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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 - Incorrect fold of 'x & (-1 >> y) s>= x'"
href="https://bugs.llvm.org/show_bug.cgi?id=39861">39861</a>
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<th>Summary</th>
<td>Incorrect fold of 'x & (-1 >> y) s>= x'
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>All
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Keywords</th>
<td>miscompilation
</td>
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<th>Severity</th>
<td>normal
</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>nunoplopes@sapo.pt
</td>
</tr>
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<th>CC</th>
<td>lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, regehr@cs.utah.edu, spatel+llvm@rotateright.com
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<p>
<div>
<pre>This is a bug in
test/Transforms/InstCombine/canonicalize-constant-low-bit-mask-and-icmp-sge-to-icmp-sle.ll
Output of Alive2:
declare i1 @pv(i8 %x, i8 %y) {
%tmp0 = lshr i8 255, %y
%tmp1 = and i8 %tmp0, %x
%ret = icmp sge i8 %tmp1, %x
ret i1 %ret
}
=>
declare i1 @pv(i8 %x, i8 %y) {
%tmp0 = lshr i8 255, %y
%1 = icmp sge i8 %tmp0, %x
ret i1 %1
}
Transformation doesn't verify!
ERROR: Value mismatch
Example:
i8 %x = 0x7e (126)
i8 %y = 0x0 (0)
Source:
i8 %tmp0 = 0xff (255, -1)
i8 %tmp1 = 0x7e (126)
i1 %ret = 0x1 (1, -1)
Target:
i8 %tmp0 = 0xff (255, -1)
i1 %1 = 0x0 (0)
Source value: 0x1 (1, -1)
Target value: 0x0 (0)</pre>
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