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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. 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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> |