Re: [PATCH v5 01/16] tcg: Expand usadd/ussub with umin/umax

[Matheus K. Ferst]

On 15/09/2021 18:30, Richard Henderson wrote:
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> For usadd, we only have to consider overflow.  Since ~B + B == -1,
> the maximum value for A that saturates is ~B.
>
> For ussub, we only have to consider underflow.  The minimum value
> that saturates to 0 from A - B is B.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>   tcg/tcg-op-vec.c | 37 +++++++++++++++++++++++++++++++++++--
>   1 file changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/tcg/tcg-op-vec.c b/tcg/tcg-op-vec.c
> index 15e026ae49..7705a49c0b 100644
> --- a/tcg/tcg-op-vec.c
> +++ b/tcg/tcg-op-vec.c
> @@ -119,6 +119,18 @@ bool tcg_can_emit_vecop_list(const TCGOpcode *list,
>                   continue;
>               }
>               break;
> +        case INDEX_op_usadd_vec:
> +            if (tcg_can_emit_vec_op(INDEX_op_umin_vec, type, vece) ||
> +                tcg_can_emit_vec_op(INDEX_op_cmp_vec, type, vece)) {
> +                continue;
> +            }
> +            break;
> +        case INDEX_op_ussub_vec:
> +            if (tcg_can_emit_vec_op(INDEX_op_umax_vec, type, vece) ||
> +                tcg_can_emit_vec_op(INDEX_op_cmp_vec, type, vece)) {
> +                continue;
> +            }
> +            break;
>           case INDEX_op_cmpsel_vec:
>           case INDEX_op_smin_vec:
>           case INDEX_op_smax_vec:
> @@ -603,7 +615,18 @@ void tcg_gen_ssadd_vec(unsigned vece, TCGv_vec r, TCGv_vec 
> a, TCGv_vec b)
>
>   void tcg_gen_usadd_vec(unsigned vece, TCGv_vec r, TCGv_vec a, TCGv_vec b)
>   {
> -    do_op3_nofail(vece, r, a, b, INDEX_op_usadd_vec);
> +    if (!do_op3(vece, r, a, b, INDEX_op_usadd_vec)) {
> +        const TCGOpcode *hold_list = tcg_swap_vecop_list(NULL);
> +        TCGv_vec t = tcg_temp_new_vec_matching(r);
> +
> +        /* usadd(a, b) = min(a, ~b) + b */
> +        tcg_gen_not_vec(vece, t, b);
> +        tcg_gen_umin_vec(vece, t, t, a);
> +        tcg_gen_add_vec(vece, r, r, b);

I think it should be

tcg_gen_add_vec(vece, r, t, b);

> +
> +        tcg_temp_free_vec(t);
> +        tcg_swap_vecop_list(hold_list);
> +    }
>   }
>
>   void tcg_gen_sssub_vec(unsigned vece, TCGv_vec r, TCGv_vec a, TCGv_vec b)
> @@ -613,7 +636,17 @@ void tcg_gen_sssub_vec(unsigned vece, TCGv_vec r, TCGv_vec 
> a, TCGv_vec b)
>
>   void tcg_gen_ussub_vec(unsigned vece, TCGv_vec r, TCGv_vec a, TCGv_vec b)
>   {
> -    do_op3_nofail(vece, r, a, b, INDEX_op_ussub_vec);
> +    if (!do_op3(vece, r, a, b, INDEX_op_ussub_vec)) {
> +        const TCGOpcode *hold_list = tcg_swap_vecop_list(NULL);
> +        TCGv_vec t = tcg_temp_new_vec_matching(r);
> +
> +        /* ussub(a, b) = max(a, b) - b */
> +        tcg_gen_umax_vec(vece, t, a, b);
> +        tcg_gen_sub_vec(vece, r, t, b);
> +
> +        tcg_temp_free_vec(t);
> +        tcg_swap_vecop_list(hold_list);
> +    }
>   }
>
>   static void do_minmax(unsigned vece, TCGv_vec r, TCGv_vec a,
> --
> 2.25.1


Thanks,
Matheus K. Ferst
Instituto de Pesquisas ELDORADO <http://www.eldorado.org.br/>
Analista de Software Júnior
Aviso Legal - Disclaimer <https://www.eldorado.org.br/disclaimer.html>