[1/6] Fix vectorizable_conversion costs

[Richard Biener]

On Tue, Nov 5, 2019 at 3:25 PM Richard Sandiford
<Richard.Sandiford@arm.com> wrote:
>
> This patch makes two tweaks to vectorizable_conversion.  The first
> is to use "modifier" to distinguish between promotion, demotion,
> and neither promotion nor demotion, rather than using a code for
> some cases and "modifier" for others.  The second is to take ncopies
> into account for the promotion and demotion costs; previously we gave
> multiple copies the same cost as a single copy.
>
> Later patches test this, but it seemed worth splitting out.

OK, but does ncopies properly handle unrolling with SLP?

Richard.

>
> 2019-11-05  Richard Sandiford  <richard.sandiford@arm.com>
>
> gcc/
>         * tree-vect-stmts.c (vect_model_promotion_demotion_cost): Take the
>         number of ncopies as an additional argument.
>         (vectorizable_conversion): Update call accordingly.  Use "modifier"
>         to check whether a conversion is between vectors with the same
>         numbers of units.
>
> Index: gcc/tree-vect-stmts.c
> ===================================================================
> --- gcc/tree-vect-stmts.c       2019-11-05 11:08:12.521631453 +0000
> +++ gcc/tree-vect-stmts.c       2019-11-05 14:17:43.330141911 +0000
> @@ -917,26 +917,27 @@ vect_model_simple_cost (stmt_vec_info st
>  }
>
>
> -/* Model cost for type demotion and promotion operations.  PWR is normally
> -   zero for single-step promotions and demotions.  It will be one if
> -   two-step promotion/demotion is required, and so on.  Each additional
> +/* Model cost for type demotion and promotion operations.  PWR is
> +   normally zero for single-step promotions and demotions.  It will be
> +   one if two-step promotion/demotion is required, and so on.  NCOPIES
> +   is the number of vector results (and thus number of instructions)
> +   for the narrowest end of the operation chain.  Each additional
>     step doubles the number of instructions required.  */
>
>  static void
>  vect_model_promotion_demotion_cost (stmt_vec_info stmt_info,
> -                                   enum vect_def_type *dt, int pwr,
> +                                   enum vect_def_type *dt,
> +                                   unsigned int ncopies, int pwr,
>                                     stmt_vector_for_cost *cost_vec)
>  {
> -  int i, tmp;
> +  int i;
>    int inside_cost = 0, prologue_cost = 0;
>
>    for (i = 0; i < pwr + 1; i++)
>      {
> -      tmp = (STMT_VINFO_TYPE (stmt_info) == type_promotion_vec_info_type) ?
> -       (i + 1) : i;
> -      inside_cost += record_stmt_cost (cost_vec, vect_pow2 (tmp),
> -                                      vec_promote_demote, stmt_info, 0,
> -                                      vect_body);
> +      inside_cost += record_stmt_cost (cost_vec, ncopies, vec_promote_demote,
> +                                      stmt_info, 0, vect_body);
> +      ncopies *= 2;
>      }
>
>    /* FORNOW: Assuming maximum 2 args per stmts.  */
> @@ -4981,7 +4982,7 @@ vectorizable_conversion (stmt_vec_info s
>    if (!vec_stmt)               /* transformation not required.  */
>      {
>        DUMP_VECT_SCOPE ("vectorizable_conversion");
> -      if (code == FIX_TRUNC_EXPR || code == FLOAT_EXPR)
> +      if (modifier == NONE)
>          {
>           STMT_VINFO_TYPE (stmt_info) = type_conversion_vec_info_type;
>           vect_model_simple_cost (stmt_info, ncopies, dt, ndts, slp_node,
> @@ -4990,14 +4991,17 @@ vectorizable_conversion (stmt_vec_info s
>        else if (modifier == NARROW)
>         {
>           STMT_VINFO_TYPE (stmt_info) = type_demotion_vec_info_type;
> -         vect_model_promotion_demotion_cost (stmt_info, dt, multi_step_cvt,
> -                                             cost_vec);
> +         /* The final packing step produces one vector result per copy.  */
> +         vect_model_promotion_demotion_cost (stmt_info, dt, ncopies,
> +                                             multi_step_cvt, cost_vec);
>         }
>        else
>         {
>           STMT_VINFO_TYPE (stmt_info) = type_promotion_vec_info_type;
> -         vect_model_promotion_demotion_cost (stmt_info, dt, multi_step_cvt,
> -                                             cost_vec);
> +         /* The initial unpacking step produces two vector results
> +            per copy.  */
> +         vect_model_promotion_demotion_cost (stmt_info, dt, ncopies * 2,
> +                                             multi_step_cvt, cost_vec);
>         }
>        interm_types.release ();
>        return true;