I think it makes more sense to remove the whole 
--param=riscv-autovec-preference since we should use
-fno-tree-vectorize instead of --param=riscv-autovec-preference=none which is 
more reasonable compile option
for users.

--param is just a internal testing option that we added before, ideally we 
should remove them.



juzhe.zh...@rivai.ai
 
From: Kito Cheng
Date: 2024-02-28 22:55
To: 钟居哲
CC: pan2.li; gcc-patches; yanzhang.wang; rdapp.gcc; Jeff Law
Subject: Re: Re: [PATCH v3] RISC-V: Introduce gcc option mrvv-vector-bits for 
RVV
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.zh...@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.zh...@rivai.ai
 
From: Kito Cheng
Date: 2024-02-28 20:56
To: pan2.li
CC: gcc-patches; juzhe.zhong; yanzhang.wang; rdapp.gcc; jeffreyalaw
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.
 

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