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| author | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
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| committer | alk3pInjection <webmaster@raspii.tech> | 2024-02-04 16:16:35 +0800 |
| commit | abdaadbcae30fe0c9a66c7516798279fdfd97750 (patch) | |
| tree | 00a54a6e25601e43876d03c1a4a12a749d4a914c /share/doc/gcc/Function-Multiversioning.html | |
https://developer.arm.com/downloads/-/arm-gnu-toolchain-downloads
Change-Id: I7303388733328cd98ab9aa3c30236db67f2e9e9c
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diff --git a/share/doc/gcc/Function-Multiversioning.html b/share/doc/gcc/Function-Multiversioning.html new file mode 100644 index 0000000..13386b7 --- /dev/null +++ b/share/doc/gcc/Function-Multiversioning.html @@ -0,0 +1,141 @@ +<!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): Function Multiversioning</title> + +<meta name="description" content="Using the GNU Compiler Collection (GCC): Function Multiversioning"> +<meta name="keywords" content="Using the GNU Compiler Collection (GCC): Function Multiversioning"> +<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_002b_002b-Extensions.html#C_002b_002b-Extensions" rel="up" title="C++ Extensions"> +<link href="Type-Traits.html#Type-Traits" rel="next" title="Type Traits"> +<link href="C_002b_002b-Attributes.html#C_002b_002b-Attributes" rel="previous" title="C++ Attributes"> +<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="Function-Multiversioning"></a> +<div class="header"> +<p> +Next: <a href="Type-Traits.html#Type-Traits" accesskey="n" rel="next">Type Traits</a>, Previous: <a href="C_002b_002b-Attributes.html#C_002b_002b-Attributes" accesskey="p" rel="previous">C++ Attributes</a>, Up: <a href="C_002b_002b-Extensions.html#C_002b_002b-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="Function-Multiversioning-1"></a> +<h3 class="section">7.8 Function Multiversioning</h3> +<a name="index-function-versions"></a> + +<p>With the GNU C++ front end, for x86 targets, you may specify multiple +versions of a function, where each function is specialized for a +specific target feature. At runtime, the appropriate version of the +function is automatically executed depending on the characteristics of +the execution platform. Here is an example. +</p> +<div class="smallexample"> +<pre class="smallexample">__attribute__ ((target ("default"))) +int foo () +{ + // The default version of foo. + return 0; +} + +__attribute__ ((target ("sse4.2"))) +int foo () +{ + // foo version for SSE4.2 + return 1; +} + +__attribute__ ((target ("arch=atom"))) +int foo () +{ + // foo version for the Intel ATOM processor + return 2; +} + +__attribute__ ((target ("arch=amdfam10"))) +int foo () +{ + // foo version for the AMD Family 0x10 processors. + return 3; +} + +int main () +{ + int (*p)() = &foo; + assert ((*p) () == foo ()); + return 0; +} +</pre></div> + +<p>In the above example, four versions of function foo are created. The +first version of foo with the target attribute "default" is the default +version. This version gets executed when no other target specific +version qualifies for execution on a particular platform. A new version +of foo is created by using the same function signature but with a +different target string. Function foo is called or a pointer to it is +taken just like a regular function. GCC takes care of doing the +dispatching to call the right version at runtime. Refer to the +<a href="https://gcc.gnu.org/wiki/FunctionMultiVersioning">GCC wiki on +Function Multiversioning</a> for more details. +</p> + + + +</body> +</html> |