

@menu
* Paired-Single Arithmetic::
* Paired-Single Built-in Functions::
* MIPS-3D Built-in Functions::
@end menu

@node Paired-Single Arithmetic
@subsubsection Paired-Single Arithmetic

The table below lists the @code{v2sf} operations for which hardware
support exists.  @code{a}, @code{b} and @code{c} are @code{v2sf}
values and @code{x} is an integral value.

@multitable @columnfractions .50 .50
@item C code @tab MIPS instruction
@item @code{a + b} @tab @code{add.ps}
@item @code{a - b} @tab @code{sub.ps}
@item @code{-a} @tab @code{neg.ps}
@item @code{a * b} @tab @code{mul.ps}
@item @code{a * b + c} @tab @code{madd.ps}
@item @code{a * b - c} @tab @code{msub.ps}
@item @code{-(a * b + c)} @tab @code{nmadd.ps}
@item @code{-(a * b - c)} @tab @code{nmsub.ps}
@item @code{x ? a : b} @tab @code{movn.ps}/@code{movz.ps}
@end multitable

Note that the multiply-accumulate instructions can be disabled
using the command-line option @code{-mno-fused-madd}.

@node Paired-Single Built-in Functions
@subsubsection Paired-Single Built-in Functions

The following paired-single functions map directly to a particular
MIPS instruction.  Please refer to the architecture specification
for details on what each instruction does.

@table @code
@item v2sf __builtin_mips_pll_ps (v2sf, v2sf)
Pair lower lower (@code{pll.ps}).

@item v2sf __builtin_mips_pul_ps (v2sf, v2sf)
Pair upper lower (@code{pul.ps}).

@item v2sf __builtin_mips_plu_ps (v2sf, v2sf)
Pair lower upper (@code{plu.ps}).

@item v2sf __builtin_mips_puu_ps (v2sf, v2sf)
Pair upper upper (@code{puu.ps}).

@item v2sf __builtin_mips_cvt_ps_s (float, float)
Convert pair to paired single (@code{cvt.ps.s}).

@item float __builtin_mips_cvt_s_pl (v2sf)
Convert pair lower to single (@code{cvt.s.pl}).

@item float __builtin_mips_cvt_s_pu (v2sf)
Convert pair upper to single (@code{cvt.s.pu}).

@item v2sf __builtin_mips_abs_ps (v2sf)
Absolute value (@code{abs.ps}).

@item v2sf __builtin_mips_alnv_ps (v2sf, v2sf, int)
Align variable (@code{alnv.ps}).

@emph{Note:} The value of the third parameter must be 0 or 4
modulo 8, otherwise the result is unpredictable.  Please read the
instruction description for details.
@end table

The following multi-instruction functions are also available.
In each case, @var{cond} can be any of the 16 floating-point conditions:
@code{f}, @code{un}, @code{eq}, @code{ueq}, @code{olt}, @code{ult},
@code{ole}, @code{ule}, @code{sf}, @code{ngle}, @code{seq}, @code{ngl},
@code{lt}, @code{nge}, @code{le} or @code{ngt}.

@table @code
@item v2sf __builtin_mips_movt_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx v2sf __builtin_mips_movf_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
Conditional move based on floating-point comparison (@code{c.@var{cond}.ps},
@code{movt.ps}/@code{movf.ps}).

The @code{movt} functions return the value @var{x} computed by:

@smallexample
c.@var{cond}.ps @var{cc},@var{a},@var{b}
mov.ps @var{x},@var{c}
movt.ps @var{x},@var{d},@var{cc}
@end smallexample

The @code{movf} functions are similar but use @code{movf.ps} instead
of @code{movt.ps}.

@item int __builtin_mips_upper_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_lower_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
Comparison of two paired-single values (@code{c.@var{cond}.ps},
@code{bc1t}/@code{bc1f}).

These functions compare @var{a} and @var{b} using @code{c.@var{cond}.ps}
and return either the upper or lower half of the result.  For example:

@smallexample
v2sf a, b;
if (__builtin_mips_upper_c_eq_ps (a, b))
  upper_halves_are_equal ();
else
  upper_halves_are_unequal ();

if (__builtin_mips_lower_c_eq_ps (a, b))
  lower_halves_are_equal ();
else
  lower_halves_are_unequal ();
@end smallexample
@end table

@node MIPS-3D Built-in Functions
@subsubsection MIPS-3D Built-in Functions

The MIPS-3D Application-Specific Extension (ASE) includes additional
paired-single instructions that are designed to improve the performance
of 3D graphics operations.  Support for these instructions is controlled
by the @option{-mips3d} command-line option.

The functions listed below map directly to a particular MIPS-3D
instruction.  Please refer to the architecture specification for
more details on what each instruction does.

@table @code
@item v2sf __builtin_mips_addr_ps (v2sf, v2sf)
Reduction add (@code{addr.ps}).

@item v2sf __builtin_mips_mulr_ps (v2sf, v2sf)
Reduction multiply (@code{mulr.ps}).

@item v2sf __builtin_mips_cvt_pw_ps (v2sf)
Convert paired single to paired word (@code{cvt.pw.ps}).

@item v2sf __builtin_mips_cvt_ps_pw (v2sf)
Convert paired word to paired single (@code{cvt.ps.pw}).

@item float __builtin_mips_recip1_s (float)
@itemx double __builtin_mips_recip1_d (double)
@itemx v2sf __builtin_mips_recip1_ps (v2sf)
Reduced-precision reciprocal (sequence step 1) (@code{recip1.@var{fmt}}).

@item float __builtin_mips_recip2_s (float, float)
@itemx double __builtin_mips_recip2_d (double, double)
@itemx v2sf __builtin_mips_recip2_ps (v2sf, v2sf)
Reduced-precision reciprocal (sequence step 2) (@code{recip2.@var{fmt}}).

@item float __builtin_mips_rsqrt1_s (float)
@itemx double __builtin_mips_rsqrt1_d (double)
@itemx v2sf __builtin_mips_rsqrt1_ps (v2sf)
Reduced-precision reciprocal square root (sequence step 1)
(@code{rsqrt1.@var{fmt}}).

@item float __builtin_mips_rsqrt2_s (float, float)
@itemx double __builtin_mips_rsqrt2_d (double, double)
@itemx v2sf __builtin_mips_rsqrt2_ps (v2sf, v2sf)
Reduced-precision reciprocal square root (sequence step 2)
(@code{rsqrt2.@var{fmt}}).
@end table

The following multi-instruction functions are also available.
In each case, @var{cond} can be any of the 16 floating-point conditions:
@code{f}, @code{un}, @code{eq}, @code{ueq}, @code{olt}, @code{ult},
@code{ole}, @code{ule}, @code{sf}, @code{ngle}, @code{seq},
@code{ngl}, @code{lt}, @code{nge}, @code{le} or @code{ngt}.

@table @code
@item int __builtin_mips_cabs_@var{cond}_s (float @var{a}, float @var{b})
@itemx int __builtin_mips_cabs_@var{cond}_d (double @var{a}, double @var{b})
Absolute comparison of two scalar values (@code{cabs.@var{cond}.@var{fmt}},
@code{bc1t}/@code{bc1f}).

These functions compare @var{a} and @var{b} using @code{cabs.@var{cond}.s}
or @code{cabs.@var{cond}.d} and return the result as a boolean value.
For example:

@smallexample
float a, b;
if (__builtin_mips_cabs_eq_s (a, b))
  true ();
else
  false ();
@end smallexample

@item int __builtin_mips_upper_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_lower_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
Absolute comparison of two paired-single values (@code{cabs.@var{cond}.ps},
@code{bc1t}/@code{bc1f}).

These functions compare @var{a} and @var{b} using @code{cabs.@var{cond}.ps}
and return either the upper or lower half of the result.  For example:

@smallexample
v2sf a, b;
if (__builtin_mips_upper_cabs_eq_ps (a, b))
  upper_halves_are_equal ();
else
  upper_halves_are_unequal ();

if (__builtin_mips_lower_cabs_eq_ps (a, b))
  lower_halves_are_equal ();
else
  lower_halves_are_unequal ();
@end smallexample

@item v2sf __builtin_mips_movt_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx v2sf __builtin_mips_movf_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
Conditional move based on absolute comparison (@code{cabs.@var{cond}.ps},
@code{movt.ps}/@code{movf.ps}).

The @code{movt} functions return the value @var{x} computed by:

@smallexample
cabs.@var{cond}.ps @var{cc},@var{a},@var{b}
mov.ps @var{x},@var{c}
movt.ps @var{x},@var{d},@var{cc}
@end smallexample

The @code{movf} functions are similar but use @code{movf.ps} instead
of @code{movt.ps}.

@item int __builtin_mips_any_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_all_c_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_any_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
@itemx int __builtin_mips_all_cabs_@var{cond}_ps (v2sf @var{a}, v2sf @var{b})
Comparison of two paired-single values
(@code{c.@var{cond}.ps}/@code{cabs.@var{cond}.ps},
@code{bc1any2t}/@code{bc1any2f}).

These functions compare @var{a} and @var{b} using @code{c.@var{cond}.ps}
or @code{cabs.@var{cond}.ps}.  The @code{any} forms return true if either
result is true and the @code{all} forms return true if both results are true.
For example:

@smallexample
v2sf a, b;
if (__builtin_mips_any_c_eq_ps (a, b))
  one_is_true ();
else
  both_are_false ();

if (__builtin_mips_all_c_eq_ps (a, b))
  both_are_true ();
else
  one_is_false ();
@end smallexample

@item int __builtin_mips_any_c_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx int __builtin_mips_all_c_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx int __builtin_mips_any_cabs_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
@itemx int __builtin_mips_all_cabs_@var{cond}_4s (v2sf @var{a}, v2sf @var{b}, v2sf @var{c}, v2sf @var{d})
Comparison of four paired-single values
(@code{c.@var{cond}.ps}/@code{cabs.@var{cond}.ps},
@code{bc1any4t}/@code{bc1any4f}).

These functions use @code{c.@var{cond}.ps} or @code{cabs.@var{cond}.ps}
to compare @var{a} with @var{b} and to compare @var{c} with @var{d}.
The @code{any} forms return true if any of the four results are true
and the @code{all} forms return true if all four results are true.
For example:

@smallexample
v2sf a, b, c, d;
if (__builtin_mips_any_c_eq_4s (a, b, c, d))
  some_are_true ();
else
  all_are_false ();

if (__builtin_mips_all_c_eq_4s (a, b, c, d))
  all_are_true ();
else
  some_are_false ();
@end smallexample
@end table

@node Other MIPS Built-in Functions
@subsection Other MIPS Built-in Functions

GCC provides other MIPS-specific built-in functions:

@table @code
@item void __builtin_mips_cache (int @var{op}, const volatile void *@var{addr})
Insert a @samp{cache} instruction with operands @var{op} and @var{addr}.
GCC defines the preprocessor macro @code{___GCC_HAVE_BUILTIN_MIPS_CACHE}
when this function is available.
@end table

@node picoChip Built-in Functions
@subsection picoChip Built-in Functions

GCC provides an interface to selected machine instructions from the
picoChip instruction set.

@table @code
@item int __builtin_sbc (int @var{value})
Sign bit count.  Return the number of consecutive bits in @var{value}
that have the same value as the sign bit.  The result is the number of
leading sign bits minus one, giving the number of redundant sign bits in
@var{value}.

@item int __builtin_byteswap (int @var{value})
Byte swap.  Return the result of swapping the upper and lower bytes of
@var{value}.

@item int __builtin_brev (int @var{value})
Bit reversal.  Return the result of reversing the bits in
@var{value}.  Bit 15 is swapped with bit 0, bit 14 is swapped with bit 1,
and so on.

@item int __builtin_adds (int @var{x}, int @var{y})
Saturating addition.  Return the result of adding @var{x} and @var{y},
storing the value 32767 if the result overflows.

@item int __builtin_subs (int @var{x}, int @var{y})
Saturating subtraction.  Return the result of subtracting @var{y} from
@var{x}, storing the value @minus{}32768 if the result overflows.

@item void __builtin_halt (void)
Halt.  The processor stops execution.  This built-in is useful for
implementing assertions.

@end table

@node PowerPC Built-in Functions
@subsection PowerPC Built-in Functions

These built-in functions are available for the PowerPC family of
processors:
@smallexample
float __builtin_recipdivf (float, float);
float __builtin_rsqrtf (float);
double __builtin_recipdiv (double, double);
double __builtin_rsqrt (double);
long __builtin_bpermd (long, long);
uint64_t __builtin_ppc_get_timebase ();
unsigned long __builtin_ppc_mftb ();
@end smallexample

The @code{vec_rsqrt}, @code{__builtin_rsqrt}, and
@code{__builtin_rsqrtf} functions generate multiple instructions to
implement the reciprocal sqrt functionality using reciprocal sqrt
estimate instructions.

The @code{__builtin_recipdiv}, and @code{__builtin_recipdivf}
functions generate multiple instructions to implement division using
the reciprocal estimate instructions.

The @code{__builtin_ppc_get_timebase} and @code{__builtin_ppc_mftb}
functions generate instructions to read the Time Base Register.  The
@code{__builtin_ppc_get_timebase} function may generate multiple
instructions and always returns the 64 bits of the Time Base Register.
The @code{__builtin_ppc_mftb} function always generates one instruction and
returns the Time Base Register value as an unsigned long, throwing away
the most significant word on 32-bit environments.

@node PowerPC AltiVec/VSX Built-in Functions
@subsection PowerPC AltiVec Built-in Functions

GCC provides an interface for the PowerPC family of processors to access
the AltiVec operations described in Motorola's AltiVec Programming
Interface Manual.  The interface is made available by including
@code{<altivec.h>} and using @option{-maltivec} and
@option{-mabi=altivec}.  The interface supports the following vector
types.

@smallexample
vector unsigned char
vector signed char
vector bool char

vector unsigned short
vector signed short
vector bool short
vector pixel

vector unsigned int
vector signed int
vector bool int
vector float
@end smallexample

If @option{-mvsx} is used the following additional vector types are
implemented.

@smallexample
vector unsigned long
vector signed long
vector double
@end smallexample

The long types are only implemented for 64-bit code generation, and
the long type is only used in the floating point/integer conversion
instructions.

GCC's implementation of the high-level language interface available from
C and C++ code differs from Motorola's documentation in several ways.

@itemize @bullet

@item
A vector constant is a list of constant expressions within curly braces.

@item
A vector initializer requires no cast if the vector constant is of the
same type as the variable it is initializing.

@item
If @code{signed} or @code{unsigned} is omitted, the signedness of the
vector type is the default signedness of the base type.  The default
varies depending on the operating system, so a portable program should
always specify the signedness.

@item
Compiling with @option{-maltivec} adds keywords @code{__vector},
@code{vector}, @code{__pixel}, @code{pixel}, @code{__bool} and
@code{bool}.  When compiling ISO C, the context-sensitive substitution
of the keywords @code{vector}, @code{pixel} and @code{bool} is
disabled.  To use them, you must include @code{<altivec.h>} instead.

@item
GCC allows using a @code{typedef} name as the type specifier for a
vector type.

@item
For C, overloaded functions are implemented with macros so the following
does not work:

@smallexample
  vec_add ((vector signed int)@{1, 2, 3, 4@}, foo);
@end smallexample

@noindent
Since @code{vec_add} is a macro, the vector constant in the example
is treated as four separate arguments.  Wrap the entire argument in
parentheses for this to work.
@end itemize

@emph{Note:} Only the @code{<altivec.h>} interface is supported.
Internally, GCC uses built-in functions to achieve the functionality in
the aforementioned header file, but they are not supported and are
subject to change without notice.

The following interfaces are supported for the generic and specific
AltiVec operations and the AltiVec predicates.  In cases where there
is a direct mapping between generic and specific operations, only the
generic names are shown here, although the specific operations can also
be used.

Arguments that are documented as @code{const int} require literal
integral values within the range required for that operation.

@smallexample
vector signed char vec_abs (vector signed char);
vector signed short vec_abs (vector signed short);
vector signed int vec_abs (vector signed int);
vector float vec_abs (vector float);

vector signed char vec_abss (vector signed char);
vector signed short vec_abss (vector signed short);
vector signed int vec_abss (vector signed int);

vector signed char vec_add (vector bool char, vector signed char);
vector signed char vec_add (vector signed char, vector bool char);
vector signed char vec_add (vector signed char, vector signed char);
vector unsigned char vec_add (vector bool char, vector unsigned char);
vector unsigned char vec_add (vector unsigned char, vector bool char);
vector unsigned char vec_add (vector unsigned char,
                              vector unsigned char);
vector signed short vec_add (vector bool short, vector signed short);
vector signed short vec_add (vector signed short, vector bool short);
vector signed short vec_add (vector signed short, vector signed short);
vector unsigned short vec_add (vector bool short,
                               vector unsigned short);
vector unsigned short vec_add (vector unsigned short,
                               vector bool short);
vector unsigned short vec_add (vector unsigned short,
                               vector unsigned short);
vector signed int vec_add (vector bool int, vector signed int);
vector signed int vec_add (vector signed int, vector bool int);
vector signed int vec_add (vector signed int, vector signed int);
vector unsigned int vec_add (vector bool int, vector unsigned int);
vector unsigned int vec_add (vector unsigned int, vector bool int);
vector unsigned int vec_add (vector unsigned int, vector unsigned int);
vector float vec_add (vector float, vector float);

vector float vec_vaddfp (vector float, vector float);

vector signed int vec_vadduwm (vector bool int, vector signed int);
vector signed int vec_vadduwm (vector signed int, vector bool int);
vector signed int vec_vadduwm (vector signed int, vector signed int);
vector unsigned int vec_vadduwm (vector bool int, vector unsigned int);
vector unsigned int vec_vadduwm (vector unsigned int, vector bool int);
vector unsigned int vec_vadduwm (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vadduhm (vector bool short,
                                 vector signed short);
vector signed short vec_vadduhm (vector signed short,
                                 vector bool short);
vector signed short vec_vadduhm (vector signed short,
                                 vector signed short);
vector unsigned short vec_vadduhm (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vadduhm (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vadduhm (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vaddubm (vector bool char, vector signed char);
vector signed char vec_vaddubm (vector signed char, vector bool char);
vector signed char vec_vaddubm (vector signed char, vector signed char);
vector unsigned char vec_vaddubm (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vaddubm (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vaddubm (vector unsigned char,
                                  vector unsigned char);

vector unsigned int vec_addc (vector unsigned int, vector unsigned int);

vector unsigned char vec_adds (vector bool char, vector unsigned char);
vector unsigned char vec_adds (vector unsigned char, vector bool char);
vector unsigned char vec_adds (vector unsigned char,
                               vector unsigned char);
vector signed char vec_adds (vector bool char, vector signed char);
vector signed char vec_adds (vector signed char, vector bool char);
vector signed char vec_adds (vector signed char, vector signed char);
vector unsigned short vec_adds (vector bool short,
                                vector unsigned short);
vector unsigned short vec_adds (vector unsigned short,
                                vector bool short);
vector unsigned short vec_adds (vector unsigned short,
                                vector unsigned short);
vector signed short vec_adds (vector bool short, vector signed short);
vector signed short vec_adds (vector signed short, vector bool short);
vector signed short vec_adds (vector signed short, vector signed short);
vector unsigned int vec_adds (vector bool int, vector unsigned int);
vector unsigned int vec_adds (vector unsigned int, vector bool int);
vector unsigned int vec_adds (vector unsigned int, vector unsigned int);
vector signed int vec_adds (vector bool int, vector signed int);
vector signed int vec_adds (vector signed int, vector bool int);
vector signed int vec_adds (vector signed int, vector signed int);

vector signed int vec_vaddsws (vector bool int, vector signed int);
vector signed int vec_vaddsws (vector signed int, vector bool int);
vector signed int vec_vaddsws (vector signed int, vector signed int);

vector unsigned int vec_vadduws (vector bool int, vector unsigned int);
vector unsigned int vec_vadduws (vector unsigned int, vector bool int);
vector unsigned int vec_vadduws (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vaddshs (vector bool short,
                                 vector signed short);
vector signed short vec_vaddshs (vector signed short,
                                 vector bool short);
vector signed short vec_vaddshs (vector signed short,
                                 vector signed short);

vector unsigned short vec_vadduhs (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vadduhs (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vadduhs (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vaddsbs (vector bool char, vector signed char);
vector signed char vec_vaddsbs (vector signed char, vector bool char);
vector signed char vec_vaddsbs (vector signed char, vector signed char);

vector unsigned char vec_vaddubs (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vaddubs (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vaddubs (vector unsigned char,
                                  vector unsigned char);

vector float vec_and (vector float, vector float);
vector float vec_and (vector float, vector bool int);
vector float vec_and (vector bool int, vector float);
vector bool int vec_and (vector bool int, vector bool int);
vector signed int vec_and (vector bool int, vector signed int);
vector signed int vec_and (vector signed int, vector bool int);
vector signed int vec_and (vector signed int, vector signed int);
vector unsigned int vec_and (vector bool int, vector unsigned int);
vector unsigned int vec_and (vector unsigned int, vector bool int);
vector unsigned int vec_and (vector unsigned int, vector unsigned int);
vector bool short vec_and (vector bool short, vector bool short);
vector signed short vec_and (vector bool short, vector signed short);
vector signed short vec_and (vector signed short, vector bool short);
vector signed short vec_and (vector signed short, vector signed short);
vector unsigned short vec_and (vector bool short,
                               vector unsigned short);
vector unsigned short vec_and (vector unsigned short,
                               vector bool short);
vector unsigned short vec_and (vector unsigned short,
                               vector unsigned short);
vector signed char vec_and (vector bool char, vector signed char);
vector bool char vec_and (vector bool char, vector bool char);
vector signed char vec_and (vector signed char, vector bool char);
vector signed char vec_and (vector signed char, vector signed char);
vector unsigned char vec_and (vector bool char, vector unsigned char);
vector unsigned char vec_and (vector unsigned char, vector bool char);
vector unsigned char vec_and (vector unsigned char,
                              vector unsigned char);

vector float vec_andc (vector float, vector float);
vector float vec_andc (vector float, vector bool int);
vector float vec_andc (vector bool int, vector float);
vector bool int vec_andc (vector bool int, vector bool int);
vector signed int vec_andc (vector bool int, vector signed int);
vector signed int vec_andc (vector signed int, vector bool int);
vector signed int vec_andc (vector signed int, vector signed int);
vector unsigned int vec_andc (vector bool int, vector unsigned int);
vector unsigned int vec_andc (vector unsigned int, vector bool int);
vector unsigned int vec_andc (vector unsigned int, vector unsigned int);
vector bool short vec_andc (vector bool short, vector bool short);
vector signed short vec_andc (vector bool short, vector signed short);
vector signed short vec_andc (vector signed short, vector bool short);
vector signed short vec_andc (vector signed short, vector signed short);
vector unsigned short vec_andc (vector bool short,
                                vector unsigned short);
vector unsigned short vec_andc (vector unsigned short,
                                vector bool short);
vector unsigned short vec_andc (vector unsigned short,
                                vector unsigned short);
vector signed char vec_andc (vector bool char, vector signed char);
vector bool char vec_andc (vector bool char, vector bool char);
vector signed char vec_andc (vector signed char, vector bool char);
vector signed char vec_andc (vector signed char, vector signed char);
vector unsigned char vec_andc (vector bool char, vector unsigned char);
vector unsigned char vec_andc (vector unsigned char, vector bool char);
vector unsigned char vec_andc (vector unsigned char,
                               vector unsigned char);

vector unsigned char vec_avg (vector unsigned char,
                              vector unsigned char);
vector signed char vec_avg (vector signed char, vector signed char);
vector unsigned short vec_avg (vector unsigned short,
                               vector unsigned short);
vector signed short vec_avg (vector signed short, vector signed short);
vector unsigned int vec_avg (vector unsigned int, vector unsigned int);
vector signed int vec_avg (vector signed int, vector signed int);

vector signed int vec_vavgsw (vector signed int, vector signed int);

vector unsigned int vec_vavguw (vector unsigned int,
                                vector unsigned int);

vector signed short vec_vavgsh (vector signed short,
                                vector signed short);

vector unsigned short vec_vavguh (vector unsigned short,
                                  vector unsigned short);

vector signed char vec_vavgsb (vector signed char, vector signed char);

vector unsigned char vec_vavgub (vector unsigned char,
                                 vector unsigned char);

vector float vec_copysign (vector float);

vector float vec_ceil (vector float);

vector signed int vec_cmpb (vector float, vector float);

vector bool char vec_cmpeq (vector signed char, vector signed char);
vector bool char vec_cmpeq (vector unsigned char, vector unsigned char);
vector bool short vec_cmpeq (vector signed short, vector signed short);
vector bool short vec_cmpeq (vector unsigned short,
                             vector unsigned short);
vector bool int vec_cmpeq (vector signed int, vector signed int);
vector bool int vec_cmpeq (vector unsigned int, vector unsigned int);
vector bool int vec_cmpeq (vector float, vector float);

vector bool int vec_vcmpeqfp (vector float, vector float);

vector bool int vec_vcmpequw (vector signed int, vector signed int);
vector bool int vec_vcmpequw (vector unsigned int, vector unsigned int);

vector bool short vec_vcmpequh (vector signed short,
                                vector signed short);
vector bool short vec_vcmpequh (vector unsigned short,
                                vector unsigned short);

vector bool char vec_vcmpequb (vector signed char, vector signed char);
vector bool char vec_vcmpequb (vector unsigned char,
                               vector unsigned char);

vector bool int vec_cmpge (vector float, vector float);

vector bool char vec_cmpgt (vector unsigned char, vector unsigned char);
vector bool char vec_cmpgt (vector signed char, vector signed char);
vector bool short vec_cmpgt (vector unsigned short,
                             vector unsigned short);
vector bool short vec_cmpgt (vector signed short, vector signed short);
vector bool int vec_cmpgt (vector unsigned int, vector unsigned int);
vector bool int vec_cmpgt (vector signed int, vector signed int);
vector bool int vec_cmpgt (vector float, vector float);

vector bool int vec_vcmpgtfp (vector float, vector float);

vector bool int vec_vcmpgtsw (vector signed int, vector signed int);

vector bool int vec_vcmpgtuw (vector unsigned int, vector unsigned int);

vector bool short vec_vcmpgtsh (vector signed short,
                                vector signed short);

vector bool short vec_vcmpgtuh (vector unsigned short,
                                vector unsigned short);

vector bool char vec_vcmpgtsb (vector signed char, vector signed char);

vector bool char vec_vcmpgtub (vector unsigned char,
                               vector unsigned char);

vector bool int vec_cmple (vector float, vector float);

vector bool char vec_cmplt (vector unsigned char, vector unsigned char);
vector bool char vec_cmplt (vector signed char, vector signed char);
vector bool short vec_cmplt (vector unsigned short,
                             vector unsigned short);
vector bool short vec_cmplt (vector signed short, vector signed short);
vector bool int vec_cmplt (vector unsigned int, vector unsigned int);
vector bool int vec_cmplt (vector signed int, vector signed int);
vector bool int vec_cmplt (vector float, vector float);

vector float vec_ctf (vector unsigned int, const int);
vector float vec_ctf (vector signed int, const int);

vector float vec_vcfsx (vector signed int, const int);

vector float vec_vcfux (vector unsigned int, const int);

vector signed int vec_cts (vector float, const int);

vector unsigned int vec_ctu (vector float, const int);

void vec_dss (const int);

void vec_dssall (void);

void vec_dst (const vector unsigned char *, int, const int);
void vec_dst (const vector signed char *, int, const int);
void vec_dst (const vector bool char *, int, const int);
void vec_dst (const vector unsigned short *, int, const int);
void vec_dst (const vector signed short *, int, const int);
void vec_dst (const vector bool short *, int, const int);
void vec_dst (const vector pixel *, int, const int);
void vec_dst (const vector unsigned int *, int, const int);
void vec_dst (const vector signed int *, int, const int);
void vec_dst (const vector bool int *, int, const int);
void vec_dst (const vector float *, int, const int);
void vec_dst (const unsigned char *, int, const int);
void vec_dst (const signed char *, int, const int);
void vec_dst (const unsigned short *, int, const int);
void vec_dst (const short *, int, const int);
void vec_dst (const unsigned int *, int, const int);
void vec_dst (const int *, int, const int);
void vec_dst (const unsigned long *, int, const int);
void vec_dst (const long *, int, const int);
void vec_dst (const float *, int, const int);

void vec_dstst (const vector unsigned char *, int, const int);
void vec_dstst (const vector signed char *, int, const int);
void vec_dstst (const vector bool char *, int, const int);
void vec_dstst (const vector unsigned short *, int, const int);
void vec_dstst (const vector signed short *, int, const int);
void vec_dstst (const vector bool short *, int, const int);
void vec_dstst (const vector pixel *, int, const int);
void vec_dstst (const vector unsigned int *, int, const int);
void vec_dstst (const vector signed int *, int, const int);
void vec_dstst (const vector bool int *, int, const int);
void vec_dstst (const vector float *, int, const int);
void vec_dstst (const unsigned char *, int, const int);
void vec_dstst (const signed char *, int, const int);
void vec_dstst (const unsigned short *, int, const int);
void vec_dstst (const short *, int, const int);
void vec_dstst (const unsigned int *, int, const int);
void vec_dstst (const int *, int, const int);
void vec_dstst (const unsigned long *, int, const int);
void vec_dstst (const long *, int, const int);
void vec_dstst (const float *, int, const int);

void vec_dststt (const vector unsigned char *, int, const int);
void vec_dststt (const vector signed char *, int, const int);
void vec_dststt (const vector bool char *, int, const int);
void vec_dststt (const vector unsigned short *, int, const int);
void vec_dststt (const vector signed short *, int, const int);
void vec_dststt (const vector bool short *, int, const int);
void vec_dststt (const vector pixel *, int, const int);
void vec_dststt (const vector unsigned int *, int, const int);
void vec_dststt (const vector signed int *, int, const int);
void vec_dststt (const vector bool int *, int, const int);
void vec_dststt (const vector float *, int, const int);
void vec_dststt (const unsigned char *, int, const int);
void vec_dststt (const signed char *, int, const int);
void vec_dststt (const unsigned short *, int, const int);
void vec_dststt (const short *, int, const int);
void vec_dststt (const unsigned int *, int, const int);
void vec_dststt (const int *, int, const int);
void vec_dststt (const unsigned long *, int, const int);
void vec_dststt (const long *, int, const int);
void vec_dststt (const float *, int, const int);

void vec_dstt (const vector unsigned char *, int, const int);
void vec_dstt (const vector signed char *, int, const int);
void vec_dstt (const vector bool char *, int, const int);
void vec_dstt (const vector unsigned short *, int, const int);
void vec_dstt (const vector signed short *, int, const int);
void vec_dstt (const vector bool short *, int, const int);
void vec_dstt (const vector pixel *, int, const int);
void vec_dstt (const vector unsigned int *, int, const int);
void vec_dstt (const vector signed int *, int, const int);
void vec_dstt (const vector bool int *, int, const int);
void vec_dstt (const vector float *, int, const int);
void vec_dstt (const unsigned char *, int, const int);
void vec_dstt (const signed char *, int, const int);
void vec_dstt (const unsigned short *, int, const int);
void vec_dstt (const short *, int, const int);
void vec_dstt (const unsigned int *, int, const int);
void vec_dstt (const int *, int, const int);
void vec_dstt (const unsigned long *, int, const int);
void vec_dstt (const long *, int, const int);
void vec_dstt (const float *, int, const int);

vector float vec_expte (vector float);

vector float vec_floor (vector float);

vector float vec_ld (int, const vector float *);
vector float vec_ld (int, const float *);
vector bool int vec_ld (int, const vector bool int *);
vector signed int vec_ld (int, const vector signed int *);
vector signed int vec_ld (int, const int *);
vector signed int vec_ld (int, const long *);
vector unsigned int vec_ld (int, const vector unsigned int *);
vector unsigned int vec_ld (int, const unsigned int *);
vector unsigned int vec_ld (int, const unsigned long *);
vector bool short vec_ld (int, const vector bool short *);
vector pixel vec_ld (int, const vector pixel *);
vector signed short vec_ld (int, const vector signed short *);
vector signed short vec_ld (int, const short *);
vector unsigned short vec_ld (int, const vector unsigned short *);
vector unsigned short vec_ld (int, const unsigned short *);
vector bool char vec_ld (int, const vector bool char *);
vector signed char vec_ld (int, const vector signed char *);
vector signed char vec_ld (int, const signed char *);
vector unsigned char vec_ld (int, const vector unsigned char *);
vector unsigned char vec_ld (int, const unsigned char *);

vector signed char vec_lde (int, const signed char *);
vector unsigned char vec_lde (int, const unsigned char *);
vector signed short vec_lde (int, const short *);
vector unsigned short vec_lde (int, const unsigned short *);
vector float vec_lde (int, const float *);
vector signed int vec_lde (int, const int *);
vector unsigned int vec_lde (int, const unsigned int *);
vector signed int vec_lde (int, const long *);
vector unsigned int vec_lde (int, const unsigned long *);

vector float vec_lvewx (int, float *);
vector signed int vec_lvewx (int, int *);
vector unsigned int vec_lvewx (int, unsigned int *);
vector signed int vec_lvewx (int, long *);
vector unsigned int vec_lvewx (int, unsigned long *);

vector signed short vec_lvehx (int, short *);
vector unsigned short vec_lvehx (int, unsigned short *);

vector signed char vec_lvebx (int, char *);
vector unsigned char vec_lvebx (int, unsigned char *);

vector float vec_ldl (int, const vector float *);
vector float vec_ldl (int, const float *);
vector bool int vec_ldl (int, const vector bool int *);
vector signed int vec_ldl (int, const vector signed int *);
vector signed int vec_ldl (int, const int *);
vector signed int vec_ldl (int, const long *);
vector unsigned int vec_ldl (int, const vector unsigned int *);
vector unsigned int vec_ldl (int, const unsigned int *);
vector unsigned int vec_ldl (int, const unsigned long *);
vector bool short vec_ldl (int, const vector bool short *);
vector pixel vec_ldl (int, const vector pixel *);
vector signed short vec_ldl (int, const vector signed short *);
vector signed short vec_ldl (int, const short *);
vector unsigned short vec_ldl (int, const vector unsigned short *);
vector unsigned short vec_ldl (int, const unsigned short *);
vector bool char vec_ldl (int, const vector bool char *);
vector signed char vec_ldl (int, const vector signed char *);
vector signed char vec_ldl (int, const signed char *);
vector unsigned char vec_ldl (int, const vector unsigned char *);
vector unsigned char vec_ldl (int, const unsigned char *);

vector float vec_loge (vector float);

vector unsigned char vec_lvsl (int, const volatile unsigned char *);
vector unsigned char vec_lvsl (int, const volatile signed char *);
vector unsigned char vec_lvsl (int, const volatile unsigned short *);
vector unsigned char vec_lvsl (int, const volatile short *);
vector unsigned char vec_lvsl (int, const volatile unsigned int *);
vector unsigned char vec_lvsl (int, const volatile int *);
vector unsigned char vec_lvsl (int, const volatile unsigned long *);
vector unsigned char vec_lvsl (int, const volatile long *);
vector unsigned char vec_lvsl (int, const volatile float *);

vector unsigned char vec_lvsr (int, const volatile unsigned char *);
vector unsigned char vec_lvsr (int, const volatile signed char *);
vector unsigned char vec_lvsr (int, const volatile unsigned short *);
vector unsigned char vec_lvsr (int, const volatile short *);
vector unsigned char vec_lvsr (int, const volatile unsigned int *);
vector unsigned char vec_lvsr (int, const volatile int *);
vector unsigned char vec_lvsr (int, const volatile unsigned long *);
vector unsigned char vec_lvsr (int, const volatile long *);
vector unsigned char vec_lvsr (int, const volatile float *);

vector float vec_madd (vector float, vector float, vector float);

vector signed short vec_madds (vector signed short,
                               vector signed short,
                               vector signed short);

vector unsigned char vec_max (vector bool char, vector unsigned char);
vector unsigned char vec_max (vector unsigned char, vector bool char);
vector unsigned char vec_max (vector unsigned char,
                              vector unsigned char);
vector signed char vec_max (vector bool char, vector signed char);
vector signed char vec_max (vector signed char, vector bool char);
vector signed char vec_max (vector signed char, vector signed char);
vector unsigned short vec_max (vector bool short,
                               vector unsigned short);
vector unsigned short vec_max (vector unsigned short,
                               vector bool short);
vector unsigned short vec_max (vector unsigned short,
                               vector unsigned short);
vector signed short vec_max (vector bool short, vector signed short);
vector signed short vec_max (vector signed short, vector bool short);
vector signed short vec_max (vector signed short, vector signed short);
vector unsigned int vec_max (vector bool int, vector unsigned int);
vector unsigned int vec_max (vector unsigned int, vector bool int);
vector unsigned int vec_max (vector unsigned int, vector unsigned int);
vector signed int vec_max (vector bool int, vector signed int);
vector signed int vec_max (vector signed int, vector bool int);
vector signed int vec_max (vector signed int, vector signed int);
vector float vec_max (vector float, vector float);

vector float vec_vmaxfp (vector float, vector float);

vector signed int vec_vmaxsw (vector bool int, vector signed int);
vector signed int vec_vmaxsw (vector signed int, vector bool int);
vector signed int vec_vmaxsw (vector signed int, vector signed int);

vector unsigned int vec_vmaxuw (vector bool int, vector unsigned int);
vector unsigned int vec_vmaxuw (vector unsigned int, vector bool int);
vector unsigned int vec_vmaxuw (vector unsigned int,
                                vector unsigned int);

vector signed short vec_vmaxsh (vector bool short, vector signed short);
vector signed short vec_vmaxsh (vector signed short, vector bool short);
vector signed short vec_vmaxsh (vector signed short,
                                vector signed short);

vector unsigned short vec_vmaxuh (vector bool short,
                                  vector unsigned short);
vector unsigned short vec_vmaxuh (vector unsigned short,
                                  vector bool short);
vector unsigned short vec_vmaxuh (vector unsigned short,
                                  vector unsigned short);

vector signed char vec_vmaxsb (vector bool char, vector signed char);
vector signed char vec_vmaxsb (vector signed char, vector bool char);
vector signed char vec_vmaxsb (vector signed char, vector signed char);

vector unsigned char vec_vmaxub (vector bool char,
                                 vector unsigned char);
vector unsigned char vec_vmaxub (vector unsigned char,
                                 vector bool char);
vector unsigned char vec_vmaxub (vector unsigned char,
                                 vector unsigned char);

vector bool char vec_mergeh (vector bool char, vector bool char);
vector signed char vec_mergeh (vector signed char, vector signed char);
vector unsigned char vec_mergeh (vector unsigned char,
                                 vector unsigned char);
vector bool short vec_mergeh (vector bool short, vector bool short);
vector pixel vec_mergeh (vector pixel, vector pixel);
vector signed short vec_mergeh (vector signed short,
                                vector signed short);
vector unsigned short vec_mergeh (vector unsigned short,
                                  vector unsigned short);
vector float vec_mergeh (vector float, vector float);
vector bool int vec_mergeh (vector bool int, vector bool int);
vector signed int vec_mergeh (vector signed int, vector signed int);
vector unsigned int vec_mergeh (vector unsigned int,
                                vector unsigned int);

vector float vec_vmrghw (vector float, vector float);
vector bool int vec_vmrghw (vector bool int, vector bool int);
vector signed int vec_vmrghw (vector signed int, vector signed int);
vector unsigned int vec_vmrghw (vector unsigned int,
                                vector unsigned int);

vector bool short vec_vmrghh (vector bool short, vector bool short);
vector signed short vec_vmrghh (vector signed short,
                                vector signed short);
vector unsigned short vec_vmrghh (vector unsigned short,
                                  vector unsigned short);
vector pixel vec_vmrghh (vector pixel, vector pixel);

vector bool char vec_vmrghb (vector bool char, vector bool char);
vector signed char vec_vmrghb (vector signed char, vector signed char);
vector unsigned char vec_vmrghb (vector unsigned char,
                                 vector unsigned char);

vector bool char vec_mergel (vector bool char, vector bool char);
vector signed char vec_mergel (vector signed char, vector signed char);
vector unsigned char vec_mergel (vector unsigned char,
                                 vector unsigned char);
vector bool short vec_mergel (vector bool short, vector bool short);
vector pixel vec_mergel (vector pixel, vector pixel);
vector signed short vec_mergel (vector signed short,
                                vector signed short);
vector unsigned short vec_mergel (vector unsigned short,
                                  vector unsigned short);
vector float vec_mergel (vector float, vector float);
vector bool int vec_mergel (vector bool int, vector bool int);
vector signed int vec_mergel (vector signed int, vector signed int);
vector unsigned int vec_mergel (vector unsigned int,
                                vector unsigned int);

vector float vec_vmrglw (vector float, vector float);
vector signed int vec_vmrglw (vector signed int, vector signed int);
vector unsigned int vec_vmrglw (vector unsigned int,
                                vector unsigned int);
vector bool int vec_vmrglw (vector bool int, vector bool int);

vector bool short vec_vmrglh (vector bool short, vector bool short);
vector signed short vec_vmrglh (vector signed short,
                                vector signed short);
vector unsigned short vec_vmrglh (vector unsigned short,
                                  vector unsigned short);
vector pixel vec_vmrglh (vector pixel, vector pixel);

vector bool char vec_vmrglb (vector bool char, vector bool char);
vector signed char vec_vmrglb (vector signed char, vector signed char);
vector unsigned char vec_vmrglb (vector unsigned char,
                                 vector unsigned char);

vector unsigned short vec_mfvscr (void);

vector unsigned char vec_min (vector bool char, vector unsigned char);
vector unsigned char vec_min (vector unsigned char, vector bool char);
vector unsigned char vec_min (vector unsigned char,
                              vector unsigned char);
vector signed char vec_min (vector bool char, vector signed char);
vector signed char vec_min (vector signed char, vector bool char);
vector signed char vec_min (vector signed char, vector signed char);
vector unsigned short vec_min (vector bool short,
                               vector unsigned short);
vector unsigned short vec_min (vector unsigned short,
                               vector bool short);
vector unsigned short vec_min (vector unsigned short,
                               vector unsigned short);
vector signed short vec_min (vector bool short, vector signed short);
vector signed short vec_min (vector signed short, vector bool short);
vector signed short vec_min (vector signed short, vector signed short);
vector unsigned int vec_min (vector bool int, vector unsigned int);
vector unsigned int vec_min (vector unsigned int, vector bool int);
vector unsigned int vec_min (vector unsigned int, vector unsigned int);
vector signed int vec_min (vector bool int, vector signed int);
vector signed int vec_min (vector signed int, vector bool int);
vector signed int vec_min (vector signed int, vector signed int);
vector float vec_min (vector float, vector float);

vector float vec_vminfp (vector float, vector float);

vector signed int vec_vminsw (vector bool int, vector signed int);
vector signed int vec_vminsw (vector signed int, vector bool int);
vector signed int vec_vminsw (vector signed int, vector signed int);

vector unsigned int vec_vminuw (vector bool int, vector unsigned int);
vector unsigned int vec_vminuw (vector unsigned int, vector bool int);
vector unsigned int vec_vminuw (vector unsigned int,
                                vector unsigned int);

vector signed short vec_vminsh (vector bool short, vector signed short);
vector signed short vec_vminsh (vector signed short, vector bool short);
vector signed short vec_vminsh (vector signed short,
                                vector signed short);

vector unsigned short vec_vminuh (vector bool short,
                                  vector unsigned short);
vector unsigned short vec_vminuh (vector unsigned short,
                                  vector bool short);
vector unsigned short vec_vminuh (vector unsigned short,
                                  vector unsigned short);

vector signed char vec_vminsb (vector bool char, vector signed char);
vector signed char vec_vminsb (vector signed char, vector bool char);
vector signed char vec_vminsb (vector signed char, vector signed char);

vector unsigned char vec_vminub (vector bool char,
                                 vector unsigned char);
vector unsigned char vec_vminub (vector unsigned char,
                                 vector bool char);
vector unsigned char vec_vminub (vector unsigned char,
                                 vector unsigned char);

vector signed short vec_mladd (vector signed short,
                               vector signed short,
                               vector signed short);
vector signed short vec_mladd (vector signed short,
                               vector unsigned short,
                               vector unsigned short);
vector signed short vec_mladd (vector unsigned short,
                               vector signed short,
                               vector signed short);
vector unsigned short vec_mladd (vector unsigned short,
                                 vector unsigned short,
                                 vector unsigned short);

vector signed short vec_mradds (vector signed short,
                                vector signed short,
                                vector signed short);

vector unsigned int vec_msum (vector unsigned char,
                              vector unsigned char,
                              vector unsigned int);
vector signed int vec_msum (vector signed char,
                            vector unsigned char,
                            vector signed int);
vector unsigned int vec_msum (vector unsigned short,
                              vector unsigned short,
                              vector unsigned int);
vector signed int vec_msum (vector signed short,
                            vector signed short,
                            vector signed int);

vector signed int vec_vmsumshm (vector signed short,
                                vector signed short,
                                vector signed int);

vector unsigned int vec_vmsumuhm (vector unsigned short,
                                  vector unsigned short,
                                  vector unsigned int);

vector signed int vec_vmsummbm (vector signed char,
                                vector unsigned char,
                                vector signed int);

vector unsigned int vec_vmsumubm (vector unsigned char,
                                  vector unsigned char,
                                  vector unsigned int);

vector unsigned int vec_msums (vector unsigned short,
                               vector unsigned short,
                               vector unsigned int);
vector signed int vec_msums (vector signed short,
                             vector signed short,
                             vector signed int);

vector signed int vec_vmsumshs (vector signed short,
                                vector signed short,
                                vector signed int);

vector unsigned int vec_vmsumuhs (vector unsigned short,
                                  vector unsigned short,
                                  vector unsigned int);

void vec_mtvscr (vector signed int);
void vec_mtvscr (vector unsigned int);
void vec_mtvscr (vector bool int);
void vec_mtvscr (vector signed short);
void vec_mtvscr (vector unsigned short);
void vec_mtvscr (vector bool short);
void vec_mtvscr (vector pixel);
void vec_mtvscr (vector signed char);
void vec_mtvscr (vector unsigned char);
void vec_mtvscr (vector bool char);

vector unsigned short vec_mule (vector unsigned char,
                                vector unsigned char);
vector signed short vec_mule (vector signed char,
                              vector signed char);
vector unsigned int vec_mule (vector unsigned short,
                              vector unsigned short);
vector signed int vec_mule (vector signed short, vector signed short);

vector signed int vec_vmulesh (vector signed short,
                               vector signed short);

vector unsigned int vec_vmuleuh (vector unsigned short,
                                 vector unsigned short);

vector signed short vec_vmulesb (vector signed char,
                                 vector signed char);

vector unsigned short vec_vmuleub (vector unsigned char,
                                  vector unsigned char);

vector unsigned short vec_mulo (vector unsigned char,
                                vector unsigned char);
vector signed short vec_mulo (vector signed char, vector signed char);
vector unsigned int vec_mulo (vector unsigned short,
                              vector unsigned short);
vector signed int vec_mulo (vector signed short, vector signed short);

vector signed int vec_vmulosh (vector signed short,
                               vector signed short);

vector unsigned int vec_vmulouh (vector unsigned short,
                                 vector unsigned short);

vector signed short vec_vmulosb (vector signed char,
                                 vector signed char);

vector unsigned short vec_vmuloub (vector unsigned char,
                                   vector unsigned char);

vector float vec_nmsub (vector float, vector float, vector float);

vector float vec_nor (vector float, vector float);
vector signed int vec_nor (vector signed int, vector signed int);
vector unsigned int vec_nor (vector unsigned int, vector unsigned int);
vector bool int vec_nor (vector bool int, vector bool int);
vector signed short vec_nor (vector signed short, vector signed short);
vector unsigned short vec_nor (vector unsigned short,
                               vector unsigned short);
vector bool short vec_nor (vector bool short, vector bool short);
vector signed char vec_nor (vector signed char, vector signed char);
vector unsigned char vec_nor (vector unsigned char,
                              vector unsigned char);
vector bool char vec_nor (vector bool char, vector bool char);

vector float vec_or (vector float, vector float);
vector float vec_or (vector float, vector bool int);
vector float vec_or (vector bool int, vector float);
vector bool int vec_or (vector bool int, vector bool int);
vector signed int vec_or (vector bool int, vector signed int);
vector signed int vec_or (vector signed int, vector bool int);
vector signed int vec_or (vector signed int, vector signed int);
vector unsigned int vec_or (vector bool int, vector unsigned int);
vector unsigned int vec_or (vector unsigned int, vector bool int);
vector unsigned int vec_or (vector unsigned int, vector unsigned int);
vector bool short vec_or (vector bool short, vector bool short);
vector signed short vec_or (vector bool short, vector signed short);
vector signed short vec_or (vector signed short, vector bool short);
vector signed short vec_or (vector signed short, vector signed short);
vector unsigned short vec_or (vector bool short, vector unsigned short);
vector unsigned short vec_or (vector unsigned short, vector bool short);
vector unsigned short vec_or (vector unsigned short,
                              vector unsigned short);
vector signed char vec_or (vector bool char, vector signed char);
vector bool char vec_or (vector bool char, vector bool char);
vector signed char vec_or (vector signed char, vector bool char);
vector signed char vec_or (vector signed char, vector signed char);
vector unsigned char vec_or (vector bool char, vector unsigned char);
vector unsigned char vec_or (vector unsigned char, vector bool char);
vector unsigned char vec_or (vector unsigned char,
                             vector unsigned char);

vector signed char vec_pack (vector signed short, vector signed short);
vector unsigned char vec_pack (vector unsigned short,
                               vector unsigned short);
vector bool char vec_pack (vector bool short, vector bool short);
vector signed short vec_pack (vector signed int, vector signed int);
vector unsigned short vec_pack (vector unsigned int,
                                vector unsigned int);
vector bool short vec_pack (vector bool int, vector bool int);

vector bool short vec_vpkuwum (vector bool int, vector bool int);
vector signed short vec_vpkuwum (vector signed int, vector signed int);
vector unsigned short vec_vpkuwum (vector unsigned int,
                                   vector unsigned int);

vector bool char vec_vpkuhum (vector bool short, vector bool short);
vector signed char vec_vpkuhum (vector signed short,
                                vector signed short);
vector unsigned char vec_vpkuhum (vector unsigned short,
                                  vector unsigned short);

vector pixel vec_packpx (vector unsigned int, vector unsigned int);

vector unsigned char vec_packs (vector unsigned short,
                                vector unsigned short);
vector signed char vec_packs (vector signed short, vector signed short);
vector unsigned short vec_packs (vector unsigned int,
                                 vector unsigned int);
vector signed short vec_packs (vector signed int, vector signed int);

vector signed short vec_vpkswss (vector signed int, vector signed int);

vector unsigned short vec_vpkuwus (vector unsigned int,
                                   vector unsigned int);

vector signed char vec_vpkshss (vector signed short,
                                vector signed short);

vector unsigned char vec_vpkuhus (vector unsigned short,
                                  vector unsigned short);

vector unsigned char vec_packsu (vector unsigned short,
                                 vector unsigned short);
vector unsigned char vec_packsu (vector signed short,
                                 vector signed short);
vector unsigned short vec_packsu (vector unsigned int,
                                  vector unsigned int);
vector unsigned short vec_packsu (vector signed int, vector signed int);

vector unsigned short vec_vpkswus (vector signed int,
                                   vector signed int);

vector unsigned char vec_vpkshus (vector signed short,
                                  vector signed short);

vector float vec_perm (vector float,
                       vector float,
                       vector unsigned char);
vector signed int vec_perm (vector signed int,
                            vector signed int,
                            vector unsigned char);
vector unsigned int vec_perm (vector unsigned int,
                              vector unsigned int,
                              vector unsigned char);
vector bool int vec_perm (vector bool int,
                          vector bool int,
                          vector unsigned char);
vector signed short vec_perm (vector signed short,
                              vector signed short,
                              vector unsigned char);
vector unsigned short vec_perm (vector unsigned short,
                                vector unsigned short,
                                vector unsigned char);
vector bool short vec_perm (vector bool short,
                            vector bool short,
                            vector unsigned char);
vector pixel vec_perm (vector pixel,
                       vector pixel,
                       vector unsigned char);
vector signed char vec_perm (vector signed char,
                             vector signed char,
                             vector unsigned char);
vector unsigned char vec_perm (vector unsigned char,
                               vector unsigned char,
                               vector unsigned char);
vector bool char vec_perm (vector bool char,
                           vector bool char,
                           vector unsigned char);

vector float vec_re (vector float);

vector signed char vec_rl (vector signed char,
                           vector unsigned char);
vector unsigned char vec_rl (vector unsigned char,
                             vector unsigned char);
vector signed short vec_rl (vector signed short, vector unsigned short);
vector unsigned short vec_rl (vector unsigned short,
                              vector unsigned short);
vector signed int vec_rl (vector signed int, vector unsigned int);
vector unsigned int vec_rl (vector unsigned int, vector unsigned int);

vector signed int vec_vrlw (vector signed int, vector unsigned int);
vector unsigned int vec_vrlw (vector unsigned int, vector unsigned int);

vector signed short vec_vrlh (vector signed short,
                              vector unsigned short);
vector unsigned short vec_vrlh (vector unsigned short,
                                vector unsigned short);

vector signed char vec_vrlb (vector signed char, vector unsigned char);
vector unsigned char vec_vrlb (vector unsigned char,
                               vector unsigned char);

vector float vec_round (vector float);

vector float vec_recip (vector float, vector float);

vector float vec_rsqrt (vector float);

vector float vec_rsqrte (vector float);

vector float vec_sel (vector float, vector float, vector bool int);
vector float vec_sel (vector float, vector float, vector unsigned int);
vector signed int vec_sel (vector signed int,
                           vector signed int,
                           vector bool int);
vector signed int vec_sel (vector signed int,
                           vector signed int,
                           vector unsigned int);
vector unsigned int vec_sel (vector unsigned int,
                             vector unsigned int,
                             vector bool int);
vector unsigned int vec_sel (vector unsigned int,
                             vector unsigned int,
                             vector unsigned int);
vector bool int vec_sel (vector bool int,
                         vector bool int,
                         vector bool int);
vector bool int vec_sel (vector bool int,
                         vector bool int,
                         vector unsigned int);
vector signed short vec_sel (vector signed short,
                             vector signed short,
                             vector bool short);
vector signed short vec_sel (vector signed short,
                             vector signed short,
                             vector unsigned short);
vector unsigned short vec_sel (vector unsigned short,
                               vector unsigned short,
                               vector bool short);
vector unsigned short vec_sel (vector unsigned short,
                               vector unsigned short,
                               vector unsigned short);
vector bool short vec_sel (vector bool short,
                           vector bool short,
                           vector bool short);
vector bool short vec_sel (vector bool short,
                           vector bool short,
                           vector unsigned short);
vector signed char vec_sel (vector signed char,
                            vector signed char,
                            vector bool char);
vector signed char vec_sel (vector signed char,
                            vector signed char,
                            vector unsigned char);
vector unsigned char vec_sel (vector unsigned char,
                              vector unsigned char,
                              vector bool char);
vector unsigned char vec_sel (vector unsigned char,
                              vector unsigned char,
                              vector unsigned char);
vector bool char vec_sel (vector bool char,
                          vector bool char,
                          vector bool char);
vector bool char vec_sel (vector bool char,
                          vector bool char,
                          vector unsigned char);

vector signed char vec_sl (vector signed char,
                           vector unsigned char);
vector unsigned char vec_sl (vector unsigned char,
                             vector unsigned char);
vector signed short vec_sl (vector signed short, vector unsigned short);
vector unsigned short vec_sl (vector unsigned short,
                              vector unsigned short);
vector signed int vec_sl (vector signed int, vector unsigned int);
vector unsigned int vec_sl (vector unsigned int, vector unsigned int);

vector signed int vec_vslw (vector signed int, vector unsigned int);
vector unsigned int vec_vslw (vector unsigned int, vector unsigned int);

vector signed short vec_vslh (vector signed short,
                              vector unsigned short);
vector unsigned short vec_vslh (vector unsigned short,
                                vector unsigned short);

vector signed char vec_vslb (vector signed char, vector unsigned char);
vector unsigned char vec_vslb (vector unsigned char,
                               vector unsigned char);

vector float vec_sld (vector float, vector float, const int);
vector signed int vec_sld (vector signed int,
                           vector signed int,
                           const int);
vector unsigned int vec_sld (vector unsigned int,
                             vector unsigned int,
                             const int);
vector bool int vec_sld (vector bool int,
                         vector bool int,
                         const int);
vector signed short vec_sld (vector signed short,
                             vector signed short,
                             const int);
vector unsigned short vec_sld (vector unsigned short,
                               vector unsigned short,
                               const int);
vector bool short vec_sld (vector bool short,
                           vector bool short,
                           const int);
vector pixel vec_sld (vector pixel,
                      vector pixel,
                      const int);
vector signed char vec_sld (vector signed char,
                            vector signed char,
                            const int);
vector unsigned char vec_sld (vector unsigned char,
                              vector unsigned char,
                              const int);
vector bool char vec_sld (vector bool char,
                          vector bool char,
                          const int);

vector signed int vec_sll (vector signed int,
                           vector unsigned int);
vector signed int vec_sll (vector signed int,
                           vector unsigned short);
vector signed int vec_sll (vector signed int,
                           vector unsigned char);
vector unsigned int vec_sll (vector unsigned int,
                             vector unsigned int);
vector unsigned int vec_sll (vector unsigned int,
                             vector unsigned short);
vector unsigned int vec_sll (vector unsigned int,
                             vector unsigned char);
vector bool int vec_sll (vector bool int,
                         vector unsigned int);
vector bool int vec_sll (vector bool int,
                         vector unsigned short);
vector bool int vec_sll (vector bool int,
                         vector unsigned char);
vector signed short vec_sll (vector signed short,
                             vector unsigned int);
vector signed short vec_sll (vector signed short,
                             vector unsigned short);
vector signed short vec_sll (vector signed short,
                             vector unsigned char);
vector unsigned short vec_sll (vector unsigned short,
                               vector unsigned int);
vector unsigned short vec_sll (vector unsigned short,
                               vector unsigned short);
vector unsigned short vec_sll (vector unsigned short,
                               vector unsigned char);
vector bool short vec_sll (vector bool short, vector unsigned int);
vector bool short vec_sll (vector bool short, vector unsigned short);
vector bool short vec_sll (vector bool short, vector unsigned char);
vector pixel vec_sll (vector pixel, vector unsigned int);
vector pixel vec_sll (vector pixel, vector unsigned short);
vector pixel vec_sll (vector pixel, vector unsigned char);
vector signed char vec_sll (vector signed char, vector unsigned int);
vector signed char vec_sll (vector signed char, vector unsigned short);
vector signed char vec_sll (vector signed char, vector unsigned char);
vector unsigned char vec_sll (vector unsigned char,
                              vector unsigned int);
vector unsigned char vec_sll (vector unsigned char,
                              vector unsigned short);
vector unsigned char vec_sll (vector unsigned char,
                              vector unsigned char);
vector bool char vec_sll (vector bool char, vector unsigned int);
vector bool char vec_sll (vector bool char, vector unsigned short);
vector bool char vec_sll (vector bool char, vector unsigned char);

vector float vec_slo (vector float, vector signed char);
vector float vec_slo (vector float, vector unsigned char);
vector signed int vec_slo (vector signed int, vector signed char);
vector signed int vec_slo (vector signed int, vector unsigned char);
vector unsigned int vec_slo (vector unsigned int, vector signed char);
vector unsigned int vec_slo (vector unsigned int, vector unsigned char);
vector signed short vec_slo (vector signed short, vector signed char);
vector signed short vec_slo (vector signed short, vector unsigned char);
vector unsigned short vec_slo (vector unsigned short,
                               vector signed char);
vector unsigned short vec_slo (vector unsigned short,
                               vector unsigned char);
vector pixel vec_slo (vector pixel, vector signed char);
vector pixel vec_slo (vector pixel, vector unsigned char);
vector signed char vec_slo (vector signed char, vector signed char);
vector signed char vec_slo (vector signed char, vector unsigned char);
vector unsigned char vec_slo (vector unsigned char, vector signed char);
vector unsigned char vec_slo (vector unsigned char,
                              vector unsigned char);

vector signed char vec_splat (vector signed char, const int);
vector unsigned char vec_splat (vector unsigned char, const int);
vector bool char vec_splat (vector bool char, const int);
vector signed short vec_splat (vector signed short, const int);
vector unsigned short vec_splat (vector unsigned short, const int);
vector bool short vec_splat (vector bool short, const int);
vector pixel vec_splat (vector pixel, const int);
vector float vec_splat (vector float, const int);
vector signed int vec_splat (vector signed int, const int);
vector unsigned int vec_splat (vector unsigned int, const int);
vector bool int vec_splat (vector bool int, const int);

vector float vec_vspltw (vector float, const int);
vector signed int vec_vspltw (vector signed int, const int);
vector unsigned int vec_vspltw (vector unsigned int, const int);
vector bool int vec_vspltw (vector bool int, const int);

vector bool short vec_vsplth (vector bool short, const int);
vector signed short vec_vsplth (vector signed short, const int);
vector unsigned short vec_vsplth (vector unsigned short, const int);
vector pixel vec_vsplth (vector pixel, const int);

vector signed char vec_vspltb (vector signed char, const int);
vector unsigned char vec_vspltb (vector unsigned char, const int);
vector bool char vec_vspltb (vector bool char, const int);

vector signed char vec_splat_s8 (const int);

vector signed short vec_splat_s16 (const int);

vector signed int vec_splat_s32 (const int);

vector unsigned char vec_splat_u8 (const int);

vector unsigned short vec_splat_u16 (const int);

vector unsigned int vec_splat_u32 (const int);

vector signed char vec_sr (vector signed char, vector unsigned char);
vector unsigned char vec_sr (vector unsigned char,
                             vector unsigned char);
vector signed short vec_sr (vector signed short,
                            vector unsigned short);
vector unsigned short vec_sr (vector unsigned short,
                              vector unsigned short);
vector signed int vec_sr (vector signed int, vector unsigned int);
vector unsigned int vec_sr (vector unsigned int, vector unsigned int);

vector signed int vec_vsrw (vector signed int, vector unsigned int);
vector unsigned int vec_vsrw (vector unsigned int, vector unsigned int);

vector signed short vec_vsrh (vector signed short,
                              vector unsigned short);
vector unsigned short vec_vsrh (vector unsigned short,
                                vector unsigned short);

vector signed char vec_vsrb (vector signed char, vector unsigned char);
vector unsigned char vec_vsrb (vector unsigned char,
                               vector unsigned char);

vector signed char vec_sra (vector signed char, vector unsigned char);
vector unsigned char vec_sra (vector unsigned char,
                              vector unsigned char);
vector signed short vec_sra (vector signed short,
                             vector unsigned short);
vector unsigned short vec_sra (vector unsigned short,
                               vector unsigned short);
vector signed int vec_sra (vector signed int, vector unsigned int);
vector unsigned int vec_sra (vector unsigned int, vector unsigned int);

vector signed int vec_vsraw (vector signed int, vector unsigned int);
vector unsigned int vec_vsraw (vector unsigned int,
                               vector unsigned int);

vector signed short vec_vsrah (vector signed short,
                               vector unsigned short);
vector unsigned short vec_vsrah (vector unsigned short,
                                 vector unsigned short);

vector signed char vec_vsrab (vector signed char, vector unsigned char);
vector unsigned char vec_vsrab (vector unsigned char,
                                vector unsigned char);

vector signed int vec_srl (vector signed int, vector unsigned int);
vector signed int vec_srl (vector signed int, vector unsigned short);
vector signed int vec_srl (vector signed int, vector unsigned char);
vector unsigned int vec_srl (vector unsigned int, vector unsigned int);
vector unsigned int vec_srl (vector unsigned int,
                             vector unsigned short);
vector unsigned int vec_srl (vector unsigned int, vector unsigned char);
vector bool int vec_srl (vector bool int, vector unsigned int);
vector bool int vec_srl (vector bool int, vector unsigned short);
vector bool int vec_srl (vector bool int, vector unsigned char);
vector signed short vec_srl (vector signed short, vector unsigned int);
vector signed short vec_srl (vector signed short,
                             vector unsigned short);
vector signed short vec_srl (vector signed short, vector unsigned char);
vector unsigned short vec_srl (vector unsigned short,
                               vector unsigned int);
vector unsigned short vec_srl (vector unsigned short,
                               vector unsigned short);
vector unsigned short vec_srl (vector unsigned short,
                               vector unsigned char);
vector bool short vec_srl (vector bool short, vector unsigned int);
vector bool short vec_srl (vector bool short, vector unsigned short);
vector bool short vec_srl (vector bool short, vector unsigned char);
vector pixel vec_srl (vector pixel, vector unsigned int);
vector pixel vec_srl (vector pixel, vector unsigned short);
vector pixel vec_srl (vector pixel, vector unsigned char);
vector signed char vec_srl (vector signed char, vector unsigned int);
vector signed char vec_srl (vector signed char, vector unsigned short);
vector signed char vec_srl (vector signed char, vector unsigned char);
vector unsigned char vec_srl (vector unsigned char,
                              vector unsigned int);
vector unsigned char vec_srl (vector unsigned char,
                              vector unsigned short);
vector unsigned char vec_srl (vector unsigned char,
                              vector unsigned char);
vector bool char vec_srl (vector bool char, vector unsigned int);
vector bool char vec_srl (vector bool char, vector unsigned short);
vector bool char vec_srl (vector bool char, vector unsigned char);

vector float vec_sro (vector float, vector signed char);
vector float vec_sro (vector float, vector unsigned char);
vector signed int vec_sro (vector signed int, vector signed char);
vector signed int vec_sro (vector signed int, vector unsigned char);
vector unsigned int vec_sro (vector unsigned int, vector signed char);
vector unsigned int vec_sro (vector unsigned int, vector unsigned char);
vector signed short vec_sro (vector signed short, vector signed char);
vector signed short vec_sro (vector signed short, vector unsigned char);
vector unsigned short vec_sro (vector unsigned short,
                               vector signed char);
vector unsigned short vec_sro (vector unsigned short,
                               vector unsigned char);
vector pixel vec_sro (vector pixel, vector signed char);
vector pixel vec_sro (vector pixel, vector unsigned char);
vector signed char vec_sro (vector signed char, vector signed char);
vector signed char vec_sro (vector signed char, vector unsigned char);
vector unsigned char vec_sro (vector unsigned char, vector signed char);
vector unsigned char vec_sro (vector unsigned char,
                              vector unsigned char);

void vec_st (vector float, int, vector float *);
void vec_st (vector float, int, float *);
void vec_st (vector signed int, int, vector signed int *);
void vec_st (vector signed int, int, int *);
void vec_st (vector unsigned int, int, vector unsigned int *);
void vec_st (vector unsigned int, int, unsigned int *);
void vec_st (vector bool int, int, vector bool int *);
void vec_st (vector bool int, int, unsigned int *);
void vec_st (vector bool int, int, int *);
void vec_st (vector signed short, int, vector signed short *);
void vec_st (vector signed short, int, short *);
void vec_st (vector unsigned short, int, vector unsigned short *);
void vec_st (vector unsigned short, int, unsigned short *);
void vec_st (vector bool short, int, vector bool short *);
void vec_st (vector bool short, int, unsigned short *);
void vec_st (vector pixel, int, vector pixel *);
void vec_st (vector pixel, int, unsigned short *);
void vec_st (vector pixel, int, short *);
void vec_st (vector bool short, int, short *);
void vec_st (vector signed char, int, vector signed char *);
void vec_st (vector signed char, int, signed char *);
void vec_st (vector unsigned char, int, vector unsigned char *);
void vec_st (vector unsigned char, int, unsigned char *);
void vec_st (vector bool char, int, vector bool char *);
void vec_st (vector bool char, int, unsigned char *);
void vec_st (vector bool char, int, signed char *);

void vec_ste (vector signed char, int, signed char *);
void vec_ste (vector unsigned char, int, unsigned char *);
void vec_ste (vector bool char, int, signed char *);
void vec_ste (vector bool char, int, unsigned char *);
void vec_ste (vector signed short, int, short *);
void vec_ste (vector unsigned short, int, unsigned short *);
void vec_ste (vector bool short, int, short *);
void vec_ste (vector bool short, int, unsigned short *);
void vec_ste (vector pixel, int, short *);
void vec_ste (vector pixel, int, unsigned short *);
void vec_ste (vector float, int, float *);
void vec_ste (vector signed int, int, int *);
void vec_ste (vector unsigned int, int, unsigned int *);
void vec_ste (vector bool int, int, int *);
void vec_ste (vector bool int, int, unsigned int *);

void vec_stvewx (vector float, int, float *);
void vec_stvewx (vector signed int, int, int *);
void vec_stvewx (vector unsigned int, int, unsigned int *);
void vec_stvewx (vector bool int, int, int *);
void vec_stvewx (vector bool int, int, unsigned int *);

void vec_stvehx (vector signed short, int, short *);
void vec_stvehx (vector unsigned short, int, unsigned short *);
void vec_stvehx (vector bool short, int, short *);
void vec_stvehx (vector bool short, int, unsigned short *);
void vec_stvehx (vector pixel, int, short *);
void vec_stvehx (vector pixel, int, unsigned short *);

void vec_stvebx (vector signed char, int, signed char *);
void vec_stvebx (vector unsigned char, int, unsigned char *);
void vec_stvebx (vector bool char, int, signed char *);
void vec_stvebx (vector bool char, int, unsigned char *);

void vec_stl (vector float, int, vector float *);
void vec_stl (vector float, int, float *);
void vec_stl (vector signed int, int, vector signed int *);
void vec_stl (vector signed int, int, int *);
void vec_stl (vector unsigned int, int, vector unsigned int *);
void vec_stl (vector unsigned int, int, unsigned int *);
void vec_stl (vector bool int, int, vector bool int *);
void vec_stl (vector bool int, int, unsigned int *);
void vec_stl (vector bool int, int, int *);
void vec_stl (vector signed short, int, vector signed short *);
void vec_stl (vector signed short, int, short *);
void vec_stl (vector unsigned short, int, vector unsigned short *);
void vec_stl (vector unsigned short, int, unsigned short *);
void vec_stl (vector bool short, int, vector bool short *);
void vec_stl (vector bool short, int, unsigned short *);
void vec_stl (vector bool short, int, short *);
void vec_stl (vector pixel, int, vector pixel *);
void vec_stl (vector pixel, int, unsigned short *);
void vec_stl (vector pixel, int, short *);
void vec_stl (vector signed char, int, vector signed char *);
void vec_stl (vector signed char, int, signed char *);
void vec_stl (vector unsigned char, int, vector unsigned char *);
void vec_stl (vector unsigned char, int, unsigned char *);
void vec_stl (vector bool char, int, vector bool char *);
void vec_stl (vector bool char, int, unsigned char *);
void vec_stl (vector bool char, int, signed char *);

vector signed char vec_sub (vector bool char, vector signed char);
vector signed char vec_sub (vector signed char, vector bool char);
vector signed char vec_sub (vector signed char, vector signed char);
vector unsigned char vec_sub (vector bool char, vector unsigned char);
vector unsigned char vec_sub (vector unsigned char, vector bool char);
vector unsigned char vec_sub (vector unsigned char,
                              vector unsigned char);
vector signed short vec_sub (vector bool short, vector signed short);
vector signed short vec_sub (vector signed short, vector bool short);
vector signed short vec_sub (vector signed short, vector signed short);
vector unsigned short vec_sub (vector bool short,
                               vector unsigned short);
vector unsigned short vec_sub (vector unsigned short,
                               vector bool short);
vector unsigned short vec_sub (vector unsigned short,
                               vector unsigned short);
vector signed int vec_sub (vector bool int, vector signed int);
vector signed int vec_sub (vector signed int, vector bool int);
vector signed int vec_sub (vector signed int, vector signed int);
vector unsigned int vec_sub (vector bool int, vector unsigned int);
vector unsigned int vec_sub (vector unsigned int, vector bool int);
vector unsigned int vec_sub (vector unsigned int, vector unsigned int);
vector float vec_sub (vector float, vector float);

vector float vec_vsubfp (vector float, vector float);

vector signed int vec_vsubuwm (vector bool int, vector signed int);
vector signed int vec_vsubuwm (vector signed int, vector bool int);
vector signed int vec_vsubuwm (vector signed int, vector signed int);
vector unsigned int vec_vsubuwm (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuwm (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuwm (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vsubuhm (vector bool short,
                                 vector signed short);
vector signed short vec_vsubuhm (vector signed short,
                                 vector bool short);
vector signed short vec_vsubuhm (vector signed short,
                                 vector signed short);
vector unsigned short vec_vsubuhm (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vsubuhm (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vsubuhm (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vsububm (vector bool char, vector signed char);
vector signed char vec_vsububm (vector signed char, vector bool char);
vector signed char vec_vsububm (vector signed char, vector signed char);
vector unsigned char vec_vsububm (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vsububm (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vsububm (vector unsigned char,
                                  vector unsigned char);

vector unsigned int vec_subc (vector unsigned int, vector unsigned int);

vector unsigned char vec_subs (vector bool char, vector unsigned char);
vector unsigned char vec_subs (vector unsigned char, vector bool char);
vector unsigned char vec_subs (vector unsigned char,
                               vector unsigned char);
vector signed char vec_subs (vector bool char, vector signed char);
vector signed char vec_subs (vector signed char, vector bool char);
vector signed char vec_subs (vector signed char, vector signed char);
vector unsigned short vec_subs (vector bool short,
                                vector unsigned short);
vector unsigned short vec_subs (vector unsigned short,
                                vector bool short);
vector unsigned short vec_subs (vector unsigned short,
                                vector unsigned short);
vector signed short vec_subs (vector bool short, vector signed short);
vector signed short vec_subs (vector signed short, vector bool short);
vector signed short vec_subs (vector signed short, vector signed short);
vector unsigned int vec_subs (vector bool int, vector unsigned int);
vector unsigned int vec_subs (vector unsigned int, vector bool int);
vector unsigned int vec_subs (vector unsigned int, vector unsigned int);
vector signed int vec_subs (vector bool int, vector signed int);
vector signed int vec_subs (vector signed int, vector bool int);
vector signed int vec_subs (vector signed int, vector signed int);

vector signed int vec_vsubsws (vector bool int, vector signed int);
vector signed int vec_vsubsws (vector signed int, vector bool int);
vector signed int vec_vsubsws (vector signed int, vector signed int);

vector unsigned int vec_vsubuws (vector bool int, vector unsigned int);
vector unsigned int vec_vsubuws (vector unsigned int, vector bool int);
vector unsigned int vec_vsubuws (vector unsigned int,
                                 vector unsigned int);

vector signed short vec_vsubshs (vector bool short,
                                 vector signed short);
vector signed short vec_vsubshs (vector signed short,
                                 vector bool short);
vector signed short vec_vsubshs (vector signed short,
                                 vector signed short);

vector unsigned short vec_vsubuhs (vector bool short,
                                   vector unsigned short);
vector unsigned short vec_vsubuhs (vector unsigned short,
                                   vector bool short);
vector unsigned short vec_vsubuhs (vector unsigned short,
                                   vector unsigned short);

vector signed char vec_vsubsbs (vector bool char, vector signed char);
vector signed char vec_vsubsbs (vector signed char, vector bool char);
vector signed char vec_vsubsbs (vector signed char, vector signed char);

vector unsigned char vec_vsububs (vector bool char,
                                  vector unsigned char);
vector unsigned char vec_vsububs (vector unsigned char,
                                  vector bool char);
vector unsigned char vec_vsububs (vector unsigned char,
                                  vector unsigned char);

vector unsigned int vec_sum4s (vector unsigned char,
                               vector unsigned int);
vector signed int vec_sum4s (vector signed char, vector signed int);
vector signed int vec_sum4s (vector signed short, vector signed int);

vector signed int vec_vsum4shs (vector signed short, vector signed int);

vector signed int vec_vsum4sbs (vector signed char, vector signed int);

vector unsigned int vec_vsum4ubs (vector unsigned char,
                                  vector unsigned int);

vector signed int vec_sum2s (vector signed int, vector signed int);

vector signed int vec_sums (vector signed int, vector signed int);

vector float vec_trunc (vector float);

vector signed short vec_unpackh (vector signed char);
vector bool short vec_unpackh (vector bool char);
vector signed int vec_unpackh (vector signed short);
vector bool int vec_unpackh (vector bool short);
vector unsigned int vec_unpackh (vector pixel);

vector bool int vec_vupkhsh (vector bool short);
vector signed int vec_vupkhsh (vector signed short);

vector unsigned int vec_vupkhpx (vector pixel);

vector bool short vec_vupkhsb (vector bool char);
vector signed short vec_vupkhsb (vector signed char);

vector signed short vec_unpackl (vector signed char);
vector bool short vec_unpackl (vector bool char);
vector unsigned int vec_unpackl (vector pixel);
vector signed int vec_unpackl (vector signed short);
vector bool int vec_unpackl (vector bool short);

vector unsigned int vec_vupklpx (vector pixel);

vector bool int vec_vupklsh (vector bool short);
vector signed int vec_vupklsh (vector signed short);

vector bool short vec_vupklsb (vector bool char);
vector signed short vec_vupklsb (vector signed char);

vector float vec_xor (vector float, vector float);
vector float vec_xor (vector float, vector bool int);
vector float vec_xor (vector bool int, vector float);
vector bool int vec_xor (vector bool int, vector bool int);
vector signed int vec_xor (vector bool int, vector signed int);
vector signed int vec_xor (vector signed int, vector bool int);
vector signed int vec_xor (vector signed int, vector signed int);
vector unsigned int vec_xor (vector bool int, vector unsigned int);
vector unsigned int vec_xor (vector unsigned int, vector bool int);
vector unsigned int vec_xor (vector unsigned int, vector unsigned int);
vector bool short vec_xor (vector bool short, vector bool short);
vector signed short vec_xor (vector bool short, vector signed short);
vector signed short vec_xor (vector signed short, vector bool short);
vector signed short vec_xor (vector signed short, vector signed short);
vector unsigned short vec_xor (vector bool short,
                               vector unsigned short);
vector unsigned short vec_xor (vector unsigned short,
                               vector bool short);
vector unsigned short vec_xor (vector unsigned short,
                               vector unsigned short);
vector signed char vec_xor (vector bool char, vector signed char);
vector bool char vec_xor (vector bool char, vector bool char);
vector signed char vec_xor (vector signed char, vector bool char);
vector signed char vec_xor (vector signed char, vector signed char);
vector unsigned char vec_xor (vector bool char, vector unsigned char);
vector unsigned char vec_xor (vector unsigned char, vector bool char);
vector unsigned char vec_xor (vector unsigned char,
                              vector unsigned char);

int vec_all_eq (vector signed char, vector bool char);
int vec_all_eq (vector signed char, vector signed char);
int vec_all_eq (vector unsigned char, vector bool char);
int vec_all_eq (vector unsigned char, vector unsigned char);
int vec_all_eq (vector bool char, vector bool char);
int vec_all_eq (vector bool char, vector unsigned char);
int vec_all_eq (vector bool char, vector signed char);
int vec_all_eq (vector signed short, vector bool short);
int vec_all_eq (vector signed short, vector signed short);
int vec_all_eq (vector unsigned short, vector bool short);
int vec_all_eq (vector unsigned short, vector unsigned short);
int vec_all_eq (vector bool short, vector bool short);
int vec_all_eq (vector bool short, vector unsigned short);
int vec_all_eq (vector bool short, vector signed short);
int vec_all_eq (vector pixel, vector pixel);
int vec_all_eq (vector signed int, vector bool int);
int vec_all_eq (vector signed int, vector signed int);
int vec_all_eq (vector unsigned int, vector bool int);
int vec_all_eq (vector unsigned int, vector unsigned int);
int vec_all_eq (vector bool int, vector bool int);
int vec_all_eq (vector bool int, vector unsigned int);
int vec_all_eq (vector bool int, vector signed int);
int vec_all_eq (vector float, vector float);

int vec_all_ge (vector bool char, vector unsigned char);
int vec_all_ge (vector unsigned char, vector bool char);
int vec_all_ge (vector unsigned char, vector unsigned char);
int vec_all_ge (vector bool char, vector signed char);
int vec_all_ge (vector signed char, vector bool char);
int vec_all_ge (vector signed char, vector signed char);
int vec_all_ge (vector bool short, vector unsigned short);
int vec_all_ge (vector unsigned short, vector bool short);
int vec_all_ge (vector unsigned short, vector unsigned short);
int vec_all_ge (vector signed short, vector signed short);
int vec_all_ge (vector bool short, vector signed short);
int vec_all_ge (vector signed short, vector bool short);
int vec_all_ge (vector bool int, vector unsigned int);
int vec_all_ge (vector unsigned int, vector bool int);
int vec_all_ge (vector unsigned int, vector unsigned int);
int vec_all_ge (vector bool int, vector signed int);
int vec_all_ge (vector signed int, vector bool int);
int vec_all_ge (vector signed int, vector signed int);
int vec_all_ge (vector float, vector float);

int vec_all_gt (vector bool char, vector unsigned char);
int vec_all_gt (vector unsigned char, vector bool char);
int vec_all_gt (vector unsigned char, vector unsigned char);
int vec_all_gt (vector bool char, vector signed char);
int vec_all_gt (vector signed char, vector bool char);
int vec_all_gt (vector signed char, vector signed char);
int vec_all_gt (vector bool short, vector unsigned short);
int vec_all_gt (vector unsigned short, vector bool short);
int vec_all_gt (vector unsigned short, vector unsigned short);
int vec_all_gt (vector bool short, vector signed short);
int vec_all_gt (vector signed short, vector bool short);
int vec_all_gt (vector signed short, vector signed short);
int vec_all_gt (vector bool int, vector unsigned int);
int vec_all_gt (vector unsigned int, vector bool int);
int vec_all_gt (vector unsigned int, vector unsigned int);
int vec_all_gt (vector bool int, vector signed int);
int vec_all_gt (vector signed int, vector bool int);
int vec_all_gt (vector signed int, vector signed int);
int vec_all_gt (vector float, vector float);

int vec_all_in (vector float, vector float);

int vec_all_le (vector bool char, vector unsigned char);
int vec_all_le (vector unsigned char, vector bool char);
int vec_all_le (vector unsigned char, vector unsigned char);
int vec_all_le (vector bool char, vector signed char);
int vec_all_le (vector signed char, vector bool char);
int vec_all_le (vector signed char, vector signed char);
int vec_all_le (vector bool short, vector unsigned short);
int vec_all_le (vector unsigned short, vector bool short);
int vec_all_le (vector unsigned short, vector unsigned short);
int vec_all_le (vector bool short, vector signed short);
int vec_all_le (vector signed short, vector bool short);
int vec_all_le (vector signed short, vector signed short);
int vec_all_le (vector bool int, vector unsigned int);
int vec_all_le (vector unsigned int, vector bool int);
int vec_all_le (vector unsigned int, vector unsigned int);
int vec_all_le (vector bool int, vector signed int);
int vec_all_le (vector signed int, vector bool int);
int vec_all_le (vector signed int, vector signed int);
int vec_all_le (vector float, vector float);

int vec_all_lt (vector bool char, vector unsigned char);
int vec_all_lt (vector unsigned char, vector bool char);
int vec_all_lt (vector unsigned char, vector unsigned char);
int vec_all_lt (vector bool char, vector signed char);
int vec_all_lt (vector signed char, vector bool char);
int vec_all_lt (vector signed char, vector signed char);
int vec_all_lt (vector bool short, vector unsigned short);
int vec_all_lt (vector unsigned short, vector bool short);
int vec_all_lt (vector unsigned short, vector unsigned short);
int vec_all_lt (vector bool short, vector signed short);
int vec_all_lt (vector signed short, vector bool short);
int vec_all_lt (vector signed short, vector signed short);
int vec_all_lt (vector bool int, vector unsigned int);
int vec_all_lt (vector unsigned int, vector bool int);
int vec_all_lt (vector unsigned int, vector unsigned int);
int vec_all_lt (vector bool int, vector signed int);
int vec_all_lt (vector signed int, vector bool int);
int vec_all_lt (vector signed int, vector signed int);
int vec_all_lt (vector float, vector float);

int vec_all_nan (vector float);

int vec_all_ne (vector signed char, vector bool char);
int vec_all_ne (vector signed char, vector signed char);
int vec_all_ne (vector unsigned char, vector bool char);
int vec_all_ne (vector unsigned char, vector unsigned char);
int vec_all_ne (vector bool char, vector bool char);
int vec_all_ne (vector bool char, vector unsigned char);
int vec_all_ne (vector bool char, vector signed char);
int vec_all_ne (vector signed short, vector bool short);
int vec_all_ne (vector signed short, vector signed short);
int vec_all_ne (vector unsigned short, vector bool short);
int vec_all_ne (vector unsigned short, vector unsigned short);
int vec_all_ne (vector bool short, vector bool short);
int vec_all_ne (vector bool short, vector unsigned short);
int vec_all_ne (vector bool short, vector signed short);
int vec_all_ne (vector pixel, vector pixel);
int vec_all_ne (vector signed int, vector bool int);
int vec_all_ne (vector signed int, vector signed int);
int vec_all_ne (vector unsigned int, vector bool int);
int vec_all_ne (vector unsigned int, vector unsigned int);
int vec_all_ne (vector bool int, vector bool int);
int vec_all_ne (vector bool int, vector unsigned int);
int vec_all_ne (vector bool int, vector signed int);
int vec_all_ne (vector float, vector float);

int vec_all_nge (vector float, vector float);

int vec_all_ngt (vector float, vector float);

int vec_all_nle (vector float, vector float);

int vec_all_nlt (vector float, vector float);

int vec_all_numeric (vector float);

int vec_any_eq (vector signed char, vector bool char);
int vec_any_eq (vector signed char, vector signed char);
int vec_any_eq (vector unsigned char, vector bool char);
int vec_any_eq (vector unsigned char, vector unsigned char);
int vec_any_eq (vector bool char, vector bool char);
int vec_any_eq (vector bool char, vector unsigned char);
int vec_any_eq (vector bool char, vector signed char);
int vec_any_eq (vector signed short, vector bool short);
int vec_any_eq (vector signed short, vector signed short);
int vec_any_eq (vector unsigned short, vector bool short);
int vec_any_eq (vector unsigned short, vector unsigned short);
int vec_any_eq (vector bool short, vector bool short);
int vec_any_eq (vector bool short, vector unsigned short);
int vec_any_eq (vector bool short, vector signed short);
int vec_any_eq (vector pixel, vector pixel);
int vec_any_eq (vector signed int, vector bool int);
int vec_any_eq (vector signed int, vector signed int);
int vec_any_eq (vector unsigned int, vector bool int);
int vec_any_eq (vector unsigned int, vector unsigned int);
int vec_any_eq (vector bool int, vector bool int);
int vec_any_eq (vector bool int, vector unsigned int);
int vec_any_eq (vector bool int, vector signed int);
int vec_any_eq (vector float, vector float);

int vec_any_ge (vector signed char, vector bool char);
int vec_any_ge (vector unsigned char, vector bool char);
int vec_any_ge (vector unsigned char, vector unsigned char);
int vec_any_ge (vector signed char, vector signed char);
int vec_any_ge (vector bool char, vector unsigned char);
int vec_any_ge (vector bool char, vector signed char);
int vec_any_ge (vector unsigned short, vector bool short);
int vec_any_ge (vector unsigned short, vector unsigned short);
int vec_any_ge (vector signed short, vector signed short);
int vec_any_ge (vector signed short, vector bool short);
int vec_any_ge (vector bool short, vector unsigned short);
int vec_any_ge (vector bool short, vector signed short);
int vec_any_ge (vector signed int, vector bool int);
int vec_any_ge (vector unsigned int, vector bool int);
int vec_any_ge (vector unsigned int, vector unsigned int);
int vec_any_ge (vector signed int, vector signed int);
int vec_any_ge (vector bool int, vector unsigned int);
int vec_any_ge (vector bool int, vector signed int);
int vec_any_ge (vector float, vector float);

int vec_any_gt (vector bool char, vector unsigned char);
int vec_any_gt (vector unsigned char, vector bool char);
int vec_any_gt (vector unsigned char, vector unsigned char);
int vec_any_gt (vector bool char, vector signed char);
int vec_any_gt (vector signed char, vector bool char);
int vec_any_gt (vector signed char, vector signed char);
int vec_any_gt (vector bool short, vector unsigned short);
int vec_any_gt (vector unsigned short, vector bool short);
int vec_any_gt (vector unsigned short, vector unsigned short);
int vec_any_gt (vector bool short, vector signed short);
int vec_any_gt (vector signed short, vector bool short);
int vec_any_gt (vector signed short, vector signed short);
int vec_any_gt (vector bool int, vector unsigned int);
int vec_any_gt (vector unsigned int, vector bool int);
int vec_any_gt (vector unsigned int, vector unsigned int);
int vec_any_gt (vector bool int, vector signed int);
int vec_any_gt (vector signed int, vector bool int);
int vec_any_gt (vector signed int, vector signed int);
int vec_any_gt (vector float, vector float);

int vec_any_le (vector bool char, vector unsigned char);
int vec_any_le (vector unsigned char, vector bool char);
int vec_any_le (vector unsigned char, vector unsigned char);
int vec_any_le (vector bool char, vector signed char);
int vec_any_le (vector signed char, vector bool char);
int vec_any_le (vector signed char, vector signed char);
int vec_any_le (vector bool short, vector unsigned short);
int vec_any_le (vector unsigned short, vector bool short);
int vec_any_le (vector unsigned short, vector unsigned short);
int vec_any_le (vector bool short, vector signed short);
int vec_any_le (vector signed short, vector bool short);
int vec_any_le (vector signed short, vector signed short);
int vec_any_le (vector bool int, vector unsigned int);
int vec_any_le (vector unsigned int, vector bool int);
int vec_any_le (vector unsigned int, vector unsigned int);
int vec_any_le (vector bool int, vector signed int);
int vec_any_le (vector signed int, vector bool int);
int vec_any_le (vector signed int, vector signed int);
int vec_any_le (vector float, vector float);

int vec_any_lt (vector bool char, vector unsigned char);
int vec_any_lt (vector unsigned char, vector bool char);
int vec_any_lt (vector unsigned char, vector unsigned char);
int vec_any_lt (vector bool char, vector signed char);
int vec_any_lt (vector signed char, vector bool char);
int vec_any_lt (vector signed char, vector signed char);
int vec_any_lt (vector bool short, vector unsigned short);
int vec_any_lt (vector unsigned short, vector bool short);
int vec_any_lt (vector unsigned short, vector unsigned short);
int vec_any_lt (vector bool short, vector signed short);
int vec_any_lt (vector signed short, vector bool short);
int vec_any_lt (vector signed short, vector signed short);
int vec_any_lt (vector bool int, vector unsigned int);
int vec_any_lt (vector unsigned int, vector bool int);
int vec_any_lt (vector unsigned int, vector unsigned int);
int vec_any_lt (vector bool int, vector signed int);
int vec_any_lt (vector signed int, vector bool int);
int vec_any_lt (vector signed int, vector signed int);
int vec_any_lt (vector float, vector float);

int vec_any_nan (vector float);

int vec_any_ne (vector signed char, vector bool char);
int vec_any_ne (vector signed char, vector signed char);
int vec_any_ne (vector unsigned char, vector bool char);
int vec_any_ne (vector unsigned char, vector unsigned char);
int vec_any_ne (vector bool char, vector bool char);
int vec_any_ne (vector bool char, vector unsigned char);
int vec_any_ne (vector bool char, vector signed char);
int vec_any_ne (vector signed short, vector bool short);
int vec_any_ne (vector signed short, vector signed short);
int vec_any_ne (vector unsigned short, vector bool short);
int vec_any_ne (vector unsigned short, vector unsigned short);
int vec_any_ne (vector bool short, vector bool short);
int vec_any_ne (vector bool short, vector unsigned short);
int vec_any_ne (vector bool short, vector signed short);
int vec_any_ne (vector pixel, vector pixel);
int vec_any_ne (vector signed int, vector bool int);
int vec_any_ne (vector signed int, vector signed int);
int vec_any_ne (vector unsigned int, vector bool int);
int vec_any_ne (vector unsigned int, vector unsigned int);
int vec_any_ne (vector bool int, vector bool int);
int vec_any_ne (vector bool int, vector unsigned int);
int vec_any_ne (vector bool int, vector signed int);
int vec_any_ne (vector float, vector float);

int vec_any_nge (vector float, vector float);

int vec_any_ngt (vector float, vector float);

int vec_any_nle (vector float, vector float);

int vec_any_nlt (vector float, vector float);

int vec_any_numeric (vector float);

int vec_any_out (vector float, vector float);
@end smallexample

If the vector/scalar (VSX) instruction set is available, the following
additional functions are available:

@smallexample
vector double vec_abs (vector double);
vector double vec_add (vector double, vector double);
vector double vec_and (vector double, vector double);
vector double vec_and (vector double, vector bool long);
vector double vec_and (vector bool long, vector double);
vector double vec_andc (vector double, vector double);
vector double vec_andc (vector double, vector bool long);
vector double vec_andc (vector bool long, vector double);
vector double vec_ceil (vector double);
vector bool long vec_cmpeq (vector double, vector double);
vector bool long vec_cmpge (vector double, vector double);
vector bool long vec_cmpgt (vector double, vector double);
vector bool long vec_cmple (vector double, vector double);
vector bool long vec_cmplt (vector double, vector double);
vector float vec_div (vector float, vector float);
vector double vec_div (vector double, vector double);
vector double vec_floor (vector double);
vector double vec_ld (int, const vector double *);
vector double vec_ld (int, const double *);
vector double vec_ldl (int, const vector double *);
vector double vec_ldl (int, const double *);
vector unsigned char vec_lvsl (int, const volatile double *);
vector unsigned char vec_lvsr (int, const volatile double *);
vector double vec_madd (vector double, vector double, vector double);
vector double vec_max (vector double, vector double);
vector double vec_min (vector double, vector double);
vector float vec_msub (vector float, vector float, vector float);
vector double vec_msub (vector double, vector double, vector double);
vector float vec_mul (vector float, vector float);
vector double vec_mul (vector double, vector double);
vector float vec_nearbyint (vector float);
vector double vec_nearbyint (vector double);
vector float vec_nmadd (vector float, vector float, vector float);
vector double vec_nmadd (vector double, vector double, vector double);
vector double vec_nmsub (vector double, vector double, vector double);
vector double vec_nor (vector double, vector double);
vector double vec_or (vector double, vector double);
vector double vec_or (vector double, vector bool long);
vector double vec_or (vector bool long, vector double);
vector double vec_perm (vector double,
                        vector double,
                        vector unsigned char);
vector double vec_rint (vector double);
vector double vec_recip (vector double, vector double);
vector double vec_rsqrt (vector double);
vector double vec_rsqrte (vector double);
vector double vec_sel (vector double, vector double, vector bool long);
vector double vec_sel (vector double, vector double, vector unsigned long);
vector double vec_sub (vector double, vector double);
vector float vec_sqrt (vector float);
vector double vec_sqrt (vector double);
void vec_st (vector double, int, vector double *);
void vec_st (vector double, int, double *);
vector double vec_trunc (vector double);
vector double vec_xor (vector double, vector double);
vector double vec_xor (vector double, vector bool long);
vector double vec_xor (vector bool long, vector double);
int vec_all_eq (vector double, vector double);
int vec_all_ge (vector double, vector double);
int vec_all_gt (vector double, vector double);
int vec_all_le (vector double, vector double);
int vec_all_lt (vector double, vector double);
int vec_all_nan (vector double);
int vec_all_ne (vector double, vector double);
int vec_all_nge (vector double, vector double);
int vec_all_ngt (vector double, vector double);
int vec_all_nle (vector double, vector double);
int vec_all_nlt (vector double, vector double);
int vec_all_numeric (vector double);
int vec_any_eq (vector double, vector double);
int vec_any_ge (vector double, vector double);
int vec_any_gt (vector double, vector double);
int vec_any_le (vector double, vector double);
int vec_any_lt (vector double, vector double);
int vec_any_nan (vector double);
int vec_any_ne (vector double, vector double);
int vec_any_nge (vector double, vector double);
int vec_any_ngt (vector double, vector double);
int vec_any_nle (vector double, vector double);
int vec_any_nlt (vector double, vector double);
int vec_any_numeric (vector double);

vector double vec_vsx_ld (int, const vector double *);
vector double vec_vsx_ld (int, const double *);
vector float vec_vsx_ld (int, const vector float *);
vector float vec_vsx_ld (int, const float *);
vector bool int vec_vsx_ld (int, const vector bool int *);
vector signed int vec_vsx_ld (int, const vector signed int *);
vector signed int vec_vsx_ld (int, const int *);
vector signed int vec_vsx_ld (int, const long *);
vector unsigned int vec_vsx_ld (int, const vector unsigned int *);
vector unsigned int vec_vsx_ld (int, const unsigned int *);
vector unsigned int vec_vsx_ld (int, const unsigned long *);
vector bool short vec_vsx_ld (int, const vector bool short *);
vector pixel vec_vsx_ld (int, const vector pixel *);
vector signed short vec_vsx_ld (int, const vector signed short *);
vector signed short vec_vsx_ld (int, const short *);
vector unsigned short vec_vsx_ld (int, const vector unsigned short *);
vector unsigned short vec_vsx_ld (int, const unsigned short *);
vector bool char vec_vsx_ld (int, const vector bool char *);
vector signed char vec_vsx_ld (int, const vector signed char *);
vector signed char vec_vsx_ld (int, const signed char *);
vector unsigned char vec_vsx_ld (int, const vector unsigned char *);
vector unsigned char vec_vsx_ld (int, const unsigned char *);

void vec_vsx_st (vector double, int, vector double *);
void vec_vsx_st (vector double, int, double *);
void vec_vsx_st (vector float, int, vector float *);
void vec_vsx_st (vector float, int, float *);
void vec_vsx_st (vector signed int, int, vector signed int *);
void vec_vsx_st (vector signed int, int, int *);
void vec_vsx_st (vector unsigned int, int, vector unsigned int *);
void vec_vsx_st (vector unsigned int, int, unsigned int *);
void vec_vsx_st (vector bool int, int, vector bool int *);
void vec_vsx_st (vector bool int, int, unsigned int *);
void vec_vsx_st (vector bool int, int, int *);
void vec_vsx_st (vector signed short, int, vector signed short *);
void vec_vsx_st (vector signed short, int, short *);
void vec_vsx_st (vector unsigned short, int, vector unsigned short *);
void vec_vsx_st (vector unsigned short, int, unsigned short *);
void vec_vsx_st (vector bool short, int, vector bool short *);
void vec_vsx_st (vector bool short, int, unsigned short *);
void vec_vsx_st (vector pixel, int, vector pixel *);
void vec_vsx_st (vector pixel, int, unsigned short *);
void vec_vsx_st (vector pixel, int, short *);
void vec_vsx_st (vector bool short, int, short *);
void vec_vsx_st (vector signed char, int, vector signed char *);
void vec_vsx_st (vector signed char, int, signed char *);
void vec_vsx_st (vector unsigned char, int, vector unsigned char *);
void vec_vsx_st (vector unsigned char, int, unsigned char *);
void vec_vsx_st (vector bool char, int, vector bool char *);
void vec_vsx_st (vector bool char, int, unsigned char *);
void vec_vsx_st (vector bool char, int, signed char *);
@end smallexample

Note that the @samp{vec_ld} and @samp{vec_st} built-in functions always
generate the AltiVec @samp{LVX} and @samp{STVX} instructions even
if the VSX instruction set is available.  The @samp{vec_vsx_ld} and
@samp{vec_vsx_st} built-in functions always generate the VSX @samp{LXVD2X},
@samp{LXVW4X}, @samp{STXVD2X}, and @samp{STXVW4X} instructions.

If the ISA 2.07 additions to the vector/scalar (power8-vector)
instruction set is available, the following additional functions are
available for both 32-bit and 64-bit targets.  For 64-bit targets, you
can use @var{vector long} instead of @var{vector long long},
@var{vector bool long} instead of @var{vector bool long long}, and
@var{vector unsigned long} instead of @var{vector unsigned long long}.

@smallexample
vector long long vec_abs (vector long long);

vector long long vec_add (vector long long, vector long long);
vector unsigned long long vec_add (vector unsigned long long,
                                   vector unsigned long long);

int vec_all_eq (vector long long, vector long long);
int vec_all_ge (vector long long, vector long long);
int vec_all_gt (vector long long, vector long long);
int vec_all_le (vector long long, vector long long);
int vec_all_lt (vector long long, vector long long);
int vec_all_ne (vector long long, vector long long);
int vec_any_eq (vector long long, vector long long);
int vec_any_ge (vector long long, vector long long);
int vec_any_gt (vector long long, vector long long);
int vec_any_le (vector long long, vector long long);
int vec_any_lt (vector long long, vector long long);
int vec_any_ne (vector long long, vector long long);

vector long long vec_eqv (vector long long, vector long long);
vector long long vec_eqv (vector bool long long, vector long long);
vector long long vec_eqv (vector long long, vector bool long long);
vector unsigned long long vec_eqv (vector unsigned long long,
                                   vector unsigned long long);
vector unsigned long long vec_eqv (vector bool long long,
                                   vector unsigned long long);
vector unsigned long long vec_eqv (vector unsigned long long,
                                   vector bool long long);
vector int vec_eqv (vector int, vector int);
vector int vec_eqv (vector bool int, vector int);
vector int vec_eqv (vector int, vector bool int);
vector unsigned int vec_eqv (vector unsigned int, vector unsigned int);
vector unsigned int vec_eqv (vector bool unsigned int,
                             vector unsigned int);
vector unsigned int vec_eqv (vector unsigned int,
                             vector bool unsigned int);
vector short vec_eqv (vector short, vector short);
vector short vec_eqv (vector bool short, vector short);
vector short vec_eqv (vector short, vector bool short);
vector unsigned short vec_eqv (vector unsigned short, vector unsigned short);
vector unsigned short vec_eqv (vector bool unsigned short,
                               vector unsigned short);
vector unsigned short vec_eqv (vector unsigned short,
                               vector bool unsigned short);
vector signed char vec_eqv (vector signed char, vector signed char);
vector signed char vec_eqv (vector bool signed char, vector signed char);
vector signed char vec_eqv (vector signed char, vector bool signed char);
vector unsigned char vec_eqv (vector unsigned char, vector unsigned char);
vector unsigned char vec_eqv (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_eqv (vector unsigned char, vector bool unsigned char);

vector long long vec_max (vector long long, vector long long);
vector unsigned long long vec_max (vector unsigned long long,
                                   vector unsigned long long);

vector long long vec_min (vector long long, vector long long);
vector unsigned long long vec_min (vector unsigned long long,
                                   vector unsigned long long);

vector long long vec_nand (vector long long, vector long long);
vector long long vec_nand (vector bool long long, vector long long);
vector long long vec_nand (vector long long, vector bool long long);
vector unsigned long long vec_nand (vector unsigned long long,
                                    vector unsigned long long);
vector unsigned long long vec_nand (vector bool long long,
                                   vector unsigned long long);
vector unsigned long long vec_nand (vector unsigned long long,
                                    vector bool long long);
vector int vec_nand (vector int, vector int);
vector int vec_nand (vector bool int, vector int);
vector int vec_nand (vector int, vector bool int);
vector unsigned int vec_nand (vector unsigned int, vector unsigned int);
vector unsigned int vec_nand (vector bool unsigned int,
                              vector unsigned int);
vector unsigned int vec_nand (vector unsigned int,
                              vector bool unsigned int);
vector short vec_nand (vector short, vector short);
vector short vec_nand (vector bool short, vector short);
vector short vec_nand (vector short, vector bool short);
vector unsigned short vec_nand (vector unsigned short, vector unsigned short);
vector unsigned short vec_nand (vector bool unsigned short,
                                vector unsigned short);
vector unsigned short vec_nand (vector unsigned short,
                                vector bool unsigned short);
vector signed char vec_nand (vector signed char, vector signed char);
vector signed char vec_nand (vector bool signed char, vector signed char);
vector signed char vec_nand (vector signed char, vector bool signed char);
vector unsigned char vec_nand (vector unsigned char, vector unsigned char);
vector unsigned char vec_nand (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_nand (vector unsigned char, vector bool unsigned char);

vector long long vec_orc (vector long long, vector long long);
vector long long vec_orc (vector bool long long, vector long long);
vector long long vec_orc (vector long long, vector bool long long);
vector unsigned long long vec_orc (vector unsigned long long,
                                   vector unsigned long long);
vector unsigned long long vec_orc (vector bool long long,
                                   vector unsigned long long);
vector unsigned long long vec_orc (vector unsigned long long,
                                   vector bool long long);
vector int vec_orc (vector int, vector int);
vector int vec_orc (vector bool int, vector int);
vector int vec_orc (vector int, vector bool int);
vector unsigned int vec_orc (vector unsigned int, vector unsigned int);
vector unsigned int vec_orc (vector bool unsigned int,
                             vector unsigned int);
vector unsigned int vec_orc (vector unsigned int,
                             vector bool unsigned int);
vector short vec_orc (vector short, vector short);
vector short vec_orc (vector bool short, vector short);
vector short vec_orc (vector short, vector bool short);
vector unsigned short vec_orc (vector unsigned short, vector unsigned short);
vector unsigned short vec_orc (vector bool unsigned short,
                               vector unsigned short);
vector unsigned short vec_orc (vector unsigned short,
                               vector bool unsigned short);
vector signed char vec_orc (vector signed char, vector signed char);
vector signed char vec_orc (vector bool signed char, vector signed char);
vector signed char vec_orc (vector signed char, vector bool signed char);
vector unsigned char vec_orc (vector unsigned char, vector unsigned char);
vector unsigned char vec_orc (vector bool unsigned char, vector unsigned char);
vector unsigned char vec_orc (vector unsigned char, vector bool unsigned char);

vector int vec_pack (vector long long, vector long long);
vector unsigned int vec_pack (vector unsigned long long,
                              vector unsigned long long);
vector bool int vec_pack (vector bool long long, vector bool long long);

vector int vec_packs (vector long long, vector long long);
vector unsigned int vec_packs (vector unsigned long long,
                               vector unsigned long long);

vector unsigned int vec_packsu (vector long long, vector long long);

vector long long vec_rl (vector long long,
                         vector unsigned long long);
vector long long vec_rl (vector unsigned long long,
                         vector unsigned long long);

vector long long vec_sl (vector long long, vector unsigned long long);
vector long long vec_sl (vector unsigned long long,
                         vector unsigned long long);

vector long long vec_sr (vector long long, vector unsigned long long);
vector unsigned long long char vec_sr (vector unsigned long long,
                                       vector unsigned long long);

vector long long vec_sra (vector long long, vector unsigned long long);
vector unsigned long long vec_sra (vector unsigned long long,
                                   vector unsigned long long);

vector long long vec_sub (vector long long, vector long long);
vector unsigned long long vec_sub (vector unsigned long long,
                                   vector unsigned long long);

vector long long vec_unpackh (vector int);
vector unsigned long long vec_unpackh (vector unsigned int);

vector long long vec_unpackl (vector int);
vector unsigned long long vec_unpackl (vector unsigned int);

vector long long vec_vaddudm (vector long long, vector long long);
vector long long vec_vaddudm (vector bool long long, vector long long);
vector long long vec_vaddudm (vector long long, vector bool long long);
vector unsigned long long vec_vaddudm (vector unsigned long long,
                                       vector unsigned long long);
vector unsigned long long vec_vaddudm (vector bool unsigned long long,
                                       vector unsigned long long);
vector unsigned long long vec_vaddudm (vector unsigned long long,
                                       vector bool unsigned long long);

vector long long vec_vclz (vector long long);
vector unsigned long long vec_vclz (vector unsigned long long);
vector int vec_vclz (vector int);
vector unsigned int vec_vclz (vector int);
vector short vec_vclz (vector short);
vector unsigned short vec_vclz (vector unsigned short);
vector signed char vec_vclz (vector signed char);
vector unsigned char vec_vclz (vector unsigned char);

vector signed char vec_vclzb (vector signed char);
vector unsigned char vec_vclzb (vector unsigned char);

vector long long vec_vclzd (vector long long);
vector unsigned long long vec_vclzd (vector unsigned long long);

vector short vec_vclzh (vector short);
vector unsigned short vec_vclzh (vector unsigned short);

vector int vec_vclzw (vector int);
vector unsigned int vec_vclzw (vector int);

vector long long vec_vmaxsd (vector long long, vector long long);

vector unsigned long long vec_vmaxud (vector unsigned long long,
                                      unsigned vector long long);

vector long long vec_vminsd (vector long long, vector long long);

vector unsigned long long vec_vminud (vector long long,
                                      vector long long);

vector int vec_vpksdss (vector long long, vector long long);
vector unsigned int vec_vpksdss (vector long long, vector long long);

vector unsigned int vec_vpkudus (vector unsigned long long,
                                 vector unsigned long long);

vector int vec_vpkudum (vector long long, vector long long);
vector unsigned int vec_vpkudum (vector unsigned long long,
                                 vector unsigned long long);
vector bool int vec_vpkudum (vector bool long long, vector bool long long);

vector long long vec_vpopcnt (vector long long);
vector unsigned long long vec_vpopcnt (vector unsigned long long);
vector int vec_vpopcnt (vector int);
vector unsigned int vec_vpopcnt (vector int);
vector short vec_vpopcnt (vector short);
vector unsigned short vec_vpopcnt (vector unsigned short);
vector signed char vec_vpopcnt (vector signed char);
vector unsigned char vec_vpopcnt (vector unsigned char);

vector signed char vec_vpopcntb (vector signed char);
vector unsigned char vec_vpopcntb (vector unsigned char);

vector long long vec_vpopcntd (vector long long);
vector unsigned long long vec_vpopcntd (vector unsigned long long);

vector short vec_vpopcnth (vector short);
vector unsigned short vec_vpopcnth (vector unsigned short);

vector int vec_vpopcntw (vector int);
vector unsigned int vec_vpopcntw (vector int);

vector long long vec_vrld (vector long long, vector unsigned long long);
vector unsigned long long vec_vrld (vector unsigned long long,
                                    vector unsigned long long);

vector long long vec_vsld (vector long long, vector unsigned long long);
vector long long vec_vsld (vector unsigned long long,
                           vector unsigned long long);

vector long long vec_vsrad (vector long long, vector unsigned long long);
vector unsigned long long vec_vsrad (vector unsigned long long,
                                     vector unsigned long long);

vector long long vec_vsrd (vector long long, vector unsigned long long);
vector unsigned long long char vec_vsrd (vector unsigned long long,
                                         vector unsigned long long);

vector long long vec_vsubudm (vector long long, vector long long);
vector long long vec_vsubudm (vector bool long long, vector long long);
vector long long vec_vsubudm (vector long long, vector bool long long);
vector unsigned long long vec_vsubudm (vector unsigned long long,
                                       vector unsigned long long);
vector unsigned long long vec_vsubudm (vector bool long long,
                                       vector unsigned long long);
vector unsigned long long vec_vsubudm (vector unsigned long long,
                                       vector bool long long);

vector long long vec_vupkhsw (vector int);
vector unsigned long long vec_vupkhsw (vector unsigned int);

vector long long vec_vupklsw (vector int);
vector unsigned long long vec_vupklsw (vector int);
@end smallexample

If the cryptographic instructions are enabled (@option{-mcrypto} or
@option{-mcpu=power8}), the following builtins are enabled.

@smallexample
vector unsigned long long __builtin_crypto_vsbox (vector unsigned long long);

vector unsigned long long __builtin_crypto_vcipher (vector unsigned long long,
                                                    vector unsigned long long);

vector unsigned long long __builtin_crypto_vcipherlast
                                     (vector unsigned long long,
                                      vector unsigned long long);

vector unsigned long long __builtin_crypto_vncipher (vector unsigned long long,
                                                     vector unsigned long long);

vector unsigned long long __builtin_crypto_vncipherlast
                                     (vector unsigned long long,
                                      vector unsigned long long);

vector unsigned char __builtin_crypto_vpermxor (vector unsigned char,
                                                vector unsigned char,
                                                vector unsigned char);

vector unsigned short __builtin_crypto_vpermxor (vector unsigned short,
                                                 vector unsigned short,
                                                 vector unsigned short);

vector unsigned int __builtin_crypto_vpermxor (vector unsigned int,
                                               vector unsigned int,
                                               vector unsigned int);

vector unsigned long long __builtin_crypto_vpermxor (vector unsigned long long,
                                                     vector unsigned long long,
                                                     vector unsigned long long);

vector unsigned char __builtin_crypto_vpmsumb (vector unsigned char,
                                               vector unsigned char);

vector unsigned short __builtin_crypto_vpmsumb (vector unsigned short,
                                                vector unsigned short);

vector unsigned int __builtin_crypto_vpmsumb (vector unsigned int,
                                              vector unsigned int);

vector unsigned long long __builtin_crypto_vpmsumb (vector unsigned long long,
                                                    vector unsigned long long);

vector unsigned long long __builtin_crypto_vshasigmad
                               (vector unsigned long long, int, int);

vector unsigned int __builtin_crypto_vshasigmaw (vector unsigned int,
                                                 int, int);
@end smallexample

The second argument to the @var{__builtin_crypto_vshasigmad} and
@var{__builtin_crypto_vshasigmaw} builtin functions must be a constant
integer that is 0 or 1.  The third argument to these builtin functions
must be a constant integer in the range of 0 to 15.

@node RX Built-in Functions
@subsection RX Built-in Functions
GCC supports some of the RX instructions which cannot be expressed in
the C programming language via the use of built-in functions.  The
following functions are supported:

@deftypefn {Built-in Function}  void __builtin_rx_brk (void)
Generates the @code{brk} machine instruction.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_clrpsw (int)
Generates the @code{clrpsw} machine instruction to clear the specified
bit in the processor status word.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_int (int)
Generates the @code{int} machine instruction to generate an interrupt
with the specified value.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_machi (int, int)
Generates the @code{machi} machine instruction to add the result of
multiplying the top 16 bits of the two arguments into the
accumulator.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_maclo (int, int)
Generates the @code{maclo} machine instruction to add the result of
multiplying the bottom 16 bits of the two arguments into the
accumulator.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_mulhi (int, int)
Generates the @code{mulhi} machine instruction to place the result of
multiplying the top 16 bits of the two arguments into the
accumulator.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_mullo (int, int)
Generates the @code{mullo} machine instruction to place the result of
multiplying the bottom 16 bits of the two arguments into the
accumulator.
@end deftypefn

@deftypefn {Built-in Function}  int  __builtin_rx_mvfachi (void)
Generates the @code{mvfachi} machine instruction to read the top
32 bits of the accumulator.
@end deftypefn

@deftypefn {Built-in Function}  int  __builtin_rx_mvfacmi (void)
Generates the @code{mvfacmi} machine instruction to read the middle
32 bits of the accumulator.
@end deftypefn

@deftypefn {Built-in Function}  int __builtin_rx_mvfc (int)
Generates the @code{mvfc} machine instruction which reads the control
register specified in its argument and returns its value.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_mvtachi (int)
Generates the @code{mvtachi} machine instruction to set the top
32 bits of the accumulator.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_mvtaclo (int)
Generates the @code{mvtaclo} machine instruction to set the bottom
32 bits of the accumulator.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_mvtc (int reg, int val)
Generates the @code{mvtc} machine instruction which sets control
register number @code{reg} to @code{val}.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_mvtipl (int)
Generates the @code{mvtipl} machine instruction set the interrupt
priority level.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_racw (int)
Generates the @code{racw} machine instruction to round the accumulator
according to the specified mode.
@end deftypefn

@deftypefn {Built-in Function}  int __builtin_rx_revw (int)
Generates the @code{revw} machine instruction which swaps the bytes in
the argument so that bits 0--7 now occupy bits 8--15 and vice versa,
and also bits 16--23 occupy bits 24--31 and vice versa.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_rmpa (void)
Generates the @code{rmpa} machine instruction which initiates a
repeated multiply and accumulate sequence.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_round (float)
Generates the @code{round} machine instruction which returns the
floating-point argument rounded according to the current rounding mode
set in the floating-point status word register.
@end deftypefn

@deftypefn {Built-in Function}  int __builtin_rx_sat (int)
Generates the @code{sat} machine instruction which returns the
saturated value of the argument.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_setpsw (int)
Generates the @code{setpsw} machine instruction to set the specified
bit in the processor status word.
@end deftypefn

@deftypefn {Built-in Function}  void __builtin_rx_wait (void)
Generates the @code{wait} machine instruction.
@end deftypefn

@node SH Built-in Functions
@subsection SH Built-in Functions
The following built-in functions are supported on the SH1, SH2, SH3 and SH4
families of processors:

@deftypefn {Built-in Function} {void} __builtin_set_thread_pointer (void *@var{ptr})
Sets the @samp{GBR} register to the specified value @var{ptr}.  This is usually
used by system code that manages threads and execution contexts.  The compiler
normally does not generate code that modifies the contents of @samp{GBR} and
thus the value is preserved across function calls.  Changing the @samp{GBR}
value in user code must be done with caution, since the compiler might use
@samp{GBR} in order to access thread local variables.

@end deftypefn

@deftypefn {Built-in Function} {void *} __builtin_thread_pointer (void)
Returns the value that is currently set in the @samp{GBR} register.
Memory loads and stores that use the thread pointer as a base address are
turned into @samp{GBR} based displacement loads and stores, if possible.
For example:
@smallexample
struct my_tcb
@{
   int a, b, c, d, e;
@};

int get_tcb_value (void)
@{
  // Generate @samp{mov.l @@(8,gbr),r0} instruction
  return ((my_tcb*)__builtin_thread_pointer ())->c;
@}

@end smallexample
@end deftypefn

@node SPARC VIS Built-in Functions
@subsection SPARC VIS Built-in Functions

GCC supports SIMD operations on the SPARC using both the generic vector
extensions (@pxref{Vector Extensions}) as well as built-in functions for
the SPARC Visual Instruction Set (VIS).  When you use the @option{-mvis}
switch, the VIS extension is exposed as the following built-in functions:

@smallexample
typedef int v1si __attribute__ ((vector_size (4)));
typedef int v2si __attribute__ ((vector_size (8)));
typedef short v4hi __attribute__ ((vector_size (8)));
typedef short v2hi __attribute__ ((vector_size (4)));
typedef unsigned char v8qi __attribute__ ((vector_size (8)));
typedef unsigned char v4qi __attribute__ ((vector_size (4)));

void __builtin_vis_write_gsr (int64_t);
int64_t __builtin_vis_read_gsr (void);

void * __builtin_vis_alignaddr (void *, long);
void * __builtin_vis_alignaddrl (void *, long);
int64_t __builtin_vis_faligndatadi (int64_t, int64_t);
v2si __builtin_vis_faligndatav2si (v2si, v2si);
v4hi __builtin_vis_faligndatav4hi (v4si, v4si);
v8qi __builtin_vis_faligndatav8qi (v8qi, v8qi);

v4hi __builtin_vis_fexpand (v4qi);

v4hi __builtin_vis_fmul8x16 (v4qi, v4hi);
v4hi __builtin_vis_fmul8x16au (v4qi, v2hi);
v4hi __builtin_vis_fmul8x16al (v4qi, v2hi);
v4hi __builtin_vis_fmul8sux16 (v8qi, v4hi);
v4hi __builtin_vis_fmul8ulx16 (v8qi, v4hi);
v2si __builtin_vis_fmuld8sux16 (v4qi, v2hi);
v2si __builtin_vis_fmuld8ulx16 (v4qi, v2hi);

v4qi __builtin_vis_fpack16 (v4hi);
v8qi __builtin_vis_fpack32 (v2si, v8qi);
v2hi __builtin_vis_fpackfix (v2si);
v8qi __builtin_vis_fpmerge (v4qi, v4qi);

int64_t __builtin_vis_pdist (v8qi, v8qi, int64_t);

long __builtin_vis_edge8 (void *, void *);
long __builtin_vis_edge8l (void *, void *);
long __builtin_vis_edge16 (void *, void *);
long __builtin_vis_edge16l (void *, void *);
long __builtin_vis_edge32 (void *, void *);
long __builtin_vis_edge32l (void *, void *);

long __builtin_vis_fcmple16 (v4hi, v4hi);
long __builtin_vis_fcmple32 (v2si, v2si);
long __builtin_vis_fcmpne16 (v4hi, v4hi);
long __builtin_vis_fcmpne32 (v2si, v2si);
long __builtin_vis_fcmpgt16 (v4hi, v4hi);
long __builtin_vis_fcmpgt32 (v2si, v2si);
long __builtin_vis_fcmpeq16 (v4hi, v4hi);
long __builtin_vis_fcmpeq32 (v2si, v2si);

v4hi __builtin_vis_fpadd16 (v4hi, v4hi);
v2hi __builtin_vis_fpadd16s (v2hi, v2hi);
v2si __builtin_vis_fpadd32 (v2si, v2si);
v1si __builtin_vis_fpadd32s (v1si, v1si);
v4hi __builtin_vis_fpsub16 (v4hi, v4hi);
v2hi __builtin_vis_fpsub16s (v2hi, v2hi);
v2si __builtin_vis_fpsub32 (v2si, v2si);
v1si __builtin_vis_fpsub32s (v1si, v1si);

long __builtin_vis_array8 (long, long);
long __builtin_vis_array16 (long, long);
long __builtin_vis_array32 (long, long);
@end smallexample

When you use the @option{-mvis2} switch, the VIS version 2.0 built-in
functions also become available:

@smallexample
long __builtin_vis_bmask (long, long);
int64_t __builtin_vis_bshuffledi (int64_t, int64_t);
v2si __builtin_vis_bshufflev2si (v2si, v2si);
v4hi __builtin_vis_bshufflev2si (v4hi, v4hi);
v8qi __builtin_vis_bshufflev2si (v8qi, v8qi);

long __builtin_vis_edge8n (void *, void *);
long __builtin_vis_edge8ln (void *, void *);
long __builtin_vis_edge16n (void *, void *);
long __builtin_vis_edge16ln (void *, void *);
long __builtin_vis_edge32n (void *, void *);
long __builtin_vis_edge32ln (void *, void *);
@end smallexample

When you use the @option{-mvis3} switch, the VIS version 3.0 built-in
functions also become available:

@smallexample
void __builtin_vis_cmask8 (long);
void __builtin_vis_cmask16 (long);
void __builtin_vis_cmask32 (long);

v4hi __builtin_vis_fchksm16 (v4hi, v4hi);

v4hi __builtin_vis_fsll16 (v4hi, v4hi);
v4hi __builtin_vis_fslas16 (v4hi, v4hi);
v4hi __builtin_vis_fsrl16 (v4hi, v4hi);
v4hi __builtin_vis_fsra16 (v4hi, v4hi);
v2si __builtin_vis_fsll16 (v2si, v2si);
v2si __builtin_vis_fslas16 (v2si, v2si);
v2si __builtin_vis_fsrl16 (v2si, v2si);
v2si __builtin_vis_fsra16 (v2si, v2si);

long __builtin_vis_pdistn (v8qi, v8qi);

v4hi __builtin_vis_fmean16 (v4hi, v4hi);

int64_t __builtin_vis_fpadd64 (int64_t, int64_t);
int64_t __builtin_vis_fpsub64 (int64_t, int64_t);

v4hi __builtin_vis_fpadds16 (v4hi, v4hi);
v2hi __builtin_vis_fpadds16s (v2hi, v2hi);
v4hi __builtin_vis_fpsubs16 (v4hi, v4hi);
v2hi __builtin_vis_fpsubs16s (v2hi, v2hi);
v2si __builtin_vis_fpadds32 (v2si, v2si);
v1si __builtin_vis_fpadds32s (v1si, v1si);
v2si __builtin_vis_fpsubs32 (v2si, v2si);
v1si __builtin_vis_fpsubs32s (v1si, v1si);

long __builtin_vis_fucmple8 (v8qi, v8qi);
long __builtin_vis_fucmpne8 (v8qi, v8qi);
long __builtin_vis_fucmpgt8 (v8qi, v8qi);
long __builtin_vis_fucmpeq8 (v8qi, v8qi);

float __builtin_vis_fhadds (float, float);
double __builtin_vis_fhaddd (double, double);
float __builtin_vis_fhsubs (float, float);
double __builtin_vis_fhsubd (double, double);
float __builtin_vis_fnhadds (float, float);
double __builtin_vis_fnhaddd (double, double);

int64_t __builtin_vis_umulxhi (int64_t, int64_t);
int64_t __builtin_vis_xmulx (int64_t, int64_t);
int64_t __builtin_vis_xmulxhi (int64_t, int64_t);
@end smallexample

@node SPU Built-in Functions
@subsection SPU Built-in Functions

GCC provides extensions for the SPU processor as described in the
Sony/Toshiba/IBM SPU Language Extensions Specification, which can be
found at @uref{http://cell.scei.co.jp/} or
@uref{http://www.ibm.com/developerworks/power/cell/}.  GCC's
implementation differs in several ways.

@itemize @bullet

@item
The optional extension of specifying vector constants in parentheses is
not supported.

@item
A vector initializer requires no cast if the vector constant is of the
same type as the variable it is initializing.

@item
If @code{signed} or @code{unsigned} is omitted, the signedness of the
vector type is the default signedness of the base type.  The default
varies depending on the operating system, so a portable program should
always specify the signedness.

@item
By default, the keyword @code{__vector} is added. The macro
@code{vector} is defined in @code{<spu_intrinsics.h>} and can be
undefined.

@item
GCC allows using a @code{typedef} name as the type specifier for a
vector type.

@item
For C, overloaded functions are implemented with macros so the following
does not work:

@smallexample
  spu_add ((vector signed int)@{1, 2, 3, 4@}, foo);
@end smallexample

@noindent
Since @code{spu_add} is a macro, the vector constant in the example
is treated as four separate arguments.  Wrap the entire argument in
parentheses for this to work.

@item
The extended version of @code{__builtin_expect} is not supported.

@end itemize

@emph{Note:} Only the interface described in the aforementioned
specification is supported. Internally, GCC uses built-in functions to
implement the required functionality, but these are not supported and
are subject to change without notice.

@node TI C6X Built-in Functions
@subsection TI C6X Built-in Functions

GCC provides intrinsics to access certain instructions of the TI C6X
processors.  These intrinsics, listed below, are available after
inclusion of the @code{c6x_intrinsics.h} header file.  They map directly
to C6X instructions.

@smallexample

int _sadd (int, int)
int _ssub (int, int)
int _sadd2 (int, int)
int _ssub2 (int, int)
long long _mpy2 (int, int)
long long _smpy2 (int, int)
int _add4 (int, int)
int _sub4 (int, int)
int _saddu4 (int, int)

int _smpy (int, int)
int _smpyh (int, int)
int _smpyhl (int, int)
int _smpylh (int, int)

int _sshl (int, int)
int _subc (int, int)

int _avg2 (int, int)
int _avgu4 (int, int)

int _clrr (int, int)
int _extr (int, int)
int _extru (int, int)
int _abs (int)
int _abs2 (int)

@end smallexample

@node TILE-Gx Built-in Functions
@subsection TILE-Gx Built-in Functions

GCC provides intrinsics to access every instruction of the TILE-Gx
processor.  The intrinsics are of the form:

@smallexample

unsigned long long __insn_@var{op} (...)

@end smallexample

Where @var{op} is the name of the instruction.  Refer to the ISA manual
for the complete list of instructions.

GCC also provides intrinsics to directly access the network registers.
The intrinsics are:

@smallexample

unsigned long long __tile_idn0_receive (void)
unsigned long long __tile_idn1_receive (void)
unsigned long long __tile_udn0_receive (void)
unsigned long long __tile_udn1_receive (void)
unsigned long long __tile_udn2_receive (void)
unsigned long long __tile_udn3_receive (void)
void __tile_idn_send (unsigned long long)
void __tile_udn_send (unsigned long long)

@end smallexample

The intrinsic @code{void __tile_network_barrier (void)} is used to
guarantee that no network operations before it are reordered with
those after it.

@node TILEPro Built-in Functions
@subsection TILEPro Built-in Functions

GCC provides intrinsics to access every instruction of the TILEPro
processor.  The intrinsics are of the form:

@smallexample

unsigned __insn_@var{op} (...)

@end smallexample

@noindent
where @var{op} is the name of the instruction.  Refer to the ISA manual
for the complete list of instructions.

GCC also provides intrinsics to directly access the network registers.
The intrinsics are:

@smallexample

unsigned __tile_idn0_receive (void)
unsigned __tile_idn1_receive (void)
unsigned __tile_sn_receive (void)
unsigned __tile_udn0_receive (void)
unsigned __tile_udn1_receive (void)
unsigned __tile_udn2_receive (void)
unsigned __tile_udn3_receive (void)
void __tile_idn_send (unsigned)
void __tile_sn_send (unsigned)
void __tile_udn_send (unsigned)

@end smallexample

The intrinsic @code{void __tile_network_barrier (void)} is used to
guarantee that no network operations before it are reordered with
those after it.

@node Target Format Checks
@section Format Checks Specific to Particular Target Machines

For some target machines, GCC supports additional options to the
format attribute
(@pxref{Function Attributes,,Declaring Attributes of Functions}).

@menu
* Solaris Format Checks::
* Darwin Format Checks::
@end menu

@node Solaris Format Checks
@subsection Solaris Format Checks

Solaris targets support the @code{cmn_err} (or @code{__cmn_err__}) format
check.  @code{cmn_err} accepts a subset of the standard @code{printf}
conversions, and the two-argument @code{%b} conversion for displaying
bit-fields.  See the Solaris man page for @code{cmn_err} for more information.

@node Darwin Format Checks
@subsection Darwin Format Checks

Darwin targets support the @code{CFString} (or @code{__CFString__}) in the format
attribute context.  Declarations made with such attribution are parsed for correct syntax
and format argument types.  However, parsing of the format string itself is currently undefined
and is not carried out by this version of the compiler.

Additionally, @code{CFStringRefs} (defined by the @code{CoreFoundation} headers) may
also be used as format arguments.  Note that the relevant headers are only likely to be
available on Darwin (OSX) installations.  On such installations, the XCode and system
documentation provide descriptions of @code{CFString}, @code{CFStringRefs} and
associated functions.

@node Pragmas
@section Pragmas Accepted by GCC
@cindex pragmas
@cindex @code{#pragma}

GCC supports several types of pragmas, primarily in order to compile
code originally written for other compilers.  Note that in general
we do not recommend the use of pragmas; @xref{Function Attributes},
for further explanation.

@menu
* ARM Pragmas::
* M32C Pragmas::
* MeP Pragmas::
* RS/6000 and PowerPC Pragmas::
* Darwin Pragmas::
* Solaris Pragmas::
* Symbol-Renaming Pragmas::
* Structure-Packing Pragmas::
* Weak Pragmas::
* Diagnostic Pragmas::
* Visibility Pragmas::
* Push/Pop Macro Pragmas::
* Function Specific Option Pragmas::
@end menu

@node ARM Pragmas
@subsection ARM Pragmas

The ARM target defines pragmas for controlling the default addition of
@code{long_call} and @code{short_call} attributes to functions.
@xref{Function Attributes}, for information about the effects of these
attributes.

@table @code
@item long_calls
@cindex pragma, long_calls
Set all subsequent functions to have the @code{long_call} attribute.

@item no_long_calls
@cindex pragma, no_long_calls
Set all subsequent functions to have the @code{short_call} attribute.

@item long_calls_off
@cindex pragma, long_calls_off
Do not affect the @code{long_call} or @code{short_call} attributes of
subsequent functions.
@end table

@node M32C Pragmas
@subsection M32C Pragmas

@table @code
@item GCC memregs @var{number}
@cindex pragma, memregs
Overrides the command-line option @code{-memregs=} for the current
file.  Use with care!  This pragma must be before any function in the
file, and mixing different memregs values in different objects may
make them incompatible.  This pragma is useful when a
performance-critical function uses a memreg for temporary values,
as it may allow you to reduce the number of memregs used.

@item ADDRESS @var{name} @var{address}
@cindex pragma, address
For any declared symbols matching @var{name}, this does three things
to that symbol: it forces the symbol to be located at the given
address (a number), it forces the symbol to be volatile, and it
changes the symbol's scope to be static.  This pragma exists for
compatibility with other compilers, but note that the common
@code{1234H} numeric syntax is not supported (use @code{0x1234}
instead).  Example:

@smallexample
#pragma ADDRESS port3 0x103
char port3;
@end smallexample

@end table

@node MeP Pragmas
@subsection MeP Pragmas

@table @code

@item custom io_volatile (on|off)
@cindex pragma, custom io_volatile
Overrides the command-line option @code{-mio-volatile} for the current
file.  Note that for compatibility with future GCC releases, this
option should only be used once before any @code{io} variables in each
file.

@item GCC coprocessor available @var{registers}
@cindex pragma, coprocessor available
Specifies which coprocessor registers are available to the register
allocator.  @var{registers} may be a single register, register range
separated by ellipses, or comma-separated list of those.  Example:

@smallexample
#pragma GCC coprocessor available $c0...$c10, $c28
@end smallexample

@item GCC coprocessor call_saved @var{registers}
@cindex pragma, coprocessor call_saved
Specifies which coprocessor registers are to be saved and restored by
any function using them.  @var{registers} may be a single register,
register range separated by ellipses, or comma-separated list of
those.  Example:

@smallexample
#pragma GCC coprocessor call_saved $c4...$c6, $c31
@end smallexample

@item GCC coprocessor subclass '(A|B|C|D)' = @var{registers}
@cindex pragma, coprocessor subclass
Creates and defines a register class.  These register classes can be
used by inline @code{asm} constructs.  @var{registers} may be a single
register, register range separated by ellipses, or comma-separated
list of those.  Example:

@smallexample
#pragma GCC coprocessor subclass 'B' = $c2, $c4, $c6

asm ("cpfoo %0" : "=B" (x));
@end smallexample

@item GCC disinterrupt @var{name} , @var{name} @dots{}
@cindex pragma, disinterrupt
For the named functions, the compiler adds code to disable interrupts
for the duration of those functions.  If any functions so named 
are not encountered in the source, a warning is emitted that the pragma is
not used.  Examples:

@smallexample
#pragma disinterrupt foo
#pragma disinterrupt bar, grill
int foo () @{ @dots{} @}
@end smallexample

@item GCC call @var{name} , @var{name} @dots{}
@cindex pragma, call
For the named functions, the compiler always uses a register-indirect
call model when calling the named functions.  Examples:

@smallexample
extern int foo ();
#pragma call foo
@end smallexample

@end table

@node RS/6000 and PowerPC Pragmas
@subsection RS/6000 and PowerPC Pragmas

The RS/6000 and PowerPC targets define one pragma for controlling
whether or not the @code{longcall} attribute is added to function
declarations by default.  This pragma overrides the @option{-mlongcall}
option, but not the @code{longcall} and @code{shortcall} attributes.
@xref{RS/6000 and PowerPC Options}, for more information about when long
calls are and are not necessary.

@table @code
@item longcall (1)
@cindex pragma, longcall
Apply the @code{longcall} attribute to all subsequent function
declarations.

@item longcall (0)
Do not apply the @code{longcall} attribute to subsequent function
declarations.
@end table

@c Describe h8300 pragmas here.
@c Describe sh pragmas here.
@c Describe v850 pragmas here.

@node Darwin Pragmas
@subsection Darwin Pragmas

The following pragmas are available for all architectures running the
Darwin operating system.  These are useful for compatibility with other
Mac OS compilers.

@table @code
@item mark @var{tokens}@dots{}
@cindex pragma, mark
This pragma is accepted, but has no effect.

@item options align=@var{alignment}
@cindex pragma, options align
This pragma sets the alignment of fields in structures.  The values of
@var{alignment} may be @code{mac68k}, to emulate m68k alignment, or
@code{power}, to emulate PowerPC alignment.  Uses of this pragma nest
properly; to restore the previous setting, use @code{reset} for the
@var{alignment}.

@item segment @var{tokens}@dots{}
@cindex pragma, segment
This pragma is accepted, but has no effect.

@item unused (@var{var} [, @var{var}]@dots{})
@cindex pragma, unused
This pragma declares variables to be possibly unused.  GCC does not
produce warnings for the listed variables.  The effect is similar to
that of the @code{unused} attribute, except that this pragma may appear
anywhere within the variables' scopes.
@end table

@node Solaris Pragmas
@subsection Solaris Pragmas

The Solaris target supports @code{#pragma redefine_extname}
(@pxref{Symbol-Renaming Pragmas}).  It also supports additional
@code{#pragma} directives for compatibility with the system compiler.

@table @code
@item align @var{alignment} (@var{variable} [, @var{variable}]...)
@cindex pragma, align

Increase the minimum alignment of each @var{variable} to @var{alignment}.
This is the same as GCC's @code{aligned} attribute @pxref{Variable
Attributes}).  Macro expansion occurs on the arguments to this pragma
when compiling C and Objective-C@.  It does not currently occur when
compiling C++, but this is a bug which may be fixed in a future
release.

@item fini (@var{function} [, @var{function}]...)
@cindex pragma, fini

This pragma causes each listed @var{function} to be called after
main, or during shared module unloading, by adding a call to the
@code{.fini} section.

@item init (@var{function} [, @var{function}]...)
@cindex pragma, init

This pragma causes each listed @var{function} to be called during
initialization (before @code{main}) or during shared module loading, by
adding a call to the @code{.init} section.

@end table

@node Symbol-Renaming Pragmas
@subsection Symbol-Renaming Pragmas

For compatibility with the Solaris system headers, GCC
supports two @code{#pragma} directives that change the name used in
assembly for a given declaration. To get this effect
on all platforms supported by GCC, use the asm labels extension (@pxref{Asm
Labels}).

@table @code
@item redefine_extname @var{oldname} @var{newname}
@cindex pragma, redefine_extname

This pragma gives the C function @var{oldname} the assembly symbol
@var{newname}.  The preprocessor macro @code{__PRAGMA_REDEFINE_EXTNAME}
is defined if this pragma is available (currently on all platforms).
@end table

This pragma and the asm labels extension interact in a complicated
manner.  Here are some corner cases you may want to be aware of.

@enumerate
@item Both pragmas silently apply only to declarations with external
linkage.  Asm labels do not have this restriction.

@item In C++, both pragmas silently apply only to declarations with
``C'' linkage.  Again, asm labels do not have this restriction.

@item If any of the three ways of changing the assembly name of a
declaration is applied to a declaration whose assembly name has
already been determined (either by a previous use of one of these
features, or because the compiler needed the assembly name in order to
generate code), and the new name is different, a warning issues and
the name does not change.

@item The @var{oldname} used by @code{#pragma redefine_extname} is
always the C-language name.
@end enumerate

@node Structure-Packing Pragmas
@subsection Structure-Packing Pragmas

For compatibility with Microsoft Windows compilers, GCC supports a
set of @code{#pragma} directives that change the maximum alignment of
members of structures (other than zero-width bit-fields), unions, and
classes subsequently defined. The @var{n} value below always is required
to be a small power of two and specifies the new alignment in bytes.

@enumerate
@item @code{#pragma pack(@var{n})} simply sets the new alignment.
@item @code{#pragma pack()} sets the alignment to the one that was in
effect when compilation started (see also command-line option
@option{-fpack-struct[=@var{n}]} @pxref{Code Gen Options}).
@item @code{#pragma pack(push[,@var{n}])} pushes the current alignment
setting on an internal stack and then optionally sets the new alignment.
@item @code{#pragma pack(pop)} restores the alignment setting to the one
saved at the top of the internal stack (and removes that stack entry).
Note that @code{#pragma pack([@var{n}])} does not influence this internal
stack; thus it is possible to have @code{#pragma pack(push)} followed by
multiple @code{#pragma pack(@var{n})} instances and finalized by a single
@code{#pragma pack(pop)}.
@end enumerate

Some targets, e.g.@: i386 and PowerPC, support the @code{ms_struct}
@code{#pragma} which lays out a structure as the documented
@code{__attribute__ ((ms_struct))}.
@enumerate
@item @code{#pragma ms_struct on} turns on the layout for structures
declared.
@item @code{#pragma ms_struct off} turns off the layout for structures
declared.
@item @code{#pragma ms_struct reset} goes back to the default layout.
@end enumerate

@node Weak Pragmas
@subsection Weak Pragmas

For compatibility with SVR4, GCC supports a set of @code{#pragma}
directives for declaring symbols to be weak, and defining weak
aliases.

@table @code
@item #pragma weak @var{symbol}
@cindex pragma, weak
This pragma declares @var{symbol} to be weak, as if the declaration
had the attribute of the same name.  The pragma may appear before
or after the declaration of @var{symbol}.  It is not an error for
@var{symbol} to never be defined at all.

@item #pragma weak @var{symbol1} = @var{symbol2}
This pragma declares @var{symbol1} to be a weak alias of @var{symbol2}.
It is an error if @var{symbol2} is not defined in the current
translation unit.
@end table

@node Diagnostic Pragmas
@subsection Diagnostic Pragmas

GCC allows the user to selectively enable or disable certain types of
diagnostics, and change the kind of the diagnostic.  For example, a
project's policy might require that all sources compile with
@option{-Werror} but certain files might have exceptions allowing
specific types of warnings.  Or, a project might selectively enable
diagnostics and treat them as errors depending on which preprocessor
macros are defined.

@table @code
@item #pragma GCC diagnostic @var{kind} @var{option}
@cindex pragma, diagnostic

Modifies the disposition of a diagnostic.  Note that not all
diagnostics are modifiable; at the moment only warnings (normally
controlled by @samp{-W@dots{}}) can be controlled, and not all of them.
Use @option{-fdiagnostics-show-option} to determine which diagnostics
are controllable and which option controls them.

@var{kind} is @samp{error} to treat this diagnostic as an error,
@samp{warning} to treat it like a warning (even if @option{-Werror} is
in effect), or @samp{ignored} if the diagnostic is to be ignored.
@var{option} is a double quoted string that matches the command-line
option.

@smallexample
#pragma GCC diagnostic warning "-Wformat"
#pragma GCC diagnostic error "-Wformat"
#pragma GCC diagnostic ignored "-Wformat"
@end smallexample

Note that these pragmas override any command-line options.  GCC keeps
track of the location of each pragma, and issues diagnostics according
to the state as of that point in the source file.  Thus, pragmas occurring
after a line do not affect diagnostics caused by that line.

@item #pragma GCC diagnostic push
@itemx #pragma GCC diagnostic pop

Causes GCC to remember the state of the diagnostics as of each
@code{push}, and restore to that point at each @code{pop}.  If a
@code{pop} has no matching @code{push}, the command-line options are
restored.

@smallexample
#pragma GCC diagnostic error "-Wuninitialized"
  foo(a);                       /* error is given for this one */
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wuninitialized"
  foo(b);                       /* no diagnostic for this one */
#pragma GCC diagnostic pop
  foo(c);                       /* error is given for this one */
#pragma GCC diagnostic pop
  foo(d);                       /* depends on command-line options */
@end smallexample

@end table

GCC also offers a simple mechanism for printing messages during
compilation.

@table @code
@item #pragma message @var{string}
@cindex pragma, diagnostic

Prints @var{string} as a compiler message on compilation.  The message
is informational only, and is neither a compilation warning nor an error.

@smallexample
#pragma message "Compiling " __FILE__ "..."
@end smallexample

@var{string} may be parenthesized, and is printed with location
information.  For example,

@smallexample
#define DO_PRAGMA(x) _Pragma (#x)
#define TODO(x) DO_PRAGMA(message ("TODO - " #x))

TODO(Remember to fix this)
@end smallexample

@noindent
prints @samp{/tmp/file.c:4: note: #pragma message:
TODO - Remember to fix this}.

@end table

@node Visibility Pragmas
@subsection Visibility Pragmas

@table @code
@item #pragma GCC visibility push(@var{visibility})
@itemx #pragma GCC visibility pop
@cindex pragma, visibility

This pragma allows the user to set the visibility for multiple
declarations without having to give each a visibility attribute
@xref{Function Attributes}, for more information about visibility and
the attribute syntax.

In C++, @samp{#pragma GCC visibility} affects only namespace-scope
declarations.  Class members and template specializations are not
affected; if you want to override the visibility for a particular
member or instantiation, you must use an attribute.

@end table


@node Push/Pop Macro Pragmas
@subsection Push/Pop Macro Pragmas

For compatibility with Microsoft Windows compilers, GCC supports
@samp{#pragma push_macro(@var{"macro_name"})}
and @samp{#pragma pop_macro(@var{"macro_name"})}.

@table @code
@item #pragma push_macro(@var{"macro_name"})
@cindex pragma, push_macro
This pragma saves the value of the macro named as @var{macro_name} to
the top of the stack for this macro.

@item #pragma pop_macro(@var{"macro_name"})
@cindex pragma, pop_macro
This pragma sets the value of the macro named as @var{macro_name} to
the value on top of the stack for this macro. If the stack for
@var{macro_name} is empty, the value of the macro remains unchanged.
@end table

For example:

@smallexample
#define X  1
#pragma push_macro("X")
#undef X
#define X -1
#pragma pop_macro("X")
int x [X];
@end smallexample

@noindent
In this example, the definition of X as 1 is saved by @code{#pragma
push_macro} and restored by @code{#pragma pop_macro}.

@node Function Specific Option Pragmas
@subsection Function Specific Option Pragmas

@table @code
@item #pragma GCC target (@var{"string"}...)
@cindex pragma GCC target

This pragma allows you to set target specific options for functions
defined later in the source file.  One or more strings can be
specified.  Each function that is defined after this point is as
if @code{attribute((target("STRING")))} was specified for that
function.  The parenthesis around the options is optional.
@xref{Function Attributes}, for more information about the
@code{target} attribute and the attribute syntax.

The @code{#pragma GCC target} attribute is not implemented in GCC versions earlier
than 4.4 for the i386/x86_64 and 4.6 for the PowerPC back ends.  At
present, it is not implemented for other back ends.
@end table

@table @code
@item #pragma GCC optimize (@var{"string"}...)
@cindex pragma GCC optimize

This pragma allows you to set global optimization options for functions
defined later in the source file.  One or more strings can be
specified.  Each function that is defined after this point is as
if @code{attribute((optimize("STRING")))} was specified for that
function.  The parenthesis around the options is optional.
@xref{Function Attributes}, for more information about the
@code{optimize} attribute and the attribute syntax.

The @samp{#pragma GCC optimize} pragma is not implemented in GCC
versions earlier than 4.4.
@end table

@table @code
@item #pragma GCC push_options
@itemx #pragma GCC pop_options
@cindex pragma GCC push_options
@cindex pragma GCC pop_options

These pragmas maintain a stack of the current target and optimization
options.  It is intended for include files where you temporarily want
to switch to using a different @samp{#pragma GCC target} or
@samp{#pragma GCC optimize} and then to pop back to the previous
options.

The @samp{#pragma GCC push_options} and @samp{#pragma GCC pop_options}
pragmas are not implemented in GCC versions earlier than 4.4.
@end table

@table @code
@item #pragma GCC reset_options
@cindex pragma GCC reset_options

This pragma clears the current @code{#pragma GCC target} and
@code{#pragma GCC optimize} to use the default switches as specified
on the command line.

The @samp{#pragma GCC reset_options} pragma is not implemented in GCC
versions earlier than 4.4.
@end table

@node Unnamed Fields
@section Unnamed struct/union fields within structs/unions
@cindex @code{struct}
@cindex @code{union}

As permitted by ISO C11 and for compatibility with other compilers,
GCC allows you to define
a structure or union that contains, as fields, structures and unions
without names.  For example:

@smallexample
struct @{
  int a;
  union @{
    int b;
    float c;
  @};
  int d;
@} foo;
@end smallexample

@noindent
In this example, you are able to access members of the unnamed
union with code like @samp{foo.b}.  Note that only unnamed structs and
unions are allowed, you may not have, for example, an unnamed
@code{int}.

You must never create such structures that cause ambiguous field definitions.
For example, in this structure:

@smallexample
struct @{
  int a;
  struct @{
    int a;
  @};
@} foo;
@end smallexample

@noindent
it is ambiguous which @code{a} is being referred to with @samp{foo.a}.
The compiler gives errors for such constructs.

@opindex fms-extensions
Unless @option{-fms-extensions} is used, the unnamed field must be a
structure or union definition without a tag (for example, @samp{struct
@{ int a; @};}).  If @option{-fms-extensions} is used, the field may
also be a definition with a tag such as @samp{struct foo @{ int a;
@};}, a reference to a previously defined structure or union such as
@samp{struct foo;}, or a reference to a @code{typedef} name for a
previously defined structure or union type.

@opindex fplan9-extensions
The option @option{-fplan9-extensions} enables
@option{-fms-extensions} as well as two other extensions.  First, a
pointer to a structure is automatically converted to a pointer to an
anonymous field for assignments and function calls.  For example:

@smallexample
struct s1 @{ int a; @};
struct s2 @{ struct s1; @};
extern void f1 (struct s1 *);
void f2 (struct s2 *p) @{ f1 (p); @}
@end smallexample

@noindent
In the call to @code{f1} inside @code{f2}, the pointer @code{p} is
converted into a pointer to the anonymous field.

Second, when the type of an anonymous field is a @code{typedef} for a
@code{struct} or @code{union}, code may refer to the field using the
name of the @code{typedef}.

@smallexample
typedef struct @{ int a; @} s1;
struct s2 @{ s1; @};
s1 f1 (struct s2 *p) @{ return p->s1; @}
@end smallexample

These usages are only permitted when they are not ambiguous.

@node Thread-Local
@section Thread-Local Storage
@cindex Thread-Local Storage
@cindex @acronym{TLS}
@cindex @code{__thread}

Thread-local storage (@acronym{TLS}) is a mechanism by which variables
are allocated such that there is one instance of the variable per extant
thread.  The runtime model GCC uses to implement this originates
in the IA-64 processor-specific ABI, but has since been migrated
to other processors as well.  It requires significant support from
the linker (@command{ld}), dynamic linker (@command{ld.so}), and
system libraries (@file{libc.so} and @file{libpthread.so}), so it
is not available everywhere.

At the user level, the extension is visible with a new storage
class keyword: @code{__thread}.  For example:

@smallexample
__thread int i;
extern __thread struct state s;
static __thread char *p;
@end smallexample

The @code{__thread} specifier may be used alone, with the @code{extern}
or @code{static} specifiers, but with no other storage class specifier.
When used with @code{extern} or @code{static}, @code{__thread} must appear
immediately after the other storage class specifier.

The @code{__thread} specifier may be applied to any global, file-scoped
static, function-scoped static, or static data member of a class.  It may
not be applied to block-scoped automatic or non-static data member.

When the address-of operator is applied to a thread-local variable, it is
evaluated at run time and returns the address of the current thread's
instance of that variable.  An address so obtained may be used by any
thread.  When a thread terminates, any pointers to thread-local variables
in that thread become invalid.

No static initialization may refer to the address of a thread-local variable.

In C++, if an initializer is present for a thread-local variable, it must
be a @var{constant-expression}, as defined in 5.19.2 of the ANSI/ISO C++
standard.

See @uref{http://www.akkadia.org/drepper/tls.pdf,
ELF Handling For Thread-Local Storage} for a detailed explanation of
the four thread-local storage addressing models, and how the runtime
is expected to function.

@menu
* C99 Thread-Local Edits::
* C++98 Thread-Local Edits::
@end menu

@node C99 Thread-Local Edits
@subsection ISO/IEC 9899:1999 Edits for Thread-Local Storage

The following are a set of changes to ISO/IEC 9899:1999 (aka C99)
that document the exact semantics of the language extension.

@itemize @bullet
@item
@cite{5.1.2  Execution environments}

Add new text after paragraph 1

@quotation
Within either execution environment, a @dfn{thread} is a flow of
control within a program.  It is implementation defined whether
or not there may be more than one thread associated with a program.
It is implementation defined how threads beyond the first are
created, the name and type of the function called at thread
startup, and how threads may be terminated.  However, objects
with thread storage duration shall be initialized before thread
startup.
@end quotation

@item
@cite{6.2.4  Storage durations of objects}

Add new text before paragraph 3

@quotation
An object whose identifier is declared with the storage-class
specifier @w{@code{__thread}} has @dfn{thread storage duration}.
Its lifetime is the entire execution of the thread, and its
stored value is initialized only once, prior to thread startup.
@end quotation

@item
@cite{6.4.1  Keywords}

Add @code{__thread}.

@item
@cite{6.7.1  Storage-class specifiers}

Add @code{__thread} to the list of storage class specifiers in
paragraph 1.

Change paragraph 2 to

@quotation
With the exception of @code{__thread}, at most one storage-class
specifier may be given [@dots{}].  The @code{__thread} specifier may
be used alone, or immediately following @code{extern} or
@code{static}.
@end quotation

Add new text after paragraph 6

@quotation
The declaration of an identifier for a variable that has
block scope that specifies @code{__thread} shall also
specify either @code{extern} or @code{static}.

The @code{__thread} specifier shall be used only with
variables.
@end quotation
@end itemize

@node C++98 Thread-Local Edits
@subsection ISO/IEC 14882:1998 Edits for Thread-Local Storage

The following are a set of changes to ISO/IEC 14882:1998 (aka C++98)
that document the exact semantics of the language extension.

@itemize @bullet
@item
@b{[intro.execution]}

New text after paragraph 4

@quotation
A @dfn{thread} is a flow of control within the abstract machine.
It is implementation defined whether or not there may be more than
one thread.
@end quotation

New text after paragraph 7

@quotation
It is unspecified whether additional action must be taken to
ensure when and whether side effects are visible to other threads.
@end quotation

@item
@b{[lex.key]}

Add @code{__thread}.

@item
@b{[basic.start.main]}

Add after paragraph 5

@quotation
The thread that begins execution at the @code{main} function is called
the @dfn{main thread}.  It is implementation defined how functions
beginning threads other than the main thread are designated or typed.
A function so designated, as well as the @code{main} function, is called
a @dfn{thread startup function}.  It is implementation defined what
happens if a thread startup function returns.  It is implementation
defined what happens to other threads when any thread calls @code{exit}.
@end quotation

@item
@b{[basic.start.init]}

Add after paragraph 4

@quotation
The storage for an object of thread storage duration shall be
statically initialized before the first statement of the thread startup
function.  An object of thread storage duration shall not require
dynamic initialization.
@end quotation

@item
@b{[basic.start.term]}

Add after paragraph 3

@quotation
The type of an object with thread storage duration shall not have a
non-trivial destructor, nor shall it be an array type whose elements
(directly or indirectly) have non-trivial destructors.
@end quotation

@item
@b{[basic.stc]}

Add ``thread storage duration'' to the list in paragraph 1.

Change paragraph 2

@quotation
Thread, static, and automatic storage durations are associated with
objects introduced by declarations [@dots{}].
@end quotation

Add @code{__thread} to the list of specifiers in paragraph 3.

@item
@b{[basic.stc.thread]}

New section before @b{[basic.stc.static]}

@quotation
The keyword @code{__thread} applied to a non-local object gives the
object thread storage duration.

A local variable or class data member declared both @code{static}
and @code{__thread} gives the variable or member thread storage
duration.
@end quotation

@item
@b{[basic.stc.static]}

Change paragraph 1

@quotation
All objects that have neither thread storage duration, dynamic
storage duration nor are local [@dots{}].
@end quotation

@item
@b{[dcl.stc]}

Add @code{__thread} to the list in paragraph 1.

Change paragraph 1

@quotation
With the exception of @code{__thread}, at most one
@var{storage-class-specifier} shall appear in a given
@var{decl-specifier-seq}.  The @code{__thread} specifier may
be used alone, or immediately following the @code{extern} or
@code{static} specifiers.  [@dots{}]
@end quotation

Add after paragraph 5

@quotation
The @code{__thread} specifier can be applied only to the names of objects
and to anonymous unions.
@end quotation

@item
@b{[class.mem]}

Add after paragraph 6

@quotation
Non-@code{static} members shall not be @code{__thread}.
@end quotation
@end itemize

@node Binary constants
@section Binary constants using the @samp{0b} prefix
@cindex Binary constants using the @samp{0b} prefix

Integer constants can be written as binary constants, consisting of a
sequence of @samp{0} and @samp{1} digits, prefixed by @samp{0b} or
@samp{0B}.  This is particularly useful in environments that operate a
lot on the bit level (like microcontrollers).

The following statements are identical:

@smallexample
i =       42;
i =     0x2a;
i =      052;
i = 0b101010;
@end smallexample

The type of these constants follows the same rules as for octal or
hexadecimal integer constants, so suffixes like @samp{L} or @samp{UL}
can be applied.

@node C++ Extensions
@chapter Extensions to the C++ Language
@cindex extensions, C++ language
@cindex C++ language extensions

The GNU compiler provides these extensions to the C++ language (and you
can also use most of the C language extensions in your C++ programs).  If you
want to write code that checks whether these features are available, you can
test for the GNU compiler the same way as for C programs: check for a
predefined macro @code{__GNUC__}.  You can also use @code{__GNUG__} to
test specifically for GNU C++ (@pxref{Common Predefined Macros,,
Predefined Macros,cpp,The GNU C Preprocessor}).

@menu
* C++ Volatiles::       What constitutes an access to a volatile object.
* Restricted Pointers:: C99 restricted pointers and references.
* Vague Linkage::       Where G++ puts inlines, vtables and such.
* C++ Interface::       You can use a single C++ header file for both
                        declarations and definitions.
* Template Instantiation:: Methods for ensuring that exactly one copy of
                        each needed template instantiation is emitted.
* Bound member functions:: You can extract a function pointer to the
                        method denoted by a @samp{->*} or @samp{.*} expression.
* C++ Attributes::      Variable, function, and type attributes for C++ only.
* Function Multiversioning::   Declaring multiple function versions.
* Namespace Association:: Strong using-directives for namespace association.
* Type Traits::         Compiler support for type traits
* Java Exceptions::     Tweaking exception handling to work with Java.
* Deprecated Features:: Things will disappear from G++.
* Backwards Compatibility:: Compatibilities with earlier definitions of C++.
@end menu

@node C++ Volatiles
@section When is a Volatile C++ Object Accessed?
@cindex accessing volatiles
@cindex volatile read
@cindex volatile write
@cindex volatile access

The C++ standard differs from the C standard in its treatment of
volatile objects.  It fails to specify what constitutes a volatile
access, except to say that C++ should behave in a similar manner to C
with respect to volatiles, where possible.  However, the different
lvalueness of expressions between C and C++ complicate the behavior.
G++ behaves the same as GCC for volatile access, @xref{C
Extensions,,Volatiles}, for a description of GCC's behavior.

The C and C++ language specifications differ when an object is
accessed in a void context:

@smallexample
volatile int *src = @var{somevalue};
*src;
@end smallexample

The C++ standard specifies that such expressions do not undergo lvalue
to rvalue conversion, and that the type of the dereferenced object may
be incomplete.  The C++ standard does not specify explicitly that it
is lvalue to rvalue conversion that is responsible for causing an
access.  There is reason to believe that it is, because otherwise
certain simple expressions become undefined.  However, because it
would surprise most programmers, G++ treats dereferencing a pointer to
volatile object of complete type as GCC would do for an equivalent
type in C@.  When the object has incomplete type, G++ issues a
warning; if you wish to force an error, you must force a conversion to
rvalue with, for instance, a static cast.

When using a reference to volatile, G++ does not treat equivalent
expressions as accesses to volatiles, but instead issues a warning that
no volatile is accessed.  The rationale for this is that otherwise it
becomes difficult to determine where volatile access occur, and not
possible to ignore the return value from functions returning volatile
references.  Again, if you wish to force a read, cast the reference to
an rvalue.

G++ implements the same behavior as GCC does when assigning to a
volatile object---there is no reread of the assigned-to object, the
assigned rvalue is reused.  Note that in C++ assignment expressions
are lvalues, and if used as an lvalue, the volatile object is
referred to.  For instance, @var{vref} refers to @var{vobj}, as
expected, in the following example:

@smallexample
volatile int vobj;
volatile int &vref = vobj = @var{something};
@end smallexample

@node Restricted Pointers
@section Restricting Pointer Aliasing
@cindex restricted pointers
@cindex restricted references
@cindex restricted this pointer

As with the C front end, G++ understands the C99 feature of restricted pointers,
specified with the @code{__restrict__}, or @code{__restrict} type
qualifier.  Because you cannot compile C++ by specifying the @option{-std=c99}
language flag, @code{restrict} is not a keyword in C++.

In addition to allowing restricted pointers, you can specify restricted
references, which indicate that the reference is not aliased in the local
context.

@smallexample
void fn (int *__restrict__ rptr, int &__restrict__ rref)
@{
  /* @r{@dots{}} */
@}
@end smallexample

@noindent
In the body of @code{fn}, @var{rptr} points to an unaliased integer and
@var{rref} refers to a (different) unaliased integer.

You may also specify whether a member function's @var{this} pointer is
unaliased by using @code{__restrict__} as a member function qualifier.

@smallexample
void T::fn () __restrict__
@{
  /* @r{@dots{}} */
@}
@end smallexample

@noindent
Within the body of @code{T::fn}, @var{this} has the effective
definition @code{T *__restrict__ const this}.  Notice that the
interpretation of a @code{__restrict__} member function qualifier is
different to that of @code{const} or @code{volatile} qualifier, in that it
is applied to the pointer rather than the object.  This is consistent with
other compilers that implement restricted pointers.

As with all outermost parameter qualifiers, @code{__restrict__} is
ignored in function definition matching.  This means you only need to
specify @code{__restrict__} in a function definition, rather than
in a function prototype as well.

@node Vague Linkage
@section Vague Linkage
@cindex vague linkage

There are several constructs in C++ that require space in the object
file but are not clearly tied to a single translation unit.  We say that
these constructs have ``vague linkage''.  Typically such constructs are
emitted wherever they are needed, though sometimes we can be more
clever.

@table @asis
@item Inline Functions
Inline functions are typically defined in a header file which can be
included in many different compilations.  Hopefully they can usually be
inlined, but sometimes an out-of-line copy is necessary, if the address
of the function is taken or if inlining fails.  In general, we emit an
out-of-line copy in all translation units where one is needed.  As an
exception, we only emit inline virtual functions with the vtable, since
it always requires a copy.

Local static variables and string constants used in an inline function
are also considered to have vague linkage, since they must be shared
between all inlined and out-of-line instances of the function.

@item VTables
@cindex vtable
C++ virtual functions are implemented in most compilers using a lookup
table, known as a vtable.  The vtable contains pointers to the virtual
functions provided by a class, and each object of the class contains a
pointer to its vtable (or vtables, in some multiple-inheritance
situations).  If the class declares any non-inline, non-pure virtual
functions, the first one is chosen as the ``key method'' for the class,
and the vtable is only emitted in the translation unit where the key
method is defined.

@emph{Note:} If the chosen key method is later defined as inline, the
vtable is still emitted in every translation unit that defines it.
Make sure that any inline virtuals are declared inline in the class
body, even if they are not defined there.

@item @code{type_info} objects
@cindex @code{type_info}
@cindex RTTI
C++ requires information about types to be written out in order to
implement @samp{dynamic_cast}, @samp{typeid} and exception handling.
For polymorphic classes (classes with virtual functions), the @samp{type_info}
object is written out along with the vtable so that @samp{dynamic_cast}
can determine the dynamic type of a class object at run time.  For all
other types, we write out the @samp{type_info} object when it is used: when
applying @samp{typeid} to an expression, throwing an object, or
referring to a type in a catch clause or exception specification.

@item Template Instantiations
Most everything in this section also applies to template instantiations,
but there are other options as well.
@xref{Template Instantiation,,Where's the Template?}.

@end table

When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, duplicate copies of
these constructs will be discarded at link time.  This is known as
COMDAT support.

On targets that don't support COMDAT, but do support weak symbols, GCC
uses them.  This way one copy overrides all the others, but
the unused copies still take up space in the executable.

For targets that do not support either COMDAT or weak symbols,
most entities with vague linkage are emitted as local symbols to
avoid duplicate definition errors from the linker.  This does not happen
for local statics in inlines, however, as having multiple copies
almost certainly breaks things.

@xref{C++ Interface,,Declarations and Definitions in One Header}, for
another way to control placement of these constructs.

@node C++ Interface
@section #pragma interface and implementation

@cindex interface and implementation headers, C++
@cindex C++ interface and implementation headers
@cindex pragmas, interface and implementation

@code{#pragma interface} and @code{#pragma implementation} provide the
user with a way of explicitly directing the compiler to emit entities
with vague linkage (and debugging information) in a particular
translation unit.

@emph{Note:} As of GCC 2.7.2, these @code{#pragma}s are not useful in
most cases, because of COMDAT support and the ``key method'' heuristic
mentioned in @ref{Vague Linkage}.  Using them can actually cause your
program to grow due to unnecessary out-of-line copies of inline
functions.  Currently (3.4) the only benefit of these
@code{#pragma}s is reduced duplication of debugging information, and
that should be addressed soon on DWARF 2 targets with the use of
COMDAT groups.

@table @code
@item #pragma interface
@itemx #pragma interface "@var{subdir}/@var{objects}.h"
@kindex #pragma interface
Use this directive in @emph{header files} that define object classes, to save
space in most of the object files that use those classes.  Normally,
local copies of certain information (backup copies of inline member
functions, debugging information, and the internal tables that implement
virtual functions) must be kept in each object file that includes class
definitions.  You can use this pragma to avoid such duplication.  When a
header file containing @samp{#pragma interface} is included in a
compilation, this auxiliary information is not generated (unless
the main input source file itself uses @samp{#pragma implementation}).
Instead, the object files contain references to be resolved at link
time.

The second form of this directive is useful for the case where you have
multiple headers with the same name in different directories.  If you
use this form, you must specify the same string to @samp{#pragma
implementation}.

@item #pragma implementation
@itemx #pragma implementation "@var{objects}.h"
@kindex #pragma implementation
Use this pragma in a @emph{main input file}, when you want full output from
included header files to be generated (and made globally visible).  The
included header file, in turn, should use @samp{#pragma interface}.
Backup copies of inline member functions, debugging information, and the
internal tables used to implement virtual functions are all generated in
implementation files.

@cindex implied @code{#pragma implementation}
@cindex @code{#pragma implementation}, implied
@cindex naming convention, implementation headers
If you use @samp{#pragma implementation} with no argument, it applies to
an include file with the same basename@footnote{A file's @dfn{basename}
is the name stripped of all leading path information and of trailing
suffixes, such as @samp{.h} or @samp{.C} or @samp{.cc}.} as your source
file.  For example, in @file{allclass.cc}, giving just
@samp{#pragma implementation}
by itself is equivalent to @samp{#pragma implementation "allclass.h"}.

In versions of GNU C++ prior to 2.6.0 @file{allclass.h} was treated as
an implementation file whenever you would include it from
@file{allclass.cc} even if you never specified @samp{#pragma
implementation}.  This was deemed to be more trouble than it was worth,
however, and disabled.

Use the string argument if you want a single implementation file to
include code from multiple header files.  (You must also use
@samp{#include} to include the header file; @samp{#pragma
implementation} only specifies how to use the file---it doesn't actually
include it.)

There is no way to split up the contents of a single header file into
multiple implementation files.
@end table

@cindex inlining and C++ pragmas
@cindex C++ pragmas, effect on inlining
@cindex pragmas in C++, effect on inlining
@samp{#pragma implementation} and @samp{#pragma interface} also have an
effect on function inlining.

If you define a class in a header file marked with @samp{#pragma
interface}, the effect on an inline function defined in that class is
similar to an explicit @code{extern} declaration---the compiler emits
no code at all to define an independent version of the function.  Its
definition is used only for inlining with its callers.

@opindex fno-implement-inlines
Conversely, when you include the same header file in a main source file
that declares it as @samp{#pragma implementation}, the compiler emits
code for the function itself; this defines a version of the function
that can be found via pointers (or by callers compiled without
inlining).  If all calls to the function can be inlined, you can avoid
emitting the function by compiling with @option{-fno-implement-inlines}.
If any calls are not inlined, you will get linker errors.

@node Template Instantiation
@section Where's the Template?
@cindex template instantiation

C++ templates are the first language feature to require more
intelligence from the environment than one usually finds on a UNIX
system.  Somehow the compiler and linker have to make sure that each
template instance occurs exactly once in the executable if it is needed,
and not at all otherwise.  There are two basic approaches to this
problem, which are referred to as the Borland model and the Cfront model.

@table @asis
@item Borland model
Borland C++ solved the template instantiation problem by adding the code
equivalent of common blocks to their linker; the compiler emits template
instances in each translation unit that uses them, and the linker
collapses them together.  The advantage of this model is that the linker
only has to consider the object files themselves; there is no external
complexity to worry about.  This disadvantage is that compilation time
is increased because the template code is being compiled repeatedly.
Code written for this model tends to include definitions of all
templates in the header file, since they must be seen to be
instantiated.

@item Cfront model
The AT&T C++ translator, Cfront, solved the template instantiation
problem by creating the notion of a template repository, an
automatically maintained place where template instances are stored.  A
more modern version of the repository works as follows: As individual
object files are built, the compiler places any template definitions and
instantiations encountered in the repository.  At link time, the link
wrapper adds in the objects in the repository and compiles any needed
instances that were not previously emitted.  The advantages of this
model are more optimal compilation speed and the ability to use the
system linker; to implement the Borland model a compiler vendor also
needs to replace the linker.  The disadvantages are vastly increased
complexity, and thus potential for error; for some code this can be
just as transparent, but in practice it can been very difficult to build
multiple programs in one directory and one program in multiple
directories.  Code written for this model tends to separate definitions
of non-inline member templates into a separate file, which should be
compiled separately.
@end table

When used with GNU ld version 2.8 or later on an ELF system such as
GNU/Linux or Solaris 2, or on Microsoft Windows, G++ supports the
Borland model.  On other systems, G++ implements neither automatic
model.

You have the following options for dealing with template instantiations:

@enumerate
@item
@opindex frepo
Compile your template-using code with @option{-frepo}.  The compiler
generates files with the extension @samp{.rpo} listing all of the
template instantiations used in the corresponding object files that
could be instantiated there; the link wrapper, @samp{collect2},
then updates the @samp{.rpo} files to tell the compiler where to place
those instantiations and rebuild any affected object files.  The
link-time overhead is negligible after the first pass, as the compiler
continues to place the instantiations in the same files.

This is your best option for application code written for the Borland
model, as it just works.  Code written for the Cfront model 
needs to be modified so that the template definitions are available at
one or more points of instantiation; usually this is as simple as adding
@code{#include <tmethods.cc>} to the end of each template header.

For library code, if you want the library to provide all of the template
instantiations it needs, just try to link all of its object files
together; the link will fail, but cause the instantiations to be
generated as a side effect.  Be warned, however, that this may cause
conflicts if multiple libraries try to provide the same instantiations.
For greater control, use explicit instantiation as described in the next
option.

@item
@opindex fno-implicit-templates
Compile your code with @option{-fno-implicit-templates} to disable the
implicit generation of template instances, and explicitly instantiate
all the ones you use.  This approach requires more knowledge of exactly
which instances you need than do the others, but it's less
mysterious and allows greater control.  You can scatter the explicit
instantiations throughout your program, perhaps putting them in the
translation units where the instances are used or the translation units
that define the templates themselves; you can put all of the explicit
instantiations you need into one big file; or you can create small files
like

@smallexample
#include "Foo.h"
#include "Foo.cc"

template class Foo<int>;
template ostream& operator <<
                (ostream&, const Foo<int>&);
@end smallexample

@noindent
for each of the instances you need, and create a template instantiation
library from those.

If you are using Cfront-model code, you can probably get away with not
using @option{-fno-implicit-templates} when compiling files that don't
@samp{#include} the member template definitions.

If you use one big file to do the instantiations, you may want to
compile it without @option{-fno-implicit-templates} so you get all of the
instances required by your explicit instantiations (but not by any
other files) without having to specify them as well.

The ISO C++ 2011 standard allows forward declaration of explicit
instantiations (with @code{extern}). G++ supports explicit instantiation
declarations in C++98 mode and has extended the template instantiation
syntax to support instantiation of the compiler support data for a
template class (i.e.@: the vtable) without instantiating any of its
members (with @code{inline}), and instantiation of only the static data
members of a template class, without the support data or member
functions (with (@code{static}):

@smallexample
extern template int max (int, int);
inline template class Foo<int>;
static template class Foo<int>;
@end smallexample

@item
Do nothing.  Pretend G++ does implement automatic instantiation
management.  Code written for the Borland model works fine, but
each translation unit contains instances of each of the templates it
uses.  In a large program, this can lead to an unacceptable amount of code
duplication.
@end enumerate

@node Bound member functions
@section Extracting the function pointer from a bound pointer to member function
@cindex pmf
@cindex pointer to member function
@cindex bound pointer to member function

In C++, pointer to member functions (PMFs) are implemented using a wide
pointer of sorts to handle all the possible call mechanisms; the PMF
needs to store information about how to adjust the @samp{this} pointer,
and if the function pointed to is virtual, where to find the vtable, and
where in the vtable to look for the member function.  If you are using
PMFs in an inner loop, you should really reconsider that decision.  If
that is not an option, you can extract the pointer to the function that
would be called for a given object/PMF pair and call it directly inside
the inner loop, to save a bit of time.

Note that you still pay the penalty for the call through a
function pointer; on most modern architectures, such a call defeats the
branch prediction features of the CPU@.  This is also true of normal
virtual function calls.

The syntax for this extension is

@smallexample
extern A a;
extern int (A::*fp)();
typedef int (*fptr)(A *);

fptr p = (fptr)(a.*fp);
@end smallexample

For PMF constants (i.e.@: expressions of the form @samp{&Klasse::Member}),
no object is needed to obtain the address of the function.  They can be
converted to function pointers directly:

@smallexample
fptr p1 = (fptr)(&A::foo);
@end smallexample

@opindex Wno-pmf-conversions
You must specify @option{-Wno-pmf-conversions} to use this extension.

@node C++ Attributes
@section C++-Specific Variable, Function, and Type Attributes

Some attributes only make sense for C++ programs.

@table @code
@item abi_tag ("@var{tag}", ...)
@cindex @code{abi_tag} attribute
The @code{abi_tag} attribute can be applied to a function or class
declaration.  It modifies the mangled name of the function or class to
incorporate the tag name, in order to distinguish the function or
class from an earlier version with a different ABI; perhaps the class
has changed size, or the function has a different return type that is
not encoded in the mangled name.

The argument can be a list of strings of arbitrary length.  The
strings are sorted on output, so the order of the list is
unimportant.

A redeclaration of a function or class must not add new ABI tags,
since doing so would change the mangled name.

The @option{-Wabi-tag} flag enables a warning about a class which does
not have all the ABI tags used by its subobjects and virtual functions; for users with code
that needs to coexist with an earlier ABI, using this option can help
to find all affected types that need to be tagged.

@item init_priority (@var{priority})
@cindex @code{init_priority} attribute


In Standard C++, objects defined at namespace scope are guaranteed to be
initialized in an order in strict accordance with that of their definitions
@emph{in a given translation unit}.  No guarantee is made for initializations
across translation units.  However, GNU C++ allows users to control the
order of initialization of objects defined at namespace scope with the
@code{init_priority} attribute by specifying a relative @var{priority},
a constant integral expression currently bounded between 101 and 65535
inclusive.  Lower numbers indicate a higher priority.

In the following example, @code{A} would normally be created before
@code{B}, but the @code{init_priority} attribute reverses that order:

@smallexample
Some_Class  A  __attribute__ ((init_priority (2000)));
Some_Class  B  __attribute__ ((init_priority (543)));
@end smallexample

@noindent
Note that the particular values of @var{priority} do not matter; only their
relative ordering.

@item java_interface
@cindex @code{java_interface} attribute

This type attribute informs C++ that the class is a Java interface.  It may
only be applied to classes declared within an @code{extern "Java"} block.
Calls to methods declared in this interface are dispatched using GCJ's
interface table mechanism, instead of regular virtual table dispatch.

@end table

See also @ref{Namespace Association}.

@node Function Multiversioning
@section Function Multiversioning
@cindex function versions

With the GNU C++ front end, for target i386, you may specify multiple
versions of a function, where each function is specialized for a
specific target feature.  At runtime, the appropriate version of the
function is automatically executed depending on the characteristics of
the execution platform.  Here is an example.

@smallexample
__attribute__ ((target ("default")))
int foo ()
@{
  // The default version of foo.
  return 0;
@}

__attribute__ ((target ("sse4.2")))
int foo ()
@{
  // foo version for SSE4.2
  return 1;
@}

__attribute__ ((target ("arch=atom")))
int foo ()
@{
  // foo version for the Intel ATOM processor
  return 2;
@}

__attribute__ ((target ("arch=amdfam10")))
int foo ()
@{
  // foo version for the AMD Family 0x10 processors.
  return 3;
@}

int main ()
@{
  int (*p)() = &foo;
  assert ((*p) () == foo ());
  return 0;
@}
@end smallexample

In the above example, four versions of function foo are created. The
first version of foo with the target attribute "default" is the default
version.  This version gets executed when no other target specific
version qualifies for execution on a particular platform. A new version
of foo is created by using the same function signature but with a
different target string.  Function foo is called or a pointer to it is
taken just like a regular function.  GCC takes care of doing the
dispatching to call the right version at runtime.  Refer to the
@uref{http://gcc.gnu.org/wiki/FunctionMultiVersioning, GCC wiki on
Function Multiversioning} for more details.

@node Namespace Association
@section Namespace Association

@strong{Caution:} The semantics of this extension are equivalent
to C++ 2011 inline namespaces.  Users should use inline namespaces
instead as this extension will be removed in future versions of G++.

A using-directive with @code{__attribute ((strong))} is stronger
than a normal using-directive in two ways:

@itemize @bullet
@item
Templates from the used namespace can be specialized and explicitly
instantiated as though they were members of the using namespace.

@item
The using namespace is considered an associated namespace of all
templates in the used namespace for purposes of argument-dependent
name lookup.
@end itemize

The used namespace must be nested within the using namespace so that
normal unqualified lookup works properly.

This is useful for composing a namespace transparently from
implementation namespaces.  For example:

@smallexample
namespace std @{
  namespace debug @{
    template <class T> struct A @{ @};
  @}
  using namespace debug __attribute ((__strong__));
  template <> struct A<int> @{ @};   // @r{ok to specialize}

  template <class T> void f (A<T>);
@}

int main()
@{
  f (std::A<float>());             // @r{lookup finds} std::f
  f (std::A<int>());
@}
@end smallexample

@node Type Traits
@section Type Traits

The C++ front end implements syntactic extensions that allow
compile-time determination of 
various characteristics of a type (or of a
pair of types).

@table @code
@item __has_nothrow_assign (type)
If @code{type} is const qualified or is a reference type then the trait is
false.  Otherwise if @code{__has_trivial_assign (type)} is true then the trait
is true, else if @code{type} is a cv class or union type with copy assignment
operators that are known not to throw an exception then the trait is true,
else it is false.  Requires: @code{type} shall be a complete type,
(possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __has_nothrow_copy (type)
If @code{__has_trivial_copy (type)} is true then the trait is true, else if
@code{type} is a cv class or union type with copy constructors that
are known not to throw an exception then the trait is true, else it is false.
Requires: @code{type} shall be a complete type, (possibly cv-qualified)
@code{void}, or an array of unknown bound.

@item __has_nothrow_constructor (type)
If @code{__has_trivial_constructor (type)} is true then the trait is
true, else if @code{type} is a cv class or union type (or array
thereof) with a default constructor that is known not to throw an
exception then the trait is true, else it is false.  Requires:
@code{type} shall be a complete type, (possibly cv-qualified)
@code{void}, or an array of unknown bound.

@item __has_trivial_assign (type)
If @code{type} is const qualified or is a reference type then the trait is
false.  Otherwise if @code{__is_pod (type)} is true then the trait is
true, else if @code{type} is a cv class or union type with a trivial
copy assignment ([class.copy]) then the trait is true, else it is
false.  Requires: @code{type} shall be a complete type, (possibly
cv-qualified) @code{void}, or an array of unknown bound.

@item __has_trivial_copy (type)
If @code{__is_pod (type)} is true or @code{type} is a reference type
then the trait is true, else if @code{type} is a cv class or union type
with a trivial copy constructor ([class.copy]) then the trait
is true, else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __has_trivial_constructor (type)
If @code{__is_pod (type)} is true then the trait is true, else if
@code{type} is a cv class or union type (or array thereof) with a
trivial default constructor ([class.ctor]) then the trait is true,
else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __has_trivial_destructor (type)
If @code{__is_pod (type)} is true or @code{type} is a reference type then
the trait is true, else if @code{type} is a cv class or union type (or
array thereof) with a trivial destructor ([class.dtor]) then the trait
is true, else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __has_virtual_destructor (type)
If @code{type} is a class type with a virtual destructor
([class.dtor]) then the trait is true, else it is false.  Requires:
@code{type} shall be a complete type, (possibly cv-qualified)
@code{void}, or an array of unknown bound.

@item __is_abstract (type)
If @code{type} is an abstract class ([class.abstract]) then the trait
is true, else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __is_base_of (base_type, derived_type)
If @code{base_type} is a base class of @code{derived_type}
([class.derived]) then the trait is true, otherwise it is false.
Top-level cv qualifications of @code{base_type} and
@code{derived_type} are ignored.  For the purposes of this trait, a
class type is considered is own base.  Requires: if @code{__is_class
(base_type)} and @code{__is_class (derived_type)} are true and
@code{base_type} and @code{derived_type} are not the same type
(disregarding cv-qualifiers), @code{derived_type} shall be a complete
type.  Diagnostic is produced if this requirement is not met.

@item __is_class (type)
If @code{type} is a cv class type, and not a union type
([basic.compound]) the trait is true, else it is false.

@item __is_empty (type)
If @code{__is_class (type)} is false then the trait is false.
Otherwise @code{type} is considered empty if and only if: @code{type}
has no non-static data members, or all non-static data members, if
any, are bit-fields of length 0, and @code{type} has no virtual
members, and @code{type} has no virtual base classes, and @code{type}
has no base classes @code{base_type} for which
@code{__is_empty (base_type)} is false.  Requires: @code{type} shall
be a complete type, (possibly cv-qualified) @code{void}, or an array
of unknown bound.

@item __is_enum (type)
If @code{type} is a cv enumeration type ([basic.compound]) the trait is
true, else it is false.

@item __is_literal_type (type)
If @code{type} is a literal type ([basic.types]) the trait is
true, else it is false.  Requires: @code{type} shall be a complete type,
(possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __is_pod (type)
If @code{type} is a cv POD type ([basic.types]) then the trait is true,
else it is false.  Requires: @code{type} shall be a complete type,
(possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __is_polymorphic (type)
If @code{type} is a polymorphic class ([class.virtual]) then the trait
is true, else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __is_standard_layout (type)
If @code{type} is a standard-layout type ([basic.types]) the trait is
true, else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __is_trivial (type)
If @code{type} is a trivial type ([basic.types]) the trait is
true, else it is false.  Requires: @code{type} shall be a complete
type, (possibly cv-qualified) @code{void}, or an array of unknown bound.

@item __is_union (type)
If @code{type} is a cv union type ([basic.compound]) the trait is
true, else it is false.

@item __underlying_type (type)
The underlying type of @code{type}.  Requires: @code{type} shall be
an enumeration type ([dcl.enum]).

@end table

@node Java Exceptions
@section Java Exceptions

The Java language uses a slightly different exception handling model
from C++.  Normally, GNU C++ automatically detects when you are
writing C++ code that uses Java exceptions, and handle them
appropriately.  However, if C++ code only needs to execute destructors
when Java exceptions are thrown through it, GCC guesses incorrectly.
Sample problematic code is:

@smallexample
  struct S @{ ~S(); @};
  extern void bar();    // @r{is written in Java, and may throw exceptions}
  void foo()
  @{
    S s;
    bar();
  @}
@end smallexample

@noindent
The usual effect of an incorrect guess is a link failure, complaining of
a missing routine called @samp{__gxx_personality_v0}.

You can inform the compiler that Java exceptions are to be used in a
translation unit, irrespective of what it might think, by writing
@samp{@w{#pragma GCC java_exceptions}} at the head of the file.  This
@samp{#pragma} must appear before any functions that throw or catch
exceptions, or run destructors when exceptions are thrown through them.

You cannot mix Java and C++ exceptions in the same translation unit.  It
is believed to be safe to throw a C++ exception from one file through
another file compiled for the Java exception model, or vice versa, but
there may be bugs in this area.

@node Deprecated Features
@section Deprecated Features

In the past, the GNU C++ compiler was extended to experiment with new
features, at a time when the C++ language was still evolving.  Now that
the C++ standard is complete, some of those features are superseded by
superior alternatives.  Using the old features might cause a warning in
some cases that the feature will be dropped in the future.  In other
cases, the feature might be gone already.

While the list below is not exhaustive, it documents some of the options
that are now deprecated:

@table @code
@item -fexternal-templates
@itemx -falt-external-templates
These are two of the many ways for G++ to implement template
instantiation.  @xref{Template Instantiation}.  The C++ standard clearly
defines how template definitions have to be organized across
implementation units.  G++ has an implicit instantiation mechanism that
should work just fine for standard-conforming code.

@item -fstrict-prototype
@itemx -fno-strict-prototype
Previously it was possible to use an empty prototype parameter list to
indicate an unspecified number of parameters (like C), rather than no
parameters, as C++ demands.  This feature has been removed, except where
it is required for backwards compatibility.   @xref{Backwards Compatibility}.
@end table

G++ allows a virtual function returning @samp{void *} to be overridden
by one returning a different pointer type.  This extension to the
covariant return type rules is now deprecated and will be removed from a
future version.

The G++ minimum and maximum operators (@samp{<?} and @samp{>?}) and
their compound forms (@samp{<?=}) and @samp{>?=}) have been deprecated
and are now removed from G++.  Code using these operators should be
modified to use @code{std::min} and @code{std::max} instead.

The named return value extension has been deprecated, and is now
removed from G++.

The use of initializer lists with new expressions has been deprecated,
and is now removed from G++.

Floating and complex non-type template parameters have been deprecated,
and are now removed from G++.

The implicit typename extension has been deprecated and is now
removed from G++.

The use of default arguments in function pointers, function typedefs
and other places where they are not permitted by the standard is
deprecated and will be removed from a future version of G++.

G++ allows floating-point literals to appear in integral constant expressions,
e.g.@: @samp{ enum E @{ e = int(2.2 * 3.7) @} }
This extension is deprecated and will be removed from a future version.

G++ allows static data members of const floating-point type to be declared
with an initializer in a class definition. The standard only allows
initializers for static members of const integral types and const
enumeration types so this extension has been deprecated and will be removed
from a future version.

@node Backwards Compatibility
@section Backwards Compatibility
@cindex Backwards Compatibility
@cindex ARM [Annotated C++ Reference Manual]

Now that there is a definitive ISO standard C++, G++ has a specification
to adhere to.  The C++ language evolved over time, and features that
used to be acceptable in previous drafts of the standard, such as the ARM
[Annotated C++ Reference Manual], are no longer accepted.  In order to allow
compilation of C++ written to such drafts, G++ contains some backwards
compatibilities.  @emph{All such backwards compatibility features are
liable to disappear in future versions of G++.} They should be considered
deprecated.   @xref{Deprecated Features}.

@table @code
@item For scope
If a variable is declared at for scope, it used to remain in scope until
the end of the scope that contained the for statement (rather than just
within the for scope).  G++ retains this, but issues a warning, if such a
variable is accessed outside the for scope.

@item Implicit C language
Old C system header files did not contain an @code{extern "C" @{@dots{}@}}
scope to set the language.  On such systems, all header files are
implicitly scoped inside a C language scope.  Also, an empty prototype
@code{()} is treated as an unspecified number of arguments, rather
than no arguments, as C++ demands.
@end table