Re: [Qemu-devel] [PATCH v5 30/35] target/arm: Pass index to AdvSIMD FCMLA (indexed)

[Peter Maydell]

On 21 June 2018 at 02:53, Richard Henderson
<address@hidden> wrote:
> The original commit failed to pass, or use, the index.
>
> Fixes: d17b7cdcf4ea
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  target/arm/translate-a64.c | 21 ++++++++++++---------
>  target/arm/vec_helper.c    | 10 ++++++----
>  2 files changed, 18 insertions(+), 13 deletions(-)
>
> diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
> index 8d8a4cecb0..038e48278f 100644
> --- a/target/arm/translate-a64.c
> +++ b/target/arm/translate-a64.c
> @@ -12669,15 +12669,18 @@ static void disas_simd_indexed(DisasContext *s, 
> uint32_t insn)
>      case 0x13: /* FCMLA #90 */
>      case 0x15: /* FCMLA #180 */
>      case 0x17: /* FCMLA #270 */
> -        tcg_gen_gvec_3_ptr(vec_full_reg_offset(s, rd),
> -                           vec_full_reg_offset(s, rn),
> -                           vec_reg_offset(s, rm, index, size), fpst,
> -                           is_q ? 16 : 8, vec_full_reg_size(s),
> -                           extract32(insn, 13, 2), /* rot */
> -                           size == MO_64
> -                           ? gen_helper_gvec_fcmlas_idx
> -                           : gen_helper_gvec_fcmlah_idx);
> -        tcg_temp_free_ptr(fpst);
> +        {
> +            int rot = extract32(insn, 13, 2);
> +            int data = index * 4 + rot;

Using arithmetic to do bit operations again.

> +            tcg_gen_gvec_3_ptr(vec_full_reg_offset(s, rd),
> +                               vec_full_reg_offset(s, rn),
> +                               vec_reg_offset(s, rm, index, size), fpst,
> +                               is_q ? 16 : 8, vec_full_reg_size(s), data,
> +                               size == MO_64
> +                               ? gen_helper_gvec_fcmlas_idx
> +                               : gen_helper_gvec_fcmlah_idx);

We're already using vec_reg_offset() to pass the helper the address
of the index'th element in Vm -- why do we need to also add
2*index when we use that pointer as an array base in the helper?

thanks
-- PMM