[PATCH PR82726/PR70754][2/2]New fix by finding correct root reference in combined chains

[Bin Cheng <Bin dot Cheng at arm dot com>]

Hi,
As described in message of previous patch:

This patch set fixes both PRs in the opposite way: Instead of find dominance
insertion position for root reference, we resort zero-distance references of
combined chain by their position information so that new root reference must
dominate others.  This should be more efficient because we avoid function call
to stmt_dominates_stmt_p.
Bootstrap and test on x86_64 and AArch64 in patch set.  Is it OK?

Thanks,
bin
2017-11-02  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/82726
	PR tree-optimization/70754
	* tree-predcom.c (<map>, INCLUDE_ALGORITHM): New headers.
	(order_drefs_by_pos): New function.
	(combine_chains): Move code setting has_max_use_after to...
	(try_combine_chains): ...here.  New parameter.  Sort combined chains
	according to position information.
	(tree_predictive_commoning_loop): Update call to above function.
	(update_pos_for_combined_chains, pcom_stmt_dominates_stmt_p): New.

gcc/testsuite
2017-11-02  Bin Cheng  <bin.cheng@arm.com>

	PR tree-optimization/82726
	* gcc.dg/tree-ssa/pr82726.c: New test.

From 843cef544a46236e40063416cebc8037736ad18a Mon Sep 17 00:00:00 2001
From: Bin Cheng <binche01@e108451-lin.cambridge.arm.com>
Date: Wed, 1 Nov 2017 17:43:55 +0000
Subject: [PATCH 2/2] pr82726-20171102.txt

---
 gcc/testsuite/gcc.dg/tree-ssa/pr82726.c |  26 ++++++
 gcc/tree-predcom.c                      | 159 ++++++++++++++++++++++++++++----
 2 files changed, 169 insertions(+), 16 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr82726.c

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr82726.c b/gcc/testsuite/gcc.dg/tree-ssa/pr82726.c
new file mode 100644
index 0000000..179f93a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr82726.c
@@ -0,0 +1,26 @@
+/* { dg-do compile } */
+/* { dg-options "-O3 --param tree-reassoc-width=4" } */
+/* { dg-additional-options "-mavx2" { target avx2_runtime } } */
+
+#define N 40
+#define M 128
+unsigned int in[N+M];
+unsigned short out[N];
+
+/* Outer-loop vectorization. */
+
+void
+foo (){
+  int i,j;
+  unsigned int diff;
+
+  for (i = 0; i < N; i++) {
+    diff = 0;
+    for (j = 0; j < M; j+=8) {
+      diff += in[j+i];
+    }
+    out[i]=(unsigned short)diff;
+  }
+
+  return;
+}
diff --git a/gcc/tree-predcom.c b/gcc/tree-predcom.c
index 24d7c9c..a243bce 100644
--- a/gcc/tree-predcom.c
+++ b/gcc/tree-predcom.c
@@ -201,6 +201,8 @@ along with GCC; see the file COPYING3.  If not see
    i * i with ii_last + 2 * i + 1), to generalize strength reduction.  */
 
 #include "config.h"
+#include <map>
+#define INCLUDE_ALGORITHM /* std::sort */
 #include "system.h"
 #include "coretypes.h"
 #include "backend.h"
@@ -1020,6 +1022,14 @@ order_drefs (const void *a, const void *b)
   return (*da)->pos - (*db)->pos;
 }
 
+/* Compares two drefs A and B by their position.  Callback for std::sort.  */
+
+static bool
+order_drefs_by_pos (dref a, dref b)
+{
+  return a->pos < b->pos;
+}
+
 /* Returns root of the CHAIN.  */
 
 static inline dref
@@ -2633,7 +2643,6 @@ combine_chains (chain_p ch1, chain_p ch2)
   bool swap = false;
   chain_p new_chain;
   unsigned i;
-  gimple *root_stmt;
   tree rslt_type = NULL_TREE;
 
   if (ch1 == ch2)
@@ -2675,31 +2684,56 @@ combine_chains (chain_p ch1, chain_p ch2)
       new_chain->refs.safe_push (nw);
     }
 
-  new_chain->has_max_use_after = false;
-  root_stmt = get_chain_root (new_chain)->stmt;
-  for (i = 1; new_chain->refs.iterate (i, &nw); i++)
-    {
-      if (nw->distance == new_chain->length
-	  && !stmt_dominates_stmt_p (nw->stmt, root_stmt))
-	{
-	  new_chain->has_max_use_after = true;
-	  break;
-	}
-    }
-
   ch1->combined = true;
   ch2->combined = true;
   return new_chain;
 }
 
-/* Try to combine the CHAINS.  */
+/* Recursively update position information of all offspring chains to ROOT
+   chain's position information.  */
+
+static void
+update_pos_for_combined_chains (chain_p root)
+{
+  chain_p ch1 = root->ch1, ch2 = root->ch2;
+  dref ref, ref1, ref2;
+  for (unsigned j = 0; (root->refs.iterate (j, &ref)
+			&& ch1->refs.iterate (j, &ref1)
+			&& ch2->refs.iterate (j, &ref2)); ++j)
+    ref1->pos = ref2->pos = ref->pos;
+
+  if (ch1->type == CT_COMBINATION)
+    update_pos_for_combined_chains (ch1);
+  if (ch2->type == CT_COMBINATION)
+    update_pos_for_combined_chains (ch2);
+}
+
+/* Returns true if statement S1 dominates statement S2.  */
+
+static bool
+pcom_stmt_dominates_stmt_p (std::map<gimple *, int> &stmts_map,
+			    gimple *s1, gimple *s2)
+{
+  basic_block bb1 = gimple_bb (s1), bb2 = gimple_bb (s2);
+
+  if (!bb1 || s1 == s2)
+    return true;
+
+  if (bb1 == bb2)
+    return stmts_map[s1] < stmts_map[s2];
+
+  return dominated_by_p (CDI_DOMINATORS, bb2, bb1);
+}
+
+/* Try to combine the CHAINS in LOOP.  */
 
 static void
-try_combine_chains (vec<chain_p> *chains)
+try_combine_chains (struct loop *loop, vec<chain_p> *chains)
 {
   unsigned i, j;
   chain_p ch1, ch2, cch;
   auto_vec<chain_p> worklist;
+  bool combined_p = false;
 
   FOR_EACH_VEC_ELT (*chains, i, ch1)
     if (chain_can_be_combined_p (ch1))
@@ -2721,6 +2755,99 @@ try_combine_chains (vec<chain_p> *chains)
 	    {
 	      worklist.safe_push (cch);
 	      chains->safe_push (cch);
+	      combined_p = true;
+	      break;
+	    }
+	}
+    }
+  if (!combined_p)
+    return;
+
+  /* Setup UID for all statements in dominance order.  */
+  std::map<gimple *, int> stmts_map;
+  basic_block *bbs = get_loop_body_in_dom_order (loop);
+  for (i = 0; i < loop->num_nodes; i++)
+    {
+      int uid = 0;
+      basic_block bb = bbs[i];
+
+      for (gimple_stmt_iterator bsi = gsi_start_phis (bb); !gsi_end_p (bsi);
+	   gsi_next (&bsi))
+	{
+	  gimple *stmt = gsi_stmt (bsi);
+	  if (!virtual_operand_p (gimple_phi_result (as_a<gphi *> (stmt))))
+	    stmts_map[stmt] = uid;
+	}
+
+      for (gimple_stmt_iterator bsi = gsi_start_bb (bb); !gsi_end_p (bsi);
+	   gsi_next (&bsi))
+	{
+	  gimple *stmt = gsi_stmt (bsi);
+	  if (gimple_code (stmt) != GIMPLE_LABEL && !is_gimple_debug (stmt))
+	    stmts_map[stmt] = ++uid;
+	}
+    }
+  free (bbs);
+
+  /* Re-association in combined chains may generate statements different to
+     order of references of the original chain.  We need to keep references
+     of combined chain in dominance order so that all uses will be inserted
+     after definitions.  Note:
+       A) This is necessary for all combined chains.
+       B) This is only necessary for ZERO distance references because other
+	  references inherit value from loop carried PHIs.
+
+     We first update position information for all combined chains.  */
+  dref ref;
+  for (i = 0; chains->iterate (i, &ch1); ++i)
+    {
+      if (ch1->type != CT_COMBINATION || ch1->combined)
+	continue;
+
+      for (j = 0; ch1->refs.iterate (j, &ref); ++j)
+	ref->pos = stmts_map[ref->stmt];
+
+      update_pos_for_combined_chains (ch1);
+    }
+  /* Then sort references according to newly updated position information.  */
+  for (i = 0; chains->iterate (i, &ch1); ++i)
+    {
+      if (ch1->type != CT_COMBINATION && !ch1->combined)
+	continue;
+
+      /* Find the first reference with non-ZERO distance.  */
+      if (ch1->length == 0)
+	j = ch1->refs.length();
+      else
+	{
+	  for (j = 0; ch1->refs.iterate (j, &ref); ++j)
+	    if (ref->distance != 0)
+	      break;
+	}
+
+      /* Sort all ZERO distance references by position.  */
+      std::sort (&ch1->refs[0], &ch1->refs[0] + j, order_drefs_by_pos);
+
+      if (ch1->combined)
+	continue;
+
+      /* For ZERO length chain, has_max_use_after must be true since root
+	 combined stmt must dominates others.  */
+      if (ch1->length == 0)
+	{
+	  ch1->has_max_use_after = true;
+	  continue;
+	}
+      /* Check if there is use at max distance after root for combined chains
+	 and set flag accordingly.  */
+      ch1->has_max_use_after = false;
+      gimple *root_stmt = get_chain_root (ch1)->stmt;
+      for (j = 1; ch1->refs.iterate (j, &ref); ++j)
+	{
+	  if (ref->distance == ch1->length
+	      && !pcom_stmt_dominates_stmt_p (stmts_map, ref->stmt, root_stmt))
+	    {
+	      ch1->has_max_use_after = true;
 	      break;
 	    }
 	}
@@ -3058,7 +3185,7 @@ tree_predictive_commoning_loop (struct loop *loop)
   loop_closed_ssa = prepare_finalizers (loop, chains);
 
   /* Try to combine the chains that are always worked with together.  */
-  try_combine_chains (&chains);
+  try_combine_chains (loop, &chains);
 
   insert_init_seqs (loop, chains);
 
-- 
1.9.1