https://bugs.llvm.org/show_bug.cgi?id=42633
Bug ID: 42633
Summary: [X86] Avoid scalar/vector transfers for scalar
arithmetic
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: craig.top...@gmail.com, llvm-bugs@lists.llvm.org,
llvm-...@redking.me.uk, spatel+l...@rotateright.com
https://godbolt.org/z/LvQiCP
#include <x86intrin.h>
auto add(__v4si x) {
return _mm_set1_epi32(x[1] + x[3]);
}
_Z3addDv4_i:
vextractps $1, %xmm0, %eax
vextractps $3, %xmm0, %ecx
addl %eax, %ecx
vmovd %ecx, %xmm0
vpshufd $0, %xmm0, %xmm0 # xmm0 = xmm0[0,0,0,0]
retq
A more optimal method would be something like:
add(int __vector(4)):
vpshufd xmm1, xmm0, 78 # xmm1 = xmm0[2,3,0,1]
vpaddd xmm0, xmm1, xmm0
vpshufd xmm0, xmm0, 85 # xmm0 = xmm0[1,1,1,1]
ret
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