139 lines
7.3 KiB
HTML
139 lines
7.3 KiB
HTML
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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) 1988-2016 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 5.2, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>GNU Compiler Collection (GCC) Internals: GENERIC</title>
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<meta name="description" content="GNU Compiler Collection (GCC) Internals: GENERIC">
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<meta name="keywords" content="GNU Compiler Collection (GCC) Internals: GENERIC">
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<meta name="resource-type" content="document">
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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="index.html#Top" rel="up" title="Top">
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<link href="Deficiencies.html#Deficiencies" rel="next" title="Deficiencies">
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<link href="Dump-examples.html#Dump-examples" rel="prev" title="Dump examples">
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-->
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</style>
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</head>
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<body lang="en" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000">
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<a name="GENERIC"></a>
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<div class="header">
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<p>
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Next: <a href="GIMPLE.html#GIMPLE" accesskey="n" rel="next">GIMPLE</a>, Previous: <a href="Passes.html#Passes" accesskey="p" rel="prev">Passes</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>
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</div>
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<hr>
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<a name="GENERIC-1"></a>
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<h2 class="chapter">10 GENERIC</h2>
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<a name="index-GENERIC-1"></a>
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<p>The purpose of GENERIC is simply to provide a
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language-independent way of representing an entire function in
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trees. To this end, it was necessary to add a few new tree codes
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to the back end, but almost everything was already there. If you
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can express it with the codes in <code>gcc/tree.def</code>, it’s
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GENERIC.
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</p>
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<p>Early on, there was a great deal of debate about how to think
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about statements in a tree IL. In GENERIC, a statement is
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defined as any expression whose value, if any, is ignored. A
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statement will always have <code>TREE_SIDE_EFFECTS</code> set (or it
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will be discarded), but a non-statement expression may also have
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side effects. A <code>CALL_EXPR</code>, for instance.
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</p>
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<p>It would be possible for some local optimizations to work on the
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GENERIC form of a function; indeed, the adapted tree inliner
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works fine on GENERIC, but the current compiler performs inlining
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after lowering to GIMPLE (a restricted form described in the next
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section). Indeed, currently the frontends perform this lowering
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before handing off to <code>tree_rest_of_compilation</code>, but this
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seems inelegant.
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</p>
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<table class="menu" border="0" cellspacing="0">
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<tr><td align="left" valign="top">• <a href="Deficiencies.html#Deficiencies" accesskey="1">Deficiencies</a>:</td><td> </td><td align="left" valign="top">Topics net yet covered in this document.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Tree-overview.html#Tree-overview" accesskey="2">Tree overview</a>:</td><td> </td><td align="left" valign="top">All about <code>tree</code>s.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Types.html#Types" accesskey="3">Types</a>:</td><td> </td><td align="left" valign="top">Fundamental and aggregate types.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Declarations.html#Declarations" accesskey="4">Declarations</a>:</td><td> </td><td align="left" valign="top">Type declarations and variables.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Attributes.html#Attributes" accesskey="5">Attributes</a>:</td><td> </td><td align="left" valign="top">Declaration and type attributes.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Expression-trees.html#Expression-trees" accesskey="6">Expressions</a>:</td><td> </td><td align="left" valign="top">Operating on data.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Statements.html#Statements" accesskey="7">Statements</a>:</td><td> </td><td align="left" valign="top">Control flow and related trees.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Functions.html#Functions" accesskey="8">Functions</a>:</td><td> </td><td align="left" valign="top">Function bodies, linkage, and other aspects.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Language_002ddependent-trees.html#Language_002ddependent-trees" accesskey="9">Language-dependent trees</a>:</td><td> </td><td align="left" valign="top">Topics and trees specific to language front ends.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees">C and C++ Trees</a>:</td><td> </td><td align="left" valign="top">Trees specific to C and C++.
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</td></tr>
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<tr><td align="left" valign="top">• <a href="Java-Trees.html#Java-Trees">Java Trees</a>:</td><td> </td><td align="left" valign="top">Trees specific to Java.
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</td></tr>
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</table>
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<hr>
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<div class="header">
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<p>
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Next: <a href="GIMPLE.html#GIMPLE" accesskey="n" rel="next">GIMPLE</a>, Previous: <a href="Passes.html#Passes" accesskey="p" rel="prev">Passes</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>
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</div>
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</body>
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</html>
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