https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121290
--- Comment #15 from Tamar Christina <tnfchris at gcc dot gnu.org> ---
(In reply to Soumya AR from comment #13)
> Hi Tamar,
>
> Thanks for the fix.
>
> This has now brought back performance for the mentioned kernels with -Ofast
> but is now regressing with -O3 ...
>
> Is this something you're still looking at? Just wanted to put it up here
> anyway.
>
> Example, for the inner loop in s314:
>
> #define iterations 100000
> #define LEN_1D 32000
>
> float a[LEN_1D];
>
> int main()
> {
> for (int i = 0; i < LEN_1D; i++) {
> a[i] = i;
> }
>
> float x;
> for (int nl = 0; nl < iterations*5; nl++) {
> x = a[0];
> for (int i = 0; i < LEN_1D; i++) {
> if (a[i] > x) {
> x = a[i];
> }
> }
> }
>
> return x;
> }
>
> Now:
>
> .L3:
> ldr s25, [x0], 4
> fcmpe s25, s26
> fcsel s26, s25, s26, gt
> cmp x0, x1
> bne .L3
> subs w2, w2, #1
> bne .L4
> fcvtzs w0, s26
> ret
>
>
> Before:
>
> .L3:
> ld1r {v25.4s}, [x0], 4
> fcmgt v24.4s, v25.4s, v26.4s
> bsl v24.16b, v25.16b, v26.16b
> mov v26.16b, v24.16b
> cmp x1, x0
> bne .L3
> add w2, w2, 1
> cmp w2, w4
> bne .L4
> dup s24, v24.s[3]
> fcvtzs w0, s24
> ret
>
>
> Looks like we don't vectorize the inner loop at all now.
Yeah we shouldn't it should do outer-loop vect like it did in GCC 15,
interestingly trunk seems to segfault in vect on this loop. so taking a look at
that first https://godbolt.org/z/Wj5GWox5s
