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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 - Missing 32 - __builtin_popcount(x | -x) -> __builtin_ctz(x)"
href="https://bugs.llvm.org/show_bug.cgi?id=43513">43513</a>
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</tr>
<tr>
<th>Summary</th>
<td>Missing 32 - __builtin_popcount(x | -x) -> __builtin_ctz(x)
</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>
<tr>
<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>Transformation Utilities
</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>-O3 -march=haswell
int foo(int i) {
return i == 0 ? 32 : __builtin_ctz(i);
// return __builtin_ctz(i);
}
int food(int i) {
return 32 - __builtin_popcount(i | -i);
}
int foodd(int i) {
return __builtin_popcount(~i & (i-1));
}
foo(int): # @foo(int)
tzcnt eax, edi
ret
food(int): # @food(int)
mov eax, edi
neg eax
or eax, edi
popcnt ecx, eax
mov eax, 32
sub eax, ecx
ret
foodd(int): # @foodd(int)
lea eax, [rdi - 1]
andn eax, edi, eax
popcnt eax, eax
ret
<a href="https://godbolt.org/z/iNeY43">https://godbolt.org/z/iNeY43</a></pre>
</div>
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