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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 - Optimizer does not take advantage of `-value == !(value -1)`"
href="https://bugs.llvm.org/show_bug.cgi?id=48559">48559</a>
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<th>Summary</th>
<td>Optimizer does not take advantage of `-value == !(value -1)`
</td>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>11.0
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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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>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>ju.orth@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Test case:
long f(long align) {
return (align - 1) & -align;
}
long g(long align) {
return (align - 1) & ~(align - 1);
}
int h(long align) {
return -align == ~(align - 1);
}
Generated assembly:
f:
leaq -1(%rdi), %rax
negq %rdi
andq %rdi, %rax
retq
g:
xorl %eax, %eax
retq
h:
movl $1, %eax
retq</pre>
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