[PATCH] Implement correct std::variant triviality rules from P0602R4

[Jonathan Wakely]

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.

Tested powerpc64le-linux, committed to trunk.



commit be9abfb0cf0ccb183fde175762778409d901f708
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Apr 23 13:31:24 2019 +0100

    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.

diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index d65084eeb1f..0c9f8a39c5c 100644
--- a/libstdc++-v3/include/std/variant
+++ b/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...>
diff --git a/libstdc++-v3/testsuite/20_util/variant/compile.cc 
b/libstdc++-v3/testsuite/20_util/variant/compile.cc
index 6acf5bc627e..c6b18d08258 100644
--- a/libstdc++-v3/testsuite/20_util/variant/compile.cc
+++ b/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)