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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [aarch64] optimize obscured vector integer comparisons against zero"
href="https://llvm.org/bugs/show_bug.cgi?id=26819">26819</a>
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<th>Summary</th>
<td>[aarch64] optimize obscured vector integer comparisons against zero
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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
</td>
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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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</tr>
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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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</tr></table>
<p>
<div>
<pre>I think the AArch64 backend is missing a couple of folds related to vector
integer comparisons ( related x86 bug: <a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [x86, SSE] missing optimizations for pos/neg integer vector comparisons"
href="show_bug.cgi?id=26701">bug 26701</a> ).
I'm not sure why anyone would write NEON code like this, but it could happen?
// Are elements of 'a' > -1? Ie, is 'a' positive?
int32x2_t test_vcgt_s32(int32x2_t a) {
return vcgt_s32(a, vceq_s32(a, a));
}
$ ./clang -O1 ...
test_vcge_s32:
sshr v0.2s, v0.2s, #31
mvn v0.8b, v0.8b
ret
The IR is optimized from a compare+sext to a shift+not in InstCombine.
But this can be optimized to: is 'a' >= 0?
So is this the optimal codegen?
cmge v0.2s, v0.2s, #0
ret
Similarly, for:
// Are elements of 'a' <= -1? Ie, is 'a' negative?
int32x2_t test_vcle_s32(int32x2_t a) {
return vcle_s32(a, vceq_s32(a, a) );
}
$ ./clang -O1 ...
test_vcle_s32:
movi d1, #0xffffffffffffffff
cmge v0.2s, v1.2s, v0.2s
ret
Should this be:
cmlt v0.2s, v0.2s, #0
ret</pre>
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