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<html>
<head>
+ <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>LLVM gold plugin</title>
- <link rel="stylesheet" href="llvm.css" type="text/css">
+ <link rel="stylesheet" href="_static/llvm.css" type="text/css">
</head>
<body>
<h2><a name="usage">Usage</a></h2>
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<div>
+
<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
<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
+
+ <p>You can produce bitcode files from <tt>clang</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>
+
+ <p>Any of these flags will also cause <tt>clang</tt> to look for the
+ gold plugin in the <tt>lib</tt> directory under its prefix and pass the
+ <tt>-plugin</tt> option to <tt>ld</tt>. It will not look for an alternate
+ linker, which is why you need gold to be the installed system linker in
+ your path.</p>
+
<p>If you want <tt>ar</tt> and <tt>nm</tt> to work seamlessly as well, install
<tt>LLVMgold.so</tt> to <tt>/usr/lib/bfd-plugins</tt>. If you built your
own gold, be sure to install the <tt>ar</tt> and <tt>nm-new</tt> you built to
- <tt>/usr/bin</tt>.
- <p>
+ <tt>/usr/bin</tt>.<p>
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<h3>
}
--- command lines ---
-$ llvm-gcc -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
-$ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
-$ llvm-gcc b.c -c -o b.o # <-- b.o is native object file
-$ llvm-gcc -use-gold-plugin a.a b.o -o main # <-- link with LLVMgold plugin
+$ clang -flto a.c -c -o a.o # <-- a.o is LLVM bitcode file
+$ ar q a.a a.o # <-- a.a is an archive with LLVM bitcode
+$ clang b.c -c -o b.o # <-- b.o is native object file
+$ clang -flto a.a 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="LinkTimeOptimization.html#example1">libLTO
</h2>
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<div>
- <p>Once your system <tt>ld</tt>, <tt>ar</tt> and <tt>nm</tt> all support LLVM
- bitcode, everything is in place for an easy to use LTO build of autotooled
- projects:</p>
+ <p>Once your system <tt>ld</tt>, <tt>ar</tt>, and <tt>nm</tt> all support LLVM
+ bitcode, everything is in place for an easy to use LTO build of autotooled
+ projects:</p>
+
<ul>
<li>Follow the instructions <a href="#build">on how to build LLVMgold.so</a>.</li>
<li>Install the newly built binutils to <tt>$PREFIX</tt></li>
<li>Copy <tt>Release/lib/LLVMgold.so</tt> to
- <tt>$PREFIX/libexec/gcc/x86_64-unknown-linux-gnu/4.2.1/</tt> and
- <tt>$PREFIX/lib/bfd-plugins/</tt></li>
- <li>Set environment variables (<tt>$PREFIX</tt> is where you installed llvm-gcc and
- binutils):
- <pre class="doc_code">
-export CC="$PREFIX/bin/llvm-gcc -use-gold-plugin"
-export CXX="$PREFIX/bin/llvm-g++ -use-gold-plugin"
+ <tt>$PREFIX/lib/bfd-plugins/</tt></li>
+ <li>Set environment variables (<tt>$PREFIX</tt> is where you installed clang and
+ binutils):
+<pre class="doc_code">
+export CC="$PREFIX/bin/clang -flto"
+export CXX="$PREFIX/bin/clang++ -flto"
export AR="$PREFIX/bin/ar"
export NM="$PREFIX/bin/nm"
export RANLIB=/bin/true #ranlib is not needed, and doesn't support .bc files in .a
</pre>
</li>
<li>Or you can just set your path:
+<pre class="doc_code">
export PATH="$PREFIX/bin:$PATH"
-export CC="llvm-gcc -use-gold-plugin"
-export CXX="llvm-g++ -use-gold-plugin"
+export CC="clang -flto"
+export CXX="clang++ -flto"
export RANLIB=/bin/true
export CFLAGS="-O4"
-</pre>
- </li>
- <li>Configure & build the project as usual: <tt>./configure && make && make check</tt> </li>
+</pre></li>
+ <li>Configure & build the project as usual:
+<pre class="doc_code">
+% ./configure && make && make check
+</pre></li>
</ul>
- <p> The environment variable settings may work for non-autotooled projects
- too, but you may need to set the <tt>LD</tt> environment variable as well.</p>
+
+ <p>The environment variable settings may work for non-autotooled projects
+ too, but you may need to set the <tt>LD</tt> environment variable as
+ well.</p>
</div>
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projects / oota-llvm.git / blobdiff