https://llvm.org/bugs/show_bug.cgi?id=27924
Bug ID: 27924
Summary: [x86, SSE] failed to eliminate unused instruction
Product: libraries
Version: trunk
Hardware: PC
OS: All
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
Classification: Unclassified
declare <4 x i32> @llvm.x86.sse41.pmaxsd(<4 x i32>, <4 x i32>) #3
define <4 x i32> @maxmax(<4 x i32> %a, <4 x i32> %b) {
%cmp = icmp sgt <4 x i32> %a, %b
%max = select <4 x i1> %cmp, <4 x i32> %a, <4 x i32> %b
%sse_max = tail call <4 x i32> @llvm.x86.sse41.pmaxsd(<4 x i32> %a, <4 x i32>
%b)
%truth = icmp eq <4 x i32> %max, %sse_max
%ret = sext <4 x i1> %truth to <4 x i32>
ret <4 x i32> %ret
}
We match the compare+select as an 'smax', and we lower the SSE intrinsic to the
same 'smax' node, so we should know that the final comparison is all ones, but
the max instruction remains:
$ ./llc -o - smaxnode.ll -mattr=avx
...
vpmaxsd %xmm1, %xmm0, %xmm0
vpcmpeqd %xmm0, %xmm0, %xmm0
retq
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