RISC-V: Fix backward_propagate_worthwhile_p

From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>

gcc/ChangeLog:

        * config/riscv/riscv-vsetvl.cc (loop_basic_block_p): Adjust function.
        (backward_propagate_worthwhile_p): Fix non-worthwhile.

---
 gcc/config/riscv/riscv-vsetvl.cc | 91 +++++++++++++++++++++++++-------
 1 file changed, 71 insertions(+), 20 deletions(-)

committed, thanks.

On Tue, Jan 3, 2023 at 3:17 PM <juzhe.zhong@rivai.ai> wrote:

> From: Ju-Zhe Zhong <juzhe.zhong@rivai.ai>
>
> gcc/ChangeLog:
>
>         * config/riscv/riscv-vsetvl.cc (loop_basic_block_p): Adjust
> function.
>         (backward_propagate_worthwhile_p): Fix non-worthwhile.
>
> ---
>  gcc/config/riscv/riscv-vsetvl.cc | 91 +++++++++++++++++++++++++-------
>  1 file changed, 71 insertions(+), 20 deletions(-)
>
> diff --git a/gcc/config/riscv/riscv-vsetvl.cc
> b/gcc/config/riscv/riscv-vsetvl.cc
> index ad0457ed89d..fe76bea297e 100644
> --- a/gcc/config/riscv/riscv-vsetvl.cc
> +++ b/gcc/config/riscv/riscv-vsetvl.cc
> @@ -116,10 +116,27 @@ vlmax_avl_insn_p (rtx_insn *rinsn)
>           || INSN_CODE (rinsn) == CODE_FOR_vlmax_avldi);
>  }
>
> +/* Return true if the block is a loop itself:
> +         local_dem
> +            __________
> +        ____|____     |
> +       |        |     |
> +       |________|     |
> +            |_________|
> +         reaching_out
> +*/
>  static bool
>  loop_basic_block_p (const basic_block cfg_bb)
>  {
> -  return JUMP_P (BB_END (cfg_bb)) && any_condjump_p (BB_END (cfg_bb));
> +  if (JUMP_P (BB_END (cfg_bb)) && any_condjump_p (BB_END (cfg_bb)))
> +    {
> +      edge e;
> +      edge_iterator ei;
> +      FOR_EACH_EDGE (e, ei, cfg_bb->succs)
> +       if (e->dest->index == cfg_bb->index)
> +         return true;
> +    }
> +  return false;
>  }
>
>  /* Return true if it is an RVV instruction depends on VTYPE global
> @@ -271,26 +288,60 @@ backward_propagate_worthwhile_p (const basic_block
> cfg_bb,
>  {
>    if (loop_basic_block_p (cfg_bb))
>      {
> -      if (block_info.local_dem.compatible_p (block_info.reaching_out))
> -       return true;
> -
> -      /* There is a obvious case that is not worthwhile and meaningless
> -        to propagate the demand information:
> -                         local_dem
> -                            __________
> -                        ____|____     |
> -                       |        |     |
> -                       |________|     |
> -                            |_________|
> -                         reaching_out
> -         Header is incompatible with reaching_out and the block is loop
> itself,
> -         we don't backward propagate the local_dem since we can't avoid
> emit
> -         vsetvl for the local_dem.  */
> -      edge e;
> -      edge_iterator ei;
> -      FOR_EACH_EDGE (e, ei, cfg_bb->succs)
> -       if (e->dest->index == cfg_bb->index)
> +      if (block_info.reaching_out.valid_or_dirty_p ())
> +       {
> +         if (block_info.local_dem.compatible_p (block_info.reaching_out))
> +           {
> +             /* Case 1 (Can backward propagate):
> +                ....
> +                bb0:
> +                ...
> +                for (int i = 0; i < n; i++)
> +                  {
> +                    vint16mf4_t v = __riscv_vle16_v_i16mf4 (in + i + 5,
> 7);
> +                    __riscv_vse16_v_i16mf4 (out + i + 5, v, 7);
> +                  }
> +                The local_dem is compatible with reaching_out. Such case
> is
> +                worthwhile backward propagation.  */
> +             return true;
> +           }
> +         else
> +           {
> +             /* Case 2 (Don't backward propagate):
> +                   ....
> +                   bb0:
> +                   ...
> +                   for (int i = 0; i < n; i++)
> +                     {
> +                       vint16mf4_t v = __riscv_vle16_v_i16mf4 (in + i +
> 5, 7);
> +                       __riscv_vse16_v_i16mf4 (out + i + 5, v, 7);
> +                       vint16mf2_t v2 = __riscv_vle16_v_i16mf2 (in + i +
> 6, 8);
> +                       __riscv_vse16_v_i16mf2 (out + i + 6, v, 8);
> +                     }
> +                The local_dem is incompatible with reaching_out.
> +                It makes no sense to backward propagate the local_dem
> since we
> +                can't avoid VSETVL inside the loop.  */
> +             return false;
> +           }
> +       }
> +      else
> +       {
> +         gcc_assert (block_info.reaching_out.unknown_p ());
> +         /* Case 3 (Don't backward propagate):
> +               ....
> +               bb0:
> +               ...
> +               for (int i = 0; i < n; i++)
> +                 {
> +                   vint16mf4_t v = __riscv_vle16_v_i16mf4 (in + i + 5, 7);
> +                   __riscv_vse16_v_i16mf4 (out + i + 5, v, 7);
> +                   fn3 ();
> +                 }
> +           The local_dem is VALID, but the reaching_out is UNKNOWN.
> +           It makes no sense to backward propagate the local_dem since we
> +           can't avoid VSETVL inside the loop.  */
>           return false;
> +       }
>      }
>
>    return true;
> --
> 2.36.3
>
>