re PR sanitizer/81275 (-fsanitize=thread produce incorrect -Wreturn-type warning)

	PR sanitizer/81275
	* tree-cfg.c (group_case_labels_stmt): Don't optimize away
	C++ FE implicitly added __builtin_unreachable () until -Wreturn-type
	is diagnosed.

	* c-c++-common/tsan/pr81275.c: Remove dg-skip-if.

From-SVN: r255296

gcc/ChangeLog

 2017-12-01  Jakub Jelinek  <jakub@redhat.com>
 
+	PR sanitizer/81275
+	* tree-cfg.c (group_case_labels_stmt): Don't optimize away
+	C++ FE implicitly added __builtin_unreachable () until -Wreturn-type
+	is diagnosed.
+
 	PR sanitizer/83219
 	* tree-cfg.c: Include asan.h.
 	(gimple_seq_unreachable_p): Return false for -fsanitize=unreachable.

gcc/testsuite/ChangeLog

+2017-12-01  Jakub Jelinek  <jakub@redhat.com>
+
+	PR sanitizer/81275
+	* c-c++-common/tsan/pr81275.c: Remove dg-skip-if.
+
 2017-12-01  Thomas Koenig  <tkoenig@gcc.gnu.org>
 
 	PR fortran/83224

gcc/testsuite/c-c++-common/tsan/pr81275.c

 /* PR sanitizer/81275 */
 /* { dg-do compile } */
 /* { dg-options "-Wreturn-type -fsanitize=thread" } */
-/* { dg-skip-if "" { c++ } { "*" } { "-O0" } } */
 
 int
 f1 (int a, int b)

gcc/tree-cfg.c

@@ -1750,7 +1750,14 @@ group_case_labels_stmt (gswitch *stmt)
 
       /* Discard cases that have an unreachable destination block.  */
       if (EDGE_COUNT (base_bb->succs) == 0
-	  && gimple_seq_unreachable_p (bb_seq (base_bb)))
+	  && gimple_seq_unreachable_p (bb_seq (base_bb))
+	  /* Don't optimize this if __builtin_unreachable () is the
+	     implicitly added one by the C++ FE too early, before
+	     -Wreturn-type can be diagnosed.  We'll optimize it later
+	     during switchconv pass or any other cfg cleanup.  */
+	  && (gimple_in_ssa_p (cfun)
+	      || (LOCATION_LOCUS (gimple_location (last_stmt (base_bb)))
+		  != BUILTINS_LOCATION)))
 	{
 	  edge base_edge = find_edge (gimple_bb (stmt), base_bb);
 	  if (base_edge != NULL)