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
