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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 - Swap binop operands to avoid useless move before return"
href="https://bugs.llvm.org/show_bug.cgi?id=38929">38929</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Swap binop operands to avoid useless move before return
</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>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>unsigned f(unsigned x, unsigned y) {
int p = (~x & y) | ~(x | y);
// p =(x ^ y) | ~(x | y);
return p;
}
Clang:
f(unsigned int, unsigned int): # @f(unsigned
int, unsigned int)
mov eax, edi
not eax
and eax, esi
or esi, edi
not esi
or esi, eax // or eax, edi
mov eax, esi // not needed
ret
GCC:
f(unsigned int, unsigned int):
mov eax, edi
or edi, esi
not eax
not edi
and eax, esi
or eax, edi
ret
+ same for xor, etc...</pre>
</div>
</p>
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