Re: [PATCH V2] RISC-V: Enable basic VLS auto-vectorization

[Robin Dapp <rdapp.gcc@gmail.com>]

> +;; -----------------------------------------------------------------
> +;; ---- Duplicate Operations
> +;; -----------------------------------------------------------------
> +
> +(define_insn_and_split "@vec_duplicate<mode>"
> +  [(set (match_operand:VLS 0 "register_operand")
> +        (vec_duplicate:VLS
> +          (match_operand:<VEL> 1 "reg_or_int_operand")))]
> +  "TARGET_VECTOR && can_create_pseudo_p ()"
> +  "#"
> +  "&& 1"
> +  [(const_int 0)]
> +  {
> +    riscv_vector::emit_vlmax_insn (code_for_pred_broadcast (<MODE>mode),
> +                                   riscv_vector::RVV_UNOP, operands);
> +    DONE;
> +  }
> +)

Ah, nice.  The same thing helps for vv -> vx (for non-VLS modes) because we
can keep the non-expanded version around longer which allows more fwprop
opportunities.

> +      /* Enable VECT_COMPARE_COSTS between VLA modes VLS modes for scalable
> +	 auto-vectorization.  */
> +      flag |= VECT_COMPARE_COSTS;

I think it's good to activate this here for now.  After a while when
costing is reliable we probably want to have it unconditionally even
for pure scalable/fixed-vlmax.

Regards
 Robin