Re: [PATCH]middle-end: replace GET_MODE_WIDER_MODE with GET_MODE_NEXT_MODE

[Richard Sandiford via Gcc-patches]

Tamar Christina via Gcc-patches <gcc-patches@gcc.gnu.org> writes:
> Hi All,
>
> After the fix to the addsub patch yesterday for bootstrap I had only 
> regtested on x86.
> While looking today it seemed the new tests were failing, this was caused
> by a change in the behavior of the GET_MODE_WIDER_MODE macro on trunk.
>
> This patch fixes that issue. Sorry for the mess, have rebased all branches 
> now.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
>
> Ok for master?
>
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
>       * match.pd: Replace GET_MODE_WIDER_MODE with
>       GET_MODE_NEXT_MODE.
>
> --- inline copy of patch -- 
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 
> 1b0ab7cf60fa4772fbe8304c622b0b8fab1bdefa..28191a992039c6f3a1dab5f7c0e35dd58dc47092
>  100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -7997,7 +7997,7 @@ and,
>         machine_mode wide_mode;
>       }
>       (if (sel.series_p (0, 2, 0, 2)
> -          && GET_MODE_WIDER_MODE (vec_mode).exists (&wide_mode)
> +          && GET_MODE_NEXT_MODE (vec_mode).exists (&wide_mode)
>         && VECTOR_MODE_P (wide_mode)
>         && (GET_MODE_UNIT_BITSIZE (vec_mode) * 2
>             == GET_MODE_UNIT_BITSIZE (wide_mode)))

Does anything guarantee that the next mode will be the right one?
It think it would be safer to replace the last three && conditions with:

   && GET_MODE_2XWIDER_MODE (GET_MODE_INNER (vec_mode)).exists (&wide_elt_mode)
   && multiple_p (GET_MODE_NUNITS (vec_mode), 2, &wide_nunits)
   && related_vector_mode (vec_mode, wide_elt_mode,
                           wide_nunits).exists (&wide_mode)

Thanks,
Richard