<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 - shuffle undef mask on vectors with poison"
href="https://bugs.llvm.org/show_bug.cgi?id=43958">43958</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>shuffle undef mask on vectors with poison
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>liuz@cs.utah.edu
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>A shuffle undef mask should select either of the elements. If one of them
happens to be poison, then the result can be poison. The langref [1] and a
transformation in instcombine seems forgot considering the poison case.
See below the transformation of insertelement to shufflevector. Assume the
function input %arg is poison, the target program shuffles the vector <poison,
undef, undef, undef> with mask <undef, 0, 0, 0>, the result should be <poison,
poison, poison, poison>, whereas the source program evaluates to <undef,
poison, poison, poison>. The target is more poisonous than the source.
llvm/test/Transforms/InstCombine/broadcast.ll
define <4 x float> @splat_undef1(float %arg) {
; CHECK-LABEL: @splat_undef1(
; CHECK-NEXT: [[TMP1:%.*]] = insertelement <4 x float> undef, float
[[ARG:%.*]], i32 0
; CHECK-NEXT: [[T6:%.*]] = shufflevector <4 x float> [[TMP1]], <4 x float>
undef, <4 x i32> <i32 undef, i32 0, i32 0, i32 0>
; CHECK-NEXT: ret <4 x float> [[T6]]
;
%t = insertelement <4 x float> undef, float %arg, i32 1
%t4 = insertelement <4 x float> %t, float %arg, i32 1
%t5 = insertelement <4 x float> %t4, float %arg, i32 2
%t6 = insertelement <4 x float> %t5, float %arg, i32 3
ret <4 x float> %t6
}
[1] <a href="https://llvm.org/docs/LangRef.html#id186">https://llvm.org/docs/LangRef.html#id186</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>