re PR c++/64647 ([C++14] std::__max_element contains code not allowed in constexpr function)

	PR c++/64647
	* constexpr.c (ensure_literal_type_for_constexpr_object): Don't
	give a hard error in a template instantiation.

From-SVN: r219965

gcc/cp/ChangeLog

+2015-01-21  Jason Merrill  <jason@redhat.com>
+
+	PR c++/64647
+	* constexpr.c (ensure_literal_type_for_constexpr_object): Don't
+	give a hard error in a template instantiation.
+
 2015-01-21  Richard Biener  <rguenther@suse.de>
 
 	PR middle-end/64313

gcc/cp/constexpr.c

@@ -102,15 +102,21 @@ ensure_literal_type_for_constexpr_object (tree decl)
       else if (!literal_type_p (type))
 	{
 	  if (DECL_DECLARED_CONSTEXPR_P (decl))
-	    error ("the type %qT of constexpr variable %qD is not literal",
-		   type, decl);
+	    {
+	      error ("the type %qT of constexpr variable %qD is not literal",
+		     type, decl);
+	      explain_non_literal_class (type);
+	    }
 	  else
 	    {
-	      error ("variable %qD of non-literal type %qT in %<constexpr%> "
-		     "function", decl, type);
+	      if (!DECL_TEMPLATE_INSTANTIATION (current_function_decl))
+		{
+		  error ("variable %qD of non-literal type %qT in %<constexpr%> "
+			 "function", decl, type);
+		  explain_non_literal_class (type);
+		}
 	      cp_function_chain->invalid_constexpr = true;
 	    }
-	  explain_non_literal_class (type);
 	  return NULL;
 	}
     }

gcc/testsuite/g++.dg/cpp1y/constexpr-local3.C

+// PR c++/64647
+// { dg-do compile { target c++14 } }
+
+template<typename T>
+constexpr T foo(T t)
+{
+  T tt = t;
+  return tt;
+}
+
+struct X
+{
+  X() { }
+};
+
+int main()
+{
+  X x;
+  foo(x);
+}