http://llvm.org/bugs/show_bug.cgi?id=22206
Bug ID: 22206
Summary: extra moves generated for unary SSE ops
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
This is SSE (but not AVX) fallout from fixing correctness in bug 14221. This
was originally reported by Michael Kuperstein in http://reviews.llvm.org/D6885.
Using llc built from r225612:
$ cat sqrtss.ll
define float @sqrtss(<4 x float> %a) {
%res = tail call <4 x float> @llvm.x86.sse.sqrt.ss(<4 x float> %a) nounwind
%new = extractelement <4 x float> %res, i32 0
%orig = extractelement <4 x float> %a, i32 0
%add = fadd float %new, %orig
ret float %add
}
declare <4 x float> @llvm.x86.sse.sqrt.ss(<4 x float>) nounwind readnone
$ ./llc sqrtss.ll -o -
..
movaps %xmm0, %xmm1 ## copy original value because...
sqrtss %xmm1, %xmm1 ## current unary op def requires src == dst
addss %xmm0, %xmm1 ## different bug here...
movaps %xmm1, %xmm0 ## could have swapped add operands to avoid mov
retq
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