2016-03-31  Nathan Sidwell  <nathan@acm.org>

	PR c++/68475
	* decl.c (check_redeclaration_exception_specification): Check
	regardless of -fno-exceptions.
	* typeck2.c (merge_exception_specifiers): Relax assert by checking
	flag_exceptions too.

	PR c++/68475
	* g++.dg/g++.dg/cpp0x/noexcept29.C: New.

Index: cp/decl.c
===================================================================
--- cp/decl.c	(revision 234641)
+++ cp/decl.c	(working copy)
@@ -1202,16 +1202,19 @@ check_redeclaration_exception_specificat
      specialization, of that function shall have an
      exception-specification with the same set of type-ids.  */
   if (! DECL_IS_BUILTIN (old_decl)
-      && flag_exceptions
       && !comp_except_specs (new_exceptions, old_exceptions, ce_normal))
     {
       const char *msg
 	= "declaration of %q+F has a different exception specifier";
       bool complained = true;
-      if (! DECL_IN_SYSTEM_HEADER (old_decl))
-	error (msg, new_decl);
-      else
+      if (DECL_IN_SYSTEM_HEADER (old_decl))
 	complained = pedwarn (0, OPT_Wsystem_headers, msg, new_decl);
+      else if (!flag_exceptions)
+	/* We used to silently permit mismatched eh specs with
+	   -fno-exceptions, so make them a pedwarn now.  */
+	complained = pedwarn (0, OPT_Wpedantic, msg, new_decl);
+      else
+	error (msg, new_decl);
       if (complained)
 	inform (0, "from previous declaration %q+F", old_decl);
     }
Index: cp/typeck2.c
===================================================================
--- cp/typeck2.c	(revision 234641)
+++ cp/typeck2.c	(working copy)
@@ -2143,7 +2143,7 @@ merge_exception_specifiers (tree list, t
     return add;
   noex = TREE_PURPOSE (list);
   gcc_checking_assert (!TREE_PURPOSE (add)
-		       || errorcount
+		       || errorcount || !flag_exceptions
 		       || cp_tree_equal (noex, TREE_PURPOSE (add)));
 
   /* Combine the dynamic-exception-specifiers, if any.  */
Index: testsuite/g++.dg/cpp0x/noexcept29.C
===================================================================
--- testsuite/g++.dg/cpp0x/noexcept29.C	(nonexistent)
+++ testsuite/g++.dg/cpp0x/noexcept29.C	(working copy)
@@ -0,0 +1,19 @@
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "-fno-exceptions" }
+
+// PR68475 we used to not check eh spec matching with -fno-exceptions,
+// but this could lead to ICEs.
+
+template <typename> struct traits;
+
+template <typename T> struct X
+{
+  void Foo () noexcept (traits <T>::foo ()); // { dg-message "previous declaration" }
+};
+
+template <typename T>
+void
+X<T>::Foo () noexcept (traits <T>::bar ()) // { dg-error "different exception specifier" }
+{
+}
+