From: Bin Cheng Date: Wed, 5 Jul 2017 12:08:28 +0000 (+0000) Subject: tree-loop-distribution.c: Add general explanantion on the pass. X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=a8745cc231e043dc9e455ea2a5897d30c14fd95a;p=gcc.git tree-loop-distribution.c: Add general explanantion on the pass. * tree-loop-distribution.c: Add general explanantion on the pass. (generate_loops_for_partition): Mark distributed loop. (pg_add_dependence_edges): New parameter. Handle alias data dependence specially and record it in the parameter if asked. (struct pg_vdata, pg_edata, pg_edge_callback_data): New structs. (init_partition_graph_vertices, add_partition_graph_edge): New. (pg_skip_alias_edge, free_partition_graph_edata_cb): New. (free_partition_graph_vdata, build_partition_graph): New. (sort_partitions_by_post_order, merge_dep_scc_partitions): New. (pg_collect_alias_ddrs, break_alias_scc_partitions): New. (data_ref_segment_size, latch_dominated_by_data_ref): New. (compute_alias_check_pairs, version_loop_by_alias_check): New. (version_for_distribution_p, finalize_partitions): New. (distribute_loop): Handle alias data dependence specially. Factor out loop fusion code as functions and call these functions. gcc/testsuite * gcc.dg/tree-ssa/ldist-4.c: Adjust test string. * gcc.dg/tree-ssa/ldist-12.c: Ditto. * gcc.dg/tree-ssa/ldist-13.c: Ditto. * gcc.dg/tree-ssa/ldist-14.c: Ditto. From-SVN: r249994 --- diff --git a/gcc/ChangeLog b/gcc/ChangeLog index 0b1e653ffa1..2f11b143c96 100644 --- a/gcc/ChangeLog +++ b/gcc/ChangeLog @@ -1,3 +1,21 @@ +2017-07-05 Bin Cheng + + * tree-loop-distribution.c: Add general explanantion on the pass. + (generate_loops_for_partition): Mark distributed loop. + (pg_add_dependence_edges): New parameter. Handle alias data + dependence specially and record it in the parameter if asked. + (struct pg_vdata, pg_edata, pg_edge_callback_data): New structs. + (init_partition_graph_vertices, add_partition_graph_edge): New. + (pg_skip_alias_edge, free_partition_graph_edata_cb): New. + (free_partition_graph_vdata, build_partition_graph): New. + (sort_partitions_by_post_order, merge_dep_scc_partitions): New. + (pg_collect_alias_ddrs, break_alias_scc_partitions): New. + (data_ref_segment_size, latch_dominated_by_data_ref): New. + (compute_alias_check_pairs, version_loop_by_alias_check): New. + (version_for_distribution_p, finalize_partitions): New. + (distribute_loop): Handle alias data dependence specially. Factor + out loop fusion code as functions and call these functions. + 2017-07-05 Bin Cheng * tree-loop-distribution.c (classify_partition): New parameter and diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog index 4dbfcc3ae79..36b23092711 100644 --- a/gcc/testsuite/ChangeLog +++ b/gcc/testsuite/ChangeLog @@ -1,3 +1,10 @@ +2017-07-05 Bin Cheng + + * gcc.dg/tree-ssa/ldist-4.c: Adjust test string. + * gcc.dg/tree-ssa/ldist-12.c: Ditto. + * gcc.dg/tree-ssa/ldist-13.c: Ditto. + * gcc.dg/tree-ssa/ldist-14.c: Ditto. + 2017-07-05 Bin Cheng * gcc.dg/tree-ssa/ldist-26.c: New test. diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c b/gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c index 53551cabd1e..625dd92128e 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c @@ -18,4 +18,5 @@ int foo (int * __restrict__ ia, return oya[22] + oyb[21]; } -/* { dg-final { scan-tree-dump-times "distributed: split to 2 loops" 1 "ldist" } } */ +/* Distributing the loop doesn't expose more parallelism. */ +/* { dg-final { scan-tree-dump-times "distributed: split to 2 loops" 0 "ldist" } } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ldist-13.c b/gcc/testsuite/gcc.dg/tree-ssa/ldist-13.c index ba39d4dfce7..8c9fd567e1e 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ldist-13.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ldist-13.c @@ -16,6 +16,5 @@ float foo (int n) return tmp; } -/* We should apply loop distribution. */ - -/* { dg-final { scan-tree-dump "Loop 1 distributed: split to 2 loops" "ldist" } } */ +/* Distributing the loop doesn't expose more parallelism. */ +/* { dg-final { scan-tree-dump-not "Loop 1 distributed: split to 2 loops" "ldist" } } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ldist-14.c b/gcc/testsuite/gcc.dg/tree-ssa/ldist-14.c index 48c1040f4b3..fa4d1a82879 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ldist-14.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ldist-14.c @@ -21,6 +21,5 @@ float foo (int n) return tmp; } -/* We should apply loop distribution. */ - -/* { dg-final { scan-tree-dump "Loop 1 distributed: split to 2 loops" "ldist" } } */ +/* Distributing the loop doesn't expose more parallelism. */ +/* { dg-final { scan-tree-dump-not "Loop 1 distributed: split to 2 loops" "ldist" } } */ diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ldist-4.c b/gcc/testsuite/gcc.dg/tree-ssa/ldist-4.c index c36daf0714b..4def9b4719d 100644 --- a/gcc/testsuite/gcc.dg/tree-ssa/ldist-4.c +++ b/gcc/testsuite/gcc.dg/tree-ssa/ldist-4.c @@ -20,7 +20,5 @@ int loop1 (int k) return b[100-1][1]; } -/* The current cost model fuses the two partitions because they have - similar memory accesses. */ -/* { dg-final { scan-tree-dump "similar memory accesses" "ldist" } } */ +/* Distributing inner loop doesn't expose more parallelism. */ /* { dg-final { scan-tree-dump-times "distributed: split to 2 loops" 0 "ldist" } } */ diff --git a/gcc/tree-loop-distribution.c b/gcc/tree-loop-distribution.c index b15ec045521..be0a6603ed2 100644 --- a/gcc/tree-loop-distribution.c +++ b/gcc/tree-loop-distribution.c @@ -36,10 +36,58 @@ along with GCC; see the file COPYING3. If not see | D(I) = A(I-1)*E |ENDDO - This pass uses an RDG, Reduced Dependence Graph built on top of the - data dependence relations. The RDG is then topologically sorted to - obtain a map of information producers/consumers based on which it - generates the new loops. */ + Loop distribution is the dual of loop fusion. It separates statements + of a loop (or loop nest) into multiple loops (or loop nests) with the + same loop header. The major goal is to separate statements which may + be vectorized from those that can't. This pass implements distribution + in the following steps: + + 1) Seed partitions with specific type statements. For now we support + two types seed statements: statement defining variable used outside + of loop; statement storing to memory. + 2) Build reduced dependence graph (RDG) for loop to be distributed. + The vertices (RDG:V) model all statements in the loop and the edges + (RDG:E) model flow and control dependencies between statements. + 3) Apart from RDG, compute data dependencies between memory references. + 4) Starting from seed statement, build up partition by adding depended + statements according to RDG's dependence information. Partition is + classified as parallel type if it can be executed paralleled; or as + sequential type if it can't. Parallel type partition is further + classified as different builtin kinds if it can be implemented as + builtin function calls. + 5) Build partition dependence graph (PG) based on data dependencies. + The vertices (PG:V) model all partitions and the edges (PG:E) model + all data dependencies between every partitions pair. In general, + data dependence is either compilation time known or unknown. In C + family languages, there exists quite amount compilation time unknown + dependencies because of possible alias relation of data references. + We categorize PG's edge to two types: "true" edge that represents + compilation time known data dependencies; "alias" edge for all other + data dependencies. + 6) Traverse subgraph of PG as if all "alias" edges don't exist. Merge + partitions in each strong connected component (SCC) correspondingly. + Build new PG for merged partitions. + 7) Traverse PG again and this time with both "true" and "alias" edges + included. We try to break SCCs by removing some edges. Because + SCCs by "true" edges are all fused in step 6), we can break SCCs + by removing some "alias" edges. It's NP-hard to choose optimal + edge set, fortunately simple approximation is good enough for us + given the small problem scale. + 8) Collect all data dependencies of the removed "alias" edges. Create + runtime alias checks for collected data dependencies. + 9) Version loop under the condition of runtime alias checks. Given + loop distribution generally introduces additional overhead, it is + only useful if vectorization is achieved in distributed loop. We + version loop with internal function call IFN_LOOP_DIST_ALIAS. If + no distributed loop can be vectorized, we simply remove distributed + loops and recover to the original one. + + TODO: + 1) We only distribute innermost loops now. This pass should handle loop + nests in the future. + 2) We only fuse partitions in SCC now. A better fusion algorithm is + desired to minimize loop overhead, maximize parallelism and maximize + data reuse. */ #include "config.h" #include "system.h" @@ -744,11 +792,18 @@ generate_loops_for_partition (struct loop *loop, partition *partition, if (copy_p) { + int orig_loop_num = loop->orig_loop_num; loop = copy_loop_before (loop); gcc_assert (loop != NULL); + loop->orig_loop_num = orig_loop_num; create_preheader (loop, CP_SIMPLE_PREHEADERS); create_bb_after_loop (loop); } + else + { + /* Origin number is set to the new versioned loop's num. */ + gcc_assert (loop->orig_loop_num != loop->num); + } /* Remove stmts not in the PARTITION bitmap. */ bbs = get_loop_body_in_dom_order (loop); @@ -1601,11 +1656,14 @@ partition_contains_all_rw (struct graph *rdg, } /* Compute partition dependence created by the data references in DRS1 - and DRS2 and modify and return DIR according to that. */ + and DRS2, modify and return DIR according to that. IF ALIAS_DDR is + not NULL, we record dependence introduced by possible alias between + two data references in ALIAS_DDRS; otherwise, we simply ignore such + dependence as if it doesn't exist at all. */ static int pg_add_dependence_edges (struct graph *rdg, int dir, - bitmap drs1, bitmap drs2) + bitmap drs1, bitmap drs2, vec *alias_ddrs) { unsigned i, j; bitmap_iterator bi, bj; @@ -1619,6 +1677,9 @@ pg_add_dependence_edges (struct graph *rdg, int dir, EXECUTE_IF_SET_IN_BITMAP (drs2, 0, j, bj) { + int res, this_dir = 1; + ddr_p ddr; + dr2 = datarefs_vec[j]; /* Skip all data dependence. */ @@ -1626,9 +1687,7 @@ pg_add_dependence_edges (struct graph *rdg, int dir, continue; saved_dr1 = dr1; - int this_dir = 1; - ddr_p ddr; - /* Re-shuffle data-refs to be in dominator order. */ + /* Re-shuffle data-refs to be in topological order. */ if (rdg_vertex_for_stmt (rdg, DR_STMT (dr1)) > rdg_vertex_for_stmt (rdg, DR_STMT (dr2))) { @@ -1637,14 +1696,33 @@ pg_add_dependence_edges (struct graph *rdg, int dir, } ddr = get_data_dependence (rdg, dr1, dr2); if (DDR_ARE_DEPENDENT (ddr) == chrec_dont_know) - this_dir = 2; + { + this_dir = 0; + res = data_ref_compare_tree (DR_BASE_ADDRESS (dr1), + DR_BASE_ADDRESS (dr2)); + /* Be conservative. If data references are not well analyzed, + or the two data references have the same base address and + offset, add dependence and consider it alias to each other. + In other words, the dependence can not be resolved by + runtime alias check. */ + if (!DR_BASE_ADDRESS (dr1) || !DR_BASE_ADDRESS (dr2) + || !DR_OFFSET (dr1) || !DR_OFFSET (dr2) + || !DR_INIT (dr1) || !DR_INIT (dr2) + || !DR_STEP (dr1) || !tree_fits_uhwi_p (DR_STEP (dr1)) + || !DR_STEP (dr2) || !tree_fits_uhwi_p (DR_STEP (dr2)) + || res == 0) + this_dir = 2; + /* Data dependence could be resolved by runtime alias check, + record it in ALIAS_DDRS. */ + else if (alias_ddrs != NULL) + alias_ddrs->safe_push (ddr); + /* Or simply ignore it. */ + } else if (DDR_ARE_DEPENDENT (ddr) == NULL_TREE) { if (DDR_REVERSED_P (ddr)) - { - std::swap (dr1, dr2); - this_dir = -this_dir; - } + this_dir = -this_dir; + /* Known dependences can still be unordered througout the iteration space, see gcc.dg/tree-ssa/ldist-16.c. */ if (DDR_NUM_DIST_VECTS (ddr) != 1) @@ -1652,12 +1730,10 @@ pg_add_dependence_edges (struct graph *rdg, int dir, /* If the overlap is exact preserve stmt order. */ else if (lambda_vector_zerop (DDR_DIST_VECT (ddr, 0), 1)) ; + /* Else as the distance vector is lexicographic positive swap + the dependence direction. */ else - { - /* Else as the distance vector is lexicographic positive - swap the dependence direction. */ - this_dir = -this_dir; - } + this_dir = -this_dir; } else this_dir = 0; @@ -1684,11 +1760,609 @@ pgcmp (const void *v1_, const void *v2_) return v2->post - v1->post; } -/* Distributes the code from LOOP in such a way that producer - statements are placed before consumer statements. Tries to separate - only the statements from STMTS into separate loops. - Returns the number of distributed loops. Set *DESTROY_P to whether - LOOP needs to be destroyed. */ +/* Data attached to vertices of partition dependence graph. */ +struct pg_vdata +{ + /* ID of the corresponding partition. */ + int id; + /* The partition. */ + struct partition *partition; +}; + +/* Data attached to edges of partition dependence graph. */ +struct pg_edata +{ + /* If the dependence edge can be resolved by runtime alias check, + this vector contains data dependence relations for runtime alias + check. On the other hand, if the dependence edge is introduced + because of compilation time known data dependence, this vector + contains nothing. */ + vec alias_ddrs; +}; + +/* Callback data for traversing edges in graph. */ +struct pg_edge_callback_data +{ + /* Bitmap contains strong connected components should be merged. */ + bitmap sccs_to_merge; + /* Array constains component information for all vertices. */ + int *vertices_component; + /* Vector to record all data dependence relations which are needed + to break strong connected components by runtime alias checks. */ + vec *alias_ddrs; +}; + +/* Initialize vertice's data for partition dependence graph PG with + PARTITIONS. */ + +static void +init_partition_graph_vertices (struct graph *pg, + vec *partitions) +{ + int i; + partition *partition; + struct pg_vdata *data; + + for (i = 0; partitions->iterate (i, &partition); ++i) + { + data = new pg_vdata; + pg->vertices[i].data = data; + data->id = i; + data->partition = partition; + } +} + +/* Add edge to partition dependence graph PG. Attach vector of data + dependence relations to the EDGE if DDRS isn't NULL. */ + +static void +add_partition_graph_edge (struct graph *pg, int i, int j, vec *ddrs) +{ + struct graph_edge *e = add_edge (pg, i, j); + + /* If the edge is attached with data dependence relations, it means this + dependence edge can be resolved by runtime alias checks. */ + if (ddrs != NULL) + { + struct pg_edata *data = new pg_edata; + + gcc_assert (ddrs->length () > 0); + e->data = data; + data->alias_ddrs = vNULL; + data->alias_ddrs.safe_splice (*ddrs); + } +} + +/* Callback function for graph travesal algorithm. It returns true + if edge E should skipped when traversing the graph. */ + +static bool +pg_skip_alias_edge (struct graph_edge *e) +{ + struct pg_edata *data = (struct pg_edata *)e->data; + return (data != NULL && data->alias_ddrs.length () > 0); +} + +/* Callback function freeing data attached to edge E of graph. */ + +static void +free_partition_graph_edata_cb (struct graph *, struct graph_edge *e, void *) +{ + if (e->data != NULL) + { + struct pg_edata *data = (struct pg_edata *)e->data; + data->alias_ddrs.release (); + delete data; + } +} + +/* Free data attached to vertice of partition dependence graph PG. */ + +static void +free_partition_graph_vdata (struct graph *pg) +{ + int i; + struct pg_vdata *data; + + for (i = 0; i < pg->n_vertices; ++i) + { + data = (struct pg_vdata *)pg->vertices[i].data; + delete data; + } +} + +/* Build and return partition dependence graph for PARTITIONS. RDG is + reduced dependence graph for the loop to be distributed. If IGNORE_ALIAS_P + is true, data dependence caused by possible alias between references + is ignored, as if it doesn't exist at all; otherwise all depdendences + are considered. */ + +static struct graph * +build_partition_graph (struct graph *rdg, + vec *partitions, + bool ignore_alias_p) +{ + int i, j; + struct partition *partition1, *partition2; + graph *pg = new_graph (partitions->length ()); + auto_vec alias_ddrs, *alias_ddrs_p; + + alias_ddrs_p = ignore_alias_p ? NULL : &alias_ddrs; + + init_partition_graph_vertices (pg, partitions); + + for (i = 0; partitions->iterate (i, &partition1); ++i) + { + for (j = i + 1; partitions->iterate (j, &partition2); ++j) + { + /* dependence direction - 0 is no dependence, -1 is back, + 1 is forth, 2 is both (we can stop then, merging will occur). */ + int dir = 0; + + /* If the first partition has reduction, add back edge; if the + second partition has reduction, add forth edge. This makes + sure that reduction partition will be sorted as the last one. */ + if (partition_reduction_p (partition1)) + dir = -1; + else if (partition_reduction_p (partition2)) + dir = 1; + + /* Cleanup the temporary vector. */ + alias_ddrs.truncate (0); + + dir = pg_add_dependence_edges (rdg, dir, partition1->datarefs, + partition2->datarefs, alias_ddrs_p); + + /* Add edge to partition graph if there exists dependence. There + are two types of edges. One type edge is caused by compilation + time known dependence, this type can not be resolved by runtime + alias check. The other type can be resolved by runtime alias + check. */ + if (dir == 1 || dir == 2 + || alias_ddrs.length () > 0) + { + /* Attach data dependence relations to edge that can be resolved + by runtime alias check. */ + bool alias_edge_p = (dir != 1 && dir != 2); + add_partition_graph_edge (pg, i, j, + (alias_edge_p) ? &alias_ddrs : NULL); + } + if (dir == -1 || dir == 2 + || alias_ddrs.length () > 0) + { + /* Attach data dependence relations to edge that can be resolved + by runtime alias check. */ + bool alias_edge_p = (dir != -1 && dir != 2); + add_partition_graph_edge (pg, j, i, + (alias_edge_p) ? &alias_ddrs : NULL); + } + } + } + return pg; +} + +/* Sort partitions in PG by post order and store them in PARTITIONS. */ + +static void +sort_partitions_by_post_order (struct graph *pg, + vec *partitions) +{ + int i; + struct pg_vdata *data; + + /* Now order the remaining nodes in postorder. */ + qsort (pg->vertices, pg->n_vertices, sizeof (vertex), pgcmp); + partitions->truncate (0); + for (i = 0; i < pg->n_vertices; ++i) + { + data = (struct pg_vdata *)pg->vertices[i].data; + if (data->partition) + partitions->safe_push (data->partition); + } +} + +/* Given reduced dependence graph RDG merge strong connected components + of PARTITIONS. If IGNORE_ALIAS_P is true, data dependence caused by + possible alias between references is ignored, as if it doesn't exist + at all; otherwise all depdendences are considered. */ + +static void +merge_dep_scc_partitions (struct graph *rdg, + vec *partitions, + bool ignore_alias_p) +{ + struct partition *partition1, *partition2; + struct pg_vdata *data; + graph *pg = build_partition_graph (rdg, partitions, ignore_alias_p); + int i, j, num_sccs = graphds_scc (pg, NULL); + + /* Strong connected compoenent means dependence cycle, we cannot distribute + them. So fuse them together. */ + if ((unsigned) num_sccs < partitions->length ()) + { + for (i = 0; i < num_sccs; ++i) + { + for (j = 0; partitions->iterate (j, &partition1); ++j) + if (pg->vertices[j].component == i) + break; + for (j = j + 1; partitions->iterate (j, &partition2); ++j) + if (pg->vertices[j].component == i) + { + partition_merge_into (NULL, partition1, + partition2, FUSE_SAME_SCC); + partition1->type = PTYPE_SEQUENTIAL; + (*partitions)[j] = NULL; + partition_free (partition2); + data = (struct pg_vdata *)pg->vertices[j].data; + data->partition = NULL; + } + } + sort_partitions_by_post_order (pg, partitions); + } + gcc_assert (partitions->length () == (unsigned)num_sccs); + free_partition_graph_vdata (pg); + free_graph (pg); +} + +/* Callback function for traversing edge E in graph G. DATA is private + callback data. */ + +static void +pg_collect_alias_ddrs (struct graph *g, struct graph_edge *e, void *data) +{ + int i, j, component; + struct pg_edge_callback_data *cbdata; + struct pg_edata *edata = (struct pg_edata *) e->data; + + /* If the edge doesn't have attached data dependence, it represents + compilation time known dependences. This type dependence cannot + be resolved by runtime alias check. */ + if (edata == NULL || edata->alias_ddrs.length () == 0) + return; + + cbdata = (struct pg_edge_callback_data *) data; + i = e->src; + j = e->dest; + component = cbdata->vertices_component[i]; + /* Vertices are topologically sorted according to compilation time + known dependences, so we can break strong connected components + by removing edges of the opposite direction, i.e, edges pointing + from vertice with smaller post number to vertice with bigger post + number. */ + if (g->vertices[i].post < g->vertices[j].post + /* We only need to remove edges connecting vertices in the same + strong connected component to break it. */ + && component == cbdata->vertices_component[j] + /* Check if we want to break the strong connected component or not. */ + && !bitmap_bit_p (cbdata->sccs_to_merge, component)) + cbdata->alias_ddrs->safe_splice (edata->alias_ddrs); +} + +/* This is the main function breaking strong conected components in + PARTITIONS giving reduced depdendence graph RDG. Store data dependence + relations for runtime alias check in ALIAS_DDRS. */ + +static void +break_alias_scc_partitions (struct graph *rdg, + vec *partitions, + vec *alias_ddrs) +{ + int i, j, num_sccs, num_sccs_no_alias; + /* Build partition dependence graph. */ + graph *pg = build_partition_graph (rdg, partitions, false); + + alias_ddrs->truncate (0); + /* Find strong connected components in the graph, with all dependence edges + considered. */ + num_sccs = graphds_scc (pg, NULL); + /* All SCCs now can be broken by runtime alias checks because SCCs caused by + compilation time known dependences are merged before this function. */ + if ((unsigned) num_sccs < partitions->length ()) + { + struct pg_edge_callback_data cbdata; + auto_bitmap sccs_to_merge; + auto_vec scc_types; + struct partition *partition, *first; + + /* If all paritions in a SCC has the same type, we can simply merge the + SCC. This loop finds out such SCCS and record them in bitmap. */ + bitmap_set_range (sccs_to_merge, 0, (unsigned) num_sccs); + for (i = 0; i < num_sccs; ++i) + { + for (j = 0; partitions->iterate (j, &first); ++j) + if (pg->vertices[j].component == i) + break; + for (++j; partitions->iterate (j, &partition); ++j) + { + if (pg->vertices[j].component != i) + continue; + + if (first->type != partition->type) + { + bitmap_clear_bit (sccs_to_merge, i); + break; + } + } + } + + /* Initialize callback data for traversing. */ + cbdata.sccs_to_merge = sccs_to_merge; + cbdata.alias_ddrs = alias_ddrs; + cbdata.vertices_component = XNEWVEC (int, pg->n_vertices); + /* Record the component information which will be corrupted by next + graph scc finding call. */ + for (i = 0; i < pg->n_vertices; ++i) + cbdata.vertices_component[i] = pg->vertices[i].component; + + /* Collect data dependences for runtime alias checks to break SCCs. */ + if (bitmap_count_bits (sccs_to_merge) != (unsigned) num_sccs) + { + /* Run SCC finding algorithm again, with alias dependence edges + skipped. This is to topologically sort paritions according to + compilation time known dependence. Note the topological order + is stored in the form of pg's post order number. */ + num_sccs_no_alias = graphds_scc (pg, NULL, pg_skip_alias_edge); + gcc_assert (partitions->length () == (unsigned) num_sccs_no_alias); + /* With topological order, we can construct two subgraphs L and R. + L contains edge where x < y in terms of post order, while + R contains edge where x > y. Edges for compilation time + known dependence all fall in R, so we break SCCs by removing all + (alias) edges of in subgraph L. */ + for_each_edge (pg, pg_collect_alias_ddrs, &cbdata); + } + + /* For SCC that doesn't need to be broken, merge it. */ + for (i = 0; i < num_sccs; ++i) + { + if (!bitmap_bit_p (sccs_to_merge, i)) + continue; + + for (j = 0; partitions->iterate (j, &first); ++j) + if (cbdata.vertices_component[j] == i) + break; + for (++j; partitions->iterate (j, &partition); ++j) + { + struct pg_vdata *data; + + if (cbdata.vertices_component[j] != i) + continue; + + partition_merge_into (NULL, first, partition, FUSE_SAME_SCC); + (*partitions)[j] = NULL; + partition_free (partition); + data = (struct pg_vdata *)pg->vertices[j].data; + gcc_assert (data->id == j); + data->partition = NULL; + } + } + } + + sort_partitions_by_post_order (pg, partitions); + free_partition_graph_vdata (pg); + for_each_edge (pg, free_partition_graph_edata_cb, NULL); + free_graph (pg); + + if (dump_file && (dump_flags & TDF_DETAILS)) + { + fprintf (dump_file, "Possible alias data dependence to break:\n"); + dump_data_dependence_relations (dump_file, *alias_ddrs); + } +} + +/* Compute and return an expression whose value is the segment length which + will be accessed by DR in NITERS iterations. */ + +static tree +data_ref_segment_size (struct data_reference *dr, tree niters) +{ + tree segment_length; + + if (integer_zerop (DR_STEP (dr))) + segment_length = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (dr))); + else + segment_length = size_binop (MULT_EXPR, + fold_convert (sizetype, DR_STEP (dr)), + fold_convert (sizetype, niters)); + + return segment_length; +} + +/* Return true if LOOP's latch is dominated by statement for data reference + DR. */ + +static inline bool +latch_dominated_by_data_ref (struct loop *loop, data_reference *dr) +{ + return dominated_by_p (CDI_DOMINATORS, single_exit (loop)->src, + gimple_bb (DR_STMT (dr))); +} + +/* Compute alias check pairs and store them in COMP_ALIAS_PAIRS for LOOP's + data dependence relations ALIAS_DDRS. */ + +static void +compute_alias_check_pairs (struct loop *loop, vec *alias_ddrs, + vec *comp_alias_pairs) +{ + unsigned int i; + unsigned HOST_WIDE_INT factor = 1; + tree niters_plus_one, niters = number_of_latch_executions (loop); + + gcc_assert (niters != NULL_TREE && niters != chrec_dont_know); + niters = fold_convert (sizetype, niters); + niters_plus_one = size_binop (PLUS_EXPR, niters, size_one_node); + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, "Creating alias check pairs:\n"); + + /* Iterate all data dependence relations and compute alias check pairs. */ + for (i = 0; i < alias_ddrs->length (); i++) + { + ddr_p ddr = (*alias_ddrs)[i]; + struct data_reference *dr_a = DDR_A (ddr); + struct data_reference *dr_b = DDR_B (ddr); + tree seg_length_a, seg_length_b; + int comp_res = data_ref_compare_tree (DR_BASE_ADDRESS (dr_a), + DR_BASE_ADDRESS (dr_b)); + + if (comp_res == 0) + comp_res = data_ref_compare_tree (DR_OFFSET (dr_a), DR_OFFSET (dr_b)); + gcc_assert (comp_res != 0); + + if (latch_dominated_by_data_ref (loop, dr_a)) + seg_length_a = data_ref_segment_size (dr_a, niters_plus_one); + else + seg_length_a = data_ref_segment_size (dr_a, niters); + + if (latch_dominated_by_data_ref (loop, dr_b)) + seg_length_b = data_ref_segment_size (dr_b, niters_plus_one); + else + seg_length_b = data_ref_segment_size (dr_b, niters); + + dr_with_seg_len_pair_t dr_with_seg_len_pair + (dr_with_seg_len (dr_a, seg_length_a), + dr_with_seg_len (dr_b, seg_length_b)); + + /* Canonicalize pairs by sorting the two DR members. */ + if (comp_res > 0) + std::swap (dr_with_seg_len_pair.first, dr_with_seg_len_pair.second); + + comp_alias_pairs->safe_push (dr_with_seg_len_pair); + } + + if (tree_fits_uhwi_p (niters)) + factor = tree_to_uhwi (niters); + + /* Prune alias check pairs. */ + prune_runtime_alias_test_list (comp_alias_pairs, factor); + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Improved number of alias checks from %d to %d\n", + alias_ddrs->length (), comp_alias_pairs->length ()); +} + +/* Given data dependence relations in ALIAS_DDRS, generate runtime alias + checks and version LOOP under condition of these runtime alias checks. */ + +static void +version_loop_by_alias_check (struct loop *loop, vec *alias_ddrs) +{ + profile_probability prob; + basic_block cond_bb; + struct loop *nloop; + tree lhs, arg0, cond_expr = NULL_TREE; + gimple_seq cond_stmts = NULL; + gimple *call_stmt = NULL; + auto_vec comp_alias_pairs; + + /* Generate code for runtime alias checks if necessary. */ + gcc_assert (alias_ddrs->length () > 0); + + if (dump_file && (dump_flags & TDF_DETAILS)) + fprintf (dump_file, + "Version loop <%d> with runtime alias check\n", loop->num); + + compute_alias_check_pairs (loop, alias_ddrs, &comp_alias_pairs); + create_runtime_alias_checks (loop, &comp_alias_pairs, &cond_expr); + cond_expr = force_gimple_operand_1 (cond_expr, &cond_stmts, + is_gimple_condexpr, NULL_TREE); + + /* Depend on vectorizer to fold IFN_LOOP_DIST_ALIAS. */ + if (flag_tree_loop_vectorize) + { + /* Generate internal function call for loop distribution alias check. */ + call_stmt = gimple_build_call_internal (IFN_LOOP_DIST_ALIAS, + 2, NULL_TREE, cond_expr); + lhs = make_ssa_name (boolean_type_node); + gimple_call_set_lhs (call_stmt, lhs); + } + else + lhs = cond_expr; + + prob = profile_probability::guessed_always ().apply_scale (9, 10); + initialize_original_copy_tables (); + nloop = loop_version (loop, lhs, &cond_bb, prob, prob.invert (), + prob, prob.invert (), true); + free_original_copy_tables (); + /* Record the original loop number in newly generated loops. In case of + distribution, the original loop will be distributed and the new loop + is kept. */ + loop->orig_loop_num = nloop->num; + nloop->orig_loop_num = nloop->num; + nloop->dont_vectorize = true; + nloop->force_vectorize = false; + + if (call_stmt) + { + /* Record new loop's num in IFN_LOOP_DIST_ALIAS because the original + loop could be destroyed. */ + arg0 = build_int_cst (integer_type_node, loop->orig_loop_num); + gimple_call_set_arg (call_stmt, 0, arg0); + gimple_seq_add_stmt_without_update (&cond_stmts, call_stmt); + } + + if (cond_stmts) + { + gimple_stmt_iterator cond_gsi = gsi_last_bb (cond_bb); + gsi_insert_seq_before (&cond_gsi, cond_stmts, GSI_SAME_STMT); + } + update_ssa (TODO_update_ssa); +} + +/* Return true if loop versioning is needed to distrubute PARTITIONS. + ALIAS_DDRS are data dependence relations for runtime alias check. */ + +static inline bool +version_for_distribution_p (vec *partitions, + vec *alias_ddrs) +{ + /* No need to version loop if we have only one partition. */ + if (partitions->length () == 1) + return false; + + /* Need to version loop if runtime alias check is necessary. */ + return (alias_ddrs->length () > 0); +} + +/* Fuse all partitions if necessary before finalizing distribution. */ + +static void +finalize_partitions (vec *partitions, + vec *alias_ddrs) +{ + unsigned i; + struct partition *a, *partition; + + if (partitions->length () == 1 + || alias_ddrs->length () > 0) + return; + + a = (*partitions)[0]; + if (a->kind != PKIND_NORMAL) + return; + + for (i = 1; partitions->iterate (i, &partition); ++i) + { + /* Don't fuse if partition has different type or it is a builtin. */ + if (partition->type != a->type + || partition->kind != PKIND_NORMAL) + return; + } + + /* Fuse all partitions. */ + for (i = 1; partitions->iterate (i, &partition); ++i) + { + partition_merge_into (NULL, a, partition, FUSE_FINALIZE); + partition_free (partition); + } + partitions->truncate (1); +} + +/* Distributes the code from LOOP in such a way that producer statements + are placed before consumer statements. Tries to separate only the + statements from STMTS into separate loops. Returns the number of + distributed loops. Set NB_CALLS to number of generated builtin calls. + Set *DESTROY_P to whether LOOP needs to be destroyed. */ static int distribute_loop (struct loop *loop, vec stmts, @@ -1698,8 +2372,6 @@ distribute_loop (struct loop *loop, vec stmts, partition *partition; bool any_builtin; int i, nbp; - graph *pg = NULL; - int num_sccs = 1; *destroy_p = false; *nb_calls = 0; @@ -1747,6 +2419,11 @@ distribute_loop (struct loop *loop, vec stmts, auto_vec partitions; rdg_build_partitions (rdg, stmts, &partitions); + /* Can't do runtime alias check if loop niter is unknown. */ + tree niters = number_of_latch_executions (loop); + bool rt_alias_check_p = (niters != NULL_TREE && niters != chrec_dont_know); + auto_vec alias_ddrs; + auto_bitmap stmt_in_all_partitions; bitmap_copy (stmt_in_all_partitions, partitions[0]->stmts); for (i = 1; partitions.iterate (i, &partition); ++i) @@ -1833,81 +2510,14 @@ distribute_loop (struct loop *loop, vec stmts, /* Build the partition dependency graph. */ if (partitions.length () > 1) { - pg = new_graph (partitions.length ()); - struct pgdata { - struct partition *partition; - }; -#define PGDATA(i) ((pgdata *)(pg->vertices[i].data)) - for (i = 0; partitions.iterate (i, &partition); ++i) - { - vertex *v = &pg->vertices[i]; - pgdata *data = new pgdata; - /* FIXME - leaks. */ - v->data = data; - data->partition = partition; - } - struct partition *partition1, *partition2; - for (i = 0; partitions.iterate (i, &partition1); ++i) - for (int j = i + 1; partitions.iterate (j, &partition2); ++j) - { - /* dependence direction - 0 is no dependence, -1 is back, - 1 is forth, 2 is both (we can stop then, merging will occur). */ - int dir = pg_add_dependence_edges (rdg, 0, - partition1->datarefs, - partition2->datarefs); - if (dir == 1 || dir == 2) - add_edge (pg, i, j); - if (dir == -1 || dir == 2) - add_edge (pg, j, i); - } - - /* Add edges to the reduction partition (if any) to force it last. */ - unsigned j; - for (j = 0; partitions.iterate (j, &partition); ++j) - if (partition_reduction_p (partition)) - break; - if (j < partitions.length ()) - { - for (unsigned i = 0; partitions.iterate (i, &partition); ++i) - if (i != j) - add_edge (pg, i, j); - } - - /* Compute partitions we cannot separate and fuse them. */ - num_sccs = graphds_scc (pg, NULL); - for (i = 0; i < num_sccs; ++i) - { - struct partition *first; - int j; - for (j = 0; partitions.iterate (j, &first); ++j) - if (pg->vertices[j].component == i) - break; - for (j = j + 1; partitions.iterate (j, &partition); ++j) - if (pg->vertices[j].component == i) - { - partition_merge_into (NULL, first, - partition, FUSE_SAME_SCC); - first->type = PTYPE_SEQUENTIAL; - partitions[j] = NULL; - partition_free (partition); - PGDATA (j)->partition = NULL; - } - } - - /* Now order the remaining nodes in postorder. */ - qsort (pg->vertices, pg->n_vertices, sizeof (vertex), pgcmp); - partitions.truncate (0); - for (i = 0; i < pg->n_vertices; ++i) - { - pgdata *data = PGDATA (i); - if (data->partition) - partitions.safe_push (data->partition); - delete data; - } - gcc_assert (partitions.length () == (unsigned)num_sccs); - free_graph (pg); + merge_dep_scc_partitions (rdg, &partitions, rt_alias_check_p); + alias_ddrs.truncate (0); + if (rt_alias_check_p && partitions.length () > 1) + break_alias_scc_partitions (rdg, &partitions, &alias_ddrs); } + finalize_partitions (&partitions, &alias_ddrs); + nbp = partitions.length (); if (nbp == 0 || (nbp == 1 && !partition_builtin_p (partitions[0])) @@ -1917,8 +2527,15 @@ distribute_loop (struct loop *loop, vec stmts, goto ldist_done; } + if (version_for_distribution_p (&partitions, &alias_ddrs)) + version_loop_by_alias_check (loop, &alias_ddrs); + if (dump_file && (dump_flags & TDF_DETAILS)) - dump_rdg_partitions (dump_file, partitions); + { + fprintf (dump_file, + "distribute loop <%d> into partitions:\n", loop->num); + dump_rdg_partitions (dump_file, partitions); + } FOR_EACH_VEC_ELT (partitions, i, partition) {