https://llvm.org/bugs/show_bug.cgi?id=23073
Bug ID: 23073
Summary: [AVX] bloated vector permute mask generation
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
$ cat badperm.ll
define <8 x float> @shuffle_v8f32_70000000(<8 x float> %a, <8 x float> %b) {
%shuffle = shufflevector <8 x float> %a, <8 x float> %b, <8 x i32> <i32 7,
i32 0, i32 0, i32 0, i32 0, i32 0, i32 0, i32 0>
ret <8 x float> %shuffle
}
$ ./llc -mattr=avx2 badperm.ll -o -
...
movl $7, %eax
vmovd %eax, %xmm1
vpxor %ymm2, %ymm2, %ymm2
vpblendd $1, %ymm1, %ymm2, %ymm1 ## ymm1 = ymm1[0],ymm2[1,2,3,4,5,6,7]
vpermps %ymm0, %ymm1, %ymm0
retq
As noticed by Andrea in http://reviews.llvm.org/D8341, this could've been a
vmovaps + vpermd (or vpermps depending on int/fp domain).
Or since we know that all of the high elements of the mask are zeros, the
permute mask could be shortened to a single 32-bit constant '7' load (vmovd
instead of vmovaps)?
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