--- /dev/null
+/* Linear Loop transforms
+ Copyright (C) 2003, 2004, 2005, 2007, 2008, 2009
+ Free Software Foundation, Inc.
+ Contributed by Daniel Berlin <dberlin@dberlin.org>.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "ggc.h"
+#include "tree.h"
+#include "target.h"
+
+#include "rtl.h"
+#include "basic-block.h"
+#include "diagnostic.h"
+#include "obstack.h"
+#include "tree-flow.h"
+#include "tree-dump.h"
+#include "timevar.h"
+#include "cfgloop.h"
+#include "expr.h"
+#include "optabs.h"
+#include "tree-chrec.h"
+#include "tree-data-ref.h"
+#include "tree-scalar-evolution.h"
+#include "tree-pass.h"
+#include "lambda.h"
+
+/* Linear loop transforms include any composition of interchange,
+ scaling, skewing, and reversal. They are used to change the
+ iteration order of loop nests in order to optimize data locality of
+ traversals, or remove dependences that prevent
+ parallelization/vectorization/etc.
+
+ TODO: Determine reuse vectors/matrix and use it to determine optimal
+ transform matrix for locality purposes.
+ TODO: Completion of partial transforms. */
+
+/* Gather statistics for loop interchange. LOOP is the loop being
+ considered. The first loop in the considered loop nest is
+ FIRST_LOOP, and consequently, the index of the considered loop is
+ obtained by LOOP->DEPTH - FIRST_LOOP->DEPTH
+
+ Initializes:
+ - DEPENDENCE_STEPS the sum of all the data dependence distances
+ carried by loop LOOP,
+
+ - NB_DEPS_NOT_CARRIED_BY_LOOP the number of dependence relations
+ for which the loop LOOP is not carrying any dependence,
+
+ - ACCESS_STRIDES the sum of all the strides in LOOP.
+
+ Example: for the following loop,
+
+ | loop_1 runs 1335 times
+ | loop_2 runs 1335 times
+ | A[{{0, +, 1}_1, +, 1335}_2]
+ | B[{{0, +, 1}_1, +, 1335}_2]
+ | endloop_2
+ | A[{0, +, 1336}_1]
+ | endloop_1
+
+ gather_interchange_stats (in loop_1) will return
+ DEPENDENCE_STEPS = 3002
+ NB_DEPS_NOT_CARRIED_BY_LOOP = 5
+ ACCESS_STRIDES = 10694
+
+ gather_interchange_stats (in loop_2) will return
+ DEPENDENCE_STEPS = 3000
+ NB_DEPS_NOT_CARRIED_BY_LOOP = 7
+ ACCESS_STRIDES = 8010
+*/
+
+static void
+gather_interchange_stats (VEC (ddr_p, heap) *dependence_relations ATTRIBUTE_UNUSED,
+ VEC (data_reference_p, heap) *datarefs ATTRIBUTE_UNUSED,
+ struct loop *loop ATTRIBUTE_UNUSED,
+ struct loop *first_loop ATTRIBUTE_UNUSED,
+ unsigned int *dependence_steps ATTRIBUTE_UNUSED,
+ unsigned int *nb_deps_not_carried_by_loop ATTRIBUTE_UNUSED,
+ double_int *access_strides ATTRIBUTE_UNUSED)
+{
+ unsigned int i, j;
+ struct data_dependence_relation *ddr;
+ struct data_reference *dr;
+
+ *dependence_steps = 0;
+ *nb_deps_not_carried_by_loop = 0;
+ *access_strides = double_int_zero;
+
+ for (i = 0; VEC_iterate (ddr_p, dependence_relations, i, ddr); i++)
+ {
+ /* If we don't know anything about this dependence, or the distance
+ vector is NULL, or there is no dependence, then there is no reuse of
+ data. */
+ if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know
+ || DDR_ARE_DEPENDENT (ddr) == chrec_known
+ || DDR_NUM_DIST_VECTS (ddr) == 0)
+ continue;
+
+ for (j = 0; j < DDR_NUM_DIST_VECTS (ddr); j++)
+ {
+ int dist = DDR_DIST_VECT (ddr, j)[loop_depth (loop) - loop_depth (first_loop)];
+
+ if (dist == 0)
+ (*nb_deps_not_carried_by_loop) += 1;
+
+ else if (dist < 0)
+ (*dependence_steps) += -dist;
+
+ else
+ (*dependence_steps) += dist;
+ }
+ }
+
+ /* Compute the access strides. */
+ for (i = 0; VEC_iterate (data_reference_p, datarefs, i, dr); i++)
+ {
+ unsigned int it;
+ tree ref = DR_REF (dr);
+ gimple stmt = DR_STMT (dr);
+ struct loop *stmt_loop = loop_containing_stmt (stmt);
+ struct loop *inner_loop = first_loop->inner;
+
+ if (inner_loop != stmt_loop
+ && !flow_loop_nested_p (inner_loop, stmt_loop))
+ continue;
+
+ for (it = 0; it < DR_NUM_DIMENSIONS (dr);
+ it++, ref = TREE_OPERAND (ref, 0))
+ {
+ int num = am_vector_index_for_loop (DR_ACCESS_MATRIX (dr), loop->num);
+ int istride = AM_GET_ACCESS_MATRIX_ELEMENT (DR_ACCESS_MATRIX (dr), it, num);
+ tree array_size = TYPE_SIZE (TREE_TYPE (ref));
+ double_int dstride;
+
+ if (array_size == NULL_TREE
+ || TREE_CODE (array_size) != INTEGER_CST)
+ continue;
+
+ dstride = double_int_mul (tree_to_double_int (array_size),
+ shwi_to_double_int (istride));
+ (*access_strides) = double_int_add (*access_strides, dstride);
+ }
+ }
+}
+
+/* Attempt to apply interchange transformations to TRANS to maximize the
+ spatial and temporal locality of the loop.
+ Returns the new transform matrix. The smaller the reuse vector
+ distances in the inner loops, the fewer the cache misses.
+ FIRST_LOOP is the loop->num of the first loop in the analyzed loop
+ nest. */
+
+
+static lambda_trans_matrix
+try_interchange_loops (lambda_trans_matrix trans,
+ unsigned int depth,
+ VEC (ddr_p, heap) *dependence_relations,
+ VEC (data_reference_p, heap) *datarefs,
+ struct loop *first_loop)
+{
+ bool res;
+ struct loop *loop_i;
+ struct loop *loop_j;
+ unsigned int dependence_steps_i, dependence_steps_j;
+ double_int access_strides_i, access_strides_j;
+ double_int small, large, nb_iter;
+ double_int l1_cache_size, l2_cache_size;
+ int cmp;
+ unsigned int nb_deps_not_carried_by_i, nb_deps_not_carried_by_j;
+ struct data_dependence_relation *ddr;
+
+ if (VEC_length (ddr_p, dependence_relations) == 0)
+ return trans;
+
+ /* When there is an unknown relation in the dependence_relations, we
+ know that it is no worth looking at this loop nest: give up. */
+ ddr = VEC_index (ddr_p, dependence_relations, 0);
+ if (ddr == NULL || DDR_ARE_DEPENDENT (ddr) == chrec_dont_know)
+ return trans;
+
+ l1_cache_size = uhwi_to_double_int (L1_CACHE_SIZE * 1024);
+ l2_cache_size = uhwi_to_double_int (L2_CACHE_SIZE * 1024);
+
+ /* LOOP_I is always the outer loop. */
+ for (loop_j = first_loop->inner;
+ loop_j;
+ loop_j = loop_j->inner)
+ for (loop_i = first_loop;
+ loop_depth (loop_i) < loop_depth (loop_j);
+ loop_i = loop_i->inner)
+ {
+ gather_interchange_stats (dependence_relations, datarefs,
+ loop_i, first_loop,
+ &dependence_steps_i,
+ &nb_deps_not_carried_by_i,
+ &access_strides_i);
+ gather_interchange_stats (dependence_relations, datarefs,
+ loop_j, first_loop,
+ &dependence_steps_j,
+ &nb_deps_not_carried_by_j,
+ &access_strides_j);
+
+ /* Heuristics for loop interchange profitability:
+
+ 0. Don't transform if the smallest stride is larger than
+ the L2 cache, or if the largest stride multiplied by the
+ number of iterations is smaller than the L1 cache.
+
+ 1. (spatial locality) Inner loops should have smallest
+ dependence steps.
+
+ 2. (spatial locality) Inner loops should contain more
+ dependence relations not carried by the loop.
+
+ 3. (temporal locality) Inner loops should have smallest
+ array access strides.
+ */
+
+ cmp = double_int_ucmp (access_strides_i, access_strides_j);
+ small = cmp < 0 ? access_strides_i : access_strides_j;
+ large = cmp < 0 ? access_strides_j : access_strides_i;
+
+ if (double_int_ucmp (small, l2_cache_size) > 0)
+ continue;
+
+ res = cmp < 0 ?
+ estimated_loop_iterations (loop_j, false, &nb_iter):
+ estimated_loop_iterations (loop_i, false, &nb_iter);
+ large = double_int_mul (large, nb_iter);
+
+ if (res && double_int_ucmp (large, l1_cache_size) < 0)
+ continue;
+
+ if (dependence_steps_i < dependence_steps_j
+ || nb_deps_not_carried_by_i > nb_deps_not_carried_by_j
+ || cmp < 0)
+ {
+ lambda_matrix_row_exchange (LTM_MATRIX (trans),
+ loop_depth (loop_i) - loop_depth (first_loop),
+ loop_depth (loop_j) - loop_depth (first_loop));
+ /* Validate the resulting matrix. When the transformation
+ is not valid, reverse to the previous transformation. */
+ if (!lambda_transform_legal_p (trans, depth, dependence_relations))
+ lambda_matrix_row_exchange (LTM_MATRIX (trans),
+ loop_depth (loop_i) - loop_depth (first_loop),
+ loop_depth (loop_j) - loop_depth (first_loop));
+ }
+ }
+
+ return trans;
+}
+
+/* Return the number of nested loops in LOOP_NEST, or 0 if the loops
+ are not perfectly nested. */
+
+unsigned int
+perfect_loop_nest_depth (struct loop *loop_nest)
+{
+ struct loop *temp;
+ unsigned int depth = 1;
+
+ /* If it's not a loop nest, we don't want it. We also don't handle
+ sibling loops properly, which are loops of the following form:
+
+ | for (i = 0; i < 50; i++)
+ | {
+ | for (j = 0; j < 50; j++)
+ | {
+ | ...
+ | }
+ | for (j = 0; j < 50; j++)
+ | {
+ | ...
+ | }
+ | }
+ */
+
+ if (!loop_nest->inner || !single_exit (loop_nest))
+ return 0;
+
+ for (temp = loop_nest->inner; temp; temp = temp->inner)
+ {
+ /* If we have a sibling loop or multiple exit edges, jump ship. */
+ if (temp->next || !single_exit (temp))
+ return 0;
+
+ depth++;
+ }
+
+ return depth;
+}
+
+/* Perform a set of linear transforms on loops. */
+
+void
+linear_transform_loops (void)
+{
+ bool modified = false;
+ loop_iterator li;
+ VEC(tree,heap) *oldivs = NULL;
+ VEC(tree,heap) *invariants = NULL;
+ VEC(tree,heap) *lambda_parameters = NULL;
+ VEC(gimple,heap) *remove_ivs = VEC_alloc (gimple, heap, 3);
+ struct loop *loop_nest;
+ gimple oldiv_stmt;
+ unsigned i;
+
+ FOR_EACH_LOOP (li, loop_nest, 0)
+ {
+ unsigned int depth = 0;
+ VEC (ddr_p, heap) *dependence_relations;
+ VEC (data_reference_p, heap) *datarefs;
+
+ lambda_loopnest before, after;
+ lambda_trans_matrix trans;
+ struct obstack lambda_obstack;
+ struct loop *loop;
+ VEC(loop_p,heap) *nest;
+
+ depth = perfect_loop_nest_depth (loop_nest);
+ if (depth == 0)
+ continue;
+
+ nest = VEC_alloc (loop_p, heap, 3);
+ for (loop = loop_nest; loop; loop = loop->inner)
+ VEC_safe_push (loop_p, heap, nest, loop);
+
+ gcc_obstack_init (&lambda_obstack);
+ VEC_truncate (tree, oldivs, 0);
+ VEC_truncate (tree, invariants, 0);
+ VEC_truncate (tree, lambda_parameters, 0);
+
+ datarefs = VEC_alloc (data_reference_p, heap, 10);
+ dependence_relations = VEC_alloc (ddr_p, heap, 10 * 10);
+ if (!compute_data_dependences_for_loop (loop_nest, true, &datarefs,
+ &dependence_relations))
+ goto free_and_continue;
+
+ lambda_collect_parameters (datarefs, &lambda_parameters);
+ if (!lambda_compute_access_matrices (datarefs, lambda_parameters, nest))
+ goto free_and_continue;
+
+ if (dump_file && (dump_flags & TDF_DETAILS))
+ dump_ddrs (dump_file, dependence_relations);
+
+ /* Build the transformation matrix. */
+ trans = lambda_trans_matrix_new (depth, depth);
+ lambda_matrix_id (LTM_MATRIX (trans), depth);
+ trans = try_interchange_loops (trans, depth, dependence_relations,
+ datarefs, loop_nest);
+
+ if (lambda_trans_matrix_id_p (trans))
+ {
+ if (dump_file)
+ fprintf (dump_file, "Won't transform loop. Optimal transform is the identity transform\n");
+ goto free_and_continue;
+ }
+
+ /* Check whether the transformation is legal. */
+ if (!lambda_transform_legal_p (trans, depth, dependence_relations))
+ {
+ if (dump_file)
+ fprintf (dump_file, "Can't transform loop, transform is illegal:\n");
+ goto free_and_continue;
+ }
+
+ before = gcc_loopnest_to_lambda_loopnest (loop_nest, &oldivs,
+ &invariants, &lambda_obstack);
+
+ if (!before)
+ goto free_and_continue;
+
+ if (dump_file)
+ {
+ fprintf (dump_file, "Before:\n");
+ print_lambda_loopnest (dump_file, before, 'i');
+ }
+
+ after = lambda_loopnest_transform (before, trans, &lambda_obstack);
+
+ if (dump_file)
+ {
+ fprintf (dump_file, "After:\n");
+ print_lambda_loopnest (dump_file, after, 'u');
+ }
+
+ lambda_loopnest_to_gcc_loopnest (loop_nest, oldivs, invariants,
+ &remove_ivs,
+ after, trans, &lambda_obstack);
+ modified = true;
+
+ if (dump_file)
+ fprintf (dump_file, "Successfully transformed loop.\n");
+
+ free_and_continue:
+ obstack_free (&lambda_obstack, NULL);
+ free_dependence_relations (dependence_relations);
+ free_data_refs (datarefs);
+ VEC_free (loop_p, heap, nest);
+ }
+
+ for (i = 0; VEC_iterate (gimple, remove_ivs, i, oldiv_stmt); i++)
+ remove_iv (oldiv_stmt);
+
+ VEC_free (tree, heap, oldivs);
+ VEC_free (tree, heap, invariants);
+ VEC_free (gimple, heap, remove_ivs);
+ scev_reset ();
+
+ if (modified)
+ rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa_full_phi);
+}
projects / msp430-gcc.git / blobdiff