Fix sigsegv in find_same_succ_bb

2017-07-03  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/81192
	* tree-ssa-tail-merge.c (same_succ_flush_bb): Handle
	BB_SAME_SUCC (bb) == NULL.

	* gcc.dg/pr81192.c: New test.

From-SVN: r249893

gcc/ChangeLog

+2017-07-03  Tom de Vries  <tom@codesourcery.com>
+
+	PR tree-optimization/81192
+	* tree-ssa-tail-merge.c (same_succ_flush_bb): Handle
+	BB_SAME_SUCC (bb) == NULL.
+
 2017-07-02  Jan Hubicka  <hubicka@ucw.cz>
 
 	* cfgrtl.c (rtl_verify_edges): Enable checking of profile_probability

gcc/testsuite/ChangeLog

+2017-07-03  Tom de Vries  <tom@codesourcery.com>
+
+	PR tree-optimization/81192
+	* gcc.dg/pr81192.c: New test.
+
 2017-07-02  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	* gfortran/eoshift_3.f90:  New test.

gcc/testsuite/gcc.dg/pr81192.c

+/* { dg-options "-Os -fdump-tree-pre-details" } */
+
+unsigned a;
+int b, c;
+
+static int
+fn1 (int p1, int p2)
+{
+  return p1 > 2147483647 - p2 ? p1 : p1 + p2;
+}
+
+void
+fn2 (void)
+{
+  int j;
+  a = 30;
+  for (; a;)
+    for (; c; b = fn1 (j, 1))
+      ;
+}
+
+/* { dg-final { scan-tree-dump-times "(?n)find_duplicates: <bb .*> duplicate of <bb .*>" 1 "pre" } } */

gcc/tree-ssa-tail-merge.c

@@ -809,6 +809,9 @@ static void
 same_succ_flush_bb (basic_block bb)
 {
   same_succ *same = BB_SAME_SUCC (bb);
+  if (! same)
+    return;
+
   BB_SAME_SUCC (bb) = NULL;
   if (bitmap_single_bit_set_p (same->bbs))
     same_succ_htab->remove_elt_with_hash (same, same->hashval);