| Message ID | 20180807142403.GO25399@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | fix std::variant::swap for trivially-move-assignable types | expand |
On 07/08/18 15:24 +0100, Jonathan Wakely wrote: >This patch fixes the bug, but is it correct? > >IIUC the _M_destructive_move effects don't depend on whether move >assignment is trivial, so should be defined the same way in both >specializations. It also looks like we can use it in the non-trivial >move assignment. > >Should we define _M_destructive_move on _Move_ctor_base instead of >_Move_assign_base, so the duplication could be avoided? Or maybe into _Move_ctor_base as in the attached patch. That allows it to be used in _Copy_assign_base, and means we can omit the try-catch block when the move construction is trivial. diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 66d878142a4..5dd00b05f1f 100644 --- a/libstdc++-v3/include/std/variant +++ b/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> @@ -544,16 +564,7 @@ namespace __variant else { _Copy_assign_base __tmp(__rhs); - this->~_Copy_assign_base(); - __try - { - ::new (this) _Copy_assign_base(std::move(__tmp)); - } - __catch (...) - { - this->_M_index = variant_npos; - __throw_exception_again; - } + this->_M_destructive_move(std::move(__tmp)); } __glibcxx_assert(this->_M_index == __rhs._M_index); return *this; @@ -582,20 +593,6 @@ 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 +610,7 @@ namespace __variant else { _Move_assign_base __tmp(std::move(__rhs)); - this->~_Move_assign_base(); - __try - { - ::new (this) _Move_assign_base(std::move(__tmp)); - } - __catch (...) - { - this->_M_index = variant_npos; - __throw_exception_again; - } + this->_M_destructive_move(std::move(__tmp)); } __glibcxx_assert(this->_M_index == __rhs._M_index); return *this; @@ -638,6 +626,20 @@ 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; + } + } }; template<typename... _Types>
On 7 August 2018 at 17:29, Jonathan Wakely <jwakely@redhat.com> wrote: > On 07/08/18 15:24 +0100, Jonathan Wakely wrote: >> >> This patch fixes the bug, but is it correct? >> >> IIUC the _M_destructive_move effects don't depend on whether move >> assignment is trivial, so should be defined the same way in both >> specializations. It also looks like we can use it in the non-trivial >> move assignment. >> >> Should we define _M_destructive_move on _Move_ctor_base instead of >> _Move_assign_base, so the duplication could be avoided? > > > Or maybe into _Move_ctor_base as in the attached patch. That allows it > to be used in _Copy_assign_base, and means we can omit the try-catch > block when the move construction is trivial. > _Move_ctor_base seems fine to me. I plan to revamp our variant to bring it up to the changes done before C++17 was done, to fix https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85517, and I plan to do it shortly.
On 07/08/18 17:57 +0300, Ville Voutilainen wrote: >On 7 August 2018 at 17:29, Jonathan Wakely <jwakely@redhat.com> wrote: >> On 07/08/18 15:24 +0100, Jonathan Wakely wrote: >>> >>> This patch fixes the bug, but is it correct? >>> >>> IIUC the _M_destructive_move effects don't depend on whether move >>> assignment is trivial, so should be defined the same way in both >>> specializations. It also looks like we can use it in the non-trivial >>> move assignment. >>> >>> Should we define _M_destructive_move on _Move_ctor_base instead of >>> _Move_assign_base, so the duplication could be avoided? >> >> >> Or maybe into _Move_ctor_base as in the attached patch. That allows it >> to be used in _Copy_assign_base, and means we can omit the try-catch >> block when the move construction is trivial. >> > >_Move_ctor_base seems fine to me. I plan to revamp our variant to >bring it up to the changes done before C++17 >was done, to fix https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85517, >and I plan to do it shortly. OK, here's what I've committed after testing. commit 15e32f819c03a268c11ad48e45c87e996be02479 Author: Jonathan Wakely <jwakely@redhat.com> Date: Tue Aug 7 19:06:08 2018 +0100 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. diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 66d878142a4..2d86a704c63 100644 --- a/libstdc++-v3/include/std/variant +++ b/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(); - __try - { - ::new (this) _Copy_assign_base(std::move(__tmp)); - } - __catch (...) - { - this->_M_index = variant_npos; - __throw_exception_again; - } + this->_M_destructive_move(std::move(__tmp)); } __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(); - __try - { - ::new (this) _Move_assign_base(std::move(__tmp)); - } - __catch (...) - { - this->_M_index = variant_npos; - __throw_exception_again; - } + this->_M_destructive_move(std::move(__tmp)); } __glibcxx_assert(this->_M_index == __rhs._M_index); return *this; diff --git a/libstdc++-v3/testsuite/20_util/variant/86874.cc b/libstdc++-v3/testsuite/20_util/variant/86874.cc new file mode 100644 index 00000000000..b595f9581a1 --- /dev/null +++ b/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(); +}
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant index 66d878142a4..7d691c487fd 100644 --- a/libstdc++-v3/include/std/variant +++ b/libstdc++-v3/include/std/variant @@ -613,16 +613,7 @@ namespace __variant else { _Move_assign_base __tmp(std::move(__rhs)); - this->~_Move_assign_base(); - __try - { - ::new (this) _Move_assign_base(std::move(__tmp)); - } - __catch (...) - { - this->_M_index = variant_npos; - __throw_exception_again; - } + _M_destructive_move(std::move(__tmp)); } __glibcxx_assert(this->_M_index == __rhs._M_index); return *this; @@ -638,6 +629,19 @@ 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; + } + } }; template<typename... _Types>