On Tue, Nov 5, 2019 at 3:25 PM Richard Sandiford
<richard.sandif...@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.sandif...@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;
