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Recommend the -flto flag instead of -use-gold-plugin, and update

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other aspects of the gold plugin docs to reflect reality.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@143785 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Peter Collingbourne 2011-11-05 04:17:28 +00:00
parent 988fdc5f28
commit 5f73f68d39
1 changed files with 13 additions and 14 deletions
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docs/GoldPlugin.html
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@ -89,11 +89,11 @@ placed.
<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>Clang</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 <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>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
@ -141,10 +141,10 @@ void foo4(void) {
}
--- command lines ---
$ clang -flto a.c -c -o a.o # &lt;-- a.o is LLVM bitcode file
$ ar q a.a a.o # &lt;-- a.a is an archive with LLVM bitcode
$ clang b.c -c -o b.o # &lt;-- b.o is native object file
$ clang -use-gold-plugin a.a b.o -o main # &lt;-- link with LLVMgold plugin
$ clang -flto a.c -c -o a.o # &lt;-- a.o is LLVM bitcode file
$ ar q a.a a.o # &lt;-- a.a is an archive with LLVM bitcode
$ clang b.c -c -o b.o # &lt;-- b.o is native object file
$ clang -flto a.a b.o -o main # &lt;-- link with LLVMgold plugin
</pre>
<p>Gold informs the plugin that foo3 is never referenced outside the IR,
@ -171,13 +171,12 @@ $ clang -use-gold-plugin a.a b.o -o main # &lt;-- link with LLVMgold plugin
<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 clang and
binutils):
<pre class="doc_code">
export CC="$PREFIX/bin/clang -use-gold-plugin"
export CXX="$PREFIX/bin/clang++ -use-gold-plugin"
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
@ -187,8 +186,8 @@ export CFLAGS="-O4"
<li>Or you can just set your path:
<pre class="doc_code">
export PATH="$PREFIX/bin:$PATH"
export CC="clang -use-gold-plugin"
export CXX="clang++ -use-gold-plugin"
export CC="clang -flto"
export CXX="clang++ -flto"
export RANLIB=/bin/true
export CFLAGS="-O4"
</pre></li>