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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [AArch64] orr wzr vs. mov"
href="https://llvm.org/bugs/show_bug.cgi?id=28966">28966</a>
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<th>Summary</th>
<td>[AArch64] orr wzr vs. mov
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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>All
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>Backend: AArch64
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>spatel+llvm@rotateright.com
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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<th>Classification</th>
<td>Unclassified
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<p>
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<pre>Forking this off <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [AArch64] missed opportunity to use conditional select invert (csinv)"
href="show_bug.cgi?id=28965">bug 28965</a>.
I can't imagine this would make any perf difference in practice, but it
suggests that there's some missing analysis/fold/pattern-matching because
functionally equivalent IR is producing different code:
$ cat cmpsel.ll
define i32 @goo(i32 %x) {
%cmp = icmp eq i32 %x, 1
%sel = select i1 %cmp, i32 1, i32 -1
ret i32 %sel
}
define i32 @hoo(i32 %x) {
%cmp = icmp ne i32 %x, 1 <--- inverse condition
%sel = select i1 %cmp, i32 -1, i32 1 <--- swap select operands
ret i32 %sel
}
$ ./llc -o - cmpsel.ll -mtriple=aarch64
goo: // @goo
cmp w0, #1 // =1
orr w8, wzr, #0x1
cneg w0, w8, ne
ret
hoo: // @hoo
cmp w0, #1 // =1
mov w8, #-1
cneg w0, w8, eq
ret</pre>
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