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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Missing pattern (32 - popcount(a)) - > (popcount(~a))"
href="https://bugs.llvm.org/show_bug.cgi?id=50104">50104</a>
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<th>Summary</th>
<td>Missing pattern (32 - popcount(a)) - > (popcount(~a))
</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>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<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>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Found in PR50096.
int A(unsigned int a)
{
return (32 -__builtin_popcount(a));
}
int B(unsigned int a)
{
return (__builtin_popcount(~a)) ;
}
A(unsigned int): # @A(unsigned int)
popcnt ecx, edi
mov eax, 32
sub eax, ecx
ret
B(unsigned int): # @B(unsigned int)
not edi
popcnt eax, edi
ret
'not' form is better for analysis than a 'sub' form.
----------------------------------------
define i8 @src(i8 %x) {
%0:
%p = ctpop i8 %x
%a = sub i8 8, %p
ret i8 %a
}
=>
define i8 @tgt(i8 %x) {
%0:
%n = xor i8 %x, 255
%p = ctpop i8 %n
ret i8 %p
}
Transformation seems to be correct!</pre>
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