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91 lines
4.3 KiB
HTML
91 lines
4.3 KiB
HTML
4 years ago
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<title>Hints implementation - Using the GNU Compiler Collection (GCC)</title>
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<meta name="description" content="Using the GNU Compiler Collection (GCC)">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="C-Implementation.html#C-Implementation" title="C Implementation">
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<link rel="prev" href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" title="Arrays and pointers implementation">
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<link rel="next" href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation" title="Structures unions enumerations and bit-fields implementation">
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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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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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</head>
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<body>
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<div class="node">
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<a name="Hints-implementation"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Structures-unions-enumerations-and-bit_002dfields-implementation.html#Structures-unions-enumerations-and-bit_002dfields-implementation">Structures unions enumerations and bit-fields implementation</a>,
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Previous: <a rel="previous" accesskey="p" href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation">Arrays and pointers implementation</a>,
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Up: <a rel="up" accesskey="u" href="C-Implementation.html#C-Implementation">C Implementation</a>
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<hr>
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</div>
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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 </cite><code>register</code><cite>
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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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<ul>
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<li>When used as part of the register variable extension, see
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<a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>.
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<li>When <samp><span class="option">-O0</span></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>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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</ul>
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<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><span class="option">-fno-inline</span></samp> option is
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used or if <samp><span class="option">-O0</span></samp> is used. Otherwise, GCC may still be unable to
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inline a function for many reasons; the <samp><span class="option">-Winline</span></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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</ul>
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</body></html>
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