<html>
<head>
<base href="https://bugs.llvm.org/">
</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 - llvm.experimental.vector.reduce.{fmin,fmax} incorrect for vectors with NaN in the last place"
href="https://bugs.llvm.org/show_bug.cgi?id=36982">36982</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>llvm.experimental.vector.reduce.{fmin,fmax} incorrect for vectors with NaN in the last place
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</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>gonzalobg88@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>On x86_64:
define float @example::foo(<2 x float>* noalias nocapture readonly
dereferenceable(8) %x) unnamed_addr #0 {
%0 = load <2 x float>, <2 x float>* %x, align 8
%1 = tail call float @llvm.experimental.vector.reduce.fmin.f32.v2f32(<2 x
float> %0)
ret float %1
}
lowers to:
example::foo:
movq xmm0, qword ptr [rdi]
pshufd xmm1, xmm0, 229
minps xmm0, xmm1
ret
which for the following inputs produces the respective outputs:
* <1.0, -1.0> => -1.0
* <NaN, -1.0> => -1.0
* <-1.0, NaN> => NaN
I think this is basically equivalent to a vector fcmp + select, but the default
semantics of the reductions (that is, without math flags) should be that of
minnum/maxnum.
The llvm.experimental.vector.reduce.fmin/fmax intrinsics do not specify their
semantics in the reference, so it is hard to tell whether the current behavior
is intended or an oversight.
This bug is Rust's bug: <a href="https://github.com/rust-lang-nursery/stdsimd/issues/408">https://github.com/rust-lang-nursery/stdsimd/issues/408</a></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>