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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Use movzx instead of mov + shr"
href="https://bugs.llvm.org/show_bug.cgi?id=44796">44796</a>
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<th>Summary</th>
<td>Use movzx instead of mov + shr
</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>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>
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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
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<p>
<div>
<pre>unsigned char sum2(const void* ptr)
{
const unsigned k = 2;
unsigned char bytes[k], result = 0;
memcpy(bytes, ptr, k);
for(unsigned n=0; n<k; ++n) result += bytes[n];
return result;
}
GCC:
sum2(void const*):
movzx edx, WORD PTR [rdi]
movzx eax, dh
add eax, edx
ret
Clang:
sum2(void const*): # @sum2(void const*)
movzx ecx, word ptr [rdi]
mov eax, ecx
shr eax, 8
add al, cl
ret
<a href="https://godbolt.org/z/dTuEJb">https://godbolt.org/z/dTuEJb</a></pre>
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