mirror of
https://github.com/RPCS3/llvm.git
synced 2024-12-29 16:04:33 +00:00
f3888ba23f
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@65789 91177308-0d34-0410-b5e6-96231b3b80d8
161 lines
5.9 KiB
HTML
161 lines
5.9 KiB
HTML
<!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">
|
|
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.
|
|
</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>
|