[PATCH] Fix PR87169

[Richard Biener]

Bootstrapped and tested on x86_64-unkown-linux-gnu, applied.

Richard.

2018-09-03  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87169
	* tree-ssa-sccvn.c (do_rpo_vn): When marking loops for not
	iterating make sure there's no extra backedges from irreducible
	regions feeding the header.  Mark the destination block
	executable.

	* gcc.dg/torture/pr87169.c: New testcase.

Index: gcc/tree-ssa-sccvn.c
===================================================================
--- gcc/tree-ssa-sccvn.c	(revision 264052)
+++ gcc/tree-ssa-sccvn.c	(working copy)
@@ -6360,12 +6360,28 @@ do_rpo_vn (function *fn, edge entry, bit
 	       i < loop_depth (loop) - max_depth; ++i)
 	    {
 	      basic_block header = superloop_at_depth (loop, i)->header;
-	      rpo_state[bb_to_rpo[header->index]].iterate = false;
+	      bool non_latch_backedge = false;
 	      edge e;
 	      edge_iterator ei;
 	      FOR_EACH_EDGE (e, ei, header->preds)
 		if (e->flags & EDGE_DFS_BACK)
-		  e->flags |= EDGE_EXECUTABLE;
+		  {
+		    e->flags |= EDGE_EXECUTABLE;
+		    e->dest->flags |= BB_EXECUTABLE;
+		    /* There can be a non-latch backedge into the header
+		       which is part of an outer irreducible region.  We
+		       cannot avoid iterating this block then.  */
+		    if (!dominated_by_p (CDI_DOMINATORS,
+					 e->src, e->dest))
+		      {
+			if (dump_file && (dump_flags & TDF_DETAILS))
+			  fprintf (dump_file, "non-latch backedge %d -> %d "
+				   "forces iteration of loop %d\n",
+				   e->src->index, e->dest->index, loop->num);
+			non_latch_backedge = true;
+		      }
+		  }
+	      rpo_state[bb_to_rpo[header->index]].iterate = non_latch_backedge;
 	    }
     }
 
Index: gcc/testsuite/gcc.dg/torture/pr87169.c
===================================================================
--- gcc/testsuite/gcc.dg/torture/pr87169.c	(revision 0)
+++ gcc/testsuite/gcc.dg/torture/pr87169.c	(working copy)
@@ -0,0 +1,41 @@
+/* { dg-do compile } */
+/* { dg-additional-options "--param rpo-vn-max-loop-depth=7" } */
+
+int a, b, c;
+
+int main ()
+{ 
+  int d;
+  b = 1;
+L1:
+  for (; b > 1;)
+    goto L2;
+    { 
+      int e[1];
+L3:;
+    }
+L2:
+  while (a)
+    { 
+      d--;
+      goto L1;
+    }
+  while (c)
+    { 
+      if (a)
+	goto L3;
+      if (a)
+	break;
+      if (a)
+	goto L2;
+      while (c)
+	while (c)
+	  while (c)
+	    while (c)
+	      while (c)
+		while (c)
+		  while (c)
+		    ;
+    }
+  return 0;
+}