On Tue, 27 Apr 2021, Jakub Jelinek wrote:
> Hi!
>
> The following testcase ICEs at -O0, because lower_vec_perm sees the
> _1 = { 0, 0, 0, 0, 0, 0, 0, 0 };
> _2 = VEC_COND_EXPR <_1, { -1, -1, -1, -1, -1, -1, -1, -1 }, { 0, 0, 0, 0,
> 0, 0, 0, 0 }>;
> _3 = { 6, 0, 0, 0, 0, 0, 0, 0 };
> _4 = VEC_PERM_EXPR <{ 0, 0, 0, 0, 0, 0, 0, 0 }, _2, _3>;
> and as the ISA is SSE2, there is no support for the particular permutation
> nor for variable mask permutation. But, the code to match vec_shl matches
> it, because the permutation has the first operand a zero vector and the
> mask picks all elements randomly from that vector.
> So, in the end that isn't a vec_shl, but the permutation could be in theory
> optimized into the first argument. As we keep it as is, it will fail
> during expansion though, because that for vec_shl correctly requires that
> it actually is a shift:
> unsigned firstidx = 0;
> for (unsigned int i = 0; i < nelt; i++)
> {
> if (known_eq (sel[i], nelt))
> {
> if (i == 0 || firstidx)
> return NULL_RTX;
> firstidx = i;
> }
> else if (firstidx
> ? maybe_ne (sel[i], nelt + i - firstidx)
> : maybe_ge (sel[i], nelt))
> return NULL_RTX;
> }
>
> if (firstidx == 0)
> return NULL_RTX;
> first = firstidx;
> The if (firstidx == 0) return NULL; is what is missing a counterpart
> on the lower_vec_perm side.
> As with optimize != 0 we fold it in other spots, I think it is not needed
> to optimize this cornercase in lower_vec_perm (which would mean we'd need
> to recurse on the newly created _4 = { 0, 0, 0, 0, 0, 0, 0, 0 };
> whether it is supported or not).
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
OK.
Thanks,
Richard.
> 2021-04-27 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/100239
> * tree-vect-generic.c (lower_vec_perm): Don't accept constant
> permutations with all indices from the first zero element as vec_shl.
>
> * gcc.dg/pr100239.c: New test.
>
> --- gcc/tree-vect-generic.c.jj 2021-01-27 19:30:20.763625450 +0100
> +++ gcc/tree-vect-generic.c 2021-04-26 14:41:37.909432994 +0200
> @@ -1515,7 +1515,7 @@ lower_vec_perm (gimple_stmt_iterator *gs
> elements + i - first)
> : maybe_ge (poly_uint64 (indices[i]), elements))
> break;
> - if (i == elements)
> + if (first && i == elements)
> {
> gimple_assign_set_rhs3 (stmt, mask);
> update_stmt (stmt);
> --- gcc/testsuite/gcc.dg/pr100239.c.jj 2021-04-26 14:45:28.517819255
> +0200
> +++ gcc/testsuite/gcc.dg/pr100239.c 2021-04-26 14:45:09.985029312 +0200
> @@ -0,0 +1,12 @@
> +/* PR tree-optimization/100239 */
> +/* { dg-do compile } */
> +/* { dg-options "-O0" } */
> +
> +typedef short __attribute__((__vector_size__ (8 * sizeof (short)))) V;
> +V v, w;
> +
> +void
> +foo (void)
> +{
> + w = __builtin_shuffle (v != v, 0 < (V) {}, (V) {192} >> 5);
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Maxfeldstrasse 5, 90409 Nuernberg,
Germany; GF: Felix Imendörffer; HRB 36809 (AG Nuernberg)
