You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
135 lines
6.9 KiB
HTML
135 lines
6.9 KiB
HTML
4 years ago
|
<html lang="en">
|
||
|
|
<head>
|
||
|
|
<title>GIMPLE - GNU Compiler Collection (GCC) Internals</title>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html">
|
||
|
|
<meta name="description" content="GNU Compiler Collection (GCC) Internals">
|
||
|
|
<meta name="generator" content="makeinfo 4.13">
|
||
|
|
<link title="Top" rel="start" href="index.html#Top">
|
||
|
|
<link rel="prev" href="GENERIC.html#GENERIC" title="GENERIC">
|
||
|
|
<link rel="next" href="Tree-SSA.html#Tree-SSA" title="Tree SSA">
|
||
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
||
|
|
<!--
|
||
|
|
Copyright (C) 1988-2015 Free Software Foundation, Inc.
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
||
|
|
any later version published by the Free Software Foundation; with the
|
||
|
|
Invariant Sections being ``Funding Free Software'', the Front-Cover
|
||
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
||
|
|
(see below). A copy of the license is included in the section entitled
|
||
|
|
``GNU Free Documentation License''.
|
||
|
|
|
||
|
|
(a) The FSF's Front-Cover Text is:
|
||
|
|
|
||
|
|
A GNU Manual
|
||
|
|
|
||
|
|
(b) The FSF's Back-Cover Text is:
|
||
|
|
|
||
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
||
|
|
software. Copies published by the Free Software Foundation raise
|
||
|
|
funds for GNU development.-->
|
||
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
||
|
|
<style type="text/css"><!--
|
||
|
|
pre.display { font-family:inherit }
|
||
|
|
pre.format { font-family:inherit }
|
||
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
||
|
|
pre.smallexample { font-size:smaller }
|
||
|
|
pre.smalllisp { font-size:smaller }
|
||
|
|
span.sc { font-variant:small-caps }
|
||
|
|
span.roman { font-family:serif; font-weight:normal; }
|
||
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
||
|
|
--></style>
|
||
|
|
</head>
|
||
|
|
<body>
|
||
|
|
<div class="node">
|
||
|
|
<a name="GIMPLE"></a>
|
||
|
|
<p>
|
||
|
|
Next: <a rel="next" accesskey="n" href="Tree-SSA.html#Tree-SSA">Tree SSA</a>,
|
||
|
|
Previous: <a rel="previous" accesskey="p" href="GENERIC.html#GENERIC">GENERIC</a>,
|
||
|
|
Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a>
|
||
|
|
<hr>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
<h2 class="chapter">11 GIMPLE</h2>
|
||
|
|
|
||
|
|
<p><a name="index-GIMPLE-2132"></a>
|
||
|
|
GIMPLE is a three-address representation derived from GENERIC by
|
||
|
|
breaking down GENERIC expressions into tuples of no more than 3
|
||
|
|
operands (with some exceptions like function calls). GIMPLE was
|
||
|
|
heavily influenced by the SIMPLE IL used by the McCAT compiler
|
||
|
|
project at McGill University, though we have made some different
|
||
|
|
choices. For one thing, SIMPLE doesn't support <code>goto</code>.
|
||
|
|
|
||
|
|
<p>Temporaries are introduced to hold intermediate values needed to
|
||
|
|
compute complex expressions. Additionally, all the control
|
||
|
|
structures used in GENERIC are lowered into conditional jumps,
|
||
|
|
lexical scopes are removed and exception regions are converted
|
||
|
|
into an on the side exception region tree.
|
||
|
|
|
||
|
|
<p>The compiler pass which converts GENERIC into GIMPLE is referred to as
|
||
|
|
the ‘<samp><span class="samp">gimplifier</span></samp>’. The gimplifier works recursively, generating
|
||
|
|
GIMPLE tuples out of the original GENERIC expressions.
|
||
|
|
|
||
|
|
<p>One of the early implementation strategies used for the GIMPLE
|
||
|
|
representation was to use the same internal data structures used
|
||
|
|
by front ends to represent parse trees. This simplified
|
||
|
|
implementation because we could leverage existing functionality
|
||
|
|
and interfaces. However, GIMPLE is a much more restrictive
|
||
|
|
representation than abstract syntax trees (AST), therefore it
|
||
|
|
does not require the full structural complexity provided by the
|
||
|
|
main tree data structure.
|
||
|
|
|
||
|
|
<p>The GENERIC representation of a function is stored in the
|
||
|
|
<code>DECL_SAVED_TREE</code> field of the associated <code>FUNCTION_DECL</code>
|
||
|
|
tree node. It is converted to GIMPLE by a call to
|
||
|
|
<code>gimplify_function_tree</code>.
|
||
|
|
|
||
|
|
<p>If a front end wants to include language-specific tree codes in the tree
|
||
|
|
representation which it provides to the back end, it must provide a
|
||
|
|
definition of <code>LANG_HOOKS_GIMPLIFY_EXPR</code> which knows how to
|
||
|
|
convert the front end trees to GIMPLE. Usually such a hook will involve
|
||
|
|
much of the same code for expanding front end trees to RTL. This function
|
||
|
|
can return fully lowered GIMPLE, or it can return GENERIC trees and let the
|
||
|
|
main gimplifier lower them the rest of the way; this is often simpler.
|
||
|
|
GIMPLE that is not fully lowered is known as “High GIMPLE” and
|
||
|
|
consists of the IL before the pass <code>pass_lower_cf</code>. High GIMPLE
|
||
|
|
contains some container statements like lexical scopes
|
||
|
|
(represented by <code>GIMPLE_BIND</code>) and nested expressions (e.g.,
|
||
|
|
<code>GIMPLE_TRY</code>), while “Low GIMPLE” exposes all of the
|
||
|
|
implicit jumps for control and exception expressions directly in
|
||
|
|
the IL and EH region trees.
|
||
|
|
|
||
|
|
<p>The C and C++ front ends currently convert directly from front end
|
||
|
|
trees to GIMPLE, and hand that off to the back end rather than first
|
||
|
|
converting to GENERIC. Their gimplifier hooks know about all the
|
||
|
|
<code>_STMT</code> nodes and how to convert them to GENERIC forms. There
|
||
|
|
was some work done on a genericization pass which would run first, but
|
||
|
|
the existence of <code>STMT_EXPR</code> meant that in order to convert all
|
||
|
|
of the C statements into GENERIC equivalents would involve walking the
|
||
|
|
entire tree anyway, so it was simpler to lower all the way. This
|
||
|
|
might change in the future if someone writes an optimization pass
|
||
|
|
which would work better with higher-level trees, but currently the
|
||
|
|
optimizers all expect GIMPLE.
|
||
|
|
|
||
|
|
<p>You can request to dump a C-like representation of the GIMPLE form
|
||
|
|
with the flag <samp><span class="option">-fdump-tree-gimple</span></samp>.
|
||
|
|
|
||
|
|
<ul class="menu">
|
||
|
|
<li><a accesskey="1" href="Tuple-representation.html#Tuple-representation">Tuple representation</a>
|
||
|
|
<li><a accesskey="2" href="Class-hierarchy-of-GIMPLE-statements.html#Class-hierarchy-of-GIMPLE-statements">Class hierarchy of GIMPLE statements</a>
|
||
|
|
<li><a accesskey="3" href="GIMPLE-instruction-set.html#GIMPLE-instruction-set">GIMPLE instruction set</a>
|
||
|
|
<li><a accesskey="4" href="GIMPLE-Exception-Handling.html#GIMPLE-Exception-Handling">GIMPLE Exception Handling</a>
|
||
|
|
<li><a accesskey="5" href="Temporaries.html#Temporaries">Temporaries</a>
|
||
|
|
<li><a accesskey="6" href="Operands.html#Operands">Operands</a>
|
||
|
|
<li><a accesskey="7" href="Manipulating-GIMPLE-statements.html#Manipulating-GIMPLE-statements">Manipulating GIMPLE statements</a>
|
||
|
|
<li><a accesskey="8" href="Tuple-specific-accessors.html#Tuple-specific-accessors">Tuple specific accessors</a>
|
||
|
|
<li><a accesskey="9" href="GIMPLE-sequences.html#GIMPLE-sequences">GIMPLE sequences</a>
|
||
|
|
<li><a href="Sequence-iterators.html#Sequence-iterators">Sequence iterators</a>
|
||
|
|
<li><a href="Adding-a-new-GIMPLE-statement-code.html#Adding-a-new-GIMPLE-statement-code">Adding a new GIMPLE statement code</a>
|
||
|
|
<li><a href="Statement-and-operand-traversals.html#Statement-and-operand-traversals">Statement and operand traversals</a>
|
||
|
|
</ul>
|
||
|
|
|
||
|
|
</body></html>
|
||
|
|
|