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209 lines
8.0 KiB
HTML
209 lines
8.0 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>Function Basics (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Function Basics (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Function Basics (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="Functions.html#Functions" rel="up" title="Functions">
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<link href="Function-Properties.html#Function-Properties" rel="next" title="Function Properties">
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<link href="Functions.html#Functions" rel="prev" title="Functions">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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blockquote.indentedblock {margin-right: 0em}
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blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
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blockquote.smallquotation {font-size: smaller}
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div.display {margin-left: 3.2em}
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div.example {margin-left: 3.2em}
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div.lisp {margin-left: 3.2em}
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div.smalldisplay {margin-left: 3.2em}
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div.smalllisp {margin-left: 3.2em}
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kbd {font-style: oblique}
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pre.display {font-family: inherit}
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pre.format {font-family: inherit}
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pre.menu-comment {font-family: serif}
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pre.menu-preformatted {font-family: serif}
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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pre.smallformat {font-family: inherit; font-size: smaller}
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pre.smalllisp {font-size: smaller}
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span.nolinebreak {white-space: nowrap}
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span.roman {font-family: initial; font-weight: normal}
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ul.no-bullet {list-style: none}
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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="Function-Basics"></a>
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<div class="header">
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<p>
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Next: <a href="Function-Properties.html#Function-Properties" accesskey="n" rel="next">Function Properties</a>, Up: <a href="Functions.html#Functions" accesskey="u" rel="up">Functions</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="Function-Basics-1"></a>
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<h4 class="subsection">11.8.1 Function Basics</h4>
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<a name="index-DECL_005fNAME-1"></a>
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<a name="index-DECL_005fASSEMBLER_005fNAME"></a>
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<a name="index-TREE_005fPUBLIC"></a>
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<a name="index-DECL_005fARTIFICIAL-1"></a>
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<a name="index-DECL_005fFUNCTION_005fSPECIFIC_005fTARGET"></a>
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<a name="index-DECL_005fFUNCTION_005fSPECIFIC_005fOPTIMIZATION"></a>
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<p>A function has four core parts: the name, the parameters, the result,
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and the body. The following macros and functions access these parts
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of a <code>FUNCTION_DECL</code> as well as other basic features:
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</p><dl compact="compact">
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<dt><code>DECL_NAME</code>
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<a name="index-DECL_005fNAME-2"></a>
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</dt>
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<dd><p>This macro returns the unqualified name of the function, as an
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<code>IDENTIFIER_NODE</code>. For an instantiation of a function template,
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the <code>DECL_NAME</code> is the unqualified name of the template, not
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something like <code>f<int></code>. The value of <code>DECL_NAME</code> is
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undefined when used on a constructor, destructor, overloaded operator,
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or type-conversion operator, or any function that is implicitly
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generated by the compiler. See below for macros that can be used to
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distinguish these cases.
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</p>
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</dd>
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<dt><code>DECL_ASSEMBLER_NAME</code>
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<a name="index-DECL_005fASSEMBLER_005fNAME-1"></a>
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</dt>
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<dd><p>This macro returns the mangled name of the function, also an
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<code>IDENTIFIER_NODE</code>. This name does not contain leading underscores
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on systems that prefix all identifiers with underscores. The mangled
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name is computed in the same way on all platforms; if special processing
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is required to deal with the object file format used on a particular
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platform, it is the responsibility of the back end to perform those
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modifications. (Of course, the back end should not modify
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<code>DECL_ASSEMBLER_NAME</code> itself.)
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</p>
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<p>Using <code>DECL_ASSEMBLER_NAME</code> will cause additional memory to be
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allocated (for the mangled name of the entity) so it should be used
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only when emitting assembly code. It should not be used within the
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optimizers to determine whether or not two declarations are the same,
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even though some of the existing optimizers do use it in that way.
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These uses will be removed over time.
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</p>
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</dd>
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<dt><code>DECL_ARGUMENTS</code>
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<a name="index-DECL_005fARGUMENTS"></a>
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</dt>
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<dd><p>This macro returns the <code>PARM_DECL</code> for the first argument to the
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function. Subsequent <code>PARM_DECL</code> nodes can be obtained by
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following the <code>TREE_CHAIN</code> links.
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</p>
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</dd>
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<dt><code>DECL_RESULT</code>
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<a name="index-DECL_005fRESULT"></a>
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</dt>
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<dd><p>This macro returns the <code>RESULT_DECL</code> for the function.
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</p>
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</dd>
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<dt><code>DECL_SAVED_TREE</code>
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<a name="index-DECL_005fSAVED_005fTREE"></a>
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</dt>
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<dd><p>This macro returns the complete body of the function.
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</p>
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</dd>
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<dt><code>TREE_TYPE</code>
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<a name="index-TREE_005fTYPE-5"></a>
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</dt>
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<dd><p>This macro returns the <code>FUNCTION_TYPE</code> or <code>METHOD_TYPE</code> for
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the function.
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</p>
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</dd>
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<dt><code>DECL_INITIAL</code>
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<a name="index-DECL_005fINITIAL-1"></a>
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</dt>
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<dd><p>A function that has a definition in the current translation unit will
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have a non-<code>NULL</code> <code>DECL_INITIAL</code>. However, back ends should not make
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use of the particular value given by <code>DECL_INITIAL</code>.
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</p>
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<p>It should contain a tree of <code>BLOCK</code> nodes that mirrors the scopes
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that variables are bound in the function. Each block contains a list
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of decls declared in a basic block, a pointer to a chain of blocks at
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the next lower scope level, then a pointer to the next block at the
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same level and a backpointer to the parent <code>BLOCK</code> or
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<code>FUNCTION_DECL</code>. So given a function as follows:
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</p>
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<div class="smallexample">
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<pre class="smallexample">void foo()
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{
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int a;
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{
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int b;
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}
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int c;
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}
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</pre></div>
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<p>you would get the following:
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</p>
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<div class="smallexample">
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<pre class="smallexample">tree foo = FUNCTION_DECL;
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tree decl_a = VAR_DECL;
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tree decl_b = VAR_DECL;
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tree decl_c = VAR_DECL;
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tree block_a = BLOCK;
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tree block_b = BLOCK;
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tree block_c = BLOCK;
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BLOCK_VARS(block_a) = decl_a;
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BLOCK_SUBBLOCKS(block_a) = block_b;
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BLOCK_CHAIN(block_a) = block_c;
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BLOCK_SUPERCONTEXT(block_a) = foo;
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BLOCK_VARS(block_b) = decl_b;
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BLOCK_SUPERCONTEXT(block_b) = block_a;
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BLOCK_VARS(block_c) = decl_c;
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BLOCK_SUPERCONTEXT(block_c) = foo;
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DECL_INITIAL(foo) = block_a;
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</pre></div>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Function-Properties.html#Function-Properties" accesskey="n" rel="next">Function Properties</a>, Up: <a href="Functions.html#Functions" accesskey="u" rel="up">Functions</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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