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125 lines
5.9 KiB
HTML
125 lines
5.9 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being "Funding Free Software", the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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"GNU Free Documentation License".
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Gimplification pass (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Gimplification pass (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Gimplification pass (GNU Compiler Collection (GCC) Internals)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Passes.html#Passes" rel="up" title="Passes">
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<link href="Pass-manager.html#Pass-manager" rel="next" title="Pass manager">
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<link href="Parsing-pass.html#Parsing-pass" rel="prev" title="Parsing pass">
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<style type="text/css">
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Gimplification-pass"></a>
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<div class="header">
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<p>
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Next: <a href="Pass-manager.html#Pass-manager" accesskey="n" rel="next">Pass manager</a>, Previous: <a href="Parsing-pass.html#Parsing-pass" accesskey="p" rel="prev">Parsing pass</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</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>
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</div>
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<hr>
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<a name="Gimplification-pass-1"></a>
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<h3 class="section">9.2 Gimplification pass</h3>
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<a name="index-gimplification-1"></a>
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<a name="index-GIMPLE-1"></a>
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<p><em>Gimplification</em> is a whimsical term for the process of converting
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the intermediate representation of a function into the GIMPLE language
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(see <a href="GIMPLE.html#GIMPLE">GIMPLE</a>). The term stuck, and so words like “gimplification”,
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“gimplify”, “gimplifier” and the like are sprinkled throughout this
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section of code.
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</p>
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<p>While a front end may certainly choose to generate GIMPLE directly if
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it chooses, this can be a moderately complex process unless the
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intermediate language used by the front end is already fairly simple.
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Usually it is easier to generate GENERIC trees plus extensions
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and let the language-independent gimplifier do most of the work.
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</p>
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<a name="index-gimplify_005ffunction_005ftree"></a>
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<a name="index-gimplify_005fexpr"></a>
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<a name="index-lang_005fhooks_002egimplify_005fexpr"></a>
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<p>The main entry point to this pass is <code>gimplify_function_tree</code>
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located in <samp>gimplify.c</samp>. From here we process the entire
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function gimplifying each statement in turn. The main workhorse
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for this pass is <code>gimplify_expr</code>. Approximately everything
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passes through here at least once, and it is from here that we
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invoke the <code>lang_hooks.gimplify_expr</code> callback.
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</p>
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<p>The callback should examine the expression in question and return
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<code>GS_UNHANDLED</code> if the expression is not a language specific
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construct that requires attention. Otherwise it should alter the
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expression in some way to such that forward progress is made toward
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producing valid GIMPLE. If the callback is certain that the
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transformation is complete and the expression is valid GIMPLE, it
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should return <code>GS_ALL_DONE</code>. Otherwise it should return
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<code>GS_OK</code>, which will cause the expression to be processed again.
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If the callback encounters an error during the transformation (because
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the front end is relying on the gimplification process to finish
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semantic checks), it should return <code>GS_ERROR</code>.
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</p>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Pass-manager.html#Pass-manager" accesskey="n" rel="next">Pass manager</a>, Previous: <a href="Parsing-pass.html#Parsing-pass" accesskey="p" rel="prev">Parsing pass</a>, Up: <a href="Passes.html#Passes" accesskey="u" rel="up">Passes</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>
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</div>
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</body>
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</html>
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