On Wed, Nov 20, 2019 at 4:28 PM Richard Sandiford
<richard.sandif...@arm.com> wrote:
>
> Allowing mixed vector sizes broke the assumption in the following assert,
> since it's now possible for different accesses to require different
> levels of alignment:
>
> /* FORNOW: use the same mask to test all potentially unaligned
> references in the loop. The vectorizer currently supports
> a single vector size, see the reference to
> GET_MODE_NUNITS (TYPE_MODE (vectype)) where the
> vectorization factor is computed. */
> gcc_assert (!LOOP_VINFO_PTR_MASK (loop_vinfo)
> || LOOP_VINFO_PTR_MASK (loop_vinfo) == mask);
>
> I guess we could try to over-align smaller accesses so that all
> of them are consistent, or try to support multiple alignment masks,
> but for now the easiest fix seems to be to turn the assert into a
> bail-out check.
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu. OK to install?
OK.
> Richard
>
>
> 2019-11-20 Richard Sandiford <richard.sandif...@arm.com>
>
> gcc/
> PR tree-optimization/92526
> * tree-vect-data-refs.c (vect_enhance_data_refs_alignment): Reject
> versioning for alignment if the accesses do not have a consistent
> mask, rather than asserting that the masks are consistent.
>
> gcc/testsuite/
> PR tree-optimization/92526
> * gcc.target/aarch64/pr92526.c: New test.
>
> Index: gcc/tree-vect-data-refs.c
> ===================================================================
> --- gcc/tree-vect-data-refs.c 2019-11-16 11:40:19.105159717 +0000
> +++ gcc/tree-vect-data-refs.c 2019-11-20 15:27:49.385346722 +0000
> @@ -2266,13 +2266,15 @@ vect_enhance_data_refs_alignment (loop_v
> mask must be 15 = 0xf. */
> mask = size - 1;
>
> - /* FORNOW: use the same mask to test all potentially unaligned
> - references in the loop. The vectorizer currently supports
> - a single vector size, see the reference to
> - GET_MODE_NUNITS (TYPE_MODE (vectype)) where the
> - vectorization factor is computed. */
> - gcc_assert (!LOOP_VINFO_PTR_MASK (loop_vinfo)
> - || LOOP_VINFO_PTR_MASK (loop_vinfo) == mask);
> + /* FORNOW: use the same mask to test all potentially unaligned
> + references in the loop. */
> + if (LOOP_VINFO_PTR_MASK (loop_vinfo)
> + && LOOP_VINFO_PTR_MASK (loop_vinfo) != mask)
> + {
> + do_versioning = false;
> + break;
> + }
> +
> LOOP_VINFO_PTR_MASK (loop_vinfo) = mask;
> LOOP_VINFO_MAY_MISALIGN_STMTS (loop_vinfo).safe_push
> (stmt_info);
> }
> Index: gcc/testsuite/gcc.target/aarch64/pr92526.c
> ===================================================================
> --- /dev/null 2019-09-17 11:41:18.176664108 +0100
> +++ gcc/testsuite/gcc.target/aarch64/pr92526.c 2019-11-20 15:27:49.385346722
> +0000
> @@ -0,0 +1,9 @@
> +/* { dg-options "-O3 -mstrict-align" } */
> +
> +void
> +f (unsigned int *restrict x, unsigned int *restrict y,
> + unsigned char *restrict z, unsigned int n)
> +{
> + for (unsigned int i = 0; i < n % 4; ++i)
> + x[i] = x[i] + y[i] + z[i];
> +}
