Implement correct std::variant triviality rules from P0602R4

The std::variant move assignment operator should not be trivial if the
variant is not trivially move constructible.

	* include/std/variant (__detail::__variant::_Traits): Make
	_S_trivial_copy_assign depend on _S_trivial_copy_ctor and make
	_S_trivial_move_assign depend on _S_trivial_move_ctor, as per
	P0602R4.
	(__detail::__variant::_Copy_assign_alias): Only depend on
	_S_trivial_copy_assign, which subsumes _S_trivial_copy_ctor now.
	* testsuite/20_util/variant/compile.cc: Correct checks for trivial
	move assignment operators.

From-SVN: r270510

libstdc++-v3/ChangeLog

 2019-04-23  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/variant (__detail::__variant::_Traits): Make
+	_S_trivial_copy_assign depend on _S_trivial_copy_ctor and make
+	_S_trivial_move_assign depend on _S_trivial_move_ctor, as per
+	P0602R4.
+	(__detail::__variant::_Copy_assign_alias): Only depend on
+	_S_trivial_copy_assign, which subsumes _S_trivial_copy_ctor now.
+	* testsuite/20_util/variant/compile.cc: Correct checks for trivial
+	move assignment operators.
+
 	PR libstdc++/90165
 	* include/std/variant (variant::__not_self): New helper for the
 	is_same_v<remove_cvref_t<T>, variant>==false constraints.

libstdc++-v3/include/std/variant

@@ -289,9 +289,11 @@ namespace __variant
       static constexpr bool _S_trivial_move_ctor =
 	  (is_trivially_move_constructible_v<_Types> && ...);
       static constexpr bool _S_trivial_copy_assign =
-	  _S_trivial_dtor && (is_trivially_copy_assignable_v<_Types> && ...);
+	  _S_trivial_dtor && _S_trivial_copy_ctor
+	  && (is_trivially_copy_assignable_v<_Types> && ...);
       static constexpr bool _S_trivial_move_assign =
-	  _S_trivial_dtor && (is_trivially_move_assignable_v<_Types> && ...);
+	  _S_trivial_dtor && _S_trivial_move_ctor
+	  && (is_trivially_move_assignable_v<_Types> && ...);
 
       // The following nothrow traits are for non-trivial SMFs. Trivial SMFs
       // are always nothrow.
@@ -303,7 +305,8 @@ namespace __variant
 	  (is_nothrow_move_constructible_v<_Types> && ...);
       static constexpr bool _S_nothrow_copy_assign = false;
       static constexpr bool _S_nothrow_move_assign =
-	  _S_nothrow_move_ctor && (is_nothrow_move_assignable_v<_Types> && ...);
+	  _S_nothrow_move_ctor
+	  && (is_nothrow_move_assignable_v<_Types> && ...);
     };
 
   // Defines members and ctors.
@@ -654,9 +657,7 @@ namespace __variant
 
   template<typename... _Types>
     using _Copy_assign_alias =
-	_Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign
-			  && _Traits<_Types...>::_S_trivial_copy_ctor,
-			  _Types...>;
+      _Copy_assign_base<_Traits<_Types...>::_S_trivial_copy_assign, _Types...>;
 
   template<bool, typename... _Types>
     struct _Move_assign_base : _Copy_assign_alias<_Types...>

libstdc++-v3/testsuite/20_util/variant/compile.cc

@@ -522,17 +522,17 @@ void test_triviality()
   TEST_TEMPLATE(=default, =default, =default, =default,         ,  true,  true,  true, false)
   TEST_TEMPLATE(=default, =default, =default,         , =default,  true,  true, false,  true)
   TEST_TEMPLATE(=default, =default, =default,         ,         ,  true,  true, false, false)
-  TEST_TEMPLATE(=default, =default,         , =default, =default,  true, false,  true,  true)
+  TEST_TEMPLATE(=default, =default,         , =default, =default,  true, false,  true, false)
   TEST_TEMPLATE(=default, =default,         , =default,         ,  true, false,  true, false)
-  TEST_TEMPLATE(=default, =default,         ,         , =default,  true, false, false,  true)
+  TEST_TEMPLATE(=default, =default,         ,         , =default,  true, false, false, false)
   TEST_TEMPLATE(=default, =default,         ,         ,         ,  true, false, false, false)
-  TEST_TEMPLATE(=default,         , =default, =default, =default, false,  true,  false,  true)
-  TEST_TEMPLATE(=default,         , =default, =default,         , false,  true,  false, false)
+  TEST_TEMPLATE(=default,         , =default, =default, =default, false,  true, false,  true)
+  TEST_TEMPLATE(=default,         , =default, =default,         , false,  true, false, false)
   TEST_TEMPLATE(=default,         , =default,         , =default, false,  true, false,  true)
   TEST_TEMPLATE(=default,         , =default,         ,         , false,  true, false, false)
-  TEST_TEMPLATE(=default,         ,         , =default, =default, false, false,  false,  true)
-  TEST_TEMPLATE(=default,         ,         , =default,         , false, false,  false, false)
-  TEST_TEMPLATE(=default,         ,         ,         , =default, false, false, false,  true)
+  TEST_TEMPLATE(=default,         ,         , =default, =default, false, false, false, false)
+  TEST_TEMPLATE(=default,         ,         , =default,         , false, false, false, false)
+  TEST_TEMPLATE(=default,         ,         ,         , =default, false, false, false, false)
   TEST_TEMPLATE(=default,         ,         ,         ,         , false, false, false, false)
   TEST_TEMPLATE(        , =default, =default, =default, =default, false, false, false, false)
   TEST_TEMPLATE(        , =default, =default, =default,         , false, false, false, false)