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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 - [X86] Unnecessary sign extension in bextr second arg"
href="https://bugs.llvm.org/show_bug.cgi?id=34042">34042</a>
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<th>Summary</th>
<td>[X86] Unnecessary sign extension in bextr second arg
</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>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
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<p>
<div>
<pre>#include <stdint.h>
uint64_t bextr64_demanded(uint64_t a, int32_t b)
{
return __builtin_ia32_bextr_u64(a, b);
}
define i64 @bextr64_demanded(i64, i32) {
%3 = sext i32 %1 to i64
%4 = tail call i64 @llvm.x86.bmi.bextr.64(i64 %0, i64 %3)
ret i64 %4
}
declare i64 @llvm.x86.bmi.bextr.64(i64, i64)
bextr64_demanded:
movslq %esi, %rax
bextrq %rax, %rdi, %rax
retq
As only the bottom 16 bits of the second argument is needed for BEXTR we are
performing an unnecessary sign extension.</pre>
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