PR libstdc++/86874 fix std::variant::swap regression

PR libstdc++/86874
	* include/std/variant (_Copy_ctor_base::_M_destructive_move): Define
	here instead of in _Move_assign_base.
	(_Copy_ctor_base<true, _Types...>::_M_destructive_move): Define.
	(_Copy_assign_base::operator=): Use _M_destructive_move when changing
	the contained value to another alternative.
	(_Move_assign_base::operator=): Likewise.
	(_Move_assign_base::_M_destructive_move): Remove.
	* testsuite/20_util/variant/86874.cc: New test.

From-SVN: r263365

libstdc++-v3/ChangeLog

@@ -1,5 +1,15 @@
 2018-08-07  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/86874
+	* include/std/variant (_Copy_ctor_base::_M_destructive_move): Define
+	here instead of in _Move_assign_base.
+	(_Copy_ctor_base<true, _Types...>::_M_destructive_move): Define.
+	(_Copy_assign_base::operator=): Use _M_destructive_move when changing
+	the contained value to another alternative.
+	(_Move_assign_base::operator=): Likewise.
+	(_Move_assign_base::_M_destructive_move): Remove.
+	* testsuite/20_util/variant/86874.cc: New test.
+
 	PR libstdc++/86861
 	* libsupc++/new_opa.cc [_GLIBCXX_HAVE_MEMALIGN] (aligned_alloc):
 	Replace macro with inline function.

libstdc++-v3/include/std/variant

@@ -506,6 +506,20 @@ namespace __variant
 	  }
       }
 
+      void _M_destructive_move(_Move_ctor_base&& __rhs)
+      {
+	this->~_Move_ctor_base();
+	__try
+	  {
+	    ::new (this) _Move_ctor_base(std::move(__rhs));
+	  }
+	__catch (...)
+	  {
+	    this->_M_index = variant_npos;
+	    __throw_exception_again;
+	  }
+      }
+
       _Move_ctor_base(const _Move_ctor_base&) = default;
       _Move_ctor_base& operator=(const _Move_ctor_base&) = default;
       _Move_ctor_base& operator=(_Move_ctor_base&&) = default;
@@ -516,6 +530,12 @@ namespace __variant
     {
       using _Base = _Copy_ctor_alias<_Types...>;
       using _Base::_Base;
+
+      void _M_destructive_move(_Move_ctor_base&& __rhs)
+      {
+	this->~_Move_ctor_base();
+	::new (this) _Move_ctor_base(std::move(__rhs));
+      }
     };
 
   template<typename... _Types>
@@ -538,22 +558,14 @@ namespace __variant
 	      {
 		static constexpr void (*_S_vtable[])(void*, void*) =
 		  { &__erased_assign<_Types&, const _Types&>... };
-		_S_vtable[__rhs._M_index](this->_M_storage(), __rhs._M_storage());
+		_S_vtable[__rhs._M_index](this->_M_storage(),
+					  __rhs._M_storage());
 	      }
 	  }
 	else
 	  {
 	    _Copy_assign_base __tmp(__rhs);
-	    this->~_Copy_assign_base();
+	    this->_M_destructive_move(std::move(__tmp));
-	    __try
-	      {
-		::new (this) _Copy_assign_base(std::move(__tmp));
-	      }
-	    __catch (...)
-	      {
-		this->_M_index = variant_npos;
-		__throw_exception_again;
-	      }
 	  }
 	__glibcxx_assert(this->_M_index == __rhs._M_index);
 	return *this;
@@ -582,20 +594,6 @@ namespace __variant
       using _Base = _Copy_assign_alias<_Types...>;
       using _Base::_Base;
 
-      void _M_destructive_move(_Move_assign_base&& __rhs)
-      {
-	this->~_Move_assign_base();
-	__try
-	  {
-	    ::new (this) _Move_assign_base(std::move(__rhs));
-	  }
-	__catch (...)
-	  {
-	    this->_M_index = variant_npos;
-	    __throw_exception_again;
-	  }
-      }
-
       _Move_assign_base&
       operator=(_Move_assign_base&& __rhs)
 	  noexcept(_Traits<_Types...>::_S_nothrow_move_assign)
@@ -613,16 +611,7 @@ namespace __variant
 	else
 	  {
 	    _Move_assign_base __tmp(std::move(__rhs));
-	    this->~_Move_assign_base();
+	    this->_M_destructive_move(std::move(__tmp));
-	    __try
-	      {
-		::new (this) _Move_assign_base(std::move(__tmp));
-	      }
-	    __catch (...)
-	      {
-		this->_M_index = variant_npos;
-		__throw_exception_again;
-	      }
 	  }
 	__glibcxx_assert(this->_M_index == __rhs._M_index);
 	return *this;

libstdc++-v3/testsuite/20_util/variant/86874.cc

@@ -0,0 +1,55 @@
+// Copyright (C) 2018 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/>.
+
+// { dg-options "-std=gnu++17" }
+// { dg-do run { target c++17 } }
+
+#include <variant>
+#include <testsuite_hooks.h>
+
+void
+test01()
+{
+  std::variant<std::monostate> v1, v2;
+  std::swap(v1, v2);
+}
+
+void
+test02()
+{
+  std::variant<int> v1{1}, v2{2};
+  std::swap(v1, v2);
+  VERIFY( std::get<0>(v1) == 2 );
+  VERIFY( std::get<0>(v2) == 1 );
+}
+
+void
+test03()
+{
+  std::variant<double, int> v1{1}, v2{2.3};
+  std::swap(v1, v2);
+  VERIFY( std::get<double>(v1) == 2.3 );
+  VERIFY( std::get<int>(v2) == 1 );
+}
+
+int
+main()
+{
+  test01();
+  test02();
+  test03();
+}