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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 - [InstCombine] sign bit extract + trunc => icmp + zext?"
href="https://bugs.llvm.org/show_bug.cgi?id=43594">43594</a>
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<th>Summary</th>
<td>[InstCombine] sign bit extract + trunc => icmp + zext?
</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>PC
</td>
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<th>OS</th>
<td>Linux
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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
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>lebedev.ri@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<p>
<div>
<pre><a href="https://godbolt.org/z/iSlCpW">https://godbolt.org/z/iSlCpW</a>
For
int good(unsigned long input) {
return (signed long)input < 0;
}
we produce
define dso_local i32 @_Z4goodm(i64 %0) local_unnamed_addr #0 {
%2 = lshr i64 %0, 63
%3 = trunc i64 %2 to i32
ret i32 %3
}
Should this be instead:
define dso_local i32 @_Z4goodm(i64 %0) local_unnamed_addr #0 {
%2 = icmp slt i64 %0, 0
%3 = zext i1 %2 to i32
ret i32 %3
}
?</pre>
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