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5 <title>LLVM gold plugin</title>
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10 <div class="doc_title">LLVM gold plugin</div>
12 <li><a href="#introduction">Introduction</a></li>
13 <li><a href="#build">How to build it</a></li>
14 <li><a href="#usage">Usage</a></li>
15 <li><a href="#licensing">Licensing</a></li>
17 <div class="doc_author">Written by Nick Lewycky</div>
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20 <div class="doc_section"><a name="introduction">Introduction</a></div>
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22 <div class="doc_text">
23 <p>Building with link time optimization requires cooperation from the
24 system linker. LTO support on Linux systems requires that you use
25 the <a href="http://sourceware.org/binutils">gold linker</a> which supports
26 LTO via plugins. This is the same system used by the upcoming
27 <a href="http://gcc.gnu.org/wiki/LinkTimeOptimization">GCC LTO</a>
29 <p>The LLVM gold plugin implements the
30 <a href="http://gcc.gnu.org/wiki/whopr/driver">gold plugin interface</a>
32 <a href="http://llvm.org/docs/LinkTimeOptimization.html#lto">libLTO</a>.
33 The same plugin can also be used by other tools such as <tt>ar</tt> and
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37 <div class="doc_section"><a name="build">How to build it</a></div>
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39 <div class="doc_text">
40 <p>You need to build gold with plugin support and build the LLVMgold
43 <li>Build gold with plugin support:
44 <pre class="doc_code">
47 cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src login
48 <em>{enter "anoncvs" as the password}</em>
49 cvs -z 9 -d :pserver:anoncvs@sourceware.org:/cvs/src co src
52 ../src/configure --enable-gold --enable-plugins
55 That should leave you with binutils/build/gold/ld-new which supports the
58 <li>Build the LLVMgold plugin: Configure LLVM with
59 <tt>--with-binutils-include=/path/to/binutils/src/include</tt> and run
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64 <div class="doc_section"><a name="usage">Usage</a></div>
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66 <div class="doc_text">
67 <p>The linker takes a <tt>-plugin</tt> option that points to the path of
68 the plugin <tt>.so</tt> file. To find out what link command <tt>gcc</tt>
69 would run in a given situation, run <tt>gcc -v <em>[...]</em></tt> and look
70 for the line where it runs <tt>collect2</tt>. Replace that with
71 <tt>ld-new -plugin /path/to/LLVMgold.so</tt> to test it out. Once you're
72 ready to switch to using gold, backup your existing <tt>/usr/bin/ld</tt>
73 then replace it with <tt>ld-new</tt>.</p>
74 <p>You can produce bitcode files from <tt>llvm-gcc</tt> using
75 <tt>-emit-llvm</tt> or <tt>-flto</tt>, or the <tt>-O4</tt> flag which is
76 synonymous with <tt>-O3 -flto</tt>.</p>
77 <p><tt>llvm-gcc</tt> has a <tt>-use-gold-plugin</tt> option which looks
78 for the gold plugin in the same directories as it looks for <tt>cc1</tt> and
79 passes the <tt>-plugin</tt> option to ld. It will not look for an alternate
80 linker, which is why you need gold to be the installed system linker in your
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84 <div class="doc_section"><a name="licensing">Licensing</a></div>
85 <!--=========================================================================-->
86 <div class="doc_text">
87 Gold is licensed under the GPLv3. LLVMgold uses the interface file
88 <tt>plugin-api.h</tt> from gold which means that the resulting LLVMgold.so
89 binary is also GPLv3. This can still be used to link non-GPLv3 programs just
90 as much as gold could without the plugin.
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100 <a href="mailto:nicholas@metrix.on.ca">Nick Lewycky</a><br>
101 <a href="http://llvm.org">The LLVM Compiler Infrastructure</a><br>
102 Last modified: $Date: 2009-01-01 23:10:51 -0800 (Thu, 01 Jan 2009) $