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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 - Failure to optimize simple selection properly, somehow the code degenerates"
href="https://bugs.llvm.org/show_bug.cgi?id=47237">47237</a>
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<tr>
<th>Summary</th>
<td>Failure to optimize simple selection properly, somehow the code degenerates
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>gabravier@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>int f(int x, int y)
{
return (x & y) == 0 ? x & ~y : x;
}
GCC outputs this :
f(int, int):
andn edx, esi, edi
mov eax, edi
test edi, esi
cmove eax, edx
ret
And LLVM outputs this :
f(int, int): # @f(int, int)
mov ecx, esi
and ecx, edi
not esi
xor eax, eax
cmp ecx, 1
sbb eax, eax
not eax
or eax, esi
and eax, edi
ret
Most likely some sort of transformation in LLVM makes this code completely
degenerate into the result given here.</pre>
</div>
</p>
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