* method.c (synthesized_method_walk): operator= can also be constexpr.

From-SVN: r233956

gcc/cp/ChangeLog

 2016-03-03  Jason Merrill  <jason@redhat.com>
 
+	* method.c (synthesized_method_walk): operator= can also be constexpr.
+
 	* pt.c (tsubst_copy_and_build) [LAMBDA_EXPR]: Get
 	LAMBDA_EXPR_RETURN_TYPE from the instantiated closure.
 

gcc/cp/method.c

@@ -1379,9 +1379,18 @@ synthesized_method_walk (tree ctype, special_function_kind sfk, bool const_p,
 
   /* If that user-written default constructor would satisfy the
      requirements of a constexpr constructor (7.1.5), the
-     implicitly-defined default constructor is constexpr.  */
+     implicitly-defined default constructor is constexpr.
+
+     The implicitly-defined copy/move assignment operator is constexpr if
+      - X is a literal type, and
+      - the assignment operator selected to copy/move each direct base class
+	subobject is a constexpr function, and
+      - for each non-static data member of X that is of class type (or array
+	thereof), the assignment operator selected to copy/move that member is a
+	constexpr function.  */
   if (constexpr_p)
-    *constexpr_p = ctor_p;
+    *constexpr_p = ctor_p
+      || (assign_p && cxx_dialect >= cxx14);
 
   move_p = false;
   switch (sfk)

gcc/testsuite/g++.dg/cpp1y/constexpr-assign1.C

+// { dg-do compile { target c++14 } }
+
+struct A { };
+
+struct B
+{
+  A a;
+  constexpr B& operator=(const B&) = default;
+};