re PR tree-optimization/68465 (pass_lim doesn't detect identical loop entry conditions)

2015-11-23  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/68465
	* tree-ssa-sccvn.c (sccvn_dom_walker::before_dom_children):
	Also record equalities from multiple predecessor blocks if
	only one non-backedge exists.

	* gcc.dg/tree-ssa/ssa-fre-52.c: New testcase.

From-SVN: r230764

gcc/ChangeLog

+2015-11-23  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/68465
+	* tree-ssa-sccvn.c (sccvn_dom_walker::before_dom_children):
+	Also record equalities from multiple predecessor blocks if
+	only one non-backedge exists.
+
 2015-11-23  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	PR target/68363

gcc/testsuite/ChangeLog

+2015-11-23  Richard Biener  <rguenther@suse.de>
+
+	PR tree-optimization/68465
+	* gcc.dg/tree-ssa/ssa-fre-52.c: New testcase.
+
 2015-11-23  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
 
 	PR target/68363

gcc/testsuite/gcc.dg/tree-ssa/ssa-fre-52.c

+/* { dg-do compile } */
+/* { dg-options "-O -fdump-tree-fre1" } */
+
+void bar ();
+void foo (int n)
+{
+  if (n > 0)
+    {
+      int j = 0;
+      do
+	{
+	  if (n > 0)
+	    {
+	      int i = 0;
+	      do
+		{
+		  bar ();
+		}
+	      while (i < n);
+	    }
+	}
+      while (j < n);
+    }
+}
+
+/* { dg-final { scan-tree-dump-times "if" 1 "fre1" } } */

gcc/tree-ssa-sccvn.c

@@ -4357,20 +4357,34 @@ sccvn_dom_walker::before_dom_children (basic_block bb)
 
   /* If we have a single predecessor record the equivalence from a
      possible condition on the predecessor edge.  */
-  if (single_pred_p (bb))
+  edge pred_e = NULL;
+  FOR_EACH_EDGE (e, ei, bb->preds)
+    {
+      /* Ignore simple backedges from this to allow recording conditions
+         in loop headers.  */
+      if (dominated_by_p (CDI_DOMINATORS, e->src, e->dest))
+	continue;
+      if (! pred_e)
+	pred_e = e;
+      else
+	{
+	  pred_e = NULL;
+	  break;
+	}
+    }
+  if (pred_e)
     {
-      edge e = single_pred_edge (bb);
       /* Check if there are multiple executable successor edges in
 	 the source block.  Otherwise there is no additional info
 	 to be recorded.  */
       edge e2;
-      FOR_EACH_EDGE (e2, ei, e->src->succs)
-	if (e2 != e
+      FOR_EACH_EDGE (e2, ei, pred_e->src->succs)
+	if (e2 != pred_e
 	    && e2->flags & EDGE_EXECUTABLE)
 	  break;
       if (e2 && (e2->flags & EDGE_EXECUTABLE))
 	{
-	  gimple *stmt = last_stmt (e->src);
+	  gimple *stmt = last_stmt (pred_e->src);
 	  if (stmt
 	      && gimple_code (stmt) == GIMPLE_COND)
 	    {
@@ -4378,11 +4392,11 @@ sccvn_dom_walker::before_dom_children (basic_block bb)
 	      tree lhs = gimple_cond_lhs (stmt);
 	      tree rhs = gimple_cond_rhs (stmt);
 	      record_conds (bb, code, lhs, rhs,
-			    (e->flags & EDGE_TRUE_VALUE) != 0);
+			    (pred_e->flags & EDGE_TRUE_VALUE) != 0);
 	      code = invert_tree_comparison (code, HONOR_NANS (lhs));
 	      if (code != ERROR_MARK)
 		record_conds (bb, code, lhs, rhs,
-			      (e->flags & EDGE_TRUE_VALUE) == 0);
+			      (pred_e->flags & EDGE_TRUE_VALUE) == 0);
 	    }
 	}
     }