Re: [Qemu-devel] [PATCH v4 10/69] target/arm: Simplify op_smlaxxx for SMLAL*

[Laurent Desnogues]

Hi Richard,

On Wed, Sep 4, 2019 at 9:39 PM Richard Henderson
<address@hidden> wrote:
>
> Since all of the inputs and outputs are i32, dispense with
> the intermediate promotion to i64 and use tcg_gen_add2_i32.
>
> Reviewed-by: Peter Maydell <address@hidden>
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  target/arm/translate.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/target/arm/translate.c b/target/arm/translate.c
> index 5306e93470..37aa873e25 100644
> --- a/target/arm/translate.c
> +++ b/target/arm/translate.c
> @@ -8177,8 +8177,7 @@ DO_QADDSUB(QDSUB, false, true)
>  static bool op_smlaxxx(DisasContext *s, arg_rrrr *a,
>                         int add_long, bool nt, bool mt)
>  {
> -    TCGv_i32 t0, t1;
> -    TCGv_i64 t64;
> +    TCGv_i32 t0, t1, tl, th;
>
>      if (s->thumb
>          ? !arm_dc_feature(s, ARM_FEATURE_THUMB_DSP)
> @@ -8202,12 +8201,14 @@ static bool op_smlaxxx(DisasContext *s, arg_rrrr *a,
>          store_reg(s, a->rd, t0);
>          break;
>      case 2:
> -        t64 = tcg_temp_new_i64();
> -        tcg_gen_ext_i32_i64(t64, t0);
> +        tl = load_reg(s, a->ra);
> +        th = load_reg(s, a->rd);
> +        t1 = tcg_const_i32(0);

The product is sign-extended before the addition so t1 is not always 0.

Thanks,

Laurent

> +        tcg_gen_add2_i32(tl, th, tl, th, t0, t1);
>          tcg_temp_free_i32(t0);
> -        gen_addq(s, t64, a->ra, a->rd);
> -        gen_storeq_reg(s, a->ra, a->rd, t64);
> -        tcg_temp_free_i64(t64);
> +        tcg_temp_free_i32(t1);
> +        store_reg(s, a->ra, tl);
> +        store_reg(s, a->rd, th);
>          break;
>      default:
>          g_assert_not_reached();
> --
> 2.17.1
>
>