https://llvm.org/bugs/show_bug.cgi?id=31024
Bug ID: 31024
Summary: [X86] Unnecessary register moves
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: normal
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: llvm-...@redking.me.uk
CC: llvm-bugs@lists.llvm.org
Classification: Unclassified
define <8 x i64> @sext_16i8_to_8i64(<16 x i8> %A) nounwind uwtable readnone ssp
{
entry:
%B = shufflevector <16 x i8> %A, <16 x i8> undef, <8 x i32> <i32 0, i32 1,
i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
%C = sext <8 x i8> %B to <8 x i64>
ret <8 x i64> %C
}
llc -mtriple=x86_64-unknown-unknown -mattr=+avx2
sext_16i8_to_8i64:
vpmovsxbq %xmm0, %ymm2
vpshufd {{.*#+}} xmm0 = xmm0[1,1,2,3]
vpmovsxbq %xmm0, %ymm1
vmovdqa %ymm2, %ymm0
retq
This could avoid the register move:
sext_16i8_to_8i64:
vpshufd {{.*#+}} xmm1 = xmm0[1,1,2,3]
vpmovsxbq %xmm0, %ymm0
vpmovsxbq %xmm1, %ymm1
retq
Reg-reg moves are almost free but its still better to avoid them if we can.
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