117 lines
5.4 KiB
HTML
117 lines
5.4 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>Using the GNU Compiler Collection (GCC): Hints implementation</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC): Hints implementation">
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<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Hints implementation">
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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="C-Implementation.html#C-Implementation" rel="up" title="C Implementation">
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<link href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" rel="next" title="Structures unions enumerations and bit-fields implementation">
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<link href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" rel="prev" title="Arrays and pointers implementation">
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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="Hints-implementation"></a>
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<div class="header">
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<p>
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Next: <a href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" accesskey="n" rel="next">Structures unions enumerations and bit-fields implementation</a>, Previous: <a href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" accesskey="p" rel="prev">Arrays and pointers implementation</a>, Up: <a href="C-Implementation.html#C-Implementation" accesskey="u" rel="up">C Implementation</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="Hints"></a>
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<h3 class="section">4.8 Hints</h3>
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<ul>
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<li> <cite>The extent to which suggestions made by using the <code>register</code>
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storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).</cite>
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<p>The <code>register</code> specifier affects code generation only in these ways:
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</p>
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<ul>
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<li> When used as part of the register variable extension, see
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<a href="Explicit-Register-Variables.html#Explicit-Register-Variables">Explicit Register Variables</a>.
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</li><li> When <samp>-O0</samp> is in use, the compiler allocates distinct stack
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memory for all variables that do not have the <code>register</code>
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storage-class specifier; if <code>register</code> is specified, the variable
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may have a shorter lifespan than the code would indicate and may never
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be placed in memory.
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</li><li> On some rare x86 targets, <code>setjmp</code> doesn’t save the registers in
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all circumstances. In those cases, GCC doesn’t allocate any variables
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in registers unless they are marked <code>register</code>.
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</li></ul>
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</li><li> <cite>The extent to which suggestions made by using the inline function
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specifier are effective (C99 and C11 6.7.4).</cite>
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<p>GCC will not inline any functions if the <samp>-fno-inline</samp> option is
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used or if <samp>-O0</samp> is used. Otherwise, GCC may still be unable to
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inline a function for many reasons; the <samp>-Winline</samp> option may be
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used to determine if a function has not been inlined and why not.
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</p>
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</li></ul>
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</body>
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</html>
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