On Mon, 5 Oct 2026, Alfie Richards wrote:
> gcc/ChangeLog:
>
> * tree-vect-loop.cc: Add ranger check to check if VF is safe.
>
> gcc/testsuite/ChangeLog:
>
> * gcc.target/aarch64/sve/vect-safe-max-vf.c: New test.
> * gcc.target/aarch64/sve/vect-safe-max-vf2.c: New test.
>
> -- >8 --
>
> This is a little hacky as it ends up taking a poly int, making a const
> tree GENERIC representation of it, then using ranger logic on that
> which converts it back to a poly int.
>
> Regr tested and bootstrapped on aarch64-linux-gnu, armhf-linux-gnu,
> x86_64-linux-gnu.
> (Requires my aarch64: Add --param=aarch64-autovec-mode patch for the
> tests)
>
> Okay for master?
>
> KR,
> Alfie
> ---
> .../gcc.target/aarch64/sve/vect-safe-max-vf.c | 15 +++++++++++++++
> .../gcc.target/aarch64/sve/vect-safe-max-vf2.c | 15 +++++++++++++++
> gcc/tree-vect-loop.cc | 11 ++++++++++-
> 3 files changed, 40 insertions(+), 1 deletion(-)
> create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf.c
> create mode 100644 gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf2.c
>
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf.c
> b/gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf.c
> new file mode 100644
> index 00000000000..cfd88ab1318
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf.c
> @@ -0,0 +1,15 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-all
> -fno-vect-cost-model --param=aarch64-autovec-mode=VNx16QI" } */
> +
> +void foo1 (char *a, unsigned n) {
> + for (int i = 0; i < n; ++i)
> + a[i+256] += a[i];
> +}
> +
> +void foo2 (char *a, unsigned n) {
> + for (int i = 0; i < n; ++i)
> + a[i+255] += a[i];
> +}
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
> +/* { dg-final { scan-tree-dump "bad data dependence" "vect" } } */
> diff --git a/gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf2.c
> b/gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf2.c
> new file mode 100644
> index 00000000000..631a21e21ff
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/aarch64/sve/vect-safe-max-vf2.c
> @@ -0,0 +1,15 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -ftree-vectorize -fdump-tree-vect-all
> -fno-vect-cost-model --param=aarch64-autovec-mode=VNx4QI" } */
> +
> +void foo3 (int *a, unsigned n) {
> + for (int i = 0; i < n; ++i)
> + a[i+64] += a[i];
> +}
> +
> +void foo4 (int *a, unsigned n) {
> + for (int i = 0; i < n; ++i)
> + a[i+63] += a[i];
> +}
> +
> +/* { dg-final { scan-tree-dump-times "vectorized 1 loops" 1 "vect" } } */
> +/* { dg-final { scan-tree-dump "bad data dependence" "vect" } } */
> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
> index 9b2afad6034..656039d2b32 100644
> --- a/gcc/tree-vect-loop.cc
> +++ b/gcc/tree-vect-loop.cc
> @@ -2338,7 +2338,16 @@ start_over:
>
> if (max_vf != MAX_VECTORIZATION_FACTOR
> && maybe_lt (max_vf, LOOP_VINFO_VECT_FACTOR (loop_vinfo)))
> - return opt_result::failure_at (vect_location, "bad data dependence.\n");
> + {
> + tree vf = build_int_cst (sizetype, vectorization_factor);
> + /* If the max_vf is less than the upper bound of the vectorization
> + factor, then this is not safe. */
I think this needs clarification that VF is a POLY_INT_CST here (is it?),
which IMO means this doesn't need ranger at all?
> + int_range_max r;
> + get_range_query (cfun)->range_of_expr (r, vf);
> + if (r.varying_p () || r.undefined_p ()
> + || wi::ltu_p (max_vf, r.upper_bound ()))
> + return opt_result::failure_at (vect_location, "bad data dependence.\n");
> + }
>
> loop_vinfo->vector_costs = init_cost (loop_vinfo, false);
>
>
--
Richard Biener <[email protected]>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Stefan Gaiser, Jochen Jaser, Abhinav Puri; (HRB 36809, AG Nuernberg)
