https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88259
Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ramana at gcc dot gnu.org
--- Comment #2 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> ---
(In reply to ktkachov from comment #1)
> Confirmed.
> Trying to find just the index (not the max value) vectorises as well:
> void test_vec(int *data, int n) {
> int best_i, best = 0;
>
> for (int i = 0; i < n; i++) {
> if (data[i] > best) {
> // best = data[i];
> best_i = i;
> }
> }
>
> data[best_i] = data[0];
> data[0] = best;
> }
>
>
> -O3:
> .L4:
> ldr q1, [x2], 16
> mov v3.16b, v2.16b
> add v2.4s, v2.4s, v4.4s
> cmle v1.4s, v1.4s, #0
> cmp x2, x3
> bif v0.16b, v3.16b, v1.16b
> bne .L4
> smaxv s0, v0.4s
> and w3, w1, -4
> umov w2, v0.s[0]
> cmn w2, #1
> csel w2, w2, wzr, ne
> tst x1, 3
> beq .L2
> .L3:
>
> But their combination seems like it's throwing the machinery off. I'm
> guessing the index-finding needs some if-conversion and masking to happen in
> the vectoriser
ISTR there is some limit in if conversion around the vectorizer where it only
works on very simple if-blocks. But this is from memory and it's a bit fuzzy
now.
