https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126385
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Last reconfirmed| |2026-07-24
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
enhancing outer loop vectorization would get you unroll-and-jam.
t.c:12:21: note: === vect_analyze_data_ref_accesses ===
t.c:12:21: note: grouped access in outer loop.
t.c:12:21: missed: not vectorized: complicated access pattern.
t.c:16:24: missed: not vectorized: complicated access pattern.
t.c:12:21: missed: bad data access.
That's the weights[i * IN_DIM + j] access. Outer loop vectorization of
the following variant works fine:
for (int i = 0; i < OUT_DIM; ++i)
{
int32_t s = biases[i];
for (int j = 0; j < IN_DIM; ++j)
s += (int32_t) weights[/*i * IN_DIM +*/ j] * (int32_t) input[j];
out[i] = s;
}
the i * IN_DIM biasing effectively turns this into a gather, [j] indexing
is a splat.
Your unroll-and-jam input would result in the same if we use a SLP
reduction vectorization (a single vector IV), instead of doing N
separate reduction vectorizations which is what you want I think.
