PR libstdc++/95915

	PR libstdc++/95915
	* include/std/variant (_Uninitialized):
	Adjust the condition and the comment.
	* testsuite/20_util/variant/95915.cc: New.
	* testsuite/20_util/variant/compile.cc: Add new test.

(cherry picked from commit 24b54628cfa95194a8de4071c28cb56e6e81c08e)

libstdc++-v3/include/std/variant

@@ -202,15 +202,9 @@ namespace __variant
 	  std::forward<_Variants>(__variants)...);
     }
 
-  // _Uninitialized<T> is guaranteed to be a literal type, even if T is not.
-  // We have to do this, because [basic.types]p10.5.3 (n4606) is not implemented
-  // yet. When it's implemented, _Uninitialized<T> can be changed to the alias
-  // to T, therefore equivalent to being removed entirely.
-  //
-  // Another reason we may not want to remove _Uninitialzied<T> may be that, we
-  // want _Uninitialized<T> to be trivially destructible, no matter whether T
-  // is; but we will see.
-  template<typename _Type, bool = std::is_literal_type_v<_Type>>
+  // _Uninitialized<T> is guaranteed to be a trivially destructible type,
+  // even if T is not.
+  template<typename _Type, bool = std::is_trivially_destructible_v<_Type>>
     struct _Uninitialized;
 
   template<typename _Type>

libstdc++-v3/testsuite/20_util/variant/95915.cc

+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+
+// Copyright (C) 2020 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+#include <variant>
+
+using namespace std;
+
+struct virtual_default_dtor {
+   virtual ~virtual_default_dtor() = default;
+};
+
+void default_ctor()
+{
+  {
+    variant<virtual_default_dtor> a;
+  }
+}
+

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

@@ -84,6 +84,10 @@ struct nonliteral
   bool operator>(const nonliteral&) const;
 };
 
+struct virtual_default_dtor {
+   virtual ~virtual_default_dtor() = default;
+};
+
 void default_ctor()
 {
   static_assert(is_default_constructible_v<variant<int, string>>);
@@ -95,6 +99,9 @@ void default_ctor()
   static_assert(noexcept(variant<int>()));
   static_assert(!noexcept(variant<Empty>()));
   static_assert(noexcept(variant<DefaultNoexcept>()));
+  {
+    variant<virtual_default_dtor> a;
+  }
 }
 
 void copy_ctor()