Re: Move EXTRACT_LAST_REDUCTION costing to vectorizable_condition

[Richard Biener <richard.guenther@gmail.com>]

On Thu, Nov 21, 2019 at 1:07 PM Richard Sandiford
<richard.sandiford@arm.com> wrote:
>
> gcc.target/aarch64/sve/clastb_[57].c started failing after the increase
> in the cost of vec_to_scalar (r278452).  The problem is that we were
> double-counting the cost of the CLASTB: once in vect_model_reduction_cost
> as a vec_to_scalar and once in vectorizable_condition as a plain
> vector_stmt.
>
> Based on the TODO above vect_model_reduction_cost, I think the
> preferred long-term direction is for vectorizable_* to cost these
> things itself, so that's what the patch does (for this one case only).
>
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?

OK.

> Richard
>
>
> 2019-11-21  Richard Sandiford  <richard.sandiford@arm.com>
>
> gcc/
>         * tree-vect-stmts.c (vect_model_simple_cost): Take an optional
>         vect_cost_for_stmt.
>         (vectorizable_condition): Calculate the cost of EXTRACT_LAST_REDUCTION
>         here rather than...
>         * tree-vect-loop.c (vect_model_reduction_cost): ...here.
>
> Index: gcc/tree-vect-stmts.c
> ===================================================================
> --- gcc/tree-vect-stmts.c       2019-11-16 10:29:21.211212189 +0000
> +++ gcc/tree-vect-stmts.c       2019-11-21 12:02:44.058240392 +0000
> @@ -860,7 +860,8 @@ vect_model_simple_cost (stmt_vec_info st
>                         enum vect_def_type *dt,
>                         int ndts,
>                         slp_tree node,
> -                       stmt_vector_for_cost *cost_vec)
> +                       stmt_vector_for_cost *cost_vec,
> +                       vect_cost_for_stmt kind = vector_stmt)
>  {
>    int inside_cost = 0, prologue_cost = 0;
>
> @@ -907,7 +908,7 @@ vect_model_simple_cost (stmt_vec_info st
>      }
>
>    /* Pass the inside-of-loop statements to the target-specific cost model.  */
> -  inside_cost += record_stmt_cost (cost_vec, ncopies, vector_stmt,
> +  inside_cost += record_stmt_cost (cost_vec, ncopies, kind,
>                                    stmt_info, 0, vect_body);
>
>    if (dump_enabled_p ())
> @@ -10081,15 +10082,18 @@ vectorizable_condition (stmt_vec_info st
>                 return false;
>             }
>         }
> -      if (expand_vec_cond_expr_p (vectype, comp_vectype,
> -                                    cond_code))
> -       {
> -         STMT_VINFO_TYPE (stmt_info) = condition_vec_info_type;
> -         vect_model_simple_cost (stmt_info, ncopies, dts, ndts, slp_node,
> -                                 cost_vec);
> -         return true;
> -       }
> -      return false;
> +
> +      vect_cost_for_stmt kind = vector_stmt;
> +      if (reduction_type == EXTRACT_LAST_REDUCTION)
> +       /* Count one reduction-like operation per vector.  */
> +       kind = vec_to_scalar;
> +      else if (!expand_vec_cond_expr_p (vectype, comp_vectype, cond_code))
> +       return false;
> +
> +      STMT_VINFO_TYPE (stmt_info) = condition_vec_info_type;
> +      vect_model_simple_cost (stmt_info, ncopies, dts, ndts, slp_node,
> +                             cost_vec, kind);
> +      return true;
>      }
>
>    /* Transform.  */
> Index: gcc/tree-vect-loop.c
> ===================================================================
> --- gcc/tree-vect-loop.c        2019-11-19 16:25:24.882645490 +0000
> +++ gcc/tree-vect-loop.c        2019-11-21 12:02:44.050240447 +0000
> @@ -3924,8 +3924,11 @@ vect_model_reduction_cost (stmt_vec_info
>
>    code = gimple_assign_rhs_code (orig_stmt_info->stmt);
>
> -  if (reduction_type == EXTRACT_LAST_REDUCTION
> -      || reduction_type == FOLD_LEFT_REDUCTION)
> +  if (reduction_type == EXTRACT_LAST_REDUCTION)
> +    /* No extra instructions are needed in the prologue.  The loop body
> +       operations are costed in vectorizable_condition.  */
> +    inside_cost = 0;
> +  else if (reduction_type == FOLD_LEFT_REDUCTION)
>      {
>        /* No extra instructions needed in the prologue.  */
>        prologue_cost = 0;