Merge in trunk.

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

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index fc5e1a544b3207e8b5a174c3c8d0e2cb2ae15adb..79111346a03206314f3a0fa8bbd22e9fb166201f 100644 (file)
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -9672,14 +9672,8 @@ Returns the negative of the floating point value @var{x}.
 Returns the absolute value of @var{x}.
 @end deftypefn
 
-@deftypefn Macro void REAL_VALUE_TO_INT (HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, REAL_VALUE_TYPE @var{x})
-Converts a floating point value @var{x} into a double-precision integer
-which is then stored into @var{low} and @var{high}.  If the value is not
-integral, it is truncated.
-@end deftypefn
-
-@deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{low}, HOST_WIDE_INT @var{high}, enum machine_mode @var{mode})
-Converts a double-precision integer found in @var{low} and @var{high},
+@deftypefn Macro void REAL_VALUE_FROM_INT (REAL_VALUE_TYPE @var{x}, HOST_WIDE_INT @var{val}, enum machine_mode @var{mode})
+Converts a double-precision integer found in @var{val},
 into a floating point value which is then stored into @var{x}.  The
 value is truncated to fit in mode @var{mode}.
 @end deftypefn
@@ -11474,3 +11468,50 @@ It returns true if the target supports GNU indirect functions.
 The support includes the assembler, linker and dynamic linker.
 The default value of this hook is based on target's libc.
 @end deftypefn
+
+@defmac TARGET_SUPPORTS_WIDE_INT
+
+On older ports, large integers are stored in @code{CONST_DOUBLE} rtl
+objects.  Newer ports define @code{TARGET_SUPPORTS_WIDE_INT} to be non
+zero to indicate that large integers are stored in
+@code{CONST_WIDE_INT} rtl objects.  The @code{CONST_WIDE_INT} allows
+very large integer constants to be represented.  @code{CONST_DOUBLE}
+are limited to twice the size of host's @code{HOST_WIDE_INT}
+representation.
+
+Converting a port mostly requires looking for the places where
+@code{CONST_DOUBLES} are used with @code{VOIDmode} and replacing that
+code with code that accesses @code{CONST_WIDE_INT}s.  @samp{"grep -i
+const_double"} at the port level gets you to 95% of the changes that
+need to be made.  There are a few places that require a deeper look.
+
+@itemize @bullet
+@item
+There is no equivalent to @code{hval} and @code{lval} for
+@code{CONST_WIDE_INT}s.  This would be difficult to express in the md
+language since there are a variable number of elements.
+
+Most ports only check that @code{hval} is either 0 or -1 to see if the
+value is small.  As mentioned above, this will no longer be necessary
+since small constants are always @code{CONST_INT}.  Of course there
+are still a few exceptions, the alpha's constraint used by the zap
+instruction certainly requires careful examination by C code.
+However, all the current code does is pass the hval and lval to C
+code, so evolving the c code to look at the @code{CONST_WIDE_INT} is
+not really a large change.
+
+@item
+Because there is no standard template that ports use to materialize
+constants, there is likely to be some futzing that is unique to each
+port in this code.
+
+@item
+The rtx costs may have to be adjusted to properly account for larger
+constants that are represented as @code{CONST_WIDE_INT}.
+@end itemize
+
+All and all it does not takes long to convert ports that the
+maintainer is familiar with.
+
+@end defmac
+