Re: [PATCH v2 2/6] target/arm: Fix nregs computation in do_ld_zpa

[Peter Maydell]

On Tue, 6 Feb 2024 at 03:06, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> The field is encoded as [0-3], which is convenient for
> indexing our array of function pointers, but the true
> value is [1-4].  Adjust before calling do_mem_zpa.
>
> Add an assert, and move the comment re passing ZT to
> the helper back next to the relevant code.
>
> Cc: qemu-stable@nongnu.org
> Fixes: 206adacfb8d ("target/arm: Add mte helpers for sve scalar + int loads")
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/tcg/translate-sve.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/target/arm/tcg/translate-sve.c b/target/arm/tcg/translate-sve.c
> index 296e7d1ce2..f50a426c98 100644
> --- a/target/arm/tcg/translate-sve.c
> +++ b/target/arm/tcg/translate-sve.c
> @@ -4445,11 +4445,7 @@ static void do_mem_zpa(DisasContext *s, int zt, int 
> pg, TCGv_i64 addr,
>      TCGv_ptr t_pg;
>      int desc = 0;
>
> -    /*
> -     * For e.g. LD4, there are not enough arguments to pass all 4
> -     * registers as pointers, so encode the regno into the data field.
> -     * For consistency, do this even for LD1.
> -     */
> +    assert(mte_n >= 1 && mte_n <= 4);
>      if (s->mte_active[0]) {
>          int msz = dtype_msz(dtype);
>
> @@ -4463,6 +4459,11 @@ static void do_mem_zpa(DisasContext *s, int zt, int 
> pg, TCGv_i64 addr,
>          addr = clean_data_tbi(s, addr);
>      }
>
> +    /*
> +     * For e.g. LD4, there are not enough arguments to pass all 4
> +     * registers as pointers, so encode the regno into the data field.
> +     * For consistency, do this even for LD1.
> +     */
>      desc = simd_desc(vsz, vsz, zt | desc);
>      t_pg = tcg_temp_new_ptr();
>
> @@ -4600,7 +4601,7 @@ static void do_ld_zpa(DisasContext *s, int zt, int pg,
>       * accessible via the instruction encoding.
>       */
>      assert(fn != NULL);
> -    do_mem_zpa(s, zt, pg, addr, dtype, nreg, false, fn);
> +    do_mem_zpa(s, zt, pg, addr, dtype, nreg + 1, false, fn);
>  }
>
>  static bool trans_LD_zprr(DisasContext *s, arg_rprr_load *a)

What about do_st_zpa() ? It's not obvious what the 'nreg'
encoding is in the a->nreg field in arg_rprr_store, but
it's definitely confusing that do_st_zpa() calls
do_mem_zpa() passing "nreg" whereas do_ld_zpa() now
passes it "nreg + 1". Can we make it so the handling
in these two functions lines up?

thanks
-- PMM