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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - InstructionSimplify broadens undef when simplifying from"
href="https://llvm.org/bugs/show_bug.cgi?id=26863">26863</a>
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<th>Summary</th>
<td>InstructionSimplify broadens undef when simplifying from
</td>
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<th>Product</th>
<td>libraries
</td>
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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>Global Analyses
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>davemm@cs.rutgers.edu
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, santosh.nagarakatte@gmail.com
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<th>Classification</th>
<td>Unclassified
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</tr></table>
<p>
<div>
<pre>These optimizations in SimplifyFRemInst, from
lib/Analysis/InstructionSimplify.cpp, potentially introduce new behavior.
// undef % X -> undef (the undef could be a snan).
if (match(Op0, m_Undef()))
return Op0;
// X % undef -> undef
if (match(Op1, m_Undef()))
return Op1;
In the first optimization, undef % X must either result in NaN or a value less
than X.
In the second optimization, X % undef will usually result in NaN or a value
less than X when X is normal.</pre>
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