https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65962
Bug ID: 65962
Summary: Missed vectorization of strided stores
Product: gcc
Version: 5.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: alalaw01 at gcc dot gnu.org
Target Milestone: ---
This does not vectorize at -O3 on x86_64/-mavx or aarch64:
int
loop (int *data)
{
int tot = 0;
for (int i = 0; i < 256; i++)
data[i * 2] += 7;
return tot;
}
-fdump-tree-vect-details reveals:
loadstore.c:6:3: note: === vect_analyze_data_ref_accesses ===
loadstore.c:6:3: note: Detected single element interleaving *_8 step 8
loadstore.c:6:3: note: Data access with gaps requires scalar epilogue loop
loadstore.c:6:3: note: not consecutive access *_8 = _10;
loadstore.c:6:3: note: not vectorized: complicated access pattern.
loadstore.c:6:3: note: bad data access.
However, a similar testcase that only reads from those locations, vectorizes
ok:
int
loop_12 (int *data)
{
int tot = 0;
for (int i = 0; i < 256; i++)
tot += data[i * 2];
return tot;
}
blocksort.c:6:3: note: === vect_analyze_data_ref_accesses ===
blocksort.c:6:3: note: Detected single element interleaving *_7 step 8
blocksort.c:6:3: note: Data access with gaps requires scalar epilogue loop
