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diff --git a/share/doc/gccint/GIMPLE.html b/share/doc/gccint/GIMPLE.html new file mode 100644 index 0000000..0b11b8a --- /dev/null +++ b/share/doc/gccint/GIMPLE.html @@ -0,0 +1,178 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- Copyright (C) 1988-2023 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. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>GNU Compiler Collection (GCC) Internals: GIMPLE</title> + +<meta name="description" content="GNU Compiler Collection (GCC) Internals: GIMPLE"> +<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: GIMPLE"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Option-Index.html#Option-Index" rel="index" title="Option Index"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="index.html#Top" rel="up" title="Top"> +<link href="Tuple-representation.html#Tuple-representation" rel="next" title="Tuple representation"> +<link href="C_002b_002b-Expressions.html#C_002b_002b-Expressions" rel="previous" title="C++ Expressions"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="GIMPLE"></a> +<div class="header"> +<p> +Next: <a href="Tree-SSA.html#Tree-SSA" accesskey="n" rel="next">Tree SSA</a>, Previous: <a href="GENERIC.html#GENERIC" accesskey="p" rel="previous">GENERIC</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="GIMPLE-1"></a> +<h2 class="chapter">12 GIMPLE</h2> +<a name="index-GIMPLE-2"></a> + +<p>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> +<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> +<p>The compiler pass which converts GENERIC into GIMPLE is referred to as +the ‘<samp>gimplifier</samp>’. The gimplifier works recursively, generating +GIMPLE tuples out of the original GENERIC expressions. +</p> +<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> +<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> +<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> +<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> +<p>You can request to dump a C-like representation of the GIMPLE form +with the flag <samp>-fdump-tree-gimple</samp>. +</p> +<table class="menu" border="0" cellspacing="0"> +<tr><td align="left" valign="top">• <a href="Tuple-representation.html#Tuple-representation" accesskey="1">Tuple representation</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Class-hierarchy-of-GIMPLE-statements.html#Class-hierarchy-of-GIMPLE-statements" accesskey="2">Class hierarchy of GIMPLE statements</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="GIMPLE-instruction-set.html#GIMPLE-instruction-set" accesskey="3">GIMPLE instruction set</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="GIMPLE-Exception-Handling.html#GIMPLE-Exception-Handling" accesskey="4">GIMPLE Exception Handling</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Temporaries.html#Temporaries" accesskey="5">Temporaries</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Operands.html#Operands" accesskey="6">Operands</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Manipulating-GIMPLE-statements.html#Manipulating-GIMPLE-statements" accesskey="7">Manipulating GIMPLE statements</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Tuple-specific-accessors.html#Tuple-specific-accessors" accesskey="8">Tuple specific accessors</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="GIMPLE-sequences.html#GIMPLE-sequences" accesskey="9">GIMPLE sequences</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Sequence-iterators.html#Sequence-iterators">Sequence iterators</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Adding-a-new-GIMPLE-statement-code.html#Adding-a-new-GIMPLE-statement-code">Adding a new GIMPLE statement code</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +<tr><td align="left" valign="top">• <a href="Statement-and-operand-traversals.html#Statement-and-operand-traversals">Statement and operand traversals</a>:</td><td> </td><td align="left" valign="top"> +</td></tr> +</table> + +<hr> +<div class="header"> +<p> +Next: <a href="Tree-SSA.html#Tree-SSA" accesskey="n" rel="next">Tree SSA</a>, Previous: <a href="GENERIC.html#GENERIC" accesskey="p" rel="previous">GENERIC</a>, Up: <a href="index.html#Top" accesskey="u" rel="up">Top</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |