https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115192
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #7)
> I'm looking into the first issue. Interesting fact:
>
> > /space/rguenther/install/gcc-14.1/bin/g++ t.C -O3 -fopt-info-vec
> > -fno-tree-slp-vectorize --param vect-epilogues-nomask=0
> t.C:7:21: optimized: loop vectorized using 16 byte vectors
> t.C:7:21: optimized: loop versioned for vectorization because of possible
> aliasing
> rguenther@localhost:/tmp> ./a.out
> > /space/rguenther/install/gcc-14.1/bin/g++ t.C -O3 -fopt-info-vec
> > -fno-tree-slp-vectorize --param vect-epilogues-nomask=1
> t.C:7:21: optimized: loop vectorized using 16 byte vectors
> t.C:7:21: optimized: loop versioned for vectorization because of possible
> aliasing
> t.C:7:21: optimized: loop vectorized using 8 byte vectors
> rguenther@localhost:/tmp> ./a.out
> Aborted (core dumped)
>
> so avoiding the vectorized epilog fixes this (I've also placed #pragma GCC
> novector on the loop in main and noipa on foo).
Actually with -fno-vect-cost-model even --param vect-epilogues-nomask=0 fails.
Since we are vectorizing
for (int y = 1; y < n; y++)
{
a[y * n][0] = d[y * n] + a[(y - 1) * n][0];
a[y * n][1] = d[y * n] + a[(y - 1) * n][1];
}
with a VF of two this is a failure to identify the dependence between
the iterations, so possibly related to r11-6380 as well.
(compute_affine_dependence
ref_a: BIT_FIELD_REF <*_37, 32, 0>, stmt_a: _38 = BIT_FIELD_REF <*_37, 32,
0>; ref_b: BIT_FIELD_REF <*_40, 32, 0>, stmt_b: BIT_FIELD_REF <*_40, 32, 0> =
_41;
) -> dependence analysis failed
Creating dr for BIT_FIELD_REF <*_37, 32, 0>
analyze_innermost: success.
base_address: a_23(D)
offset from base address: 0
constant offset from base address: 0
step: (ssizetype) ((long unsigned int) n_20(D) * 16)
base alignment: 16
base misalignment: 0
offset alignment: 128
step alignment: 16
base_object: BIT_FIELD_REF <*_37, 32, 0>
Creating dr for BIT_FIELD_REF <*_40, 32, 0>
analyze_innermost: success.
base_address: (float4_t *) a_23(D) + (sizetype) n_20(D) * 16
offset from base address: 0
constant offset from base address: 0
step: (ssizetype) ((long unsigned int) n_20(D) * 16)
base alignment: 16
base misalignment: 0
offset alignment: 128
step alignment: 16
base_object: BIT_FIELD_REF <*_40, 32, 0>
and for reference
Creating dr for BIT_FIELD_REF <*_37, 32, 32>
analyze_innermost: success.
base_address: a_23(D)
offset from base address: 0
constant offset from base address: 4
step: (ssizetype) ((long unsigned int) n_20(D) * 16)
base alignment: 16
base misalignment: 0
offset alignment: 128
step alignment: 16
base_object: BIT_FIELD_REF <*_37, 32, 32>
that looks sensible. And 'a' is indeed properly aligned.
t.c:6:21: note: recording new base alignment for d_22(D) + (sizetype) n_20(D)
* 4
alignment: 4
misalignment: 0
based on: _32 = *_31;
t.c:6:21: note: recording new base alignment for a_23(D)
alignment: 16
misalignment: 0
based on: _38 = BIT_FIELD_REF <*_37, 32, 0>;
t.c:6:21: note: recording new base alignment for (float4_t *) a_23(D) +
(sizetype) n_20(D) * 16
alignment: 16
misalignment: 0
based on: BIT_FIELD_REF <*_40, 32, 0> = _41;
t.c:6:21: note: vect_compute_data_ref_alignment:
t.c:6:21: missed: step doesn't divide the vector alignment.
t.c:6:21: missed: Unknown alignment for access: *_31
t.c:6:21: note: vect_compute_data_ref_alignment:
t.c:6:21: missed: Unknown alignment for access: BIT_FIELD_REF <*_37, 32, 0>
t.c:6:21: note: vect_compute_data_ref_alignment:
t.c:6:21: missed: Unknown alignment for access: BIT_FIELD_REF <*_40, 32, 0>
