Re: [PATCH v1 04/46] target/loongarch: Implement xvadd/xvsub

[Richard Henderson <richard.henderson@linaro.org>]

On 6/20/23 11:37, Song Gao wrote:
> +static bool gvec_xxx(DisasContext *ctx, arg_xxx *a, MemOp mop,
> +                     void (*func)(unsigned, uint32_t, uint32_t,
> +                                  uint32_t, uint32_t, uint32_t))
> +{
> +    uint32_t xd_ofs, xj_ofs, xk_ofs;
> +
> +    CHECK_ASXE;
> +
> +    xd_ofs = vec_full_offset(a->xd);
> +    xj_ofs = vec_full_offset(a->xj);
> +    xk_ofs = vec_full_offset(a->xk);
> +
> +    func(mop, xd_ofs, xj_ofs, xk_ofs, 32, ctx->vl / 8);
> +    return true;
> +}

Comparing gvec_xxx vs gvec_vvv for LSX,

>     func(mop, vd_ofs, vj_ofs, vk_ofs, 16, ctx->vl/8);

gvec_vvv will write 16 bytes of output, followed by 16 bytes of zero to satisfy vl / 8.

I presume this is the intended behaviour of mixing LSX with LASX, that the high 128-bits 
that are not considered by the LSX instruction are zeroed on write?

Which means that your macros from patch 1,

> +#if HOST_BIG_ENDIAN
...
> +#define XB(x)  XB[31 - (x)]
> +#define XH(x)  XH[15 - (x)]

are incorrect.  We need big-endian within the Int128, but little-endian ordering of the 
two Int128. This can be done with

#define XB(x)  XB[(x) ^ 15]
#define XH(x)  XH[(x) ^ 7]

etc.

It would be nice to share more code with trans_lsx.c, if possible.


r~