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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 transformation rotr(X,C1) == C2 --> X == C3"
href="https://bugs.llvm.org/show_bug.cgi?id=51567">51567</a>
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<th>Summary</th>
<td>Missing transformation rotr(X,C1) == C2 --> X == C3
</td>
</tr>
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<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>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<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
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</tr>
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<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>// rotr(X, C1) == C2 --> X == C3 where C3 = rotl(C2, C1)
// rotl(X,C1) == C2 --> X == C3 where C3 = rotr(C2,C1)
bool foo(unsigned int x)
{
unsigned int rx = rotr(x, 7);
return rx == 5;
}
bool bar(unsigned int x)
{
return x == rotl(5, 7);
}
Trunk -O2:
foo(unsigned int): # @foo(unsigned int)
rol edi, 25
cmp edi, 5
sete al
ret
bar(unsigned int): # @bar(unsigned int)
cmp edi, 640
sete al
ret
Current codegen:
<a href="https://godbolt.org/z/xb1vPa5Pq">https://godbolt.org/z/xb1vPa5Pq</a>
Alive:
<a href="https://alive2.llvm.org/ce/z/GdY8Jm">https://alive2.llvm.org/ce/z/GdY8Jm</a></pre>
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