Re: [PATCH 1/1] target/ppc: Move VMX integer add/sub saturate insns to decodetree.

[Chinmay Rath]

Hi Richard,

On 5/12/24 17:08, Richard Henderson wrote:
> On 5/12/24 11:38, Chinmay Rath wrote:
> > @@ -2934,6 +2870,184 @@ static bool do_vx_vaddsubcuw(DisasContext 
> > *ctx, arg_VX *a, int add)
> >       return true;
> >   }
> >   +static inline void do_vadd_vsub_sat
> > +(
> > +    unsigned vece, TCGv_vec t, TCGv_vec sat, TCGv_vec a, TCGv_vec b,
> > +    void (*norm_op)(unsigned, TCGv_vec, TCGv_vec, TCGv_vec),
> > +    void (*sat_op)(unsigned, TCGv_vec, TCGv_vec, TCGv_vec))
> > +{
> > +    TCGv_vec x = tcg_temp_new_vec_matching(t);
> > +    norm_op(vece, x, a, b);
> > +    sat_op(vece, t, a, b);
> > +    tcg_gen_cmp_vec(TCG_COND_NE, vece, x, x, t);
> > +    tcg_gen_or_vec(vece, sat, sat, x);
> > +}
>
> As a separate change, before or after, the cmp_vec may be simplified 
> to xor_vec.  Which means that INDEX_op_cmp_vec need not be probed in 
> the vecop_lists.  See
>
> https://lore.kernel.org/qemu-devel/20240506010403.6204-31-richard.henderson@linaro.org/ 
>
>
> which is performing the same operation on AArch64.
Noted ! Will do.
> > +static bool do_vx_vadd_vsub_sat(DisasContext *ctx, arg_VX *a,
> > +                                int sign, int vece, int add)
> > +{
> > +    static const TCGOpcode vecop_list_sub_u[] = {
> > +        INDEX_op_sub_vec, INDEX_op_ussub_vec, INDEX_op_cmp_vec, 0
> > +    };
> > +    static const TCGOpcode vecop_list_sub_s[] = {
> > +        INDEX_op_sub_vec, INDEX_op_sssub_vec, INDEX_op_cmp_vec, 0
> > +    };
> > +    static const TCGOpcode vecop_list_add_u[] = {
> > +        INDEX_op_add_vec, INDEX_op_usadd_vec, INDEX_op_cmp_vec, 0
> > +    };
> > +    static const TCGOpcode vecop_list_add_s[] = {
> > +        INDEX_op_add_vec, INDEX_op_ssadd_vec, INDEX_op_cmp_vec, 0
> > +    };
> > +
> > +    static const GVecGen4 op[2][3][2] = {
> > +        {
> > +            {
> > +                {
> > +                    .fniv = gen_vsub_sat_u,
> > +                    .fno = gen_helper_VSUBUBS,
> > +                    .opt_opc = vecop_list_sub_u,
> > +                    .write_aofs = true,
> > +                    .vece = MO_8
> > +                },
.
.
.
> > +                {
> > +                    .fniv = gen_vadd_sat_s,
> > +                    .fno = gen_helper_VADDSWS,
> > +                    .opt_opc = vecop_list_add_s,
> > +                    .write_aofs = true,
> > +                    .vece = MO_32
> > +                },
> > +            },
> > +        },
> > +    };
>
> While this table is not wrong, I think it is clearer to have separate 
> tables, one per operation, which are then passed in to a common expander.
>
> > +
> > +    REQUIRE_INSNS_FLAGS(ctx, ALTIVEC);
> > +    REQUIRE_VECTOR(ctx);
> > +
> > +    tcg_gen_gvec_4(avr_full_offset(a->vrt), offsetof(CPUPPCState, 
> > vscr_sat),
> > +                   avr_full_offset(a->vra), avr_full_offset(a->vrb), 
> > 16, 16,
> > +                   &op[sign][vece][add]);
> > +
> > +    return true;
> > +}
> > +
> > +TRANS(VSUBUBS, do_vx_vadd_vsub_sat, 0, MO_8, 0)
>
> I think it is clearer to use TRANS_FLAGS than to sink the ISA check 
> into the helper.  In general I seem to find the helper later gets 
> reused for something else with a different ISA check.
>
> Thus
>
> static const TCGOpcode vecop_list_vsub_sat_u[] = {
>     INDEX_op_sub_vec, INDEX_op_ussub_vec, 0
> };
> static const GVecGen4 op_vsububs = {
>     .fno = gen_helper_VSUBUBS,
>     .fniv = gen_vsub_sat_u,
>     .opt_opc = vecop_list_vsub_sat_u,
>     .write_aofs = true,
>     .vece = MO_8
> };
> TRANS_FLAGS(VSUBUBS, do_vx_vadd_vsub_sat, &op_vsububs)
>
> static const GVecGen4 op_vsubuhs = {
>     .fno = gen_helper_VSUBUHS,
>     .fniv = gen_vsub_sat_u,
>     .opt_opc = vecop_list_vsub_sat_u,
>     .write_aofs = true,
>     .vece = MO_16
> };
> TRANS_FLAGS(VSUBUHS, do_vx_vadd_vsub_sat, &op_vsubuhs)
>
> etc.
Will add those changes in v2.
> > -GEN_VXFORM_DUAL(vaddubs, vmul10uq, 0, 8, PPC_ALTIVEC, PPC_NONE),
>
> You are correct in your cover letter that this is not right.
> We should have been testing ISA300 for vmul10uq here.
Thank you very much for the clarification !
> > +GEN_VXFORM(vmul10euq, 0, 9),
>
> And thus need GEN_VXFORM_300 here.
>
> > +GEN_VXFORM(vmul10euq, 0, 9),
> > +GEN_VXFORM(bcdcpsgn, 0, 13),
> > +GEN_VXFORM(bcdadd, 0, 24),
> > +GEN_VXFORM(bcdsub, 0, 25),
> ...
> > +GEN_VXFORM(xpnd04_2, 0, 30),
>
> None of these are in the base ISA, so all need a flag check.
>
>
>
> r~
Thanks & Regards,
Chinmay