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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Generated code contains unnecessary movzx"
href="https://bugs.llvm.org/show_bug.cgi?id=41770">41770</a>
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<th>Summary</th>
<td>Generated code contains unnecessary movzx
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</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>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>LLVM Codegen
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>mvels@google.com
</td>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org, neeilans@live.com, richard-llvm@metafoo.co.uk
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<p>
<div>
<pre>I ran into this playing around with alternative SSO encodings and simplified in
godbolt. <a href="https://gcc.godbolt.org/z/n2BNiB">https://gcc.godbolt.org/z/n2BNiB</a>
It correctly recognizes the jns opportunity, but then adds an additional movzx
at the end.
GetLength(str const&):
movzx eax, BYTE PTR [rdi+15]
sub al, 15
js .L2
movzx eax, al
ret
.L2:
movabs rax, 9223372036854775807
and rax, QWORD PTR [rdi+8]
ret</pre>
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