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diff --git a/share/doc/gcc/Inline.html b/share/doc/gcc/Inline.html new file mode 100644 index 0000000..332cdb0 --- /dev/null +++ b/share/doc/gcc/Inline.html @@ -0,0 +1,211 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 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. --> +<!-- Created by GNU Texinfo 5.1, http://www.gnu.org/software/texinfo/ --> +<head> +<title>Using the GNU Compiler Collection (GCC): Inline</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Inline"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Inline"> +<meta name="resource-type" content="document"> +<meta name="distribution" content="global"> +<meta name="Generator" content="makeinfo"> +<meta http-equiv="Content-Type" content="text/html; charset=utf-8"> +<link href="index.html#Top" rel="start" title="Top"> +<link href="Indices.html#Indices" rel="index" title="Indices"> +<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> +<link href="C-Extensions.html#C-Extensions" rel="up" title="C Extensions"> +<link href="Volatiles.html#Volatiles" rel="next" title="Volatiles"> +<link href="Alignment.html#Alignment" rel="previous" title="Alignment"> +<style type="text/css"> +<!-- +a.summary-letter {text-decoration: none} +blockquote.smallquotation {font-size: smaller} +div.display {margin-left: 3.2em} +div.example {margin-left: 3.2em} +div.indentedblock {margin-left: 3.2em} +div.lisp {margin-left: 3.2em} +div.smalldisplay {margin-left: 3.2em} +div.smallexample {margin-left: 3.2em} +div.smallindentedblock {margin-left: 3.2em; font-size: smaller} +div.smalllisp {margin-left: 3.2em} +kbd {font-style:oblique} +pre.display {font-family: inherit} +pre.format {font-family: inherit} +pre.menu-comment {font-family: serif} +pre.menu-preformatted {font-family: serif} +pre.smalldisplay {font-family: inherit; font-size: smaller} +pre.smallexample {font-size: smaller} +pre.smallformat {font-family: inherit; font-size: smaller} +pre.smalllisp {font-size: smaller} +span.nocodebreak {white-space:nowrap} +span.nolinebreak {white-space:nowrap} +span.roman {font-family:serif; font-weight:normal} +span.sansserif {font-family:sans-serif; font-weight:normal} +ul.no-bullet {list-style: none} +--> +</style> + + +</head> + +<body lang="en_US" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#800080" alink="#FF0000"> +<a name="Inline"></a> +<div class="header"> +<p> +Next: <a href="Volatiles.html#Volatiles" accesskey="n" rel="next">Volatiles</a>, Previous: <a href="Alignment.html#Alignment" accesskey="p" rel="previous">Alignment</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> +<hr> +<a name="An-Inline-Function-is-As-Fast-As-a-Macro"></a> +<h3 class="section">6.45 An Inline Function is As Fast As a Macro</h3> +<a name="index-inline-functions"></a> +<a name="index-integrating-function-code"></a> +<a name="index-open-coding"></a> +<a name="index-macros_002c-inline-alternative"></a> + +<p>By declaring a function inline, you can direct GCC to make +calls to that function faster. One way GCC can achieve this is to +integrate that function’s code into the code for its callers. This +makes execution faster by eliminating the function-call overhead; in +addition, if any of the actual argument values are constant, their +known values may permit simplifications at compile time so that not +all of the inline function’s code needs to be included. The effect on +code size is less predictable; object code may be larger or smaller +with function inlining, depending on the particular case. You can +also direct GCC to try to integrate all “simple enough” functions +into their callers with the option <samp>-finline-functions</samp>. +</p> +<p>GCC implements three different semantics of declaring a function +inline. One is available with <samp>-std=gnu89</samp> or +<samp>-fgnu89-inline</samp> or when <code>gnu_inline</code> attribute is present +on all inline declarations, another when +<samp>-std=c99</samp>, +<samp>-std=gnu99</samp> or an option for a later C version is used +(without <samp>-fgnu89-inline</samp>), and the third +is used when compiling C++. +</p> +<p>To declare a function inline, use the <code>inline</code> keyword in its +declaration, like this: +</p> +<div class="smallexample"> +<pre class="smallexample">static inline int +inc (int *a) +{ + return (*a)++; +} +</pre></div> + +<p>If you are writing a header file to be included in ISO C90 programs, write +<code>__inline__</code> instead of <code>inline</code>. See <a href="Alternate-Keywords.html#Alternate-Keywords">Alternate Keywords</a>. +</p> +<p>The three types of inlining behave similarly in two important cases: +when the <code>inline</code> keyword is used on a <code>static</code> function, +like the example above, and when a function is first declared without +using the <code>inline</code> keyword and then is defined with +<code>inline</code>, like this: +</p> +<div class="smallexample"> +<pre class="smallexample">extern int inc (int *a); +inline int +inc (int *a) +{ + return (*a)++; +} +</pre></div> + +<p>In both of these common cases, the program behaves the same as if you +had not used the <code>inline</code> keyword, except for its speed. +</p> +<a name="index-inline-functions_002c-omission-of"></a> +<a name="index-fkeep_002dinline_002dfunctions-1"></a> +<p>When a function is both inline and <code>static</code>, if all calls to the +function are integrated into the caller, and the function’s address is +never used, then the function’s own assembler code is never referenced. +In this case, GCC does not actually output assembler code for the +function, unless you specify the option <samp>-fkeep-inline-functions</samp>. +If there is a nonintegrated call, then the function is compiled to +assembler code as usual. The function must also be compiled as usual if +the program refers to its address, because that cannot be inlined. +</p> +<a name="index-Winline-1"></a> +<p>Note that certain usages in a function definition can make it unsuitable +for inline substitution. Among these usages are: variadic functions, +use of <code>alloca</code>, use of computed goto (see <a href="Labels-as-Values.html#Labels-as-Values">Labels as Values</a>), +use of nonlocal goto, use of nested functions, use of <code>setjmp</code>, use +of <code>__builtin_longjmp</code> and use of <code>__builtin_return</code> or +<code>__builtin_apply_args</code>. Using <samp>-Winline</samp> warns when a +function marked <code>inline</code> could not be substituted, and gives the +reason for the failure. +</p> +<a name="index-automatic-inline-for-C_002b_002b-member-fns"></a> +<a name="index-inline-automatic-for-C_002b_002b-member-fns"></a> +<a name="index-member-fns_002c-automatically-inline"></a> +<a name="index-C_002b_002b-member-fns_002c-automatically-inline"></a> +<a name="index-fno_002ddefault_002dinline"></a> +<p>As required by ISO C++, GCC considers member functions defined within +the body of a class to be marked inline even if they are +not explicitly declared with the <code>inline</code> keyword. You can +override this with <samp>-fno-default-inline</samp>; see <a href="C_002b_002b-Dialect-Options.html#C_002b_002b-Dialect-Options">Options Controlling C++ Dialect</a>. +</p> +<p>GCC does not inline any functions when not optimizing unless you specify +the ‘<samp>always_inline</samp>’ attribute for the function, like this: +</p> +<div class="smallexample"> +<pre class="smallexample">/* <span class="roman">Prototype.</span> */ +inline void foo (const char) __attribute__((always_inline)); +</pre></div> + +<p>The remainder of this section is specific to GNU C90 inlining. +</p> +<a name="index-non_002dstatic-inline-function"></a> +<p>When an inline function is not <code>static</code>, then the compiler must assume +that there may be calls from other source files; since a global symbol can +be defined only once in any program, the function must not be defined in +the other source files, so the calls therein cannot be integrated. +Therefore, a non-<code>static</code> inline function is always compiled on its +own in the usual fashion. +</p> +<p>If you specify both <code>inline</code> and <code>extern</code> in the function +definition, then the definition is used only for inlining. In no case +is the function compiled on its own, not even if you refer to its +address explicitly. Such an address becomes an external reference, as +if you had only declared the function, and had not defined it. +</p> +<p>This combination of <code>inline</code> and <code>extern</code> has almost the +effect of a macro. The way to use it is to put a function definition in +a header file with these keywords, and put another copy of the +definition (lacking <code>inline</code> and <code>extern</code>) in a library file. +The definition in the header file causes most calls to the function +to be inlined. If any uses of the function remain, they refer to +the single copy in the library. +</p> +<hr> +<div class="header"> +<p> +Next: <a href="Volatiles.html#Volatiles" accesskey="n" rel="next">Volatiles</a>, Previous: <a href="Alignment.html#Alignment" accesskey="p" rel="previous">Alignment</a>, Up: <a href="C-Extensions.html#C-Extensions" accesskey="u" rel="up">C Extensions</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |