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docs: Sphinxify GoldPlugin document.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@165198 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Sean Silva
parent
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commit
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@ -1,227 +0,0 @@
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
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"http://www.w3.org/TR/html4/strict.dtd">
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<html>
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<title>LLVM gold plugin</title>
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<link rel="stylesheet" href="_static/llvm.css" type="text/css">
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</head>
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<body>
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<h1>LLVM gold plugin</h1>
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<ol>
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<li><a href="#introduction">Introduction</a></li>
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<li><a href="#build">How to build it</a></li>
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<li><a href="#usage">Usage</a>
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<ul>
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<li><a href="#example1">Example of link time optimization</a></li>
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<li><a href="#lto_autotools">Quickstart for using LTO with autotooled projects</a></li>
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</ul></li>
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<li><a href="#licensing">Licensing</a></li>
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</ol>
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<div class="doc_author">Written by Nick Lewycky</div>
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<!--=========================================================================-->
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<h2><a name="introduction">Introduction</a></h2>
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<!--=========================================================================-->
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<div>
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<p>Building with link time optimization requires cooperation from the
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system linker. LTO support on Linux systems requires that you use
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the <a href="http://sourceware.org/binutils">gold linker</a> which supports
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LTO via plugins. This is the same mechanism used by the
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<a href="http://gcc.gnu.org/wiki/LinkTimeOptimization">GCC LTO</a>
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project.</p>
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<p>The LLVM gold plugin implements the
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<a href="http://gcc.gnu.org/wiki/whopr/driver">gold plugin interface</a>
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on top of
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<a href="LinkTimeOptimization.html#lto">libLTO</a>.
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The same plugin can also be used by other tools such as <tt>ar</tt> and
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<tt>nm</tt>.
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</div>
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<!--=========================================================================-->
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<h2><a name="build">How to build it</a></h2>
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<!--=========================================================================-->
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<div>
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<p>You need to have gold with plugin support and build the LLVMgold
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plugin. Check whether you have gold running <tt>/usr/bin/ld -v</tt>. It will
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report “GNU gold” or else “GNU ld” if not. If you have
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gold, check for plugin support by running <tt>/usr/bin/ld -plugin</tt>. If it
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complains “missing argument” then you have plugin support. If not,
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such as an “unknown option” error then you will either need to
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build gold or install a version with plugin support.</p>
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<ul>
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<li>To build gold with plugin support:
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<pre class="doc_code">
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mkdir binutils
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cd binutils
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cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
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<em>{enter "anoncvs" as the password}</em>
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cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co binutils
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mkdir build
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cd build
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../src/configure --enable-gold --enable-plugins
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make all-gold
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</pre>
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That should leave you with <tt>binutils/build/gold/ld-new</tt> which supports the <tt>-plugin</tt> option. It also built would have
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<tt>binutils/build/binutils/ar</tt> and <tt>nm-new</tt> which support plugins
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but don't have a visible -plugin option, instead relying on the gold plugin
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being present in <tt>../lib/bfd-plugins</tt> relative to where the binaries are
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placed.
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<li>Build the LLVMgold plugin: Configure LLVM with
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<tt>--with-binutils-include=/path/to/binutils/src/include</tt> and run
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<tt>make</tt>.
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</ul>
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</div>
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<!--=========================================================================-->
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<h2><a name="usage">Usage</a></h2>
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<!--=========================================================================-->
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<div>
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<p>The linker takes a <tt>-plugin</tt> option that points to the path of
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the plugin <tt>.so</tt> file. To find out what link command <tt>gcc</tt>
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would run in a given situation, run <tt>gcc -v <em>[...]</em></tt> and look
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for the line where it runs <tt>collect2</tt>. Replace that with
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<tt>ld-new -plugin /path/to/LLVMgold.so</tt> to test it out. Once you're
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ready to switch to using gold, backup your existing <tt>/usr/bin/ld</tt>
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then replace it with <tt>ld-new</tt>.</p>
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<p>You can produce bitcode files from <tt>clang</tt> using
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<tt>-emit-llvm</tt> or <tt>-flto</tt>, or the <tt>-O4</tt> flag which is
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synonymous with <tt>-O3 -flto</tt>.</p>
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<p>Any of these flags will also cause <tt>clang</tt> to look for the
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gold plugin in the <tt>lib</tt> directory under its prefix and pass the
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<tt>-plugin</tt> option to <tt>ld</tt>. It will not look for an alternate
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linker, which is why you need gold to be the installed system linker in
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your path.</p>
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<p>If you want <tt>ar</tt> and <tt>nm</tt> to work seamlessly as well, install
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<tt>LLVMgold.so</tt> to <tt>/usr/lib/bfd-plugins</tt>. If you built your
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own gold, be sure to install the <tt>ar</tt> and <tt>nm-new</tt> you built to
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<tt>/usr/bin</tt>.<p>
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<!-- ======================================================================= -->
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<h3>
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<a name="example1">Example of link time optimization</a>
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</h3>
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<div>
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<p>The following example shows a worked example of the gold plugin mixing
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LLVM bitcode and native code.
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<pre class="doc_code">
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--- a.c ---
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#include <stdio.h>
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extern void foo1(void);
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extern void foo4(void);
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void foo2(void) {
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printf("Foo2\n");
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}
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void foo3(void) {
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foo4();
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}
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int main(void) {
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foo1();
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}
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--- b.c ---
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#include <stdio.h>
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extern void foo2(void);
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void foo1(void) {
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foo2();
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}
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void foo4(void) {
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printf("Foo4");
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}
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--- command lines ---
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$ clang -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
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$ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
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$ clang b.c -c -o b.o # <-- b.o is native object file
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$ clang -flto a.a b.o -o main # <-- link with LLVMgold plugin
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</pre>
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<p>Gold informs the plugin that foo3 is never referenced outside the IR,
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leading LLVM to delete that function. However, unlike in the
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<a href="LinkTimeOptimization.html#example1">libLTO
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example</a> gold does not currently eliminate foo4.</p>
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</div>
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</div>
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<!--=========================================================================-->
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<h2>
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<a name="lto_autotools">
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Quickstart for using LTO with autotooled projects
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</a>
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</h2>
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<!--=========================================================================-->
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<div>
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<p>Once your system <tt>ld</tt>, <tt>ar</tt>, and <tt>nm</tt> all support LLVM
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bitcode, everything is in place for an easy to use LTO build of autotooled
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projects:</p>
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<ul>
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<li>Follow the instructions <a href="#build">on how to build LLVMgold.so</a>.</li>
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<li>Install the newly built binutils to <tt>$PREFIX</tt></li>
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<li>Copy <tt>Release/lib/LLVMgold.so</tt> to
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<tt>$PREFIX/lib/bfd-plugins/</tt></li>
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<li>Set environment variables (<tt>$PREFIX</tt> is where you installed clang and
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binutils):
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<pre class="doc_code">
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export CC="$PREFIX/bin/clang -flto"
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export CXX="$PREFIX/bin/clang++ -flto"
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export AR="$PREFIX/bin/ar"
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export NM="$PREFIX/bin/nm"
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export RANLIB=/bin/true #ranlib is not needed, and doesn't support .bc files in .a
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export CFLAGS="-O4"
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</pre>
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</li>
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<li>Or you can just set your path:
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<pre class="doc_code">
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export PATH="$PREFIX/bin:$PATH"
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export CC="clang -flto"
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export CXX="clang++ -flto"
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export RANLIB=/bin/true
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export CFLAGS="-O4"
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</pre></li>
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<li>Configure & build the project as usual:
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<pre class="doc_code">
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% ./configure && make && make check
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</pre></li>
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</ul>
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<p>The environment variable settings may work for non-autotooled projects
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too, but you may need to set the <tt>LD</tt> environment variable as
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well.</p>
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</div>
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<!--=========================================================================-->
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<h2><a name="licensing">Licensing</a></h2>
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<!--=========================================================================-->
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<div>
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<p>Gold is licensed under the GPLv3. LLVMgold uses the interface file
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<tt>plugin-api.h</tt> from gold which means that the resulting LLVMgold.so
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binary is also GPLv3. This can still be used to link non-GPLv3 programs just
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as much as gold could without the plugin.</p>
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</div>
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<!-- *********************************************************************** -->
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<hr>
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<address>
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<a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
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<a href="http://validator.w3.org/check/referer"><img
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src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
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<a href="mailto:nicholas@metrix.on.ca">Nick Lewycky</a><br>
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<a href="http://llvm.org/">The LLVM Compiler Infrastructure</a><br>
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Last modified: $Date: 2010-04-16 23:58:21 -0800 (Fri, 16 Apr 2010) $
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</address>
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</body>
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</html>
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186
docs/GoldPlugin.rst
Normal file
186
docs/GoldPlugin.rst
Normal file
@ -0,0 +1,186 @@
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.. _gold-plugin:
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====================
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The LLVM gold plugin
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====================
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.. sectionauthor:: Nick Lewycky
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Introduction
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============
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Building with link time optimization requires cooperation from
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the system linker. LTO support on Linux systems requires that you use the
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`gold linker`_ which supports LTO via plugins. This is the same mechanism
|
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used by the `GCC LTO`_ project.
|
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|
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The LLVM gold plugin implements the gold plugin interface on top of
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:ref:`libLTO`. The same plugin can also be used by other tools such as
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``ar`` and ``nm``.
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.. _`gold linker`: http://sourceware.org/binutils
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.. _`GCC LTO`: http://gcc.gnu.org/wiki/LinkTimeOptimization
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.. _`gold plugin interface`: http://gcc.gnu.org/wiki/whopr/driver
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.. _lto-how-to-build:
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How to build it
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===============
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You need to have gold with plugin support and build the LLVMgold plugin.
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Check whether you have gold running ``/usr/bin/ld -v``. It will report "GNU
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gold" or else "GNU ld" if not. If you have gold, check for plugin support
|
||||
by running ``/usr/bin/ld -plugin``. If it complains "missing argument" then
|
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you have plugin support. If not, such as an "unknown option" error then you
|
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will either need to build gold or install a version with plugin support.
|
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|
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* To build gold with plugin support:
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.. code-block:: bash
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$ mkdir binutils
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$ cd binutils
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$ cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
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{enter "anoncvs" as the password}
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$ cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co binutils
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$ mkdir build
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$ cd build
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$ ../src/configure --enable-gold --enable-plugins
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$ make all-gold
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That should leave you with ``binutils/build/gold/ld-new`` which supports
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the ``-plugin`` option. It also built would have
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``binutils/build/binutils/ar`` and ``nm-new`` which support plugins but
|
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don't have a visible -plugin option, instead relying on the gold plugin
|
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being present in ``../lib/bfd-plugins`` relative to where the binaries
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are placed.
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* Build the LLVMgold plugin: Configure LLVM with
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``--with-binutils-include=/path/to/binutils/src/include`` and run
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``make``.
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Usage
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=====
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The linker takes a ``-plugin`` option that points to the path of
|
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the plugin ``.so`` file. To find out what link command ``gcc``
|
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would run in a given situation, run ``gcc -v [...]`` and
|
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look for the line where it runs ``collect2``. Replace that with
|
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``ld-new -plugin /path/to/LLVMgold.so`` to test it out. Once you're
|
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ready to switch to using gold, backup your existing ``/usr/bin/ld``
|
||||
then replace it with ``ld-new``.
|
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|
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You can produce bitcode files from ``clang`` using ``-emit-llvm`` or
|
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``-flto``, or the ``-O4`` flag which is synonymous with ``-O3 -flto``.
|
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|
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Any of these flags will also cause ``clang`` to look for the gold plugin in
|
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the ``lib`` directory under its prefix and pass the ``-plugin`` option to
|
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``ld``. It will not look for an alternate linker, which is why you need
|
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gold to be the installed system linker in your path.``
|
||||
|
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If you want ``ar`` and ``nm`` to work seamlessly as well, install
|
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``LLVMgold.so`` to ``/usr/lib/bfd-plugins``. If you built your own gold, be
|
||||
sure to install the ``ar`` and ``nm-new`` you built to ``/usr/bin``
|
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|
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Example of link time optimization
|
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---------------------------------
|
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|
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The following example shows a worked example of the gold plugin mixing LLVM
|
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bitcode and native code.
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|
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.. code-block:: c
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|
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--- a.c ---
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#include <stdio.h>
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|
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extern void foo1(void);
|
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extern void foo4(void);
|
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|
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void foo2(void) {
|
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printf("Foo2\n");
|
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}
|
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|
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void foo3(void) {
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foo4();
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}
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int main(void) {
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foo1();
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}
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--- b.c ---
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#include <stdio.h>
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extern void foo2(void);
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|
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void foo1(void) {
|
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foo2();
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}
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|
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void foo4(void) {
|
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printf("Foo4");
|
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}
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|
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.. code-block:: bash
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|
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--- command lines ---
|
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$ clang -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
|
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$ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
|
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$ clang b.c -c -o b.o # <-- b.o is native object file
|
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$ clang -flto a.a b.o -o main # <-- link with LLVMgold plugin
|
||||
|
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Gold informs the plugin that foo3 is never referenced outside the IR,
|
||||
leading LLVM to delete that function. However, unlike in the :ref:`libLTO
|
||||
example <libLTO-example>` gold does not currently eliminate foo4.
|
||||
|
||||
Quickstart for using LTO with autotooled projects
|
||||
=================================================
|
||||
|
||||
Once your system ``ld``, ``ar``, and ``nm`` all support LLVM bitcode,
|
||||
everything is in place for an easy to use LTO build of autotooled projects:
|
||||
|
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* Follow the instructions :ref:`on how to build LLVMgold.so
|
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<lto-how-to-build>`.
|
||||
|
||||
* Install the newly built binutils to ``$PREFIX``
|
||||
|
||||
* Copy ``Release/lib/LLVMgold.so`` to ``$PREFIX/lib/bfd-plugins/``
|
||||
|
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* Set environment variables (``$PREFIX`` is where you installed clang and
|
||||
binutils):
|
||||
|
||||
.. code-block:: bash
|
||||
|
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export CC="$PREFIX/bin/clang -flto"
|
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export CXX="$PREFIX/bin/clang++ -flto"
|
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export AR="$PREFIX/bin/ar"
|
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export NM="$PREFIX/bin/nm"
|
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export RANLIB=/bin/true #ranlib is not needed, and doesn't support .bc files in .a
|
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export CFLAGS="-O4"
|
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|
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* Or you can just set your path:
|
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|
||||
.. code-block:: bash
|
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|
||||
export PATH="$PREFIX/bin:$PATH"
|
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export CC="clang -flto"
|
||||
export CXX="clang++ -flto"
|
||||
export RANLIB=/bin/true
|
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export CFLAGS="-O4"
|
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* Configure and build the project as usual:
|
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|
||||
.. code-block:: bash
|
||||
|
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% ./configure && make && make check
|
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|
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The environment variable settings may work for non-autotooled projects too,
|
||||
but you may need to set the ``LD`` environment variable as well.
|
||||
|
||||
Licensing
|
||||
=========
|
||||
|
||||
Gold is licensed under the GPLv3. LLVMgold uses the interface file
|
||||
``plugin-api.h`` 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.
|
||||
@ -29,6 +29,8 @@ bitcode files. This tight integration between the linker and LLVM optimizer
|
||||
helps to do optimizations that are not possible in other models. The linker
|
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input allows the optimizer to avoid relying on conservative escape analysis.
|
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|
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.. _libLTO-example:
|
||||
|
||||
Example of link time optimization
|
||||
---------------------------------
|
||||
|
||||
|
||||
@ -16,6 +16,7 @@ Subsystem Documentation
|
||||
SegmentedStacks
|
||||
TableGenFundamentals
|
||||
DebuggingJITedCode
|
||||
GoldPlugin
|
||||
|
||||
* `Writing an LLVM Pass <WritingAnLLVMPass.html>`_
|
||||
|
||||
@ -75,7 +76,7 @@ Subsystem Documentation
|
||||
This document describes the interface between LLVM intermodular optimizer
|
||||
and the linker and its design
|
||||
|
||||
* `The LLVM gold plugin <GoldPlugin.html>`_
|
||||
* :ref:`gold-plugin`
|
||||
|
||||
How to build your programs with link-time optimization on Linux.
|
||||
|
||||
|
||||
Loading…
Reference in New Issue
Block a user