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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 - Optimize ((a >> c1) & c2) eq/ne 0"
href="https://bugs.llvm.org/show_bug.cgi?id=42697">42697</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Optimize ((a >> c1) & c2) eq/ne 0
</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>Scalar Optimizations
</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>int f(int a) {
return ((a >> 7) & 8) == 0;
}
int f2(int a) {
return (a & (8 << 7)) == 0;
}
Clang:
f(int): # @f(int)
mov eax, edi
shr eax, 10
not eax
and eax, 1
ret
f2(int): # @f2(int)
mov eax, edi
shr eax, 10
not eax
and eax, 1
ret
I expected atleast 'f2' give us what we want:
xor eax, eax
and edi, 1024
sete al
ret
GCC:
f(int):
xor eax, eax
and edi, 1024
sete al
ret
f2(int):
xor eax, eax
and edi, 1024
sete al
ret
Codegen: <a href="https://godbolt.org/z/HE-ZPA">https://godbolt.org/z/HE-ZPA</a></pre>
</div>
</p>
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