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* [PATCH GCC][13/13]Distribute loop with loop versioning under runtime alias check
@ 2017-06-12 17:03 Bin Cheng
  2017-06-20  9:22 ` Bin.Cheng
  0 siblings, 1 reply; 16+ messages in thread
From: Bin Cheng @ 2017-06-12 17:03 UTC (permalink / raw)
  To: gcc-patches; +Cc: nd

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Hi,
This is the main patch rewriting loop distribution in order to handle hmmer.
It improves loop distribution by versioning loop under runtime alias check conditions.
As described in comments, the patch basically 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.

Also, there are some more to improve in the future (which isn't difficult I think):
   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

Bootstrap and test on x86_64 and AArch64.  Is it OK?

Thanks,
bin
2017-06-07  Bin Cheng  <bin.cheng@arm.com>

	* tree-loop-distribution.c: Add general explanantion on the pass.
	(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 fustion code as functions.


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From ab801ff60a3a92d7ee90b422b89d9a96a003b7ba Mon Sep 17 00:00:00 2001
From: Bin Cheng <binche01@e108451-lin.cambridge.arm.com>
Date: Fri, 9 Jun 2017 14:24:52 +0100
Subject: [PATCH 13/13] loop-distribution-20170607.txt

---
 gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c |   3 +-
 gcc/testsuite/gcc.dg/tree-ssa/ldist-13.c |   5 +-
 gcc/testsuite/gcc.dg/tree-ssa/ldist-14.c |   5 +-
 gcc/testsuite/gcc.dg/tree-ssa/ldist-4.c  |   4 +-
 gcc/tree-loop-distribution.c             | 843 +++++++++++++++++++++++++++----
 5 files changed, 743 insertions(+), 117 deletions(-)

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c b/gcc/testsuite/gcc.dg/tree-ssa/ldist-12.c
index 53551ca..625dd92 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 ba39d4d..8c9fd56 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 48c1040..fa4d1a8 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 c36daf071..4def9b4 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 167155e..b28a499 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 dependences between statements.
+     3) Apart from RDG, compute data dependences 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 parallelly; 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 dependences.
+	The vertices (PG:V) model all partitions and the edges (PG:E) model
+	all data dependences 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
+	dependences because of possible alias relation of data references.
+	We categorize PG's edge to two types: "true" edge that represents
+	compilation time known data dependences; "alias" edge for all other
+	data dependences.
+     6) Traverse subgraph of PG as if all "alias" edges don't exist.  Merge
+	partitions in each strong connected commponent (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 dependences of the removed "alias" edges.  Create
+	runtime alias checks for collected data dependences.
+     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"
@@ -1676,11 +1724,14 @@ 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<ddr_p> *alias_ddrs)
 {
   unsigned i, j;
   bitmap_iterator bi, bj;
@@ -1694,11 +1745,12 @@ 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];
 	  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)))
 	    {
@@ -1707,14 +1759,33 @@ 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)
@@ -1722,12 +1793,10 @@ 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;
@@ -1754,11 +1823,635 @@ 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<ddr_p> 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<ddr_p> *alias_ddrs;
+};
+
+/* Initialize vertice's data for partition dependence graph PG with
+   PARTITIONS.  */
+
+static void
+init_partition_graph_vertices (struct graph *pg,
+			       vec<struct partition *> *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 <I, J> 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<ddr_p> *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<struct partition *> *partitions,
+		       bool ignore_alias_p)
+{
+  int i, j;
+  struct partition *partition1, *partition2;
+  graph *pg = new_graph (partitions->length ());
+  auto_vec<ddr_p> 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->writes,
+					 partition2->reads, alias_ddrs_p);
+	  if (dir != 2)
+	    dir = pg_add_dependence_edges (rdg, dir, partition1->reads,
+					   partition2->writes, alias_ddrs_p);
+	  if (dir != 2)
+	    dir = pg_add_dependence_edges (rdg, dir, partition1->writes,
+					   partition2->writes, 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<struct partition *> *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<struct partition *> *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 (partition1, partition2, FUSE_SAME_SCC);
+		(*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<struct partition *> *partitions,
+			    vec<ddr_p> *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<enum partition_type> 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 <x, y> where x < y in terms of post order, while
+	     R contains edge <x, y> 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 (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<ddr_p> *alias_ddrs,
+			   vec<dr_with_seg_len_pair_t> *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<ddr_p> *alias_ddrs)
+{
+  unsigned then_prob, else_prob, then_scale, else_scale;
+  basic_block cond_bb;
+  struct loop *nloop;
+  tree lhs, arg0, cond_expr = NULL_TREE;
+  gimple_seq cond_stmts = NULL;
+  gimple *stmt;
+  auto_vec<dr_with_seg_len_pair_t> comp_alias_pairs;
+
+  /* Generate code for runtime alias checks if necessary.  */
+  if (alias_ddrs->length () > 0)
+    {
+      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);
+      then_prob = 9 * REG_BR_PROB_BASE / 10;
+      else_prob = REG_BR_PROB_BASE - then_prob;
+      then_scale = 9 * REG_BR_PROB_BASE / 10;
+      else_scale = REG_BR_PROB_BASE - then_scale;
+    }
+  else
+    {
+      cond_expr = boolean_true_node;
+      /* Use REG_BR_PROB_BASE for both branches since only one branch
+	 will be kept in the end.  */
+      then_prob = REG_BR_PROB_BASE;
+      else_prob = REG_BR_PROB_BASE;
+      then_scale = REG_BR_PROB_BASE;
+      else_scale = REG_BR_PROB_BASE;
+    }
+
+  /* Depend on vectorizer to fold IFN_LOOP_DIST_ALIAS.  */
+  if (flag_tree_loop_vectorize)
+    {
+      /* Generate internal function call for loop distribution alias check.  */
+      arg0 = build_int_cst (integer_type_node, loop->num);
+      stmt = gimple_build_call_internal (IFN_LOOP_DIST_ALIAS,
+					 2, arg0, cond_expr);
+      lhs = make_ssa_name (boolean_type_node);
+      gimple_call_set_lhs (stmt, lhs);
+      gimple_seq_add_stmt (&cond_stmts, stmt);
+    }
+  else
+    lhs = cond_expr;
+
+  if (dump_file && (dump_flags & TDF_DETAILS))
+    fprintf (dump_file,
+	     "Version loop <%d> with runtime alias check\n", loop->num);
+
+  initialize_original_copy_tables ();
+  nloop = loop_version (loop, lhs, &cond_bb, then_prob,
+			else_prob, then_scale, else_scale, true);
+  free_original_copy_tables ();
+  nloop->aux = (void *)nloop;
+  /* Record the original loop number in newly generated loops.  */
+  nloop->ldist_alias_id = loop->num;
+  nloop->dont_vectorize = true;
+  nloop->force_vectorize = false;
+
+  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<struct partition *> *partitions,
+			    vec<ddr_p> *alias_ddrs)
+{
+  unsigned i;
+  struct partition *partition;
+
+  /* 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.  */
+  if (alias_ddrs->length () > 0)
+    return true;
+
+  /* Don't version the loop with call to IFN_LOOP_DIST_ALIAS if
+     vectorizer is not enable because no other pass can fold it.  */
+  if (!flag_tree_loop_vectorize)
+    return false;
+
+  /* Don't version loop if any partition is builtin.  */
+  for (i = 0; partitions->iterate (i, &partition); ++i)
+    {
+      if (partition->kind != PKIND_NORMAL)
+	break;
+    }
+  return (i == partitions->length ());
+}
+
+/* Fuse all partitions if necessary before finalizing distribution.  */
+
+static void
+finalize_partitions (vec<struct partition *> *partitions,
+		     vec<ddr_p> *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 (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<gimple *> stmts,
@@ -1768,8 +2461,6 @@ distribute_loop (struct loop *loop, vec<gimple *> stmts,
   partition *partition;
   bool any_builtin;
   int i, nbp;
-  graph *pg = NULL;
-  int num_sccs = 1;
 
   *destroy_p = false;
   *nb_calls = 0;
@@ -1826,6 +2517,11 @@ distribute_loop (struct loop *loop, vec<gimple *> stmts,
   ddrs_vec = new vec<ddr_p> ();
   ddrs_table = new hash_table<ddr_entry_hasher> (389);
 
+  /* 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<ddr_p> alias_ddrs;
+
   auto_bitmap stmt_in_all_partitions;
   auto_vec<struct partition *, 3> partitions;
   bitmap_set_range (stmt_in_all_partitions, 0, rdg->n_vertices);
@@ -1912,88 +2608,14 @@ distribute_loop (struct loop *loop, vec<gimple *> 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 = 0;
-	    dir = pg_add_dependence_edges (rdg, dir,
-					   partition1->writes,
-					   partition2->reads);
-	    if (dir != 2)
-	      dir = pg_add_dependence_edges (rdg, dir,
-					     partition1->reads,
-					     partition2->writes);
-	    if (dir != 2)
-	      dir = pg_add_dependence_edges (rdg, dir,
-					     partition1->writes,
-					     partition2->writes);
-	    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 (first, partition, FUSE_SAME_SCC);
-		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]))
@@ -2003,8 +2625,15 @@ distribute_loop (struct loop *loop, vec<gimple *> 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)
     {
-- 
1.9.1


^ permalink raw reply	[flat|nested] 16+ messages in thread
end of thread, other threads:[~2017-07-18  9:04 UTC | newest]

Thread overview: 16+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2017-06-12 17:03 [PATCH GCC][13/13]Distribute loop with loop versioning under runtime alias check Bin Cheng
2017-06-20  9:22 ` Bin.Cheng
2017-06-23 10:30   ` Bin.Cheng
2017-06-27 12:44     ` Richard Biener
2017-06-27 14:07       ` Bin.Cheng
2017-06-28 10:58         ` Richard Biener
2017-06-28 11:46           ` Bin.Cheng
2017-06-28 12:29             ` Richard Biener
2017-06-28 13:09               ` Bin.Cheng
2017-06-30 10:43                 ` Bin.Cheng
2017-07-03 11:50                   ` Richard Biener
2017-07-10  9:32                   ` Christophe Lyon
2017-07-10  9:39                     ` Bin.Cheng
2017-07-17 10:06                     ` Bin.Cheng
2017-07-17 12:09                       ` Christophe Lyon
2017-07-18  9:04                         ` Bin.Cheng

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