c2fb0a1a2e
The C++ LWG recently confirmed that self-move assignment should not have undefined behaviour for standard containers (see the proposed resolution of LWG 2839). The result should be a valid but unspecified value, just like other times when a container is moved from. Our std::list, std::__cxx11::basic_string and unordered containers all have bugs which result in undefined behaviour. For std::list the problem is that we clear the previous contents using _M_clear() instead of clear(). This means the _M_next, _M_prev and _M_size members are not zeroed, and so after we "update" them (with their existing values), we are left with dangling pointers and a non-zero size, but no elements. For the unordered containers the problem is similar. _Hashtable first deallocates the existing contents, then takes ownership of the pointers from the RHS object (which has just had its contents deallocated so the pointers are dangling). For std::basic_string it's a little more subtle. When the string is local (i.e. fits in the SSO buffer) we use char_traits::copy to copy the contents from this->data() to __rhs.data(). When &__rhs == this that copy violates the precondition that the ranges don't overlap. We only need to check for self-move for this case where it's local, because the only other case that can be true for self-move is that it's non-local but the allocators compare equal. In that case the data pointer is neither deallocated nor leaked, so the result is well-defined. This patch also makes a small optimization for std::deque move assignment, to use the efficient move when is_always_equal is false, but the allocators compare equal at runtime. Finally, we need to remove all the Debug Mode checks which abort the program when a self-move is detected, because it's not undefined to do that. Before PR 85828 can be closed we should also look into fixing std::shuffle so it doesn't do any redundant self-swaps. libstdc++-v3/ChangeLog: PR libstdc++/85828 * include/bits/basic_string.h (operator=(basic_string&&)): Check for self-move before copying with char_traits::copy. * include/bits/hashtable.h (operator=(_Hashtable&&)): Check for self-move. * include/bits/stl_deque.h (_M_move_assign1(deque&&, false_type)): Check for equal allocators. * include/bits/stl_list.h (_M_move_assign(list&&, true_type)): Call clear() instead of _M_clear(). * include/debug/formatter.h (__msg_self_move_assign): Change comment. * include/debug/macros.h (__glibcxx_check_self_move_assign): (_GLIBCXX_DEBUG_VERIFY): Remove. * include/debug/safe_container.h (operator=(_Safe_container&&)): Remove assertion check for safe move and make it well-defined. * include/debug/safe_iterator.h (operator=(_Safe_iterator&&)): Remove assertion check for self-move. * include/debug/safe_local_iterator.h (operator=(_Safe_local_iterator&&)): Likewise. * testsuite/21_strings/basic_string/cons/char/self_move.cc: New test. * testsuite/23_containers/deque/cons/self_move.cc: New test. * testsuite/23_containers/forward_list/cons/self_move.cc: New test. * testsuite/23_containers/list/cons/self_move.cc: New test. * testsuite/23_containers/set/cons/self_move.cc: New test. * testsuite/23_containers/unordered_set/cons/self_move.cc: New test. * testsuite/23_containers/vector/cons/self_move.cc: New test.
130 lines
3.6 KiB
C++
130 lines
3.6 KiB
C++
// Safe container implementation -*- C++ -*-
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// Copyright (C) 2014-2020 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// Under Section 7 of GPL version 3, you are granted additional
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// permissions described in the GCC Runtime Library Exception, version
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// 3.1, as published by the Free Software Foundation.
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// You should have received a copy of the GNU General Public License and
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// a copy of the GCC Runtime Library Exception along with this program;
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// see the files COPYING3 and COPYING.RUNTIME respectively. If not, see
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// <http://www.gnu.org/licenses/>.
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/** @file debug/safe_container.h
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* This file is a GNU debug extension to the Standard C++ Library.
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*/
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#ifndef _GLIBCXX_DEBUG_SAFE_CONTAINER_H
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#define _GLIBCXX_DEBUG_SAFE_CONTAINER_H 1
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#include <ext/alloc_traits.h>
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namespace __gnu_debug
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{
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/// Safe class dealing with some allocator dependent operations.
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template<typename _SafeContainer,
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typename _Alloc,
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template<typename> class _SafeBase,
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bool _IsCxx11AllocatorAware = true>
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class _Safe_container
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: public _SafeBase<_SafeContainer>
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{
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typedef _SafeBase<_SafeContainer> _Base;
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_SafeContainer&
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_M_cont() _GLIBCXX_NOEXCEPT
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{ return *static_cast<_SafeContainer*>(this); }
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protected:
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_Safe_container&
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_M_safe() _GLIBCXX_NOEXCEPT
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{ return *this; }
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#if __cplusplus >= 201103L
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_Safe_container() = default;
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_Safe_container(const _Safe_container&) = default;
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_Safe_container(_Safe_container&&) = default;
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_Safe_container(_Safe_container&& __x, const _Alloc& __a)
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: _Safe_container()
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{
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if (__x._M_cont().get_allocator() == __a)
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_Base::_M_swap(__x);
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else
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__x._M_invalidate_all();
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}
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#endif
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public:
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// Copy assignment invalidate all iterators.
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_Safe_container&
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operator=(const _Safe_container&) _GLIBCXX_NOEXCEPT
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{
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this->_M_invalidate_all();
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return *this;
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}
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#if __cplusplus >= 201103L
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_Safe_container&
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operator=(_Safe_container&& __x) noexcept
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{
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if (std::__addressof(__x) == this)
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{
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// Standard containers have a valid but unspecified value after
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// self-move, so we invalidate all debug iterators even if the
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// underlying container happens to preserve its contents.
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this->_M_invalidate_all();
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return *this;
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}
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if (_IsCxx11AllocatorAware)
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{
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typedef __gnu_cxx::__alloc_traits<_Alloc> _Alloc_traits;
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bool __xfer_memory = _Alloc_traits::_S_propagate_on_move_assign()
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|| _M_cont().get_allocator() == __x._M_cont().get_allocator();
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if (__xfer_memory)
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_Base::_M_swap(__x);
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else
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this->_M_invalidate_all();
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}
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else
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_Base::_M_swap(__x);
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__x._M_invalidate_all();
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return *this;
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}
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void
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_M_swap(_Safe_container& __x) noexcept
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{
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if (_IsCxx11AllocatorAware)
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{
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typedef __gnu_cxx::__alloc_traits<_Alloc> _Alloc_traits;
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if (!_Alloc_traits::_S_propagate_on_swap())
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__glibcxx_check_equal_allocs(this->_M_cont()._M_base(),
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__x._M_cont()._M_base());
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}
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_Base::_M_swap(__x);
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}
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#endif
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};
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} // namespace __gnu_debug
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#endif
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