Re: [PATCH] vect: Allow unsigned-to-signed promotion in vect_look_through_possible_promotion [PR115707]

[Richard Biener]

On Mon, Aug 5, 2024 at 12:34 PM Feng Xue OS <f...@os.amperecomputing.com> wrote:
>
> The function vect_look_through_possible_promotion() fails to figure out root
> definition if casts involves more than two promotions with sign change as:
>
> long a = (long)b;       // promotion cast
>  -> int b = (int)c;     // promotion cast, sign change
>    -> unsigned short c = ...;
>
> For this case, the function thinks the 2nd cast has different sign as the 1st,
> so stop looking through, while "unsigned short -> integer" is a nature sign
> extension. This patch allows this unsigned-to-signed promotion in the 
> function.

OK.

Thanks,
Richard.

> Thanks,
> Feng
>
> ---
> gcc/
>         * tree-vect-patterns.cc (vect_look_through_possible_promotion): Allow
>         unsigned-to-signed promotion.
> ---
>  gcc/tree-vect-patterns.cc | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/tree-vect-patterns.cc b/gcc/tree-vect-patterns.cc
> index 4674a16d15f..b2c83cfd219 100644
> --- a/gcc/tree-vect-patterns.cc
> +++ b/gcc/tree-vect-patterns.cc
> @@ -434,7 +434,9 @@ vect_look_through_possible_promotion (vec_info *vinfo, 
> tree op,
>              sign of the previous promotion.  */
>           if (!res
>               || TYPE_PRECISION (unprom->type) == orig_precision
> -             || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type))
> +             || TYPE_SIGN (unprom->type) == TYPE_SIGN (op_type)
> +             || (TYPE_UNSIGNED (op_type)
> +                 && TYPE_PRECISION (op_type) < TYPE_PRECISION 
> (unprom->type)))
>             {
>               unprom->set_op (op, dt, caster);
>               min_precision = TYPE_PRECISION (op_type);
> --
> 2.17.1