<html>
<head>
<base href="https://llvm.org/bugs/" />
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - InstructionSimplify broadens undef when simplifying fdiv"
href="https://llvm.org/bugs/show_bug.cgi?id=26862">26862</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>InstructionSimplify broadens undef when simplifying fdiv
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Global Analyses
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>davemm@cs.rutgers.edu
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, santosh.nagarakatte@gmail.com
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>These optimizations in SimplifyFDivInst, 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, for any value of X, there will be some floating
point values that undef/X cannot produce. For example, if X is 0, the original
code can only evaluate to Infinity, -Infinity, or NaN, but the transformed code
may produce any value.
The second optimization is similar. For example, if X is 0, x/undef is either
0, -0, or NaN.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>