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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 - Extra mov in naive int swap"
href="https://bugs.llvm.org/show_bug.cgi?id=42324">42324</a>
</td>
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<th>Summary</th>
<td>Extra mov in naive int swap
</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>Backend: X86
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
</td>
</tr></table>
<p>
<div>
<pre>#include <algorithm>
unsigned int stdswap(unsigned int u, unsigned int v)
{
if(u>v) std::swap(u,v);
return u / v;
}
unsigned int naiveswap(unsigned int u, unsigned int v)
{
if (u > v) {
unsigned int t = v;
v = u;
u = t;
}
return u / v;
}
Clang -O3:
stdswap(unsigned int, unsigned int):
cmp edi, esi
mov eax, edi
cmova eax, esi
cmova esi, edi
xor edx, edx
div esi
ret
naiveswap(unsigned int, unsigned int):
mov eax, edi
cmp edi, esi
mov ecx, esi // this mov
cmova ecx, edi
cmova eax, esi
xor edx, edx
div ecx
ret</pre>
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