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diff --git a/docs/GoldPlugin.html b/docs/GoldPlugin.html new file mode 100644 index 0000000000000..ee014101bc240 --- /dev/null +++ b/docs/GoldPlugin.html @@ -0,0 +1,160 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" + "http://www.w3.org/TR/html4/strict.dtd"> +<html> +<head> + <title>LLVM gold plugin</title> + <link rel="stylesheet" href="llvm.css" type="text/css"> +</head> +<body> + +<div class="doc_title">LLVM gold plugin</div> +<ol> + <li><a href="#introduction">Introduction</a></li> + <li><a href="#build">How to build it</a></li> + <li><a href="#usage">Usage</a> + <ul> + <li><a href="#example1">Example of link time optimization</a></li> + </ul></li> + <li><a href="#licensing">Licensing</a></li> +</ol> +<div class="doc_author">Written by Nick Lewycky</div> + +<!--=========================================================================--> +<div class="doc_section"><a name="introduction">Introduction</a></div> +<!--=========================================================================--> +<div class="doc_text"> + <p>Building with link time optimization requires cooperation from the +system linker. LTO support on Linux systems requires that you use +the <a href="http://sourceware.org/binutils">gold linker</a> which supports +LTO via plugins. This is the same system used by the upcoming +<a href="http://gcc.gnu.org/wiki/LinkTimeOptimization">GCC LTO</a> +project.</p> + <p>The LLVM gold plugin implements the +<a href="http://gcc.gnu.org/wiki/whopr/driver">gold plugin interface</a> +on top of +<a href="http://llvm.org/docs/LinkTimeOptimization.html#lto">libLTO</a>. +The same plugin can also be used by other tools such as <tt>ar</tt> and +<tt>nm</tt>. +</div> +<!--=========================================================================--> +<div class="doc_section"><a name="build">How to build it</a></div> +<!--=========================================================================--> +<div class="doc_text"> + <p>You need to build gold with plugin support and build the LLVMgold +plugin.</p> +<ul> + <li>Build gold with plugin support: + <pre class="doc_code"> +mkdir binutils +cd binutils +cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login +<em>{enter "anoncvs" as the password}</em> +cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co src +mkdir build +cd build +../src/configure --enable-gold --enable-plugins +make all-gold +</pre> + That should leave you with binutils/build/gold/ld-new which supports the +<tt>-plugin</tt> option. + + <li>Build the LLVMgold plugin: Configure LLVM with + <tt>--with-binutils-include=/path/to/binutils/src/include</tt> and run + <tt>make</tt>. +</ul> +</div> +<!--=========================================================================--> +<div class="doc_section"><a name="usage">Usage</a></div> +<!--=========================================================================--> +<div class="doc_text"> + <p>The linker takes a <tt>-plugin</tt> option that points to the path of + the plugin <tt>.so</tt> file. To find out what link command <tt>gcc</tt> + would run in a given situation, run <tt>gcc -v <em>[...]</em></tt> and look + for the line where it runs <tt>collect2</tt>. Replace that with + <tt>ld-new -plugin /path/to/LLVMgold.so</tt> to test it out. Once you're + ready to switch to using gold, backup your existing <tt>/usr/bin/ld</tt> + then replace it with <tt>ld-new</tt>.</p> + <p>You can produce bitcode files from <tt>llvm-gcc</tt> using + <tt>-emit-llvm</tt> or <tt>-flto</tt>, or the <tt>-O4</tt> flag which is + synonymous with <tt>-O3 -flto</tt>.</p> + <p><tt>llvm-gcc</tt> has a <tt>-use-gold-plugin</tt> option which looks + for the gold plugin in the same directories as it looks for <tt>cc1</tt> and + passes the <tt>-plugin</tt> option to ld. It will not look for an alternate + linker, which is why you need gold to be the installed system linker in your + path.</p> +</div> + +<!-- ======================================================================= --> +<div class="doc_subsection"> + <a name="example1">Example of link time optimization</a> +</div> + +<div class="doc_text"> + <p>The following example shows a worked example of the gold plugin mixing + LLVM bitcode and native code. +<pre class="doc_code"> +--- a.c --- +#include <stdio.h> + +extern void foo1(void); +extern void foo4(void); + +void foo2(void) { + printf("Foo2\n"); +} + +void foo3(void) { + foo4(); +} + +int main(void) { + foo1(); +} + +--- b.c --- +#include <stdio.h> + +extern void foo2(void); + +void foo1(void) { + foo2(); +} + +void foo4(void) { + printf("Foo4"); +} + +--- command lines --- +$ llvm-gcc -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file +$ llvm-gcc b.c -c -o b.o # <-- b.o is native object file +$ llvm-gcc -use-gold-plugin a.o b.o -o main # <-- link with LLVMgold plugin +</pre> + <p>Gold informs the plugin that foo3 is never referenced outside the IR, + leading LLVM to delete that function. However, unlike in the + <a href="http://llvm.org/docs/LinkTimeOptimization.html#example1">libLTO + example</a> gold does not currently eliminate foo4.</p> +</div> + +<!--=========================================================================--> +<div class="doc_section"><a name="licensing">Licensing</a></div> +<!--=========================================================================--> +<div class="doc_text"> + <p>Gold is licensed under the GPLv3. LLVMgold uses the interface file +<tt>plugin-api.h</tt> from gold which means that the resulting LLVMgold.so +binary is also GPLv3. This can still be used to link non-GPLv3 programs just +as much as gold could without the plugin.</p> +</div> + +<!-- *********************************************************************** --> +<hr> +<address> + <a href="http://jigsaw.w3.org/css-validator/check/referer"><img + src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a> + <a href="http://validator.w3.org/check/referer"><img + src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a> + <a href="mailto:nicholas@metrix.on.ca">Nick Lewycky</a><br> + <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br> + Last modified: $Date: 2009-01-01 23:10:51 -0800 (Thu, 01 Jan 2009) $ +</address> +</body> +</html> |