https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101637
Bug ID: 101637
Summary: #pragma omp for simd defeats VECT_COMPARE_COSTS
optimisations
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: rsandifo at gcc dot gnu.org
Target Milestone: ---
Target: aarch64*-*-*
Compiling this with -O3 -march=armv8.2-a+sve:
void
foo (__INT64_TYPE__ *a, __INT32_TYPE__ *b, __INT16_TYPE__ *c)
{
//#pragma omp for simd
for (int i = 0; i < 100; ++i)
a[i] = b[i] + c[i];
}
gives:
.L2:
ld1w z1.s, p0/z, [x1, x3, lsl 2]
ld1sh z0.s, p0/z, [x2, x3, lsl 1]
punpklo p1.h, p0.b
add z0.s, z0.s, z1.s
punpkhi p0.h, p0.b
sunpklo z1.d, z0.s
sunpkhi z0.d, z0.s
st1d z1.d, p1, [x0, x3, lsl 3]
st1d z0.d, p0, [x5, x3, lsl 3]
add x3, x3, x6
whilelo p0.s, w3, w4
b.any .L2
whereas uncommenting the pragma gives the considerably uglier:
.L2:
ld1h z0.h, p0/z, [x2, x3, lsl 1]
punpklo p1.h, p0.b
punpkhi p0.h, p0.b
ld1w z2.s, p1/z, [x1, x3, lsl 2]
ld1w z3.s, p0/z, [x7, x3, lsl 2]
punpklo p2.h, p1.b
punpkhi p1.h, p1.b
sunpklo z1.s, z0.h
sunpkhi z0.s, z0.h
add z1.s, z1.s, z2.s
add z0.s, z0.s, z3.s
sunpklo z2.d, z1.s
sunpklo z3.d, z0.s
sunpkhi z1.d, z1.s
sunpkhi z0.d, z0.s
st1d z1.d, p1, [x0, #1, mul vl]
punpklo p1.h, p0.b
punpkhi p0.h, p0.b
st1d z3.d, p1, [x0, #2, mul vl]
st1d z0.d, p0, [x0, #3, mul vl]
st1d z2.d, p2, [x0]
add x3, x3, x6
add x0, x0, x5
whilelo p0.h, w3, w4
b.any .L2
For VECT_COMPARE_COSTS targets, we should probably still consider all
possibilities and pick the “best” vector implementation (ignoring the
comparison with scalar code).
