Re: [PATCH v2][RFC] vect: Verify that GET_MODE_NUNITS is greater than one for vect_grouped_store_supported

[Richard Biener <richard.guenther@gmail.com>]

On Mon, Mar 27, 2023 at 6:02 PM Kevin Lee <kevinl@rivosinc.com> wrote:
>
> This patch is a proper fix to the previous patch
> https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614463.html
> vect_grouped_store_supported checks if the count is a power of 2, but
> doesn't check the size of the GET_MODE_NUNITS.
> This should handle the riscv case where the mode is VNx1DI since the
> nelt would be {1, 1}.
> It was tested on RISCV and x86_64-linux-gnu. Would this be correct
> for the vectors with size smaller than 2?
>
> ---
>  gcc/tree-vect-data-refs.cc | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/gcc/tree-vect-data-refs.cc b/gcc/tree-vect-data-refs.cc
> index 8daf7bd7dd3..04ad12f7d04 100644
> --- a/gcc/tree-vect-data-refs.cc
> +++ b/gcc/tree-vect-data-refs.cc
> @@ -5399,6 +5399,8 @@ vect_grouped_store_supported (tree vectype, unsigned HOST_WIDE_INT count)
>           poly_uint64 nelt = GET_MODE_NUNITS (mode);
>
>           /* The encoding has 2 interleaved stepped patterns.  */
> +    if(!nelt.is_constant() && maybe_lt(nelt, (unsigned int) 2))
> +      return false;

Indentation is off (or your MUA is broken).  I think the nelt.is_constant ()
check is superfluous but with constant nelt we'd never end up with a
grouped store.

Note the calls are guarded with

         && ! known_eq (TYPE_VECTOR_SUBPARTS (vectype), 1U)

maybe the better fix is to change those to ! maybe_eq?

Richard should know best here.

Richard.

>           vec_perm_builder sel (nelt, 2, 3);
>           sel.quick_grow (6);
>           for (i = 0; i < 3; i++)
> --
> 2.25.1
>