Re: [PATCH 16/20] target/arm: Fix sve_zip_p vs odd vector lengths

[Peter Maydell <peter.maydell@linaro.org>]

On Sat, 15 Aug 2020 at 02:32, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> Wrote too much with low-half zip (zip1) with vl % 512 != 0.
>
> Adjust all of the x + (y << s) to x | (y << s) as a style fix.
>
> Reported-by: Laurent Desnogues <laurent.desnogues@gmail.com>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  target/arm/sve_helper.c | 25 ++++++++++++++-----------
>  1 file changed, 14 insertions(+), 11 deletions(-)
>
> diff --git a/target/arm/sve_helper.c b/target/arm/sve_helper.c
> index fcb46f150f..b8651ae173 100644
> --- a/target/arm/sve_helper.c
> +++ b/target/arm/sve_helper.c
> @@ -1870,6 +1870,7 @@ void HELPER(sve_zip_p)(void *vd, void *vn, void *vm, uint32_t pred_desc)
>      intptr_t oprsz = extract32(pred_desc, 0, SIMD_OPRSZ_BITS) + 2;
>      int esz = extract32(pred_desc, SIMD_DATA_SHIFT, 2);
>      intptr_t high = extract32(pred_desc, SIMD_DATA_SHIFT + 2, 1);
> +    int esize = 1 << esz;
>      uint64_t *d = vd;
>      intptr_t i;
>
> @@ -1882,33 +1883,35 @@ void HELPER(sve_zip_p)(void *vd, void *vn, void *vm, uint32_t pred_desc)
>          mm = extract64(mm, high * half, half);
>          nn = expand_bits(nn, esz);
>          mm = expand_bits(mm, esz);
> -        d[0] = nn + (mm << (1 << esz));
> +        d[0] = nn | (mm << esize);
>      } else {
> -        ARMPredicateReg tmp_n, tmp_m;
> +        ARMPredicateReg tmp;
>
>          /* We produce output faster than we consume input.
>             Therefore we must be mindful of possible overlap.  */
> -        if ((vn - vd) < (uintptr_t)oprsz) {
> -            vn = memcpy(&tmp_n, vn, oprsz);
> -        }
> -        if ((vm - vd) < (uintptr_t)oprsz) {
> -            vm = memcpy(&tmp_m, vm, oprsz);
> +        if (vd == vn) {
> +            vn = memcpy(&tmp, vn, oprsz);
> +            if (vd == vm) {
> +                vm = vn;
> +            }
> +        } else if (vd == vm) {
> +            vm = memcpy(&tmp, vm, oprsz);

Why is it OK to only check vd==vn etc rather than checking for
overlap the way the old code did ? The commit message doesn't
mention this.

thanks
-- PMM