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[thirdparty/gcc.git] / gcc / jit / docs / _build / texinfo / libgccjit.texi

\input texinfo   @c -*-texinfo-*-
@c %**start of header
@setfilename libgccjit.info
@documentencoding UTF-8
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@*Generated by Sphinx 1.1.3.@*
@end ifinfo
@settitle libgccjit Documentation
@defindex ge
@paragraphindent 2
@exampleindent 4
@afourlatex
@dircategory Miscellaneous
@direntry
* libgccjit: (libgccjit.info). One line description of project.
@end direntry

@c %**end of header

@copying
@quotation
libgccjit 6.0.0 (experimental 20150803), August 03, 2015

David Malcolm

Copyright @copyright{} 2014-2016 Free Software Foundation, Inc.
@end quotation

@end copying

@titlepage
@title libgccjit Documentation
@insertcopying
@end titlepage
@contents

@c %** start of user preamble

@c %** end of user preamble

@ifnottex
@node Top
@top libgccjit Documentation
@insertcopying
@end ifnottex

@c %**start of body
@anchor{index doc}@anchor{0}
@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

This document describes libgccjit@footnote{http://gcc.gnu.org/wiki/JIT}, an API
for embedding GCC inside programs and libraries.

Note that libgccjit is currently of "Alpha" quality;
the APIs are not yet set in stone, and they shouldn't be used in
production yet.

There are actually two APIs for the library:


@itemize *

@item 
a pure C API: @code{libgccjit.h}

@item 
a C++ wrapper API: @code{libgccjit++.h}.  This is a collection of "thin"
wrapper classes around the C API, to save typing.
@end itemize

Contents:

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@menu
* Tutorial:: 
* Topic Reference:: 
* C++ bindings for libgccjit:: 
* Internals:: 
* Indices and tables:: 
* Index:: 

@detailmenu
 --- The Detailed Node Listing ---

Tutorial

* Tutorial part 1; "Hello world": Tutorial part 1 "Hello world". 
* Tutorial part 2; Creating a trivial machine code function: Tutorial part 2 Creating a trivial machine code function. 
* Tutorial part 3; Loops and variables: Tutorial part 3 Loops and variables. 
* Tutorial part 4; Adding JIT-compilation to a toy interpreter: Tutorial part 4 Adding JIT-compilation to a toy interpreter. 
* Tutorial part 5; Implementing an Ahead-of-Time compiler: Tutorial part 5 Implementing an Ahead-of-Time compiler. 

Tutorial part 2: Creating a trivial machine code function

* Error-handling:: 
* Options:: 
* Full example:: 

Tutorial part 3: Loops and variables

* Expressions; lvalues and rvalues: Expressions lvalues and rvalues. 
* Control flow:: 
* Visualizing the control flow graph:: 
* Full example: Full example<2>. 

Tutorial part 4: Adding JIT-compilation to a toy interpreter

* Our toy interpreter:: 
* Compiling to machine code:: 
* Setting things up:: 
* Populating the function:: 
* Verifying the control flow graph:: 
* Compiling the context:: 
* Single-stepping through the generated code:: 
* Examining the generated code:: 
* Putting it all together:: 
* Behind the curtain; How does our code get optimized?: Behind the curtain How does our code get optimized?. 

Behind the curtain: How does our code get optimized?

* Optimizing away stack manipulation:: 
* Elimination of tail recursion:: 

Tutorial part 5: Implementing an Ahead-of-Time compiler

* The "brainf" language:: 
* Converting a brainf script to libgccjit IR:: 
* Compiling a context to a file:: 
* Other forms of ahead-of-time-compilation:: 

Topic Reference

* Compilation contexts:: 
* Objects:: 
* Types:: 
* Expressions:: 
* Creating and using functions:: 
* Source Locations:: 
* Compiling a context:: 
* ABI and API compatibility:: 
* Performance:: 

Compilation contexts

* Lifetime-management:: 
* Thread-safety:: 
* Error-handling: Error-handling<2>. 
* Debugging:: 
* Options: Options<2>. 

Options

* String Options:: 
* Boolean options:: 
* Integer options:: 
* Additional command-line options:: 

Types

* Standard types:: 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile. 
* Structures and unions:: 

Expressions

* Rvalues:: 
* Lvalues:: 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions. 

Rvalues

* Simple expressions:: 
* Unary Operations:: 
* Binary Operations:: 
* Comparisons:: 
* Function calls:: 
* Type-coercion:: 

Lvalues

* Global variables:: 

Creating and using functions

* Params:: 
* Functions:: 
* Blocks:: 
* Statements:: 

Source Locations

* Faking it:: 

Compiling a context

* In-memory compilation:: 
* Ahead-of-time compilation:: 

ABI and API compatibility

* ABI symbol tags:: 

ABI symbol tags

* LIBGCCJIT_ABI_0:: 
* LIBGCCJIT_ABI_1:: 
* LIBGCCJIT_ABI_2:: 
* LIBGCCJIT_ABI_3:: 
* LIBGCCJIT_ABI_4:: 

Performance

* The timing API:: 

C++ bindings for libgccjit

* Tutorial: Tutorial<2>. 
* Topic Reference: Topic Reference<2>. 

Tutorial

* Tutorial part 1; "Hello world": Tutorial part 1 "Hello world"<2>. 
* Tutorial part 2; Creating a trivial machine code function: Tutorial part 2 Creating a trivial machine code function<2>. 
* Tutorial part 3; Loops and variables: Tutorial part 3 Loops and variables<2>. 
* Tutorial part 4; Adding JIT-compilation to a toy interpreter: Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>. 

Tutorial part 2: Creating a trivial machine code function

* Options: Options<3>. 
* Full example: Full example<3>. 

Tutorial part 3: Loops and variables

* Expressions; lvalues and rvalues: Expressions lvalues and rvalues<2>. 
* Control flow: Control flow<2>. 
* Visualizing the control flow graph: Visualizing the control flow graph<2>. 
* Full example: Full example<4>. 

Tutorial part 4: Adding JIT-compilation to a toy interpreter

* Our toy interpreter: Our toy interpreter<2>. 
* Compiling to machine code: Compiling to machine code<2>. 
* Setting things up: Setting things up<2>. 
* Populating the function: Populating the function<2>. 
* Verifying the control flow graph: Verifying the control flow graph<2>. 
* Compiling the context: Compiling the context<2>. 
* Single-stepping through the generated code: Single-stepping through the generated code<2>. 
* Examining the generated code: Examining the generated code<2>. 
* Putting it all together: Putting it all together<2>. 
* Behind the curtain; How does our code get optimized?: Behind the curtain How does our code get optimized?<2>. 

Behind the curtain: How does our code get optimized?

* Optimizing away stack manipulation: Optimizing away stack manipulation<2>. 
* Elimination of tail recursion: Elimination of tail recursion<2>. 

Topic Reference

* Compilation contexts: Compilation contexts<2>. 
* Objects: Objects<2>. 
* Types: Types<2>. 
* Expressions: Expressions<2>. 
* Creating and using functions: Creating and using functions<2>. 
* Source Locations: Source Locations<2>. 
* Compiling a context: Compiling a context<2>. 

Compilation contexts

* Lifetime-management: Lifetime-management<2>. 
* Thread-safety: Thread-safety<2>. 
* Error-handling: Error-handling<3>. 
* Debugging: Debugging<2>. 
* Options: Options<4>. 

Options

* String Options: String Options<2>. 
* Boolean options: Boolean options<2>. 
* Integer options: Integer options<2>. 
* Additional command-line options: Additional command-line options<2>. 

Types

* Standard types: Standard types<2>. 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile<2>. 
* Structures and unions: Structures and unions<2>. 

Expressions

* Rvalues: Rvalues<2>. 
* Lvalues: Lvalues<2>. 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions<2>. 

Rvalues

* Simple expressions: Simple expressions<2>. 
* Unary Operations: Unary Operations<2>. 
* Binary Operations: Binary Operations<2>. 
* Comparisons: Comparisons<2>. 
* Function calls: Function calls<2>. 
* Type-coercion: Type-coercion<2>. 

Lvalues

* Global variables: Global variables<2>. 

Creating and using functions

* Params: Params<2>. 
* Functions: Functions<2>. 
* Blocks: Blocks<2>. 
* Statements: Statements<2>. 

Source Locations

* Faking it: Faking it<2>. 

Compiling a context

* In-memory compilation: In-memory compilation<2>. 
* Ahead-of-time compilation: Ahead-of-time compilation<2>. 

Internals

* Working on the JIT library:: 
* Running the test suite:: 
* Environment variables:: 
* Packaging notes:: 
* Overview of code structure:: 
* Design notes:: 
* Submitting patches:: 

Running the test suite

* Running under valgrind:: 

@end detailmenu
@end menu


@node Tutorial,Topic Reference,Top,Top
@anchor{intro/index libgccjit}@anchor{1}@anchor{intro/index doc}@anchor{2}@anchor{intro/index tutorial}@anchor{3}
@chapter Tutorial


@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@menu
* Tutorial part 1; "Hello world": Tutorial part 1 "Hello world". 
* Tutorial part 2; Creating a trivial machine code function: Tutorial part 2 Creating a trivial machine code function. 
* Tutorial part 3; Loops and variables: Tutorial part 3 Loops and variables. 
* Tutorial part 4; Adding JIT-compilation to a toy interpreter: Tutorial part 4 Adding JIT-compilation to a toy interpreter. 
* Tutorial part 5; Implementing an Ahead-of-Time compiler: Tutorial part 5 Implementing an Ahead-of-Time compiler. 

@end menu

@node Tutorial part 1 "Hello world",Tutorial part 2 Creating a trivial machine code function,,Tutorial
@anchor{intro/tutorial01 doc}@anchor{4}@anchor{intro/tutorial01 tutorial-part-1-hello-world}@anchor{5}
@section Tutorial part 1: "Hello world"


Before we look at the details of the API, let's look at building and
running programs that use the library.

Here's a toy "hello world" program that uses the library to synthesize
a call to @cite{printf} and uses it to write a message to stdout.

Don't worry about the content of the program for now; we'll cover
the details in later parts of this tutorial.

@quotation

@example
/* Smoketest example for libgccjit.so
   Copyright (C) 2014-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <libgccjit.h>

#include <stdlib.h>
#include <stdio.h>

static void
create_code (gcc_jit_context *ctxt)
@{
  /* Let's try to inject the equivalent of:
     void
     greet (const char *name)
     @{
        printf ("hello %s\n", name);
     @}
  */
  gcc_jit_type *void_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_VOID);
  gcc_jit_type *const_char_ptr_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_CONST_CHAR_PTR);
  gcc_jit_param *param_name =
    gcc_jit_context_new_param (ctxt, NULL, const_char_ptr_type, "name");
  gcc_jit_function *func =
    gcc_jit_context_new_function (ctxt, NULL,
                                  GCC_JIT_FUNCTION_EXPORTED,
                                  void_type,
                                  "greet",
                                  1, &param_name,
                                  0);

  gcc_jit_param *param_format =
    gcc_jit_context_new_param (ctxt, NULL, const_char_ptr_type, "format");
  gcc_jit_function *printf_func =
    gcc_jit_context_new_function (ctxt, NULL,
				  GCC_JIT_FUNCTION_IMPORTED,
				  gcc_jit_context_get_type (
				     ctxt, GCC_JIT_TYPE_INT),
				  "printf",
				  1, &param_format,
				  1);
  gcc_jit_rvalue *args[2];
  args[0] = gcc_jit_context_new_string_literal (ctxt, "hello %s\n");
  args[1] = gcc_jit_param_as_rvalue (param_name);

  gcc_jit_block *block = gcc_jit_function_new_block (func, NULL);

  gcc_jit_block_add_eval (
    block, NULL,
    gcc_jit_context_new_call (ctxt,
                              NULL,
                              printf_func,
                              2, args));
  gcc_jit_block_end_with_void_return (block, NULL);
@}

int
main (int argc, char **argv)
@{
  gcc_jit_context *ctxt;
  gcc_jit_result *result;

  /* Get a "context" object for working with the library.  */
  ctxt = gcc_jit_context_acquire ();
  if (!ctxt)
    @{
      fprintf (stderr, "NULL ctxt");
      exit (1);
    @}

  /* Set some options on the context.
     Let's see the code being generated, in assembler form.  */
  gcc_jit_context_set_bool_option (
    ctxt,
    GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
    0);

  /* Populate the context.  */
  create_code (ctxt);

  /* Compile the code.  */
  result = gcc_jit_context_compile (ctxt);
  if (!result)
    @{
      fprintf (stderr, "NULL result");
      exit (1);
    @}

  /* Extract the generated code from "result".  */
  typedef void (*fn_type) (const char *);
  fn_type greet =
    (fn_type)gcc_jit_result_get_code (result, "greet");
  if (!greet)
    @{
      fprintf (stderr, "NULL greet");
      exit (1);
    @}

  /* Now call the generated function: */
  greet ("world");
  fflush (stdout);

  gcc_jit_context_release (ctxt);
  gcc_jit_result_release (result);
  return 0;
@}

@end example

@noindent
@end quotation

Copy the above to @cite{tut01-hello-world.c}.

Assuming you have the jit library installed, build the test program
using:

@example
$ gcc \
    tut01-hello-world.c \
    -o tut01-hello-world \
    -lgccjit
@end example

@noindent

You should then be able to run the built program:

@example
$ ./tut01-hello-world
hello world
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 2 Creating a trivial machine code function,Tutorial part 3 Loops and variables,Tutorial part 1 "Hello world",Tutorial
@anchor{intro/tutorial02 doc}@anchor{6}@anchor{intro/tutorial02 tutorial-part-2-creating-a-trivial-machine-code-function}@anchor{7}
@section Tutorial part 2: Creating a trivial machine code function


Consider this C function:

@example
int square (int i)
@{
  return i * i;
@}
@end example

@noindent

How can we construct this at run-time using libgccjit?

First we need to include the relevant header:

@example
#include <libgccjit.h>
@end example

@noindent

All state associated with compilation is associated with a
@pxref{8,,gcc_jit_context *}.

Create one using @pxref{9,,gcc_jit_context_acquire()}:

@example
gcc_jit_context *ctxt;
ctxt = gcc_jit_context_acquire ();
@end example

@noindent

The JIT library has a system of types.  It is statically-typed: every
expression is of a specific type, fixed at compile-time.  In our example,
all of the expressions are of the C @cite{int} type, so let's obtain this from
the context, as a @pxref{a,,gcc_jit_type *}, using
@pxref{b,,gcc_jit_context_get_type()}:

@example
gcc_jit_type *int_type =
  gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
@end example

@noindent

@pxref{a,,gcc_jit_type *} is an example of a "contextual" object: every
entity in the API is associated with a @pxref{8,,gcc_jit_context *}.

Memory management is easy: all such "contextual" objects are automatically
cleaned up for you when the context is released, using
@pxref{c,,gcc_jit_context_release()}:

@example
gcc_jit_context_release (ctxt);
@end example

@noindent

so you don't need to manually track and cleanup all objects, just the
contexts.

Although the API is C-based, there is a form of class hierarchy, which
looks like this:

@example
+- gcc_jit_object
    +- gcc_jit_location
    +- gcc_jit_type
       +- gcc_jit_struct
    +- gcc_jit_field
    +- gcc_jit_function
    +- gcc_jit_block
    +- gcc_jit_rvalue
        +- gcc_jit_lvalue
           +- gcc_jit_param
@end example

@noindent

There are casting methods for upcasting from subclasses to parent classes.
For example, @pxref{d,,gcc_jit_type_as_object()}:

@example
gcc_jit_object *obj = gcc_jit_type_as_object (int_type);
@end example

@noindent

One thing you can do with a @pxref{e,,gcc_jit_object *} is
to ask it for a human-readable description, using
@pxref{f,,gcc_jit_object_get_debug_string()}:

@example
printf ("obj: %s\n", gcc_jit_object_get_debug_string (obj));
@end example

@noindent

giving this text on stdout:

@example
obj: int
@end example

@noindent

This is invaluable when debugging.

Let's create the function.  To do so, we first need to construct
its single parameter, specifying its type and giving it a name,
using @pxref{10,,gcc_jit_context_new_param()}:

@example
gcc_jit_param *param_i =
  gcc_jit_context_new_param (ctxt, NULL, int_type, "i");
@end example

@noindent

Now we can create the function, using
@pxref{11,,gcc_jit_context_new_function()}:

@example
gcc_jit_function *func =
  gcc_jit_context_new_function (ctxt, NULL,
                                GCC_JIT_FUNCTION_EXPORTED,
                                int_type,
                                "square",
                                1, &param_i,
                                0);
@end example

@noindent

To define the code within the function, we must create basic blocks
containing statements.

Every basic block contains a list of statements, eventually terminated
by a statement that either returns, or jumps to another basic block.

Our function has no control-flow, so we just need one basic block:

@example
gcc_jit_block *block = gcc_jit_function_new_block (func, NULL);
@end example

@noindent

Our basic block is relatively simple: it immediately terminates by
returning the value of an expression.

We can build the expression using @pxref{12,,gcc_jit_context_new_binary_op()}:

@example
gcc_jit_rvalue *expr =
  gcc_jit_context_new_binary_op (
    ctxt, NULL,
    GCC_JIT_BINARY_OP_MULT, int_type,
    gcc_jit_param_as_rvalue (param_i),
    gcc_jit_param_as_rvalue (param_i));
@end example

@noindent

A @pxref{13,,gcc_jit_rvalue *} is another example of a
@pxref{e,,gcc_jit_object *} subclass.  We can upcast it using
@pxref{14,,gcc_jit_rvalue_as_object()} and as before print it with
@pxref{f,,gcc_jit_object_get_debug_string()}.

@example
printf ("expr: %s\n",
        gcc_jit_object_get_debug_string (
          gcc_jit_rvalue_as_object (expr)));
@end example

@noindent

giving this output:

@example
expr: i * i
@end example

@noindent

Creating the expression in itself doesn't do anything; we have to add
this expression to a statement within the block.  In this case, we use it
to build a return statement, which terminates the basic block:

@example
gcc_jit_block_end_with_return (block, NULL, expr);
@end example

@noindent

OK, we've populated the context.  We can now compile it using
@pxref{15,,gcc_jit_context_compile()}:

@example
gcc_jit_result *result;
result = gcc_jit_context_compile (ctxt);
@end example

@noindent

and get a @pxref{16,,gcc_jit_result *}.

At this point we're done with the context; we can release it:

@example
gcc_jit_context_release (ctxt);
@end example

@noindent

We can now use @pxref{17,,gcc_jit_result_get_code()} to look up a specific
machine code routine within the result, in this case, the function we
created above.

@example
void *fn_ptr = gcc_jit_result_get_code (result, "square");
if (!fn_ptr)
  @{
    fprintf (stderr, "NULL fn_ptr");
    goto error;
  @}
@end example

@noindent

We can now cast the pointer to an appropriate function pointer type, and
then call it:

@example
typedef int (*fn_type) (int);
fn_type square = (fn_type)fn_ptr;
printf ("result: %d", square (5));
@end example

@noindent

@example
result: 25
@end example

@noindent

Once we're done with the code, we can release the result:

@example
gcc_jit_result_release (result);
@end example

@noindent

We can't call @code{square} anymore once we've released @code{result}.

@menu
* Error-handling:: 
* Options:: 
* Full example:: 

@end menu

@node Error-handling,Options,,Tutorial part 2 Creating a trivial machine code function
@anchor{intro/tutorial02 error-handling}@anchor{18}
@subsection Error-handling


Various kinds of errors are possible when using the API, such as
mismatched types in an assignment.  You can only compile and get code
from a context if no errors occur.

Errors are printed on stderr; they typically contain the name of the API
entrypoint where the error occurred, and pertinent information on the
problem:

@example
./buggy-program: error: gcc_jit_block_add_assignment: mismatching types: assignment to i (type: int) from "hello world" (type: const char *)
@end example

@noindent

The API is designed to cope with errors without crashing, so you can get
away with having a single error-handling check in your code:

@example
void *fn_ptr = gcc_jit_result_get_code (result, "square");
if (!fn_ptr)
  @{
    fprintf (stderr, "NULL fn_ptr");
    goto error;
  @}
@end example

@noindent

For more information, see the @pxref{19,,error-handling guide}
within the Topic eference.

@node Options,Full example,Error-handling,Tutorial part 2 Creating a trivial machine code function
@anchor{intro/tutorial02 options}@anchor{1a}
@subsection Options


To get more information on what's going on, you can set debugging flags
on the context using @pxref{1b,,gcc_jit_context_set_bool_option()}.

@c (I'm deliberately not mentioning
@c :c:macro:`GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE` here since I think
@c it's probably more of use to implementors than to users)

Setting @pxref{1c,,GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE} will dump a
C-like representation to stderr when you compile (GCC's "GIMPLE"
representation):

@example
gcc_jit_context_set_bool_option (
  ctxt,
  GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE,
  1);
result = gcc_jit_context_compile (ctxt);
@end example

@noindent

@example
square (signed int i)
@{
  signed int D.260;

  entry:
  D.260 = i * i;
  return D.260;
@}
@end example

@noindent

We can see the generated machine code in assembler form (on stderr) by
setting @pxref{1d,,GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE} on the context
before compiling:

@example
gcc_jit_context_set_bool_option (
  ctxt,
  GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
  1);
result = gcc_jit_context_compile (ctxt);
@end example

@noindent

@example
      .file   "fake.c"
      .text
      .globl  square
      .type   square, @@function
square:
.LFB6:
      .cfi_startproc
      pushq   %rbp
      .cfi_def_cfa_offset 16
      .cfi_offset 6, -16
      movq    %rsp, %rbp
      .cfi_def_cfa_register 6
      movl    %edi, -4(%rbp)
.L14:
      movl    -4(%rbp), %eax
      imull   -4(%rbp), %eax
      popq    %rbp
      .cfi_def_cfa 7, 8
      ret
      .cfi_endproc
.LFE6:
      .size   square, .-square
      .ident  "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.2-0.5.1920c315ff984892399893b380305ab36e07b455.fc20)"
      .section       .note.GNU-stack,"",@@progbits
@end example

@noindent

By default, no optimizations are performed, the equivalent of GCC's
@cite{-O0} option.  We can turn things up to e.g. @cite{-O3} by calling
@pxref{1e,,gcc_jit_context_set_int_option()} with
@pxref{1f,,GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL}:

@example
gcc_jit_context_set_int_option (
  ctxt,
  GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL,
  3);
@end example

@noindent

@example
      .file   "fake.c"
      .text
      .p2align 4,,15
      .globl  square
      .type   square, @@function
square:
.LFB7:
      .cfi_startproc
.L16:
      movl    %edi, %eax
      imull   %edi, %eax
      ret
      .cfi_endproc
.LFE7:
      .size   square, .-square
      .ident  "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.2-0.5.1920c315ff984892399893b380305ab36e07b455.fc20)"
      .section        .note.GNU-stack,"",@@progbits
@end example

@noindent

Naturally this has only a small effect on such a trivial function.

@node Full example,,Options,Tutorial part 2 Creating a trivial machine code function
@anchor{intro/tutorial02 full-example}@anchor{20}
@subsection Full example


Here's what the above looks like as a complete program:

@quotation

@example
/* Usage example for libgccjit.so
   Copyright (C) 2014-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <libgccjit.h>

#include <stdlib.h>
#include <stdio.h>

void
create_code (gcc_jit_context *ctxt)
@{
  /* Let's try to inject the equivalent of:

      int square (int i)
      @{
        return i * i;
      @}
  */
  gcc_jit_type *int_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
  gcc_jit_param *param_i =
    gcc_jit_context_new_param (ctxt, NULL, int_type, "i");
  gcc_jit_function *func =
    gcc_jit_context_new_function (ctxt, NULL,
                                  GCC_JIT_FUNCTION_EXPORTED,
                                  int_type,
                                  "square",
                                  1, &param_i,
                                  0);

  gcc_jit_block *block = gcc_jit_function_new_block (func, NULL);

  gcc_jit_rvalue *expr =
    gcc_jit_context_new_binary_op (
      ctxt, NULL,
      GCC_JIT_BINARY_OP_MULT, int_type,
      gcc_jit_param_as_rvalue (param_i),
      gcc_jit_param_as_rvalue (param_i));

   gcc_jit_block_end_with_return (block, NULL, expr);
@}

int
main (int argc, char **argv)
@{
  gcc_jit_context *ctxt = NULL;
  gcc_jit_result *result = NULL;

  /* Get a "context" object for working with the library.  */
  ctxt = gcc_jit_context_acquire ();
  if (!ctxt)
    @{
      fprintf (stderr, "NULL ctxt");
      goto error;
    @}

  /* Set some options on the context.
     Let's see the code being generated, in assembler form.  */
  gcc_jit_context_set_bool_option (
    ctxt,
    GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
    0);

  /* Populate the context.  */
  create_code (ctxt);

  /* Compile the code.  */
  result = gcc_jit_context_compile (ctxt);
  if (!result)
    @{
      fprintf (stderr, "NULL result");
      goto error;
    @}

  /* We're done with the context; we can release it: */
  gcc_jit_context_release (ctxt);
  ctxt = NULL;

  /* Extract the generated code from "result".  */
  void *fn_ptr = gcc_jit_result_get_code (result, "square");
  if (!fn_ptr)
     @{
       fprintf (stderr, "NULL fn_ptr");
       goto error;
     @}

  typedef int (*fn_type) (int);
  fn_type square = (fn_type)fn_ptr;
  printf ("result: %d\n", square (5));

 error:
  if (ctxt)
    gcc_jit_context_release (ctxt);
  if (result)
    gcc_jit_result_release (result);
  return 0;
@}

@end example

@noindent
@end quotation

Building and running it:

@example
$ gcc \
    tut02-square.c \
    -o tut02-square \
    -lgccjit

# Run the built program:
$ ./tut02-square
result: 25
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 3 Loops and variables,Tutorial part 4 Adding JIT-compilation to a toy interpreter,Tutorial part 2 Creating a trivial machine code function,Tutorial
@anchor{intro/tutorial03 tutorial-part-3-loops-and-variables}@anchor{21}@anchor{intro/tutorial03 doc}@anchor{22}
@section Tutorial part 3: Loops and variables


Consider this C function:

@quotation

@example
int loop_test (int n)
@{
  int sum = 0;
  for (int i = 0; i < n; i++)
    sum += i * i;
  return sum;
@}
@end example

@noindent
@end quotation

This example demonstrates some more features of libgccjit, with local
variables and a loop.

To break this down into libgccjit terms, it's usually easier to reword
the @cite{for} loop as a @cite{while} loop, giving:

@quotation

@example
int loop_test (int n)
@{
  int sum = 0;
  int i = 0;
  while (i < n)
  @{
    sum += i * i;
    i++;
  @}
  return sum;
@}
@end example

@noindent
@end quotation

Here's what the final control flow graph will look like:

@quotation


@float Figure

@image{sum-of-squares1,,,image of a control flow graph,png}

@end float

@end quotation

As before, we include the libgccjit header and make a
@pxref{8,,gcc_jit_context *}.

@example
#include <libgccjit.h>

void test (void)
@{
  gcc_jit_context *ctxt;
  ctxt = gcc_jit_context_acquire ();
@end example

@noindent

The function works with the C @cite{int} type:

@example
gcc_jit_type *the_type =
  gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
gcc_jit_type *return_type = the_type;
@end example

@noindent

though we could equally well make it work on, say, @cite{double}:

@example
gcc_jit_type *the_type =
  gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_DOUBLE);
@end example

@noindent

Let's build the function:

@example
gcc_jit_param *n =
  gcc_jit_context_new_param (ctxt, NULL, the_type, "n");
gcc_jit_param *params[1] = @{n@};
gcc_jit_function *func =
  gcc_jit_context_new_function (ctxt, NULL,
                                GCC_JIT_FUNCTION_EXPORTED,
                                return_type,
                                "loop_test",
                                1, params, 0);
@end example

@noindent

@menu
* Expressions; lvalues and rvalues: Expressions lvalues and rvalues. 
* Control flow:: 
* Visualizing the control flow graph:: 
* Full example: Full example<2>. 

@end menu

@node Expressions lvalues and rvalues,Control flow,,Tutorial part 3 Loops and variables
@anchor{intro/tutorial03 expressions-lvalues-and-rvalues}@anchor{23}
@subsection Expressions: lvalues and rvalues


The base class of expression is the @pxref{13,,gcc_jit_rvalue *},
representing an expression that can be on the @emph{right}-hand side of
an assignment: a value that can be computed somehow, and assigned
@emph{to} a storage area (such as a variable).  It has a specific
@pxref{a,,gcc_jit_type *}.

Anothe important class is @pxref{24,,gcc_jit_lvalue *}.
A @pxref{24,,gcc_jit_lvalue *}. is something that can of the @emph{left}-hand
side of an assignment: a storage area (such as a variable).

In other words, every assignment can be thought of as:

@example
LVALUE = RVALUE;
@end example

@noindent

Note that @pxref{24,,gcc_jit_lvalue *} is a subclass of
@pxref{13,,gcc_jit_rvalue *}, where in an assignment of the form:

@example
LVALUE_A = LVALUE_B;
@end example

@noindent

the @cite{LVALUE_B} implies reading the current value of that storage
area, assigning it into the @cite{LVALUE_A}.

So far the only expressions we've seen are @cite{i * i}:

@example
gcc_jit_rvalue *expr =
  gcc_jit_context_new_binary_op (
    ctxt, NULL,
    GCC_JIT_BINARY_OP_MULT, int_type,
    gcc_jit_param_as_rvalue (param_i),
    gcc_jit_param_as_rvalue (param_i));
@end example

@noindent

which is a @pxref{13,,gcc_jit_rvalue *}, and the various function
parameters: @cite{param_i} and @cite{param_n}, instances of
@pxref{25,,gcc_jit_param *}, which is a subclass of
@pxref{24,,gcc_jit_lvalue *} (and, in turn, of @pxref{13,,gcc_jit_rvalue *}):
we can both read from and write to function parameters within the
body of a function.

Our new example has a couple of local variables.  We create them by
calling @pxref{26,,gcc_jit_function_new_local()}, supplying a type and a
name:

@example
/* Build locals:  */
gcc_jit_lvalue *i =
  gcc_jit_function_new_local (func, NULL, the_type, "i");
gcc_jit_lvalue *sum =
  gcc_jit_function_new_local (func, NULL, the_type, "sum");
@end example

@noindent

These are instances of @pxref{24,,gcc_jit_lvalue *} - they can be read from
and written to.

Note that there is no precanned way to create @emph{and} initialize a variable
like in C:

@example
int i = 0;
@end example

@noindent

Instead, having added the local to the function, we have to separately add
an assignment of @cite{0} to @cite{local_i} at the beginning of the function.

@node Control flow,Visualizing the control flow graph,Expressions lvalues and rvalues,Tutorial part 3 Loops and variables
@anchor{intro/tutorial03 control-flow}@anchor{27}
@subsection Control flow


This function has a loop, so we need to build some basic blocks to
handle the control flow.  In this case, we need 4 blocks:


@enumerate 

@item 
before the loop (initializing the locals)

@item 
the conditional at the top of the loop (comparing @cite{i < n})

@item 
the body of the loop

@item 
after the loop terminates (@cite{return sum})
@end enumerate

so we create these as @pxref{28,,gcc_jit_block *} instances within the
@pxref{29,,gcc_jit_function *}:

@example
gcc_jit_block *b_initial =
  gcc_jit_function_new_block (func, "initial");
gcc_jit_block *b_loop_cond =
  gcc_jit_function_new_block (func, "loop_cond");
gcc_jit_block *b_loop_body =
  gcc_jit_function_new_block (func, "loop_body");
gcc_jit_block *b_after_loop =
  gcc_jit_function_new_block (func, "after_loop");
@end example

@noindent

We now populate each block with statements.

The entry block @cite{b_initial} consists of initializations followed by a jump
to the conditional.  We assign @cite{0} to @cite{i} and to @cite{sum}, using
@pxref{2a,,gcc_jit_block_add_assignment()} to add
an assignment statement, and using @pxref{2b,,gcc_jit_context_zero()} to get
the constant value @cite{0} for the relevant type for the right-hand side of
the assignment:

@example
/* sum = 0; */
gcc_jit_block_add_assignment (
  b_initial, NULL,
  sum,
  gcc_jit_context_zero (ctxt, the_type));

/* i = 0; */
gcc_jit_block_add_assignment (
  b_initial, NULL,
  i,
  gcc_jit_context_zero (ctxt, the_type));
@end example

@noindent

We can then terminate the entry block by jumping to the conditional:

@example
gcc_jit_block_end_with_jump (b_initial, NULL, b_loop_cond);
@end example

@noindent

The conditional block is equivalent to the line @cite{while (i < n)} from our
C example. It contains a single statement: a conditional, which jumps to
one of two destination blocks depending on a boolean
@pxref{13,,gcc_jit_rvalue *}, in this case the comparison of @cite{i} and @cite{n}.
We build the comparison using @pxref{2c,,gcc_jit_context_new_comparison()}:

@example
/* (i >= n) */
 gcc_jit_rvalue *guard =
   gcc_jit_context_new_comparison (
     ctxt, NULL,
     GCC_JIT_COMPARISON_GE,
     gcc_jit_lvalue_as_rvalue (i),
     gcc_jit_param_as_rvalue (n));
@end example

@noindent

and can then use this to add @cite{b_loop_cond}'s sole statement, via
@pxref{2d,,gcc_jit_block_end_with_conditional()}:

@example
/* Equivalent to:
     if (guard)
       goto after_loop;
     else
       goto loop_body;  */
gcc_jit_block_end_with_conditional (
  b_loop_cond, NULL,
  guard,
  b_after_loop, /* on_true */
  b_loop_body); /* on_false */
@end example

@noindent

Next, we populate the body of the loop.

The C statement @cite{sum += i * i;} is an assignment operation, where an
lvalue is modified "in-place".  We use
@pxref{2e,,gcc_jit_block_add_assignment_op()} to handle these operations:

@example
/* sum += i * i */
gcc_jit_block_add_assignment_op (
  b_loop_body, NULL,
  sum,
  GCC_JIT_BINARY_OP_PLUS,
  gcc_jit_context_new_binary_op (
    ctxt, NULL,
    GCC_JIT_BINARY_OP_MULT, the_type,
    gcc_jit_lvalue_as_rvalue (i),
    gcc_jit_lvalue_as_rvalue (i)));
@end example

@noindent

The @cite{i++} can be thought of as @cite{i += 1}, and can thus be handled in
a similar way.  We use @pxref{2f,,gcc_jit_context_one()} to get the constant
value @cite{1} (for the relevant type) for the right-hand side
of the assignment.

@example
/* i++ */
gcc_jit_block_add_assignment_op (
  b_loop_body, NULL,
  i,
  GCC_JIT_BINARY_OP_PLUS,
  gcc_jit_context_one (ctxt, the_type));
@end example

@noindent

@cartouche
@quotation Note 
For numeric constants other than 0 or 1, we could use
@pxref{30,,gcc_jit_context_new_rvalue_from_int()} and
@pxref{31,,gcc_jit_context_new_rvalue_from_double()}.
@end quotation
@end cartouche

The loop body completes by jumping back to the conditional:

@example
gcc_jit_block_end_with_jump (b_loop_body, NULL, b_loop_cond);
@end example

@noindent

Finally, we populate the @cite{b_after_loop} block, reached when the loop
conditional is false.  We want to generate the equivalent of:

@example
return sum;
@end example

@noindent

so the block is just one statement:

@example
/* return sum */
gcc_jit_block_end_with_return (
  b_after_loop,
  NULL,
  gcc_jit_lvalue_as_rvalue (sum));
@end example

@noindent

@cartouche
@quotation Note 
You can intermingle block creation with statement creation,
but given that the terminator statements generally include references
to other blocks, I find it's clearer to create all the blocks,
@emph{then} all the statements.
@end quotation
@end cartouche

We've finished populating the function.  As before, we can now compile it
to machine code:

@example
gcc_jit_result *result;
result = gcc_jit_context_compile (ctxt);

typedef int (*loop_test_fn_type) (int);
loop_test_fn_type loop_test =
 (loop_test_fn_type)gcc_jit_result_get_code (result, "loop_test");
if (!loop_test)
  goto error;
printf ("result: %d", loop_test (10));
@end example

@noindent

@example
result: 285
@end example

@noindent

@node Visualizing the control flow graph,Full example<2>,Control flow,Tutorial part 3 Loops and variables
@anchor{intro/tutorial03 visualizing-the-control-flow-graph}@anchor{32}
@subsection Visualizing the control flow graph


You can see the control flow graph of a function using
@pxref{33,,gcc_jit_function_dump_to_dot()}:

@example
gcc_jit_function_dump_to_dot (func, "/tmp/sum-of-squares.dot");
@end example

@noindent

giving a .dot file in GraphViz format.

You can convert this to an image using @cite{dot}:

@example
$ dot -Tpng /tmp/sum-of-squares.dot -o /tmp/sum-of-squares.png
@end example

@noindent

or use a viewer (my preferred one is xdot.py; see
@indicateurl{https://github.com/jrfonseca/xdot.py}; on Fedora you can
install it with @cite{yum install python-xdot}):

@quotation


@float Figure

@image{sum-of-squares1,,,image of a control flow graph,png}

@end float

@end quotation

@node Full example<2>,,Visualizing the control flow graph,Tutorial part 3 Loops and variables
@anchor{intro/tutorial03 full-example}@anchor{34}
@subsection Full example


@quotation

@example
/* Usage example for libgccjit.so
   Copyright (C) 2014-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <libgccjit.h>

#include <stdlib.h>
#include <stdio.h>

void
create_code (gcc_jit_context *ctxt)
@{
  /*
    Simple sum-of-squares, to test conditionals and looping

    int loop_test (int n)
    @{
      int i;
      int sum = 0;
      for (i = 0; i < n ; i ++)
      @{
	sum += i * i;
      @}
      return sum;
   */
  gcc_jit_type *the_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
  gcc_jit_type *return_type = the_type;

  gcc_jit_param *n =
    gcc_jit_context_new_param (ctxt, NULL, the_type, "n");
  gcc_jit_param *params[1] = @{n@};
  gcc_jit_function *func =
    gcc_jit_context_new_function (ctxt, NULL,
				  GCC_JIT_FUNCTION_EXPORTED,
				  return_type,
				  "loop_test",
				  1, params, 0);

  /* Build locals:  */
  gcc_jit_lvalue *i =
    gcc_jit_function_new_local (func, NULL, the_type, "i");
  gcc_jit_lvalue *sum =
    gcc_jit_function_new_local (func, NULL, the_type, "sum");

  gcc_jit_block *b_initial =
    gcc_jit_function_new_block (func, "initial");
  gcc_jit_block *b_loop_cond =
    gcc_jit_function_new_block (func, "loop_cond");
  gcc_jit_block *b_loop_body =
    gcc_jit_function_new_block (func, "loop_body");
  gcc_jit_block *b_after_loop =
    gcc_jit_function_new_block (func, "after_loop");

  /* sum = 0; */
  gcc_jit_block_add_assignment (
    b_initial, NULL,
    sum,
    gcc_jit_context_zero (ctxt, the_type));

  /* i = 0; */
  gcc_jit_block_add_assignment (
    b_initial, NULL,
    i,
    gcc_jit_context_zero (ctxt, the_type));

  gcc_jit_block_end_with_jump (b_initial, NULL, b_loop_cond);

  /* if (i >= n) */
  gcc_jit_block_end_with_conditional (
    b_loop_cond, NULL,
    gcc_jit_context_new_comparison (
       ctxt, NULL,
       GCC_JIT_COMPARISON_GE,
       gcc_jit_lvalue_as_rvalue (i),
       gcc_jit_param_as_rvalue (n)),
    b_after_loop,
    b_loop_body);

  /* sum += i * i */
  gcc_jit_block_add_assignment_op (
    b_loop_body, NULL,
    sum,
    GCC_JIT_BINARY_OP_PLUS,
    gcc_jit_context_new_binary_op (
      ctxt, NULL,
      GCC_JIT_BINARY_OP_MULT, the_type,
      gcc_jit_lvalue_as_rvalue (i),
      gcc_jit_lvalue_as_rvalue (i)));

  /* i++ */
  gcc_jit_block_add_assignment_op (
    b_loop_body, NULL,
    i,
    GCC_JIT_BINARY_OP_PLUS,
    gcc_jit_context_one (ctxt, the_type));

  gcc_jit_block_end_with_jump (b_loop_body, NULL, b_loop_cond);

  /* return sum */
  gcc_jit_block_end_with_return (
    b_after_loop,
    NULL,
    gcc_jit_lvalue_as_rvalue (sum));
@}

int
main (int argc, char **argv)
@{
  gcc_jit_context *ctxt = NULL;
  gcc_jit_result *result = NULL;

  /* Get a "context" object for working with the library.  */
  ctxt = gcc_jit_context_acquire ();
  if (!ctxt)
    @{
      fprintf (stderr, "NULL ctxt");
      goto error;
    @}

  /* Set some options on the context.
     Let's see the code being generated, in assembler form.  */
  gcc_jit_context_set_bool_option (
    ctxt,
    GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
    0);

  /* Populate the context.  */
  create_code (ctxt);

  /* Compile the code.  */
  result = gcc_jit_context_compile (ctxt);
  if (!result)
    @{
      fprintf (stderr, "NULL result");
      goto error;
    @}

  /* Extract the generated code from "result".  */
  typedef int (*loop_test_fn_type) (int);
  loop_test_fn_type loop_test =
    (loop_test_fn_type)gcc_jit_result_get_code (result, "loop_test");
  if (!loop_test)
    @{
      fprintf (stderr, "NULL loop_test");
      goto error;
    @}

  /* Run the generated code.  */
  int val = loop_test (10);
  printf("loop_test returned: %d\n", val);

 error:
  gcc_jit_context_release (ctxt);
  gcc_jit_result_release (result);
  return 0;
@}

@end example

@noindent
@end quotation

Building and running it:

@example
$ gcc \
    tut03-sum-of-squares.c \
    -o tut03-sum-of-squares \
    -lgccjit

# Run the built program:
$ ./tut03-sum-of-squares
loop_test returned: 285
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 4 Adding JIT-compilation to a toy interpreter,Tutorial part 5 Implementing an Ahead-of-Time compiler,Tutorial part 3 Loops and variables,Tutorial
@anchor{intro/tutorial04 tutorial-part-4-adding-jit-compilation-to-a-toy-interpreter}@anchor{35}@anchor{intro/tutorial04 doc}@anchor{36}
@section Tutorial part 4: Adding JIT-compilation to a toy interpreter


In this example we construct a "toy" interpreter, and add JIT-compilation
to it.

@menu
* Our toy interpreter:: 
* Compiling to machine code:: 
* Setting things up:: 
* Populating the function:: 
* Verifying the control flow graph:: 
* Compiling the context:: 
* Single-stepping through the generated code:: 
* Examining the generated code:: 
* Putting it all together:: 
* Behind the curtain; How does our code get optimized?: Behind the curtain How does our code get optimized?. 

@end menu

@node Our toy interpreter,Compiling to machine code,,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 our-toy-interpreter}@anchor{37}
@subsection Our toy interpreter


It's a stack-based interpreter, and is intended as a (very simple) example
of the kind of bytecode interpreter seen in dynamic languages such as
Python, Ruby etc.

For the sake of simplicity, our toy virtual machine is very limited:

@quotation


@itemize *

@item 
The only data type is @cite{int}

@item 
It can only work on one function at a time (so that the only
function call that can be made is to recurse).

@item 
Functions can only take one parameter.

@item 
Functions have a stack of @cite{int} values.

@item 
We'll implement function call within the interpreter by calling a
function in our implementation, rather than implementing our own
frame stack.

@item 
The parser is only good enough to get the examples to work.
@end itemize
@end quotation

Naturally, a real interpreter would be much more complicated that this.

The following operations are supported:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxx} 
@headitem

Operation

@tab

Meaning

@tab

Old Stack

@tab

New Stack

@item

DUP

@tab

Duplicate top of stack.

@tab

@code{[..., x]}

@tab

@code{[..., x, x]}

@item

ROT

@tab

Swap top two elements
of stack.

@tab

@code{[..., x, y]}

@tab

@code{[..., y, x]}

@item

BINARY_ADD

@tab

Add the top two elements
on the stack.

@tab

@code{[..., x, y]}

@tab

@code{[..., (x+y)]}

@item

BINARY_SUBTRACT

@tab

Likewise, but subtract.

@tab

@code{[..., x, y]}

@tab

@code{[..., (x-y)]}

@item

BINARY_MULT

@tab

Likewise, but multiply.

@tab

@code{[..., x, y]}

@tab

@code{[..., (x*y)]}

@item

BINARY_COMPARE_LT

@tab

Compare the top two
elements on the stack
and push a nonzero/zero
if (x<y).

@tab

@code{[..., x, y]}

@tab

@code{[..., (x<y)]}

@item

RECURSE

@tab

Recurse, passing the top
of the stack, and
popping the result.

@tab

@code{[..., x]}

@tab

@code{[..., fn(x)]}

@item

RETURN

@tab

Return the top of the
stack.

@tab

@code{[x]}

@tab

@code{[]}

@item

PUSH_CONST @cite{arg}

@tab

Push an int const.

@tab

@code{[...]}

@tab

@code{[..., arg]}

@item

JUMP_ABS_IF_TRUE @cite{arg}

@tab

Pop; if top of stack was
nonzero, jump to
@code{arg}.

@tab

@code{[..., x]}

@tab

@code{[...]}

@end multitable


Programs can be interpreted, disassembled, and compiled to machine code.

The interpreter reads @code{.toy} scripts.  Here's what a simple recursive
factorial program looks like, the script @code{factorial.toy}.
The parser ignores lines beginning with a @cite{#}.

@quotation

@example
# Simple recursive factorial implementation, roughly equivalent to:
#
#  int factorial (int arg)
#  @{
#     if (arg < 2)
#       return arg
#     return arg * factorial (arg - 1)
#  @}

# Initial state:
# stack: [arg]

# 0:
DUP
# stack: [arg, arg]

# 1:
PUSH_CONST 2
# stack: [arg, arg, 2]

# 2:
BINARY_COMPARE_LT
# stack: [arg, (arg < 2)]

# 3:
JUMP_ABS_IF_TRUE 9
# stack: [arg]

# 4:
DUP
# stack: [arg, arg]

# 5:
PUSH_CONST 1
# stack: [arg, arg, 1]

# 6:
BINARY_SUBTRACT
# stack: [arg,  (arg - 1)

# 7:
RECURSE
# stack: [arg, factorial(arg - 1)]

# 8:
BINARY_MULT
# stack: [arg * factorial(arg - 1)]

# 9:
RETURN

@end example

@noindent
@end quotation

The interpreter is a simple infinite loop with a big @code{switch} statement
based on what the next opcode is:

@quotation

@example

static int
toyvm_function_interpret (toyvm_function *fn, int arg, FILE *trace)
@{
  toyvm_frame frame;
#define PUSH(ARG) (toyvm_frame_push (&frame, (ARG)))
#define POP(ARG) (toyvm_frame_pop (&frame))

  frame.frm_function = fn;
  frame.frm_pc = 0;
  frame.frm_cur_depth = 0;

  PUSH (arg);

  while (1)
    @{
      toyvm_op *op;
      int x, y;
      assert (frame.frm_pc < fn->fn_num_ops);
      op = &fn->fn_ops[frame.frm_pc++];

      if (trace)
	@{
	  toyvm_frame_dump_stack (&frame, trace);
	  toyvm_function_disassemble_op (fn, op, frame.frm_pc, trace);
	@}

      switch (op->op_opcode)
	@{
	  /* Ops taking no operand.  */
	case DUP:
	  x = POP ();
	  PUSH (x);
	  PUSH (x);
	  break;

	case ROT:
	  y = POP ();
	  x = POP ();
	  PUSH (y);
	  PUSH (x);
	  break;

	case BINARY_ADD:
	  y = POP ();
	  x = POP ();
	  PUSH (x + y);
	  break;

	case BINARY_SUBTRACT:
	  y = POP ();
	  x = POP ();
	  PUSH (x - y);
	  break;

	case BINARY_MULT:
	  y = POP ();
	  x = POP ();
	  PUSH (x * y);
	  break;

	case BINARY_COMPARE_LT:
	  y = POP ();
	  x = POP ();
	  PUSH (x < y);
	  break;

	case RECURSE:
	  x = POP ();
	  x = toyvm_function_interpret (fn, x, trace);
	  PUSH (x);
	  break;

	case RETURN:
	  return POP ();

	  /* Ops taking an operand.  */
	case PUSH_CONST:
	  PUSH (op->op_operand);
	  break;

	case JUMP_ABS_IF_TRUE:
	  x = POP ();
	  if (x)
	    frame.frm_pc = op->op_operand;
	  break;

	default:
	  assert (0); /* unknown opcode */

	@} /* end of switch on opcode */
    @} /* end of while loop */

#undef PUSH
#undef POP
@}


@end example

@noindent
@end quotation

@node Compiling to machine code,Setting things up,Our toy interpreter,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 compiling-to-machine-code}@anchor{38}
@subsection Compiling to machine code


We want to generate machine code that can be cast to this type and
then directly executed in-process:

@quotation

@example
typedef int (*toyvm_compiled_code) (int);


@end example

@noindent
@end quotation

The lifetime of the code is tied to that of a @pxref{16,,gcc_jit_result *}.
We'll handle this by bundling them up in a structure, so that we can
clean them up together by calling @pxref{39,,gcc_jit_result_release()}:

@quotation

@example

struct toyvm_compiled_function
@{
  gcc_jit_result *cf_jit_result;
  toyvm_compiled_code cf_code;
@};


@end example

@noindent
@end quotation

Our compiler isn't very sophisticated; it takes the implementation of
each opcode above, and maps it directly to the operations supported by
the libgccjit API.

How should we handle the stack?  In theory we could calculate what the
stack depth will be at each opcode, and optimize away the stack
manipulation "by hand".  We'll see below that libgccjit is able to do
this for us, so we'll implement stack manipulation
in a direct way, by creating a @code{stack} array and @code{stack_depth}
variables, local within the generated function, equivalent to this C code:

@example
int stack_depth;
int stack[MAX_STACK_DEPTH];
@end example

@noindent

We'll also have local variables @code{x} and @code{y} for use when implementing
the opcodes, equivalent to this:

@example
int x;
int y;
@end example

@noindent

This means our compiler has the following state:

@quotation

@example

struct compilation_state
@{
  gcc_jit_context *ctxt;

  gcc_jit_type *int_type;
  gcc_jit_type *bool_type;
  gcc_jit_type *stack_type; /* int[MAX_STACK_DEPTH] */

  gcc_jit_rvalue *const_one;

  gcc_jit_function *fn;
  gcc_jit_param *param_arg;
  gcc_jit_lvalue *stack;
  gcc_jit_lvalue *stack_depth;
  gcc_jit_lvalue *x;
  gcc_jit_lvalue *y;

  gcc_jit_location *op_locs[MAX_OPS];
  gcc_jit_block *initial_block;
  gcc_jit_block *op_blocks[MAX_OPS];

@};


@end example

@noindent
@end quotation

@node Setting things up,Populating the function,Compiling to machine code,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 setting-things-up}@anchor{3a}
@subsection Setting things up


First we create our types:

@quotation

@example
  state.int_type =
    gcc_jit_context_get_type (state.ctxt, GCC_JIT_TYPE_INT);
  state.bool_type =
    gcc_jit_context_get_type (state.ctxt, GCC_JIT_TYPE_BOOL);
  state.stack_type =
    gcc_jit_context_new_array_type (state.ctxt, NULL,
				    state.int_type, MAX_STACK_DEPTH);


@end example

@noindent
@end quotation

along with extracting a useful @cite{int} constant:

@quotation

@example
  state.const_one = gcc_jit_context_one (state.ctxt, state.int_type);


@end example

@noindent
@end quotation

We'll implement push and pop in terms of the @code{stack} array and
@code{stack_depth}.  Here are helper functions for adding statements to
a block, implementing pushing and popping values:

@quotation

@example

static void
add_push (compilation_state *state,
	  gcc_jit_block *block,
	  gcc_jit_rvalue *rvalue,
	  gcc_jit_location *loc)
@{
  /* stack[stack_depth] = RVALUE */
  gcc_jit_block_add_assignment (
    block,
    loc,
    /* stack[stack_depth] */
    gcc_jit_context_new_array_access (
      state->ctxt,
      loc,
      gcc_jit_lvalue_as_rvalue (state->stack),
      gcc_jit_lvalue_as_rvalue (state->stack_depth)),
    rvalue);

  /* "stack_depth++;".  */
  gcc_jit_block_add_assignment_op (
    block,
    loc,
    state->stack_depth,
    GCC_JIT_BINARY_OP_PLUS,
    state->const_one);
@}

static void
add_pop (compilation_state *state,
	 gcc_jit_block *block,
	 gcc_jit_lvalue *lvalue,
	 gcc_jit_location *loc)
@{
  /* "--stack_depth;".  */
  gcc_jit_block_add_assignment_op (
    block,
    loc,
    state->stack_depth,
    GCC_JIT_BINARY_OP_MINUS,
    state->const_one);

  /* "LVALUE = stack[stack_depth];".  */
  gcc_jit_block_add_assignment (
    block,
    loc,
    lvalue,
    /* stack[stack_depth] */
    gcc_jit_lvalue_as_rvalue (
      gcc_jit_context_new_array_access (
	state->ctxt,
	loc,
	gcc_jit_lvalue_as_rvalue (state->stack),
	gcc_jit_lvalue_as_rvalue (state->stack_depth))));
@}


@end example

@noindent
@end quotation

We will support single-stepping through the generated code in the
debugger, so we need to create @pxref{3b,,gcc_jit_location} instances, one
per operation in the source code.  These will reference the lines of
e.g. @code{factorial.toy}.

@quotation

@example
  for (pc = 0; pc < fn->fn_num_ops; pc++)
    @{
      toyvm_op *op = &fn->fn_ops[pc];

      state.op_locs[pc] = gcc_jit_context_new_location (state.ctxt,
							fn->fn_filename,
							op->op_linenum,
							0); /* column */
    @}


@end example

@noindent
@end quotation

Let's create the function itself.  As usual, we create its parameter
first, then use the parameter to create the function:

@quotation

@example
  state.param_arg =
    gcc_jit_context_new_param (state.ctxt, state.op_locs[0],
			       state.int_type, "arg");
  state.fn =
    gcc_jit_context_new_function (state.ctxt,
				  state.op_locs[0],
				  GCC_JIT_FUNCTION_EXPORTED,
				  state.int_type,
				  funcname,
				  1, &state.param_arg, 0);


@end example

@noindent
@end quotation

We create the locals within the function.

@quotation

@example
  state.stack =
    gcc_jit_function_new_local (state.fn, NULL,
				state.stack_type, "stack");
  state.stack_depth =
    gcc_jit_function_new_local (state.fn, NULL,
				state.int_type, "stack_depth");
  state.x =
    gcc_jit_function_new_local (state.fn, NULL,
				state.int_type, "x");
  state.y =
    gcc_jit_function_new_local (state.fn, NULL,
				state.int_type, "y");


@end example

@noindent
@end quotation

@node Populating the function,Verifying the control flow graph,Setting things up,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 populating-the-function}@anchor{3c}
@subsection Populating the function


There's some one-time initialization, and the API treats the first block
you create as the entrypoint of the function, so we need to create that
block first:

@quotation

@example
  state.initial_block = gcc_jit_function_new_block (state.fn, "initial");


@end example

@noindent
@end quotation

We can now create blocks for each of the operations.  Most of these will
be consolidated into larger blocks when the optimizer runs.

@quotation

@example
  for (pc = 0; pc < fn->fn_num_ops; pc++)
    @{
      char buf[16];
      sprintf (buf, "instr%i", pc);
      state.op_blocks[pc] = gcc_jit_function_new_block (state.fn, buf);
    @}


@end example

@noindent
@end quotation

Now that we have a block it can jump to when it's done, we can populate
the initial block:

@quotation

@example

  /* "stack_depth = 0;".  */
  gcc_jit_block_add_assignment (
    state.initial_block,
    state.op_locs[0],
    state.stack_depth,
    gcc_jit_context_zero (state.ctxt, state.int_type));

  /* "PUSH (arg);".  */
  add_push (&state,
	    state.initial_block,
	    gcc_jit_param_as_rvalue (state.param_arg),
	    state.op_locs[0]);

  /* ...and jump to insn 0.  */
  gcc_jit_block_end_with_jump (state.initial_block,
			       state.op_locs[0],
			       state.op_blocks[0]);


@end example

@noindent
@end quotation

We can now populate the blocks for the individual operations.  We loop
through them, adding instructions to their blocks:

@quotation

@example
  for (pc = 0; pc < fn->fn_num_ops; pc++)
    @{
      gcc_jit_location *loc = state.op_locs[pc];

      gcc_jit_block *block = state.op_blocks[pc];
      gcc_jit_block *next_block = (pc < fn->fn_num_ops
				   ? state.op_blocks[pc + 1]
				   : NULL);

      toyvm_op *op;
      op = &fn->fn_ops[pc];


@end example

@noindent
@end quotation

We're going to have another big @code{switch} statement for implementing
the opcodes, this time for compiling them, rather than interpreting
them.  It's helpful to have macros for implementing push and pop, so that
we can make the @code{switch} statement that's coming up look as much as
possible like the one above within the interpreter:

@example

#define X_EQUALS_POP()\
      add_pop (&state, block, state.x, loc)
#define Y_EQUALS_POP()\
      add_pop (&state, block, state.y, loc)
#define PUSH_RVALUE(RVALUE)\
      add_push (&state, block, (RVALUE), loc)
#define PUSH_X()\
      PUSH_RVALUE (gcc_jit_lvalue_as_rvalue (state.x))
#define PUSH_Y() \
      PUSH_RVALUE (gcc_jit_lvalue_as_rvalue (state.y))


@end example

@noindent

@cartouche
@quotation Note 
A particularly clever implementation would have an @emph{identical}
@code{switch} statement shared by the interpreter and the compiler, with
some preprocessor "magic".  We're not doing that here, for the sake
of simplicity.
@end quotation
@end cartouche

When I first implemented this compiler, I accidentally missed an edit
when copying and pasting the @code{Y_EQUALS_POP} macro, so that popping the
stack into @code{y} instead erroneously assigned it to @code{x}, leaving @code{y}
uninitialized.

To track this kind of thing down, we can use
@pxref{3d,,gcc_jit_block_add_comment()} to add descriptive comments
to the internal representation.  This is invaluable when looking through
the generated IR for, say @code{factorial}:

@quotation

@example

      gcc_jit_block_add_comment (block, loc, opcode_names[op->op_opcode]);


@end example

@noindent
@end quotation

We can now write the big @code{switch} statement that implements the
individual opcodes, populating the relevant block with statements:

@quotation

@example

      switch (op->op_opcode)
	@{
	case DUP:
	  X_EQUALS_POP ();
	  PUSH_X ();
	  PUSH_X ();
	  break;

	case ROT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_Y ();
	  PUSH_X ();
	  break;

	case BINARY_ADD:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
	   gcc_jit_context_new_binary_op (
	     state.ctxt,
	     loc,
	     GCC_JIT_BINARY_OP_PLUS,
	     state.int_type,
	     gcc_jit_lvalue_as_rvalue (state.x),
	     gcc_jit_lvalue_as_rvalue (state.y)));
	  break;

	case BINARY_SUBTRACT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
	   gcc_jit_context_new_binary_op (
	     state.ctxt,
	     loc,
	     GCC_JIT_BINARY_OP_MINUS,
	     state.int_type,
	     gcc_jit_lvalue_as_rvalue (state.x),
	     gcc_jit_lvalue_as_rvalue (state.y)));
	  break;

	case BINARY_MULT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
	   gcc_jit_context_new_binary_op (
	     state.ctxt,
	     loc,
	     GCC_JIT_BINARY_OP_MULT,
	     state.int_type,
	     gcc_jit_lvalue_as_rvalue (state.x),
	     gcc_jit_lvalue_as_rvalue (state.y)));
	  break;

	case BINARY_COMPARE_LT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
	     /* cast of bool to int */
	     gcc_jit_context_new_cast (
	       state.ctxt,
	       loc,
	       /* (x < y) as a bool */
	       gcc_jit_context_new_comparison (
		 state.ctxt,
		 loc,
		 GCC_JIT_COMPARISON_LT,
		 gcc_jit_lvalue_as_rvalue (state.x),
		 gcc_jit_lvalue_as_rvalue (state.y)),
	       state.int_type));
	  break;

	case RECURSE:
	  @{
	    X_EQUALS_POP ();
	    gcc_jit_rvalue *arg = gcc_jit_lvalue_as_rvalue (state.x);
	    PUSH_RVALUE (
	      gcc_jit_context_new_call (
		state.ctxt,
		loc,
		state.fn,
		1, &arg));
	    break;
	  @}

	case RETURN:
	  X_EQUALS_POP ();
	  gcc_jit_block_end_with_return (
	    block,
	    loc,
	    gcc_jit_lvalue_as_rvalue (state.x));
	  break;

	  /* Ops taking an operand.  */
	case PUSH_CONST:
	  PUSH_RVALUE (
	    gcc_jit_context_new_rvalue_from_int (
	      state.ctxt,
	      state.int_type,
	      op->op_operand));
	  break;

	case JUMP_ABS_IF_TRUE:
	  X_EQUALS_POP ();
	  gcc_jit_block_end_with_conditional (
	    block,
	    loc,
	    /* "(bool)x".  */
	    gcc_jit_context_new_cast (
	      state.ctxt,
	      loc,
	      gcc_jit_lvalue_as_rvalue (state.x),
	      state.bool_type),
	    state.op_blocks[op->op_operand], /* on_true */
	    next_block); /* on_false */
	  break;

	default:
	  assert(0);
	@} /* end of switch on opcode */


@end example

@noindent
@end quotation

Every block must be terminated, via a call to one of the
@code{gcc_jit_block_end_with_} entrypoints.  This has been done for two
of the opcodes, but we need to do it for the other ones, by jumping
to the next block.

@quotation

@example
      if (op->op_opcode != JUMP_ABS_IF_TRUE
	  && op->op_opcode != RETURN)
	gcc_jit_block_end_with_jump (
	  block,
	  loc,
	  next_block);


@end example

@noindent
@end quotation

This is analogous to simply incrementing the program counter.

@node Verifying the control flow graph,Compiling the context,Populating the function,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 verifying-the-control-flow-graph}@anchor{3e}
@subsection Verifying the control flow graph


Having finished looping over the blocks, the context is complete.

As before, we can verify that the control flow and statements are sane by
using @pxref{33,,gcc_jit_function_dump_to_dot()}:

@example
gcc_jit_function_dump_to_dot (state.fn, "/tmp/factorial.dot");
@end example

@noindent

and viewing the result.  Note how the label names, comments, and
variable names show up in the dump, to make it easier to spot
errors in our compiler.

@quotation


@float Figure

@image{factorial1,,,image of a control flow graph,png}

@end float

@end quotation

@node Compiling the context,Single-stepping through the generated code,Verifying the control flow graph,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 compiling-the-context}@anchor{3f}
@subsection Compiling the context


Having finished looping over the blocks and populating them with
statements, the context is complete.

We can now compile it, and extract machine code from the result:

@quotation

@example
  gcc_jit_result *jit_result = gcc_jit_context_compile (state.ctxt);
  gcc_jit_context_release (state.ctxt);

  toyvm_compiled_function *toyvm_result =
    (toyvm_compiled_function *)calloc (1, sizeof (toyvm_compiled_function));
  if (!toyvm_result)
    @{
      fprintf (stderr, "out of memory allocating toyvm_compiled_function\n");
      gcc_jit_result_release (jit_result);
      return NULL;
    @}

  toyvm_result->cf_jit_result = jit_result;
  toyvm_result->cf_code =
    (toyvm_compiled_code)gcc_jit_result_get_code (jit_result,
						  funcname);

  free (funcname);

  return toyvm_result;
@}

char test[1024];

#define CHECK_NON_NULL(PTR) \
  do @{                                       \
    if ((PTR) != NULL)                       \
      @{                                      \
	pass ("%s: %s is non-null", test, #PTR); \
      @}                                      \
    else                                     \
      @{                                      \
	fail ("%s: %s is NULL", test, #PTR); \
	abort ();                            \
    @}                                        \
  @} while (0)

#define CHECK_VALUE(ACTUAL, EXPECTED) \
  do @{                                       \
    if ((ACTUAL) == (EXPECTED))              \
      @{                                      \
	pass ("%s: actual: %s == expected: %s", test, #ACTUAL, #EXPECTED); \
      @}                                      \
    else                                     \
      @{                                        \
	fail ("%s: actual: %s != expected: %s", test, #ACTUAL, #EXPECTED); \
	fprintf (stderr, "incorrect value\n"); \
	abort ();                              \
    @}                                        \
  @} while (0)

static void
test_script (const char *scripts_dir, const char *script_name, int input,
	     int expected_result)
@{
  char *script_path;
  toyvm_function *fn;
  int interpreted_result;
  toyvm_compiled_function *compiled_fn;
  toyvm_compiled_code code;
  int compiled_result;

  snprintf (test, sizeof (test), "toyvm.c: %s", script_name);

  script_path = (char *)malloc (strlen (scripts_dir)
				+ strlen (script_name) + 1);
  CHECK_NON_NULL (script_path);
  sprintf (script_path, "%s%s", scripts_dir, script_name);

  fn = toyvm_function_parse (script_path, script_name);
  CHECK_NON_NULL (fn);

  interpreted_result = toyvm_function_interpret (fn, input, NULL);
  CHECK_VALUE (interpreted_result, expected_result);

  compiled_fn = toyvm_function_compile (fn);
  CHECK_NON_NULL (compiled_fn);

  code = (toyvm_compiled_code)compiled_fn->cf_code;
  CHECK_NON_NULL (code);

  compiled_result = code (input);
  CHECK_VALUE (compiled_result, expected_result);

  gcc_jit_result_release (compiled_fn->cf_jit_result);
  free (compiled_fn);
  free (fn);
  free (script_path);
@}

#define PATH_TO_SCRIPTS  ("/jit/docs/examples/tut04-toyvm/")

static void
test_suite (void)
@{
  const char *srcdir;
  char *scripts_dir;

  snprintf (test, sizeof (test), "toyvm.c");

  /* We need to locate the test scripts.
     Rely on "srcdir" being set in the environment.  */

  srcdir = getenv ("srcdir");
  CHECK_NON_NULL (srcdir);

  scripts_dir = (char *)malloc (strlen (srcdir) + strlen(PATH_TO_SCRIPTS)
				+ 1);
  CHECK_NON_NULL (scripts_dir);
  sprintf (scripts_dir, "%s%s", srcdir, PATH_TO_SCRIPTS);

  test_script (scripts_dir, "factorial.toy", 10, 3628800);
  test_script (scripts_dir, "fibonacci.toy", 10, 55);

  free (scripts_dir);
@}

int
main (int argc, char **argv)
@{
  const char *filename = NULL;
  toyvm_function *fn = NULL;

  /* If called with no args, assume we're being run by the test suite.  */
  if (argc < 3)
    @{
      test_suite ();
      return 0;
    @}

  if (argc != 3)
    @{
      fprintf (stdout,
	"%s FILENAME INPUT: Parse and run a .toy file\n",
	argv[0]);
      exit (1);
    @}

  filename = argv[1];
  fn = toyvm_function_parse (filename, filename);
  if (!fn)
    exit (1);

  if (0)
    toyvm_function_disassemble (fn, stdout);

  printf ("interpreter result: %d\n",
	  toyvm_function_interpret (fn, atoi (argv[2]), NULL));

  /* JIT-compilation.  */
  toyvm_compiled_function *compiled_fn
    = toyvm_function_compile (fn);

  toyvm_compiled_code code = compiled_fn->cf_code;
  printf ("compiler result: %d\n",
	  code (atoi (argv[2])));

  gcc_jit_result_release (compiled_fn->cf_jit_result);
  free (compiled_fn);

 return 0;
@}

@end example

@noindent
@end quotation

We can now run the result:

@quotation

@example
  toyvm_compiled_function *compiled_fn
    = toyvm_function_compile (fn);

  toyvm_compiled_code code = compiled_fn->cf_code;
  printf ("compiler result: %d\n",
	  code (atoi (argv[2])));

  gcc_jit_result_release (compiled_fn->cf_jit_result);
  free (compiled_fn);


@end example

@noindent
@end quotation

@node Single-stepping through the generated code,Examining the generated code,Compiling the context,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 single-stepping-through-the-generated-code}@anchor{40}
@subsection Single-stepping through the generated code


It's possible to debug the generated code.  To do this we need to both:

@quotation


@itemize *

@item 
Set up source code locations for our statements, so that we can
meaningfully step through the code.  We did this above by
calling @pxref{41,,gcc_jit_context_new_location()} and using the
results.

@item 
Enable the generation of debugging information, by setting
@pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} on the
@pxref{8,,gcc_jit_context} via
@pxref{1b,,gcc_jit_context_set_bool_option()}:

@example
gcc_jit_context_set_bool_option (
  ctxt,
  GCC_JIT_BOOL_OPTION_DEBUGINFO,
  1);
@end example

@noindent
@end itemize
@end quotation

Having done this, we can put a breakpoint on the generated function:

@example
$ gdb --args ./toyvm factorial.toy 10
(gdb) break factorial
Function "factorial" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (factorial) pending.
(gdb) run
Breakpoint 1, factorial (arg=10) at factorial.toy:14
14    DUP
@end example

@noindent

We've set up location information, which references @code{factorial.toy}.
This allows us to use e.g. @code{list} to see where we are in the script:

@example
(gdb) list
9
10    # Initial state:
11    # stack: [arg]
12
13    # 0:
14    DUP
15    # stack: [arg, arg]
16
17    # 1:
18    PUSH_CONST 2
@end example

@noindent

and to step through the function, examining the data:

@example
(gdb) n
18    PUSH_CONST 2
(gdb) n
22    BINARY_COMPARE_LT
(gdb) print stack
$5 = @{10, 10, 2, 0, -7152, 32767, 0, 0@}
(gdb) print stack_depth
$6 = 3
@end example

@noindent

You'll see that the parts of the @code{stack} array that haven't been
touched yet are uninitialized.

@cartouche
@quotation Note 
Turning on optimizations may lead to unpredictable results when
stepping through the generated code: the execution may appear to
"jump around" the source code.  This is analogous to turning up the
optimization level in a regular compiler.
@end quotation
@end cartouche

@node Examining the generated code,Putting it all together,Single-stepping through the generated code,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 examining-the-generated-code}@anchor{43}
@subsection Examining the generated code


How good is the optimized code?

We can turn up optimizations, by calling
@pxref{1e,,gcc_jit_context_set_int_option()} with
@pxref{1f,,GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL}:

@example
gcc_jit_context_set_int_option (
  ctxt,
  GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL,
  3);
@end example

@noindent

One of GCC's internal representations is called "gimple".  A dump of the
initial gimple representation of the code can be seen by setting:

@example
gcc_jit_context_set_bool_option (ctxt,
                                 GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE,
                                 1);
@end example

@noindent

With optimization on and source locations displayed, this gives:

@c We'll use "c" for gimple dumps

@example
factorial (signed int arg)
@{
  <unnamed type> D.80;
  signed int D.81;
  signed int D.82;
  signed int D.83;
  signed int D.84;
  signed int D.85;
  signed int y;
  signed int x;
  signed int stack_depth;
  signed int stack[8];

  try
    @{
      initial:
      stack_depth = 0;
      stack[stack_depth] = arg;
      stack_depth = stack_depth + 1;
      goto instr0;
      instr0:
      /* DUP */:
      stack_depth = stack_depth + -1;
      x = stack[stack_depth];
      stack[stack_depth] = x;
      stack_depth = stack_depth + 1;
      stack[stack_depth] = x;
      stack_depth = stack_depth + 1;
      goto instr1;
      instr1:
      /* PUSH_CONST */:
      stack[stack_depth] = 2;
      stack_depth = stack_depth + 1;
      goto instr2;

      /* etc */
@end example

@noindent

You can see the generated machine code in assembly form via:

@example
gcc_jit_context_set_bool_option (
  ctxt,
  GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
  1);
result = gcc_jit_context_compile (ctxt);
@end example

@noindent

which shows that (on this x86_64 box) the compiler has unrolled the loop
and is using MMX instructions to perform several multiplications
simultaneously:

@example
        .file   "fake.c"
        .text
.Ltext0:
        .p2align 4,,15
        .globl  factorial
        .type   factorial, @@function
factorial:
.LFB0:
        .file 1 "factorial.toy"
        .loc 1 14 0
        .cfi_startproc
.LVL0:
.L2:
        .loc 1 26 0
        cmpl    $1, %edi
        jle     .L13
        leal    -1(%rdi), %edx
        movl    %edx, %ecx
        shrl    $2, %ecx
        leal    0(,%rcx,4), %esi
        testl   %esi, %esi
        je      .L14
        cmpl    $9, %edx
        jbe     .L14
        leal    -2(%rdi), %eax
        movl    %eax, -16(%rsp)
        leal    -3(%rdi), %eax
        movd    -16(%rsp), %xmm0
        movl    %edi, -16(%rsp)
        movl    %eax, -12(%rsp)
        movd    -16(%rsp), %xmm1
        xorl    %eax, %eax
        movl    %edx, -16(%rsp)
        movd    -12(%rsp), %xmm4
        movd    -16(%rsp), %xmm6
        punpckldq       %xmm4, %xmm0
        movdqa  .LC1(%rip), %xmm4
        punpckldq       %xmm6, %xmm1
        punpcklqdq      %xmm0, %xmm1
        movdqa  .LC0(%rip), %xmm0
        jmp     .L5
        # etc - edited for brevity
@end example

@noindent

This is clearly overkill for a function that will likely overflow the
@code{int} type before the vectorization is worthwhile - but then again, this
is a toy example.

Turning down the optimization level to 2:

@example
gcc_jit_context_set_int_option (
  ctxt,
  GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL,
  3);
@end example

@noindent

yields this code, which is simple enough to quote in its entirety:

@example
        .file   "fake.c"
        .text
        .p2align 4,,15
        .globl  factorial
        .type   factorial, @@function
factorial:
.LFB0:
        .cfi_startproc
.L2:
        cmpl    $1, %edi
        jle     .L8
        movl    $1, %edx
        jmp     .L4
        .p2align 4,,10
        .p2align 3
.L6:
        movl    %eax, %edi
.L4:
.L5:
        leal    -1(%rdi), %eax
        imull   %edi, %edx
        cmpl    $1, %eax
        jne     .L6
.L3:
.L7:
        imull   %edx, %eax
        ret
.L8:
        movl    %edi, %eax
        movl    $1, %edx
        jmp     .L7
        .cfi_endproc
.LFE0:
        .size   factorial, .-factorial
        .ident  "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.2-%@{gcc_release@})"
        .section        .note.GNU-stack,"",@@progbits
@end example

@noindent

Note that the stack pushing and popping have been eliminated, as has the
recursive call (in favor of an iteration).

@node Putting it all together,Behind the curtain How does our code get optimized?,Examining the generated code,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 putting-it-all-together}@anchor{44}
@subsection Putting it all together


The complete example can be seen in the source tree at
@code{gcc/jit/docs/examples/tut04-toyvm/toyvm.c}

along with a Makefile and a couple of sample .toy scripts:

@example
$ ls -al
drwxrwxr-x. 2 david david   4096 Sep 19 17:46 .
drwxrwxr-x. 3 david david   4096 Sep 19 15:26 ..
-rw-rw-r--. 1 david david    615 Sep 19 12:43 factorial.toy
-rw-rw-r--. 1 david david    834 Sep 19 13:08 fibonacci.toy
-rw-rw-r--. 1 david david    238 Sep 19 14:22 Makefile
-rw-rw-r--. 1 david david  16457 Sep 19 17:07 toyvm.c

$ make toyvm
g++ -Wall -g -o toyvm toyvm.c -lgccjit

$ ./toyvm factorial.toy 10
interpreter result: 3628800
compiler result: 3628800

$ ./toyvm fibonacci.toy 10
interpreter result: 55
compiler result: 55
@end example

@noindent

@node Behind the curtain How does our code get optimized?,,Putting it all together,Tutorial part 4 Adding JIT-compilation to a toy interpreter
@anchor{intro/tutorial04 behind-the-curtain-how-does-our-code-get-optimized}@anchor{45}
@subsection Behind the curtain: How does our code get optimized?


Our example is done, but you may be wondering about exactly how the
compiler turned what we gave it into the machine code seen above.

We can examine what the compiler is doing in detail by setting:

@example
gcc_jit_context_set_bool_option (state.ctxt,
                                 GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING,
                                 1);
gcc_jit_context_set_bool_option (state.ctxt,
                                 GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES,
                                 1);
@end example

@noindent

This will dump detailed information about the compiler's state to a
directory under @code{/tmp}, and keep it from being cleaned up.

The precise names and their formats of these files is subject to change.
Higher optimization levels lead to more files.
Here's what I saw (edited for brevity; there were almost 200 files):

@example
intermediate files written to /tmp/libgccjit-KPQbGw
$ ls /tmp/libgccjit-KPQbGw/
fake.c.000i.cgraph
fake.c.000i.type-inheritance
fake.c.004t.gimple
fake.c.007t.omplower
fake.c.008t.lower
fake.c.011t.eh
fake.c.012t.cfg
fake.c.014i.visibility
fake.c.015i.early_local_cleanups
fake.c.016t.ssa
# etc
@end example

@noindent

The gimple code is converted into Static Single Assignment form,
with annotations for use when generating the debuginfo:

@example
$ less /tmp/libgccjit-KPQbGw/fake.c.016t.ssa
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;
  signed int _56;

initial:
  stack_depth_3 = 0;
  # DEBUG stack_depth => stack_depth_3
  stack[stack_depth_3] = arg_5(D);
  stack_depth_7 = stack_depth_3 + 1;
  # DEBUG stack_depth => stack_depth_7
  # DEBUG instr0 => NULL
  # DEBUG /* DUP */ => NULL
  stack_depth_8 = stack_depth_7 + -1;
  # DEBUG stack_depth => stack_depth_8
  x_9 = stack[stack_depth_8];
  # DEBUG x => x_9
  stack[stack_depth_8] = x_9;
  stack_depth_11 = stack_depth_8 + 1;
  # DEBUG stack_depth => stack_depth_11
  stack[stack_depth_11] = x_9;
  stack_depth_13 = stack_depth_11 + 1;
  # DEBUG stack_depth => stack_depth_13
  # DEBUG instr1 => NULL
  # DEBUG /* PUSH_CONST */ => NULL
  stack[stack_depth_13] = 2;

  /* etc; edited for brevity */
@end example

@noindent

We can perhaps better see the code by turning off
@pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} to suppress all those @code{DEBUG}
statements, giving:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.016t.ssa
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;
  signed int _56;

initial:
  stack_depth_3 = 0;
  stack[stack_depth_3] = arg_5(D);
  stack_depth_7 = stack_depth_3 + 1;
  stack_depth_8 = stack_depth_7 + -1;
  x_9 = stack[stack_depth_8];
  stack[stack_depth_8] = x_9;
  stack_depth_11 = stack_depth_8 + 1;
  stack[stack_depth_11] = x_9;
  stack_depth_13 = stack_depth_11 + 1;
  stack[stack_depth_13] = 2;
  stack_depth_15 = stack_depth_13 + 1;
  stack_depth_16 = stack_depth_15 + -1;
  y_17 = stack[stack_depth_16];
  stack_depth_18 = stack_depth_16 + -1;
  x_19 = stack[stack_depth_18];
  _20 = x_19 < y_17;
  _21 = (signed int) _20;
  stack[stack_depth_18] = _21;
  stack_depth_23 = stack_depth_18 + 1;
  stack_depth_24 = stack_depth_23 + -1;
  x_25 = stack[stack_depth_24];
  if (x_25 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  stack_depth_26 = stack_depth_24 + -1;
  x_27 = stack[stack_depth_26];
  stack[stack_depth_26] = x_27;
  stack_depth_29 = stack_depth_26 + 1;
  stack[stack_depth_29] = x_27;
  stack_depth_31 = stack_depth_29 + 1;
  stack[stack_depth_31] = 1;
  stack_depth_33 = stack_depth_31 + 1;
  stack_depth_34 = stack_depth_33 + -1;
  y_35 = stack[stack_depth_34];
  stack_depth_36 = stack_depth_34 + -1;
  x_37 = stack[stack_depth_36];
  _38 = x_37 - y_35;
  stack[stack_depth_36] = _38;
  stack_depth_40 = stack_depth_36 + 1;
  stack_depth_41 = stack_depth_40 + -1;
  x_42 = stack[stack_depth_41];
  _44 = factorial (x_42);
  stack[stack_depth_41] = _44;
  stack_depth_46 = stack_depth_41 + 1;
  stack_depth_47 = stack_depth_46 + -1;
  y_48 = stack[stack_depth_47];
  stack_depth_49 = stack_depth_47 + -1;
  x_50 = stack[stack_depth_49];
  _51 = x_50 * y_48;
  stack[stack_depth_49] = _51;
  stack_depth_53 = stack_depth_49 + 1;

  # stack_depth_1 = PHI <stack_depth_24(2), stack_depth_53(3)>
instr9:
/* RETURN */:
  stack_depth_54 = stack_depth_1 + -1;
  x_55 = stack[stack_depth_54];
  _56 = x_55;
  stack =@{v@} @{CLOBBER@};
  return _56;

@}
@end example

@noindent

Note in the above how all the @pxref{28,,gcc_jit_block} instances we
created have been consolidated into just 3 blocks in GCC's internal
representation: @code{initial}, @code{instr4} and @code{instr9}.

@menu
* Optimizing away stack manipulation:: 
* Elimination of tail recursion:: 

@end menu

@node Optimizing away stack manipulation,Elimination of tail recursion,,Behind the curtain How does our code get optimized?
@anchor{intro/tutorial04 optimizing-away-stack-manipulation}@anchor{46}
@subsubsection Optimizing away stack manipulation


Recall our simple implementation of stack operations.  Let's examine
how the stack operations are optimized away.

After a pass of constant-propagation, the depth of the stack at each
opcode can be determined at compile-time:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.021t.ccp1
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;

initial:
  stack[0] = arg_5(D);
  x_9 = stack[0];
  stack[0] = x_9;
  stack[1] = x_9;
  stack[2] = 2;
  y_17 = stack[2];
  x_19 = stack[1];
  _20 = x_19 < y_17;
  _21 = (signed int) _20;
  stack[1] = _21;
  x_25 = stack[1];
  if (x_25 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  x_27 = stack[0];
  stack[0] = x_27;
  stack[1] = x_27;
  stack[2] = 1;
  y_35 = stack[2];
  x_37 = stack[1];
  _38 = x_37 - y_35;
  stack[1] = _38;
  x_42 = stack[1];
  _44 = factorial (x_42);
  stack[1] = _44;
  y_48 = stack[1];
  x_50 = stack[0];
  _51 = x_50 * y_48;
  stack[0] = _51;

instr9:
/* RETURN */:
  x_55 = stack[0];
  x_56 = x_55;
  stack =@{v@} @{CLOBBER@};
  return x_56;

@}
@end example

@noindent

Note how, in the above, all those @code{stack_depth} values are now just
constants: we're accessing specific stack locations at each opcode.

The "esra" pass ("Early Scalar Replacement of Aggregates") breaks
out our "stack" array into individual elements:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.024t.esra
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

Created a replacement for stack offset: 0, size: 32: stack$0
Created a replacement for stack offset: 32, size: 32: stack$1
Created a replacement for stack offset: 64, size: 32: stack$2

Symbols to be put in SSA form
@{ D.89 D.90 D.91 @}
Incremental SSA update started at block: 0
Number of blocks in CFG: 5
Number of blocks to update: 4 ( 80%)


factorial (signed int arg)
@{
  signed int stack$2;
  signed int stack$1;
  signed int stack$0;
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;

initial:
  stack$0_45 = arg_5(D);
  x_9 = stack$0_45;
  stack$0_39 = x_9;
  stack$1_32 = x_9;
  stack$2_30 = 2;
  y_17 = stack$2_30;
  x_19 = stack$1_32;
  _20 = x_19 < y_17;
  _21 = (signed int) _20;
  stack$1_28 = _21;
  x_25 = stack$1_28;
  if (x_25 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  x_27 = stack$0_39;
  stack$0_22 = x_27;
  stack$1_14 = x_27;
  stack$2_12 = 1;
  y_35 = stack$2_12;
  x_37 = stack$1_14;
  _38 = x_37 - y_35;
  stack$1_10 = _38;
  x_42 = stack$1_10;
  _44 = factorial (x_42);
  stack$1_6 = _44;
  y_48 = stack$1_6;
  x_50 = stack$0_22;
  _51 = x_50 * y_48;
  stack$0_1 = _51;

  # stack$0_52 = PHI <stack$0_39(2), stack$0_1(3)>
instr9:
/* RETURN */:
  x_55 = stack$0_52;
  x_56 = x_55;
  stack =@{v@} @{CLOBBER@};
  return x_56;

@}
@end example

@noindent

Hence at this point, all those pushes and pops of the stack are now
simply assignments to specific temporary variables.

After some copy propagation, the stack manipulation has been completely
optimized away:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.026t.copyprop1
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack$2;
  signed int stack$1;
  signed int stack$0;
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;

initial:
  stack$0_39 = arg_5(D);
  _20 = arg_5(D) <= 1;
  _21 = (signed int) _20;
  if (_21 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  _38 = arg_5(D) + -1;
  _44 = factorial (_38);
  _51 = arg_5(D) * _44;
  stack$0_1 = _51;

  # stack$0_52 = PHI <arg_5(D)(2), _51(3)>
instr9:
/* RETURN */:
  stack =@{v@} @{CLOBBER@};
  return stack$0_52;

@}
@end example

@noindent

Later on, another pass finally eliminated @code{stack_depth} local and the
unused parts of the @cite{stack`} array altogether:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.036t.release_ssa
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

Released 44 names, 314.29%, removed 44 holes
factorial (signed int arg)
@{
  signed int stack$0;
  signed int mult_acc_1;
  <unnamed type> _5;
  signed int _6;
  signed int _7;
  signed int mul_tmp_10;
  signed int mult_acc_11;
  signed int mult_acc_13;

  # arg_9 = PHI <arg_8(D)(0)>
  # mult_acc_13 = PHI <1(0)>
initial:

  <bb 5>:
  # arg_4 = PHI <arg_9(2), _7(3)>
  # mult_acc_1 = PHI <mult_acc_13(2), mult_acc_11(3)>
  _5 = arg_4 <= 1;
  _6 = (signed int) _5;
  if (_6 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  _7 = arg_4 + -1;
  mult_acc_11 = mult_acc_1 * arg_4;
  goto <bb 5>;

  # stack$0_12 = PHI <arg_4(5)>
instr9:
/* RETURN */:
  mul_tmp_10 = mult_acc_1 * stack$0_12;
  return mul_tmp_10;

@}
@end example

@noindent

@node Elimination of tail recursion,,Optimizing away stack manipulation,Behind the curtain How does our code get optimized?
@anchor{intro/tutorial04 elimination-of-tail-recursion}@anchor{47}
@subsubsection Elimination of tail recursion


Another significant optimization is the detection that the call to
@code{factorial} is tail recursion, which can be eliminated in favor of
an iteration:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.030t.tailr1
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)


Symbols to be put in SSA form
@{ D.88 @}
Incremental SSA update started at block: 0
Number of blocks in CFG: 5
Number of blocks to update: 4 ( 80%)


factorial (signed int arg)
@{
  signed int stack$2;
  signed int stack$1;
  signed int stack$0;
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  signed int mult_acc_1;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int mul_tmp_44;
  signed int mult_acc_51;

  # arg_5 = PHI <arg_39(D)(0), _38(3)>
  # mult_acc_1 = PHI <1(0), mult_acc_51(3)>
initial:
  _20 = arg_5 <= 1;
  _21 = (signed int) _20;
  if (_21 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  _38 = arg_5 + -1;
  mult_acc_51 = mult_acc_1 * arg_5;
  goto <bb 2> (initial);

  # stack$0_52 = PHI <arg_5(2)>
instr9:
/* RETURN */:
  stack =@{v@} @{CLOBBER@};
  mul_tmp_44 = mult_acc_1 * stack$0_52;
  return mul_tmp_44;

@}
@end example

@noindent

@c Copyright (C) 2015-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 5 Implementing an Ahead-of-Time compiler,,Tutorial part 4 Adding JIT-compilation to a toy interpreter,Tutorial
@anchor{intro/tutorial05 doc}@anchor{48}@anchor{intro/tutorial05 tutorial-part-5-implementing-an-ahead-of-time-compiler}@anchor{49}
@section Tutorial part 5: Implementing an Ahead-of-Time compiler


If you have a pre-existing language frontend that's compatible with
libgccjit's license, it's possible to hook it up to libgccjit as a
backend.  In the previous example we showed
how to do that for in-memory JIT-compilation, but libgccjit can also
compile code directly to a file, allowing you to implement a more
traditional ahead-of-time compiler ("JIT" is something of a misnomer
for this use-case).

The essential difference is to compile the context using
@pxref{4a,,gcc_jit_context_compile_to_file()} rather than
@pxref{15,,gcc_jit_context_compile()}.

@menu
* The "brainf" language:: 
* Converting a brainf script to libgccjit IR:: 
* Compiling a context to a file:: 
* Other forms of ahead-of-time-compilation:: 

@end menu

@node The "brainf" language,Converting a brainf script to libgccjit IR,,Tutorial part 5 Implementing an Ahead-of-Time compiler
@anchor{intro/tutorial05 the-brainf-language}@anchor{4b}
@subsection The "brainf" language


In this example we use libgccjit to construct an ahead-of-time compiler
for an esoteric programming language that we shall refer to as "brainf".

brainf scripts operate on an array of bytes, with a notional data pointer
within the array.

brainf is hard for humans to read, but it's trivial to write a parser for
it, as there is no lexing; just a stream of bytes.  The operations are:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@headitem

Character

@tab

Meaning

@item

@code{>}

@tab

@code{idx += 1}

@item

@code{<}

@tab

@code{idx -= 1}

@item

@code{+}

@tab

@code{data[idx] += 1}

@item

@code{-}

@tab

@code{data[idx] -= 1}

@item

@code{.}

@tab

@code{output (data[idx])}

@item

@code{,}

@tab

@code{data[idx] = input ()}

@item

@code{[}

@tab

loop until @code{data[idx] == 0}

@item

@code{]}

@tab

end of loop

@item

Anything else

@tab

ignored

@end multitable


Unlike the previous example, we'll implement an ahead-of-time compiler,
which reads @code{.bf} scripts and outputs executables (though it would
be trivial to have it run them JIT-compiled in-process).

Here's what a simple @code{.bf} script looks like:

@quotation

@example
[
  Emit the uppercase alphabet
]

cell 0 = 26
++++++++++++++++++++++++++

cell 1 = 65
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<

while cell#0 != 0
[
 >
 .      emit cell#1
 +      increment cell@@1
 <-     decrement cell@@0
]

@end example

@noindent
@end quotation

@cartouche
@quotation Note 
This example makes use of whitespace and comments for legibility, but
could have been written as:

@example
++++++++++++++++++++++++++
>+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<
[>.+<-]
@end example

@noindent

It's not a particularly useful language, except for providing
compiler-writers with a test case that's easy to parse.  The point
is that you can use @pxref{4a,,gcc_jit_context_compile_to_file()}
to use libgccjit as a backend for a pre-existing language frontend
(provided that the pre-existing frontend is compatible with libgccjit's
license).
@end quotation
@end cartouche

@node Converting a brainf script to libgccjit IR,Compiling a context to a file,The "brainf" language,Tutorial part 5 Implementing an Ahead-of-Time compiler
@anchor{intro/tutorial05 converting-a-brainf-script-to-libgccjit-ir}@anchor{4c}
@subsection Converting a brainf script to libgccjit IR


As before we write simple code to populate a @pxref{8,,gcc_jit_context *}.

@quotation

@example

typedef struct bf_compiler
@{
  const char *filename;
  int line;
  int column;

  gcc_jit_context *ctxt;

  gcc_jit_type *void_type;
  gcc_jit_type *int_type;
  gcc_jit_type *byte_type;
  gcc_jit_type *array_type;

  gcc_jit_function *func_getchar;
  gcc_jit_function *func_putchar;

  gcc_jit_function *func;
  gcc_jit_block *curblock;

  gcc_jit_rvalue *int_zero;
  gcc_jit_rvalue *int_one;
  gcc_jit_rvalue *byte_zero;
  gcc_jit_rvalue *byte_one;
  gcc_jit_lvalue *data_cells;
  gcc_jit_lvalue *idx;

  int num_open_parens;
  gcc_jit_block *paren_test[MAX_OPEN_PARENS];
  gcc_jit_block *paren_body[MAX_OPEN_PARENS];
  gcc_jit_block *paren_after[MAX_OPEN_PARENS];

@} bf_compiler;

/* Bail out, with a message on stderr.  */

static void
fatal_error (bf_compiler *bfc, const char *msg)
@{
  fprintf (stderr,
	   "%s:%i:%i: %s",
	   bfc->filename, bfc->line, bfc->column, msg);
  abort ();
@}

/* Get "data_cells[idx]" as an lvalue.  */

static gcc_jit_lvalue *
bf_get_current_data (bf_compiler *bfc, gcc_jit_location *loc)
@{
  return gcc_jit_context_new_array_access (
    bfc->ctxt,
    loc,
    gcc_jit_lvalue_as_rvalue (bfc->data_cells),
    gcc_jit_lvalue_as_rvalue (bfc->idx));
@}

/* Get "data_cells[idx] == 0" as a boolean rvalue.  */

static gcc_jit_rvalue *
bf_current_data_is_zero (bf_compiler *bfc, gcc_jit_location *loc)
@{
  return gcc_jit_context_new_comparison (
    bfc->ctxt,
    loc,
    GCC_JIT_COMPARISON_EQ,
    gcc_jit_lvalue_as_rvalue (bf_get_current_data (bfc, loc)),
    bfc->byte_zero);
@}

/* Compile one bf character.  */

static void
bf_compile_char (bf_compiler *bfc,
		 unsigned char ch)
@{
  gcc_jit_location *loc =
    gcc_jit_context_new_location (bfc->ctxt,
				  bfc->filename,
				  bfc->line,
				  bfc->column);

  /* Turn this on to trace execution, by injecting putchar ()
     of each source char. */
  if (0)
    @{
      gcc_jit_rvalue *arg =
	gcc_jit_context_new_rvalue_from_int (
					     bfc->ctxt,
					     bfc->int_type,
					     ch);
      gcc_jit_rvalue *call =
	gcc_jit_context_new_call (bfc->ctxt,
				  loc,
				  bfc->func_putchar,
				  1, &arg);
      gcc_jit_block_add_eval (bfc->curblock,
			      loc,
			      call);
    @}

  switch (ch)
    @{
      case '>':
	gcc_jit_block_add_comment (bfc->curblock,
				   loc,
				   "'>': idx += 1;");
	gcc_jit_block_add_assignment_op (bfc->curblock,
					 loc,
					 bfc->idx,
					 GCC_JIT_BINARY_OP_PLUS,
					 bfc->int_one);
	break;

      case '<':
	gcc_jit_block_add_comment (bfc->curblock,
				   loc,
				   "'<': idx -= 1;");
	gcc_jit_block_add_assignment_op (bfc->curblock,
					 loc,
					 bfc->idx,
					 GCC_JIT_BINARY_OP_MINUS,
					 bfc->int_one);
	break;

      case '+':
	gcc_jit_block_add_comment (bfc->curblock,
				   loc,
				   "'+': data[idx] += 1;");
	gcc_jit_block_add_assignment_op (bfc->curblock,
					 loc,
					 bf_get_current_data (bfc, loc),
					 GCC_JIT_BINARY_OP_PLUS,
					 bfc->byte_one);
	break;

      case '-':
	gcc_jit_block_add_comment (bfc->curblock,
				   loc,
				   "'-': data[idx] -= 1;");
	gcc_jit_block_add_assignment_op (bfc->curblock,
					 loc,
					 bf_get_current_data (bfc, loc),
					 GCC_JIT_BINARY_OP_MINUS,
					 bfc->byte_one);
	break;

      case '.':
	@{
	  gcc_jit_rvalue *arg =
	    gcc_jit_context_new_cast (
	      bfc->ctxt,
	      loc,
	      gcc_jit_lvalue_as_rvalue (bf_get_current_data (bfc, loc)),
	      bfc->int_type);
	  gcc_jit_rvalue *call =
	    gcc_jit_context_new_call (bfc->ctxt,
				      loc,
				      bfc->func_putchar,
				      1, &arg);
	  gcc_jit_block_add_comment (bfc->curblock,
				     loc,
				     "'.': putchar ((int)data[idx]);");
	  gcc_jit_block_add_eval (bfc->curblock,
				  loc,
				  call);
	@}
	break;

      case ',':
	@{
	  gcc_jit_rvalue *call =
	    gcc_jit_context_new_call (bfc->ctxt,
				      loc,
				      bfc->func_getchar,
				      0, NULL);
	  gcc_jit_block_add_comment (
	    bfc->curblock,
	    loc,
	    "',': data[idx] = (unsigned char)getchar ();");
	  gcc_jit_block_add_assignment (bfc->curblock,
					loc,
					bf_get_current_data (bfc, loc),
					gcc_jit_context_new_cast (
					  bfc->ctxt,
					  loc,
					  call,
					  bfc->byte_type));
	@}
	break;

      case '[':
	@{
	  gcc_jit_block *loop_test =
	    gcc_jit_function_new_block (bfc->func, NULL);
	  gcc_jit_block *on_zero =
	    gcc_jit_function_new_block (bfc->func, NULL);
	  gcc_jit_block *on_non_zero =
	    gcc_jit_function_new_block (bfc->func, NULL);

	  if (bfc->num_open_parens == MAX_OPEN_PARENS)
	    fatal_error (bfc, "too many open parens");

	  gcc_jit_block_end_with_jump (
	    bfc->curblock,
	    loc,
	    loop_test);

	  gcc_jit_block_add_comment (
	    loop_test,
	    loc,
	    "'['");
	  gcc_jit_block_end_with_conditional (
	    loop_test,
	    loc,
	    bf_current_data_is_zero (bfc, loc),
	    on_zero,
	    on_non_zero);
	  bfc->paren_test[bfc->num_open_parens] = loop_test;
	  bfc->paren_body[bfc->num_open_parens] = on_non_zero;
	  bfc->paren_after[bfc->num_open_parens] = on_zero;
	  bfc->num_open_parens += 1;
	  bfc->curblock = on_non_zero;
	@}
	break;

      case ']':
	@{
	  gcc_jit_block_add_comment (
	    bfc->curblock,
	    loc,
	    "']'");

	  if (bfc->num_open_parens == 0)
	    fatal_error (bfc, "mismatching parens");
	  bfc->num_open_parens -= 1;
	  gcc_jit_block_end_with_jump (
	    bfc->curblock,
	    loc,
	    bfc->paren_test[bfc->num_open_parens]);
	  bfc->curblock = bfc->paren_after[bfc->num_open_parens];
	@}
	break;

    case '\n':
      bfc->line +=1;
      bfc->column = 0;
      break;
    @}

  if (ch != '\n')
    bfc->column += 1;
@}

/* Compile the given .bf file into a gcc_jit_context, containing a
   single "main" function suitable for compiling into an executable.  */

gcc_jit_context *
bf_compile (const char *filename)
@{
  bf_compiler bfc;
  FILE *f_in;
  int ch;

  memset (&bfc, 0, sizeof (bfc));

  bfc.filename = filename;
  f_in = fopen (filename, "r");
  if (!f_in)
    fatal_error (&bfc, "unable to open file");
  bfc.line = 1;

  bfc.ctxt = gcc_jit_context_acquire ();

  gcc_jit_context_set_int_option (
    bfc.ctxt,
    GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL,
    3);
  gcc_jit_context_set_bool_option (
    bfc.ctxt,
    GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE,
    0);
  gcc_jit_context_set_bool_option (
    bfc.ctxt,
    GCC_JIT_BOOL_OPTION_DEBUGINFO,
    1);
  gcc_jit_context_set_bool_option (
    bfc.ctxt,
    GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING,
    0);
  gcc_jit_context_set_bool_option (
    bfc.ctxt,
    GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES,
    0);

  bfc.void_type =
    gcc_jit_context_get_type (bfc.ctxt, GCC_JIT_TYPE_VOID);
  bfc.int_type =
    gcc_jit_context_get_type (bfc.ctxt, GCC_JIT_TYPE_INT);
  bfc.byte_type =
    gcc_jit_context_get_type (bfc.ctxt, GCC_JIT_TYPE_UNSIGNED_CHAR);
  bfc.array_type =
    gcc_jit_context_new_array_type (bfc.ctxt,
				    NULL,
				    bfc.byte_type,
				    30000);

  bfc.func_getchar =
    gcc_jit_context_new_function (bfc.ctxt, NULL,
				  GCC_JIT_FUNCTION_IMPORTED,
				  bfc.int_type,
				  "getchar",
				  0, NULL,
				  0);

  gcc_jit_param *param_c =
    gcc_jit_context_new_param (bfc.ctxt, NULL, bfc.int_type, "c");
  bfc.func_putchar =
    gcc_jit_context_new_function (bfc.ctxt, NULL,
				  GCC_JIT_FUNCTION_IMPORTED,
				  bfc.void_type,
				  "putchar",
				  1, &param_c,
				  0);

  bfc.func = make_main (bfc.ctxt);
   bfc.curblock =
    gcc_jit_function_new_block (bfc.func, "initial");
  bfc.int_zero = gcc_jit_context_zero (bfc.ctxt, bfc.int_type);
  bfc.int_one = gcc_jit_context_one (bfc.ctxt, bfc.int_type);
  bfc.byte_zero = gcc_jit_context_zero (bfc.ctxt, bfc.byte_type);
  bfc.byte_one = gcc_jit_context_one (bfc.ctxt, bfc.byte_type);

  bfc.data_cells =
    gcc_jit_context_new_global (bfc.ctxt, NULL,
				 GCC_JIT_GLOBAL_INTERNAL,
				 bfc.array_type,
				 "data_cells");
  bfc.idx =
    gcc_jit_function_new_local (bfc.func, NULL,
				bfc.int_type,
				"idx");

  gcc_jit_block_add_comment (bfc.curblock,
			     NULL,
			     "idx = 0;");
  gcc_jit_block_add_assignment (bfc.curblock,
				NULL,
				bfc.idx,
				bfc.int_zero);

  bfc.num_open_parens = 0;

  while ( EOF != (ch = fgetc (f_in)))
    bf_compile_char (&bfc, (unsigned char)ch);

  gcc_jit_block_end_with_return (bfc.curblock, NULL, bfc.int_zero);

  fclose (f_in);

  return bfc.ctxt;
@}


@end example

@noindent
@end quotation

@node Compiling a context to a file,Other forms of ahead-of-time-compilation,Converting a brainf script to libgccjit IR,Tutorial part 5 Implementing an Ahead-of-Time compiler
@anchor{intro/tutorial05 compiling-a-context-to-a-file}@anchor{4d}
@subsection Compiling a context to a file


Unlike the previous tutorial, this time we'll compile the context
directly to an executable, using @pxref{4a,,gcc_jit_context_compile_to_file()}:

@example
gcc_jit_context_compile_to_file (ctxt,
                                 GCC_JIT_OUTPUT_KIND_EXECUTABLE,
                                 output_file);
@end example

@noindent

Here's the top-level of the compiler, which is what actually calls into
@pxref{4a,,gcc_jit_context_compile_to_file()}:

@quotation

@example

int
main (int argc, char **argv)
@{
  const char *input_file;
  const char *output_file;
  gcc_jit_context *ctxt;
  const char *err;

  if (argc != 3)
    @{
      fprintf (stderr, "%s: INPUT_FILE OUTPUT_FILE\n", argv[0]);
      return 1;
    @}

  input_file = argv[1];
  output_file = argv[2];
  ctxt = bf_compile (input_file);

  gcc_jit_context_compile_to_file (ctxt,
				   GCC_JIT_OUTPUT_KIND_EXECUTABLE,
				   output_file);

  err = gcc_jit_context_get_first_error (ctxt);

  if (err)
    @{
      gcc_jit_context_release (ctxt);
      return 1;
    @}

  gcc_jit_context_release (ctxt);
  return 0;
@}


@end example

@noindent
@end quotation

Note how once the context is populated you could trivially instead compile
it to memory using @pxref{15,,gcc_jit_context_compile()} and run it in-process
as in the previous tutorial.

To create an executable, we need to export a @code{main} function.  Here's
how to create one from the JIT API:

@quotation

@example

/* Make "main" function:
     int
     main (int argc, char **argv)
     @{
       ...
     @}
*/
static gcc_jit_function *
make_main (gcc_jit_context *ctxt)
@{
  gcc_jit_type *int_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
  gcc_jit_param *param_argc =
    gcc_jit_context_new_param (ctxt, NULL, int_type, "argc");
  gcc_jit_type *char_ptr_ptr_type =
    gcc_jit_type_get_pointer (
      gcc_jit_type_get_pointer (
	gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_CHAR)));
  gcc_jit_param *param_argv =
    gcc_jit_context_new_param (ctxt, NULL, char_ptr_ptr_type, "argv");
  gcc_jit_param *params[2] = @{param_argc, param_argv@};
  gcc_jit_function *func_main =
    gcc_jit_context_new_function (ctxt, NULL,
				  GCC_JIT_FUNCTION_EXPORTED,
				  int_type,
				  "main",
				  2, params,
				  0);
  return func_main;
@}


@end example

@noindent
@end quotation

@cartouche
@quotation Note 
The above implementation ignores @code{argc} and @code{argv}, but you could
make use of them by exposing @code{param_argc} and @code{param_argv} to the
caller.
@end quotation
@end cartouche

Upon compiling this C code, we obtain a bf-to-machine-code compiler;
let's call it @code{bfc}:

@example
$ gcc \
    tut05-bf.c \
    -o bfc \
    -lgccjit
@end example

@noindent

We can now use @code{bfc} to compile .bf files into machine code executables:

@example
$ ./bfc \
     emit-alphabet.bf \
     a.out
@end example

@noindent

which we can run directly:

@example
$ ./a.out
ABCDEFGHIJKLMNOPQRSTUVWXYZ
@end example

@noindent

Success!

We can also inspect the generated executable using standard tools:

@example
$ objdump -d a.out |less
@end example

@noindent

which shows that libgccjit has managed to optimize the function
somewhat (for example, the runs of 26 and 65 increment operations
have become integer constants 0x1a and 0x41):

@example
0000000000400620 <main>:
  400620:     80 3d 39 0a 20 00 00    cmpb   $0x0,0x200a39(%rip)        # 601060 <data
  400627:     74 07                   je     400630 <main
  400629:     eb fe                   jmp    400629 <main+0x9>
  40062b:     0f 1f 44 00 00          nopl   0x0(%rax,%rax,1)
  400630:     48 83 ec 08             sub    $0x8,%rsp
  400634:     0f b6 05 26 0a 20 00    movzbl 0x200a26(%rip),%eax        # 601061 <data_cells+0x1>
  40063b:     c6 05 1e 0a 20 00 1a    movb   $0x1a,0x200a1e(%rip)       # 601060 <data_cells>
  400642:     8d 78 41                lea    0x41(%rax),%edi
  400645:     40 88 3d 15 0a 20 00    mov    %dil,0x200a15(%rip)        # 601061 <data_cells+0x1>
  40064c:     0f 1f 40 00             nopl   0x0(%rax)
  400650:     40 0f b6 ff             movzbl %dil,%edi
  400654:     e8 87 fe ff ff          callq  4004e0 <putchar@@plt>
  400659:     0f b6 05 01 0a 20 00    movzbl 0x200a01(%rip),%eax        # 601061 <data_cells+0x1>
  400660:     80 2d f9 09 20 00 01    subb   $0x1,0x2009f9(%rip)        # 601060 <data_cells>
  400667:     8d 78 01                lea    0x1(%rax),%edi
  40066a:     40 88 3d f0 09 20 00    mov    %dil,0x2009f0(%rip)        # 601061 <data_cells+0x1>
  400671:     75 dd                   jne    400650 <main+0x30>
  400673:     31 c0                   xor    %eax,%eax
  400675:     48 83 c4 08             add    $0x8,%rsp
  400679:     c3                      retq
  40067a:     66 0f 1f 44 00 00       nopw   0x0(%rax,%rax,1)
@end example

@noindent

We also set up debugging information (via
@pxref{41,,gcc_jit_context_new_location()} and
@pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO}), so it's possible to use @code{gdb}
to singlestep through the generated binary and inspect the internal
state @code{idx} and @code{data_cells}:

@example
(gdb) break main
Breakpoint 1 at 0x400790
(gdb) run
Starting program: a.out

Breakpoint 1, 0x0000000000400790 in main (argc=1, argv=0x7fffffffe448)
(gdb) stepi
0x0000000000400797 in main (argc=1, argv=0x7fffffffe448)
(gdb) stepi
0x00000000004007a0 in main (argc=1, argv=0x7fffffffe448)
(gdb) stepi
9     >+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<
(gdb) list
4
5     cell 0 = 26
6     ++++++++++++++++++++++++++
7
8     cell 1 = 65
9     >+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<
10
11    while cell#0 != 0
12    [
13     >
(gdb) n
6     ++++++++++++++++++++++++++
(gdb) n
9     >+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<
(gdb) p idx
$1 = 1
(gdb) p data_cells
$2 = "\032", '\000' <repeats 29998 times>
(gdb) p data_cells[0]
$3 = 26 '\032'
(gdb) p data_cells[1]
$4 = 0 '\000'
(gdb) list
4
5     cell 0 = 26
6     ++++++++++++++++++++++++++
7
8     cell 1 = 65
9     >+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++<
10
11    while cell#0 != 0
12    [
13     >
@end example

@noindent

@node Other forms of ahead-of-time-compilation,,Compiling a context to a file,Tutorial part 5 Implementing an Ahead-of-Time compiler
@anchor{intro/tutorial05 other-forms-of-ahead-of-time-compilation}@anchor{4e}
@subsection Other forms of ahead-of-time-compilation


The above demonstrates compiling a @pxref{8,,gcc_jit_context *} directly
to an executable.  It's also possible to compile it to an object file,
and to a dynamic library.  See the documentation of
@pxref{4a,,gcc_jit_context_compile_to_file()} for more information.

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Topic Reference,C++ bindings for libgccjit,Tutorial,Top
@anchor{topics/index doc}@anchor{4f}@anchor{topics/index topic-reference}@anchor{50}
@chapter Topic Reference


@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@menu
* Compilation contexts:: 
* Objects:: 
* Types:: 
* Expressions:: 
* Creating and using functions:: 
* Source Locations:: 
* Compiling a context:: 
* ABI and API compatibility:: 
* Performance:: 

Compilation contexts

* Lifetime-management:: 
* Thread-safety:: 
* Error-handling: Error-handling<2>. 
* Debugging:: 
* Options: Options<2>. 

Options

* String Options:: 
* Boolean options:: 
* Integer options:: 
* Additional command-line options:: 

Types

* Standard types:: 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile. 
* Structures and unions:: 

Expressions

* Rvalues:: 
* Lvalues:: 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions. 

Rvalues

* Simple expressions:: 
* Unary Operations:: 
* Binary Operations:: 
* Comparisons:: 
* Function calls:: 
* Type-coercion:: 

Lvalues

* Global variables:: 

Creating and using functions

* Params:: 
* Functions:: 
* Blocks:: 
* Statements:: 

Source Locations

* Faking it:: 

Compiling a context

* In-memory compilation:: 
* Ahead-of-time compilation:: 

ABI and API compatibility

* ABI symbol tags:: 

ABI symbol tags

* LIBGCCJIT_ABI_0:: 
* LIBGCCJIT_ABI_1:: 
* LIBGCCJIT_ABI_2:: 
* LIBGCCJIT_ABI_3:: 
* LIBGCCJIT_ABI_4:: 

Performance

* The timing API:: 

@end menu


@node Compilation contexts,Objects,,Topic Reference
@anchor{topics/contexts compilation-contexts}@anchor{51}@anchor{topics/contexts doc}@anchor{52}
@section Compilation contexts


@geindex gcc_jit_context (C type)
@anchor{topics/contexts gcc_jit_context}@anchor{8}
@deffn {C Type} gcc_jit_context
@end deffn

The top-level of the API is the @pxref{8,,gcc_jit_context} type.

A @pxref{8,,gcc_jit_context} instance encapsulates the state of a
compilation.

You can set up options on it, and add types, functions and code.
Invoking @pxref{15,,gcc_jit_context_compile()} on it gives you a
@pxref{16,,gcc_jit_result}.

@menu
* Lifetime-management:: 
* Thread-safety:: 
* Error-handling: Error-handling<2>. 
* Debugging:: 
* Options: Options<2>. 

@end menu

@node Lifetime-management,Thread-safety,,Compilation contexts
@anchor{topics/contexts lifetime-management}@anchor{53}
@subsection Lifetime-management


Contexts are the unit of lifetime-management within the API: objects
have their lifetime bounded by the context they are created within, and
cleanup of such objects is done for you when the context is released.

@geindex gcc_jit_context_acquire (C function)
@anchor{topics/contexts gcc_jit_context_acquire}@anchor{9}
@deffn {C Function} gcc_jit_context *gcc_jit_context_acquire (void)

This function acquires a new @pxref{8,,gcc_jit_context *} instance,
which is independent of any others that may be present within this
process.
@end deffn

@geindex gcc_jit_context_release (C function)
@anchor{topics/contexts gcc_jit_context_release}@anchor{c}
@deffn {C Function} void gcc_jit_context_release (gcc_jit_context@w{ }*ctxt)

This function releases all resources associated with the given context.
Both the context itself and all of its @pxref{e,,gcc_jit_object *}
instances are cleaned up.  It should be called exactly once on a given
context.

It is invalid to use the context or any of its "contextual" objects
after calling this.

@example
gcc_jit_context_release (ctxt);
@end example

@noindent
@end deffn

@geindex gcc_jit_context_new_child_context (C function)
@anchor{topics/contexts gcc_jit_context_new_child_context}@anchor{54}
@deffn {C Function} gcc_jit_context * gcc_jit_context_new_child_context (gcc_jit_context@w{ }*parent_ctxt)

Given an existing JIT context, create a child context.

The child inherits a copy of all option-settings from the parent.

The child can reference objects created within the parent, but not
vice-versa.

The lifetime of the child context must be bounded by that of the
parent: you should release a child context before releasing the parent
context.

If you use a function from a parent context within a child context,
you have to compile the parent context before you can compile the
child context, and the gcc_jit_result of the parent context must
outlive the gcc_jit_result of the child context.

This allows caching of shared initializations.  For example, you could
create types and declarations of global functions in a parent context
once within a process, and then create child contexts whenever a
function or loop becomes hot. Each such child context can be used for
JIT-compiling just one function or loop, but can reference types
and helper functions created within the parent context.

Contexts can be arbitrarily nested, provided the above rules are
followed, but it's probably not worth going above 2 or 3 levels, and
there will likely be a performance hit for such nesting.
@end deffn

@node Thread-safety,Error-handling<2>,Lifetime-management,Compilation contexts
@anchor{topics/contexts thread-safety}@anchor{55}
@subsection Thread-safety


Instances of @pxref{8,,gcc_jit_context *} created via
@pxref{9,,gcc_jit_context_acquire()} are independent from each other:
only one thread may use a given context at once, but multiple threads
could each have their own contexts without needing locks.

Contexts created via @pxref{54,,gcc_jit_context_new_child_context()} are
related to their parent context.  They can be partitioned by their
ultimate ancestor into independent "family trees".   Only one thread
within a process may use a given "family tree" of such contexts at once,
and if you're using multiple threads you should provide your own locking
around entire such context partitions.

@node Error-handling<2>,Debugging,Thread-safety,Compilation contexts
@anchor{topics/contexts error-handling}@anchor{19}@anchor{topics/contexts id1}@anchor{56}
@subsection Error-handling


Various kinds of errors are possible when using the API, such as
mismatched types in an assignment.  You can only compile and get code from
a context if no errors occur.

Errors are printed on stderr and can be queried using
@pxref{57,,gcc_jit_context_get_first_error()}.

They typically contain the name of the API entrypoint where the error
occurred, and pertinent information on the problem:

@example
./buggy-program: error: gcc_jit_block_add_assignment: mismatching types: assignment to i (type: int) from "hello world" (type: const char *)
@end example

@noindent

In general, if an error occurs when using an API entrypoint, the
entrypoint returns NULL.  You don't have to check everywhere for NULL
results, since the API handles a NULL being passed in for any
argument by issuing another error.  This typically leads to a cascade of
followup error messages, but is safe (albeit verbose).  The first error
message is usually the one to pay attention to, since it is likely to
be responsible for all of the rest:

@geindex gcc_jit_context_get_first_error (C function)
@anchor{topics/contexts gcc_jit_context_get_first_error}@anchor{57}
@deffn {C Function} const char *           gcc_jit_context_get_first_error (gcc_jit_context@w{ }*ctxt)

Returns the first error message that occurred on the context.

The returned string is valid for the rest of the lifetime of the
context.

If no errors occurred, this will be NULL.
@end deffn

If you are wrapping the C API for a higher-level language that supports
exception-handling, you may instead be interested in the last error that
occurred on the context, so that you can embed this in an exception:

@geindex gcc_jit_context_get_last_error (C function)
@anchor{topics/contexts gcc_jit_context_get_last_error}@anchor{58}
@deffn {C Function} const char *           gcc_jit_context_get_last_error (gcc_jit_context@w{ }*ctxt)

Returns the last error message that occurred on the context.

If no errors occurred, this will be NULL.

If non-NULL, the returned string is only guaranteed to be valid until
the next call to libgccjit relating to this context.
@end deffn

@node Debugging,Options<2>,Error-handling<2>,Compilation contexts
@anchor{topics/contexts debugging}@anchor{59}
@subsection Debugging


@geindex gcc_jit_context_dump_to_file (C function)
@anchor{topics/contexts gcc_jit_context_dump_to_file}@anchor{5a}
@deffn {C Function} void           gcc_jit_context_dump_to_file (gcc_jit_context@w{ }*ctxt, const char@w{ }*path, int@w{ }update_locations)

To help with debugging: dump a C-like representation to the given path,
describing what's been set up on the context.

If "update_locations" is true, then also set up @pxref{3b,,gcc_jit_location}
information throughout the context, pointing at the dump file as if it
were a source file.  This may be of use in conjunction with
@pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} to allow stepping through the
code in a debugger.
@end deffn

@geindex gcc_jit_context_set_logfile (C function)
@anchor{topics/contexts gcc_jit_context_set_logfile}@anchor{5b}
@deffn {C Function} void           gcc_jit_context_set_logfile (gcc_jit_context@w{ }*ctxt, FILE@w{ }*logfile, int@w{ }flags, int@w{ }verbosity)

To help with debugging; enable ongoing logging of the context's
activity to the given file.

For example, the following will enable logging to stderr.

@example
gcc_jit_context_set_logfile (ctxt, stderr, 0, 0);
@end example

@noindent

Examples of information logged include:


@itemize *

@item 
API calls

@item 
the various steps involved within compilation

@item 
activity on any @pxref{16,,gcc_jit_result} instances created by
the context

@item 
activity within any child contexts
@end itemize

An example of a log can be seen @pxref{5c,,here},
though the precise format and kinds of information logged is subject
to change.

The caller remains responsible for closing @cite{logfile}, and it must not
be closed until all users are released.  In particular, note that
child contexts and @pxref{16,,gcc_jit_result} instances created by
the context will use the logfile.

There may a performance cost for logging.

You can turn off logging on @cite{ctxt} by passing @cite{NULL} for @cite{logfile}.
Doing so only affects the context; it does not affect child contexts
or @pxref{16,,gcc_jit_result} instances already created by
the context.

The parameters "flags" and "verbosity" are reserved for future
expansion, and must be zero for now.
@end deffn

To contrast the above: @pxref{5a,,gcc_jit_context_dump_to_file()} dumps the
current state of a context to the given path, whereas
@pxref{5b,,gcc_jit_context_set_logfile()} enables on-going logging of
future activies on a context to the given @cite{FILE *}.

@geindex gcc_jit_context_dump_reproducer_to_file (C function)
@anchor{topics/contexts gcc_jit_context_dump_reproducer_to_file}@anchor{5d}
@deffn {C Function} void           gcc_jit_context_dump_reproducer_to_file (gcc_jit_context@w{ }*ctxt, const char@w{ }*path)

Write C source code into @cite{path} that can be compiled into a
self-contained executable (i.e. with libgccjit as the only dependency).
The generated code will attempt to replay the API calls that have been
made into the given context.

This may be useful when debugging the library or client code, for
reducing a complicated recipe for reproducing a bug into a simpler
form.  For example, consider client code that parses some source file
into some internal representation, and then walks this IR, calling into
libgccjit.  If this encounters a bug, a call to
@cite{gcc_jit_context_dump_reproducer_to_file} will write out C code for
a much simpler executable that performs the equivalent calls into
libgccjit, without needing the client code and its data.

Typically you need to supply @code{-Wno-unused-variable} when
compiling the generated file (since the result of each API call is
assigned to a unique variable within the generated C source, and not
all are necessarily then used).
@end deffn

@geindex gcc_jit_context_enable_dump (C function)
@anchor{topics/contexts gcc_jit_context_enable_dump}@anchor{5e}
@deffn {C Function} void           gcc_jit_context_enable_dump (gcc_jit_context@w{ }*ctxt, const char@w{ }*dumpname, char@w{ }**out_ptr)

Enable the dumping of a specific set of internal state from the
compilation, capturing the result in-memory as a buffer.

Parameter "dumpname" corresponds to the equivalent gcc command-line
option, without the "-fdump-" prefix.
For example, to get the equivalent of @code{-fdump-tree-vrp1},
supply @code{"tree-vrp1"}:

@example
static char *dump_vrp1;

void
create_code (gcc_jit_context *ctxt)
@{
   gcc_jit_context_enable_dump (ctxt, "tree-vrp1", &dump_vrp1);
   /* (other API calls omitted for brevity) */
@}
@end example

@noindent

The context directly stores the dumpname as a @code{(const char *)}, so
the passed string must outlive the context.

@pxref{15,,gcc_jit_context_compile()} will capture the dump as a
dynamically-allocated buffer, writing it to @code{*out_ptr}.

The caller becomes responsible for calling:

@example
free (*out_ptr)
@end example

@noindent

each time that @pxref{15,,gcc_jit_context_compile()} is called.
@code{*out_ptr} will be written to, either with the address of a buffer,
or with @code{NULL} if an error occurred.

@cartouche
@quotation Warning 
This API entrypoint is likely to be less stable than the others.
In particular, both the precise dumpnames, and the format and content
of the dumps are subject to change.

It exists primarily for writing the library's own test suite.
@end quotation
@end cartouche
@end deffn

@node Options<2>,,Debugging,Compilation contexts
@anchor{topics/contexts options}@anchor{5f}
@subsection Options


Options present in the initial release of libgccjit were handled using
enums, whereas those added subsequently have their own per-option API
entrypoints.

Adding entrypoints for each new option means that client code that use
the new options can be identified directly from binary metadata, which
would not be possible if we instead extended the various
@code{enum gcc_jit_*_option}.

@menu
* String Options:: 
* Boolean options:: 
* Integer options:: 
* Additional command-line options:: 

@end menu

@node String Options,Boolean options,,Options<2>
@anchor{topics/contexts string-options}@anchor{60}
@subsubsection String Options


@geindex gcc_jit_context_set_str_option (C function)
@anchor{topics/contexts gcc_jit_context_set_str_option}@anchor{61}
@deffn {C Function} void gcc_jit_context_set_str_option (gcc_jit_context@w{ }*ctxt, enum gcc_jit_str_option@w{ }opt, const char@w{ }*value)

Set a string option of the context.

@geindex gcc_jit_str_option (C type)
@anchor{topics/contexts gcc_jit_str_option}@anchor{62}
@deffn {C Type} enum gcc_jit_str_option
@end deffn

The parameter @code{value} can be NULL.   If non-NULL, the call takes a
copy of the underlying string, so it is valid to pass in a pointer to
an on-stack buffer.

There is just one string option specified this way:

@geindex GCC_JIT_STR_OPTION_PROGNAME (C macro)
@anchor{topics/contexts GCC_JIT_STR_OPTION_PROGNAME}@anchor{63}
@deffn {C Macro} GCC_JIT_STR_OPTION_PROGNAME

The name of the program, for use as a prefix when printing error
messages to stderr.  If @cite{NULL}, or default, "libgccjit.so" is used.
@end deffn
@end deffn

@node Boolean options,Integer options,String Options,Options<2>
@anchor{topics/contexts boolean-options}@anchor{64}
@subsubsection Boolean options


@geindex gcc_jit_context_set_bool_option (C function)
@anchor{topics/contexts gcc_jit_context_set_bool_option}@anchor{1b}
@deffn {C Function} void gcc_jit_context_set_bool_option (gcc_jit_context@w{ }*ctxt, enum gcc_jit_bool_option@w{ }opt, int@w{ }value)

Set a boolean option of the context.
Zero is "false" (the default), non-zero is "true".

@geindex gcc_jit_bool_option (C type)
@anchor{topics/contexts gcc_jit_bool_option}@anchor{65}
@deffn {C Type} enum gcc_jit_bool_option
@end deffn

@geindex GCC_JIT_BOOL_OPTION_DEBUGINFO (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_DEBUGINFO}@anchor{42}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_DEBUGINFO

If true, @pxref{15,,gcc_jit_context_compile()} will attempt to do the right
thing so that if you attach a debugger to the process, it will
be able to inspect variables and step through your code.

Note that you can't step through code unless you set up source
location information for the code (by creating and passing in
@pxref{3b,,gcc_jit_location} instances).
@end deffn

@geindex GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE}@anchor{66}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE

If true, @pxref{15,,gcc_jit_context_compile()} will dump its initial
"tree" representation of your code to stderr (before any
optimizations).

Here's some sample output (from the @cite{square} example):

@example
<statement_list 0x7f4875a62cc0
   type <void_type 0x7f4875a64bd0 VOID
       align 8 symtab 0 alias set -1 canonical type 0x7f4875a64bd0
       pointer_to_this <pointer_type 0x7f4875a64c78>>
   side-effects head 0x7f4875a761e0 tail 0x7f4875a761f8 stmts 0x7f4875a62d20 0x7f4875a62d00

   stmt <label_expr 0x7f4875a62d20 type <void_type 0x7f4875a64bd0>
       side-effects
       arg 0 <label_decl 0x7f4875a79080 entry type <void_type 0x7f4875a64bd0>
           VOID file (null) line 0 col 0
           align 1 context <function_decl 0x7f4875a77500 square>>>
   stmt <return_expr 0x7f4875a62d00
       type <integer_type 0x7f4875a645e8 public SI
           size <integer_cst 0x7f4875a623a0 constant 32>
           unit size <integer_cst 0x7f4875a623c0 constant 4>
           align 32 symtab 0 alias set -1 canonical type 0x7f4875a645e8 precision 32 min <integer_cst 0x7f4875a62340 -2147483648> max <integer_cst 0x7f4875a62360 2147483647>
           pointer_to_this <pointer_type 0x7f4875a6b348>>
       side-effects
       arg 0 <modify_expr 0x7f4875a72a78 type <integer_type 0x7f4875a645e8>
           side-effects arg 0 <result_decl 0x7f4875a7a000 D.54>
           arg 1 <mult_expr 0x7f4875a72a50 type <integer_type 0x7f4875a645e8>
               arg 0 <parm_decl 0x7f4875a79000 i> arg 1 <parm_decl 0x7f4875a79000 i>>>>>
@end example

@noindent
@end deffn

@geindex GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE}@anchor{1c}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE

If true, @pxref{15,,gcc_jit_context_compile()} will dump the "gimple"
representation of your code to stderr, before any optimizations
are performed.  The dump resembles C code:

@example
square (signed int i)
@{
  signed int D.56;

  entry:
  D.56 = i * i;
  return D.56;
@}
@end example

@noindent
@end deffn

@geindex GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE}@anchor{1d}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE

If true, @pxref{15,,gcc_jit_context_compile()} will dump the final
generated code to stderr, in the form of assembly language:

@example
    .file    "fake.c"
    .text
    .globl    square
    .type    square, @@function
square:
.LFB0:
    .cfi_startproc
    pushq    %rbp
    .cfi_def_cfa_offset 16
    .cfi_offset 6, -16
    movq    %rsp, %rbp
    .cfi_def_cfa_register 6
    movl    %edi, -4(%rbp)
.L2:
    movl    -4(%rbp), %eax
    imull    -4(%rbp), %eax
    popq    %rbp
    .cfi_def_cfa 7, 8
    ret
    .cfi_endproc
.LFE0:
    .size    square, .-square
    .ident    "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.1-%@{gcc_release@})"
    .section    .note.GNU-stack,"",@@progbits
@end example

@noindent
@end deffn

@geindex GCC_JIT_BOOL_OPTION_DUMP_SUMMARY (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_DUMP_SUMMARY}@anchor{67}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_DUMP_SUMMARY

If true, @pxref{15,,gcc_jit_context_compile()} will print information to stderr
on the actions it is performing.
@end deffn

@geindex GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING}@anchor{68}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING

If true, @pxref{15,,gcc_jit_context_compile()} will dump copious
amount of information on what it's doing to various
files within a temporary directory.  Use
@pxref{69,,GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES} (see below) to
see the results.  The files are intended to be human-readable,
but the exact files and their formats are subject to change.
@end deffn

@geindex GCC_JIT_BOOL_OPTION_SELFCHECK_GC (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_SELFCHECK_GC}@anchor{6a}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_SELFCHECK_GC

If true, libgccjit will aggressively run its garbage collector, to
shake out bugs (greatly slowing down the compile).  This is likely
to only be of interest to developers @emph{of} the library.  It is
used when running the selftest suite.
@end deffn

@geindex GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES (C macro)
@anchor{topics/contexts GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES}@anchor{69}
@deffn {C Macro} GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES

If true, the @pxref{8,,gcc_jit_context} will not clean up intermediate files
written to the filesystem, and will display their location on stderr.
@end deffn
@end deffn

@geindex gcc_jit_context_set_bool_allow_unreachable_blocks (C function)
@anchor{topics/contexts gcc_jit_context_set_bool_allow_unreachable_blocks}@anchor{6b}
@deffn {C Function} void            gcc_jit_context_set_bool_allow_unreachable_blocks (gcc_jit_context@w{ }*ctxt, int@w{ }bool_value)

By default, libgccjit will issue an error about unreachable blocks
within a function.

This entrypoint can be used to disable that error.

This entrypoint was added in @pxref{6c,,LIBGCCJIT_ABI_2}; you can test for
its presence using

@example
#ifdef LIBGCCJIT_HAVE_gcc_jit_context_set_bool_allow_unreachable_blocks
@end example

@noindent
@end deffn

@node Integer options,Additional command-line options,Boolean options,Options<2>
@anchor{topics/contexts integer-options}@anchor{6d}
@subsubsection Integer options


@geindex gcc_jit_context_set_int_option (C function)
@anchor{topics/contexts gcc_jit_context_set_int_option}@anchor{1e}
@deffn {C Function} void gcc_jit_context_set_int_option (gcc_jit_context@w{ }*ctxt, enum gcc_jit_int_option@w{ }opt, int@w{ }value)

Set an integer option of the context.

@geindex gcc_jit_int_option (C type)
@anchor{topics/contexts gcc_jit_int_option}@anchor{6e}
@deffn {C Type} enum gcc_jit_int_option
@end deffn

There is just one integer option specified this way:

@geindex GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL (C macro)
@anchor{topics/contexts GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL}@anchor{1f}
@deffn {C Macro} GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL

How much to optimize the code.

Valid values are 0-3, corresponding to GCC's command-line options
-O0 through -O3.

The default value is 0 (unoptimized).
@end deffn
@end deffn

@node Additional command-line options,,Integer options,Options<2>
@anchor{topics/contexts additional-command-line-options}@anchor{6f}
@subsubsection Additional command-line options


@geindex gcc_jit_context_add_command_line_option (C function)
@anchor{topics/contexts gcc_jit_context_add_command_line_option}@anchor{70}
@deffn {C Function} void gcc_jit_context_add_command_line_option (gcc_jit_context@w{ }*ctxt, const char@w{ }*optname)

Add an arbitrary gcc command-line option to the context, for use
by @pxref{15,,gcc_jit_context_compile()} and
@pxref{4a,,gcc_jit_context_compile_to_file()}.

The parameter @code{optname} must be non-NULL.  The underlying buffer is
copied, so that it does not need to outlive the call.

Extra options added by @cite{gcc_jit_context_add_command_line_option} are
applied @emph{after} the regular options above, potentially overriding them.
Options from parent contexts are inherited by child contexts; options
from the parent are applied @emph{before} those from the child.

For example:

@example
gcc_jit_context_add_command_line_option (ctxt, "-ffast-math");
gcc_jit_context_add_command_line_option (ctxt, "-fverbose-asm");
@end example

@noindent

Note that only some options are likely to be meaningful; there is no
"frontend" within libgccjit, so typically only those affecting
optimization and code-generation are likely to be useful.

This entrypoint was added in @pxref{71,,LIBGCCJIT_ABI_1}; you can test for
its presence using

@example
#ifdef LIBGCCJIT_HAVE_gcc_jit_context_add_command_line_option
@end example

@noindent
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Objects,Types,Compilation contexts,Topic Reference
@anchor{topics/objects objects}@anchor{72}@anchor{topics/objects doc}@anchor{73}
@section Objects


@geindex gcc_jit_object (C type)
@anchor{topics/objects gcc_jit_object}@anchor{e}
@deffn {C Type} gcc_jit_object
@end deffn

Almost every entity in the API (with the exception of
@pxref{8,,gcc_jit_context *} and @pxref{16,,gcc_jit_result *}) is a
"contextual" object, a @pxref{e,,gcc_jit_object *}

A JIT object:

@quotation


@itemize *

@item 
is associated with a @pxref{8,,gcc_jit_context *}.

@item 
is automatically cleaned up for you when its context is released so
you don't need to manually track and cleanup all objects, just the
contexts.
@end itemize
@end quotation

Although the API is C-based, there is a form of class hierarchy, which
looks like this:

@example
+- gcc_jit_object
    +- gcc_jit_location
    +- gcc_jit_type
       +- gcc_jit_struct
    +- gcc_jit_field
    +- gcc_jit_function
    +- gcc_jit_block
    +- gcc_jit_rvalue
        +- gcc_jit_lvalue
           +- gcc_jit_param
    +- gcc_jit_case
@end example

@noindent

There are casting methods for upcasting from subclasses to parent classes.
For example, @pxref{d,,gcc_jit_type_as_object()}:

@example
gcc_jit_object *obj = gcc_jit_type_as_object (int_type);
@end example

@noindent

The object "base class" has the following operations:

@geindex gcc_jit_object_get_context (C function)
@anchor{topics/objects gcc_jit_object_get_context}@anchor{74}
@deffn {C Function} gcc_jit_context *gcc_jit_object_get_context (gcc_jit_object@w{ }*obj)

Which context is "obj" within?
@end deffn

@geindex gcc_jit_object_get_debug_string (C function)
@anchor{topics/objects gcc_jit_object_get_debug_string}@anchor{f}
@deffn {C Function} const char *gcc_jit_object_get_debug_string (gcc_jit_object@w{ }*obj)

Generate a human-readable description for the given object.

For example,

@example
printf ("obj: %s\n", gcc_jit_object_get_debug_string (obj));
@end example

@noindent

might give this text on stdout:

@example
obj: 4.0 * (float)i
@end example

@noindent

@cartouche
@quotation Note 
If you call this on an object, the @cite{const char *} buffer is allocated
and generated on the first call for that object, and the buffer will
have the same lifetime as the object  i.e. it will exist until the
object's context is released.
@end quotation
@end cartouche
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Types,Expressions,Objects,Topic Reference
@anchor{topics/types doc}@anchor{75}@anchor{topics/types types}@anchor{76}
@section Types


@geindex gcc_jit_type (C type)
@anchor{topics/types gcc_jit_type}@anchor{a}
@deffn {C Type} gcc_jit_type

gcc_jit_type represents a type within the library.
@end deffn

@geindex gcc_jit_type_as_object (C function)
@anchor{topics/types gcc_jit_type_as_object}@anchor{d}
@deffn {C Function} gcc_jit_object *gcc_jit_type_as_object (gcc_jit_type@w{ }*type)

Upcast a type to an object.
@end deffn

Types can be created in several ways:


@itemize *

@item 
fundamental types can be accessed using
@pxref{b,,gcc_jit_context_get_type()}:

@example
gcc_jit_type *int_type = gcc_jit_context_get_type (GCC_JIT_TYPE_INT);
@end example

@noindent

See @pxref{b,,gcc_jit_context_get_type()} for the available types.

@item 
derived types can be accessed by using functions such as
@pxref{77,,gcc_jit_type_get_pointer()} and @pxref{78,,gcc_jit_type_get_const()}:

@example
gcc_jit_type *const_int_star = gcc_jit_type_get_pointer (gcc_jit_type_get_const (int_type));
gcc_jit_type *int_const_star = gcc_jit_type_get_const (gcc_jit_type_get_pointer (int_type));
@end example

@noindent

@item 
by creating structures (see below).
@end itemize

@menu
* Standard types:: 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile. 
* Structures and unions:: 

@end menu

@node Standard types,Pointers const and volatile,,Types
@anchor{topics/types standard-types}@anchor{79}
@subsection Standard types


@geindex gcc_jit_context_get_type (C function)
@anchor{topics/types gcc_jit_context_get_type}@anchor{b}
@deffn {C Function} gcc_jit_type *gcc_jit_context_get_type (gcc_jit_context@w{ }*ctxt, enum gcc_jit_types@w{ }type_)

Access a specific type.  The available types are:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} 
@headitem

@cite{enum gcc_jit_types} value

@tab

Meaning

@item

@code{GCC_JIT_TYPE_VOID}

@tab

C's @code{void} type.

@item

@code{GCC_JIT_TYPE_VOID_PTR}

@tab

C's @code{void *}.

@item

@code{GCC_JIT_TYPE_BOOL}

@tab

C++'s @code{bool} type; also C99's
@code{_Bool} type, aka @code{bool} if
using stdbool.h.

@item

@code{GCC_JIT_TYPE_CHAR}

@tab

C's @code{char} (of some signedness)

@item

@code{GCC_JIT_TYPE_SIGNED_CHAR}

@tab

C's @code{signed char}

@item

@code{GCC_JIT_TYPE_UNSIGNED_CHAR}

@tab

C's @code{unsigned char}

@item

@code{GCC_JIT_TYPE_SHORT}

@tab

C's @code{short} (signed)

@item

@code{GCC_JIT_TYPE_UNSIGNED_SHORT}

@tab

C's @code{unsigned short}

@item

@code{GCC_JIT_TYPE_INT}

@tab

C's @code{int} (signed)

@item

@code{GCC_JIT_TYPE_UNSIGNED_INT}

@tab

C's @code{unsigned int}

@item

@code{GCC_JIT_TYPE_LONG}

@tab

C's @code{long} (signed)

@item

@code{GCC_JIT_TYPE_UNSIGNED_LONG}

@tab

C's @code{unsigned long}

@item

@code{GCC_JIT_TYPE_LONG_LONG}

@tab

C99's @code{long long} (signed)

@item

@code{GCC_JIT_TYPE_UNSIGNED_LONG_LONG}

@tab

C99's @code{unsigned long long}

@item

@code{GCC_JIT_TYPE_FLOAT}

@tab

@item

@code{GCC_JIT_TYPE_DOUBLE}

@tab

@item

@code{GCC_JIT_TYPE_LONG_DOUBLE}

@tab

@item

@code{GCC_JIT_TYPE_CONST_CHAR_PTR}

@tab

C type: @code{(const char *)}

@item

@code{GCC_JIT_TYPE_SIZE_T}

@tab

C's @code{size_t} type

@item

@code{GCC_JIT_TYPE_FILE_PTR}

@tab

C type: @code{(FILE *)}

@item

@code{GCC_JIT_TYPE_COMPLEX_FLOAT}

@tab

C99's @code{_Complex float}

@item

@code{GCC_JIT_TYPE_COMPLEX_DOUBLE}

@tab

C99's @code{_Complex double}

@item

@code{GCC_JIT_TYPE_COMPLEX_LONG_DOUBLE}

@tab

C99's @code{_Complex long double}

@end multitable

@end deffn

@geindex gcc_jit_context_get_int_type (C function)
@anchor{topics/types gcc_jit_context_get_int_type}@anchor{7a}
@deffn {C Function} gcc_jit_type *           gcc_jit_context_get_int_type (gcc_jit_context@w{ }*ctxt, int@w{ }num_bytes, int@w{ }is_signed)

Access the integer type of the given size.
@end deffn

@node Pointers const and volatile,Structures and unions,Standard types,Types
@anchor{topics/types pointers-const-and-volatile}@anchor{7b}
@subsection Pointers, @cite{const}, and @cite{volatile}


@geindex gcc_jit_type_get_pointer (C function)
@anchor{topics/types gcc_jit_type_get_pointer}@anchor{77}
@deffn {C Function} gcc_jit_type *gcc_jit_type_get_pointer (gcc_jit_type@w{ }*type)

Given type "T", get type "T*".
@end deffn

@geindex gcc_jit_type_get_const (C function)
@anchor{topics/types gcc_jit_type_get_const}@anchor{78}
@deffn {C Function} gcc_jit_type *gcc_jit_type_get_const (gcc_jit_type@w{ }*type)

Given type "T", get type "const T".
@end deffn

@geindex gcc_jit_type_get_volatile (C function)
@anchor{topics/types gcc_jit_type_get_volatile}@anchor{7c}
@deffn {C Function} gcc_jit_type *gcc_jit_type_get_volatile (gcc_jit_type@w{ }*type)

Given type "T", get type "volatile T".
@end deffn

@geindex gcc_jit_context_new_array_type (C function)
@anchor{topics/types gcc_jit_context_new_array_type}@anchor{7d}
@deffn {C Function} gcc_jit_type *            gcc_jit_context_new_array_type (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, gcc_jit_type@w{ }*element_type, int@w{ }num_elements)

Given type "T", get type "T[N]" (for a constant N).
@end deffn

@node Structures and unions,,Pointers const and volatile,Types
@anchor{topics/types structures-and-unions}@anchor{7e}
@subsection Structures and unions


@geindex gcc_jit_struct (C type)
@anchor{topics/types gcc_jit_struct}@anchor{7f}
@deffn {C Type} gcc_jit_struct
@end deffn

A compound type analagous to a C @cite{struct}.

@geindex gcc_jit_field (C type)
@anchor{topics/types gcc_jit_field}@anchor{80}
@deffn {C Type} gcc_jit_field
@end deffn

A field within a @pxref{7f,,gcc_jit_struct}.

You can model C @cite{struct} types by creating @pxref{7f,,gcc_jit_struct *} and
@pxref{80,,gcc_jit_field} instances, in either order:


@itemize *

@item 
by creating the fields, then the structure.  For example, to model:

@example
struct coord @{double x; double y; @};
@end example

@noindent

you could call:

@example
gcc_jit_field *field_x =
  gcc_jit_context_new_field (ctxt, NULL, double_type, "x");
gcc_jit_field *field_y =
  gcc_jit_context_new_field (ctxt, NULL, double_type, "y");
gcc_jit_field *fields[2] = @{field_x, field_y@};
gcc_jit_struct *coord =
  gcc_jit_context_new_struct_type (ctxt, NULL, "coord", 2, fields);
@end example

@noindent

@item 
by creating the structure, then populating it with fields, typically
to allow modelling self-referential structs such as:

@example
struct node @{ int m_hash; struct node *m_next; @};
@end example

@noindent

like this:

@example
gcc_jit_type *node =
  gcc_jit_context_new_opaque_struct (ctxt, NULL, "node");
gcc_jit_type *node_ptr =
  gcc_jit_type_get_pointer (node);
gcc_jit_field *field_hash =
  gcc_jit_context_new_field (ctxt, NULL, int_type, "m_hash");
gcc_jit_field *field_next =
  gcc_jit_context_new_field (ctxt, NULL, node_ptr, "m_next");
gcc_jit_field *fields[2] = @{field_hash, field_next@};
gcc_jit_struct_set_fields (node, NULL, 2, fields);
@end example

@noindent
@end itemize

@geindex gcc_jit_context_new_field (C function)
@anchor{topics/types gcc_jit_context_new_field}@anchor{81}
@deffn {C Function} gcc_jit_field *           gcc_jit_context_new_field (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, gcc_jit_type@w{ }*type, const char@w{ }*name)

Construct a new field, with the given type and name.

The parameter @code{name} must be non-NULL.  The call takes a copy of the
underlying string, so it is valid to pass in a pointer to an on-stack
buffer.
@end deffn

@geindex gcc_jit_field_as_object (C function)
@anchor{topics/types gcc_jit_field_as_object}@anchor{82}
@deffn {C Function} gcc_jit_object *           gcc_jit_field_as_object (gcc_jit_field@w{ }*field)

Upcast from field to object.
@end deffn

@geindex gcc_jit_context_new_struct_type (C function)
@anchor{topics/types gcc_jit_context_new_struct_type}@anchor{83}
@deffn {C Function} gcc_jit_struct *gcc_jit_context_new_struct_type (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, const char@w{ }*name, int@w{ }num_fields, gcc_jit_field@w{ }**fields)

@quotation

Construct a new struct type, with the given name and fields.

The parameter @code{name} must be non-NULL.  The call takes a copy of
the underlying string, so it is valid to pass in a pointer to an
on-stack buffer.
@end quotation
@end deffn

@geindex gcc_jit_context_new_opaque_struct (C function)
@anchor{topics/types gcc_jit_context_new_opaque_struct}@anchor{84}
@deffn {C Function} gcc_jit_struct *         gcc_jit_context_new_opaque_struct (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, const char@w{ }*name)

Construct a new struct type, with the given name, but without
specifying the fields.   The fields can be omitted (in which case the
size of the struct is not known), or later specified using
@pxref{85,,gcc_jit_struct_set_fields()}.

The parameter @code{name} must be non-NULL.  The call takes a copy of
the underlying string, so it is valid to pass in a pointer to an
on-stack buffer.
@end deffn

@geindex gcc_jit_struct_as_type (C function)
@anchor{topics/types gcc_jit_struct_as_type}@anchor{86}
@deffn {C Function} gcc_jit_type *           gcc_jit_struct_as_type (gcc_jit_struct@w{ }*struct_type)

Upcast from struct to type.
@end deffn

@geindex gcc_jit_struct_set_fields (C function)
@anchor{topics/types gcc_jit_struct_set_fields}@anchor{85}
@deffn {C Function} void           gcc_jit_struct_set_fields (gcc_jit_struct@w{ }*struct_type, gcc_jit_location@w{ }*loc, int@w{ }num_fields, gcc_jit_field@w{ }**fields)

Populate the fields of a formerly-opaque struct type.

This can only be called once on a given struct type.
@end deffn

@geindex gcc_jit_context_new_union_type (C function)
@anchor{topics/types gcc_jit_context_new_union_type}@anchor{87}
@deffn {C Function} gcc_jit_type *         gcc_jit_context_new_union_type (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, const char@w{ }*name, int@w{ }num_fields, gcc_jit_field@w{ }**fields)

Construct a new union type, with the given name and fields.

The parameter @code{name} must be non-NULL.  It is copied, so the input
buffer does not need to outlive the call.

Example of use:

@example

union int_or_float
@{
  int as_int;
  float as_float;
@};

void
create_code (gcc_jit_context *ctxt, void *user_data)
@{
  /* Let's try to inject the equivalent of:
     float
     test_union (int i)
     @{
        union int_or_float u;
	u.as_int = i;
	return u.as_float;
     @}
  */
  gcc_jit_type *int_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
  gcc_jit_type *float_type =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_FLOAT);
  gcc_jit_field *as_int =
    gcc_jit_context_new_field (ctxt,
                               NULL,
                               int_type,
                               "as_int");
  gcc_jit_field *as_float =
    gcc_jit_context_new_field (ctxt,
                               NULL,
                               float_type,
                               "as_float");
  gcc_jit_field *fields[] = @{as_int, as_float@};
  gcc_jit_type *union_type =
    gcc_jit_context_new_union_type (ctxt, NULL,
				    "int_or_float", 2, fields);

  /* Build the test function.  */
  gcc_jit_param *param_i =
    gcc_jit_context_new_param (ctxt, NULL, int_type, "i");
  gcc_jit_function *test_fn =
    gcc_jit_context_new_function (ctxt, NULL,
                                  GCC_JIT_FUNCTION_EXPORTED,
                                  float_type,
                                  "test_union",
                                  1, &param_i,
                                  0);

  gcc_jit_lvalue *u =
    gcc_jit_function_new_local (test_fn, NULL,
				union_type, "u");

  gcc_jit_block *block = gcc_jit_function_new_block (test_fn, NULL);

  /* u.as_int = i; */
  gcc_jit_block_add_assignment (
    block,
    NULL,
    /* "u.as_int = ..." */
    gcc_jit_lvalue_access_field (u,
				 NULL,
				 as_int),
    gcc_jit_param_as_rvalue (param_i));

  /* return u.as_float; */
  gcc_jit_block_end_with_return (
    block, NULL,
    gcc_jit_rvalue_access_field (gcc_jit_lvalue_as_rvalue (u),
				 NULL,
				 as_float));
@}


@end example

@noindent
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Expressions,Creating and using functions,Types,Topic Reference
@anchor{topics/expressions expressions}@anchor{88}@anchor{topics/expressions doc}@anchor{89}
@section Expressions


@menu
* Rvalues:: 
* Lvalues:: 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions. 

Rvalues

* Simple expressions:: 
* Unary Operations:: 
* Binary Operations:: 
* Comparisons:: 
* Function calls:: 
* Type-coercion:: 

Lvalues

* Global variables:: 

@end menu


@node Rvalues,Lvalues,,Expressions
@anchor{topics/expressions rvalues}@anchor{8a}
@subsection Rvalues


@geindex gcc_jit_rvalue (C type)
@anchor{topics/expressions gcc_jit_rvalue}@anchor{13}
@deffn {C Type} gcc_jit_rvalue
@end deffn

A @pxref{13,,gcc_jit_rvalue *} is an expression that can be computed.

It can be simple, e.g.:

@quotation


@itemize *

@item 
an integer value e.g. @cite{0} or @cite{42}

@item 
a string literal e.g. @cite{"Hello world"}

@item 
a variable e.g. @cite{i}.  These are also lvalues (see below).
@end itemize
@end quotation

or compound e.g.:

@quotation


@itemize *

@item 
a unary expression e.g. @cite{!cond}

@item 
a binary expression e.g. @cite{(a + b)}

@item 
a function call e.g. @cite{get_distance (&player_ship@comma{} &target)}

@item 
etc.
@end itemize
@end quotation

Every rvalue has an associated type, and the API will check to ensure
that types match up correctly (otherwise the context will emit an error).

@geindex gcc_jit_rvalue_get_type (C function)
@anchor{topics/expressions gcc_jit_rvalue_get_type}@anchor{8b}
@deffn {C Function} gcc_jit_type *gcc_jit_rvalue_get_type (gcc_jit_rvalue@w{ }*rvalue)

Get the type of this rvalue.
@end deffn

@geindex gcc_jit_rvalue_as_object (C function)
@anchor{topics/expressions gcc_jit_rvalue_as_object}@anchor{14}
@deffn {C Function} gcc_jit_object *gcc_jit_rvalue_as_object (gcc_jit_rvalue@w{ }*rvalue)

Upcast the given rvalue to be an object.
@end deffn

@menu
* Simple expressions:: 
* Unary Operations:: 
* Binary Operations:: 
* Comparisons:: 
* Function calls:: 
* Type-coercion:: 

@end menu

@node Simple expressions,Unary Operations,,Rvalues
@anchor{topics/expressions simple-expressions}@anchor{8c}
@subsubsection Simple expressions


@geindex gcc_jit_context_new_rvalue_from_int (C function)
@anchor{topics/expressions gcc_jit_context_new_rvalue_from_int}@anchor{30}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_rvalue_from_int (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*numeric_type, int@w{ }value)

Given a numeric type (integer or floating point), build an rvalue for
the given constant @code{int} value.
@end deffn

@geindex gcc_jit_context_new_rvalue_from_long (C function)
@anchor{topics/expressions gcc_jit_context_new_rvalue_from_long}@anchor{8d}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_rvalue_from_long (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*numeric_type, long@w{ }value)

Given a numeric type (integer or floating point), build an rvalue for
the given constant @code{long} value.
@end deffn

@geindex gcc_jit_context_zero (C function)
@anchor{topics/expressions gcc_jit_context_zero}@anchor{2b}
@deffn {C Function} gcc_jit_rvalue *gcc_jit_context_zero (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*numeric_type)

Given a numeric type (integer or floating point), get the rvalue for
zero.  Essentially this is just a shortcut for:

@example
gcc_jit_context_new_rvalue_from_int (ctxt, numeric_type, 0)
@end example

@noindent
@end deffn

@geindex gcc_jit_context_one (C function)
@anchor{topics/expressions gcc_jit_context_one}@anchor{2f}
@deffn {C Function} gcc_jit_rvalue *gcc_jit_context_one (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*numeric_type)

Given a numeric type (integer or floating point), get the rvalue for
one.  Essentially this is just a shortcut for:

@example
gcc_jit_context_new_rvalue_from_int (ctxt, numeric_type, 1)
@end example

@noindent
@end deffn

@geindex gcc_jit_context_new_rvalue_from_double (C function)
@anchor{topics/expressions gcc_jit_context_new_rvalue_from_double}@anchor{31}
@deffn {C Function} gcc_jit_rvalue *            gcc_jit_context_new_rvalue_from_double (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*numeric_type, double@w{ }value)

Given a numeric type (integer or floating point), build an rvalue for
the given constant @code{double} value.
@end deffn

@geindex gcc_jit_context_new_rvalue_from_ptr (C function)
@anchor{topics/expressions gcc_jit_context_new_rvalue_from_ptr}@anchor{8e}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_rvalue_from_ptr (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*pointer_type, void@w{ }*value)

Given a pointer type, build an rvalue for the given address.
@end deffn

@geindex gcc_jit_context_null (C function)
@anchor{topics/expressions gcc_jit_context_null}@anchor{8f}
@deffn {C Function} gcc_jit_rvalue *gcc_jit_context_null (gcc_jit_context@w{ }*ctxt, gcc_jit_type@w{ }*pointer_type)

Given a pointer type, build an rvalue for @code{NULL}.  Essentially this
is just a shortcut for:

@example
gcc_jit_context_new_rvalue_from_ptr (ctxt, pointer_type, NULL)
@end example

@noindent
@end deffn

@geindex gcc_jit_context_new_string_literal (C function)
@anchor{topics/expressions gcc_jit_context_new_string_literal}@anchor{90}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_string_literal (gcc_jit_context@w{ }*ctxt, const char@w{ }*value)

Generate an rvalue for the given NIL-terminated string, of type
@code{GCC_JIT_TYPE_CONST_CHAR_PTR}.

The parameter @code{value} must be non-NULL.  The call takes a copy of the
underlying string, so it is valid to pass in a pointer to an on-stack
buffer.
@end deffn

@node Unary Operations,Binary Operations,Simple expressions,Rvalues
@anchor{topics/expressions unary-operations}@anchor{91}
@subsubsection Unary Operations


@geindex gcc_jit_context_new_unary_op (C function)
@anchor{topics/expressions gcc_jit_context_new_unary_op}@anchor{92}
@deffn {C Function} gcc_jit_rvalue *            gcc_jit_context_new_unary_op (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, enum gcc_jit_unary_op@w{ }op, gcc_jit_type@w{ }*result_type, gcc_jit_rvalue@w{ }*rvalue)

Build a unary operation out of an input rvalue.
@end deffn

@geindex gcc_jit_unary_op (C type)
@anchor{topics/expressions gcc_jit_unary_op}@anchor{93}
@deffn {C Type} enum gcc_jit_unary_op
@end deffn

The available unary operations are:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxx} 
@headitem

Unary Operation

@tab

C equivalent

@item

@pxref{94,,GCC_JIT_UNARY_OP_MINUS}

@tab

@cite{-(EXPR)}

@item

@pxref{95,,GCC_JIT_UNARY_OP_BITWISE_NEGATE}

@tab

@cite{~(EXPR)}

@item

@pxref{96,,GCC_JIT_UNARY_OP_LOGICAL_NEGATE}

@tab

@cite{!(EXPR)}

@item

@pxref{97,,GCC_JIT_UNARY_OP_ABS}

@tab

@cite{abs (EXPR)}

@end multitable


@geindex GCC_JIT_UNARY_OP_MINUS (C macro)
@anchor{topics/expressions GCC_JIT_UNARY_OP_MINUS}@anchor{94}
@deffn {C Macro} GCC_JIT_UNARY_OP_MINUS

Negate an arithmetic value; analogous to:

@example
-(EXPR)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_UNARY_OP_BITWISE_NEGATE (C macro)
@anchor{topics/expressions GCC_JIT_UNARY_OP_BITWISE_NEGATE}@anchor{95}
@deffn {C Macro} GCC_JIT_UNARY_OP_BITWISE_NEGATE

Bitwise negation of an integer value (one's complement); analogous
to:

@example
~(EXPR)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_UNARY_OP_LOGICAL_NEGATE (C macro)
@anchor{topics/expressions GCC_JIT_UNARY_OP_LOGICAL_NEGATE}@anchor{96}
@deffn {C Macro} GCC_JIT_UNARY_OP_LOGICAL_NEGATE

Logical negation of an arithmetic or pointer value; analogous to:

@example
!(EXPR)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_UNARY_OP_ABS (C macro)
@anchor{topics/expressions GCC_JIT_UNARY_OP_ABS}@anchor{97}
@deffn {C Macro} GCC_JIT_UNARY_OP_ABS

Absolute value of an arithmetic expression; analogous to:

@example
abs (EXPR)
@end example

@noindent

in C.
@end deffn

@node Binary Operations,Comparisons,Unary Operations,Rvalues
@anchor{topics/expressions binary-operations}@anchor{98}
@subsubsection Binary Operations


@geindex gcc_jit_context_new_binary_op (C function)
@anchor{topics/expressions gcc_jit_context_new_binary_op}@anchor{12}
@deffn {C Function} gcc_jit_rvalue *gcc_jit_context_new_binary_op (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, enum gcc_jit_binary_op@w{ }op, gcc_jit_type@w{ }*result_type, gcc_jit_rvalue@w{ }*a, gcc_jit_rvalue@w{ }*b)

Build a binary operation out of two constituent rvalues.
@end deffn

@geindex gcc_jit_binary_op (C type)
@anchor{topics/expressions gcc_jit_binary_op}@anchor{99}
@deffn {C Type} enum gcc_jit_binary_op
@end deffn

The available binary operations are:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxx} 
@headitem

Binary Operation

@tab

C equivalent

@item

@pxref{9a,,GCC_JIT_BINARY_OP_PLUS}

@tab

@cite{x + y}

@item

@pxref{9b,,GCC_JIT_BINARY_OP_MINUS}

@tab

@cite{x - y}

@item

@pxref{9c,,GCC_JIT_BINARY_OP_MULT}

@tab

@cite{x * y}

@item

@pxref{9d,,GCC_JIT_BINARY_OP_DIVIDE}

@tab

@cite{x / y}

@item

@pxref{9e,,GCC_JIT_BINARY_OP_MODULO}

@tab

@cite{x % y}

@item

@pxref{9f,,GCC_JIT_BINARY_OP_BITWISE_AND}

@tab

@cite{x & y}

@item

@pxref{a0,,GCC_JIT_BINARY_OP_BITWISE_XOR}

@tab

@cite{x ^ y}

@item

@pxref{a1,,GCC_JIT_BINARY_OP_BITWISE_OR}

@tab

@cite{x | y}

@item

@pxref{a2,,GCC_JIT_BINARY_OP_LOGICAL_AND}

@tab

@cite{x && y}

@item

@pxref{a3,,GCC_JIT_BINARY_OP_LOGICAL_OR}

@tab

@cite{x || y}

@item

@pxref{a4,,GCC_JIT_BINARY_OP_LSHIFT}

@tab

@cite{x << y}

@item

@pxref{a5,,GCC_JIT_BINARY_OP_RSHIFT}

@tab

@cite{x >> y}

@end multitable


@geindex GCC_JIT_BINARY_OP_PLUS (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_PLUS}@anchor{9a}
@deffn {C Macro} GCC_JIT_BINARY_OP_PLUS

Addition of arithmetic values; analogous to:

@example
(EXPR_A) + (EXPR_B)
@end example

@noindent

in C.

For pointer addition, use @pxref{a6,,gcc_jit_context_new_array_access()}.
@end deffn

@geindex GCC_JIT_BINARY_OP_MINUS (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_MINUS}@anchor{9b}
@deffn {C Macro} GCC_JIT_BINARY_OP_MINUS

Subtraction of arithmetic values; analogous to:

@example
(EXPR_A) - (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_MULT (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_MULT}@anchor{9c}
@deffn {C Macro} GCC_JIT_BINARY_OP_MULT

Multiplication of a pair of arithmetic values; analogous to:

@example
(EXPR_A) * (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_DIVIDE (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_DIVIDE}@anchor{9d}
@deffn {C Macro} GCC_JIT_BINARY_OP_DIVIDE

Quotient of division of arithmetic values; analogous to:

@example
(EXPR_A) / (EXPR_B)
@end example

@noindent

in C.

The result type affects the kind of division: if the result type is
integer-based, then the result is truncated towards zero, whereas
a floating-point result type indicates floating-point division.
@end deffn

@geindex GCC_JIT_BINARY_OP_MODULO (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_MODULO}@anchor{9e}
@deffn {C Macro} GCC_JIT_BINARY_OP_MODULO

Remainder of division of arithmetic values; analogous to:

@example
(EXPR_A) % (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_BITWISE_AND (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_BITWISE_AND}@anchor{9f}
@deffn {C Macro} GCC_JIT_BINARY_OP_BITWISE_AND

Bitwise AND; analogous to:

@example
(EXPR_A) & (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_BITWISE_XOR (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_BITWISE_XOR}@anchor{a0}
@deffn {C Macro} GCC_JIT_BINARY_OP_BITWISE_XOR

Bitwise exclusive OR; analogous to:

@example
(EXPR_A) ^ (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_BITWISE_OR (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_BITWISE_OR}@anchor{a1}
@deffn {C Macro} GCC_JIT_BINARY_OP_BITWISE_OR

Bitwise inclusive OR; analogous to:

@example
(EXPR_A) | (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_LOGICAL_AND (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_LOGICAL_AND}@anchor{a2}
@deffn {C Macro} GCC_JIT_BINARY_OP_LOGICAL_AND

Logical AND; analogous to:

@example
(EXPR_A) && (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_LOGICAL_OR (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_LOGICAL_OR}@anchor{a3}
@deffn {C Macro} GCC_JIT_BINARY_OP_LOGICAL_OR

Logical OR; analogous to:

@example
(EXPR_A) || (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_LSHIFT (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_LSHIFT}@anchor{a4}
@deffn {C Macro} GCC_JIT_BINARY_OP_LSHIFT

Left shift; analogous to:

@example
(EXPR_A) << (EXPR_B)
@end example

@noindent

in C.
@end deffn

@geindex GCC_JIT_BINARY_OP_RSHIFT (C macro)
@anchor{topics/expressions GCC_JIT_BINARY_OP_RSHIFT}@anchor{a5}
@deffn {C Macro} GCC_JIT_BINARY_OP_RSHIFT

Right shift; analogous to:

@example
(EXPR_A) >> (EXPR_B)
@end example

@noindent

in C.
@end deffn

@node Comparisons,Function calls,Binary Operations,Rvalues
@anchor{topics/expressions comparisons}@anchor{a7}
@subsubsection Comparisons


@geindex gcc_jit_context_new_comparison (C function)
@anchor{topics/expressions gcc_jit_context_new_comparison}@anchor{2c}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_comparison (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, enum gcc_jit_comparison@w{ }op, gcc_jit_rvalue@w{ }*a, gcc_jit_rvalue@w{ }*b)

Build a boolean rvalue out of the comparison of two other rvalues.
@end deffn

@geindex gcc_jit_comparison (C type)
@anchor{topics/expressions gcc_jit_comparison}@anchor{a8}
@deffn {C Type} enum gcc_jit_comparison
@end deffn


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxx} 
@headitem

Comparison

@tab

C equivalent

@item

@code{GCC_JIT_COMPARISON_EQ}

@tab

@cite{x == y}

@item

@code{GCC_JIT_COMPARISON_NE}

@tab

@cite{x != y}

@item

@code{GCC_JIT_COMPARISON_LT}

@tab

@cite{x < y}

@item

@code{GCC_JIT_COMPARISON_LE}

@tab

@cite{x <= y}

@item

@code{GCC_JIT_COMPARISON_GT}

@tab

@cite{x > y}

@item

@code{GCC_JIT_COMPARISON_GE}

@tab

@cite{x >= y}

@end multitable


@node Function calls,Type-coercion,Comparisons,Rvalues
@anchor{topics/expressions function-calls}@anchor{a9}
@subsubsection Function calls


@geindex gcc_jit_context_new_call (C function)
@anchor{topics/expressions gcc_jit_context_new_call}@anchor{aa}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_call (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, gcc_jit_function@w{ }*func, int@w{ }numargs, gcc_jit_rvalue@w{ }**args)

Given a function and the given table of argument rvalues, construct a
call to the function, with the result as an rvalue.

@cartouche
@quotation Note 
@pxref{aa,,gcc_jit_context_new_call()} merely builds a
@pxref{13,,gcc_jit_rvalue} i.e. an expression that can be evaluated,
perhaps as part of a more complicated expression.
The call @emph{won't} happen unless you add a statement to a function
that evaluates the expression.

For example, if you want to call a function and discard the result
(or to call a function with @code{void} return type), use
@pxref{ab,,gcc_jit_block_add_eval()}:

@example
/* Add "(void)printf (arg0, arg1);".  */
gcc_jit_block_add_eval (
  block, NULL,
  gcc_jit_context_new_call (
    ctxt,
    NULL,
    printf_func,
    2, args));
@end example

@noindent
@end quotation
@end cartouche
@end deffn

@node Type-coercion,,Function calls,Rvalues
@anchor{topics/expressions type-coercion}@anchor{ac}
@subsubsection Type-coercion


@geindex gcc_jit_context_new_cast (C function)
@anchor{topics/expressions gcc_jit_context_new_cast}@anchor{ad}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_context_new_cast (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, gcc_jit_rvalue@w{ }*rvalue, gcc_jit_type@w{ }*type)

Given an rvalue of T, construct another rvalue of another type.

Currently only a limited set of conversions are possible:

@quotation


@itemize *

@item 
int <-> float

@item 
int <-> bool

@item 
P*  <-> Q*, for pointer types P and Q
@end itemize
@end quotation
@end deffn

@node Lvalues,Working with pointers structs and unions,Rvalues,Expressions
@anchor{topics/expressions lvalues}@anchor{ae}
@subsection Lvalues


@geindex gcc_jit_lvalue (C type)
@anchor{topics/expressions gcc_jit_lvalue}@anchor{24}
@deffn {C Type} gcc_jit_lvalue
@end deffn

An lvalue is something that can of the @emph{left}-hand side of an assignment:
a storage area (such as a variable).  It is also usable as an rvalue,
where the rvalue is computed by reading from the storage area.

@geindex gcc_jit_lvalue_as_object (C function)
@anchor{topics/expressions gcc_jit_lvalue_as_object}@anchor{af}
@deffn {C Function} gcc_jit_object *           gcc_jit_lvalue_as_object (gcc_jit_lvalue@w{ }*lvalue)

Upcast an lvalue to be an object.
@end deffn

@geindex gcc_jit_lvalue_as_rvalue (C function)
@anchor{topics/expressions gcc_jit_lvalue_as_rvalue}@anchor{b0}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_lvalue_as_rvalue (gcc_jit_lvalue@w{ }*lvalue)

Upcast an lvalue to be an rvalue.
@end deffn

@geindex gcc_jit_lvalue_get_address (C function)
@anchor{topics/expressions gcc_jit_lvalue_get_address}@anchor{b1}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_lvalue_get_address (gcc_jit_lvalue@w{ }*lvalue, gcc_jit_location@w{ }*loc)

Take the address of an lvalue; analogous to:

@example
&(EXPR)
@end example

@noindent

in C.
@end deffn

@menu
* Global variables:: 

@end menu

@node Global variables,,,Lvalues
@anchor{topics/expressions global-variables}@anchor{b2}
@subsubsection Global variables


@geindex gcc_jit_context_new_global (C function)
@anchor{topics/expressions gcc_jit_context_new_global}@anchor{b3}
@deffn {C Function} gcc_jit_lvalue *           gcc_jit_context_new_global (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, enum gcc_jit_global_kind@w{ }kind, gcc_jit_type@w{ }*type, const char@w{ }*name)

Add a new global variable of the given type and name to the context.

The parameter @code{name} must be non-NULL.  The call takes a copy of the
underlying string, so it is valid to pass in a pointer to an on-stack
buffer.

The "kind" parameter determines the visibility of the "global" outside
of the @pxref{16,,gcc_jit_result}:

@geindex gcc_jit_global_kind (C type)
@anchor{topics/expressions gcc_jit_global_kind}@anchor{b4}
@deffn {C Type} enum gcc_jit_global_kind
@end deffn

@geindex GCC_JIT_GLOBAL_EXPORTED (C macro)
@anchor{topics/expressions GCC_JIT_GLOBAL_EXPORTED}@anchor{b5}
@deffn {C Macro} GCC_JIT_GLOBAL_EXPORTED

Global is defined by the client code and is visible
by name outside of this JIT context via
@pxref{b6,,gcc_jit_result_get_global()} (and this value is required for
the global to be accessible via that entrypoint).
@end deffn

@geindex GCC_JIT_GLOBAL_INTERNAL (C macro)
@anchor{topics/expressions GCC_JIT_GLOBAL_INTERNAL}@anchor{b7}
@deffn {C Macro} GCC_JIT_GLOBAL_INTERNAL

Global is defined by the client code, but is invisible
outside of it.  Analogous to a "static" global within a .c file.
Specifically, the variable will only be visible within this
context and within child contexts.
@end deffn

@geindex GCC_JIT_GLOBAL_IMPORTED (C macro)
@anchor{topics/expressions GCC_JIT_GLOBAL_IMPORTED}@anchor{b8}
@deffn {C Macro} GCC_JIT_GLOBAL_IMPORTED

Global is not defined by the client code; we're merely
referring to it.  Analogous to using an "extern" global from a
header file.
@end deffn
@end deffn

@node Working with pointers structs and unions,,Lvalues,Expressions
@anchor{topics/expressions working-with-pointers-structs-and-unions}@anchor{b9}
@subsection Working with pointers, structs and unions


@geindex gcc_jit_rvalue_dereference (C function)
@anchor{topics/expressions gcc_jit_rvalue_dereference}@anchor{ba}
@deffn {C Function} gcc_jit_lvalue *           gcc_jit_rvalue_dereference (gcc_jit_rvalue@w{ }*rvalue, gcc_jit_location@w{ }*loc)

Given an rvalue of pointer type @code{T *}, dereferencing the pointer,
getting an lvalue of type @code{T}.  Analogous to:

@example
*(EXPR)
@end example

@noindent

in C.
@end deffn

Field access is provided separately for both lvalues and rvalues.

@geindex gcc_jit_lvalue_access_field (C function)
@anchor{topics/expressions gcc_jit_lvalue_access_field}@anchor{bb}
@deffn {C Function} gcc_jit_lvalue *           gcc_jit_lvalue_access_field (gcc_jit_lvalue@w{ }*struct_, gcc_jit_location@w{ }*loc, gcc_jit_field@w{ }*field)

Given an lvalue of struct or union type, access the given field,
getting an lvalue of the field's type.  Analogous to:

@example
(EXPR).field = ...;
@end example

@noindent

in C.
@end deffn

@geindex gcc_jit_rvalue_access_field (C function)
@anchor{topics/expressions gcc_jit_rvalue_access_field}@anchor{bc}
@deffn {C Function} gcc_jit_rvalue *           gcc_jit_rvalue_access_field (gcc_jit_rvalue@w{ }*struct_, gcc_jit_location@w{ }*loc, gcc_jit_field@w{ }*field)

Given an rvalue of struct or union type, access the given field
as an rvalue.  Analogous to:

@example
(EXPR).field
@end example

@noindent

in C.
@end deffn

@geindex gcc_jit_rvalue_dereference_field (C function)
@anchor{topics/expressions gcc_jit_rvalue_dereference_field}@anchor{bd}
@deffn {C Function} gcc_jit_lvalue *           gcc_jit_rvalue_dereference_field (gcc_jit_rvalue@w{ }*ptr, gcc_jit_location@w{ }*loc, gcc_jit_field@w{ }*field)

Given an rvalue of pointer type @code{T *} where T is of struct or union
type, access the given field as an lvalue.  Analogous to:

@example
(EXPR)->field
@end example

@noindent

in C, itself equivalent to @code{(*EXPR).FIELD}.
@end deffn

@geindex gcc_jit_context_new_array_access (C function)
@anchor{topics/expressions gcc_jit_context_new_array_access}@anchor{a6}
@deffn {C Function} gcc_jit_lvalue *           gcc_jit_context_new_array_access (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, gcc_jit_rvalue@w{ }*ptr, gcc_jit_rvalue@w{ }*index)

Given an rvalue of pointer type @code{T *}, get at the element @cite{T} at
the given index, using standard C array indexing rules i.e. each
increment of @code{index} corresponds to @code{sizeof(T)} bytes.
Analogous to:

@example
PTR[INDEX]
@end example

@noindent

in C (or, indeed, to @code{PTR + INDEX}).
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Creating and using functions,Source Locations,Expressions,Topic Reference
@anchor{topics/functions doc}@anchor{be}@anchor{topics/functions creating-and-using-functions}@anchor{bf}
@section Creating and using functions


@menu
* Params:: 
* Functions:: 
* Blocks:: 
* Statements:: 

@end menu

@node Params,Functions,,Creating and using functions
@anchor{topics/functions params}@anchor{c0}
@subsection Params


@geindex gcc_jit_param (C type)
@anchor{topics/functions gcc_jit_param}@anchor{25}
@deffn {C Type} gcc_jit_param

A @cite{gcc_jit_param} represents a parameter to a function.
@end deffn

@geindex gcc_jit_context_new_param (C function)
@anchor{topics/functions gcc_jit_context_new_param}@anchor{10}
@deffn {C Function} gcc_jit_param *           gcc_jit_context_new_param (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, gcc_jit_type@w{ }*type, const char@w{ }*name)

In preparation for creating a function, create a new parameter of the
given type and name.

The parameter @code{name} must be non-NULL.  The call takes a copy of the
underlying string, so it is valid to pass in a pointer to an on-stack
buffer.
@end deffn

Parameters are lvalues, and thus are also rvalues (and objects), so the
following upcasts are available:

@geindex gcc_jit_param_as_lvalue (C function)
@anchor{topics/functions gcc_jit_param_as_lvalue}@anchor{c1}
@deffn {C Function} gcc_jit_lvalue *            gcc_jit_param_as_lvalue (gcc_jit_param@w{ }*param)

Upcasting from param to lvalue.
@end deffn

@geindex gcc_jit_param_as_rvalue (C function)
@anchor{topics/functions gcc_jit_param_as_rvalue}@anchor{c2}
@deffn {C Function} gcc_jit_rvalue *            gcc_jit_param_as_rvalue (gcc_jit_param@w{ }*param)

Upcasting from param to rvalue.
@end deffn

@geindex gcc_jit_param_as_object (C function)
@anchor{topics/functions gcc_jit_param_as_object}@anchor{c3}
@deffn {C Function} gcc_jit_object *            gcc_jit_param_as_object (gcc_jit_param@w{ }*param)

Upcasting from param to object.
@end deffn

@node Functions,Blocks,Params,Creating and using functions
@anchor{topics/functions functions}@anchor{c4}
@subsection Functions


@geindex gcc_jit_function (C type)
@anchor{topics/functions gcc_jit_function}@anchor{29}
@deffn {C Type} gcc_jit_function

A @cite{gcc_jit_function} represents a function - either one that we're
creating ourselves, or one that we're referencing.
@end deffn

@geindex gcc_jit_context_new_function (C function)
@anchor{topics/functions gcc_jit_context_new_function}@anchor{11}
@deffn {C Function} gcc_jit_function *            gcc_jit_context_new_function (gcc_jit_context@w{ }*ctxt, gcc_jit_location@w{ }*loc, enum gcc_jit_function_kind@w{ }kind, gcc_jit_type@w{ }*return_type, const char@w{ }*name, int@w{ }num_params, gcc_jit_param@w{ }**params, int@w{ }is_variadic)

Create a gcc_jit_function with the given name and parameters.

@geindex gcc_jit_function_kind (C type)
@anchor{topics/functions gcc_jit_function_kind}@anchor{c5}
@deffn {C Type} enum gcc_jit_function_kind
@end deffn

This enum controls the kind of function created, and has the following
values:

@quotation

@geindex GCC_JIT_FUNCTION_EXPORTED (C macro)
@anchor{topics/functions GCC_JIT_FUNCTION_EXPORTED}@anchor{c6}
@deffn {C Macro} GCC_JIT_FUNCTION_EXPORTED

Function is defined by the client code and visible
by name outside of the JIT.

This value is required if you want to extract machine code
for this function from a @pxref{16,,gcc_jit_result} via
@pxref{17,,gcc_jit_result_get_code()}.
@end deffn

@geindex GCC_JIT_FUNCTION_INTERNAL (C macro)
@anchor{topics/functions GCC_JIT_FUNCTION_INTERNAL}@anchor{c7}
@deffn {C Macro} GCC_JIT_FUNCTION_INTERNAL

Function is defined by the client code, but is invisible
outside of the JIT.  Analogous to a "static" function.
@end deffn

@geindex GCC_JIT_FUNCTION_IMPORTED (C macro)
@anchor{topics/functions GCC_JIT_FUNCTION_IMPORTED}@anchor{c8}
@deffn {C Macro} GCC_JIT_FUNCTION_IMPORTED

Function is not defined by the client code; we're merely
referring to it.  Analogous to using an "extern" function from a
header file.
@end deffn

@geindex GCC_JIT_FUNCTION_ALWAYS_INLINE (C macro)
@anchor{topics/functions GCC_JIT_FUNCTION_ALWAYS_INLINE}@anchor{c9}
@deffn {C Macro} GCC_JIT_FUNCTION_ALWAYS_INLINE

Function is only ever inlined into other functions, and is
invisible outside of the JIT.

Analogous to prefixing with @code{inline} and adding
@code{__attribute__((always_inline))}

Inlining will only occur when the optimization level is
above 0; when optimization is off, this is essentially the
same as GCC_JIT_FUNCTION_INTERNAL.
@end deffn
@end quotation

The parameter @code{name} must be non-NULL.  The call takes a copy of the
underlying string, so it is valid to pass in a pointer to an on-stack
buffer.
@end deffn

@geindex gcc_jit_context_get_builtin_function (C function)
@anchor{topics/functions gcc_jit_context_get_builtin_function}@anchor{ca}
@deffn {C Function} gcc_jit_function *gcc_jit_context_get_builtin_function (gcc_jit_context@w{ }*ctxt, const char@w{ }*name)
@end deffn

@geindex gcc_jit_function_as_object (C function)
@anchor{topics/functions gcc_jit_function_as_object}@anchor{cb}
@deffn {C Function} gcc_jit_object *           gcc_jit_function_as_object (gcc_jit_function@w{ }*func)

Upcasting from function to object.
@end deffn

@geindex gcc_jit_function_get_param (C function)
@anchor{topics/functions gcc_jit_function_get_param}@anchor{cc}
@deffn {C Function} gcc_jit_param *            gcc_jit_function_get_param (gcc_jit_function@w{ }*func, int@w{ }index)

Get the param of the given index (0-based).
@end deffn

@geindex gcc_jit_function_dump_to_dot (C function)
@anchor{topics/functions gcc_jit_function_dump_to_dot}@anchor{33}
@deffn {C Function} void             gcc_jit_function_dump_to_dot (gcc_jit_function@w{ }*func, const char@w{ }*path)

Emit the function in graphviz format to the given path.
@end deffn

@geindex gcc_jit_function_new_local (C function)
@anchor{topics/functions gcc_jit_function_new_local}@anchor{26}
@deffn {C Function} gcc_jit_lvalue *           gcc_jit_function_new_local (gcc_jit_function@w{ }*func, gcc_jit_location@w{ }*loc, gcc_jit_type@w{ }*type, const char@w{ }*name)

Create a new local variable within the function, of the given type and
name.

The parameter @code{name} must be non-NULL.  The call takes a copy of the
underlying string, so it is valid to pass in a pointer to an on-stack
buffer.
@end deffn

@node Blocks,Statements,Functions,Creating and using functions
@anchor{topics/functions blocks}@anchor{cd}
@subsection Blocks


@geindex gcc_jit_block (C type)
@anchor{topics/functions gcc_jit_block}@anchor{28}
@deffn {C Type} gcc_jit_block

A @cite{gcc_jit_block} represents a basic block within a function  i.e. a
sequence of statements with a single entry point and a single exit
point.

The first basic block that you create within a function will
be the entrypoint.

Each basic block that you create within a function must be
terminated, either with a conditional, a jump, a return, or a
switch.

It's legal to have multiple basic blocks that return within
one function.
@end deffn

@geindex gcc_jit_function_new_block (C function)
@anchor{topics/functions gcc_jit_function_new_block}@anchor{ce}
@deffn {C Function} gcc_jit_block *            gcc_jit_function_new_block (gcc_jit_function@w{ }*func, const char@w{ }*name)

Create a basic block of the given name.  The name may be NULL, but
providing meaningful names is often helpful when debugging: it may
show up in dumps of the internal representation, and in error
messages.  It is copied, so the input buffer does not need to outlive
the call; you can pass in a pointer to an on-stack buffer, e.g.:

@example
for (pc = 0; pc < fn->fn_num_ops; pc++)
 @{
   char buf[16];
   sprintf (buf, "instr%i", pc);
   state.op_blocks[pc] = gcc_jit_function_new_block (state.fn, buf);
 @}
@end example

@noindent
@end deffn

@geindex gcc_jit_block_as_object (C function)
@anchor{topics/functions gcc_jit_block_as_object}@anchor{cf}
@deffn {C Function} gcc_jit_object *            gcc_jit_block_as_object (gcc_jit_block@w{ }*block)

Upcast from block to object.
@end deffn

@geindex gcc_jit_block_get_function (C function)
@anchor{topics/functions gcc_jit_block_get_function}@anchor{d0}
@deffn {C Function} gcc_jit_function *            gcc_jit_block_get_function (gcc_jit_block@w{ }*block)

Which function is this block within?
@end deffn

@node Statements,,Blocks,Creating and using functions
@anchor{topics/functions statements}@anchor{d1}
@subsection Statements


@geindex gcc_jit_block_add_eval (C function)
@anchor{topics/functions gcc_jit_block_add_eval}@anchor{ab}
@deffn {C Function} void           gcc_jit_block_add_eval (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_rvalue@w{ }*rvalue)

Add evaluation of an rvalue, discarding the result
(e.g. a function call that "returns" void).

This is equivalent to this C code:

@example
(void)expression;
@end example

@noindent
@end deffn

@geindex gcc_jit_block_add_assignment (C function)
@anchor{topics/functions gcc_jit_block_add_assignment}@anchor{2a}
@deffn {C Function} void           gcc_jit_block_add_assignment (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_lvalue@w{ }*lvalue, gcc_jit_rvalue@w{ }*rvalue)

Add evaluation of an rvalue, assigning the result to the given
lvalue.

This is roughly equivalent to this C code:

@example
lvalue = rvalue;
@end example

@noindent
@end deffn

@geindex gcc_jit_block_add_assignment_op (C function)
@anchor{topics/functions gcc_jit_block_add_assignment_op}@anchor{2e}
@deffn {C Function} void           gcc_jit_block_add_assignment_op (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_lvalue@w{ }*lvalue, enum gcc_jit_binary_op@w{ }op, gcc_jit_rvalue@w{ }*rvalue)

Add evaluation of an rvalue, using the result to modify an
lvalue.

This is analogous to "+=" and friends:

@example
lvalue += rvalue;
lvalue *= rvalue;
lvalue /= rvalue;
@end example

@noindent

etc.  For example:

@example
/* "i++" */
gcc_jit_block_add_assignment_op (
  loop_body, NULL,
  i,
  GCC_JIT_BINARY_OP_PLUS,
  gcc_jit_context_one (ctxt, int_type));
@end example

@noindent
@end deffn

@geindex gcc_jit_block_add_comment (C function)
@anchor{topics/functions gcc_jit_block_add_comment}@anchor{3d}
@deffn {C Function} void           gcc_jit_block_add_comment (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, const char@w{ }*text)

Add a no-op textual comment to the internal representation of the
code.  It will be optimized away, but will be visible in the dumps
seen via @pxref{66,,GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE}
and @pxref{1c,,GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE},
and thus may be of use when debugging how your project's internal
representation gets converted to the libgccjit IR.

The parameter @code{text} must be non-NULL.  It is copied, so the input
buffer does not need to outlive the call.  For example:

@example
char buf[100];
snprintf (buf, sizeof (buf),
          "op%i: %s",
          pc, opcode_names[op->op_opcode]);
gcc_jit_block_add_comment (block, loc, buf);
@end example

@noindent
@end deffn

@geindex gcc_jit_block_end_with_conditional (C function)
@anchor{topics/functions gcc_jit_block_end_with_conditional}@anchor{2d}
@deffn {C Function} void           gcc_jit_block_end_with_conditional (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_rvalue@w{ }*boolval, gcc_jit_block@w{ }*on_true, gcc_jit_block@w{ }*on_false)

Terminate a block by adding evaluation of an rvalue, branching on the
result to the appropriate successor block.

This is roughly equivalent to this C code:

@example
if (boolval)
  goto on_true;
else
  goto on_false;
@end example

@noindent

block, boolval, on_true, and on_false must be non-NULL.
@end deffn

@geindex gcc_jit_block_end_with_jump (C function)
@anchor{topics/functions gcc_jit_block_end_with_jump}@anchor{d2}
@deffn {C Function} void           gcc_jit_block_end_with_jump (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_block@w{ }*target)

Terminate a block by adding a jump to the given target block.

This is roughly equivalent to this C code:

@example
goto target;
@end example

@noindent
@end deffn

@geindex gcc_jit_block_end_with_return (C function)
@anchor{topics/functions gcc_jit_block_end_with_return}@anchor{d3}
@deffn {C Function} void           gcc_jit_block_end_with_return (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_rvalue@w{ }*rvalue)

Terminate a block by adding evaluation of an rvalue, returning the value.

This is roughly equivalent to this C code:

@example
return expression;
@end example

@noindent
@end deffn

@geindex gcc_jit_block_end_with_void_return (C function)
@anchor{topics/functions gcc_jit_block_end_with_void_return}@anchor{d4}
@deffn {C Function} void           gcc_jit_block_end_with_void_return (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc)

Terminate a block by adding a valueless return, for use within a function
with "void" return type.

This is equivalent to this C code:

@example
return;
@end example

@noindent
@end deffn

@geindex gcc_jit_block_end_with_switch (C function)
@anchor{topics/functions gcc_jit_block_end_with_switch}@anchor{d5}
@deffn {C Function} void           gcc_jit_block_end_with_switch (gcc_jit_block@w{ }*block, gcc_jit_location@w{ }*loc, gcc_jit_rvalue@w{ }*expr, gcc_jit_block@w{ }*default_block, int@w{ }num_cases, gcc_jit_case@w{ }**cases)

Terminate a block by adding evalation of an rvalue, then performing
a multiway branch.

This is roughly equivalent to this C code:

@example
switch (expr)
  @{
  default:
    goto default_block;

  case C0.min_value ... C0.max_value:
    goto C0.dest_block;

  case C1.min_value ... C1.max_value:
    goto C1.dest_block;

  ...etc...

  case C[N - 1].min_value ... C[N - 1].max_value:
    goto C[N - 1].dest_block;
@}
@end example

@noindent

@code{block}, @code{expr}, @code{default_block} and @code{cases} must all be
non-NULL.

@code{expr} must be of the same integer type as all of the @code{min_value}
and @code{max_value} within the cases.

@code{num_cases} must be >= 0.

The ranges of the cases must not overlap (or have duplicate
values).

The API entrypoints relating to switch statements and cases:

@quotation


@itemize *

@item 
@pxref{d5,,gcc_jit_block_end_with_switch()}

@item 
@pxref{d6,,gcc_jit_case_as_object()}

@item 
@pxref{d7,,gcc_jit_context_new_case()}
@end itemize
@end quotation

were added in @pxref{d8,,LIBGCCJIT_ABI_3}; you can test for their presence
using

@example
#ifdef LIBGCCJIT_HAVE_SWITCH_STATEMENTS
@end example

@noindent

@geindex gcc_jit_case (C type)
@anchor{topics/functions gcc_jit_case}@anchor{d9}
@deffn {C Type} gcc_jit_case
@end deffn

A @cite{gcc_jit_case} represents a case within a switch statement, and
is created within a particular @pxref{8,,gcc_jit_context} using
@pxref{d7,,gcc_jit_context_new_case()}.

Each case expresses a multivalued range of integer values.  You
can express single-valued cases by passing in the same value for
both @cite{min_value} and @cite{max_value}.

@geindex gcc_jit_context_new_case (C function)
@anchor{topics/functions gcc_jit_context_new_case}@anchor{d7}
@deffn {C Function} gcc_jit_case *           gcc_jit_context_new_case (gcc_jit_context@w{ }*ctxt, gcc_jit_rvalue@w{ }*min_value, gcc_jit_rvalue@w{ }*max_value, gcc_jit_block@w{ }*dest_block)

Create a new gcc_jit_case instance for use in a switch statement.
@cite{min_value} and @cite{max_value} must be constants of an integer type,
which must match that of the expression of the switch statement.

@cite{dest_block} must be within the same function as the switch
statement.
@end deffn

@geindex gcc_jit_case_as_object (C function)
@anchor{topics/functions gcc_jit_case_as_object}@anchor{d6}
@deffn {C Function} gcc_jit_object *           gcc_jit_case_as_object (gcc_jit_case@w{ }*case_)

Upcast from a case to an object.
@end deffn

Here's an example of creating a switch statement:

@quotation

@example

void
create_code (gcc_jit_context *ctxt, void *user_data)
@{
  /* Let's try to inject the equivalent of:
      int
      test_switch (int x)
      @{
	switch (x)
	  @{
	  case 0 ... 5:
	     return 3;

	  case 25 ... 27:
	     return 4;

	  case -42 ... -17:
	     return 83;

	  case 40:
	     return 8;

	  default:
	     return 10;
	  @}
      @}
   */
  gcc_jit_type *t_int =
    gcc_jit_context_get_type (ctxt, GCC_JIT_TYPE_INT);
  gcc_jit_type *return_type = t_int;
  gcc_jit_param *x =
    gcc_jit_context_new_param (ctxt, NULL, t_int, "x");
  gcc_jit_param *params[1] = @{x@};
  gcc_jit_function *func =
    gcc_jit_context_new_function (ctxt, NULL,
				  GCC_JIT_FUNCTION_EXPORTED,
				  return_type,
				  "test_switch",
				  1, params, 0);

  gcc_jit_block *b_initial =
    gcc_jit_function_new_block (func, "initial");

  gcc_jit_block *b_default =
    gcc_jit_function_new_block (func, "default");
  gcc_jit_block *b_case_0_5 =
    gcc_jit_function_new_block (func, "case_0_5");
  gcc_jit_block *b_case_25_27 =
    gcc_jit_function_new_block (func, "case_25_27");
  gcc_jit_block *b_case_m42_m17 =
    gcc_jit_function_new_block (func, "case_m42_m17");
  gcc_jit_block *b_case_40 =
    gcc_jit_function_new_block (func, "case_40");

  gcc_jit_case *cases[4] = @{
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 0),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 5),
      b_case_0_5),
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 25),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 27),
      b_case_25_27),
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, -42),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, -17),
      b_case_m42_m17),
    gcc_jit_context_new_case (
      ctxt,
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 40),
      gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 40),
      b_case_40)
  @};
  gcc_jit_block_end_with_switch (
    b_initial, NULL,
    gcc_jit_param_as_rvalue (x),
    b_default,
    4, cases);

  gcc_jit_block_end_with_return (
    b_case_0_5, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 3));
  gcc_jit_block_end_with_return (
    b_case_25_27, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 4));
  gcc_jit_block_end_with_return (
    b_case_m42_m17, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 83));
  gcc_jit_block_end_with_return (
    b_case_40, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 8));
  gcc_jit_block_end_with_return (
    b_default, NULL,
    gcc_jit_context_new_rvalue_from_int (ctxt, t_int, 10));
@}


@end example

@noindent
@end quotation
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Source Locations,Compiling a context,Creating and using functions,Topic Reference
@anchor{topics/locations source-locations}@anchor{da}@anchor{topics/locations doc}@anchor{db}
@section Source Locations


@geindex gcc_jit_location (C type)
@anchor{topics/locations gcc_jit_location}@anchor{3b}
@deffn {C Type} gcc_jit_location

A @cite{gcc_jit_location} encapsulates a source code location, so that
you can (optionally) associate locations in your language with
statements in the JIT-compiled code, allowing the debugger to
single-step through your language.

@cite{gcc_jit_location} instances are optional: you can always pass NULL to
any API entrypoint accepting one.

You can construct them using @pxref{41,,gcc_jit_context_new_location()}.

You need to enable @pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} on the
@pxref{8,,gcc_jit_context} for these locations to actually be usable by
the debugger:

@example
gcc_jit_context_set_bool_option (
  ctxt,
  GCC_JIT_BOOL_OPTION_DEBUGINFO,
  1);
@end example

@noindent
@end deffn

@geindex gcc_jit_context_new_location (C function)
@anchor{topics/locations gcc_jit_context_new_location}@anchor{41}
@deffn {C Function} gcc_jit_location *           gcc_jit_context_new_location (gcc_jit_context@w{ }*ctxt, const char@w{ }*filename, int@w{ }line, int@w{ }column)

Create a @cite{gcc_jit_location} instance representing the given source
location.

The parameter @code{filename} must be non-NULL.  The call takes a copy of
the underlying string, so it is valid to pass in a pointer to an
on-stack buffer.
@end deffn

@menu
* Faking it:: 

@end menu

@node Faking it,,,Source Locations
@anchor{topics/locations faking-it}@anchor{dc}
@subsection Faking it


If you don't have source code for your internal representation, but need
to debug, you can generate a C-like representation of the functions in
your context using @pxref{5a,,gcc_jit_context_dump_to_file()}:

@example
gcc_jit_context_dump_to_file (ctxt, "/tmp/something.c",
                              1 /* update_locations */);
@end example

@noindent

This will dump C-like code to the given path.  If the @cite{update_locations}
argument is true, this will also set up @cite{gcc_jit_location} information
throughout the context, pointing at the dump file as if it were a source
file, giving you @emph{something} you can step through in the debugger.

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Compiling a context,ABI and API compatibility,Source Locations,Topic Reference
@anchor{topics/compilation compiling-a-context}@anchor{dd}@anchor{topics/compilation doc}@anchor{de}
@section Compiling a context


Once populated, a @pxref{8,,gcc_jit_context *} can be compiled to
machine code, either in-memory via @pxref{15,,gcc_jit_context_compile()} or
to disk via @pxref{4a,,gcc_jit_context_compile_to_file()}.

You can compile a context multiple times (using either form of
compilation), although any errors that occur on the context will
prevent any future compilation of that context.

@menu
* In-memory compilation:: 
* Ahead-of-time compilation:: 

@end menu

@node In-memory compilation,Ahead-of-time compilation,,Compiling a context
@anchor{topics/compilation in-memory-compilation}@anchor{df}
@subsection In-memory compilation


@geindex gcc_jit_context_compile (C function)
@anchor{topics/compilation gcc_jit_context_compile}@anchor{15}
@deffn {C Function} gcc_jit_result *           gcc_jit_context_compile (gcc_jit_context@w{ }*ctxt)

This calls into GCC and builds the code, returning a
@cite{gcc_jit_result *}.

If the result is non-NULL, the caller becomes responsible for
calling @pxref{39,,gcc_jit_result_release()} on it once they're done
with it.
@end deffn

@geindex gcc_jit_result (C type)
@anchor{topics/compilation gcc_jit_result}@anchor{16}
@deffn {C Type} gcc_jit_result

A @cite{gcc_jit_result} encapsulates the result of compiling a context
in-memory, and the lifetimes of any machine code functions or globals
that are within the result.
@end deffn

@geindex gcc_jit_result_get_code (C function)
@anchor{topics/compilation gcc_jit_result_get_code}@anchor{17}
@deffn {C Function} void *           gcc_jit_result_get_code (gcc_jit_result@w{ }*result, const char@w{ }*funcname)

Locate a given function within the built machine code.

Functions are looked up by name.  For this to succeed, a function
with a name matching @cite{funcname} must have been created on
@cite{result}'s context (or a parent context) via a call to
@pxref{11,,gcc_jit_context_new_function()} with @cite{kind}
@pxref{c6,,GCC_JIT_FUNCTION_EXPORTED}:

@example
gcc_jit_context_new_function (ctxt,
                              any_location, /* or NULL */
                              /* Required for func to be visible to
                                 gcc_jit_result_get_code: */
                              GCC_JIT_FUNCTION_EXPORTED,
                              any_return_type,
                              /* Must string-compare equal: */
                              funcname,
                              /* etc */);
@end example

@noindent

If such a function is not found (or @cite{result} or @cite{funcname} are
@code{NULL}), an error message will be emitted on stderr and
@code{NULL} will be returned.

If the function is found, the result will need to be cast to a
function pointer of the correct type before it can be called.

Note that the resulting machine code becomes invalid after
@pxref{39,,gcc_jit_result_release()} is called on the
@pxref{16,,gcc_jit_result *}; attempting to call it after that may lead
to a segmentation fault.
@end deffn

@geindex gcc_jit_result_get_global (C function)
@anchor{topics/compilation gcc_jit_result_get_global}@anchor{b6}
@deffn {C Function} void *           gcc_jit_result_get_global (gcc_jit_result@w{ }*result, const char@w{ }*name)

Locate a given global within the built machine code.

Globals are looked up by name.  For this to succeed, a global
with a name matching @cite{name} must have been created on
@cite{result}'s context (or a parent context) via a call to
@pxref{b3,,gcc_jit_context_new_global()} with @cite{kind}
@pxref{b5,,GCC_JIT_GLOBAL_EXPORTED}.

If the global is found, the result will need to be cast to a
pointer of the correct type before it can be called.

This is a @emph{pointer} to the global, so e.g. for an @code{int} this is
an @code{int *}.

For example, given an @code{int foo;} created this way:

@example
gcc_jit_lvalue *exported_global =
  gcc_jit_context_new_global (ctxt,
  any_location, /* or NULL */
  GCC_JIT_GLOBAL_EXPORTED,
  int_type,
  "foo");
@end example

@noindent

we can access it like this:

@example
int *ptr_to_foo =
  (int *)gcc_jit_result_get_global (result, "foo");
@end example

@noindent

If such a global is not found (or @cite{result} or @cite{name} are
@code{NULL}), an error message will be emitted on stderr and
@code{NULL} will be returned.

Note that the resulting address becomes invalid after
@pxref{39,,gcc_jit_result_release()} is called on the
@pxref{16,,gcc_jit_result *}; attempting to use it after that may lead
to a segmentation fault.
@end deffn

@geindex gcc_jit_result_release (C function)
@anchor{topics/compilation gcc_jit_result_release}@anchor{39}
@deffn {C Function} void           gcc_jit_result_release (gcc_jit_result@w{ }*result)

Once we're done with the code, this unloads the built .so file.
This cleans up the result; after calling this, it's no longer
valid to use the result, or any code or globals that were obtained
by calling @pxref{17,,gcc_jit_result_get_code()} or
@pxref{b6,,gcc_jit_result_get_global()} on it.
@end deffn

@node Ahead-of-time compilation,,In-memory compilation,Compiling a context
@anchor{topics/compilation ahead-of-time-compilation}@anchor{e0}
@subsection Ahead-of-time compilation


Although libgccjit is primarily aimed at just-in-time compilation, it
can also be used for implementing more traditional ahead-of-time
compilers, via the @pxref{4a,,gcc_jit_context_compile_to_file()}
API entrypoint.

@geindex gcc_jit_context_compile_to_file (C function)
@anchor{topics/compilation gcc_jit_context_compile_to_file}@anchor{4a}
@deffn {C Function} void            gcc_jit_context_compile_to_file (gcc_jit_context@w{ }*ctxt, enum gcc_jit_output_kind@w{ }output_kind, const char@w{ }*output_path)

Compile the @pxref{8,,gcc_jit_context *} to a file of the given
kind.
@end deffn

@pxref{4a,,gcc_jit_context_compile_to_file()} ignores the suffix of
@code{output_path}, and insteads uses the given
@code{enum gcc_jit_output_kind} to decide what to do.

@cartouche
@quotation Note 
This is different from the @code{gcc} program, which does make use of the
suffix of the output file when determining what to do.
@end quotation
@end cartouche

@geindex gcc_jit_output_kind (C type)
@anchor{topics/compilation gcc_jit_output_kind}@anchor{e1}
@deffn {C Type} enum gcc_jit_output_kind
@end deffn

The available kinds of output are:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxx} 
@headitem

Output kind

@tab

Typical suffix

@item

@pxref{e2,,GCC_JIT_OUTPUT_KIND_ASSEMBLER}

@tab

.s

@item

@pxref{e3,,GCC_JIT_OUTPUT_KIND_OBJECT_FILE}

@tab

.o

@item

@pxref{e4,,GCC_JIT_OUTPUT_KIND_DYNAMIC_LIBRARY}

@tab

.so or .dll

@item

@pxref{e5,,GCC_JIT_OUTPUT_KIND_EXECUTABLE}

@tab

None, or .exe

@end multitable


@geindex GCC_JIT_OUTPUT_KIND_ASSEMBLER (C macro)
@anchor{topics/compilation GCC_JIT_OUTPUT_KIND_ASSEMBLER}@anchor{e2}
@deffn {C Macro} GCC_JIT_OUTPUT_KIND_ASSEMBLER

Compile the context to an assembler file.
@end deffn

@geindex GCC_JIT_OUTPUT_KIND_OBJECT_FILE (C macro)
@anchor{topics/compilation GCC_JIT_OUTPUT_KIND_OBJECT_FILE}@anchor{e3}
@deffn {C Macro} GCC_JIT_OUTPUT_KIND_OBJECT_FILE

Compile the context to an object file.
@end deffn

@geindex GCC_JIT_OUTPUT_KIND_DYNAMIC_LIBRARY (C macro)
@anchor{topics/compilation GCC_JIT_OUTPUT_KIND_DYNAMIC_LIBRARY}@anchor{e4}
@deffn {C Macro} GCC_JIT_OUTPUT_KIND_DYNAMIC_LIBRARY

Compile the context to a dynamic library.

There is currently no support for specifying other libraries to link
against.
@end deffn

@geindex GCC_JIT_OUTPUT_KIND_EXECUTABLE (C macro)
@anchor{topics/compilation GCC_JIT_OUTPUT_KIND_EXECUTABLE}@anchor{e5}
@deffn {C Macro} GCC_JIT_OUTPUT_KIND_EXECUTABLE

Compile the context to an executable.

There is currently no support for specifying libraries to link
against.
@end deffn

@c Copyright (C) 2015-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node ABI and API compatibility,Performance,Compiling a context,Topic Reference
@anchor{topics/compatibility abi-and-api-compatibility}@anchor{e6}@anchor{topics/compatibility doc}@anchor{e7}
@section ABI and API compatibility


The libgccjit developers strive for ABI and API backward-compatibility:
programs built against libgccjit.so stand a good chance of running
without recompilation against newer versions of libgccjit.so, and
ought to recompile without modification against newer versions of
libgccjit.h.

@cartouche
@quotation Note 
The libgccjit++.h C++ API is more experimental, and less
locked-down at this time.
@end quotation
@end cartouche

API compatibility is achieved by extending the API rather than changing
it.  For ABI compatiblity, we avoid bumping the SONAME, and instead use
symbol versioning to tag each symbol, so that a binary linked against
libgccjit.so is tagged according to the symbols that it uses.

For example, @pxref{70,,gcc_jit_context_add_command_line_option()} was added in
@code{LIBGCCJIT_ABI_1}.  If a client program uses it, this can be detected
from metadata by using @code{objdump}:

@example
$ objdump -p testsuite/jit/test-extra-options.c.exe | tail -n 8

Version References:
  required from libgccjit.so.0:
    0x00824161 0x00 04 LIBGCCJIT_ABI_1
    0x00824160 0x00 03 LIBGCCJIT_ABI_0
  required from libc.so.6:
@end example

@noindent

You can see the symbol tags provided by libgccjit.so using @code{objdump}:

@example
$ objdump -p libgccjit.so | less
[...snip...]
Version definitions:
1 0x01 0x0ff81f20 libgccjit.so.0
2 0x00 0x00824160 LIBGCCJIT_ABI_0
3 0x00 0x00824161 LIBGCCJIT_ABI_1
        LIBGCCJIT_ABI_0
[...snip...]
@end example

@noindent

@menu
* ABI symbol tags:: 

ABI symbol tags

* LIBGCCJIT_ABI_0:: 
* LIBGCCJIT_ABI_1:: 
* LIBGCCJIT_ABI_2:: 
* LIBGCCJIT_ABI_3:: 
* LIBGCCJIT_ABI_4:: 

@end menu


@node ABI symbol tags,,,ABI and API compatibility
@anchor{topics/compatibility abi-symbol-tags}@anchor{e8}
@subsection ABI symbol tags


The initial release of libgccjit (in gcc 5.1) did not use symbol versioning.

Newer releases use the following tags.

@menu
* LIBGCCJIT_ABI_0:: 
* LIBGCCJIT_ABI_1:: 
* LIBGCCJIT_ABI_2:: 
* LIBGCCJIT_ABI_3:: 
* LIBGCCJIT_ABI_4:: 

@end menu

@node LIBGCCJIT_ABI_0,LIBGCCJIT_ABI_1,,ABI symbol tags
@anchor{topics/compatibility libgccjit-abi-0}@anchor{e9}@anchor{topics/compatibility id1}@anchor{ea}
@subsubsection @code{LIBGCCJIT_ABI_0}


All entrypoints in the initial release of libgccjit are tagged with
@code{LIBGCCJIT_ABI_0}, to signify the transition to symbol versioning.

Binaries built against older copies of @code{libgccjit.so} should
continue to work, with this being handled transparently by the linker
(see this post@footnote{https://gcc.gnu.org/ml/gcc-patches/2015-06/msg02126.html})

@node LIBGCCJIT_ABI_1,LIBGCCJIT_ABI_2,LIBGCCJIT_ABI_0,ABI symbol tags
@anchor{topics/compatibility libgccjit-abi-1}@anchor{71}@anchor{topics/compatibility id2}@anchor{eb}
@subsubsection @code{LIBGCCJIT_ABI_1}


@code{LIBGCCJIT_ABI_1} covers the addition of
@pxref{70,,gcc_jit_context_add_command_line_option()}

@node LIBGCCJIT_ABI_2,LIBGCCJIT_ABI_3,LIBGCCJIT_ABI_1,ABI symbol tags
@anchor{topics/compatibility libgccjit-abi-2}@anchor{6c}@anchor{topics/compatibility id3}@anchor{ec}
@subsubsection @code{LIBGCCJIT_ABI_2}


@code{LIBGCCJIT_ABI_2} covers the addition of
@pxref{6b,,gcc_jit_context_set_bool_allow_unreachable_blocks()}

@node LIBGCCJIT_ABI_3,LIBGCCJIT_ABI_4,LIBGCCJIT_ABI_2,ABI symbol tags
@anchor{topics/compatibility libgccjit-abi-3}@anchor{d8}@anchor{topics/compatibility id4}@anchor{ed}
@subsubsection @code{LIBGCCJIT_ABI_3}


@code{LIBGCCJIT_ABI_3} covers the addition of switch statements via API
entrypoints:

@quotation


@itemize *

@item 
@pxref{d5,,gcc_jit_block_end_with_switch()}

@item 
@pxref{d6,,gcc_jit_case_as_object()}

@item 
@pxref{d7,,gcc_jit_context_new_case()}
@end itemize
@end quotation

@node LIBGCCJIT_ABI_4,,LIBGCCJIT_ABI_3,ABI symbol tags
@anchor{topics/compatibility id5}@anchor{ee}@anchor{topics/compatibility libgccjit-abi-4}@anchor{ef}
@subsubsection @code{LIBGCCJIT_ABI_4}


@code{LIBGCCJIT_ABI_4} covers the addition of timers via API
entrypoints:

@quotation


@itemize *

@item 
@pxref{f0,,gcc_jit_context_get_timer()}

@item 
@pxref{f1,,gcc_jit_context_set_timer()}

@item 
@pxref{f2,,gcc_jit_timer_new()}

@item 
@pxref{f3,,gcc_jit_timer_release()}

@item 
@pxref{f4,,gcc_jit_timer_push()}

@item 
@pxref{f5,,gcc_jit_timer_pop()}

@item 
@pxref{f6,,gcc_jit_timer_print()}
@end itemize
@end quotation

@c Copyright (C) 2015-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Performance,,ABI and API compatibility,Topic Reference
@anchor{topics/performance performance}@anchor{f7}@anchor{topics/performance doc}@anchor{f8}
@section Performance


@menu
* The timing API:: 

@end menu

@node The timing API,,,Performance
@anchor{topics/performance the-timing-api}@anchor{f9}
@subsection The timing API


As of GCC 6, libgccjit exposes a timing API, for printing reports on
how long was spent in different parts of code.

You can create a @pxref{fa,,gcc_jit_timer} instance, which will
measure time spent since its creation.  The timer maintains a stack
of "timer items": as control flow moves through your code, you can push
and pop named items relating to your code onto the stack, and the timer
will account the time spent accordingly.

You can also asssociate a timer with a @pxref{8,,gcc_jit_context}, in
which case the time spent inside compilation will be subdivided.

For example, the following code uses a timer, recording client items
"create_code", "compile", and "running code":

@example
/* Create a timer.  */
gcc_jit_timer *timer = gcc_jit_timer_new ();
if (!timer)
  @{
     error ("gcc_jit_timer_new failed");
     return -1;
  @}

/* Let's repeatedly compile and run some code, accumulating it
   all into the timer.  */
for (int i = 0; i < num_iterations; i++)
  @{
    /* Create a context and associate it with the timer.  */
    gcc_jit_context *ctxt = gcc_jit_context_acquire ();
    if (!ctxt)
      @{
        error ("gcc_jit_context_acquire failed");
        return -1;
      @}
    gcc_jit_context_set_timer (ctxt, timer);

    /* Populate the context, timing it as client item "create_code".  */
    gcc_jit_timer_push (timer, "create_code");
    create_code (ctxt);
    gcc_jit_timer_pop (timer, "create_code");

    /* Compile the context, timing it as client item "compile".  */
    gcc_jit_timer_push (timer, "compile");
    result = gcc_jit_context_compile (ctxt);
    gcc_jit_timer_pop (timer, "compile");

    /* Run the generated code, timing it as client item "running code".  */
    gcc_jit_timer_push (timer, "running code");
    run_the_code (ctxt, result);
    gcc_jit_timer_pop (timer, "running code");

    /* Clean up.  */
    gcc_jit_context_release (ctxt);
    gcc_jit_result_release (result);
@}

/* Print the accumulated timings.  */
gcc_jit_timer_print (timer, stderr);
gcc_jit_timer_release (timer);
@end example

@noindent

giving output like this, showing the internal GCC items at the top, then
client items, then the total:

@example
Execution times (seconds)
GCC items:
 phase setup             :   0.29 (14%) usr   0.00 ( 0%) sys   0.32 ( 5%) wall   10661 kB (50%) ggc
 phase parsing           :   0.02 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall     653 kB ( 3%) ggc
 phase finalize          :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 dump files              :   0.02 ( 1%) usr   0.00 ( 0%) sys   0.01 ( 0%) wall       0 kB ( 0%) ggc
 callgraph construction  :   0.02 ( 1%) usr   0.01 ( 6%) sys   0.01 ( 0%) wall     242 kB ( 1%) ggc
 callgraph optimization  :   0.03 ( 2%) usr   0.00 ( 0%) sys   0.02 ( 0%) wall     142 kB ( 1%) ggc
 trivially dead code     :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 df scan insns           :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       9 kB ( 0%) ggc
 df live regs            :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.01 ( 0%) wall       0 kB ( 0%) ggc
 inline parameters       :   0.02 ( 1%) usr   0.00 ( 0%) sys   0.01 ( 0%) wall      82 kB ( 0%) ggc
 tree CFG cleanup        :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 tree PHI insertion      :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.02 ( 0%) wall      64 kB ( 0%) ggc
 tree SSA other          :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.01 ( 0%) wall      18 kB ( 0%) ggc
 expand                  :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall     398 kB ( 2%) ggc
 jump                    :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 loop init               :   0.01 ( 0%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall      67 kB ( 0%) ggc
 integrated RA           :   0.02 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall    2468 kB (12%) ggc
 thread pro- & epilogue  :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall     162 kB ( 1%) ggc
 final                   :   0.01 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall     216 kB ( 1%) ggc
 rest of compilation     :   1.37 (69%) usr   0.00 ( 0%) sys   1.13 (18%) wall    1391 kB ( 6%) ggc
 assemble JIT code       :   0.01 ( 1%) usr   0.00 ( 0%) sys   4.04 (66%) wall       0 kB ( 0%) ggc
 load JIT result         :   0.02 ( 1%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 JIT client code         :   0.00 ( 0%) usr   0.01 ( 6%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
Client items:
 create_code             :   0.00 ( 0%) usr   0.01 ( 6%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 compile                 :   0.36 (18%) usr   0.15 (83%) sys   0.86 (14%) wall   14939 kB (70%) ggc
 running code            :   0.00 ( 0%) usr   0.00 ( 0%) sys   0.00 ( 0%) wall       0 kB ( 0%) ggc
 TOTAL                   :   2.00             0.18             6.12              21444 kB
@end example

@noindent

The exact format is intended to be human-readable, and is subject to change.

@geindex LIBGCCJIT_HAVE_TIMING_API (C macro)
@anchor{topics/performance LIBGCCJIT_HAVE_TIMING_API}@anchor{fb}
@deffn {C Macro} LIBGCCJIT_HAVE_TIMING_API

The timer API was added to libgccjit in GCC 6.
This macro is only defined in versions of libgccjit.h which have the
timer API, and so can be used to guard code that may need to compile
against earlier releases:

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
gcc_jit_timer *t = gcc_jit_timer_new ();
gcc_jit_context_set_timer (ctxt, t);
#endif
@end example

@noindent
@end deffn

@geindex gcc_jit_timer (C type)
@anchor{topics/performance gcc_jit_timer}@anchor{fa}
@deffn {C Type} gcc_jit_timer
@end deffn

@geindex gcc_jit_timer_new (C function)
@anchor{topics/performance gcc_jit_timer_new}@anchor{f2}
@deffn {C Function} gcc_jit_timer * gcc_jit_timer_new (void)

Create a @pxref{fa,,gcc_jit_timer} instance, and start timing:

@example
gcc_jit_timer *t = gcc_jit_timer_new ();
@end example

@noindent

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@geindex gcc_jit_timer_release (C function)
@anchor{topics/performance gcc_jit_timer_release}@anchor{f3}
@deffn {C Function} void gcc_jit_timer_release (gcc_jit_timer@w{ }*timer)

Release a @pxref{fa,,gcc_jit_timer} instance:

@example
gcc_jit_timer_release (t);
@end example

@noindent

This should be called exactly once on a timer.

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@geindex gcc_jit_context_set_timer (C function)
@anchor{topics/performance gcc_jit_context_set_timer}@anchor{f1}
@deffn {C Function} void gcc_jit_context_set_timer (gcc_jit_context@w{ }*ctxt, gcc_jit_timer@w{ }*timer)

Associate a @pxref{fa,,gcc_jit_timer} instance with a context:

@example
gcc_jit_context_set_timer (ctxt, t);
@end example

@noindent

A timer instance can be shared between multiple
@pxref{8,,gcc_jit_context} instances.

Timers have no locking, so if you have a multithreaded program, you
must provide your own locks if more than one thread could be working
with the same timer via timer-associated contexts.

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@geindex gcc_jit_context_get_timer (C function)
@anchor{topics/performance gcc_jit_context_get_timer}@anchor{f0}
@deffn {C Function} gcc_jit_timer *gcc_jit_context_get_timer (gcc_jit_context@w{ }*ctxt)

Get the timer associated with a context (if any).

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@geindex gcc_jit_timer_push (C function)
@anchor{topics/performance gcc_jit_timer_push}@anchor{f4}
@deffn {C Function} void gcc_jit_timer_push (gcc_jit_timer@w{ }*timer, const char@w{ }*item_name)

Push the given item onto the timer's stack:

@example
gcc_jit_timer_push (t, "running code");
run_the_code (ctxt, result);
gcc_jit_timer_pop (t, "running code");
@end example

@noindent

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@geindex gcc_jit_timer_pop (C function)
@anchor{topics/performance gcc_jit_timer_pop}@anchor{f5}
@deffn {C Function} void gcc_jit_timer_pop (gcc_jit_timer@w{ }*timer, const char@w{ }*item_name)

Pop the top item from the timer's stack.

If "item_name" is provided, it must match that of the top item.
Alternatively, @code{NULL} can be passed in, to suppress checking.

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@geindex gcc_jit_timer_print (C function)
@anchor{topics/performance gcc_jit_timer_print}@anchor{f6}
@deffn {C Function} void gcc_jit_timer_print (gcc_jit_timer@w{ }*timer, FILE@w{ }*f_out)

Print timing information to the given stream about activity since
the timer was started.

This API entrypoint was added in @pxref{ef,,LIBGCCJIT_ABI_4}; you can test
for its presence using

@example
#ifdef LIBGCCJIT_HAVE_TIMING_API
@end example

@noindent
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node C++ bindings for libgccjit,Internals,Topic Reference,Top
@anchor{cp/index c-bindings-for-libgccjit}@anchor{fc}@anchor{cp/index doc}@anchor{fd}
@chapter C++ bindings for libgccjit


This document describes the C++ bindings to
libgccjit@footnote{http://gcc.gnu.org/wiki/JIT}, an API for embedding GCC
inside programs and libraries.

The C++ bindings consist of a single header file @code{libgccjit++.h}.

This is a collection of "thin" wrapper classes around the C API.
Everything is an inline function, implemented in terms of the C API,
so there is nothing extra to link against.

Note that libgccjit is currently of "Alpha" quality;
the APIs are not yet set in stone, and they shouldn't be used in
production yet.

Contents:

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@menu
* Tutorial: Tutorial<2>. 
* Topic Reference: Topic Reference<2>. 

Tutorial

* Tutorial part 1; "Hello world": Tutorial part 1 "Hello world"<2>. 
* Tutorial part 2; Creating a trivial machine code function: Tutorial part 2 Creating a trivial machine code function<2>. 
* Tutorial part 3; Loops and variables: Tutorial part 3 Loops and variables<2>. 
* Tutorial part 4; Adding JIT-compilation to a toy interpreter: Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>. 

Tutorial part 2: Creating a trivial machine code function

* Options: Options<3>. 
* Full example: Full example<3>. 

Tutorial part 3: Loops and variables

* Expressions; lvalues and rvalues: Expressions lvalues and rvalues<2>. 
* Control flow: Control flow<2>. 
* Visualizing the control flow graph: Visualizing the control flow graph<2>. 
* Full example: Full example<4>. 

Tutorial part 4: Adding JIT-compilation to a toy interpreter

* Our toy interpreter: Our toy interpreter<2>. 
* Compiling to machine code: Compiling to machine code<2>. 
* Setting things up: Setting things up<2>. 
* Populating the function: Populating the function<2>. 
* Verifying the control flow graph: Verifying the control flow graph<2>. 
* Compiling the context: Compiling the context<2>. 
* Single-stepping through the generated code: Single-stepping through the generated code<2>. 
* Examining the generated code: Examining the generated code<2>. 
* Putting it all together: Putting it all together<2>. 
* Behind the curtain; How does our code get optimized?: Behind the curtain How does our code get optimized?<2>. 

Behind the curtain: How does our code get optimized?

* Optimizing away stack manipulation: Optimizing away stack manipulation<2>. 
* Elimination of tail recursion: Elimination of tail recursion<2>. 

Topic Reference

* Compilation contexts: Compilation contexts<2>. 
* Objects: Objects<2>. 
* Types: Types<2>. 
* Expressions: Expressions<2>. 
* Creating and using functions: Creating and using functions<2>. 
* Source Locations: Source Locations<2>. 
* Compiling a context: Compiling a context<2>. 

Compilation contexts

* Lifetime-management: Lifetime-management<2>. 
* Thread-safety: Thread-safety<2>. 
* Error-handling: Error-handling<3>. 
* Debugging: Debugging<2>. 
* Options: Options<4>. 

Options

* String Options: String Options<2>. 
* Boolean options: Boolean options<2>. 
* Integer options: Integer options<2>. 
* Additional command-line options: Additional command-line options<2>. 

Types

* Standard types: Standard types<2>. 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile<2>. 
* Structures and unions: Structures and unions<2>. 

Expressions

* Rvalues: Rvalues<2>. 
* Lvalues: Lvalues<2>. 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions<2>. 

Rvalues

* Simple expressions: Simple expressions<2>. 
* Unary Operations: Unary Operations<2>. 
* Binary Operations: Binary Operations<2>. 
* Comparisons: Comparisons<2>. 
* Function calls: Function calls<2>. 
* Type-coercion: Type-coercion<2>. 

Lvalues

* Global variables: Global variables<2>. 

Creating and using functions

* Params: Params<2>. 
* Functions: Functions<2>. 
* Blocks: Blocks<2>. 
* Statements: Statements<2>. 

Source Locations

* Faking it: Faking it<2>. 

Compiling a context

* In-memory compilation: In-memory compilation<2>. 
* Ahead-of-time compilation: Ahead-of-time compilation<2>. 

@end menu


@node Tutorial<2>,Topic Reference<2>,,C++ bindings for libgccjit
@anchor{cp/intro/index doc}@anchor{fe}@anchor{cp/intro/index tutorial}@anchor{ff}
@section Tutorial


@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@menu
* Tutorial part 1; "Hello world": Tutorial part 1 "Hello world"<2>. 
* Tutorial part 2; Creating a trivial machine code function: Tutorial part 2 Creating a trivial machine code function<2>. 
* Tutorial part 3; Loops and variables: Tutorial part 3 Loops and variables<2>. 
* Tutorial part 4; Adding JIT-compilation to a toy interpreter: Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>. 

@end menu

@node Tutorial part 1 "Hello world"<2>,Tutorial part 2 Creating a trivial machine code function<2>,,Tutorial<2>
@anchor{cp/intro/tutorial01 doc}@anchor{100}@anchor{cp/intro/tutorial01 tutorial-part-1-hello-world}@anchor{101}
@subsection Tutorial part 1: "Hello world"


Before we look at the details of the API, let's look at building and
running programs that use the library.

Here's a toy "hello world" program that uses the library's C++ API to
synthesize a call to @cite{printf} and uses it to write a message to stdout.

Don't worry about the content of the program for now; we'll cover
the details in later parts of this tutorial.

@quotation

@example
/* Smoketest example for libgccjit.so C++ API
   Copyright (C) 2014-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <libgccjit++.h>

#include <stdlib.h>
#include <stdio.h>

static void
create_code (gccjit::context ctxt)
@{
  /* Let's try to inject the equivalent of this C code:
     void
     greet (const char *name)
     @{
        printf ("hello %s\n", name);
     @}
  */
  gccjit::type void_type = ctxt.get_type (GCC_JIT_TYPE_VOID);
  gccjit::type const_char_ptr_type =
    ctxt.get_type (GCC_JIT_TYPE_CONST_CHAR_PTR);
  gccjit::param param_name =
    ctxt.new_param (const_char_ptr_type, "name");
  std::vector<gccjit::param> func_params;
  func_params.push_back (param_name);
  gccjit::function func =
    ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                       void_type,
                       "greet",
                       func_params, 0);

  gccjit::param param_format =
    ctxt.new_param (const_char_ptr_type, "format");
  std::vector<gccjit::param> printf_params;
  printf_params.push_back (param_format);
  gccjit::function printf_func =
    ctxt.new_function (GCC_JIT_FUNCTION_IMPORTED,
                       ctxt.get_type (GCC_JIT_TYPE_INT),
                       "printf",
                       printf_params, 1);

  gccjit::block block = func.new_block ();
  block.add_eval (ctxt.new_call (printf_func,
                                 ctxt.new_rvalue ("hello %s\n"),
                                 param_name));
  block.end_with_return ();
@}

int
main (int argc, char **argv)
@{
  gccjit::context ctxt;
  gcc_jit_result *result;

  /* Get a "context" object for working with the library.  */
  ctxt = gccjit::context::acquire ();

  /* Set some options on the context.
     Turn this on to see the code being generated, in assembler form.  */
  ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE, 0);

  /* Populate the context.  */
  create_code (ctxt);

  /* Compile the code.  */
  result = ctxt.compile ();
  if (!result)
    @{
      fprintf (stderr, "NULL result");
      exit (1);
    @}

  ctxt.release ();

  /* Extract the generated code from "result".  */
  typedef void (*fn_type) (const char *);
  fn_type greet =
    (fn_type)gcc_jit_result_get_code (result, "greet");
  if (!greet)
    @{
      fprintf (stderr, "NULL greet");
      exit (1);
    @}

  /* Now call the generated function: */
  greet ("world");
  fflush (stdout);

  gcc_jit_result_release (result);
  return 0;
@}

@end example

@noindent
@end quotation

Copy the above to @cite{tut01-hello-world.cc}.

Assuming you have the jit library installed, build the test program
using:

@example
$ gcc \
    tut01-hello-world.cc \
    -o tut01-hello-world \
    -lgccjit
@end example

@noindent

You should then be able to run the built program:

@example
$ ./tut01-hello-world
hello world
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 2 Creating a trivial machine code function<2>,Tutorial part 3 Loops and variables<2>,Tutorial part 1 "Hello world"<2>,Tutorial<2>
@anchor{cp/intro/tutorial02 doc}@anchor{102}@anchor{cp/intro/tutorial02 tutorial-part-2-creating-a-trivial-machine-code-function}@anchor{103}
@subsection Tutorial part 2: Creating a trivial machine code function


Consider this C function:

@example
int square (int i)
@{
  return i * i;
@}
@end example

@noindent

How can we construct this at run-time using libgccjit's C++ API?

First we need to include the relevant header:

@example
#include <libgccjit++.h>
@end example

@noindent

All state associated with compilation is associated with a
@code{gccjit::context}, which is a thin C++ wrapper around the C API's
@pxref{8,,gcc_jit_context *}.

Create one using @pxref{104,,gccjit;;context;;acquire()}:

@example
gccjit::context ctxt;
ctxt = gccjit::context::acquire ();
@end example

@noindent

The JIT library has a system of types.  It is statically-typed: every
expression is of a specific type, fixed at compile-time.  In our example,
all of the expressions are of the C @cite{int} type, so let's obtain this from
the context, as a @code{gccjit::type}, using
@pxref{105,,gccjit;;context;;get_type()}:

@example
gccjit::type int_type = ctxt.get_type (GCC_JIT_TYPE_INT);
@end example

@noindent

@code{gccjit::type} is an example of a "contextual" object: every
entity in the API is associated with a @code{gccjit::context}.

Memory management is easy: all such "contextual" objects are automatically
cleaned up for you when the context is released, using
@pxref{106,,gccjit;;context;;release()}:

@example
ctxt.release ();
@end example

@noindent

so you don't need to manually track and cleanup all objects, just the
contexts.

All of the C++ classes in the API are thin wrappers around pointers to
types in the C API.

The C++ class hierarchy within the @code{gccjit} namespace looks like this:

@example
+- object
    +- location
    +- type
       +- struct
    +- field
    +- function
    +- block
    +- rvalue
        +- lvalue
           +- param
@end example

@noindent

One thing you can do with a @code{gccjit::object} is
to ask it for a human-readable description as a @code{std::string}, using
@pxref{107,,gccjit;;object;;get_debug_string()}:

@example
printf ("obj: %s\n", obj.get_debug_string ().c_str ());
@end example

@noindent

giving this text on stdout:

@example
obj: int
@end example

@noindent

This is invaluable when debugging.

Let's create the function.  To do so, we first need to construct
its single parameter, specifying its type and giving it a name,
using @pxref{108,,gccjit;;context;;new_param()}:

@example
gccjit::param param_i = ctxt.new_param (int_type, "i");
@end example

@noindent

and we can then make a vector of all of the params of the function,
in this case just one:

@example
std::vector<gccjit::param> params;
params.push_back (param_i);
@end example

@noindent

Now we can create the function, using
@code{gccjit::context::new_function()}:

@example
gccjit::function func =
  ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                     int_type,
                     "square",
                     params,
                     0);
@end example

@noindent

To define the code within the function, we must create basic blocks
containing statements.

Every basic block contains a list of statements, eventually terminated
by a statement that either returns, or jumps to another basic block.

Our function has no control-flow, so we just need one basic block:

@example
gccjit::block block = func.new_block ();
@end example

@noindent

Our basic block is relatively simple: it immediately terminates by
returning the value of an expression.

We can build the expression using @pxref{109,,gccjit;;context;;new_binary_op()}:

@example
gccjit::rvalue expr =
  ctxt.new_binary_op (
    GCC_JIT_BINARY_OP_MULT, int_type,
    param_i, param_i);
@end example

@noindent

A @code{gccjit::rvalue} is another example of a
@code{gccjit::object} subclass.  As before, we can print it with
@pxref{107,,gccjit;;object;;get_debug_string()}.

@example
printf ("expr: %s\n", expr.get_debug_string ().c_str ());
@end example

@noindent

giving this output:

@example
expr: i * i
@end example

@noindent

Note that @code{gccjit::rvalue} provides numerous overloaded operators
which can be used to dramatically reduce the amount of typing needed.
We can build the above binary operation more directly with this one-liner:

@example
gccjit::rvalue expr = param_i * param_i;
@end example

@noindent

Creating the expression in itself doesn't do anything; we have to add
this expression to a statement within the block.  In this case, we use it
to build a return statement, which terminates the basic block:

@example
block.end_with_return (expr);
@end example

@noindent

OK, we've populated the context.  We can now compile it using
@pxref{10a,,gccjit;;context;;compile()}:

@example
gcc_jit_result *result;
result = ctxt.compile ();
@end example

@noindent

and get a @pxref{16,,gcc_jit_result *}.

We can now use @pxref{17,,gcc_jit_result_get_code()} to look up a specific
machine code routine within the result, in this case, the function we
created above.

@example
void *fn_ptr = gcc_jit_result_get_code (result, "square");
if (!fn_ptr)
  @{
    fprintf (stderr, "NULL fn_ptr");
    goto error;
  @}
@end example

@noindent

We can now cast the pointer to an appropriate function pointer type, and
then call it:

@example
typedef int (*fn_type) (int);
fn_type square = (fn_type)fn_ptr;
printf ("result: %d", square (5));
@end example

@noindent

@example
result: 25
@end example

@noindent

@menu
* Options: Options<3>. 
* Full example: Full example<3>. 

@end menu

@node Options<3>,Full example<3>,,Tutorial part 2 Creating a trivial machine code function<2>
@anchor{cp/intro/tutorial02 options}@anchor{10b}
@subsubsection Options


To get more information on what's going on, you can set debugging flags
on the context using @pxref{10c,,gccjit;;context;;set_bool_option()}.

@c (I'm deliberately not mentioning
@c :c:macro:`GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE` here since I think
@c it's probably more of use to implementors than to users)

Setting @pxref{1c,,GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE} will dump a
C-like representation to stderr when you compile (GCC's "GIMPLE"
representation):

@example
ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE, 1);
result = ctxt.compile ();
@end example

@noindent

@example
square (signed int i)
@{
  signed int D.260;

  entry:
  D.260 = i * i;
  return D.260;
@}
@end example

@noindent

We can see the generated machine code in assembler form (on stderr) by
setting @pxref{1d,,GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE} on the context
before compiling:

@example
ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE, 1);
result = ctxt.compile ();
@end example

@noindent

@example
      .file   "fake.c"
      .text
      .globl  square
      .type   square, @@function
square:
.LFB6:
      .cfi_startproc
      pushq   %rbp
      .cfi_def_cfa_offset 16
      .cfi_offset 6, -16
      movq    %rsp, %rbp
      .cfi_def_cfa_register 6
      movl    %edi, -4(%rbp)
.L14:
      movl    -4(%rbp), %eax
      imull   -4(%rbp), %eax
      popq    %rbp
      .cfi_def_cfa 7, 8
      ret
      .cfi_endproc
.LFE6:
      .size   square, .-square
      .ident  "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.2-0.5.1920c315ff984892399893b380305ab36e07b455.fc20)"
      .section       .note.GNU-stack,"",@@progbits
@end example

@noindent

By default, no optimizations are performed, the equivalent of GCC's
@cite{-O0} option.  We can turn things up to e.g. @cite{-O3} by calling
@pxref{10d,,gccjit;;context;;set_int_option()} with
@pxref{1f,,GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL}:

@example
ctxt.set_int_option (GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL, 3);
@end example

@noindent

@example
      .file   "fake.c"
      .text
      .p2align 4,,15
      .globl  square
      .type   square, @@function
square:
.LFB7:
      .cfi_startproc
.L16:
      movl    %edi, %eax
      imull   %edi, %eax
      ret
      .cfi_endproc
.LFE7:
      .size   square, .-square
      .ident  "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.2-0.5.1920c315ff984892399893b380305ab36e07b455.fc20)"
      .section        .note.GNU-stack,"",@@progbits
@end example

@noindent

Naturally this has only a small effect on such a trivial function.

@node Full example<3>,,Options<3>,Tutorial part 2 Creating a trivial machine code function<2>
@anchor{cp/intro/tutorial02 full-example}@anchor{10e}
@subsubsection Full example


Here's what the above looks like as a complete program:

@quotation

@example
/* Usage example for libgccjit.so's C++ API
   Copyright (C) 2014-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <libgccjit++.h>

#include <stdlib.h>
#include <stdio.h>

void
create_code (gccjit::context ctxt)
@{
  /* Let's try to inject the equivalent of this C code:

      int square (int i)
      @{
        return i * i;
      @}
  */
  gccjit::type int_type = ctxt.get_type (GCC_JIT_TYPE_INT);
  gccjit::param param_i = ctxt.new_param (int_type, "i");
  std::vector<gccjit::param> params;
  params.push_back (param_i);
  gccjit::function func = ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                                             int_type,
                                             "square",
                                             params, 0);

  gccjit::block block = func.new_block ();

  gccjit::rvalue expr =
    ctxt.new_binary_op (GCC_JIT_BINARY_OP_MULT, int_type,
                        param_i, param_i);

  block.end_with_return (expr);
@}

int
main (int argc, char **argv)
@{
  /* Get a "context" object for working with the library.  */
  gccjit::context ctxt = gccjit::context::acquire ();

  /* Set some options on the context.
     Turn this on to see the code being generated, in assembler form.  */
  ctxt.set_bool_option (
    GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
    0);

  /* Populate the context.  */
  create_code (ctxt);

  /* Compile the code.  */
  gcc_jit_result *result = ctxt.compile ();

  /* We're done with the context; we can release it: */
  ctxt.release ();

  if (!result)
    @{
      fprintf (stderr, "NULL result");
      return 1;
    @}

  /* Extract the generated code from "result".  */
  void *fn_ptr = gcc_jit_result_get_code (result, "square");
  if (!fn_ptr)
     @{
       fprintf (stderr, "NULL fn_ptr");
       gcc_jit_result_release (result);
       return 1;
     @}

  typedef int (*fn_type) (int);
  fn_type square = (fn_type)fn_ptr;
  printf ("result: %d\n", square (5));

  gcc_jit_result_release (result);
  return 0;
@}

@end example

@noindent
@end quotation

Building and running it:

@example
$ gcc \
    tut02-square.cc \
    -o tut02-square \
    -lgccjit

# Run the built program:
$ ./tut02-square
result: 25
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 3 Loops and variables<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>,Tutorial part 2 Creating a trivial machine code function<2>,Tutorial<2>
@anchor{cp/intro/tutorial03 tutorial-part-3-loops-and-variables}@anchor{10f}@anchor{cp/intro/tutorial03 doc}@anchor{110}
@subsection Tutorial part 3: Loops and variables


Consider this C function:

@quotation

@example
int loop_test (int n)
@{
  int sum = 0;
  for (int i = 0; i < n; i++)
    sum += i * i;
  return sum;
@}
@end example

@noindent
@end quotation

This example demonstrates some more features of libgccjit, with local
variables and a loop.

To break this down into libgccjit terms, it's usually easier to reword
the @cite{for} loop as a @cite{while} loop, giving:

@quotation

@example
int loop_test (int n)
@{
  int sum = 0;
  int i = 0;
  while (i < n)
  @{
    sum += i * i;
    i++;
  @}
  return sum;
@}
@end example

@noindent
@end quotation

Here's what the final control flow graph will look like:

@quotation


@float Figure

@image{sum-of-squares,,,image of a control flow graph,png}

@end float

@end quotation

As before, we include the libgccjit++ header and make a
@code{gccjit::context}.

@example
#include <libgccjit++.h>

void test (void)
@{
  gccjit::context ctxt;
  ctxt = gccjit::context::acquire ();
@end example

@noindent

The function works with the C @cite{int} type.

In the previous tutorial we acquired this via

@example
gccjit::type the_type = ctxt.get_type (ctxt, GCC_JIT_TYPE_INT);
@end example

@noindent

though we could equally well make it work on, say, @cite{double}:

@example
gccjit::type the_type = ctxt.get_type (ctxt, GCC_JIT_TYPE_DOUBLE);
@end example

@noindent

For integer types we can use @code{gccjit::context::get_int_type}
to directly bind a specific type:

@example
gccjit::type the_type = ctxt.get_int_type <int> ();
@end example

@noindent

Let's build the function:

@example
gcc_jit_param n = ctxt.new_param (the_type, "n");
std::vector<gccjit::param> params;
params.push_back (n);
gccjit::function func =
  ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                     return_type,
                     "loop_test",
                     params, 0);
@end example

@noindent

@menu
* Expressions; lvalues and rvalues: Expressions lvalues and rvalues<2>. 
* Control flow: Control flow<2>. 
* Visualizing the control flow graph: Visualizing the control flow graph<2>. 
* Full example: Full example<4>. 

@end menu

@node Expressions lvalues and rvalues<2>,Control flow<2>,,Tutorial part 3 Loops and variables<2>
@anchor{cp/intro/tutorial03 expressions-lvalues-and-rvalues}@anchor{111}
@subsubsection Expressions: lvalues and rvalues


The base class of expression is the @code{gccjit::rvalue},
representing an expression that can be on the @emph{right}-hand side of
an assignment: a value that can be computed somehow, and assigned
@emph{to} a storage area (such as a variable).  It has a specific
@code{gccjit::type}.

Anothe important class is @code{gccjit::lvalue}.
A @code{gccjit::lvalue}. is something that can of the @emph{left}-hand
side of an assignment: a storage area (such as a variable).

In other words, every assignment can be thought of as:

@example
LVALUE = RVALUE;
@end example

@noindent

Note that @code{gccjit::lvalue} is a subclass of
@code{gccjit::rvalue}, where in an assignment of the form:

@example
LVALUE_A = LVALUE_B;
@end example

@noindent

the @cite{LVALUE_B} implies reading the current value of that storage
area, assigning it into the @cite{LVALUE_A}.

So far the only expressions we've seen are from the previous tutorial:


@enumerate 

@item 
the multiplication @cite{i * i}:
@end enumerate

@quotation

@example
gccjit::rvalue expr =
  ctxt.new_binary_op (
    GCC_JIT_BINARY_OP_MULT, int_type,
    param_i, param_i);

/* Alternatively, using operator-overloading: */
gccjit::rvalue expr = param_i * param_i;
@end example

@noindent

which is a @code{gccjit::rvalue}, and
@end quotation


@enumerate 2

@item 
the various function parameters: @cite{param_i} and @cite{param_n}, instances of
@code{gccjit::param}, which is a subclass of @code{gccjit::lvalue}
(and, in turn, of @code{gccjit::rvalue}):
we can both read from and write to function parameters within the
body of a function.
@end enumerate

Our new example has a new kind of expression: we have two local
variables.  We create them by calling
@pxref{112,,gccjit;;function;;new_local()}, supplying a type and a name:

@example
/* Build locals:  */
gccjit::lvalue i = func.new_local (the_type, "i");
gccjit::lvalue sum = func.new_local (the_type, "sum");
@end example

@noindent

These are instances of @code{gccjit::lvalue} - they can be read from
and written to.

Note that there is no precanned way to create @emph{and} initialize a variable
like in C:

@example
int i = 0;
@end example

@noindent

Instead, having added the local to the function, we have to separately add
an assignment of @cite{0} to @cite{local_i} at the beginning of the function.

@node Control flow<2>,Visualizing the control flow graph<2>,Expressions lvalues and rvalues<2>,Tutorial part 3 Loops and variables<2>
@anchor{cp/intro/tutorial03 control-flow}@anchor{113}
@subsubsection Control flow


This function has a loop, so we need to build some basic blocks to
handle the control flow.  In this case, we need 4 blocks:


@enumerate 

@item 
before the loop (initializing the locals)

@item 
the conditional at the top of the loop (comparing @cite{i < n})

@item 
the body of the loop

@item 
after the loop terminates (@cite{return sum})
@end enumerate

so we create these as @code{gccjit::block} instances within the
@code{gccjit::function}:

@example
gccjit::block b_initial = func.new_block ("initial");
gccjit::block b_loop_cond = func.new_block ("loop_cond");
gccjit::block b_loop_body = func.new_block ("loop_body");
gccjit::block b_after_loop = func.new_block ("after_loop");
@end example

@noindent

We now populate each block with statements.

The entry block @cite{b_initial} consists of initializations followed by a jump
to the conditional.  We assign @cite{0} to @cite{i} and to @cite{sum}, using
@pxref{114,,gccjit;;block;;add_assignment()} to add
an assignment statement, and using @pxref{115,,gccjit;;context;;zero()} to get
the constant value @cite{0} for the relevant type for the right-hand side of
the assignment:

@example
/* sum = 0; */
b_initial.add_assignment (sum, ctxt.zero (the_type));

/* i = 0; */
b_initial.add_assignment (i, ctxt.zero (the_type));
@end example

@noindent

We can then terminate the entry block by jumping to the conditional:

@example
b_initial.end_with_jump (b_loop_cond);
@end example

@noindent

The conditional block is equivalent to the line @cite{while (i < n)} from our
C example. It contains a single statement: a conditional, which jumps to
one of two destination blocks depending on a boolean
@code{gccjit::rvalue}, in this case the comparison of @cite{i} and @cite{n}.

We could build the comparison using @pxref{116,,gccjit;;context;;new_comparison()}:

@example
gccjit::rvalue guard =
  ctxt.new_comparison (GCC_JIT_COMPARISON_GE,
                       i, n);
@end example

@noindent

and can then use this to add @cite{b_loop_cond}'s sole statement, via
@pxref{117,,gccjit;;block;;end_with_conditional()}:

@example
b_loop_cond.end_with_conditional (guard,
                                  b_after_loop, // on_true
                                  b_loop_body); // on_false
@end example

@noindent

However @code{gccjit::rvalue} has overloaded operators for this, so we
express the conditional as

@example
gccjit::rvalue guard = (i >= n);
@end example

@noindent

and hence we can write the block more concisely as:

@example
b_loop_cond.end_with_conditional (
  i >= n,
  b_after_loop, // on_true
  b_loop_body); // on_false
@end example

@noindent

Next, we populate the body of the loop.

The C statement @cite{sum += i * i;} is an assignment operation, where an
lvalue is modified "in-place".  We use
@pxref{118,,gccjit;;block;;add_assignment_op()} to handle these operations:

@example
/* sum += i * i */
b_loop_body.add_assignment_op (sum,
                               GCC_JIT_BINARY_OP_PLUS,
                               i * i);
@end example

@noindent

The @cite{i++} can be thought of as @cite{i += 1}, and can thus be handled in
a similar way.  We use @pxref{2f,,gcc_jit_context_one()} to get the constant
value @cite{1} (for the relevant type) for the right-hand side
of the assignment.

@example
/* i++ */
b_loop_body.add_assignment_op (i,
                               GCC_JIT_BINARY_OP_PLUS,
                               ctxt.one (the_type));
@end example

@noindent

@cartouche
@quotation Note 
For numeric constants other than 0 or 1, we could use
@pxref{119,,gccjit;;context;;new_rvalue()}, which has overloads
for both @code{int} and @code{double}.
@end quotation
@end cartouche

The loop body completes by jumping back to the conditional:

@example
b_loop_body.end_with_jump (b_loop_cond);
@end example

@noindent

Finally, we populate the @cite{b_after_loop} block, reached when the loop
conditional is false.  We want to generate the equivalent of:

@example
return sum;
@end example

@noindent

so the block is just one statement:

@example
/* return sum */
b_after_loop.end_with_return (sum);
@end example

@noindent

@cartouche
@quotation Note 
You can intermingle block creation with statement creation,
but given that the terminator statements generally include references
to other blocks, I find it's clearer to create all the blocks,
@emph{then} all the statements.
@end quotation
@end cartouche

We've finished populating the function.  As before, we can now compile it
to machine code:

@example
gcc_jit_result *result;
result = ctxt.compile ();

ctxt.release ();

if (!result)
  @{
    fprintf (stderr, "NULL result");
    return 1;
  @}

typedef int (*loop_test_fn_type) (int);
loop_test_fn_type loop_test =
 (loop_test_fn_type)gcc_jit_result_get_code (result, "loop_test");
if (!loop_test)
  @{
    fprintf (stderr, "NULL loop_test");
    gcc_jit_result_release (result);
    return 1;
  @}
printf ("result: %d", loop_test (10));
@end example

@noindent

@example
result: 285
@end example

@noindent

@node Visualizing the control flow graph<2>,Full example<4>,Control flow<2>,Tutorial part 3 Loops and variables<2>
@anchor{cp/intro/tutorial03 visualizing-the-control-flow-graph}@anchor{11a}
@subsubsection Visualizing the control flow graph


You can see the control flow graph of a function using
@pxref{11b,,gccjit;;function;;dump_to_dot()}:

@example
func.dump_to_dot ("/tmp/sum-of-squares.dot");
@end example

@noindent

giving a .dot file in GraphViz format.

You can convert this to an image using @cite{dot}:

@example
$ dot -Tpng /tmp/sum-of-squares.dot -o /tmp/sum-of-squares.png
@end example

@noindent

or use a viewer (my preferred one is xdot.py; see
@indicateurl{https://github.com/jrfonseca/xdot.py}; on Fedora you can
install it with @cite{yum install python-xdot}):

@quotation


@float Figure

@image{sum-of-squares,,,image of a control flow graph,png}

@end float

@end quotation

@node Full example<4>,,Visualizing the control flow graph<2>,Tutorial part 3 Loops and variables<2>
@anchor{cp/intro/tutorial03 full-example}@anchor{11c}
@subsubsection Full example


@quotation

@example
/* Usage example for libgccjit.so's C++ API
   Copyright (C) 2014-2016 Free Software Foundation, Inc.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3, or (at your option)
any later version.

GCC is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License
along with GCC; see the file COPYING3.  If not see
<http://www.gnu.org/licenses/>.  */

#include <libgccjit++.h>

#include <stdlib.h>
#include <stdio.h>

void
create_code (gccjit::context ctxt)
@{
  /*
    Simple sum-of-squares, to test conditionals and looping

    int loop_test (int n)
    @{
      int i;
      int sum = 0;
      for (i = 0; i < n ; i ++)
      @{
	sum += i * i;
      @}
      return sum;
   */
  gccjit::type the_type = ctxt.get_int_type <int> ();
  gccjit::type return_type = the_type;

  gccjit::param n = ctxt.new_param (the_type, "n");
  std::vector<gccjit::param> params;
  params.push_back (n);
  gccjit::function func =
    ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                       return_type,
                       "loop_test",
                       params, 0);

  /* Build locals:  */
  gccjit::lvalue i = func.new_local (the_type, "i");
  gccjit::lvalue sum = func.new_local (the_type, "sum");

  gccjit::block b_initial = func.new_block ("initial");
  gccjit::block b_loop_cond = func.new_block ("loop_cond");
  gccjit::block b_loop_body = func.new_block ("loop_body");
  gccjit::block b_after_loop = func.new_block ("after_loop");

  /* sum = 0; */
  b_initial.add_assignment (sum, ctxt.zero (the_type));

  /* i = 0; */
  b_initial.add_assignment (i, ctxt.zero (the_type));

  b_initial.end_with_jump (b_loop_cond);

  /* if (i >= n) */
  b_loop_cond.end_with_conditional (
    i >= n,
    b_after_loop,
    b_loop_body);

  /* sum += i * i */
  b_loop_body.add_assignment_op (sum,
                                 GCC_JIT_BINARY_OP_PLUS,
                                 i * i);

  /* i++ */
  b_loop_body.add_assignment_op (i,
                                GCC_JIT_BINARY_OP_PLUS,
                                ctxt.one (the_type));

  b_loop_body.end_with_jump (b_loop_cond);

  /* return sum */
  b_after_loop.end_with_return (sum);
@}

int
main (int argc, char **argv)
@{
  gccjit::context ctxt;
  gcc_jit_result *result = NULL;

  /* Get a "context" object for working with the library.  */
  ctxt = gccjit::context::acquire ();

  /* Set some options on the context.
     Turn this on to see the code being generated, in assembler form.  */
  ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE,
                        0);

  /* Populate the context.  */
  create_code (ctxt);

  /* Compile the code.  */
  result = ctxt.compile ();

  ctxt.release ();

  if (!result)
    @{
      fprintf (stderr, "NULL result");
      return 1;
    @}

  /* Extract the generated code from "result".  */
  typedef int (*loop_test_fn_type) (int);
  loop_test_fn_type loop_test =
    (loop_test_fn_type)gcc_jit_result_get_code (result, "loop_test");
  if (!loop_test)
    @{
      fprintf (stderr, "NULL loop_test");
      gcc_jit_result_release (result);
      return 1;
    @}

  /* Run the generated code.  */
  int val = loop_test (10);
  printf("loop_test returned: %d\n", val);

  gcc_jit_result_release (result);
  return 0;
@}

@end example

@noindent
@end quotation

Building and running it:

@example
$ gcc \
    tut03-sum-of-squares.cc \
    -o tut03-sum-of-squares \
    -lgccjit

# Run the built program:
$ ./tut03-sum-of-squares
loop_test returned: 285
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>,,Tutorial part 3 Loops and variables<2>,Tutorial<2>
@anchor{cp/intro/tutorial04 tutorial-part-4-adding-jit-compilation-to-a-toy-interpreter}@anchor{11d}@anchor{cp/intro/tutorial04 doc}@anchor{11e}
@subsection Tutorial part 4: Adding JIT-compilation to a toy interpreter


In this example we construct a "toy" interpreter, and add JIT-compilation
to it.

@menu
* Our toy interpreter: Our toy interpreter<2>. 
* Compiling to machine code: Compiling to machine code<2>. 
* Setting things up: Setting things up<2>. 
* Populating the function: Populating the function<2>. 
* Verifying the control flow graph: Verifying the control flow graph<2>. 
* Compiling the context: Compiling the context<2>. 
* Single-stepping through the generated code: Single-stepping through the generated code<2>. 
* Examining the generated code: Examining the generated code<2>. 
* Putting it all together: Putting it all together<2>. 
* Behind the curtain; How does our code get optimized?: Behind the curtain How does our code get optimized?<2>. 

@end menu

@node Our toy interpreter<2>,Compiling to machine code<2>,,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 our-toy-interpreter}@anchor{11f}
@subsubsection Our toy interpreter


It's a stack-based interpreter, and is intended as a (very simple) example
of the kind of bytecode interpreter seen in dynamic languages such as
Python, Ruby etc.

For the sake of simplicity, our toy virtual machine is very limited:

@quotation


@itemize *

@item 
The only data type is @cite{int}

@item 
It can only work on one function at a time (so that the only
function call that can be made is to recurse).

@item 
Functions can only take one parameter.

@item 
Functions have a stack of @cite{int} values.

@item 
We'll implement function call within the interpreter by calling a
function in our implementation, rather than implementing our own
frame stack.

@item 
The parser is only good enough to get the examples to work.
@end itemize
@end quotation

Naturally, a real interpreter would be much more complicated that this.

The following operations are supported:


@multitable {xxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxx} {xxxxxxxxxxxxxxxxxx} 
@headitem

Operation

@tab

Meaning

@tab

Old Stack

@tab

New Stack

@item

DUP

@tab

Duplicate top of stack.

@tab

@code{[..., x]}

@tab

@code{[..., x, x]}

@item

ROT

@tab

Swap top two elements
of stack.

@tab

@code{[..., x, y]}

@tab

@code{[..., y, x]}

@item

BINARY_ADD

@tab

Add the top two elements
on the stack.

@tab

@code{[..., x, y]}

@tab

@code{[..., (x+y)]}

@item

BINARY_SUBTRACT

@tab

Likewise, but subtract.

@tab

@code{[..., x, y]}

@tab

@code{[..., (x-y)]}

@item

BINARY_MULT

@tab

Likewise, but multiply.

@tab

@code{[..., x, y]}

@tab

@code{[..., (x*y)]}

@item

BINARY_COMPARE_LT

@tab

Compare the top two
elements on the stack
and push a nonzero/zero
if (x<y).

@tab

@code{[..., x, y]}

@tab

@code{[..., (x<y)]}

@item

RECURSE

@tab

Recurse, passing the top
of the stack, and
popping the result.

@tab

@code{[..., x]}

@tab

@code{[..., fn(x)]}

@item

RETURN

@tab

Return the top of the
stack.

@tab

@code{[x]}

@tab

@code{[]}

@item

PUSH_CONST @cite{arg}

@tab

Push an int const.

@tab

@code{[...]}

@tab

@code{[..., arg]}

@item

JUMP_ABS_IF_TRUE @cite{arg}

@tab

Pop; if top of stack was
nonzero, jump to
@code{arg}.

@tab

@code{[..., x]}

@tab

@code{[...]}

@end multitable


Programs can be interpreted, disassembled, and compiled to machine code.

The interpreter reads @code{.toy} scripts.  Here's what a simple recursive
factorial program looks like, the script @code{factorial.toy}.
The parser ignores lines beginning with a @cite{#}.

@quotation

@example
# Simple recursive factorial implementation, roughly equivalent to:
#
#  int factorial (int arg)
#  @{
#     if (arg < 2)
#       return arg
#     return arg * factorial (arg - 1)
#  @}

# Initial state:
# stack: [arg]

# 0:
DUP
# stack: [arg, arg]

# 1:
PUSH_CONST 2
# stack: [arg, arg, 2]

# 2:
BINARY_COMPARE_LT
# stack: [arg, (arg < 2)]

# 3:
JUMP_ABS_IF_TRUE 9
# stack: [arg]

# 4:
DUP
# stack: [arg, arg]

# 5:
PUSH_CONST 1
# stack: [arg, arg, 1]

# 6:
BINARY_SUBTRACT
# stack: [arg,  (arg - 1)

# 7:
RECURSE
# stack: [arg, factorial(arg - 1)]

# 8:
BINARY_MULT
# stack: [arg * factorial(arg - 1)]

# 9:
RETURN

@end example

@noindent
@end quotation

The interpreter is a simple infinite loop with a big @code{switch} statement
based on what the next opcode is:

@quotation

@example

int
toyvm_function::interpret (int arg, FILE *trace)
@{
  toyvm_frame frame;
#define PUSH(ARG) (frame.push (ARG))
#define POP(ARG) (frame.pop ())

  frame.frm_function = this;
  frame.frm_pc = 0;
  frame.frm_cur_depth = 0;

  PUSH (arg);

  while (1)
    @{
      toyvm_op *op;
      int x, y;
      assert (frame.frm_pc < fn_num_ops);
      op = &fn_ops[frame.frm_pc++];

      if (trace)
	@{
	  frame.dump_stack (trace);
	  disassemble_op (op, frame.frm_pc, trace);
	@}

      switch (op->op_opcode)
	@{
	  /* Ops taking no operand.  */
	case DUP:
	  x = POP ();
	  PUSH (x);
	  PUSH (x);
	  break;

	case ROT:
	  y = POP ();
	  x = POP ();
	  PUSH (y);
	  PUSH (x);
	  break;

	case BINARY_ADD:
	  y = POP ();
	  x = POP ();
	  PUSH (x + y);
	  break;

	case BINARY_SUBTRACT:
	  y = POP ();
	  x = POP ();
	  PUSH (x - y);
	  break;

	case BINARY_MULT:
	  y = POP ();
	  x = POP ();
	  PUSH (x * y);
	  break;

	case BINARY_COMPARE_LT:
	  y = POP ();
	  x = POP ();
	  PUSH (x < y);
	  break;

	case RECURSE:
	  x = POP ();
	  x = interpret (x, trace);
	  PUSH (x);
	  break;

	case RETURN:
	  return POP ();

	  /* Ops taking an operand.  */
	case PUSH_CONST:
	  PUSH (op->op_operand);
	  break;

	case JUMP_ABS_IF_TRUE:
	  x = POP ();
	  if (x)
	    frame.frm_pc = op->op_operand;
	  break;

	default:
	  assert (0); /* unknown opcode */

	@} /* end of switch on opcode */
    @} /* end of while loop */

#undef PUSH
#undef POP
@}


@end example

@noindent
@end quotation

@node Compiling to machine code<2>,Setting things up<2>,Our toy interpreter<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 compiling-to-machine-code}@anchor{120}
@subsubsection Compiling to machine code


We want to generate machine code that can be cast to this type and
then directly executed in-process:

@quotation

@example
typedef int (*toyvm_compiled_func) (int);


@end example

@noindent
@end quotation

Our compiler isn't very sophisticated; it takes the implementation of
each opcode above, and maps it directly to the operations supported by
the libgccjit API.

How should we handle the stack?  In theory we could calculate what the
stack depth will be at each opcode, and optimize away the stack
manipulation "by hand".  We'll see below that libgccjit is able to do
this for us, so we'll implement stack manipulation
in a direct way, by creating a @code{stack} array and @code{stack_depth}
variables, local within the generated function, equivalent to this C code:

@example
int stack_depth;
int stack[MAX_STACK_DEPTH];
@end example

@noindent

We'll also have local variables @code{x} and @code{y} for use when implementing
the opcodes, equivalent to this:

@example
int x;
int y;
@end example

@noindent

This means our compiler has the following state:

@quotation

@example

  toyvm_function &toyvmfn;

  gccjit::context ctxt;

  gccjit::type int_type;
  gccjit::type bool_type;
  gccjit::type stack_type; /* int[MAX_STACK_DEPTH] */

  gccjit::rvalue const_one;

  gccjit::function fn;
  gccjit::param param_arg;
  gccjit::lvalue stack;
  gccjit::lvalue stack_depth;
  gccjit::lvalue x;
  gccjit::lvalue y;

  gccjit::location op_locs[MAX_OPS];
  gccjit::block initial_block;
  gccjit::block op_blocks[MAX_OPS];


@end example

@noindent
@end quotation

@node Setting things up<2>,Populating the function<2>,Compiling to machine code<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 setting-things-up}@anchor{121}
@subsubsection Setting things up


First we create our types:

@quotation

@example

void
compilation_state::create_types ()
@{
  /* Create types.  */
  int_type = ctxt.get_type (GCC_JIT_TYPE_INT);
  bool_type = ctxt.get_type (GCC_JIT_TYPE_BOOL);
  stack_type = ctxt.new_array_type (int_type, MAX_STACK_DEPTH);


@end example

@noindent
@end quotation

along with extracting a useful @cite{int} constant:

@quotation

@example
  const_one = ctxt.one (int_type);

@}


@end example

@noindent
@end quotation

We'll implement push and pop in terms of the @code{stack} array and
@code{stack_depth}.  Here are helper functions for adding statements to
a block, implementing pushing and popping values:

@quotation

@example

void
compilation_state::add_push (gccjit::block block,
                             gccjit::rvalue rvalue,
                             gccjit::location loc)
@{
  /* stack[stack_depth] = RVALUE */
  block.add_assignment (
    /* stack[stack_depth] */
    ctxt.new_array_access (
      stack,
      stack_depth,
      loc),
    rvalue,
    loc);

  /* "stack_depth++;".  */
  block.add_assignment_op (
    stack_depth,
    GCC_JIT_BINARY_OP_PLUS,
    const_one,
    loc);
@}

void
compilation_state::add_pop (gccjit::block block,
                            gccjit::lvalue lvalue,
                            gccjit::location loc)
@{
  /* "--stack_depth;".  */
  block.add_assignment_op (
    stack_depth,
    GCC_JIT_BINARY_OP_MINUS,
    const_one,
    loc);

  /* "LVALUE = stack[stack_depth];".  */
  block.add_assignment (
    lvalue,
    /* stack[stack_depth] */
    ctxt.new_array_access (stack,
                           stack_depth,
                           loc),
    loc);
@}


@end example

@noindent
@end quotation

We will support single-stepping through the generated code in the
debugger, so we need to create @code{gccjit::location} instances, one
per operation in the source code.  These will reference the lines of
e.g. @code{factorial.toy}.

@quotation

@example

void
compilation_state::create_locations ()
@{
  for (int pc = 0; pc < toyvmfn.fn_num_ops; pc++)
    @{
      toyvm_op *op = &toyvmfn.fn_ops[pc];

      op_locs[pc] = ctxt.new_location (toyvmfn.fn_filename,
                                       op->op_linenum,
                                       0); /* column */
    @}
@}


@end example

@noindent
@end quotation

Let's create the function itself.  As usual, we create its parameter
first, then use the parameter to create the function:

@quotation

@example

void
compilation_state::create_function (const char *funcname)
@{
  std::vector <gccjit::param> params;
  param_arg = ctxt.new_param (int_type, "arg", op_locs[0]);
  params.push_back (param_arg);
  fn = ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                          int_type,
                          funcname,
                          params, 0,
                          op_locs[0]);


@end example

@noindent
@end quotation

We create the locals within the function.

@quotation

@example
  stack = fn.new_local (stack_type, "stack");
  stack_depth = fn.new_local (int_type, "stack_depth");
  x = fn.new_local (int_type, "x");
  y = fn.new_local (int_type, "y");


@end example

@noindent
@end quotation

@node Populating the function<2>,Verifying the control flow graph<2>,Setting things up<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 populating-the-function}@anchor{122}
@subsubsection Populating the function


There's some one-time initialization, and the API treats the first block
you create as the entrypoint of the function, so we need to create that
block first:

@quotation

@example
  initial_block = fn.new_block ("initial");


@end example

@noindent
@end quotation

We can now create blocks for each of the operations.  Most of these will
be consolidated into larger blocks when the optimizer runs.

@quotation

@example
  for (int pc = 0; pc < toyvmfn.fn_num_ops; pc++)
    @{
      char buf[16];
      sprintf (buf, "instr%i", pc);
      op_blocks[pc] = fn.new_block (buf);
    @}


@end example

@noindent
@end quotation

Now that we have a block it can jump to when it's done, we can populate
the initial block:

@quotation

@example

  /* "stack_depth = 0;".  */
  initial_block.add_assignment (stack_depth,
                                ctxt.zero (int_type),
                                op_locs[0]);

  /* "PUSH (arg);".  */
  add_push (initial_block,
	    param_arg,
            op_locs[0]);

  /* ...and jump to insn 0.  */
  initial_block.end_with_jump (op_blocks[0],
                               op_locs[0]);


@end example

@noindent
@end quotation

We can now populate the blocks for the individual operations.  We loop
through them, adding instructions to their blocks:

@quotation

@example
  for (int pc = 0; pc < toyvmfn.fn_num_ops; pc++)
    @{
      gccjit::location loc = op_locs[pc];

      gccjit::block block = op_blocks[pc];
      gccjit::block next_block = (pc < toyvmfn.fn_num_ops
                                  ? op_blocks[pc + 1]
                                  : NULL);

      toyvm_op *op;
      op = &toyvmfn.fn_ops[pc];


@end example

@noindent
@end quotation

We're going to have another big @code{switch} statement for implementing
the opcodes, this time for compiling them, rather than interpreting
them.  It's helpful to have macros for implementing push and pop, so that
we can make the @code{switch} statement that's coming up look as much as
possible like the one above within the interpreter:

@example

#define X_EQUALS_POP()\
      add_pop (block, x, loc)
#define Y_EQUALS_POP()\
      add_pop (block, y, loc)
#define PUSH_RVALUE(RVALUE)\
      add_push (block, (RVALUE), loc)
#define PUSH_X()\
      PUSH_RVALUE (x)
#define PUSH_Y() \
      PUSH_RVALUE (y)


@end example

@noindent

@cartouche
@quotation Note 
A particularly clever implementation would have an @emph{identical}
@code{switch} statement shared by the interpreter and the compiler, with
some preprocessor "magic".  We're not doing that here, for the sake
of simplicity.
@end quotation
@end cartouche

When I first implemented this compiler, I accidentally missed an edit
when copying and pasting the @code{Y_EQUALS_POP} macro, so that popping the
stack into @code{y} instead erroneously assigned it to @code{x}, leaving @code{y}
uninitialized.

To track this kind of thing down, we can use
@pxref{123,,gccjit;;block;;add_comment()} to add descriptive comments
to the internal representation.  This is invaluable when looking through
the generated IR for, say @code{factorial}:

@quotation

@example

      block.add_comment (opcode_names[op->op_opcode], loc);


@end example

@noindent
@end quotation

We can now write the big @code{switch} statement that implements the
individual opcodes, populating the relevant block with statements:

@quotation

@example

      switch (op->op_opcode)
	@{
	case DUP:
	  X_EQUALS_POP ();
	  PUSH_X ();
	  PUSH_X ();
	  break;

	case ROT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_Y ();
	  PUSH_X ();
	  break;

	case BINARY_ADD:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
	   ctxt.new_binary_op (
	     GCC_JIT_BINARY_OP_PLUS,
	     int_type,
             x, y,
             loc));
	  break;

	case BINARY_SUBTRACT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
           ctxt.new_binary_op (
	     GCC_JIT_BINARY_OP_MINUS,
	     int_type,
             x, y,
             loc));
	  break;

	case BINARY_MULT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
           ctxt.new_binary_op (
	     GCC_JIT_BINARY_OP_MULT,
	     int_type,
             x, y,
             loc));
	  break;

	case BINARY_COMPARE_LT:
	  Y_EQUALS_POP ();
	  X_EQUALS_POP ();
	  PUSH_RVALUE (
	     /* cast of bool to int */
	     ctxt.new_cast (
	       /* (x < y) as a bool */
	       ctxt.new_comparison (
		 GCC_JIT_COMPARISON_LT,
                 x, y,
                 loc),
	       int_type,
               loc));
	  break;

	case RECURSE:
	  @{
	    X_EQUALS_POP ();
	    PUSH_RVALUE (
	      ctxt.new_call (
		fn,
		x,
                loc));
	    break;
	  @}

	case RETURN:
	  X_EQUALS_POP ();
	  block.end_with_return (x, loc);
	  break;

	  /* Ops taking an operand.  */
	case PUSH_CONST:
	  PUSH_RVALUE (
	    ctxt.new_rvalue (int_type, op->op_operand));
	  break;

	case JUMP_ABS_IF_TRUE:
	  X_EQUALS_POP ();
	  block.end_with_conditional (
	    /* "(bool)x".  */
            ctxt.new_cast (x, bool_type, loc),
	    op_blocks[op->op_operand], /* on_true */
	    next_block, /* on_false */
            loc); 
	  break;

	default:
	  assert(0);
	@} /* end of switch on opcode */


@end example

@noindent
@end quotation

Every block must be terminated, via a call to one of the
@code{gccjit::block::end_with_} entrypoints.  This has been done for two
of the opcodes, but we need to do it for the other ones, by jumping
to the next block.

@quotation

@example
      if (op->op_opcode != JUMP_ABS_IF_TRUE
	  && op->op_opcode != RETURN)
	block.end_with_jump (next_block, loc);


@end example

@noindent
@end quotation

This is analogous to simply incrementing the program counter.

@node Verifying the control flow graph<2>,Compiling the context<2>,Populating the function<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 verifying-the-control-flow-graph}@anchor{124}
@subsubsection Verifying the control flow graph


Having finished looping over the blocks, the context is complete.

As before, we can verify that the control flow and statements are sane by
using @pxref{11b,,gccjit;;function;;dump_to_dot()}:

@example
fn.dump_to_dot ("/tmp/factorial.dot");
@end example

@noindent

and viewing the result.  Note how the label names, comments, and
variable names show up in the dump, to make it easier to spot
errors in our compiler.

@quotation


@float Figure

@image{factorial,,,image of a control flow graph,png}

@end float

@end quotation

@node Compiling the context<2>,Single-stepping through the generated code<2>,Verifying the control flow graph<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 compiling-the-context}@anchor{125}
@subsubsection Compiling the context


Having finished looping over the blocks and populating them with
statements, the context is complete.

We can now compile it, and extract machine code from the result:

@quotation

@example
  gcc_jit_result *result = state.compile ();

  return (toyvm_compiled_func)gcc_jit_result_get_code (result, funcname);

@end example

@noindent
@end quotation

We can now run the result:

@quotation

@example
  toyvm_compiled_func code = fn->compile ();
  printf ("compiler result: %d\n",
	  code (atoi (argv[2])));


@end example

@noindent
@end quotation

@node Single-stepping through the generated code<2>,Examining the generated code<2>,Compiling the context<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 single-stepping-through-the-generated-code}@anchor{126}
@subsubsection Single-stepping through the generated code


It's possible to debug the generated code.  To do this we need to both:

@quotation


@itemize *

@item 
Set up source code locations for our statements, so that we can
meaningfully step through the code.  We did this above by
calling @pxref{127,,gccjit;;context;;new_location()} and using the
results.

@item 
Enable the generation of debugging information, by setting
@pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} on the
@code{gccjit::context} via
@pxref{10c,,gccjit;;context;;set_bool_option()}:

@example
ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DEBUGINFO, 1);
@end example

@noindent
@end itemize
@end quotation

Having done this, we can put a breakpoint on the generated function:

@example
$ gdb --args ./toyvm factorial.toy 10
(gdb) break factorial
Function "factorial" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (factorial) pending.
(gdb) run
Breakpoint 1, factorial (arg=10) at factorial.toy:14
14    DUP
@end example

@noindent

We've set up location information, which references @code{factorial.toy}.
This allows us to use e.g. @code{list} to see where we are in the script:

@example
(gdb) list
9
10    # Initial state:
11    # stack: [arg]
12
13    # 0:
14    DUP
15    # stack: [arg, arg]
16
17    # 1:
18    PUSH_CONST 2
@end example

@noindent

and to step through the function, examining the data:

@example
(gdb) n
18    PUSH_CONST 2
(gdb) n
22    BINARY_COMPARE_LT
(gdb) print stack
$5 = @{10, 10, 2, 0, -7152, 32767, 0, 0@}
(gdb) print stack_depth
$6 = 3
@end example

@noindent

You'll see that the parts of the @code{stack} array that haven't been
touched yet are uninitialized.

@cartouche
@quotation Note 
Turning on optimizations may lead to unpredictable results when
stepping through the generated code: the execution may appear to
"jump around" the source code.  This is analogous to turning up the
optimization level in a regular compiler.
@end quotation
@end cartouche

@node Examining the generated code<2>,Putting it all together<2>,Single-stepping through the generated code<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 examining-the-generated-code}@anchor{128}
@subsubsection Examining the generated code


How good is the optimized code?

We can turn up optimizations, by calling
@pxref{10d,,gccjit;;context;;set_int_option()} with
@pxref{1f,,GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL}:

@example
ctxt.set_int_option (GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL, 3);
@end example

@noindent

One of GCC's internal representations is called "gimple".  A dump of the
initial gimple representation of the code can be seen by setting:

@example
ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE, 1);
@end example

@noindent

With optimization on and source locations displayed, this gives:

@c We'll use "c" for gimple dumps

@example
factorial (signed int arg)
@{
  <unnamed type> D.80;
  signed int D.81;
  signed int D.82;
  signed int D.83;
  signed int D.84;
  signed int D.85;
  signed int y;
  signed int x;
  signed int stack_depth;
  signed int stack[8];

  try
    @{
      initial:
      stack_depth = 0;
      stack[stack_depth] = arg;
      stack_depth = stack_depth + 1;
      goto instr0;
      instr0:
      /* DUP */:
      stack_depth = stack_depth + -1;
      x = stack[stack_depth];
      stack[stack_depth] = x;
      stack_depth = stack_depth + 1;
      stack[stack_depth] = x;
      stack_depth = stack_depth + 1;
      goto instr1;
      instr1:
      /* PUSH_CONST */:
      stack[stack_depth] = 2;
      stack_depth = stack_depth + 1;
      goto instr2;

      /* etc */
@end example

@noindent

You can see the generated machine code in assembly form via:

@example
ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE, 1);
result = ctxt.compile ();
@end example

@noindent

which shows that (on this x86_64 box) the compiler has unrolled the loop
and is using MMX instructions to perform several multiplications
simultaneously:

@example
        .file   "fake.c"
        .text
.Ltext0:
        .p2align 4,,15
        .globl  factorial
        .type   factorial, @@function
factorial:
.LFB0:
        .file 1 "factorial.toy"
        .loc 1 14 0
        .cfi_startproc
.LVL0:
.L2:
        .loc 1 26 0
        cmpl    $1, %edi
        jle     .L13
        leal    -1(%rdi), %edx
        movl    %edx, %ecx
        shrl    $2, %ecx
        leal    0(,%rcx,4), %esi
        testl   %esi, %esi
        je      .L14
        cmpl    $9, %edx
        jbe     .L14
        leal    -2(%rdi), %eax
        movl    %eax, -16(%rsp)
        leal    -3(%rdi), %eax
        movd    -16(%rsp), %xmm0
        movl    %edi, -16(%rsp)
        movl    %eax, -12(%rsp)
        movd    -16(%rsp), %xmm1
        xorl    %eax, %eax
        movl    %edx, -16(%rsp)
        movd    -12(%rsp), %xmm4
        movd    -16(%rsp), %xmm6
        punpckldq       %xmm4, %xmm0
        movdqa  .LC1(%rip), %xmm4
        punpckldq       %xmm6, %xmm1
        punpcklqdq      %xmm0, %xmm1
        movdqa  .LC0(%rip), %xmm0
        jmp     .L5
        # etc - edited for brevity
@end example

@noindent

This is clearly overkill for a function that will likely overflow the
@code{int} type before the vectorization is worthwhile - but then again, this
is a toy example.

Turning down the optimization level to 2:

@example
ctxt.set_int_option (GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL, 2);
@end example

@noindent

yields this code, which is simple enough to quote in its entirety:

@example
        .file   "fake.c"
        .text
        .p2align 4,,15
        .globl  factorial
        .type   factorial, @@function
factorial:
.LFB0:
        .cfi_startproc
.L2:
        cmpl    $1, %edi
        jle     .L8
        movl    $1, %edx
        jmp     .L4
        .p2align 4,,10
        .p2align 3
.L6:
        movl    %eax, %edi
.L4:
.L5:
        leal    -1(%rdi), %eax
        imull   %edi, %edx
        cmpl    $1, %eax
        jne     .L6
.L3:
.L7:
        imull   %edx, %eax
        ret
.L8:
        movl    %edi, %eax
        movl    $1, %edx
        jmp     .L7
        .cfi_endproc
.LFE0:
        .size   factorial, .-factorial
        .ident  "GCC: (GNU) 4.9.0 20131023 (Red Hat 0.2-%@{gcc_release@})"
        .section        .note.GNU-stack,"",@@progbits
@end example

@noindent

Note that the stack pushing and popping have been eliminated, as has the
recursive call (in favor of an iteration).

@node Putting it all together<2>,Behind the curtain How does our code get optimized?<2>,Examining the generated code<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 putting-it-all-together}@anchor{129}
@subsubsection Putting it all together


The complete example can be seen in the source tree at
@code{gcc/jit/docs/examples/tut04-toyvm/toyvm.cc}

along with a Makefile and a couple of sample .toy scripts:

@example
$ ls -al
drwxrwxr-x. 2 david david   4096 Sep 19 17:46 .
drwxrwxr-x. 3 david david   4096 Sep 19 15:26 ..
-rw-rw-r--. 1 david david    615 Sep 19 12:43 factorial.toy
-rw-rw-r--. 1 david david    834 Sep 19 13:08 fibonacci.toy
-rw-rw-r--. 1 david david    238 Sep 19 14:22 Makefile
-rw-rw-r--. 1 david david  16457 Sep 19 17:07 toyvm.cc

$ make toyvm
g++ -Wall -g -o toyvm toyvm.cc -lgccjit

$ ./toyvm factorial.toy 10
interpreter result: 3628800
compiler result: 3628800

$ ./toyvm fibonacci.toy 10
interpreter result: 55
compiler result: 55
@end example

@noindent

@node Behind the curtain How does our code get optimized?<2>,,Putting it all together<2>,Tutorial part 4 Adding JIT-compilation to a toy interpreter<2>
@anchor{cp/intro/tutorial04 behind-the-curtain-how-does-our-code-get-optimized}@anchor{12a}
@subsubsection Behind the curtain: How does our code get optimized?


Our example is done, but you may be wondering about exactly how the
compiler turned what we gave it into the machine code seen above.

We can examine what the compiler is doing in detail by setting:

@example
state.ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING, 1);
state.ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES, 1);
@end example

@noindent

This will dump detailed information about the compiler's state to a
directory under @code{/tmp}, and keep it from being cleaned up.

The precise names and their formats of these files is subject to change.
Higher optimization levels lead to more files.
Here's what I saw (edited for brevity; there were almost 200 files):

@example
intermediate files written to /tmp/libgccjit-KPQbGw
$ ls /tmp/libgccjit-KPQbGw/
fake.c.000i.cgraph
fake.c.000i.type-inheritance
fake.c.004t.gimple
fake.c.007t.omplower
fake.c.008t.lower
fake.c.011t.eh
fake.c.012t.cfg
fake.c.014i.visibility
fake.c.015i.early_local_cleanups
fake.c.016t.ssa
# etc
@end example

@noindent

The gimple code is converted into Static Single Assignment form,
with annotations for use when generating the debuginfo:

@example
$ less /tmp/libgccjit-KPQbGw/fake.c.016t.ssa
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;
  signed int _56;

initial:
  stack_depth_3 = 0;
  # DEBUG stack_depth => stack_depth_3
  stack[stack_depth_3] = arg_5(D);
  stack_depth_7 = stack_depth_3 + 1;
  # DEBUG stack_depth => stack_depth_7
  # DEBUG instr0 => NULL
  # DEBUG /* DUP */ => NULL
  stack_depth_8 = stack_depth_7 + -1;
  # DEBUG stack_depth => stack_depth_8
  x_9 = stack[stack_depth_8];
  # DEBUG x => x_9
  stack[stack_depth_8] = x_9;
  stack_depth_11 = stack_depth_8 + 1;
  # DEBUG stack_depth => stack_depth_11
  stack[stack_depth_11] = x_9;
  stack_depth_13 = stack_depth_11 + 1;
  # DEBUG stack_depth => stack_depth_13
  # DEBUG instr1 => NULL
  # DEBUG /* PUSH_CONST */ => NULL
  stack[stack_depth_13] = 2;

  /* etc; edited for brevity */
@end example

@noindent

We can perhaps better see the code by turning off
@pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} to suppress all those @code{DEBUG}
statements, giving:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.016t.ssa
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;
  signed int _56;

initial:
  stack_depth_3 = 0;
  stack[stack_depth_3] = arg_5(D);
  stack_depth_7 = stack_depth_3 + 1;
  stack_depth_8 = stack_depth_7 + -1;
  x_9 = stack[stack_depth_8];
  stack[stack_depth_8] = x_9;
  stack_depth_11 = stack_depth_8 + 1;
  stack[stack_depth_11] = x_9;
  stack_depth_13 = stack_depth_11 + 1;
  stack[stack_depth_13] = 2;
  stack_depth_15 = stack_depth_13 + 1;
  stack_depth_16 = stack_depth_15 + -1;
  y_17 = stack[stack_depth_16];
  stack_depth_18 = stack_depth_16 + -1;
  x_19 = stack[stack_depth_18];
  _20 = x_19 < y_17;
  _21 = (signed int) _20;
  stack[stack_depth_18] = _21;
  stack_depth_23 = stack_depth_18 + 1;
  stack_depth_24 = stack_depth_23 + -1;
  x_25 = stack[stack_depth_24];
  if (x_25 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  stack_depth_26 = stack_depth_24 + -1;
  x_27 = stack[stack_depth_26];
  stack[stack_depth_26] = x_27;
  stack_depth_29 = stack_depth_26 + 1;
  stack[stack_depth_29] = x_27;
  stack_depth_31 = stack_depth_29 + 1;
  stack[stack_depth_31] = 1;
  stack_depth_33 = stack_depth_31 + 1;
  stack_depth_34 = stack_depth_33 + -1;
  y_35 = stack[stack_depth_34];
  stack_depth_36 = stack_depth_34 + -1;
  x_37 = stack[stack_depth_36];
  _38 = x_37 - y_35;
  stack[stack_depth_36] = _38;
  stack_depth_40 = stack_depth_36 + 1;
  stack_depth_41 = stack_depth_40 + -1;
  x_42 = stack[stack_depth_41];
  _44 = factorial (x_42);
  stack[stack_depth_41] = _44;
  stack_depth_46 = stack_depth_41 + 1;
  stack_depth_47 = stack_depth_46 + -1;
  y_48 = stack[stack_depth_47];
  stack_depth_49 = stack_depth_47 + -1;
  x_50 = stack[stack_depth_49];
  _51 = x_50 * y_48;
  stack[stack_depth_49] = _51;
  stack_depth_53 = stack_depth_49 + 1;

  # stack_depth_1 = PHI <stack_depth_24(2), stack_depth_53(3)>
instr9:
/* RETURN */:
  stack_depth_54 = stack_depth_1 + -1;
  x_55 = stack[stack_depth_54];
  _56 = x_55;
  stack =@{v@} @{CLOBBER@};
  return _56;

@}
@end example

@noindent

Note in the above how all the @code{gccjit::block} instances we
created have been consolidated into just 3 blocks in GCC's internal
representation: @code{initial}, @code{instr4} and @code{instr9}.

@menu
* Optimizing away stack manipulation: Optimizing away stack manipulation<2>. 
* Elimination of tail recursion: Elimination of tail recursion<2>. 

@end menu

@node Optimizing away stack manipulation<2>,Elimination of tail recursion<2>,,Behind the curtain How does our code get optimized?<2>
@anchor{cp/intro/tutorial04 optimizing-away-stack-manipulation}@anchor{12b}
@subsubsection Optimizing away stack manipulation


Recall our simple implementation of stack operations.  Let's examine
how the stack operations are optimized away.

After a pass of constant-propagation, the depth of the stack at each
opcode can be determined at compile-time:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.021t.ccp1
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;

initial:
  stack[0] = arg_5(D);
  x_9 = stack[0];
  stack[0] = x_9;
  stack[1] = x_9;
  stack[2] = 2;
  y_17 = stack[2];
  x_19 = stack[1];
  _20 = x_19 < y_17;
  _21 = (signed int) _20;
  stack[1] = _21;
  x_25 = stack[1];
  if (x_25 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  x_27 = stack[0];
  stack[0] = x_27;
  stack[1] = x_27;
  stack[2] = 1;
  y_35 = stack[2];
  x_37 = stack[1];
  _38 = x_37 - y_35;
  stack[1] = _38;
  x_42 = stack[1];
  _44 = factorial (x_42);
  stack[1] = _44;
  y_48 = stack[1];
  x_50 = stack[0];
  _51 = x_50 * y_48;
  stack[0] = _51;

instr9:
/* RETURN */:
  x_55 = stack[0];
  x_56 = x_55;
  stack =@{v@} @{CLOBBER@};
  return x_56;

@}
@end example

@noindent

Note how, in the above, all those @code{stack_depth} values are now just
constants: we're accessing specific stack locations at each opcode.

The "esra" pass ("Early Scalar Replacement of Aggregates") breaks
out our "stack" array into individual elements:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.024t.esra
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

Created a replacement for stack offset: 0, size: 32: stack$0
Created a replacement for stack offset: 32, size: 32: stack$1
Created a replacement for stack offset: 64, size: 32: stack$2

Symbols to be put in SSA form
@{ D.89 D.90 D.91 @}
Incremental SSA update started at block: 0
Number of blocks in CFG: 5
Number of blocks to update: 4 ( 80%)


factorial (signed int arg)
@{
  signed int stack$2;
  signed int stack$1;
  signed int stack$0;
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;

initial:
  stack$0_45 = arg_5(D);
  x_9 = stack$0_45;
  stack$0_39 = x_9;
  stack$1_32 = x_9;
  stack$2_30 = 2;
  y_17 = stack$2_30;
  x_19 = stack$1_32;
  _20 = x_19 < y_17;
  _21 = (signed int) _20;
  stack$1_28 = _21;
  x_25 = stack$1_28;
  if (x_25 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  x_27 = stack$0_39;
  stack$0_22 = x_27;
  stack$1_14 = x_27;
  stack$2_12 = 1;
  y_35 = stack$2_12;
  x_37 = stack$1_14;
  _38 = x_37 - y_35;
  stack$1_10 = _38;
  x_42 = stack$1_10;
  _44 = factorial (x_42);
  stack$1_6 = _44;
  y_48 = stack$1_6;
  x_50 = stack$0_22;
  _51 = x_50 * y_48;
  stack$0_1 = _51;

  # stack$0_52 = PHI <stack$0_39(2), stack$0_1(3)>
instr9:
/* RETURN */:
  x_55 = stack$0_52;
  x_56 = x_55;
  stack =@{v@} @{CLOBBER@};
  return x_56;

@}
@end example

@noindent

Hence at this point, all those pushes and pops of the stack are now
simply assignments to specific temporary variables.

After some copy propagation, the stack manipulation has been completely
optimized away:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.026t.copyprop1
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

factorial (signed int arg)
@{
  signed int stack$2;
  signed int stack$1;
  signed int stack$0;
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int _44;
  signed int _51;

initial:
  stack$0_39 = arg_5(D);
  _20 = arg_5(D) <= 1;
  _21 = (signed int) _20;
  if (_21 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  _38 = arg_5(D) + -1;
  _44 = factorial (_38);
  _51 = arg_5(D) * _44;
  stack$0_1 = _51;

  # stack$0_52 = PHI <arg_5(D)(2), _51(3)>
instr9:
/* RETURN */:
  stack =@{v@} @{CLOBBER@};
  return stack$0_52;

@}
@end example

@noindent

Later on, another pass finally eliminated @code{stack_depth} local and the
unused parts of the @cite{stack`} array altogether:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.036t.release_ssa
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)

Released 44 names, 314.29%, removed 44 holes
factorial (signed int arg)
@{
  signed int stack$0;
  signed int mult_acc_1;
  <unnamed type> _5;
  signed int _6;
  signed int _7;
  signed int mul_tmp_10;
  signed int mult_acc_11;
  signed int mult_acc_13;

  # arg_9 = PHI <arg_8(D)(0)>
  # mult_acc_13 = PHI <1(0)>
initial:

  <bb 5>:
  # arg_4 = PHI <arg_9(2), _7(3)>
  # mult_acc_1 = PHI <mult_acc_13(2), mult_acc_11(3)>
  _5 = arg_4 <= 1;
  _6 = (signed int) _5;
  if (_6 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  _7 = arg_4 + -1;
  mult_acc_11 = mult_acc_1 * arg_4;
  goto <bb 5>;

  # stack$0_12 = PHI <arg_4(5)>
instr9:
/* RETURN */:
  mul_tmp_10 = mult_acc_1 * stack$0_12;
  return mul_tmp_10;

@}
@end example

@noindent

@node Elimination of tail recursion<2>,,Optimizing away stack manipulation<2>,Behind the curtain How does our code get optimized?<2>
@anchor{cp/intro/tutorial04 elimination-of-tail-recursion}@anchor{12c}
@subsubsection Elimination of tail recursion


Another significant optimization is the detection that the call to
@code{factorial} is tail recursion, which can be eliminated in favor of
an iteration:

@example
$ less /tmp/libgccjit-1Hywc0/fake.c.030t.tailr1
@end example

@noindent

@example
;; Function factorial (factorial, funcdef_no=0, decl_uid=53, symbol_order=0)


Symbols to be put in SSA form
@{ D.88 @}
Incremental SSA update started at block: 0
Number of blocks in CFG: 5
Number of blocks to update: 4 ( 80%)


factorial (signed int arg)
@{
  signed int stack$2;
  signed int stack$1;
  signed int stack$0;
  signed int stack[8];
  signed int stack_depth;
  signed int x;
  signed int y;
  signed int mult_acc_1;
  <unnamed type> _20;
  signed int _21;
  signed int _38;
  signed int mul_tmp_44;
  signed int mult_acc_51;

  # arg_5 = PHI <arg_39(D)(0), _38(3)>
  # mult_acc_1 = PHI <1(0), mult_acc_51(3)>
initial:
  _20 = arg_5 <= 1;
  _21 = (signed int) _20;
  if (_21 != 0)
    goto <bb 4> (instr9);
  else
    goto <bb 3> (instr4);

instr4:
/* DUP */:
  _38 = arg_5 + -1;
  mult_acc_51 = mult_acc_1 * arg_5;
  goto <bb 2> (initial);

  # stack$0_52 = PHI <arg_5(2)>
instr9:
/* RETURN */:
  stack =@{v@} @{CLOBBER@};
  mul_tmp_44 = mult_acc_1 * stack$0_52;
  return mul_tmp_44;

@}
@end example

@noindent

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Topic Reference<2>,,Tutorial<2>,C++ bindings for libgccjit
@anchor{cp/topics/index doc}@anchor{12d}@anchor{cp/topics/index topic-reference}@anchor{12e}
@section Topic Reference


@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@menu
* Compilation contexts: Compilation contexts<2>. 
* Objects: Objects<2>. 
* Types: Types<2>. 
* Expressions: Expressions<2>. 
* Creating and using functions: Creating and using functions<2>. 
* Source Locations: Source Locations<2>. 
* Compiling a context: Compiling a context<2>. 

Compilation contexts

* Lifetime-management: Lifetime-management<2>. 
* Thread-safety: Thread-safety<2>. 
* Error-handling: Error-handling<3>. 
* Debugging: Debugging<2>. 
* Options: Options<4>. 

Options

* String Options: String Options<2>. 
* Boolean options: Boolean options<2>. 
* Integer options: Integer options<2>. 
* Additional command-line options: Additional command-line options<2>. 

Types

* Standard types: Standard types<2>. 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile<2>. 
* Structures and unions: Structures and unions<2>. 

Expressions

* Rvalues: Rvalues<2>. 
* Lvalues: Lvalues<2>. 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions<2>. 

Rvalues

* Simple expressions: Simple expressions<2>. 
* Unary Operations: Unary Operations<2>. 
* Binary Operations: Binary Operations<2>. 
* Comparisons: Comparisons<2>. 
* Function calls: Function calls<2>. 
* Type-coercion: Type-coercion<2>. 

Lvalues

* Global variables: Global variables<2>. 

Creating and using functions

* Params: Params<2>. 
* Functions: Functions<2>. 
* Blocks: Blocks<2>. 
* Statements: Statements<2>. 

Source Locations

* Faking it: Faking it<2>. 

Compiling a context

* In-memory compilation: In-memory compilation<2>. 
* Ahead-of-time compilation: Ahead-of-time compilation<2>. 

@end menu


@node Compilation contexts<2>,Objects<2>,,Topic Reference<2>
@anchor{cp/topics/contexts compilation-contexts}@anchor{12f}@anchor{cp/topics/contexts doc}@anchor{130}
@subsection Compilation contexts


@geindex gccjit;;context (C++ class)
@anchor{cp/topics/contexts gccjit context}@anchor{131}
@deffn {C++ Class} gccjit::context
@end deffn

The top-level of the C++ API is the @pxref{131,,gccjit;;context} type.

A @pxref{131,,gccjit;;context} instance encapsulates the state of a
compilation.

You can set up options on it, and add types, functions and code.
Invoking @pxref{10a,,gccjit;;context;;compile()} on it gives you a
@pxref{16,,gcc_jit_result *}.

It is a thin wrapper around the C API's @pxref{8,,gcc_jit_context *}.

@menu
* Lifetime-management: Lifetime-management<2>. 
* Thread-safety: Thread-safety<2>. 
* Error-handling: Error-handling<3>. 
* Debugging: Debugging<2>. 
* Options: Options<4>. 

@end menu

@node Lifetime-management<2>,Thread-safety<2>,,Compilation contexts<2>
@anchor{cp/topics/contexts lifetime-management}@anchor{132}
@subsubsection Lifetime-management


Contexts are the unit of lifetime-management within the API: objects
have their lifetime bounded by the context they are created within, and
cleanup of such objects is done for you when the context is released.

@geindex gccjit;;context;;acquire (C++ function)
@anchor{cp/topics/contexts gccjit context acquire}@anchor{104}
@deffn {C++ Function} gccjit::context gccjit::context::acquire ()

This function acquires a new @pxref{131,,gccjit;;context} instance,
which is independent of any others that may be present within this
process.
@end deffn

@geindex gccjit;;context;;release (C++ function)
@anchor{cp/topics/contexts gccjit context release}@anchor{106}
@deffn {C++ Function} void gccjit::context::release ()

This function releases all resources associated with the given context.
Both the context itself and all of its @code{gccjit::object *}
instances are cleaned up.  It should be called exactly once on a given
context.

It is invalid to use the context or any of its "contextual" objects
after calling this.

@example
ctxt.release ();
@end example

@noindent
@end deffn

@geindex gccjit;;context;;new_child_context (C++ function)
@anchor{cp/topics/contexts gccjit context new_child_context}@anchor{133}
@deffn {C++ Function} gccjit::context gccjit::context::new_child_context ()

Given an existing JIT context, create a child context.

The child inherits a copy of all option-settings from the parent.

The child can reference objects created within the parent, but not
vice-versa.

The lifetime of the child context must be bounded by that of the
parent: you should release a child context before releasing the parent
context.

If you use a function from a parent context within a child context,
you have to compile the parent context before you can compile the
child context, and the gccjit::result of the parent context must
outlive the gccjit::result of the child context.

This allows caching of shared initializations.  For example, you could
create types and declarations of global functions in a parent context
once within a process, and then create child contexts whenever a
function or loop becomes hot. Each such child context can be used for
JIT-compiling just one function or loop, but can reference types
and helper functions created within the parent context.

Contexts can be arbitrarily nested, provided the above rules are
followed, but it's probably not worth going above 2 or 3 levels, and
there will likely be a performance hit for such nesting.
@end deffn

@node Thread-safety<2>,Error-handling<3>,Lifetime-management<2>,Compilation contexts<2>
@anchor{cp/topics/contexts thread-safety}@anchor{134}
@subsubsection Thread-safety


Instances of @pxref{131,,gccjit;;context} created via
@pxref{104,,gccjit;;context;;acquire()} are independent from each other:
only one thread may use a given context at once, but multiple threads
could each have their own contexts without needing locks.

Contexts created via @pxref{133,,gccjit;;context;;new_child_context()} are
related to their parent context.  They can be partitioned by their
ultimate ancestor into independent "family trees".   Only one thread
within a process may use a given "family tree" of such contexts at once,
and if you're using multiple threads you should provide your own locking
around entire such context partitions.

@node Error-handling<3>,Debugging<2>,Thread-safety<2>,Compilation contexts<2>
@anchor{cp/topics/contexts error-handling}@anchor{135}
@subsubsection Error-handling


@c FIXME: How does error-handling work for C++ API?

You can only compile and get code from a context if no errors occur.

In general, if an error occurs when using an API entrypoint, it returns
NULL.  You don't have to check everywhere for NULL results, since the
API gracefully handles a NULL being passed in for any argument.

Errors are printed on stderr and can be queried using
@pxref{136,,gccjit;;context;;get_first_error()}.

@geindex gccjit;;context;;get_first_error (C++ function)
@anchor{cp/topics/contexts gccjit context get_first_error__gccjit contextP}@anchor{136}
@deffn {C++ Function} const char* gccjit::context::get_first_error (gccjit::context* ctxt)

Returns the first error message that occurred on the context.

The returned string is valid for the rest of the lifetime of the
context.

If no errors occurred, this will be NULL.
@end deffn

@node Debugging<2>,Options<4>,Error-handling<3>,Compilation contexts<2>
@anchor{cp/topics/contexts debugging}@anchor{137}
@subsubsection Debugging


@geindex gccjit;;context;;dump_to_file (C++ function)
@anchor{cp/topics/contexts gccjit context dump_to_file__ssCR i}@anchor{138}
@deffn {C++ Function} void gccjit::context::dump_to_file (const std::string& path, int update_locations)

To help with debugging: dump a C-like representation to the given path,
describing what's been set up on the context.

If "update_locations" is true, then also set up @pxref{139,,gccjit;;location}
information throughout the context, pointing at the dump file as if it
were a source file.  This may be of use in conjunction with
@code{GCCJIT::BOOL_OPTION_DEBUGINFO} to allow stepping through the
code in a debugger.
@end deffn

@geindex gccjit;;context;;dump_reproducer_to_file (C++ function)
@anchor{cp/topics/contexts gccjit context dump_reproducer_to_file__gcc_jit_contextP cCP}@anchor{13a}
@deffn {C++ Function} void gccjit::context::dump_reproducer_to_file (gcc_jit_context* ctxt, const char* path)

This is a thin wrapper around the C API
@pxref{5d,,gcc_jit_context_dump_reproducer_to_file()}, and hence works the
same way.

Note that the generated source is C code, not C++; this might be of use
for seeing what the C++ bindings are doing at the C level.
@end deffn

@node Options<4>,,Debugging<2>,Compilation contexts<2>
@anchor{cp/topics/contexts options}@anchor{13b}
@subsubsection Options


@menu
* String Options: String Options<2>. 
* Boolean options: Boolean options<2>. 
* Integer options: Integer options<2>. 
* Additional command-line options: Additional command-line options<2>. 

@end menu

@node String Options<2>,Boolean options<2>,,Options<4>
@anchor{cp/topics/contexts string-options}@anchor{13c}
@subsubsection String Options


@geindex gccjit;;context;;set_str_option (C++ function)
@anchor{cp/topics/contexts gccjit context set_str_option__enum cCP}@anchor{13d}
@deffn {C++ Function} void gccjit::context::set_str_option (enum gcc_jit_str_option, const char* value)

Set a string option of the context.

This is a thin wrapper around the C API
@pxref{61,,gcc_jit_context_set_str_option()}; the options have the same
meaning.
@end deffn

@node Boolean options<2>,Integer options<2>,String Options<2>,Options<4>
@anchor{cp/topics/contexts boolean-options}@anchor{13e}
@subsubsection Boolean options


@geindex gccjit;;context;;set_bool_option (C++ function)
@anchor{cp/topics/contexts gccjit context set_bool_option__enum i}@anchor{10c}
@deffn {C++ Function} void gccjit::context::set_bool_option (enum gcc_jit_bool_option, int value)

Set a boolean option of the context.

This is a thin wrapper around the C API
@pxref{1b,,gcc_jit_context_set_bool_option()}; the options have the same
meaning.
@end deffn

@geindex gccjit;;context;;set_bool_allow_unreachable_blocks (C++ function)
@anchor{cp/topics/contexts gccjit context set_bool_allow_unreachable_blocks__i}@anchor{13f}
@deffn {C++ Function} void gccjit::context::set_bool_allow_unreachable_blocks (int bool_value)

By default, libgccjit will issue an error about unreachable blocks
within a function.

This entrypoint can be used to disable that error; it is a thin wrapper
around the C API
@pxref{6b,,gcc_jit_context_set_bool_allow_unreachable_blocks()}.

This entrypoint was added in @pxref{6c,,LIBGCCJIT_ABI_2}; you can test for
its presence using

@example
#ifdef LIBGCCJIT_HAVE_gcc_jit_context_set_bool_allow_unreachable_blocks
@end example

@noindent
@end deffn

@node Integer options<2>,Additional command-line options<2>,Boolean options<2>,Options<4>
@anchor{cp/topics/contexts integer-options}@anchor{140}
@subsubsection Integer options


@geindex gccjit;;context;;set_int_option (C++ function)
@anchor{cp/topics/contexts gccjit context set_int_option__enum i}@anchor{10d}
@deffn {C++ Function} void gccjit::context::set_int_option (enum gcc_jit_int_option, int value)

Set an integer option of the context.

This is a thin wrapper around the C API
@pxref{1e,,gcc_jit_context_set_int_option()}; the options have the same
meaning.
@end deffn

@node Additional command-line options<2>,,Integer options<2>,Options<4>
@anchor{cp/topics/contexts additional-command-line-options}@anchor{141}
@subsubsection Additional command-line options


@geindex gccjit;;context;;add_command_line_option (C++ function)
@anchor{cp/topics/contexts gccjit context add_command_line_option__cCP}@anchor{142}
@deffn {C++ Function} void gccjit::context::add_command_line_option (const char* optname)

Add an arbitrary gcc command-line option to the context for use
when compiling.

This is a thin wrapper around the C API
@pxref{70,,gcc_jit_context_add_command_line_option()}.

This entrypoint was added in @pxref{71,,LIBGCCJIT_ABI_1}; you can test for
its presence using

@example
#ifdef LIBGCCJIT_HAVE_gcc_jit_context_add_command_line_option
@end example

@noindent
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Objects<2>,Types<2>,Compilation contexts<2>,Topic Reference<2>
@anchor{cp/topics/objects objects}@anchor{143}@anchor{cp/topics/objects doc}@anchor{144}
@subsection Objects


@geindex gccjit;;object (C++ class)
@anchor{cp/topics/objects gccjit object}@anchor{145}
@deffn {C++ Class} gccjit::object
@end deffn

Almost every entity in the API (with the exception of
@pxref{131,,gccjit;;context} and @pxref{16,,gcc_jit_result *}) is a
"contextual" object, a @pxref{145,,gccjit;;object}.

A JIT object:

@quotation


@itemize *

@item 
is associated with a @pxref{131,,gccjit;;context}.

@item 
is automatically cleaned up for you when its context is released so
you don't need to manually track and cleanup all objects, just the
contexts.
@end itemize
@end quotation

The C++ class hierarchy within the @code{gccjit} namespace looks like this:

@example
+- object
    +- location
    +- type
       +- struct
    +- field
    +- function
    +- block
    +- rvalue
        +- lvalue
           +- param
    +- case_
@end example

@noindent

The @pxref{145,,gccjit;;object} base class has the following operations:

@geindex gccjit;;object;;get_context (C++ function)
@anchor{cp/topics/objects gccjit object get_contextC}@anchor{146}
@deffn {C++ Function} gccjit::context gccjit::object::get_context () const

Which context is the obj within?
@end deffn

@geindex gccjit;;object;;get_debug_string (C++ function)
@anchor{cp/topics/objects gccjit object get_debug_stringC}@anchor{107}
@deffn {C++ Function} std::string gccjit::object::get_debug_string () const

Generate a human-readable description for the given object.

For example,

@example
printf ("obj: %s\n", obj.get_debug_string ().c_str ());
@end example

@noindent

might give this text on stdout:

@example
obj: 4.0 * (float)i
@end example

@noindent
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Types<2>,Expressions<2>,Objects<2>,Topic Reference<2>
@anchor{cp/topics/types doc}@anchor{147}@anchor{cp/topics/types types}@anchor{148}
@subsection Types


@geindex gccjit;;type (C++ class)
@anchor{cp/topics/types gccjit type}@anchor{149}
@deffn {C++ Class} gccjit::type

gccjit::type represents a type within the library.  It is a subclass
of @pxref{145,,gccjit;;object}.
@end deffn

Types can be created in several ways:


@itemize *

@item 
fundamental types can be accessed using
@pxref{105,,gccjit;;context;;get_type()}:

@example
gccjit::type int_type = ctxt.get_type (GCC_JIT_TYPE_INT);
@end example

@noindent

or using the @code{gccjit::context::get_int_type} template:

@example
gccjit::type t = ctxt.get_int_type <unsigned short> ();
@end example

@noindent

See @pxref{b,,gcc_jit_context_get_type()} for the available types.

@item 
derived types can be accessed by using functions such as
@pxref{14a,,gccjit;;type;;get_pointer()} and @pxref{14b,,gccjit;;type;;get_const()}:

@example
gccjit::type const_int_star = int_type.get_const ().get_pointer ();
gccjit::type int_const_star = int_type.get_pointer ().get_const ();
@end example

@noindent

@item 
by creating structures (see below).
@end itemize

@menu
* Standard types: Standard types<2>. 
* Pointers@comma{} const@comma{} and volatile: Pointers const and volatile<2>. 
* Structures and unions: Structures and unions<2>. 

@end menu

@node Standard types<2>,Pointers const and volatile<2>,,Types<2>
@anchor{cp/topics/types standard-types}@anchor{14c}
@subsubsection Standard types


@geindex gccjit;;context;;get_type (C++ function)
@anchor{cp/topics/types gccjit context get_type__enum}@anchor{105}
@deffn {C++ Function} gccjit::type gccjit::context::get_type (enum gcc_jit_types)

Access a specific type.  This is a thin wrapper around
@pxref{b,,gcc_jit_context_get_type()}; the parameter has the same meaning.
@end deffn

@geindex gccjit;;context;;get_int_type (C++ function)
@anchor{cp/topics/types gccjit context get_int_type__s i}@anchor{14d}
@deffn {C++ Function} gccjit::type gccjit::context::get_int_type (size_t num_bytes, int is_signed)

Access the integer type of the given size.
@end deffn

@geindex gccjit;;context;;get_int_type<T> (C++ function)
@anchor{cp/topics/types gccjit context get_int_type T}@anchor{14e}
@deffn {C++ Function} gccjit::type gccjit::context::get_int_type<T> ()

Access the given integer type.  For example, you could map the
@code{unsigned short} type into a gccjit::type via:

@example
gccjit::type t = ctxt.get_int_type <unsigned short> ();
@end example

@noindent
@end deffn

@node Pointers const and volatile<2>,Structures and unions<2>,Standard types<2>,Types<2>
@anchor{cp/topics/types pointers-const-and-volatile}@anchor{14f}
@subsubsection Pointers, @cite{const}, and @cite{volatile}


@geindex gccjit;;type;;get_pointer (C++ function)
@anchor{cp/topics/types gccjit type get_pointer}@anchor{14a}
@deffn {C++ Function} gccjit::type gccjit::type::get_pointer ()

Given type "T", get type "T*".
@end deffn

@c FIXME: get_const doesn't seem to exist

@geindex gccjit;;type;;get_const (C++ function)
@anchor{cp/topics/types gccjit type get_const}@anchor{14b}
@deffn {C++ Function} gccjit::type gccjit::type::get_const ()

Given type "T", get type "const T".
@end deffn

@geindex gccjit;;type;;get_volatile (C++ function)
@anchor{cp/topics/types gccjit type get_volatile}@anchor{150}
@deffn {C++ Function} gccjit::type gccjit::type::get_volatile ()

Given type "T", get type "volatile T".
@end deffn

@geindex gccjit;;context;;new_array_type (C++ function)
@anchor{cp/topics/types gccjit context new_array_type__gccjit type i gccjit location}@anchor{151}
@deffn {C++ Function} gccjit::type gccjit::context::new_array_type (gccjit::type element_type, int num_elements, gccjit::location loc)

Given type "T", get type "T[N]" (for a constant N).
Param "loc" is optional.
@end deffn

@node Structures and unions<2>,,Pointers const and volatile<2>,Types<2>
@anchor{cp/topics/types structures-and-unions}@anchor{152}
@subsubsection Structures and unions


@geindex gccjit;;struct_ (C++ class)
@anchor{cp/topics/types gccjit struct_}@anchor{153}
@deffn {C++ Class} gccjit::struct_
@end deffn

A compound type analagous to a C @cite{struct}.

@pxref{153,,gccjit;;struct_} is a subclass of @pxref{149,,gccjit;;type} (and thus
of @pxref{145,,gccjit;;object} in turn).

@geindex gccjit;;field (C++ class)
@anchor{cp/topics/types gccjit field}@anchor{154}
@deffn {C++ Class} gccjit::field
@end deffn

A field within a @pxref{153,,gccjit;;struct_}.

@pxref{154,,gccjit;;field} is a subclass of @pxref{145,,gccjit;;object}.

You can model C @cite{struct} types by creating @pxref{153,,gccjit;;struct_} and
@pxref{154,,gccjit;;field} instances, in either order:


@itemize *

@item 
by creating the fields, then the structure.  For example, to model:

@example
struct coord @{double x; double y; @};
@end example

@noindent

you could call:

@example
gccjit::field field_x = ctxt.new_field (double_type, "x");
gccjit::field field_y = ctxt.new_field (double_type, "y");
std::vector fields;
fields.push_back (field_x);
fields.push_back (field_y);
gccjit::struct_ coord = ctxt.new_struct_type ("coord", fields);
@end example

@noindent

@item 
by creating the structure, then populating it with fields, typically
to allow modelling self-referential structs such as:

@example
struct node @{ int m_hash; struct node *m_next; @};
@end example

@noindent

like this:

@example
gccjit::struct_ node = ctxt.new_opaque_struct_type ("node");
gccjit::type node_ptr = node.get_pointer ();
gccjit::field field_hash = ctxt.new_field (int_type, "m_hash");
gccjit::field field_next = ctxt.new_field (node_ptr, "m_next");
std::vector fields;
fields.push_back (field_hash);
fields.push_back (field_next);
node.set_fields (fields);
@end example

@noindent
@end itemize

@c FIXME: the above API doesn't seem to exist yet

@geindex gccjit;;context;;new_field (C++ function)
@anchor{cp/topics/types gccjit context new_field__gccjit type cCP gccjit location}@anchor{155}
@deffn {C++ Function} gccjit::field gccjit::context::new_field (gccjit::type type, const char* name, gccjit::location loc)

Construct a new field, with the given type and name.
@end deffn

@geindex gccjit;;context;;new_struct_type (C++ function)
@anchor{cp/topics/types gccjit context new_struct_type__ssCR std vector field R gccjit location}@anchor{156}
@deffn {C++ Function} gccjit::struct_ gccjit::context::new_struct_type (const std::string& name, std::vector<field>& fields, gccjit::location loc)

@quotation

Construct a new struct type, with the given name and fields.
@end quotation
@end deffn

@geindex gccjit;;context;;new_opaque_struct (C++ function)
@anchor{cp/topics/types gccjit context new_opaque_struct__ssCR gccjit location}@anchor{157}
@deffn {C++ Function} gccjit::struct_ gccjit::context::new_opaque_struct (const std::string& name, gccjit::location loc)

Construct a new struct type, with the given name, but without
specifying the fields.   The fields can be omitted (in which case the
size of the struct is not known), or later specified using
@pxref{85,,gcc_jit_struct_set_fields()}.
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Expressions<2>,Creating and using functions<2>,Types<2>,Topic Reference<2>
@anchor{cp/topics/expressions expressions}@anchor{158}@anchor{cp/topics/expressions doc}@anchor{159}
@subsection Expressions


@menu
* Rvalues: Rvalues<2>. 
* Lvalues: Lvalues<2>. 
* Working with pointers@comma{} structs and unions: Working with pointers structs and unions<2>. 

Rvalues

* Simple expressions: Simple expressions<2>. 
* Unary Operations: Unary Operations<2>. 
* Binary Operations: Binary Operations<2>. 
* Comparisons: Comparisons<2>. 
* Function calls: Function calls<2>. 
* Type-coercion: Type-coercion<2>. 

Lvalues

* Global variables: Global variables<2>. 

@end menu


@node Rvalues<2>,Lvalues<2>,,Expressions<2>
@anchor{cp/topics/expressions rvalues}@anchor{15a}
@subsubsection Rvalues


@geindex gccjit;;rvalue (C++ class)
@anchor{cp/topics/expressions gccjit rvalue}@anchor{15b}
@deffn {C++ Class} gccjit::rvalue
@end deffn

A @pxref{15b,,gccjit;;rvalue} is an expression that can be computed.  It is a
subclass of @pxref{145,,gccjit;;object}, and is a thin wrapper around
@pxref{13,,gcc_jit_rvalue *} from the C API.

It can be simple, e.g.:

@quotation


@itemize *

@item 
an integer value e.g. @cite{0} or @cite{42}

@item 
a string literal e.g. @cite{"Hello world"}

@item 
a variable e.g. @cite{i}.  These are also lvalues (see below).
@end itemize
@end quotation

or compound e.g.:

@quotation


@itemize *

@item 
a unary expression e.g. @cite{!cond}

@item 
a binary expression e.g. @cite{(a + b)}

@item 
a function call e.g. @cite{get_distance (&player_ship@comma{} &target)}

@item 
etc.
@end itemize
@end quotation

Every rvalue has an associated type, and the API will check to ensure
that types match up correctly (otherwise the context will emit an error).

@geindex gccjit;;rvalue;;get_type (C++ function)
@anchor{cp/topics/expressions gccjit rvalue get_type}@anchor{15c}
@deffn {C++ Function} gccjit::type gccjit::rvalue::get_type ()

Get the type of this rvalue.
@end deffn

@menu
* Simple expressions: Simple expressions<2>. 
* Unary Operations: Unary Operations<2>. 
* Binary Operations: Binary Operations<2>. 
* Comparisons: Comparisons<2>. 
* Function calls: Function calls<2>. 
* Type-coercion: Type-coercion<2>. 

@end menu

@node Simple expressions<2>,Unary Operations<2>,,Rvalues<2>
@anchor{cp/topics/expressions simple-expressions}@anchor{15d}
@subsubsection Simple expressions


@geindex gccjit;;context;;new_rvalue (C++ function)
@anchor{cp/topics/expressions gccjit context new_rvalue__gccjit type iC}@anchor{119}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_rvalue (gccjit::type numeric_type, int value) const

Given a numeric type (integer or floating point), build an rvalue for
the given constant @code{int} value.
@end deffn

@geindex gccjit;;context;;new_rvalue (C++ function)
@anchor{cp/topics/expressions gccjit context new_rvalue__gccjit type lC}@anchor{15e}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_rvalue (gccjit::type numeric_type, long value) const

Given a numeric type (integer or floating point), build an rvalue for
the given constant @code{long} value.
@end deffn

@geindex gccjit;;context;;zero (C++ function)
@anchor{cp/topics/expressions gccjit context zero__gccjit typeC}@anchor{115}
@deffn {C++ Function} gccjit::rvalue gccjit::context::zero (gccjit::type numeric_type) const

Given a numeric type (integer or floating point), get the rvalue for
zero.  Essentially this is just a shortcut for:

@example
ctxt.new_rvalue (numeric_type, 0)
@end example

@noindent
@end deffn

@geindex gccjit;;context;;one (C++ function)
@anchor{cp/topics/expressions gccjit context one__gccjit typeC}@anchor{15f}
@deffn {C++ Function} gccjit::rvalue gccjit::context::one (gccjit::type numeric_type) const

Given a numeric type (integer or floating point), get the rvalue for
one.  Essentially this is just a shortcut for:

@example
ctxt.new_rvalue (numeric_type, 1)
@end example

@noindent
@end deffn

@geindex gccjit;;context;;new_rvalue (C++ function)
@anchor{cp/topics/expressions gccjit context new_rvalue__gccjit type doubleC}@anchor{160}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_rvalue (gccjit::type numeric_type, double value) const

Given a numeric type (integer or floating point), build an rvalue for
the given constant @code{double} value.
@end deffn

@geindex gccjit;;context;;new_rvalue (C++ function)
@anchor{cp/topics/expressions gccjit context new_rvalue__gccjit type voidPC}@anchor{161}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_rvalue (gccjit::type pointer_type, void* value) const

Given a pointer type, build an rvalue for the given address.
@end deffn

@geindex gccjit;;context;;new_rvalue (C++ function)
@anchor{cp/topics/expressions gccjit context new_rvalue__ssCRC}@anchor{162}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_rvalue (const std::string& value) const

Generate an rvalue of type @code{GCC_JIT_TYPE_CONST_CHAR_PTR} for
the given string.  This is akin to a string literal.
@end deffn

@node Unary Operations<2>,Binary Operations<2>,Simple expressions<2>,Rvalues<2>
@anchor{cp/topics/expressions unary-operations}@anchor{163}
@subsubsection Unary Operations


@geindex gccjit;;context;;new_unary_op (C++ function)
@anchor{cp/topics/expressions gccjit context new_unary_op__enum gccjit type gccjit rvalue gccjit location}@anchor{164}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_unary_op (enum gcc_jit_unary_op, gccjit::type result_type, gccjit::rvalue rvalue, gccjit::location loc)

Build a unary operation out of an input rvalue.

Parameter @code{loc} is optional.

This is a thin wrapper around the C API's
@pxref{92,,gcc_jit_context_new_unary_op()} and the available unary
operations are documented there.
@end deffn

There are shorter ways to spell the various specific kinds of unary
operation:

@geindex gccjit;;context;;new_minus (C++ function)
@anchor{cp/topics/expressions gccjit context new_minus__gccjit type gccjit rvalue gccjit location}@anchor{165}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_minus (gccjit::type result_type, gccjit::rvalue a, gccjit::location loc)

Negate an arithmetic value; for example:

@example
gccjit::rvalue negpi = ctxt.new_minus (t_double, pi);
@end example

@noindent

builds the equivalent of this C expression:

@example
-pi
@end example

@noindent
@end deffn

@geindex new_bitwise_negate (C++ function)
@anchor{cp/topics/expressions new_bitwise_negate__gccjit type gccjit rvalue gccjit location}@anchor{166}
@deffn {C++ Function} gccjit::rvalue new_bitwise_negate (gccjit::type result_type, gccjit::rvalue a, gccjit::location loc)

Bitwise negation of an integer value (one's complement); for example:

@example
gccjit::rvalue mask = ctxt.new_bitwise_negate (t_int, a);
@end example

@noindent

builds the equivalent of this C expression:

@example
~a
@end example

@noindent
@end deffn

@geindex new_logical_negate (C++ function)
@anchor{cp/topics/expressions new_logical_negate__gccjit type gccjit rvalue gccjit location}@anchor{167}
@deffn {C++ Function} gccjit::rvalue new_logical_negate (gccjit::type result_type, gccjit::rvalue a, gccjit::location loc)

Logical negation of an arithmetic or pointer value; for example:

@example
gccjit::rvalue guard = ctxt.new_logical_negate (t_bool, cond);
@end example

@noindent

builds the equivalent of this C expression:

@example
!cond
@end example

@noindent
@end deffn

The most concise way to spell them is with overloaded operators:

@geindex operator- (C++ function)
@anchor{cp/topics/expressions sub-operator__gccjit rvalue}@anchor{168}
@deffn {C++ Function} gccjit::rvalue operator- (gccjit::rvalue a)

@example
gccjit::rvalue negpi = -pi;
@end example

@noindent
@end deffn

@geindex operator~ (C++ function)
@anchor{cp/topics/expressions inv-operator__gccjit rvalue}@anchor{169}
@deffn {C++ Function} gccjit::rvalue operator~ (gccjit::rvalue a)

@example
gccjit::rvalue mask = ~a;
@end example

@noindent
@end deffn

@geindex operator! (C++ function)
@anchor{cp/topics/expressions not-operator__gccjit rvalue}@anchor{16a}
@deffn {C++ Function} gccjit::rvalue operator! (gccjit::rvalue a)

@example
gccjit::rvalue guard = !cond;
@end example

@noindent
@end deffn

@node Binary Operations<2>,Comparisons<2>,Unary Operations<2>,Rvalues<2>
@anchor{cp/topics/expressions binary-operations}@anchor{16b}
@subsubsection Binary Operations


@geindex gccjit;;context;;new_binary_op (C++ function)
@anchor{cp/topics/expressions gccjit context new_binary_op__enum gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{109}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_binary_op (enum gcc_jit_binary_op, gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)

Build a binary operation out of two constituent rvalues.

Parameter @code{loc} is optional.

This is a thin wrapper around the C API's
@pxref{12,,gcc_jit_context_new_binary_op()} and the available binary
operations are documented there.
@end deffn

There are shorter ways to spell the various specific kinds of binary
operation:

@geindex gccjit;;context;;new_plus (C++ function)
@anchor{cp/topics/expressions gccjit context new_plus__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{16c}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_plus (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_minus (C++ function)
@anchor{cp/topics/expressions gccjit context new_minus__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{16d}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_minus (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_mult (C++ function)
@anchor{cp/topics/expressions gccjit context new_mult__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{16e}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_mult (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_divide (C++ function)
@anchor{cp/topics/expressions gccjit context new_divide__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{16f}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_divide (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_modulo (C++ function)
@anchor{cp/topics/expressions gccjit context new_modulo__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{170}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_modulo (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_bitwise_and (C++ function)
@anchor{cp/topics/expressions gccjit context new_bitwise_and__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{171}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_bitwise_and (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_bitwise_xor (C++ function)
@anchor{cp/topics/expressions gccjit context new_bitwise_xor__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{172}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_bitwise_xor (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_bitwise_or (C++ function)
@anchor{cp/topics/expressions gccjit context new_bitwise_or__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{173}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_bitwise_or (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_logical_and (C++ function)
@anchor{cp/topics/expressions gccjit context new_logical_and__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{174}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_logical_and (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_logical_or (C++ function)
@anchor{cp/topics/expressions gccjit context new_logical_or__gccjit type gccjit rvalue gccjit rvalue gccjit location}@anchor{175}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_logical_or (gccjit::type result_type, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

The most concise way to spell them is with overloaded operators:

@geindex operator+ (C++ function)
@anchor{cp/topics/expressions add-operator__gccjit rvalue gccjit rvalue}@anchor{176}
@deffn {C++ Function} gccjit::rvalue operator+ (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue sum = a + b;
@end example

@noindent
@end deffn

@geindex operator- (C++ function)
@anchor{cp/topics/expressions sub-operator__gccjit rvalue gccjit rvalue}@anchor{177}
@deffn {C++ Function} gccjit::rvalue operator- (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue diff = a - b;
@end example

@noindent
@end deffn

@geindex operator* (C++ function)
@anchor{cp/topics/expressions mul-operator__gccjit rvalue gccjit rvalue}@anchor{178}
@deffn {C++ Function} gccjit::rvalue operator* (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue prod = a * b;
@end example

@noindent
@end deffn

@geindex operator/ (C++ function)
@anchor{cp/topics/expressions div-operator__gccjit rvalue gccjit rvalue}@anchor{179}
@deffn {C++ Function} gccjit::rvalue operator/ (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue result = a / b;
@end example

@noindent
@end deffn

@geindex operator% (C++ function)
@anchor{cp/topics/expressions mod-operator__gccjit rvalue gccjit rvalue}@anchor{17a}
@deffn {C++ Function} gccjit::rvalue operator% (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue mod = a % b;
@end example

@noindent
@end deffn

@geindex operator& (C++ function)
@anchor{cp/topics/expressions and-operator__gccjit rvalue gccjit rvalue}@anchor{17b}
@deffn {C++ Function} gccjit::rvalue operator& (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue x = a & b;
@end example

@noindent
@end deffn

@geindex operator^ (C++ function)
@anchor{cp/topics/expressions xor-operator__gccjit rvalue gccjit rvalue}@anchor{17c}
@deffn {C++ Function} gccjit::rvalue operator^ (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue x = a ^ b;
@end example

@noindent
@end deffn

@geindex operator| (C++ function)
@anchor{cp/topics/expressions or-operator__gccjit rvalue gccjit rvalue}@anchor{17d}
@deffn {C++ Function} gccjit::rvalue operator| (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue x = a | b;
@end example

@noindent
@end deffn

@geindex operator&& (C++ function)
@anchor{cp/topics/expressions sand-operator__gccjit rvalue gccjit rvalue}@anchor{17e}
@deffn {C++ Function} gccjit::rvalue operator&& (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = a && b;
@end example

@noindent
@end deffn

@geindex operator|| (C++ function)
@anchor{cp/topics/expressions sor-operator__gccjit rvalue gccjit rvalue}@anchor{17f}
@deffn {C++ Function} gccjit::rvalue operator|| (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = a || b;
@end example

@noindent
@end deffn

These can of course be combined, giving a terse way to build compound
expressions:

@quotation

@example
gccjit::rvalue discriminant = (b * b) - (four * a * c);
@end example

@noindent
@end quotation

@node Comparisons<2>,Function calls<2>,Binary Operations<2>,Rvalues<2>
@anchor{cp/topics/expressions comparisons}@anchor{180}
@subsubsection Comparisons


@geindex gccjit;;context;;new_comparison (C++ function)
@anchor{cp/topics/expressions gccjit context new_comparison__enum gccjit rvalue gccjit rvalue gccjit location}@anchor{116}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_comparison (enum gcc_jit_comparison, gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)

Build a boolean rvalue out of the comparison of two other rvalues.

Parameter @code{loc} is optional.

This is a thin wrapper around the C API's
@pxref{2c,,gcc_jit_context_new_comparison()} and the available kinds
of comparison are documented there.
@end deffn

There are shorter ways to spell the various specific kinds of binary
operation:

@geindex gccjit;;context;;new_eq (C++ function)
@anchor{cp/topics/expressions gccjit context new_eq__gccjit rvalue gccjit rvalue gccjit location}@anchor{181}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_eq (gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_ne (C++ function)
@anchor{cp/topics/expressions gccjit context new_ne__gccjit rvalue gccjit rvalue gccjit location}@anchor{182}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_ne (gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_lt (C++ function)
@anchor{cp/topics/expressions gccjit context new_lt__gccjit rvalue gccjit rvalue gccjit location}@anchor{183}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_lt (gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_le (C++ function)
@anchor{cp/topics/expressions gccjit context new_le__gccjit rvalue gccjit rvalue gccjit location}@anchor{184}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_le (gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_gt (C++ function)
@anchor{cp/topics/expressions gccjit context new_gt__gccjit rvalue gccjit rvalue gccjit location}@anchor{185}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_gt (gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

@geindex gccjit;;context;;new_ge (C++ function)
@anchor{cp/topics/expressions gccjit context new_ge__gccjit rvalue gccjit rvalue gccjit location}@anchor{186}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_ge (gccjit::rvalue a, gccjit::rvalue b, gccjit::location loc)
@end deffn

The most concise way to spell them is with overloaded operators:

@geindex operator== (C++ function)
@anchor{cp/topics/expressions eq-operator__gccjit rvalue gccjit rvalue}@anchor{187}
@deffn {C++ Function} gccjit::rvalue operator== (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = (a == ctxt.zero (t_int));
@end example

@noindent
@end deffn

@geindex operator!= (C++ function)
@anchor{cp/topics/expressions neq-operator__gccjit rvalue gccjit rvalue}@anchor{188}
@deffn {C++ Function} gccjit::rvalue operator!= (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = (i != j);
@end example

@noindent
@end deffn

@geindex operator< (C++ function)
@anchor{cp/topics/expressions lt-operator__gccjit rvalue gccjit rvalue}@anchor{189}
@deffn {C++ Function} gccjit::rvalue operator< (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = i < n;
@end example

@noindent
@end deffn

@geindex operator<= (C++ function)
@anchor{cp/topics/expressions lte-operator__gccjit rvalue gccjit rvalue}@anchor{18a}
@deffn {C++ Function} gccjit::rvalue operator<= (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = i <= n;
@end example

@noindent
@end deffn

@geindex operator> (C++ function)
@anchor{cp/topics/expressions gt-operator__gccjit rvalue gccjit rvalue}@anchor{18b}
@deffn {C++ Function} gccjit::rvalue operator> (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = (ch > limit);
@end example

@noindent
@end deffn

@geindex operator>= (C++ function)
@anchor{cp/topics/expressions gte-operator__gccjit rvalue gccjit rvalue}@anchor{18c}
@deffn {C++ Function} gccjit::rvalue operator>= (gccjit::rvalue a, gccjit::rvalue b)

@example
gccjit::rvalue cond = (score >= ctxt.new_rvalue (t_int, 100));
@end example

@noindent
@end deffn

@c TODO: beyond this point

@node Function calls<2>,Type-coercion<2>,Comparisons<2>,Rvalues<2>
@anchor{cp/topics/expressions function-calls}@anchor{18d}
@subsubsection Function calls


@geindex gcc_jit_context_new_call (C++ function)
@anchor{cp/topics/expressions gcc_jit_context_new_call__gcc_jit_contextP gcc_jit_locationP gcc_jit_functionP i gcc_jit_rvaluePP}@anchor{18e}
@deffn {C++ Function} gcc_jit_rvalue* gcc_jit_context_new_call (gcc_jit_context* ctxt, gcc_jit_location* loc, gcc_jit_function* func, int numargs, gcc_jit_rvalue** args)

Given a function and the given table of argument rvalues, construct a
call to the function, with the result as an rvalue.

@cartouche
@quotation Note 
@code{gccjit::context::new_call()} merely builds a
@pxref{15b,,gccjit;;rvalue} i.e. an expression that can be evaluated,
perhaps as part of a more complicated expression.
The call @emph{won't} happen unless you add a statement to a function
that evaluates the expression.

For example, if you want to call a function and discard the result
(or to call a function with @code{void} return type), use
@pxref{18f,,gccjit;;block;;add_eval()}:

@example
/* Add "(void)printf (arg0, arg1);".  */
block.add_eval (ctxt.new_call (printf_func, arg0, arg1));
@end example

@noindent
@end quotation
@end cartouche
@end deffn

@node Type-coercion<2>,,Function calls<2>,Rvalues<2>
@anchor{cp/topics/expressions type-coercion}@anchor{190}
@subsubsection Type-coercion


@geindex gccjit;;context;;new_cast (C++ function)
@anchor{cp/topics/expressions gccjit context new_cast__gccjit rvalue gccjit type gccjit location}@anchor{191}
@deffn {C++ Function} gccjit::rvalue gccjit::context::new_cast (gccjit::rvalue rvalue, gccjit::type type, gccjit::location loc)

Given an rvalue of T, construct another rvalue of another type.

Currently only a limited set of conversions are possible:

@quotation


@itemize *

@item 
int <-> float

@item 
int <-> bool

@item 
P*  <-> Q*, for pointer types P and Q
@end itemize
@end quotation
@end deffn

@node Lvalues<2>,Working with pointers structs and unions<2>,Rvalues<2>,Expressions<2>
@anchor{cp/topics/expressions lvalues}@anchor{192}
@subsubsection Lvalues


@geindex gccjit;;lvalue (C++ class)
@anchor{cp/topics/expressions gccjit lvalue}@anchor{193}
@deffn {C++ Class} gccjit::lvalue
@end deffn

An lvalue is something that can of the @emph{left}-hand side of an assignment:
a storage area (such as a variable).  It is a subclass of
@pxref{15b,,gccjit;;rvalue}, where the rvalue is computed by reading from the
storage area.

It iss a thin wrapper around @pxref{24,,gcc_jit_lvalue *} from the C API.

@geindex gccjit;;lvalue;;get_address (C++ function)
@anchor{cp/topics/expressions gccjit lvalue get_address__gccjit location}@anchor{194}
@deffn {C++ Function} gccjit::rvalue gccjit::lvalue::get_address (gccjit::location loc)

Take the address of an lvalue; analogous to:

@example
&(EXPR)
@end example

@noindent

in C.

Parameter "loc" is optional.
@end deffn

@menu
* Global variables: Global variables<2>. 

@end menu

@node Global variables<2>,,,Lvalues<2>
@anchor{cp/topics/expressions global-variables}@anchor{195}
@subsubsection Global variables


@geindex gccjit;;context;;new_global (C++ function)
@anchor{cp/topics/expressions gccjit context new_global__enum gccjit type cCP gccjit location}@anchor{196}
@deffn {C++ Function} gccjit::lvalue gccjit::context::new_global (enum gcc_jit_global_kind, gccjit::type type, const char* name, gccjit::location loc)

Add a new global variable of the given type and name to the context.

This is a thin wrapper around @pxref{b3,,gcc_jit_context_new_global()} from
the C API; the "kind" parameter has the same meaning as there.
@end deffn

@node Working with pointers structs and unions<2>,,Lvalues<2>,Expressions<2>
@anchor{cp/topics/expressions working-with-pointers-structs-and-unions}@anchor{197}
@subsubsection Working with pointers, structs and unions


@geindex gccjit;;rvalue;;dereference (C++ function)
@anchor{cp/topics/expressions gccjit rvalue dereference__gccjit location}@anchor{198}
@deffn {C++ Function} gccjit::lvalue gccjit::rvalue::dereference (gccjit::location loc)

Given an rvalue of pointer type @code{T *}, dereferencing the pointer,
getting an lvalue of type @code{T}.  Analogous to:

@example
*(EXPR)
@end example

@noindent

in C.

Parameter "loc" is optional.
@end deffn

If you don't need to specify the location, this can also be expressed using
an overloaded operator:

@geindex gccjit;;rvalue;;operator* (C++ function)
@anchor{cp/topics/expressions gccjit rvalue mul-operator}@anchor{199}
@deffn {C++ Function} gccjit::lvalue gccjit::rvalue::operator* ()

@example
gccjit::lvalue content = *ptr;
@end example

@noindent
@end deffn

Field access is provided separately for both lvalues and rvalues:

@geindex gccjit;;lvalue;;access_field (C++ function)
@anchor{cp/topics/expressions gccjit lvalue access_field__gccjit field gccjit location}@anchor{19a}
@deffn {C++ Function} gccjit::lvalue gccjit::lvalue::access_field (gccjit::field field, gccjit::location loc)

Given an lvalue of struct or union type, access the given field,
getting an lvalue of the field's type.  Analogous to:

@example
(EXPR).field = ...;
@end example

@noindent

in C.
@end deffn

@geindex gccjit;;rvalue;;access_field (C++ function)
@anchor{cp/topics/expressions gccjit rvalue access_field__gccjit field gccjit location}@anchor{19b}
@deffn {C++ Function} gccjit::rvalue gccjit::rvalue::access_field (gccjit::field field, gccjit::location loc)

Given an rvalue of struct or union type, access the given field
as an rvalue.  Analogous to:

@example
(EXPR).field
@end example

@noindent

in C.
@end deffn

@geindex gccjit;;rvalue;;dereference_field (C++ function)
@anchor{cp/topics/expressions gccjit rvalue dereference_field__gccjit field gccjit location}@anchor{19c}
@deffn {C++ Function} gccjit::lvalue gccjit::rvalue::dereference_field (gccjit::field field, gccjit::location loc)

Given an rvalue of pointer type @code{T *} where T is of struct or union
type, access the given field as an lvalue.  Analogous to:

@example
(EXPR)->field
@end example

@noindent

in C, itself equivalent to @code{(*EXPR).FIELD}.
@end deffn

@geindex gccjit;;context;;new_array_access (C++ function)
@anchor{cp/topics/expressions gccjit context new_array_access__gccjit rvalue gccjit rvalue gccjit location}@anchor{19d}
@deffn {C++ Function} gccjit::lvalue gccjit::context::new_array_access (gccjit::rvalue ptr, gccjit::rvalue index, gccjit::location loc)

Given an rvalue of pointer type @code{T *}, get at the element @cite{T} at
the given index, using standard C array indexing rules i.e. each
increment of @code{index} corresponds to @code{sizeof(T)} bytes.
Analogous to:

@example
PTR[INDEX]
@end example

@noindent

in C (or, indeed, to @code{PTR + INDEX}).

Parameter "loc" is optional.
@end deffn

For array accesses where you don't need to specify a @pxref{139,,gccjit;;location},
two overloaded operators are available:

@quotation

gccjit::lvalue gccjit::rvalue::operator[] (gccjit::rvalue index)

@example
gccjit::lvalue element = array[idx];
@end example

@noindent

gccjit::lvalue gccjit::rvalue::operator[] (int index)

@example
gccjit::lvalue element = array[0];
@end example

@noindent
@end quotation

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Creating and using functions<2>,Source Locations<2>,Expressions<2>,Topic Reference<2>
@anchor{cp/topics/functions doc}@anchor{19e}@anchor{cp/topics/functions creating-and-using-functions}@anchor{19f}
@subsection Creating and using functions


@menu
* Params: Params<2>. 
* Functions: Functions<2>. 
* Blocks: Blocks<2>. 
* Statements: Statements<2>. 

@end menu

@node Params<2>,Functions<2>,,Creating and using functions<2>
@anchor{cp/topics/functions params}@anchor{1a0}
@subsubsection Params


@geindex gccjit;;param (C++ class)
@anchor{cp/topics/functions gccjit param}@anchor{1a1}
@deffn {C++ Class} gccjit::param

A @cite{gccjit::param} represents a parameter to a function.
@end deffn

@geindex gccjit;;context;;new_param (C++ function)
@anchor{cp/topics/functions gccjit context new_param__gccjit type cCP gccjit location}@anchor{108}
@deffn {C++ Function} gccjit::param gccjit::context::new_param (gccjit::type type, const char* name, gccjit::location loc)

In preparation for creating a function, create a new parameter of the
given type and name.
@end deffn

@pxref{1a1,,gccjit;;param} is a subclass of @pxref{193,,gccjit;;lvalue} (and thus
of @pxref{15b,,gccjit;;rvalue} and @pxref{145,,gccjit;;object}).  It is a thin
wrapper around the C API's @pxref{25,,gcc_jit_param *}.

@node Functions<2>,Blocks<2>,Params<2>,Creating and using functions<2>
@anchor{cp/topics/functions functions}@anchor{1a2}
@subsubsection Functions


@geindex gccjit;;function (C++ class)
@anchor{cp/topics/functions gccjit function}@anchor{1a3}
@deffn {C++ Class} gccjit::function

A @cite{gccjit::function} represents a function - either one that we're
creating ourselves, or one that we're referencing.
@end deffn

@geindex gccjit;;context;;new_function (C++ function)
@anchor{cp/topics/functions gccjit context new_function__enum gccjit type cCP std vector param R i gccjit location}@anchor{1a4}
@deffn {C++ Function} gccjit::function gccjit::context::new_function (enum gcc_jit_function_kind, gccjit::type return_type, const char* name, std::vector<param>& params, int is_variadic, gccjit::location loc)

Create a gcc_jit_function with the given name and parameters.

Parameters "is_variadic" and "loc" are optional.

This is a wrapper around the C API's @pxref{11,,gcc_jit_context_new_function()}.
@end deffn

@geindex gccjit;;context;;get_builtin_function (C++ function)
@anchor{cp/topics/functions gccjit context get_builtin_function__cCP}@anchor{1a5}
@deffn {C++ Function} gccjit::function gccjit::context::get_builtin_function (const char* name)

This is a wrapper around the C API's
@pxref{ca,,gcc_jit_context_get_builtin_function()}.
@end deffn

@geindex gccjit;;function;;get_param (C++ function)
@anchor{cp/topics/functions gccjit function get_param__iC}@anchor{1a6}
@deffn {C++ Function} gccjit::param gccjit::function::get_param (int index) const

Get the param of the given index (0-based).
@end deffn

@geindex gccjit;;function;;dump_to_dot (C++ function)
@anchor{cp/topics/functions gccjit function dump_to_dot__cCP}@anchor{11b}
@deffn {C++ Function} void gccjit::function::dump_to_dot (const char* path)

Emit the function in graphviz format to the given path.
@end deffn

@geindex gccjit;;function;;new_local (C++ function)
@anchor{cp/topics/functions gccjit function new_local__gccjit type cCP gccjit location}@anchor{112}
@deffn {C++ Function} gccjit::lvalue gccjit::function::new_local (gccjit::type type, const char* name, gccjit::location loc)

Create a new local variable within the function, of the given type and
name.
@end deffn

@node Blocks<2>,Statements<2>,Functions<2>,Creating and using functions<2>
@anchor{cp/topics/functions blocks}@anchor{1a7}
@subsubsection Blocks


@geindex gccjit;;block (C++ class)
@anchor{cp/topics/functions gccjit block}@anchor{1a8}
@deffn {C++ Class} gccjit::block

A @cite{gccjit::block} represents a basic block within a function  i.e. a
sequence of statements with a single entry point and a single exit
point.

@pxref{1a8,,gccjit;;block} is a subclass of @pxref{145,,gccjit;;object}.

The first basic block that you create within a function will
be the entrypoint.

Each basic block that you create within a function must be
terminated, either with a conditional, a jump, a return, or
a switch.

It's legal to have multiple basic blocks that return within
one function.
@end deffn

@geindex gccjit;;function;;new_block (C++ function)
@anchor{cp/topics/functions gccjit function new_block__cCP}@anchor{1a9}
@deffn {C++ Function} gccjit::block gccjit::function::new_block (const char* name)

Create a basic block of the given name.  The name may be NULL, but
providing meaningful names is often helpful when debugging: it may
show up in dumps of the internal representation, and in error
messages.
@end deffn

@node Statements<2>,,Blocks<2>,Creating and using functions<2>
@anchor{cp/topics/functions statements}@anchor{1aa}
@subsubsection Statements


@geindex gccjit;;block;;add_eval (C++ function)
@anchor{cp/topics/functions gccjit block add_eval__gccjit rvalue gccjit location}@anchor{18f}
@deffn {C++ Function} void gccjit::block::add_eval (gccjit::rvalue rvalue, gccjit::location loc)

Add evaluation of an rvalue, discarding the result
(e.g. a function call that "returns" void).

This is equivalent to this C code:

@example
(void)expression;
@end example

@noindent
@end deffn

@geindex gccjit;;block;;add_assignment (C++ function)
@anchor{cp/topics/functions gccjit block add_assignment__gccjit lvalue gccjit rvalue gccjit location}@anchor{114}
@deffn {C++ Function} void gccjit::block::add_assignment (gccjit::lvalue lvalue, gccjit::rvalue rvalue, gccjit::location loc)

Add evaluation of an rvalue, assigning the result to the given
lvalue.

This is roughly equivalent to this C code:

@example
lvalue = rvalue;
@end example

@noindent
@end deffn

@geindex gccjit;;block;;add_assignment_op (C++ function)
@anchor{cp/topics/functions gccjit block add_assignment_op__gccjit lvalue enum gccjit rvalue gccjit location}@anchor{118}
@deffn {C++ Function} void gccjit::block::add_assignment_op (gccjit::lvalue lvalue, enum gcc_jit_binary_op, gccjit::rvalue rvalue, gccjit::location loc)

Add evaluation of an rvalue, using the result to modify an
lvalue.

This is analogous to "+=" and friends:

@example
lvalue += rvalue;
lvalue *= rvalue;
lvalue /= rvalue;
@end example

@noindent

etc.  For example:

@example
/* "i++" */
loop_body.add_assignment_op (
  i,
  GCC_JIT_BINARY_OP_PLUS,
  ctxt.one (int_type));
@end example

@noindent
@end deffn

@geindex gccjit;;block;;add_comment (C++ function)
@anchor{cp/topics/functions gccjit block add_comment__cCP gccjit location}@anchor{123}
@deffn {C++ Function} void gccjit::block::add_comment (const char* text, gccjit::location loc)

Add a no-op textual comment to the internal representation of the
code.  It will be optimized away, but will be visible in the dumps
seen via @pxref{66,,GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE}
and @pxref{1c,,GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE},
and thus may be of use when debugging how your project's internal
representation gets converted to the libgccjit IR.

Parameter "loc" is optional.
@end deffn

@geindex gccjit;;block;;end_with_conditional (C++ function)
@anchor{cp/topics/functions gccjit block end_with_conditional__gccjit rvalue gccjit block gccjit block gccjit location}@anchor{117}
@deffn {C++ Function} void gccjit::block::end_with_conditional (gccjit::rvalue boolval, gccjit::block on_true, gccjit::block on_false, gccjit::location loc)

Terminate a block by adding evaluation of an rvalue, branching on the
result to the appropriate successor block.

This is roughly equivalent to this C code:

@example
if (boolval)
  goto on_true;
else
  goto on_false;
@end example

@noindent

block, boolval, on_true, and on_false must be non-NULL.
@end deffn

@geindex gccjit;;block;;end_with_jump (C++ function)
@anchor{cp/topics/functions gccjit block end_with_jump__gccjit block gccjit location}@anchor{1ab}
@deffn {C++ Function} void gccjit::block::end_with_jump (gccjit::block target, gccjit::location loc)

Terminate a block by adding a jump to the given target block.

This is roughly equivalent to this C code:

@example
goto target;
@end example

@noindent
@end deffn

@geindex gccjit;;block;;end_with_return (C++ function)
@anchor{cp/topics/functions gccjit block end_with_return__gccjit rvalue gccjit location}@anchor{1ac}
@deffn {C++ Function} void gccjit::block::end_with_return (gccjit::rvalue rvalue, gccjit::location loc)

Terminate a block.

Both params are optional.

An rvalue must be provided for a function returning non-void, and
must not be provided by a function "returning" @cite{void}.

If an rvalue is provided, the block is terminated by evaluating the
rvalue and returning the value.

This is roughly equivalent to this C code:

@example
return expression;
@end example

@noindent

If an rvalue is not provided, the block is terminated by adding a
valueless return, for use within a function with "void" return type.

This is equivalent to this C code:

@example
return;
@end example

@noindent
@end deffn

@geindex gccjit;;block;;end_with_switch (C++ function)
@anchor{cp/topics/functions gccjit block end_with_switch__gccjit rvalue gccjit block std vector gccjit case_ gccjit location}@anchor{1ad}
@deffn {C++ Function} void gccjit::block::end_with_switch (gccjit::rvalue expr, gccjit::block default_block, std::vector<gccjit::case_> cases, gccjit::location loc)

Terminate a block by adding evalation of an rvalue, then performing
a multiway branch.

This is roughly equivalent to this C code:

@example
switch (expr)
  @{
  default:
    goto default_block;

  case C0.min_value ... C0.max_value:
    goto C0.dest_block;

  case C1.min_value ... C1.max_value:
    goto C1.dest_block;

  ...etc...

  case C[N - 1].min_value ... C[N - 1].max_value:
    goto C[N - 1].dest_block;
@}
@end example

@noindent

@code{expr} must be of the same integer type as all of the @code{min_value}
and @code{max_value} within the cases.

The ranges of the cases must not overlap (or have duplicate
values).

The API entrypoints relating to switch statements and cases:

@quotation


@itemize *

@item 
@pxref{1ad,,gccjit;;block;;end_with_switch()}

@item 
@pxref{1ae,,gccjit;;context;;new_case()}
@end itemize
@end quotation

were added in @pxref{d8,,LIBGCCJIT_ABI_3}; you can test for their presence
using

@example
#ifdef LIBGCCJIT_HAVE_SWITCH_STATEMENTS
@end example

@noindent

@geindex gccjit;;block;;end_with_switch;;gccjit;;case_ (C++ class)
@anchor{cp/topics/functions gccjit block end_with_switch gccjit case_}@anchor{1af}
@deffn {C++ Class} gccjit::case_
@end deffn

A @cite{gccjit::case_} represents a case within a switch statement, and
is created within a particular @pxref{131,,gccjit;;context} using
@pxref{1ae,,gccjit;;context;;new_case()}.  It is a subclass of
@pxref{145,,gccjit;;object}.

Each case expresses a multivalued range of integer values.  You
can express single-valued cases by passing in the same value for
both @cite{min_value} and @cite{max_value}.

@geindex gccjit;;block;;end_with_switch;;gccjit;;context;;new_case (C++ function)
@anchor{cp/topics/functions gccjit block end_with_switch gccjit context new_case__gccjit rvalue gccjit rvalue gccjit block}@anchor{1ae}
@deffn {C++ Function} gccjit::case_* gccjit::context::new_case (gccjit::rvalue min_value, gccjit::rvalue max_value, gccjit::block dest_block)

Create a new gccjit::case for use in a switch statement.
@cite{min_value} and @cite{max_value} must be constants of an integer type,
which must match that of the expression of the switch statement.

@cite{dest_block} must be within the same function as the switch
statement.
@end deffn

Here's an example of creating a switch statement:

@quotation

@example

void
create_code (gcc_jit_context *c_ctxt, void *user_data)
@{
  /* Let's try to inject the equivalent of:
      int
      test_switch (int x)
      @{
	switch (x)
	  @{
	  case 0 ... 5:
	     return 3;

	  case 25 ... 27:
	     return 4;

	  case -42 ... -17:
	     return 83;

	  case 40:
	     return 8;

	  default:
	     return 10;
	  @}
      @}
   */
  gccjit::context ctxt (c_ctxt);
  gccjit::type t_int = ctxt.get_type (GCC_JIT_TYPE_INT);
  gccjit::type return_type = t_int;
  gccjit::param x = ctxt.new_param (t_int, "x");
  std::vector <gccjit::param> params;
  params.push_back (x);
  gccjit::function func = ctxt.new_function (GCC_JIT_FUNCTION_EXPORTED,
                                             return_type,
                                             "test_switch",
                                             params, 0);

  gccjit::block b_initial = func.new_block ("initial");

  gccjit::block b_default = func.new_block ("default");
  gccjit::block b_case_0_5 = func.new_block ("case_0_5");
  gccjit::block b_case_25_27 = func.new_block ("case_25_27");
  gccjit::block b_case_m42_m17 = func.new_block ("case_m42_m17");
  gccjit::block b_case_40 = func.new_block ("case_40");

  std::vector <gccjit::case_> cases;
  cases.push_back (ctxt.new_case (ctxt.new_rvalue (t_int, 0),
                                  ctxt.new_rvalue (t_int, 5),
                                  b_case_0_5));
  cases.push_back (ctxt.new_case (ctxt.new_rvalue (t_int, 25),
                                  ctxt.new_rvalue (t_int, 27),
                                  b_case_25_27));
  cases.push_back (ctxt.new_case (ctxt.new_rvalue (t_int, -42),
                                  ctxt.new_rvalue (t_int, -17),
                                  b_case_m42_m17));
  cases.push_back (ctxt.new_case (ctxt.new_rvalue (t_int, 40),
                                  ctxt.new_rvalue (t_int, 40),
                                  b_case_40));
  b_initial.end_with_switch (x,
                             b_default,
                             cases);

  b_case_0_5.end_with_return (ctxt.new_rvalue (t_int, 3));
  b_case_25_27.end_with_return (ctxt.new_rvalue (t_int, 4));
  b_case_m42_m17.end_with_return (ctxt.new_rvalue (t_int, 83));
  b_case_40.end_with_return (ctxt.new_rvalue (t_int, 8));
  b_default.end_with_return (ctxt.new_rvalue (t_int, 10));
@}


@end example

@noindent
@end quotation
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Source Locations<2>,Compiling a context<2>,Creating and using functions<2>,Topic Reference<2>
@anchor{cp/topics/locations source-locations}@anchor{1b0}@anchor{cp/topics/locations doc}@anchor{1b1}
@subsection Source Locations


@geindex gccjit;;location (C++ class)
@anchor{cp/topics/locations gccjit location}@anchor{139}
@deffn {C++ Class} gccjit::location

A @cite{gccjit::location} encapsulates a source code location, so that
you can (optionally) associate locations in your language with
statements in the JIT-compiled code, allowing the debugger to
single-step through your language.

@cite{gccjit::location} instances are optional: you can always omit them
from any C++ API entrypoint accepting one.

You can construct them using @pxref{127,,gccjit;;context;;new_location()}.

You need to enable @pxref{42,,GCC_JIT_BOOL_OPTION_DEBUGINFO} on the
@pxref{131,,gccjit;;context} for these locations to actually be usable by
the debugger:

@example
ctxt.set_bool_option (GCC_JIT_BOOL_OPTION_DEBUGINFO, 1);
@end example

@noindent
@end deffn

@geindex gccjit;;context;;new_location (C++ function)
@anchor{cp/topics/locations gccjit context new_location__cCP i i}@anchor{127}
@deffn {C++ Function} gccjit::location gccjit::context::new_location (const char* filename, int line, int column)

Create a @cite{gccjit::location} instance representing the given source
location.
@end deffn

@menu
* Faking it: Faking it<2>. 

@end menu

@node Faking it<2>,,,Source Locations<2>
@anchor{cp/topics/locations faking-it}@anchor{1b2}
@subsubsection Faking it


If you don't have source code for your internal representation, but need
to debug, you can generate a C-like representation of the functions in
your context using @pxref{138,,gccjit;;context;;dump_to_file()}:

@example
ctxt.dump_to_file ("/tmp/something.c",
                   1 /* update_locations */);
@end example

@noindent

This will dump C-like code to the given path.  If the @cite{update_locations}
argument is true, this will also set up @cite{gccjit::location} information
throughout the context, pointing at the dump file as if it were a source
file, giving you @emph{something} you can step through in the debugger.

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Compiling a context<2>,,Source Locations<2>,Topic Reference<2>
@anchor{cp/topics/compilation compiling-a-context}@anchor{1b3}@anchor{cp/topics/compilation doc}@anchor{1b4}
@subsection Compiling a context


Once populated, a @pxref{131,,gccjit;;context} can be compiled to
machine code, either in-memory via @pxref{10a,,gccjit;;context;;compile()} or
to disk via @pxref{1b5,,gccjit;;context;;compile_to_file()}.

You can compile a context multiple times (using either form of
compilation), although any errors that occur on the context will
prevent any future compilation of that context.

@menu
* In-memory compilation: In-memory compilation<2>. 
* Ahead-of-time compilation: Ahead-of-time compilation<2>. 

@end menu

@node In-memory compilation<2>,Ahead-of-time compilation<2>,,Compiling a context<2>
@anchor{cp/topics/compilation in-memory-compilation}@anchor{1b6}
@subsubsection In-memory compilation


@geindex gccjit;;context;;compile (C++ function)
@anchor{cp/topics/compilation gccjit context compile}@anchor{10a}
@deffn {C++ Function} gcc_jit_result* gccjit::context::compile ()

This calls into GCC and builds the code, returning a
@cite{gcc_jit_result *}.

This is a thin wrapper around the
@pxref{15,,gcc_jit_context_compile()} API entrypoint.
@end deffn

@node Ahead-of-time compilation<2>,,In-memory compilation<2>,Compiling a context<2>
@anchor{cp/topics/compilation ahead-of-time-compilation}@anchor{1b7}
@subsubsection Ahead-of-time compilation


Although libgccjit is primarily aimed at just-in-time compilation, it
can also be used for implementing more traditional ahead-of-time
compilers, via the @pxref{1b5,,gccjit;;context;;compile_to_file()} method.

@geindex gccjit;;context;;compile_to_file (C++ function)
@anchor{cp/topics/compilation gccjit context compile_to_file__enum cCP}@anchor{1b5}
@deffn {C++ Function} void gccjit::context::compile_to_file (enum gcc_jit_output_kind, const char* output_path)

Compile the @pxref{131,,gccjit;;context} to a file of the given
kind.

This is a thin wrapper around the
@pxref{4a,,gcc_jit_context_compile_to_file()} API entrypoint.
@end deffn

@c Copyright (C) 2014-2016 Free Software Foundation, Inc.
@c Originally contributed by David Malcolm <dmalcolm@redhat.com>
@c 
@c This is free software: you can redistribute it and/or modify it
@c under the terms of the GNU General Public License as published by
@c the Free Software Foundation, either version 3 of the License, or
@c (at your option) any later version.
@c 
@c This program is distributed in the hope that it will be useful, but
@c WITHOUT ANY WARRANTY; without even the implied warranty of
@c MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
@c General Public License for more details.
@c 
@c You should have received a copy of the GNU General Public License
@c along with this program.  If not, see
@c <http://www.gnu.org/licenses/>.

@node Internals,Indices and tables,C++ bindings for libgccjit,Top
@anchor{internals/index internals}@anchor{1b8}@anchor{internals/index doc}@anchor{1b9}
@chapter Internals


@menu
* Working on the JIT library:: 
* Running the test suite:: 
* Environment variables:: 
* Packaging notes:: 
* Overview of code structure:: 
* Design notes:: 
* Submitting patches:: 

@end menu

@node Working on the JIT library,Running the test suite,,Internals
@anchor{internals/index working-on-the-jit-library}@anchor{1ba}
@section Working on the JIT library


Having checked out the source code (to "src"), you can configure and build
the JIT library like this:

@example
mkdir build
mkdir install
PREFIX=$(pwd)/install
cd build
../src/configure \
   --enable-host-shared \
   --enable-languages=jit,c++ \
   --disable-bootstrap \
   --enable-checking=release \
   --prefix=$PREFIX
nice make -j4 # altering the "4" to however many cores you have
@end example

@noindent

This should build a libgccjit.so within jit/build/gcc:

@example
[build] $ file gcc/libgccjit.so*
gcc/libgccjit.so:       symbolic link to `libgccjit.so.0'
gcc/libgccjit.so.0:     symbolic link to `libgccjit.so.0.0.1'
gcc/libgccjit.so.0.0.1: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, not stripped
@end example

@noindent

Here's what those configuration options mean:

@geindex command line option; --enable-host-shared
@anchor{internals/index cmdoption--enable-host-shared}@anchor{1bb}
@deffn {Option} --enable-host-shared

Configuring with this option means that the compiler is built as
position-independent code, which incurs a slight performance hit,
but it necessary for a shared library.
@end deffn

@geindex command line option; --enable-languages=jit@comma{}c++
@anchor{internals/index cmdoption--enable-languages}@anchor{1bc}
@deffn {Option} --enable-languages=jit,c++

This specifies which frontends to build.  The JIT library looks like
a frontend to the rest of the code.

The C++ portion of the JIT test suite requires the C++ frontend to be
enabled at configure-time, or you may see errors like this when
running the test suite:

@example
xgcc: error: /home/david/jit/src/gcc/testsuite/jit.dg/test-quadratic.cc: C++ compiler not installed on this system
c++: error trying to exec 'cc1plus': execvp: No such file or directory
@end example

@noindent
@end deffn

@geindex command line option; --disable-bootstrap
@anchor{internals/index cmdoption--disable-bootstrap}@anchor{1bd}
@deffn {Option} --disable-bootstrap

For hacking on the "jit" subdirectory, performing a full
bootstrap can be overkill, since it's unused by a bootstrap.  However,
when submitting patches, you should remove this option, to ensure that
the compiler can still bootstrap itself.
@end deffn

@geindex command line option; --enable-checking=release
@anchor{internals/index cmdoption--enable-checking}@anchor{1be}
@deffn {Option} --enable-checking=release

The compile can perform extensive self-checking as it runs, useful when
debugging, but slowing things down.

For maximum speed, configure with @code{--enable-checking=release} to
disable this self-checking.
@end deffn

@node Running the test suite,Environment variables,Working on the JIT library,Internals
@anchor{internals/index running-the-test-suite}@anchor{1bf}
@section Running the test suite


@example
[build] $ cd gcc
[gcc] $ make check-jit RUNTESTFLAGS="-v -v -v"
@end example

@noindent

A summary of the tests can then be seen in:

@example
jit/build/gcc/testsuite/jit/jit.sum
@end example

@noindent

and detailed logs in:

@example
jit/build/gcc/testsuite/jit/jit.log
@end example

@noindent

The test executables can be seen as:

@example
jit/build/gcc/testsuite/jit/*.exe
@end example

@noindent

which can be run independently.

You can compile and run individual tests by passing "jit.exp=TESTNAME" to RUNTESTFLAGS e.g.:

@example
[gcc] $ make check-jit RUNTESTFLAGS="-v -v -v jit.exp=test-factorial.c"
@end example

@noindent

and once a test has been compiled, you can debug it directly:

@example
[gcc] $ PATH=.:$PATH \
        LD_LIBRARY_PATH=. \
        LIBRARY_PATH=. \
          gdb --args \
            testsuite/jit/test-factorial.c.exe
@end example

@noindent

@menu
* Running under valgrind:: 

@end menu

@node Running under valgrind,,,Running the test suite
@anchor{internals/index running-under-valgrind}@anchor{1c0}
@subsection Running under valgrind


The jit testsuite detects if RUN_UNDER_VALGRIND is present in the
environment (with any value).  If it is present, it runs the test client
code under valgrind@footnote{http://valgrind.org},
specifcally, the default
memcheck@footnote{http://valgrind.org/docs/manual/mc-manual.html}
tool with
--leak-check=full@footnote{http://valgrind.org/docs/manual/mc-manual.html#opt.leak-check}.

It automatically parses the output from valgrind, injecting XFAIL results if
any issues are found, or PASS results if the output is clean.  The output
is saved to @code{TESTNAME.exe.valgrind.txt}.

For example, the following invocation verbosely runs the testcase
@code{test-sum-of-squares.c} under valgrind, showing an issue:

@example
$ RUN_UNDER_VALGRIND= \
    make check-jit \
      RUNTESTFLAGS="-v -v -v jit.exp=test-sum-of-squares.c"

(...verbose log contains detailed valgrind errors, if any...)

                === jit Summary ===

# of expected passes            28
# of expected failures          2

$ less testsuite/jit/jit.sum
(...other results...)
XFAIL: jit.dg/test-sum-of-squares.c: test-sum-of-squares.c.exe.valgrind.txt: definitely lost: 8 bytes in 1 blocks
XFAIL: jit.dg/test-sum-of-squares.c: test-sum-of-squares.c.exe.valgrind.txt: unsuppressed errors: 1
(...other results...)

$ less testsuite/jit/test-sum-of-squares.c.exe.valgrind.txt
(...shows full valgrind report for this test case...)
@end example

@noindent

When running under valgrind, it's best to have configured gcc with
@code{--enable-valgrind-annotations}, which automatically suppresses
various known false positives.

@node Environment variables,Packaging notes,Running the test suite,Internals
@anchor{internals/index environment-variables}@anchor{1c1}
@section Environment variables


When running client code against a locally-built libgccjit, three
environment variables need to be set up:

@geindex environment variable; LD_LIBRARY_PATH
@anchor{internals/index envvar-LD_LIBRARY_PATH}@anchor{1c2}
@deffn {Environment Variable} LD_LIBRARY_PATH

@quotation

@cite{libgccjit.so} is dynamically linked into client code, so if running
against a locally-built library, @code{LD_LIBRARY_PATH} needs to be set
up appropriately.  The library can be found within the "gcc"
subdirectory of the build tree:
@end quotation

@example
$ file libgccjit.so*
libgccjit.so:       symbolic link to `libgccjit.so.0'
libgccjit.so.0:     symbolic link to `libgccjit.so.0.0.1'
libgccjit.so.0.0.1: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), dynamically linked, not stripped
@end example

@noindent
@end deffn

@geindex environment variable; PATH
@anchor{internals/index envvar-PATH}@anchor{1c3}
@deffn {Environment Variable} PATH

The library uses a driver executable for converting from .s assembler
files to .so shared libraries.  Specifically, it looks for a name
expanded from
@code{$@{target_noncanonical@}-gcc-$@{gcc_BASEVER@}$@{exeext@}}
such as @code{x86_64-unknown-linux-gnu-gcc-5.0.0}.

Hence @code{PATH} needs to include a directory where the library can
locate this executable.

The executable is normally installed to the installation bindir
(e.g. /usr/bin), but a copy is also created within the "gcc"
subdirectory of the build tree for running the testsuite, and for ease
of development.
@end deffn

@geindex environment variable; LIBRARY_PATH
@anchor{internals/index envvar-LIBRARY_PATH}@anchor{1c4}
@deffn {Environment Variable} LIBRARY_PATH

The driver executable invokes the linker, and the latter needs to locate
support libraries needed by the generated code, or you will see errors
like:

@example
ld: cannot find crtbeginS.o: No such file or directory
ld: cannot find -lgcc
ld: cannot find -lgcc_s
@end example

@noindent

Hence if running directly from a locally-built copy (without installing),
@code{LIBRARY_PATH} needs to contain the "gcc" subdirectory of the build
tree.
@end deffn

For example, to run a binary that uses the library against a non-installed
build of the library in LIBGCCJIT_BUILD_DIR you need an invocation of the
client code like this, to preprend the dir to each of the environment
variables:

@example
$ LD_LIBRARY_PATH=$(LIBGCCJIT_BUILD_DIR):$(LD_LIBRARY_PATH) \
  PATH=$(LIBGCCJIT_BUILD_DIR):$(PATH) \
  LIBRARY_PATH=$(LIBGCCJIT_BUILD_DIR):$(LIBRARY_PATH) \
    ./jit-hello-world
hello world
@end example

@noindent

@node Packaging notes,Overview of code structure,Environment variables,Internals
@anchor{internals/index packaging-notes}@anchor{1c5}
@section Packaging notes


The configure-time option @pxref{1bb,,--enable-host-shared} is needed when
building the jit in order to get position-independent code.  This will
slow down the regular compiler by a few percent.  Hence when packaging gcc
with libgccjit, please configure and build twice:

@quotation


@itemize *

@item 
once without @pxref{1bb,,--enable-host-shared} for most languages, and

@item 
once with @pxref{1bb,,--enable-host-shared} for the jit
@end itemize
@end quotation

For example:

@example
# Configure and build with --enable-host-shared
# for the jit:
mkdir configuration-for-jit
pushd configuration-for-jit
$(SRCDIR)/configure \
  --enable-host-shared \
  --enable-languages=jit \
  --prefix=$(DESTDIR)
make
popd

# Configure and build *without* --enable-host-shared
# for maximum speed:
mkdir standard-configuration
pushd standard-configuration
$(SRCDIR)/configure \
  --enable-languages=all \
  --prefix=$(DESTDIR)
make
popd

# Both of the above are configured to install to $(DESTDIR)
# Install the configuration with --enable-host-shared first
# *then* the one without, so that the faster build
# of "cc1" et al overwrites the slower build.
pushd configuration-for-jit
make install
popd

pushd standard-configuration
make install
popd
@end example

@noindent

@node Overview of code structure,Design notes,Packaging notes,Internals
@anchor{internals/index overview-of-code-structure}@anchor{1c6}
@section Overview of code structure


The library is implemented in C++.  The source files have the @code{.c}
extension for legacy reasons.


@itemize *

@item 
@code{libgccjit.c} implements the API entrypoints.  It performs error
checking, then calls into classes of the gcc::jit::recording namespace
within @code{jit-recording.c} and @code{jit-recording.h}.

@item 
The gcc::jit::recording classes (within @code{jit-recording.c} and
@code{jit-recording.h}) record the API calls that are made:

@quotation

@example

  /* Indentation indicates inheritance: */
  class context;
  class memento;
    class string;
    class location;
    class type;
      class function_type;
      class compound_type;
        class struct_;
	class union_;
    class field;
    class fields;
    class function;
    class block;
    class rvalue;
      class lvalue;
        class local;
	class global;
        class param;
    class statement;
    class case_;


@end example

@noindent
@end quotation

@item 
When the context is compiled, the gcc::jit::playback classes (within
@code{jit-playback.c} and @code{jit-playback.h}) replay the API calls
within langhook:parse_file:

@quotation

@example

  /* Indentation indicates inheritance: */
  class context;
  class wrapper;
    class type;
      class compound_type;
    class field;
    class function;
    class block;
    class rvalue;
      class lvalue;
        class param;
    class source_file;
    class source_line;
    class location;
    class case_;


@end example

@noindent

@example
Client Code   . Generated .            libgccjit.so
              . code      .
              .           . JIT API  . JIT "Frontend". (libbackend.a)
....................................................................................
   │          .           .          .               .
    ──────────────────────────>      .               .
              .           .    │     .               .
              .           .    V     .               .
              .           .    ──> libgccjit.c       .
              .           .        │ (error-checking).
              .           .        │                 .
              .           .        ──> jit-recording.c
              .           .              (record API calls)
              .           .    <───────              .
              .           .    │     .               .
   <───────────────────────────      .               .
   │          .           .          .               .
   │          .           .          .               .
   V          .           .  gcc_jit_context_compile .
    ──────────────────────────>      .               .
              .           .    │ start of recording::context::compile ()
              .           .    │     .               .
              .           .    │ start of playback::context::compile ()
              .           .    │   (create tempdir)  .
              .           .    │     .               .
              .           .    │ ACQUIRE MUTEX       .
              .           .    │     .               .
              .           .    V───────────────────────> toplev::main (for now)
              .           .          .               .       │
              .           .          .               .   (various code)
              .           .          .               .       │
              .           .          .               .       V
              .           .          .    <───────────────── langhook:parse_file
              .           .          .    │          .
              .           .          .    │ (jit_langhook_parse_file)
              .           .          .    │          .
..........................................│..................VVVVVVVVVVVVV...
              .           .          .    │          .       No GC in here
              .           .          .    │ jit-playback.c
              .           .          .    │   (playback of API calls)
              .           .          .    ───────────────> creation of functions,
              .           .          .               .     types, expression trees
              .           .          .    <──────────────── etc
              .           .          .    │(handle_locations: add locations to
              .           .          .    │ linemap and associate them with trees)
              .           .          .    │          .
              .           .          .    │          .       No GC in here
..........................................│..................AAAAAAAAAAAAA...
              .           .          .    │ for each function
              .           .          .    ──> postprocess
              .           .          .        │      .
              .           .          .        ────────────> cgraph_finalize_function
              .           .          .        <────────────
              .           .          .     <──       .
              .           .          .    │          .
              .           .          .    ──────────────────> (end of
              .           .          .               .       │ langhook_parse_file)
              .           .          .               .       │
              .           .          .               .   (various code)
              .           .          .               .       │
              .           .          .               .       ↓
              .           .          .    <───────────────── langhook:write_globals
              .           .          .    │          .
              .           .          .    │ (jit_langhook_write_globals)
              .           .          .    │          .
              .           .          .    │          .
              .           .          .    ──────────────────> finalize_compilation_unit
              .           .          .               .       │
              .           .          .               .   (the middle─end and backend)
              .           .          .               .       ↓
              .           .    <───────────────────────────── end of toplev::main
              .           .    │     .               .
              .           .    V───────────────────────> toplev::finalize
              .           .          .               . │   (purge internal state)
              .           .    <──────────────────────── end of toplev::finalize
              .           .    │     .               .
              .           .    V─> playback::context::postprocess:
              .           .      │   .               .
              .           .      │   (assuming an in-memory compile):
              .           .      │   .               .
              .           .      │   . Convert assembler to DSO ("fake.so")
              .           .      │   .               .
              .           .      │   . Load DSO (dlopen "fake.so")
              .           .      │   .               .
              .           .      │   . Bundle it up in a jit::result
              .           .    <──   .               .
              .           .    │     .               .
              .           .    │ RELEASE MUTEX       .
              .           .    │     .               .
              .           .    │ end of playback::context::compile ()
              .           .    │     .               .
              .           .    │ playback::context dtor
              .           .     ──>  .               .
              .           .       │ Normally we cleanup the tempdir here:
              .           .       │   ("fake.so" is unlinked from the
              .           .       │    filesystem at this point)
              .           .       │ If the client code requested debuginfo, the
              .           .       │ cleanup happens later (in gcc_jit_result_release)
              .           .       │ to make it easier on the debugger (see PR jit/64206)
              .           .    <──   .               .
              .           .    │     .               .
              .           .    │ end of recording::context::compile ()
   <───────────────────────────      .               .
   │          .           .          .               .
   V          .           .  gcc_jit_result_get_code .
    ──────────────────────────>      .               .
              .           .    │ dlsym () within loaded DSO
   <───────────────────────────      .               .
   Get (void*).           .          .               .
   │          .           .          .               .
   │ Call it  .           .          .               .
   ───────────────>       .          .               .
              .    │      .          .               .
              .    │      .          .               .
   <───────────────       .          .               .
   │          .           .          .               .
etc│          .           .          .               .
   │          .           .          .               .
   V          .           .  gcc_jit_result_release  .
    ──────────────────────────>      .               .
              .           .    │ dlclose () the loaded DSO
              .           .    │    (code becomes uncallable)
              .           .    │     .               .
              .           .    │ If the client code requested debuginfo, then
              .           .    │ cleanup of the tempdir was delayed.
              .           .    │ If that was the case, clean it up now.
   <───────────────────────────      .               .
   │          .           .          .               .

@end example

@noindent
@end quotation
@end itemize

Here is a high-level summary from @code{jit-common.h}:

@quotation

In order to allow jit objects to be usable outside of a compile
whilst working with the existing structure of GCC's code the
C API is implemented in terms of a gcc::jit::recording::context,
which records the calls made to it.

When a gcc_jit_context is compiled, the recording context creates a
playback context.  The playback context invokes the bulk of the GCC
code, and within the "frontend" parsing hook, plays back the recorded
API calls, creating GCC tree objects.

So there are two parallel families of classes: those relating to
recording, and those relating to playback:


@itemize *

@item 
Visibility: recording objects are exposed back to client code,
whereas playback objects are internal to the library.

@item 
Lifetime: recording objects have a lifetime equal to that of the
recording context that created them, whereas playback objects only
exist within the frontend hook.

@item 
Memory allocation: recording objects are allocated by the recording
context, and automatically freed by it when the context is released,
whereas playback objects are allocated within the GC heap, and
garbage-collected; they can own GC-references.

@item 
Integration with rest of GCC: recording objects are unrelated to the
rest of GCC, whereas playback objects are wrappers around "tree"
instances.  Hence you can't ask a recording rvalue or lvalue what its
type is, whereas you can for a playback rvalue of lvalue (since it
can work with the underlying GCC tree nodes).

@item 
Instancing: There can be multiple recording contexts "alive" at once
(albeit it only one compiling at once), whereas there can only be one
playback context alive at one time (since it interacts with the GC).
@end itemize

Ultimately if GCC could support multiple GC heaps and contexts, and
finer-grained initialization, then this recording vs playback
distinction could be eliminated.

During a playback, we associate objects from the recording with
their counterparts during this playback.  For simplicity, we store this
within the recording objects, as @code{void *m_playback_obj}, casting it to
the appropriate playback object subclass.  For these casts to make
sense, the two class hierarchies need to have the same structure.

Note that the playback objects that @code{m_playback_obj} points to are
GC-allocated, but the recording objects don't own references:
these associations only exist within a part of the code where
the GC doesn't collect, and are set back to NULL before the GC can
run.
@end quotation
@anchor{internals/index example-of-log-file}@anchor{5c}
Another way to understand the structure of the code is to enable logging,
via @pxref{5b,,gcc_jit_context_set_logfile()}.  Here is an example of a log
generated via this call:

@example
JIT: libgccjit (GCC) version 6.0.0 20150723 (experimental) (x86_64-unknown-linux-gnu)
JIT:	compiled by GNU C version 4.8.3 20140911 (Red Hat 4.8.3-7), GMP version 5.1.2, MPFR version 3.1.2, MPC version 1.0.1
JIT: entering: gcc_jit_context_set_str_option
JIT:  GCC_JIT_STR_OPTION_PROGNAME: "./test-hello-world.c.exe"
JIT: exiting: gcc_jit_context_set_str_option
JIT: entering: gcc_jit_context_set_int_option
JIT:  GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL: 3
JIT: exiting: gcc_jit_context_set_int_option
JIT: entering: gcc_jit_context_set_bool_option
JIT:  GCC_JIT_BOOL_OPTION_DEBUGINFO: true
JIT: exiting: gcc_jit_context_set_bool_option
JIT: entering: gcc_jit_context_set_bool_option
JIT:  GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE: false
JIT: exiting: gcc_jit_context_set_bool_option
JIT: entering: gcc_jit_context_set_bool_option
JIT:  GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE: false
JIT: exiting: gcc_jit_context_set_bool_option
JIT: entering: gcc_jit_context_set_bool_option
JIT:  GCC_JIT_BOOL_OPTION_SELFCHECK_GC: true
JIT: exiting: gcc_jit_context_set_bool_option
JIT: entering: gcc_jit_context_set_bool_option
JIT:  GCC_JIT_BOOL_OPTION_DUMP_SUMMARY: false
JIT: exiting: gcc_jit_context_set_bool_option
JIT: entering: gcc_jit_context_get_type
JIT: exiting: gcc_jit_context_get_type
JIT: entering: gcc_jit_context_get_type
JIT: exiting: gcc_jit_context_get_type
JIT: entering: gcc_jit_context_new_param
JIT: exiting: gcc_jit_context_new_param
JIT: entering: gcc_jit_context_new_function
JIT: exiting: gcc_jit_context_new_function
JIT: entering: gcc_jit_context_new_param
JIT: exiting: gcc_jit_context_new_param
JIT: entering: gcc_jit_context_get_type
JIT: exiting: gcc_jit_context_get_type
JIT: entering: gcc_jit_context_new_function
JIT: exiting: gcc_jit_context_new_function
JIT: entering: gcc_jit_context_new_string_literal
JIT: exiting: gcc_jit_context_new_string_literal
JIT: entering: gcc_jit_function_new_block
JIT: exiting: gcc_jit_function_new_block
JIT: entering: gcc_jit_block_add_comment
JIT: exiting: gcc_jit_block_add_comment
JIT: entering: gcc_jit_context_new_call
JIT: exiting: gcc_jit_context_new_call
JIT: entering: gcc_jit_block_add_eval
JIT: exiting: gcc_jit_block_add_eval
JIT: entering: gcc_jit_block_end_with_void_return
JIT: exiting: gcc_jit_block_end_with_void_return
JIT: entering: gcc_jit_context_dump_reproducer_to_file
JIT:  entering: void gcc::jit::recording::context::dump_reproducer_to_file(const char*)
JIT:  exiting: void gcc::jit::recording::context::dump_reproducer_to_file(const char*)
JIT: exiting: gcc_jit_context_dump_reproducer_to_file
JIT: entering: gcc_jit_context_compile
JIT:  in-memory compile of ctxt: 0x1283e20
JIT:  entering: gcc::jit::result* gcc::jit::recording::context::compile()
JIT:   GCC_JIT_STR_OPTION_PROGNAME: "./test-hello-world.c.exe"
JIT:   GCC_JIT_INT_OPTION_OPTIMIZATION_LEVEL: 3
JIT:   GCC_JIT_BOOL_OPTION_DEBUGINFO: true
JIT:   GCC_JIT_BOOL_OPTION_DUMP_INITIAL_TREE: false
JIT:   GCC_JIT_BOOL_OPTION_DUMP_INITIAL_GIMPLE: false
JIT:   GCC_JIT_BOOL_OPTION_DUMP_GENERATED_CODE: false
JIT:   GCC_JIT_BOOL_OPTION_DUMP_SUMMARY: false
JIT:   GCC_JIT_BOOL_OPTION_DUMP_EVERYTHING: false
JIT:   GCC_JIT_BOOL_OPTION_SELFCHECK_GC: true
JIT:   GCC_JIT_BOOL_OPTION_KEEP_INTERMEDIATES: false
JIT:   gcc_jit_context_set_bool_allow_unreachable_blocks: false
JIT:   entering: void gcc::jit::recording::context::validate()
JIT:   exiting: void gcc::jit::recording::context::validate()
JIT:   entering: gcc::jit::playback::context::context(gcc::jit::recording::context*)
JIT:   exiting: gcc::jit::playback::context::context(gcc::jit::recording::context*)
JIT:   entering: gcc::jit::playback::compile_to_memory::compile_to_memory(gcc::jit::recording::context*)
JIT:   exiting: gcc::jit::playback::compile_to_memory::compile_to_memory(gcc::jit::recording::context*)
JIT:   entering: void gcc::jit::playback::context::compile()
JIT:    entering: gcc::jit::tempdir::tempdir(gcc::jit::logger*, int)
JIT:    exiting: gcc::jit::tempdir::tempdir(gcc::jit::logger*, int)
JIT:    entering: bool gcc::jit::tempdir::create()
JIT:     m_path_template: /tmp/libgccjit-XXXXXX
JIT:     m_path_tempdir: /tmp/libgccjit-CKq1M9
JIT:    exiting: bool gcc::jit::tempdir::create()
JIT:    entering: void gcc::jit::playback::context::acquire_mutex()
JIT:    exiting: void gcc::jit::playback::context::acquire_mutex()
JIT:    entering: void gcc::jit::playback::context::make_fake_args(vec<char*>*, const char*, vec<gcc::jit::recording::requested_dump>*)
JIT:     reusing cached configure-time options
JIT:     configure_time_options[0]: -mtune=generic
JIT:     configure_time_options[1]: -march=x86-64
JIT:    exiting: void gcc::jit::playback::context::make_fake_args(vec<char*>*, const char*, vec<gcc::jit::recording::requested_dump>*)
JIT:    entering: toplev::main
JIT:     argv[0]: ./test-hello-world.c.exe
JIT:     argv[1]: /tmp/libgccjit-CKq1M9/fake.c
JIT:     argv[2]: -fPIC
JIT:     argv[3]: -O3
JIT:     argv[4]: -g
JIT:     argv[5]: -quiet
JIT:     argv[6]: --param
JIT:     argv[7]: ggc-min-expand=0
JIT:     argv[8]: --param
JIT:     argv[9]: ggc-min-heapsize=0
JIT:     argv[10]: -mtune=generic
JIT:     argv[11]: -march=x86-64
JIT:     entering: bool jit_langhook_init()
JIT:     exiting: bool jit_langhook_init()
JIT:     entering: void gcc::jit::playback::context::replay()
JIT:      entering: void gcc::jit::recording::context::replay_into(gcc::jit::replayer*)
JIT:      exiting: void gcc::jit::recording::context::replay_into(gcc::jit::replayer*)
JIT:      entering: void gcc::jit::recording::context::disassociate_from_playback()
JIT:      exiting: void gcc::jit::recording::context::disassociate_from_playback()
JIT:      entering: void gcc::jit::playback::context::handle_locations()
JIT:      exiting: void gcc::jit::playback::context::handle_locations()
JIT:      entering: void gcc::jit::playback::function::build_stmt_list()
JIT:      exiting: void gcc::jit::playback::function::build_stmt_list()
JIT:      entering: void gcc::jit::playback::function::build_stmt_list()
JIT:      exiting: void gcc::jit::playback::function::build_stmt_list()
JIT:      entering: void gcc::jit::playback::function::postprocess()
JIT:      exiting: void gcc::jit::playback::function::postprocess()
JIT:      entering: void gcc::jit::playback::function::postprocess()
JIT:      exiting: void gcc::jit::playback::function::postprocess()
JIT:     exiting: void gcc::jit::playback::context::replay()
JIT:    exiting: toplev::main
JIT:    entering: void gcc::jit::playback::context::extract_any_requested_dumps(vec<gcc::jit::recording::requested_dump>*)
JIT:    exiting: void gcc::jit::playback::context::extract_any_requested_dumps(vec<gcc::jit::recording::requested_dump>*)
JIT:    entering: toplev::finalize
JIT:    exiting: toplev::finalize
JIT:    entering: virtual void gcc::jit::playback::compile_to_memory::postprocess(const char*)
JIT:     entering: void gcc::jit::playback::context::convert_to_dso(const char*)
JIT:      entering: void gcc::jit::playback::context::invoke_driver(const char*, const char*, const char*, timevar_id_t, bool, bool)
JIT:       entering: void gcc::jit::playback::context::add_multilib_driver_arguments(vec<char*>*)
JIT:       exiting: void gcc::jit::playback::context::add_multilib_driver_arguments(vec<char*>*)
JIT:       argv[0]: x86_64-unknown-linux-gnu-gcc-6.0.0
JIT:       argv[1]: -m64
JIT:       argv[2]: -shared
JIT:       argv[3]: /tmp/libgccjit-CKq1M9/fake.s
JIT:       argv[4]: -o
JIT:       argv[5]: /tmp/libgccjit-CKq1M9/fake.so
JIT:       argv[6]: -fno-use-linker-plugin
JIT:       argv[7]: (null)
JIT:      exiting: void gcc::jit::playback::context::invoke_driver(const char*, const char*, const char*, timevar_id_t, bool, bool)
JIT:     exiting: void gcc::jit::playback::context::convert_to_dso(const char*)
JIT:     entering: gcc::jit::result* gcc::jit::playback::context::dlopen_built_dso()
JIT:      GCC_JIT_BOOL_OPTION_DEBUGINFO was set: handing over tempdir to jit::result
JIT:      entering: gcc::jit::result::result(gcc::jit::logger*, void*, gcc::jit::tempdir*)
JIT:      exiting: gcc::jit::result::result(gcc::jit::logger*, void*, gcc::jit::tempdir*)
JIT:     exiting: gcc::jit::result* gcc::jit::playback::context::dlopen_built_dso()
JIT:    exiting: virtual void gcc::jit::playback::compile_to_memory::postprocess(const char*)
JIT:    entering: void gcc::jit::playback::context::release_mutex()
JIT:    exiting: void gcc::jit::playback::context::release_mutex()
JIT:   exiting: void gcc::jit::playback::context::compile()
JIT:   entering: gcc::jit::playback::context::~context()
JIT:   exiting: gcc::jit::playback::context::~context()
JIT:  exiting: gcc::jit::result* gcc::jit::recording::context::compile()
JIT:  gcc_jit_context_compile: returning (gcc_jit_result *)0x12f75d0
JIT: exiting: gcc_jit_context_compile
JIT: entering: gcc_jit_result_get_code
JIT:  locating fnname: hello_world
JIT:  entering: void* gcc::jit::result::get_code(const char*)
JIT:  exiting: void* gcc::jit::result::get_code(const char*)
JIT:  gcc_jit_result_get_code: returning (void *)0x7ff6b8cd87f0
JIT: exiting: gcc_jit_result_get_code
JIT: entering: gcc_jit_context_release
JIT:  deleting ctxt: 0x1283e20
JIT:  entering: gcc::jit::recording::context::~context()
JIT:  exiting: gcc::jit::recording::context::~context()
JIT: exiting: gcc_jit_context_release
JIT: entering: gcc_jit_result_release
JIT:  deleting result: 0x12f75d0
JIT:  entering: virtual gcc::jit::result::~result()
JIT:   entering: gcc::jit::tempdir::~tempdir()
JIT:    unlinking .s file: /tmp/libgccjit-CKq1M9/fake.s
JIT:    unlinking .so file: /tmp/libgccjit-CKq1M9/fake.so
JIT:    removing tempdir: /tmp/libgccjit-CKq1M9
JIT:   exiting: gcc::jit::tempdir::~tempdir()
JIT:  exiting: virtual gcc::jit::result::~result()
JIT: exiting: gcc_jit_result_release
JIT: gcc::jit::logger::~logger()

@end example

@noindent

@node Design notes,Submitting patches,Overview of code structure,Internals
@anchor{internals/index design-notes}@anchor{1c7}
@section Design notes


It should not be possible for client code to cause an internal compiler
error.  If this @emph{does} happen, the root cause should be isolated (perhaps
using @pxref{5d,,gcc_jit_context_dump_reproducer_to_file()}) and the cause
should be rejected via additional checking.  The checking ideally should
be within the libgccjit API entrypoints in libgccjit.c, since this is as
close as possible to the error; failing that, a good place is within
@code{recording::context::validate ()} in jit-recording.c.

@node Submitting patches,,Design notes,Internals
@anchor{internals/index submitting-patches}@anchor{1c8}
@section Submitting patches


Please read the contribution guidelines for gcc at
@indicateurl{https://gcc.gnu.org/contribute.html}.

Patches for the jit should be sent to both the
@email{gcc-patches@@gcc.gnu.org} and @email{jit@@gcc.gnu.org} mailing lists,
with "jit" and "PATCH" in the Subject line.

You don't need to do a full bootstrap for code that just touches the
@code{jit} and @code{testsuite/jit.dg} subdirectories.  However, please run
@code{make check-jit} before submitting the patch, and mention the results
in your email (along with the host triple that the tests were run on).

A good patch should contain the information listed in the
gcc contribution guide linked to above; for a @code{jit} patch, the patch
shold contain:

@quotation


@itemize *

@item 
the code itself (for example, a new API entrypoint will typically
touch @code{libgccjit.h} and @code{.c}, along with support code in
@code{jit-recording.[ch]} and @code{jit-playback.[ch]} as appropriate)

@item 
test coverage

@item 
documentation for the C API

@item 
documentation for the C++ API
@end itemize
@end quotation

A patch that adds new API entrypoints should also contain:

@quotation


@itemize *

@item 
a feature macro in @code{libgccjit.h} so that client code that doesn't
use a "configure" mechanism can still easily detect the presence of
the entrypoint.  See e.g. @code{LIBGCCJIT_HAVE_SWITCH_STATEMENTS} (for
a category of entrypoints) and
@code{LIBGCCJIT_HAVE_gcc_jit_context_set_bool_allow_unreachable_blocks}
(for an individual entrypoint).

@item 
a new ABI tag containing the new symbols (in @code{libgccjit.map}), so
that we can detect client code that uses them

@item 
Support for @pxref{5d,,gcc_jit_context_dump_reproducer_to_file()}.  Most
jit testcases attempt to dump their contexts to a .c file; @code{jit.exp}
then sanity-checks the generated c by compiling them (though
not running them).   A new API entrypoint
needs to "know" how to write itself back out to C (by implementing
@code{gcc::jit::recording::memento::write_reproducer} for the appropriate
@code{memento} subclass).

@item 
C++ bindings for the new entrypoints (see @code{libgccjit++.h}); ideally
with test coverage, though the C++ API test coverage is admittedly
spotty at the moment

@item 
documentation for the new C entrypoints

@item 
documentation for the new C++ entrypoints

@item 
documentation for the new ABI tag (see @code{topics/compatibility.rst}).
@end itemize
@end quotation

Depending on the patch you can either extend an existing test case, or
add a new test case.  If you add an entirely new testcase: @code{jit.exp}
expects jit testcases to begin with @code{test-}, or @code{test-error-} (for a
testcase that generates an error on a @pxref{8,,gcc_jit_context}).

Every new testcase that doesn't generate errors should also touch
@code{gcc/testsuite/jit.dg/all-non-failing-tests.h}:

@quotation


@itemize *

@item 
Testcases that don't generate errors should ideally be added to the
@code{testcases} array in that file; this means that, in addition
to being run standalone, they also get run within
@code{test-combination.c} (which runs all successful tests inside one
big @pxref{8,,gcc_jit_context}), and @code{test-threads.c} (which runs all
successful tests in one process, each one running in a different
thread on a different @pxref{8,,gcc_jit_context}).

@cartouche
@quotation Note 
Given that exported functions within a @pxref{8,,gcc_jit_context}
must have unique names, and most testcases are run within
@code{test-combination.c}, this means that every jit-compiled test
function typically needs a name that's unique across the entire
test suite.
@end quotation
@end cartouche

@item 
Testcases that aren't to be added to the @code{testcases} array should
instead add a comment to the file clarifying why they're not in that
array. See the file for examples.
@end itemize
@end quotation

Typically a patch that touches the .rst documentation will also need the
texinfo to be regenerated.  You can do this with
Sphinx 1.0@footnote{http://sphinx-doc.org/} or later by
running @code{make texinfo} within @code{SRCDIR/gcc/jit/docs}.   Don't do this
within the patch sent to the mailing list; it can often be relatively
large and inconsequential (e.g. anchor renumbering), rather like generated
"configure" changes from configure.ac.  You can regenerate it when
committing to svn.

@node Indices and tables,Index,Internals,Top
@anchor{index indices-and-tables}@anchor{1c9}
@unnumbered Indices and tables



@itemize *

@item 
@emph{genindex}

@item 
@emph{modindex}

@item 
@emph{search}
@end itemize

@c Some notes:
@c 
@c The Sphinx C domain appears to lack explicit support for enum values,
@c so I've been using :c:macro: for them.
@c 
@c See http://sphinx-doc.org/domains.html#the-c-domain

@node Index,,Indices and tables,Top
@unnumbered Index


@printindex ge

@c %**end of body
@bye