[08/10] vect: Generalise neutral_op_for_slp_reduction

This patch generalises the interface to neutral_op_for_slp_reduction
so that it can be used for non-SLP reductions too.  This isn't much
of a win on its own, but it helps later patches.

gcc/
	* tree-vect-loop.c (neutral_op_for_slp_reduction): Replace with...
	(neutral_op_for_reduction): ...this, providing a more general
	interface.
	(vect_create_epilog_for_reduction): Update accordingly.
	(vectorizable_reduction): Likewise.
	(vect_transform_cycle_phi): Likewise.
---
 gcc/tree-vect-loop.c | 59 +++++++++++++++++++-------------------------
 1 file changed, 26 insertions(+), 33 deletions(-)

On Thu, Jul 8, 2021 at 2:48 PM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> This patch generalises the interface to neutral_op_for_slp_reduction
> so that it can be used for non-SLP reductions too.  This isn't much
> of a win on its own, but it helps later patches.

I guess that makes sense - OK.

Richard.

> gcc/
>         * tree-vect-loop.c (neutral_op_for_slp_reduction): Replace with...
>         (neutral_op_for_reduction): ...this, providing a more general
>         interface.
>         (vect_create_epilog_for_reduction): Update accordingly.
>         (vectorizable_reduction): Likewise.
>         (vect_transform_cycle_phi): Likewise.
> ---
>  gcc/tree-vect-loop.c | 59 +++++++++++++++++++-------------------------
>  1 file changed, 26 insertions(+), 33 deletions(-)
>
> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
> index a67036f92e0..744645d8bad 100644
> --- a/gcc/tree-vect-loop.c
> +++ b/gcc/tree-vect-loop.c
> @@ -3248,23 +3248,15 @@ reduction_fn_for_scalar_code (enum tree_code code, internal_fn *reduc_fn)
>      }
>  }
>
> -/* If there is a neutral value X such that SLP reduction NODE would not
> -   be affected by the introduction of additional X elements, return that X,
> -   otherwise return null.  CODE is the code of the reduction and VECTOR_TYPE
> -   is the vector type that would hold element X.  REDUC_CHAIN is true if
> -   the SLP statements perform a single reduction, false if each statement
> -   performs an independent reduction.  */
> +/* If there is a neutral value X such that a reduction would not be affected
> +   by the introduction of additional X elements, return that X, otherwise
> +   return null.  CODE is the code of the reduction and SCALAR_TYPE is type
> +   of the scalar elements.  If the reduction has just a single initial value
> +   then INITIAL_VALUE is that value, otherwise it is null.  */
>
>  static tree
> -neutral_op_for_slp_reduction (slp_tree slp_node, tree vector_type,
> -                             tree_code code, bool reduc_chain)
> +neutral_op_for_reduction (tree scalar_type, tree_code code, tree initial_value)
>  {
> -  vec<stmt_vec_info> stmts = SLP_TREE_SCALAR_STMTS (slp_node);
> -  stmt_vec_info stmt_vinfo = stmts[0];
> -  tree scalar_type = TREE_TYPE (vector_type);
> -  class loop *loop = gimple_bb (stmt_vinfo->stmt)->loop_father;
> -  gcc_assert (loop);
> -
>    switch (code)
>      {
>      case WIDEN_SUM_EXPR:
> @@ -3284,12 +3276,7 @@ neutral_op_for_slp_reduction (slp_tree slp_node, tree vector_type,
>
>      case MAX_EXPR:
>      case MIN_EXPR:
> -      /* For MIN/MAX the initial values are neutral.  A reduction chain
> -        has only a single initial value, so that value is neutral for
> -        all statements.  */
> -      if (reduc_chain)
> -       return vect_phi_initial_value (stmt_vinfo);
> -      return NULL_TREE;
> +      return initial_value;
>
>      default:
>        return NULL_TREE;
> @@ -5535,10 +5522,11 @@ vect_create_epilog_for_reduction (loop_vec_info loop_vinfo,
>        tree neutral_op = NULL_TREE;
>        if (slp_node)
>         {
> -         stmt_vec_info first = REDUC_GROUP_FIRST_ELEMENT (stmt_info);
> -         neutral_op
> -           = neutral_op_for_slp_reduction (slp_node_instance->reduc_phis,
> -                                           vectype, code, first != NULL);
> +         tree initial_value = NULL_TREE;
> +         if (REDUC_GROUP_FIRST_ELEMENT (stmt_info))
> +           initial_value = vect_phi_initial_value (orig_phis[0]);
> +         neutral_op = neutral_op_for_reduction (TREE_TYPE (vectype), code,
> +                                                initial_value);
>         }
>        if (neutral_op)
>         vector_identity = gimple_build_vector_from_val (&seq, vectype,
> @@ -6935,9 +6923,13 @@ vectorizable_reduction (loop_vec_info loop_vinfo,
>    /* For SLP reductions, see if there is a neutral value we can use.  */
>    tree neutral_op = NULL_TREE;
>    if (slp_node)
> -    neutral_op = neutral_op_for_slp_reduction
> -      (slp_node_instance->reduc_phis, vectype_out, orig_code,
> -       REDUC_GROUP_FIRST_ELEMENT (stmt_info) != NULL);
> +    {
> +      tree initial_value = NULL_TREE;
> +      if (REDUC_GROUP_FIRST_ELEMENT (stmt_info) != NULL)
> +       initial_value = vect_phi_initial_value (reduc_def_phi);
> +      neutral_op = neutral_op_for_reduction (TREE_TYPE (vectype_out),
> +                                            orig_code, initial_value);
> +    }
>
>    if (double_reduc && reduction_type == FOLD_LEFT_REDUCTION)
>      {
> @@ -7501,15 +7493,16 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
>        else
>         {
>           gcc_assert (slp_node == slp_node_instance->reduc_phis);
> -         stmt_vec_info first = REDUC_GROUP_FIRST_ELEMENT (reduc_stmt_info);
> -         tree neutral_op
> -             = neutral_op_for_slp_reduction (slp_node, vectype_out,
> -                                             STMT_VINFO_REDUC_CODE (reduc_info),
> -                                             first != NULL);
> +         tree initial_value = NULL_TREE;
> +         if (REDUC_GROUP_FIRST_ELEMENT (reduc_stmt_info))
> +           initial_value = vect_phi_initial_value (phi);
> +         tree_code code = STMT_VINFO_REDUC_CODE (reduc_info);
> +         tree neutral_op = neutral_op_for_reduction (TREE_TYPE (vectype_out),
> +                                                     code, initial_value);
>           get_initial_defs_for_reduction (loop_vinfo, reduc_info,
>                                           slp_node_instance->reduc_phis,
>                                           &vec_initial_defs, vec_num,
> -                                         first != NULL, neutral_op);
> +                                         initial_value != NULL, neutral_op);
>         }
>      }
>    else