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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - InstCombiner::commonIDivTransforms: incorrect transformation"
href="http://llvm.org/bugs/show_bug.cgi?id=21243">21243</a>
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<th>Summary</th>
<td>InstCombiner::commonIDivTransforms: incorrect transformation
</td>
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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>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>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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<th>Reporter</th>
<td>nunoplopes@sapo.pt
</td>
</tr>
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<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>One transformation done in InstCombiner::commonIDivTransforms()
(InstCombineMulDivRem.cpp) is incorrect:
(X / C1) / C2 -> 0
if C1*C2 overflows
In the following counterexample, we can see that even C1*C2 overflows (it does,
the result would be = 2), the final result may be non-zero.
----------------------------------------
Pre: !WillNotOverflowSignedMul(C1, C2)
%Op0 = sdiv %X, C1
%r = sdiv %Op0, C2
=>
%r = 0
Done: 1
ERROR: Mismatch in values of i2 %r
Example:
%X i2 = 2 (0x2)
C1 i2 = 2 (0x2)
C2 i2 = 3 (0x3)
%Op0 i2 = 1 (0x1)
Source value: 3 (0x3)
Target value: 0 (0x0)</pre>
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