Re: [PATCH v4 38/47] target/ppc: Refactor VSX_SCALAR_CMP_DP

[Richard Henderson]

On 2/24/22 09:16, Víctor Colombo wrote:
> Could you please elaborate more on how do you think using
> float*_compare and its FloatRelation result would work here?
> I noticed do_scalar_cmp modifies CR and sets FPCC flag, which
> is not what VSX_SCALAR_CMP do. Using that function would require a
> rework.
>
> An option I though would be to bring into VSX_SCALAR_CMP the
> important necessary parts, something like this:
>
> #define VSX_SCALAR_CMP(op, tp, cmp, fld, svxvc, expr)       ...
>      r = tp##_compare(xa->fld, xb->fld, &env->fp_status);        \
>      if (expr) {        \
>          memset(&t.fld, 0xFF, sizeof(t.fld));        \
>      } else if (r == float_relation_unordered) {        \
>          if (env->fp_status.float_exception_flags & float_flag_invalid_snan) { \
>              float_invalid_op_vxsnan(env, GETPC());        \
>              if (fpscr_ve == 0 && svxvc) {        \
>                  float_invalid_op_vxvc(env, 0, GETPC());        \
>              }        \
>          } else if (svxvc) {        \
>              if (tp##_is_quiet_nan(xa->fld, &env->fp_status) ||        \
>                  tp##_is_quiet_nan(xb->fld, &env->fp_status)) {        \
>                      float_invalid_op_vxvc(env, 0, GETPC());        \
>                  }        \
>          }        \
>      }        \
> ...
> VSX_SCALAR_CMP(XSCMPEQDP, float64, eq, VsrD(0), 0, r == float_relation_equal)
> VSX_SCALAR_CMP(XSCMPGEDP, float64, le, VsrD(0), 1, \
>      r == float_relation_equal || r == float_relation_greater)
> VSX_SCALAR_CMP(XSCMPGTDP, float64, lt, VsrD(0), 1, r == float_relation_greater)

I was thinking along the lines of:

    bool r;
    int flags;

    helper_reset_fpstatus(env);
    if (svxvc) {
        r = tp##cmp(...);
    } else {
        r = tp##cmp##_quiet(...);
    }

    flags = get_float_exception_flags(&env->fp_status);
    if (unlikely(flags & float_flag_invalid)) {
        bool vxvc = svxvc;
        if (flags & float_flag_invalid_snan)) {
            float_invalid_op_vxsnan(...);
            vxvc &= fpscr_ve == 0;
        }
        if (vxvc) {
            float_invalid_op_vxvc(...);
        }
    }

    memset(xt, 0, sizeof(*xt));
    memset(&xt->fld, -r, sizeof(xt->fld));
    do_float_check_status(...);


r~