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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [InstCombine] Negation not sunk through shift"
href="https://bugs.llvm.org/show_bug.cgi?id=44529">44529</a>
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<th>Summary</th>
<td>[InstCombine] Negation not sunk through shift
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Scalar Optimizations
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>nikita.ppv@gmail.com
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</tr>
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<th>CC</th>
<td>lebedev.ri@gmail.com, llvm-bugs@lists.llvm.org
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<p>
<div>
<pre>define i64 @test(i64 %a, i64 %b) {
%sub = sub i64 %a, %b
%mul = shl i64 %sub, 2
%neg = sub i64 0, %mul
ret i64 %neg
}
is not instcombined to
define i64 @test(i64 %a, i64 %b) {
%sub2 = sub i64 %b, %a
%neg = shl i64 %sub2, 2
ret i64 %neg
}
This pattern showed up as a regression when testing some instcombine worklist
order changes.
I guess the most general case of this would be handled by the negator in
<a href="https://reviews.llvm.org/D68408">https://reviews.llvm.org/D68408</a>, though a much smaller gun would do in this
case as well.</pre>
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