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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - trunc(x >> (bitwidth-1)) ^ 1 is not recognized as bt+setae"
href="https://bugs.llvm.org/show_bug.cgi?id=43515">43515</a>
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<th>Summary</th>
<td>trunc(x >> (bitwidth-1)) ^ 1 is not recognized as bt+setae
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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
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: X86
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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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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<p>
<div>
<pre><a href="https://godbolt.org/z/jUiaJg">https://godbolt.org/z/jUiaJg</a>
If we start with
int cmpge32_0(long a) {
return a>=0;
}
We get
shr rax, 63
xor eax, 1
But for less canonical
%n0 = and i64 %x, 9223372036854775808 # sign bit mask
%n1 = icmp eq i64 %n0, 0
%r = zext i1 %n1 to i32
we get seemingly-more-optimal
xor eax, eax
bt rdi, 63
setae al</pre>
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