https://llvm.org/bugs/show_bug.cgi?id=26819
Bug ID: 26819
Summary: [aarch64] optimize obscured vector integer comparisons
against zero
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: AArch64
Assignee: unassignedb...@nondot.org
Reporter: spatel+l...@rotateright.com
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
I think the AArch64 backend is missing a couple of folds related to vector
integer comparisons ( related x86 bug: bug 26701 ).
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
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