https://bugs.llvm.org/show_bug.cgi?id=34369
Bug ID: 34369
Summary: [X86][AVX512] suboptimal shuffle sequence instead of
one vpermw instruction
Product: libraries
Version: trunk
Hardware: All
OS: All
Status: NEW
Severity: enhancement
Priority: P
Component: Backend: X86
Assignee: unassignedb...@nondot.org
Reporter: ayman.m...@intel.com
CC: llvm-bugs@lists.llvm.org
For the following IR:
define <16 x i16> @test(<16 x i16> %vec) {
%shuf = shufflevector <16 x i16> %vec, <16 x i16> undef, <16 x i32> <i32 3,
i32 0, i32 0, i32 13, i32 5, i32 2, i32 2, i32 10, i32 15, i32 8, i32 14, i32
8, i32 9, i32 10, i32 12, i32 12>
%res = select <16 x i1> <i1 1, i1 1, i1 1, i1 0, i1 1, i1 0, i1 0, i1 1, i1
1, i1 1, i1 0, i1 1, i1 1, i1 1, i1 1, i1 1>, <16 x i16> %shuf, <16 x i16>
zeroinitializer
ret <16 x i16> %res
}
>> llc -mcpu=skx <file-name> -o out.s
LLVM emits (showing 9.52 throughput on IACA tool):
vextracti128 $1, %ymm0, %xmm1
vpshufb .LCPI41_0(%rip), %xmm1, %xmm2 # xmm2 =
xmm1[8,9,10,11,4,5,10,11,8,9,10,11,4,5,4,5]
vpshufb .LCPI41_1(%rip), %xmm0, %xmm0 # xmm0 =
xmm0[6,7,0,1,0,1,6,7,10,11,4,5,4,5,6,7]
vpblendw $136, %xmm2, %xmm0, %xmm0 # xmm0 =
xmm0[0,1,2],xmm2[3],xmm0[4,5,6],xmm2[7]
vpshufb .LCPI41_2(%rip), %xmm1, %xmm1 # xmm1 =
xmm1[14,15,0,1,12,13,0,1,2,3,4,5,8,9,8,9]
vinserti128 $1, %xmm1, %ymm0, %ymm0
movw $-1129, %ax # imm = 0xFB97
kmovd %eax, %k1
vmovdqu16 %ymm0, %ymm0 {%k1} {z}
retq
While it can be replaced with (showing 5.76 throughput on IACA tool):
vmovdqu .LCPI43_0(%rip), %ymm1 # ymm1 =
[3,0,0,13,5,2,2,10,15,8,14,8,9,10,12,12]
movw $-1129, %ax
kmovd %eax, %k1
vpermw %ymm0, %ymm1, %ymm0 {%k1} {z}
retq
** Throughput results from IACA tool => lower is better.
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