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
