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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - ThinLTO doesn't apply interprocedural DeadArgumentElimination optimization"
href="https://bugs.llvm.org/show_bug.cgi?id=33646">33646</a>
</td>
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<th>Summary</th>
<td>ThinLTO doesn't apply interprocedural DeadArgumentElimination optimization
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<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>
<tr>
<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>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<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 deadargelim pass, but ThinLTO can't apply this optimization
right now.
$ cat a.cc
__attribute__((noinline))
int f(const int *x, int j) {
int k = *x;
return k + 1;
}
__attribute__((noinline))
int g(int *x) {
*x++;
return *x;
}
$ cat b.cc
#include <stdio.h>
extern int f(const int *x, int j);
extern int g(int *x);
int main(void) {
int x = 3;
printf("%d\n", f(&x, x));
g(&x);
printf("%d\n", x);
}
$ ../build/bin/clang++ a.cc b.cc -O3 --for-linker=-mllvm --for-linker=-stats
-flto=thin -fuse-ld=lld -o thin &>&1 | grep deadargelim
# nothing
$ ../build/bin/clang++ a.cc b.cc -O3 --for-linker=-mllvm --for-linker=-stats
-flto -fuse-ld=lld -o lto &>&1 | grep deadargelim
1 deadargelim - Number of unread args removed
1 deadargelim - Number of unused return values removed</pre>
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