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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 - Incorrect mul foo, undef -> shl foo, undef"
href="https://bugs.llvm.org/show_bug.cgi?id=47133">47133</a>
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<th>Summary</th>
<td>Incorrect mul foo, undef -> shl foo, undef
</td>
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<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>All
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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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>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>nunoplopes@sapo.pt
</td>
</tr>
<tr>
<th>CC</th>
<td>lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, regehr@cs.utah.edu
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</tr></table>
<p>
<div>
<pre>This is a recent regression in Transforms/InstCombine/mul.ll.
shl foo, undef is poison, so we can't introduce that.
define <2 x i32> @mulsub1_vec_nonuniform_undef(<2 x i32> %a0, <2 x i32> %a1) {
%sub = sub <2 x i32> %a1, %a0
%mul = mul <2 x i32> %sub, { 4294967292, undef }
ret <2 x i32> %mul
}
=>
define <2 x i32> @mulsub1_vec_nonuniform_undef(<2 x i32> %a0, <2 x i32> %a1) {
%sub.neg = sub <2 x i32> %a0, %a1
%mul = shl <2 x i32> %sub.neg, { 2, undef }
ret <2 x i32> %mul
}
Transformation doesn't verify!
ERROR: Target is more poisonous than source
Example:
<2 x i32> %a0 = < undef, undef >
<2 x i32> %a1 = < undef, undef >
Source:
<2 x i32> %sub = < undef, undef >
<2 x i32> %mul = < #x00000000 (0), #x00000000 (0) >
Target:
<2 x i32> %sub.neg = < #x00000000 (0), #x00000000 (0) >
<2 x i32> %mul = < #x00000000 (0), poison >
Source value: < #x00000000 (0), #x00000000 (0) >
Target value: < #x00000000 (0), poison >
Probably caused by
<a href="https://github.com/llvm/llvm-project/commit/0c1c756a31536666a7b6f5bdb744dbce923a0c9e">https://github.com/llvm/llvm-project/commit/0c1c756a31536666a7b6f5bdb744dbce923a0c9e</a>
<a href="https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=b697cc49b7cc411c&test=Transforms%2FInstCombine%2Fmul.ll">https://web.ist.utl.pt/nuno.lopes/alive2/index.php?hash=b697cc49b7cc411c&test=Transforms%2FInstCombine%2Fmul.ll</a></pre>
</div>
</p>
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