On Thu, Jul 8, 2021 at 2:49 PM Richard Sandiford via Gcc-patches
<gcc-patches@gcc.gnu.org> wrote:
>
> After previous patches, we can now easily provide the neutral op
> as an argument to get_initial_def_for_reduction. This in turn
> allows the adjustment calculation to be moved outside of
> get_initial_def_for_reduction, which is the main motivation
> of the patch.
OK.
> gcc/
> * tree-vect-loop.c (get_initial_def_for_reduction): Remove
> adjustment handling. Take the neutral value as an argument,
> in place of the code argument.
> (vect_transform_cycle_phi): Update accordingly. Handle the
> initial values of cond reductions separately from code reductions.
> Choose the adjustment here rather than in
> get_initial_def_for_reduction. Sink the splat of vec_initial_def.
> ---
> gcc/tree-vect-loop.c | 177 +++++++++++++++----------------------------
> 1 file changed, 59 insertions(+), 118 deletions(-)
>
> diff --git a/gcc/tree-vect-loop.c b/gcc/tree-vect-loop.c
> index 744645d8bad..fe7e73f655f 100644
> --- a/gcc/tree-vect-loop.c
> +++ b/gcc/tree-vect-loop.c
> @@ -4614,57 +4614,26 @@ vect_model_reduction_cost (loop_vec_info loop_vinfo,
> Input:
> REDUC_INFO - the info_for_reduction
> INIT_VAL - the initial value of the reduction variable
> + NEUTRAL_OP - a value that has no effect on the reduction, as per
> + neutral_op_for_reduction
>
> Output:
> - ADJUSTMENT_DEF - a tree that holds a value to be added to the final result
> - of the reduction (used for adjusting the epilog - see below).
> Return a vector variable, initialized according to the operation that
> STMT_VINFO performs. This vector will be used as the initial value
> of the vector of partial results.
>
> - Option1 (adjust in epilog): Initialize the vector as follows:
> - add/bit or/xor: [0,0,...,0,0]
> - mult/bit and: [1,1,...,1,1]
> - min/max/cond_expr: [init_val,init_val,..,init_val,init_val]
> - and when necessary (e.g. add/mult case) let the caller know
> - that it needs to adjust the result by init_val.
> -
> - Option2: Initialize the vector as follows:
> - add/bit or/xor: [init_val,0,0,...,0]
> - mult/bit and: [init_val,1,1,...,1]
> - min/max/cond_expr: [init_val,init_val,...,init_val]
> - and no adjustments are needed.
> -
> - For example, for the following code:
> -
> - s = init_val;
> - for (i=0;i<n;i++)
> - s = s + a[i];
> -
> - STMT_VINFO is 's = s + a[i]', and the reduction variable is 's'.
> - For a vector of 4 units, we want to return either [0,0,0,init_val],
> - or [0,0,0,0] and let the caller know that it needs to adjust
> - the result at the end by 'init_val'.
> -
> - FORNOW, we are using the 'adjust in epilog' scheme, because this way the
> - initialization vector is simpler (same element in all entries), if
> - ADJUSTMENT_DEF is not NULL, and Option2 otherwise.
> -
> - A cost model should help decide between these two schemes. */
> + The value we need is a vector in which element 0 has value INIT_VAL
> + and every other element has value NEUTRAL_OP. */
>
> static tree
> get_initial_def_for_reduction (loop_vec_info loop_vinfo,
> stmt_vec_info reduc_info,
> - enum tree_code code, tree init_val,
> - tree *adjustment_def)
> + tree init_val, tree neutral_op)
> {
> class loop *loop = LOOP_VINFO_LOOP (loop_vinfo);
> tree scalar_type = TREE_TYPE (init_val);
> tree vectype = get_vectype_for_scalar_type (loop_vinfo, scalar_type);
> - tree def_for_init;
> tree init_def;
> - REAL_VALUE_TYPE real_init_val = dconst0;
> - int int_init_val = 0;
> gimple_seq stmts = NULL;
>
> gcc_assert (vectype);
> @@ -4675,75 +4644,34 @@ get_initial_def_for_reduction (loop_vec_info
> loop_vinfo,
> gcc_assert (nested_in_vect_loop_p (loop, reduc_info)
> || loop == (gimple_bb (reduc_info->stmt))->loop_father);
>
> - /* ADJUSTMENT_DEF is NULL when called from
> - vect_create_epilog_for_reduction to vectorize double reduction. */
> - if (adjustment_def)
> - *adjustment_def = NULL;
> -
> - switch (code)
> + if (operand_equal_p (init_val, neutral_op))
> {
> - case WIDEN_SUM_EXPR:
> - case DOT_PROD_EXPR:
> - case SAD_EXPR:
> - case PLUS_EXPR:
> - case MINUS_EXPR:
> - case BIT_IOR_EXPR:
> - case BIT_XOR_EXPR:
> - case MULT_EXPR:
> - case BIT_AND_EXPR:
> - {
> - if (code == MULT_EXPR)
> - {
> - real_init_val = dconst1;
> - int_init_val = 1;
> - }
> -
> - if (code == BIT_AND_EXPR)
> - int_init_val = -1;
> -
> - if (SCALAR_FLOAT_TYPE_P (scalar_type))
> - def_for_init = build_real (scalar_type, real_init_val);
> - else
> - def_for_init = build_int_cst (scalar_type, int_init_val);
> -
> - if (adjustment_def || operand_equal_p (def_for_init, init_val, 0))
> - {
> - /* Option1: the first element is '0' or '1' as well. */
> - if (!operand_equal_p (def_for_init, init_val, 0))
> - *adjustment_def = init_val;
> - init_def = gimple_build_vector_from_val (&stmts, vectype,
> - def_for_init);
> - }
> - else if (!TYPE_VECTOR_SUBPARTS (vectype).is_constant ())
> - {
> - /* Option2 (variable length): the first element is INIT_VAL. */
> - init_def = gimple_build_vector_from_val (&stmts, vectype,
> - def_for_init);
> - init_def = gimple_build (&stmts, CFN_VEC_SHL_INSERT,
> - vectype, init_def, init_val);
> - }
> - else
> - {
> - /* Option2: the first element is INIT_VAL. */
> - tree_vector_builder elts (vectype, 1, 2);
> - elts.quick_push (init_val);
> - elts.quick_push (def_for_init);
> - init_def = gimple_build_vector (&stmts, &elts);
> - }
> - }
> - break;
> -
> - case MIN_EXPR:
> - case MAX_EXPR:
> - case COND_EXPR:
> - {
> - init_val = gimple_convert (&stmts, TREE_TYPE (vectype), init_val);
> - init_def = gimple_build_vector_from_val (&stmts, vectype, init_val);
> - }
> - break;
> -
> - default:
> - gcc_unreachable ();
> + /* If both elements are equal then the vector described above is
> + just a splat. */
> + neutral_op = gimple_convert (&stmts, TREE_TYPE (vectype), neutral_op);
> + init_def = gimple_build_vector_from_val (&stmts, vectype, neutral_op);
> + }
> + else
> + {
> + neutral_op = gimple_convert (&stmts, TREE_TYPE (vectype), neutral_op);
> + init_val = gimple_convert (&stmts, TREE_TYPE (vectype), init_val);
> + if (!TYPE_VECTOR_SUBPARTS (vectype).is_constant ())
> + {
> + /* Construct a splat of NEUTRAL_OP and insert INIT_VAL into
> + element 0. */
> + init_def = gimple_build_vector_from_val (&stmts, vectype,
> + neutral_op);
> + init_def = gimple_build (&stmts, CFN_VEC_SHL_INSERT,
> + vectype, init_def, init_val);
> + }
> + else
> + {
> + /* Build {INIT_VAL, NEUTRAL_OP, NEUTRAL_OP, ...}. */
> + tree_vector_builder elts (vectype, 1, 2);
> + elts.quick_push (init_val);
> + elts.quick_push (neutral_op);
> + init_def = gimple_build_vector (&stmts, &elts);
> + }
> }
>
> if (stmts)
> @@ -7479,7 +7407,7 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
> vectype_out);
>
> /* Get the loop-entry arguments. */
> - tree vec_initial_def;
> + tree vec_initial_def = NULL_TREE;
> auto_vec<tree> vec_initial_defs;
> if (slp_node)
> {
> @@ -7529,9 +7457,6 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
> STMT_VINFO_VEC_INDUC_COND_INITIAL_VAL (reduc_info) = NULL_TREE;
> }
> vec_initial_def = build_vector_from_val (vectype_out, induc_val);
> - vec_initial_defs.create (ncopies);
> - for (i = 0; i < ncopies; ++i)
> - vec_initial_defs.quick_push (vec_initial_def);
> }
> else if (nested_cycle)
> {
> @@ -7541,23 +7466,39 @@ vect_transform_cycle_phi (loop_vec_info loop_vinfo,
> ncopies, initial_def,
> &vec_initial_defs);
> }
> + else if (STMT_VINFO_REDUC_TYPE (reduc_info) == CONST_COND_REDUCTION
> + || STMT_VINFO_REDUC_TYPE (reduc_info) == COND_REDUCTION)
> + /* Fill the initial vector with the initial scalar value. */
> + vec_initial_def
> + = get_initial_def_for_reduction (loop_vinfo, reduc_stmt_info,
> + initial_def, initial_def);
> else
> {
> - tree adjustment_def = NULL_TREE;
> - tree *adjustment_defp = &adjustment_def;
> enum tree_code code = STMT_VINFO_REDUC_CODE (reduc_info);
> - if (STMT_VINFO_DEF_TYPE (stmt_info) == vect_double_reduction_def)
> - adjustment_defp = NULL;
> + tree neutral_op = neutral_op_for_reduction (TREE_TYPE (initial_def),
> + code, initial_def);
> + gcc_assert (neutral_op);
> + /* Try to simplify the vector initialization by applying an
> + adjustment after the reduction has been performed. */
> + if (STMT_VINFO_DEF_TYPE (stmt_info) == vect_reduction_def
> + && !operand_equal_p (neutral_op, initial_def))
> + {
> + STMT_VINFO_REDUC_EPILOGUE_ADJUSTMENT (reduc_info) = initial_def;
> + initial_def = neutral_op;
> + }
> vec_initial_def
> - = get_initial_def_for_reduction (loop_vinfo, reduc_info, code,
> - initial_def, adjustment_defp);
> - STMT_VINFO_REDUC_EPILOGUE_ADJUSTMENT (reduc_info) = adjustment_def;
> - vec_initial_defs.create (ncopies);
> - for (i = 0; i < ncopies; ++i)
> - vec_initial_defs.quick_push (vec_initial_def);
> + = get_initial_def_for_reduction (loop_vinfo, reduc_info,
> + initial_def, neutral_op);
> }
> }
>
> + if (vec_initial_def)
> + {
> + vec_initial_defs.create (ncopies);
> + for (i = 0; i < ncopies; ++i)
> + vec_initial_defs.quick_push (vec_initial_def);
> + }
> +
> /* Generate the reduction PHIs upfront. */
> for (i = 0; i < vec_num; i++)
> {
