/* Linear Loop transforms Copyright (C) 2003, 2004, 2005 Free Software Foundation, Inc. Contributed by Daniel Berlin . 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 2, 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 COPYING. If not, write to the Free Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */ #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 "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, VEC (data_reference_p, heap) *datarefs, struct loop *loop, struct loop *first_loop, unsigned int *dependence_steps, unsigned int *nb_deps_not_carried_by_loop, unsigned int *access_strides) { 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 = 0; 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 - first_loop->depth]; 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 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++) { tree chrec = DR_ACCESS_FN (dr, it); tree tstride = evolution_part_in_loop_num (chrec, loop->num); if (tstride == NULL_TREE || TREE_CODE (tstride) != INTEGER_CST) continue; (*access_strides) += int_cst_value (tstride); } } } /* 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) { struct loop *loop_i; struct loop *loop_j; unsigned int dependence_steps_i, dependence_steps_j; unsigned int access_strides_i, access_strides_j; 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; /* 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_i->depth < loop_j->depth; 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: 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. */ if (dependence_steps_i < dependence_steps_j || nb_deps_not_carried_by_i > nb_deps_not_carried_by_j || access_strides_i < access_strides_j) { lambda_matrix_row_exchange (LTM_MATRIX (trans), loop_i->depth - first_loop->depth, loop_j->depth - first_loop->depth); /* 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_i->depth - first_loop->depth, loop_j->depth - first_loop->depth); } } return trans; } /* Perform a set of linear transforms on LOOPS. */ void linear_transform_loops (struct loops *loops) { bool modified = false; unsigned int i; VEC(tree,heap) *oldivs = NULL; VEC(tree,heap) *invariants = NULL; for (i = 1; i < loops->num; i++) { unsigned int depth = 0; VEC (ddr_p, heap) *dependence_relations; VEC (data_reference_p, heap) *datarefs; struct loop *loop_nest = loops->parray[i]; struct loop *temp; lambda_loopnest before, after; lambda_trans_matrix trans; bool problem = false; /* 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 || !loop_nest->inner || !loop_nest->single_exit) continue; VEC_truncate (tree, oldivs, 0); VEC_truncate (tree, invariants, 0); depth = 1; for (temp = loop_nest->inner; temp; temp = temp->inner) { /* If we have a sibling loop or multiple exit edges, jump ship. */ if (temp->next || !temp->single_exit) { problem = true; break; } depth ++; } if (problem) continue; /* Analyze data references and dependence relations using scev. */ datarefs = VEC_alloc (data_reference_p, heap, 10); dependence_relations = VEC_alloc (ddr_p, heap, 10 * 10); compute_data_dependences_for_loop (loop_nest, true, &datarefs, &dependence_relations); 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 (loops, loop_nest, &oldivs, &invariants); 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); if (dump_file) { fprintf (dump_file, "After:\n"); print_lambda_loopnest (dump_file, after, 'u'); } lambda_loopnest_to_gcc_loopnest (loop_nest, oldivs, invariants, after, trans); modified = true; if (dump_file) fprintf (dump_file, "Successfully transformed loop.\n"); free_and_continue: free_dependence_relations (dependence_relations); free_data_refs (datarefs); } VEC_free (tree, heap, oldivs); VEC_free (tree, heap, invariants); scev_reset (); if (modified) rewrite_into_loop_closed_ssa (NULL, TODO_update_ssa_full_phi); }