You cannot select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
91 lines
4.3 KiB
HTML
91 lines
4.3 KiB
HTML
<html lang="en">
|
|
<head>
|
|
<title>Hints implementation - Using the GNU Compiler Collection (GCC)</title>
|
|
<meta http-equiv="Content-Type" content="text/html">
|
|
<meta name="description" content="Using the GNU Compiler Collection (GCC)">
|
|
<meta name="generator" content="makeinfo 4.13">
|
|
<link title="Top" rel="start" href="index.html#Top">
|
|
<link rel="up" href="C-Implementation.html#C-Implementation" title="C Implementation">
|
|
<link rel="prev" href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation" title="Arrays and pointers implementation">
|
|
<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">
|
|
<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
|
|
<!--
|
|
Copyright (C) 1988-2015 Free Software Foundation, Inc.
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with the
|
|
Invariant Sections being ``Funding Free Software'', the Front-Cover
|
|
Texts being (a) (see below), and with the Back-Cover Texts being (b)
|
|
(see below). A copy of the license is included in the section entitled
|
|
``GNU Free Documentation License''.
|
|
|
|
(a) The FSF's Front-Cover Text is:
|
|
|
|
A GNU Manual
|
|
|
|
(b) The FSF's Back-Cover Text is:
|
|
|
|
You have freedom to copy and modify this GNU Manual, like GNU
|
|
software. Copies published by the Free Software Foundation raise
|
|
funds for GNU development.-->
|
|
<meta http-equiv="Content-Style-Type" content="text/css">
|
|
<style type="text/css"><!--
|
|
pre.display { font-family:inherit }
|
|
pre.format { font-family:inherit }
|
|
pre.smalldisplay { font-family:inherit; font-size:smaller }
|
|
pre.smallformat { font-family:inherit; font-size:smaller }
|
|
pre.smallexample { font-size:smaller }
|
|
pre.smalllisp { font-size:smaller }
|
|
span.sc { font-variant:small-caps }
|
|
span.roman { font-family:serif; font-weight:normal; }
|
|
span.sansserif { font-family:sans-serif; font-weight:normal; }
|
|
--></style>
|
|
</head>
|
|
<body>
|
|
<div class="node">
|
|
<a name="Hints-implementation"></a>
|
|
<p>
|
|
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>,
|
|
Previous: <a rel="previous" accesskey="p" href="Arrays-and-pointers-implementation.html#Arrays-and-pointers-implementation">Arrays and pointers implementation</a>,
|
|
Up: <a rel="up" accesskey="u" href="C-Implementation.html#C-Implementation">C Implementation</a>
|
|
<hr>
|
|
</div>
|
|
|
|
<h3 class="section">4.8 Hints</h3>
|
|
|
|
<ul>
|
|
<li><cite>The extent to which suggestions made by using the </cite><code>register</code><cite>
|
|
storage-class specifier are effective (C90 6.5.1, C99 and C11 6.7.1).</cite>
|
|
|
|
<p>The <code>register</code> specifier affects code generation only in these ways:
|
|
|
|
<ul>
|
|
<li>When used as part of the register variable extension, see
|
|
<a href="Explicit-Reg-Vars.html#Explicit-Reg-Vars">Explicit Reg Vars</a>.
|
|
|
|
<li>When <samp><span class="option">-O0</span></samp> is in use, the compiler allocates distinct stack
|
|
memory for all variables that do not have the <code>register</code>
|
|
storage-class specifier; if <code>register</code> is specified, the variable
|
|
may have a shorter lifespan than the code would indicate and may never
|
|
be placed in memory.
|
|
|
|
<li>On some rare x86 targets, <code>setjmp</code> doesn't save the registers in
|
|
all circumstances. In those cases, GCC doesn't allocate any variables
|
|
in registers unless they are marked <code>register</code>.
|
|
|
|
</ul>
|
|
|
|
<li><cite>The extent to which suggestions made by using the inline function
|
|
specifier are effective (C99 and C11 6.7.4).</cite>
|
|
|
|
<p>GCC will not inline any functions if the <samp><span class="option">-fno-inline</span></samp> option is
|
|
used or if <samp><span class="option">-O0</span></samp> is used. Otherwise, GCC may still be unable to
|
|
inline a function for many reasons; the <samp><span class="option">-Winline</span></samp> option may be
|
|
used to determine if a function has not been inlined and why not.
|
|
|
|
</ul>
|
|
|
|
</body></html>
|
|
|