From: Richard Biener <rguenther@suse.de>
Date: Wed, 7 Oct 2020 08:42:12 +0000 (+0200)
Subject: tree-optimization/97307 - improve sinking of loads
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=dae673abd37d400408959497e50fe1f3fbef5533;p=gcc.git

tree-optimization/97307 - improve sinking of loads

This improves the heuristics finding a sink location for loads that does
not cross any store.

2020-10-07  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/97307
	* tree-ssa-sink.c (statement_sink_location): Change heuristic
	for not skipping stores to look for virtual definitions
	rather than uses.

	* gcc.dg/tree-ssa/ssa-sink-17.c: New testcase.
	* gcc.dg/vect/pr65947-3.c: XFAIL.
---

diff --git a/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-17.c b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-17.c
new file mode 100644
index 00000000000..cf2e2a0f766
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/ssa-sink-17.c
@@ -0,0 +1,15 @@
+/* PR tree-optimization/97307  */
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-tree-sink-details" } */
+
+int pure_f(int a, int b) __attribute__((pure));
+int my_f(int a, int b)
+{
+  int x = pure_f(a, b);
+  if (a > 0)
+    return x;
+  return a;
+}
+
+/* We should sink the call to pure_f to the if block.  */
+/* { dg-final { scan-tree-dump "Sinking # VUSE" "sink" } } */
diff --git a/gcc/testsuite/gcc.dg/vect/pr65947-3.c b/gcc/testsuite/gcc.dg/vect/pr65947-3.c
index 6b4077e1a62..8a2608cf0f1 100644
--- a/gcc/testsuite/gcc.dg/vect/pr65947-3.c
+++ b/gcc/testsuite/gcc.dg/vect/pr65947-3.c
@@ -51,6 +51,9 @@ main (void)
   return 0;
 }
 
-/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 2 "vect" } } */
+/* XFAILed because of the fix for PR97307 which sinks the load of a[i], preventing
+   if-conversion to happen.  */
+/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 2 "vect" { xfail *-*-* } } } */
+/* { dg-final { scan-tree-dump-times "LOOP VECTORIZED" 1 "vect" } } */
 /* { dg-final { scan-tree-dump-times "optimizing condition reduction with FOLD_EXTRACT_LAST" 2 "vect" { target vect_fold_extract_last } } } */
 /* { dg-final { scan-tree-dump-not "condition expression based on integer induction." "vect" } } */
diff --git a/gcc/tree-ssa-sink.c b/gcc/tree-ssa-sink.c
index 4cc5195f2f8..ba8e5577e9c 100644
--- a/gcc/tree-ssa-sink.c
+++ b/gcc/tree-ssa-sink.c
@@ -369,10 +369,9 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 	return false;
 
       /* If this is a load then do not sink past any stores.
-	 ???  This is overly simple but cheap.  We basically look
-	 for an existing load with the same VUSE in the path to one
-	 of the sink candidate blocks and we adjust commondom to the
-	 nearest to commondom.  */
+	 Look for virtual definitions in the path from frombb to the sink
+	 location computed from the real uses and if found, adjust
+	 that it a common dominator.  */
       if (gimple_vuse (stmt))
 	{
 	  /* Do not sink loads from hard registers.  */
@@ -383,29 +382,33 @@ statement_sink_location (gimple *stmt, basic_block frombb,
 
 	  imm_use_iterator imm_iter;
 	  use_operand_p use_p;
-	  basic_block found = NULL;
 	  FOR_EACH_IMM_USE_FAST (use_p, imm_iter, gimple_vuse (stmt))
 	    {
 	      gimple *use_stmt = USE_STMT (use_p);
 	      basic_block bb = gimple_bb (use_stmt);
-	      /* For PHI nodes the block we know sth about
-		 is the incoming block with the use.  */
+	      /* For PHI nodes the block we know sth about is the incoming block
+		 with the use.  */
 	      if (gimple_code (use_stmt) == GIMPLE_PHI)
-		bb = EDGE_PRED (bb, PHI_ARG_INDEX_FROM_USE (use_p))->src;
-	      /* Any dominator of commondom would be ok with
-	         adjusting commondom to that block.  */
-	      bb = nearest_common_dominator (CDI_DOMINATORS, bb, commondom);
-	      if (!found)
-		found = bb;
-	      else if (dominated_by_p (CDI_DOMINATORS, bb, found))
-		found = bb;
-	      /* If we can't improve, stop.  */
-	      if (found == commondom)
-		break;
+		{
+		  /* In case the PHI node post-dominates the current insert location
+		     we can disregard it.  */
+		  if (commondom != bb
+		      && dominated_by_p (CDI_POST_DOMINATORS, commondom, bb))
+		    continue;
+		  bb = EDGE_PRED (bb, PHI_ARG_INDEX_FROM_USE (use_p))->src;
+		}
+	      else if (!gimple_vdef (use_stmt))
+		continue;
+	      /* If the use is not dominated by the path entry it is not on
+		 the path.  */
+	      if (!dominated_by_p (CDI_DOMINATORS, bb, frombb))
+		continue;
+	      /* There is no easy way to disregard defs not on the path from
+		 frombb to commondom so just consider them all.  */
+	      commondom = nearest_common_dominator (CDI_DOMINATORS, bb, commondom);
+	      if (commondom == frombb)
+		return false;
 	    }
-	  commondom = found;
-	  if (commondom == frombb)
-	    return false;
 	}
 
       /* Our common dominator has to be dominated by frombb in order to be a