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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ThinLTO doesn't apply interprocedural ConstMerge"
href="https://bugs.llvm.org/show_bug.cgi?id=33630">33630</a>
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<th>Summary</th>
<td>ThinLTO doesn't apply interprocedural ConstMerge
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Interprocedural Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>charles.saternos@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>LTO will apply the Constant Merging pass, but ThinLTO can't apply this
optimization right now.
Test case:
// a.c
const char *x = "blah";
// b.c
#include <stdio.h>
extern const char *x;
const char *b = "blah";
int main(void) {
puts(x);
puts(b);
}
//////////////////////
# == THINLTO ==
$ ../build/bin/clang a.c b.c --for-linker=-mllvm --for-linker=-stats -flto=thin
\
-fuse-ld=lld -o out &>&1 | grep "constmerge"
# nothing
# == LTO ==
$ ../build/bin/clang a.c b.c --for-linker=-mllvm --for-linker=-stats -flto \
-fuse-ld=lld -o out &>&1 | grep "constmerge"
1 constmerge - Number of global constants merged</pre>
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