https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82189
Bug ID: 82189
Summary: Two level SLP needed
Product: gcc
Version: 8.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Target: aarch64
Take:
void f(float *restrict a, float * restrict b, float * restrict c, float t)
{
int i = 0 ;
a[i] = b[i]/t;
a[i+1] = b[i+1]/t;
a[i+2] = c[i]/t;
a[i+3] = c[i+1]/t;
}
Right now we do SLP once (at -O3) and produce:
f:
dup v2.2s, v0.s[0]
ldr d1, [x1]
ldr d0, [x2]
fdiv v1.2s, v1.2s, v2.2s
fdiv v0.2s, v0.2s, v2.2s
stp d1, d0, [x0]
ret
But it might be better do:
f:
dup v2.4s, v0.s[0]
ldr d0, [x1]
ldr d1, [x2]
ins v0.2d[1], v1.2d[0]
fdiv v0.4s, v0.4s, v2.4s
str q0, [x0]
ret
Mainly because two div is usually not pipelined.
