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* [Bug target/114427] New: [x86] ec_pack_truncv8si/v4si can be optimized with pblendw instead of pand for AVX2 target
@ 2024-03-22 5:25 liuhongt at gcc dot gnu.org
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From: liuhongt at gcc dot gnu.org @ 2024-03-22 5:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114427
Bug ID: 114427
Summary: [x86] ec_pack_truncv8si/v4si can be optimized with
pblendw instead of pand for AVX2 target
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: target
Assignee: unassigned at gcc dot gnu.org
Reporter: liuhongt at gcc dot gnu.org
Target Milestone: ---
void
foo (int* a, short* __restrict b, int* c)
{
for (int i = 0; i != 8; i++)
b[i] = c[i] + a[i];
}
gcc -O2 -march=x86-64-v3 -S
mov eax, 65535
vmovd xmm0, eax
vpbroadcastd xmm0, xmm0
vpand xmm2, xmm0, XMMWORD PTR [rdi+16]
vpand xmm1, xmm0, XMMWORD PTR [rdi]
vpackusdw xmm1, xmm1, xmm2
vpand xmm2, xmm0, XMMWORD PTR [rdx]
vpand xmm0, xmm0, XMMWORD PTR [rdx+16]
vpackusdw xmm0, xmm2, xmm0
vpaddw xmm0, xmm1, xmm0
vmovdqu XMMWORD PTR [rsi], xmm0
It can be better with below,
vpxor %xmm0, %xmm0, %xmm0
vpblendw $85, 16(%rdi), %xmm0, %xmm2
vpblendw $85, (%rdi), %xmm0, %xmm1
vpackusdw %xmm2, %xmm1, %xmm1
vpblendw $85, (%rdx), %xmm0, %xmm2
vpblendw $85, 16(%rdx), %xmm0, %xmm0
vpackusdw %xmm0, %xmm2, %xmm0
vpaddw %xmm0, %xmm1, %xmm0
vmovdqu %xmm0, (%rsi)
Currently, we're using (const_vector:v4si (const_int 0xffff) x4) as mask to
clear upper 16 bits, but pblendw with zero vector can also be used, and zero
vector is much cheaper than (const_vector:v4si (const_int 0xffff) x4)
mov eax, 65535
vmovd xmm0, eax
vpbroadcastd xmm0, xmm0
pblendw has same latency as pand, but could be a little bit worse from
thoughput view(0.33->0.5 on ADL P-core, same on Zen4).
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2024-03-22 5:25 [Bug target/114427] New: [x86] ec_pack_truncv8si/v4si can be optimized with pblendw instead of pand for AVX2 target liuhongt at gcc dot gnu.org
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