Re: [RFC PATCH 10/43] target/loongarch: Implement vaddw/vsubw

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

On 2/27/23 02:55, gaosong wrote:
> 
> 在 2023/2/25 上午3:24, Richard Henderson 写道:
>>>          {
>>>              .fniv = gen_vaddwev_s,
>>>              .fno = gen_helper_vaddwev_q_d,
>>>              .opt_opc = vecop_list,
>>>              .vece = MO_128
>>>          },
>>
>> There are no 128-bit vector operations; you'll need to do this one differently.
>>
>> Presumably just load the two 64-bit elements, sign-extend into 128-bits, add with 
>> tcg_gen_add2_i64, and store the two 64-bit elements as output.  But that won't fit into 
>> the tcg_gen_gvec_3 interface.
>>
> 'sign-extend into 128-bits,'   Could you give a example?

Well, for vadd, as the example we have been using:

     tcg_gen_ld_i64(lo1, cpu_env, offsetof(vector_reg[A].lo));
     tcg_gen_ld_i64(lo2, cpu_env, offsetof(vector_reg[B].lo));
     tcg_gen_sari_i64(hi1, lo1, 63);
     tcg_gen_sari_i64(hi2, lo2, 63);
     tcg_gen_add2_i64(lo1, hi1, lo1, hi1, lo2, hi2);
     tcg_gen_st_i64(lo1, cpu_env, offsetof(vector_reg[R].lo));
     tcg_gen_st_i64(hi1, cpu_env, offsetof(vector_reg[R].hi));

The middle two sari operations replicate the sign bit across the entire high word, so the 
pair of variables constitute a sign-extended 128-bit value.

> I see a example at target/ppc/translate/vmx-impl.c.inc
>      static bool do_vx_vprtyb(DisasContext *ctx, arg_VX_tb *a, unsigned vece)
>      {
>              ...
>              {
>              .fno = gen_helper_VPRTYBQ,
>              .vece = MO_128
>              },
>              tcg_gen_gvec_2(avr_full_offset(a->vrt), avr_full_offset(a->vrb),
>                                 16, 16, &op[vece - MO_32]);
>          return true;
>      }
> TRANS(VPRTYBQ, do_vx_vprtyb, MO_128)
> ...
> 
> do_vx_vprtyb  fit the fno into the tcg_gen_gvec_2.
> I am not sure this  example is right.

Ah, well.  When .fno is the only callback, the implementation is entirely out-of-line, and 
the .vece member is not used.  I see that is confusing.


r~