Re: [PATCH] vect: Verify that GET_MODE_NUNITS is greater than one.

[Richard Sandiford <richard.sandiford@arm.com>]

Michael Collison <collison@rivosinc.com> writes:
> While working on autovectorizing for the RISCV port I encountered an issue
> where can_duplicate_and_interleave_p assumes that GET_MODE_NUNITS is a
> evenly divisible by two. The RISC-V target has vector modes (e.g. VNx1DImode),
> where GET_MODE_NUNITS is equal to one.
>
> Tested on RISCV and x86_64-linux-gnu. Okay?
>
> 2023-03-09  Michael Collison  <collison@rivosinc.com>
>
> 	* tree-vect-slp.cc (can_duplicate_and_interleave_p):
> 	Check that GET_MODE_NUNITS is greater than one.
> ---
>  gcc/tree-vect-slp.cc | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/tree-vect-slp.cc b/gcc/tree-vect-slp.cc
> index 9a4e000925e..add58113fa8 100644
> --- a/gcc/tree-vect-slp.cc
> +++ b/gcc/tree-vect-slp.cc
> @@ -426,7 +426,8 @@ can_duplicate_and_interleave_p (vec_info *vinfo, unsigned int count,
>  	  if (vector_type
>  	      && VECTOR_MODE_P (TYPE_MODE (vector_type))
>  	      && known_eq (GET_MODE_SIZE (TYPE_MODE (vector_type)),
> -			   GET_MODE_SIZE (base_vector_mode)))
> +			   GET_MODE_SIZE (base_vector_mode))
> +	      && known_gt (GET_MODE_NUNITS (TYPE_MODE (vector_type)), 1))
>  	    {
>  	      /* Try fusing consecutive sequences of COUNT / NVECTORS elements
>  		 together into elements of type INT_TYPE and using the result

FWIW, I think it'd better to remove:

	      poly_int64 half_nelts = exact_div (nelts, 2);

declare:

	  poly_uint64 half_nelts;

before the if condition, and use:

	    && multiple_p (GET_MODE_NUNITS (TYPE_MODE (vector_type)),
			   2, &half_nelts)

instead of the known_gt.  In other words, now that we can't assert
the exact_div, we should check it (using multiple_p) instead.

Thanks,
Richard