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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] Extract high bits + sext -> Extract high bits with sext"
href="https://bugs.llvm.org/show_bug.cgi?id=43523">43523</a>
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<th>Summary</th>
<td>[InstCombine] Extract high bits + sext -> Extract high bits with sext
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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
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>lebedev.ri@gmail.com
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</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<pre><a href="https://godbolt.org/z/qhpAcX">https://godbolt.org/z/qhpAcX</a>
int extract_high_bits_with_signext_BAD(unsigned long data, int nbits) {
return (int(data >> (64-nbits)) << (32-nbits)) >> (32-nbits);
}
int extract_high_bits_with_signext_GOOD(unsigned long data, int nbits) {
return (signed long)(data) >> (64-nbits);
}
I'm not sure yet what generalization of the pattern is there,
maybe here i can get away with just looking for that specific pattern..</pre>
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