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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 - Regression: Missed fold for x * 0"
href="https://bugs.llvm.org/show_bug.cgi?id=51286">51286</a>
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<th>Summary</th>
<td>Regression: Missed fold for x * 0
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<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>Windows NT
</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>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>llvm@rifkin.dev
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Clang trunk is not generating optimal code for a (very poor) multiplication
routine <a href="https://godbolt.org/z/GrjMhsTcv">https://godbolt.org/z/GrjMhsTcv</a>.
int mul(int x, int y) {
int p = 0;
while(x--) p += y;
return p;
}
Should compile to:
mul(int, int):
mov eax, edi
imul eax, esi
ret
And it does in clang 12 but not in clang trunk.
If I'm not mistaken it appears a select i1 (icmp eq i32 %x, 0), i32 0, i32 (mul
i32 %x, %y) -> mul i32 %x, %y fold is not firing.</pre>
</div>
</p>
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