https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113079
Bug ID: 113079
Summary: [x86] Fails to generate dot_prod instructions for
64-bit vector.
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: ---
int
foo (int n, unsigned char* p, char* pi)
{
int sum = 0;
for (int i = 0; i != 8; i++)
{
sum += p[i] * pi[i];
}
return sum;
}
We can use 128-bit dot_prod instruction + clean upper 64 bits. Currently, gcc
generates a long instruction sequence.
vmovq xmm0, QWORD PTR [rsi]
vmovq xmm2, QWORD PTR [rdx]
vpmovzxbw xmm1, xmm0
vpsrlq xmm0, xmm0, 32
vpmovsxbw xmm3, xmm2
vpmullw xmm1, xmm1, xmm3
vpsrlq xmm2, xmm2, 32
vpmovzxbw xmm0, xmm0
vpmovsxbw xmm2, xmm2
vpmullw xmm0, xmm0, xmm2
vpmovsxwd xmm2, xmm1
vpsrlq xmm1, xmm1, 32
vpmovsxwd xmm1, xmm1
vpaddd xmm2, xmm2, xmm1
vpmovsxwd xmm1, xmm0
vpsrlq xmm0, xmm0, 32
vpmovsxwd xmm0, xmm0
vpaddd xmm1, xmm1, xmm2
vpxor xmm2, xmm2, xmm2
vpshufb xmm2, xmm2, XMMWORD PTR .LC1[rip]
vpaddd xmm0, xmm0, xmm1
vpshufb xmm1, xmm0, XMMWORD PTR .LC0[rip]
vpor xmm1, xmm1, xmm2
vpaddd xmm0, xmm0, xmm1
vmovd eax, xmm0
