<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 turns 0.0 to -0.0"
href="https://llvm.org/bugs/show_bug.cgi?id=26746">26746</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>InstructionSimplify turns 0.0 to -0.0
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>3.7
</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>new bugs
</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>Given this input:
define float @foo(float %x) #0 {
entry:
%a = fsub float -0.0, %x
%b = fsub float 0.0, %a
ret float %b
}
opt -instcombine produces
define float @foo(float %x) #0 {
entry:
ret float %x
}
If %x = -0.0, the original function returns 0.0, but the optimized function
returns -0.0.
I believe this is the relevant code, from lib/Analysis/InstructionSimplify.cpp:
// fsub 0, (fsub -0.0, X) ==> X
Value *X;
if (match(Op0, m_AnyZero())) {
if (match(Op1, m_FSub(m_NegZero(), m_Value(X)))) // this clause
return X;
if (FMF.noSignedZeros() && match(Op1, m_FSub(m_AnyZero(), m_Value(X))))
return X;
}</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>