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142 lines
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142 lines
6.7 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Function Basics - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="Functions.html#Functions" title="Functions">
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<link rel="next" href="Function-Properties.html#Function-Properties" title="Function Properties">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 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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funds for GNU development.-->
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Function-Basics"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Function-Properties.html#Function-Properties">Function Properties</a>,
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Up: <a rel="up" accesskey="u" href="Functions.html#Functions">Functions</a>
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<hr>
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</div>
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<h4 class="subsection">10.8.1 Function Basics</h4>
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<p><a name="index-DECL_005fNAME-1967"></a><a name="index-DECL_005fASSEMBLER_005fNAME-1968"></a><a name="index-TREE_005fPUBLIC-1969"></a><a name="index-DECL_005fARTIFICIAL-1970"></a><a name="index-DECL_005fFUNCTION_005fSPECIFIC_005fTARGET-1971"></a><a name="index-DECL_005fFUNCTION_005fSPECIFIC_005fOPTIMIZATION-1972"></a>
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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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<dl>
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<dt><code>DECL_NAME</code><a name="index-DECL_005fNAME-1973"></a><dd>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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<br><dt><code>DECL_ASSEMBLER_NAME</code><a name="index-DECL_005fASSEMBLER_005fNAME-1974"></a><dd>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>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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<br><dt><code>DECL_ARGUMENTS</code><a name="index-DECL_005fARGUMENTS-1975"></a><dd>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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<br><dt><code>DECL_RESULT</code><a name="index-DECL_005fRESULT-1976"></a><dd>This macro returns the <code>RESULT_DECL</code> for the function.
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<br><dt><code>DECL_SAVED_TREE</code><a name="index-DECL_005fSAVED_005fTREE-1977"></a><dd>This macro returns the complete body of the function.
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<br><dt><code>TREE_TYPE</code><a name="index-TREE_005fTYPE-1978"></a><dd>This macro returns the <code>FUNCTION_TYPE</code> or <code>METHOD_TYPE</code> for
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the function.
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<br><dt><code>DECL_INITIAL</code><a name="index-DECL_005fINITIAL-1979"></a><dd>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>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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<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>
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<p>you would get the following:
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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>
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</dl>
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<!-- -->
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<!-- Function Properties -->
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<!-- -->
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</body></html>
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