[PATCH] [PR tree-optimization/68013] Make sure first block in FSM path

is in VISITED_BBs

	PR tree-optimization/68013
	* tree-ssa-threadbackward.c
	(fsm_find_control_statement_thread_paths): Make sure the first block
	in the path is in VISITED_BBs.

	PR tree-optimization/68013
	* gcc.c-torture/compile/pr68013.c: New test.

From-SVN: r229375

gcc/ChangeLog

+2015-10-26  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/68013
+	* tree-ssa-threadbackward.c
+	(fsm_find_control_statement_thread_paths): Make sure the first block
+	in the path is in VISITED_BBs.
+
 2015-10-26  Richard Biener  <rguenther@suse.de>
 	Dominik Vogt  <vogt@linux.vnet.ibm.com>
 

gcc/testsuite/ChangeLog

+2015-10-26  Jeff Law  <law@redhat.com>
+
+	PR tree-optimization/68013
+	* gcc.c-torture/compile/pr68013.c: New test.
+
 2015-10-26  Richard Biener  <rguenther@suse.de>
 	Dominik Vogt  <vogt@linux.vnet.ibm.com>
 

gcc/testsuite/gcc.c-torture/compile/pr68013.c

+int a, b, c, d, e, f;
+
+void
+fn1 ()
+{
+  for (; e;)
+    {
+      e = f;
+      for (; b;)
+	{
+	  b = a;
+	  f = a || d ? 0 : c;
+	}
+      d = 0;
+    }
+}

gcc/tree-ssa-threadbackward.c

@@ -136,6 +136,11 @@ fsm_find_control_statement_thread_paths (tree name,
       vec<basic_block, va_gc> *next_path;
       vec_alloc (next_path, n_basic_blocks_for_fn (cfun));
 
+      /* When VAR_BB == LAST_BB_IN_PATH, then the first block in the path
+	 will already be in VISITED_BBS.  When they are not equal, then we
+	 must ensure that first block is accounted for to ensure we do not
+	 create bogus jump threading paths.  */
+      visited_bbs->add ((*path)[0]);
       FOR_EACH_EDGE (e, ei, last_bb_in_path->preds)
 	{
 	  hash_set<basic_block> *visited_bbs = new hash_set<basic_block>;