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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Can't remove shufflevector if input might be poison"
href="https://bugs.llvm.org/show_bug.cgi?id=44185">44185</a>
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<th>Summary</th>
<td>Can't remove shufflevector if input might be poison
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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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>
</tr>
<tr>
<th>Keywords</th>
<td>miscompilation
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>nunoplopes@sapo.pt
</td>
</tr>
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<th>CC</th>
<td>efriedma@quicinc.com, llvm-bugs@lists.llvm.org, regehr@cs.utah.edu, spatel+llvm@rotateright.com, zhengyang@kuf.io
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<p>
<div>
<pre>Test case from Transforms/InstCombine/insert-extract-shuffle.ll:
define <4 x float> @insert_not_undef_shuffle_translate_commute(float %x, <4 x
float> %y, <4 x float> %q) {
%xv = insertelement <4 x float> %q, float %x, i32 2
%r = shufflevector <4 x float> %y, <4 x float> %xv, <4 x i32> { 0, 6, 2,
undef }
ret <4 x float> %r
}
=>
define <4 x float> @insert_not_undef_shuffle_translate_commute(float %x, <4 x
float> %y, <4 x float> %q) {
%r = insertelement <4 x float> %y, float %x, i32 1
ret <4 x float> %r
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source
Example:
float %x = poison
<4 x float> %y = < poison, poison, poison, poison >
<4 x float> %q = < poison, poison, poison, poison >
Source:
<4 x float> %xv = < poison, poison, poison, poison >
<4 x float> %r = < poison, poison, poison, undef >
Target:
<4 x float> %r = < poison, poison, poison, poison >
Source value: < poison, poison, poison, undef >
Target value: < poison, poison, poison, poison >
This is with the semantics of LangRef, where an undef mask stops propagation of
poison. This implies this kind of shufflevectors can't be removed.</pre>
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