Hmm, maybe only keep --param=riscv-autovec-preference=none and remove other
two if we think that might still useful? But anyway I have no strong
opinion to keep that, I mean I am ok to remove whole
--param=riscv-autovec-preference.

钟居哲 <juzhe.zhong@rivai.ai> 於 2024年2月28日 週三 21:59 寫道：

> I think it makes more sense to remove --param=riscv-autovec-preference and
> add -mrvv-vector-bits....
>
> ------------------------------
> juzhe.zhong@rivai.ai
>
>
> *From:* Kito Cheng <kito.cheng@gmail.com>
> *Date:* 2024-02-28 20:56
> *To:* pan2.li <pan2.li@intel.com>
> *CC:* gcc-patches <gcc-patches@gcc.gnu.org>; juzhe.zhong
> <juzhe.zhong@rivai.ai>; yanzhang.wang <yanzhang.wang@intel.com>; rdapp.gcc
> <rdapp.gcc@gmail.com>; jeffreyalaw <jeffreyalaw@gmail.com>
> *Subject:* Re: [PATCH v3] RISC-V: Introduce gcc option mrvv-vector-bits
> for RVV
> Take one more look, I think this option should work and integrate with
> --param=riscv-autovec-preference= since they have similar jobs but
> slightly different.
>
> We have 3 value for  --param=riscv-autovec-preference=: none, scalable
> and fixed-vlmax
>
> -mrvv-vector-bits=scalable is work like
> --param=riscv-autovec-preference=scalable and
> -mrvv-vector-bits=zvl is work like
> --param=riscv-autovec-preference=fixed-vlmax.
>
> So I think...we need to do some conflict check, like:
>
> -mrvv-vector-bits=zvl can't work with
> --param=riscv-autovec-preference=scalable
> -mrvv-vector-bits=scalable can't work with
> --param=riscv-autovec-preference=fixed-vlmax
>
> but it may not just alias since there is some useful combinations like:
>
> -mrvv-vector-bits=zvl with --param=riscv-autovec-preference=none:
> NO auto vectorization but intrinsic code still could benefit from the
> -mrvv-vector-bits=zvl option.
>
> -mrvv-vector-bits=scalable with --param=riscv-autovec-preference=none
> Should still work for VLS code gen, but just disable auto
> vectorization per the option semantic.
>
> However here is something we need some fix, since
> --param=riscv-autovec-preference=none still disable VLS code gen for
> now, you can see some example here:
> https://godbolt.org/z/fMTr3eW7K
>
> But I think it's really the right behavior here, this part might need
> to be fixed in vls_mode_valid_p and some other places.
>
>
> Anyway I think we need to check all use sites with RVV_FIXED_VLMAX and
> RVV_SCALABLE, and need to make sure all use site of RVV_FIXED_VLMAX
> also checked with RVV_VECTOR_BITS_ZVL.
>
>
>
> > -/* Return the VLEN value associated with -march.
> > +static int
> > +riscv_convert_vector_bits (int min_vlen)
>
> Not sure if we really need this function, it seems it always returns
> min_vlen?
>
> > +{
> > +  int rvv_bits = 0;
> > +
> > +  switch (rvv_vector_bits)
> > +    {
> > +      case RVV_VECTOR_BITS_ZVL:
> > +      case RVV_VECTOR_BITS_SCALABLE:
> > +       rvv_bits = min_vlen;
> > +       break;
> > +      default:
> > +       gcc_unreachable ();
> > +    }
> > +
> > +  return rvv_bits;
> > +}
> > +
> > +/* Return the VLEN value associated with -march and -mwrvv-vector-bits.
>
>
>