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Diffstat (limited to 'contrib/gcc/tree-loop-linear.c')
| -rw-r--r-- | contrib/gcc/tree-loop-linear.c | 360 |
1 files changed, 360 insertions, 0 deletions
diff --git a/contrib/gcc/tree-loop-linear.c b/contrib/gcc/tree-loop-linear.c new file mode 100644 index 0000000..2840e9b --- /dev/null +++ b/contrib/gcc/tree-loop-linear.c @@ -0,0 +1,360 @@ +/* Linear Loop transforms + Copyright (C) 2003, 2004, 2005 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 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); +} |
