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From: Aldy Hernandez <aldyh@gcc.gnu.org> To: gcc-cvs@gcc.gnu.org, libstdc++-cvs@gcc.gnu.org Subject: [gcc/devel/ranger] libstdc++: Fix regression in std::move algorithm (PR 93872) Date: Wed, 17 Jun 2020 19:10:41 +0000 (GMT) [thread overview] Message-ID: <20200617191041.6B17A39C5037@sourceware.org> (raw) https://gcc.gnu.org/g:5b904f175ff26269615f148459a8604f45880591 commit 5b904f175ff26269615f148459a8604f45880591 Author: Jonathan Wakely <jwakely@redhat.com> Date: Tue Feb 25 12:21:44 2020 +0000 libstdc++: Fix regression in std::move algorithm (PR 93872) The std::move and std::move_backward algorithms dispatch to the std::__memmove helper when appropriate. That function uses a pointer-to-const for the source values, preventing them from being moved. The two callers of that function have the same problem. Rather than altering __memmove and its callers to work with const or non-const source pointers, this takes a more conservative approach of casting away the const at the point where we want to do a move assignment. This relies on the fact that we only use __memmove when the type is trivially copyable, so we know the move assignment doesn't alter the source anyway. PR libstdc++/93872 * include/bits/stl_algobase.h (__memmove): Cast away const before doing move assignment. * testsuite/25_algorithms/move/93872.cc: New test. * testsuite/25_algorithms/move_backward/93872.cc: New test. Diff: --- libstdc++-v3/ChangeLog | 8 +++++ libstdc++-v3/include/bits/stl_algobase.h | 6 +++- libstdc++-v3/testsuite/25_algorithms/move/93872.cc | 39 ++++++++++++++++++++++ 3 files changed, 52 insertions(+), 1 deletion(-) diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog index 5da5c22775c..f14a6e223ea 100644 --- a/libstdc++-v3/ChangeLog +++ b/libstdc++-v3/ChangeLog @@ -1,3 +1,11 @@ +2020-02-24 Jonathan Wakely <jwakely@redhat.com> + + PR libstdc++/93872 + * include/bits/stl_algobase.h (__memmove): Cast away const before + doing move assignment. + * testsuite/25_algorithms/move/93872.cc: New test. + * testsuite/25_algorithms/move_backward/93872.cc: New test. + 2020-02-24 Patrick Palka <ppalka@redhat.com> PR libstdc++/93884 diff --git a/libstdc++-v3/include/bits/stl_algobase.h b/libstdc++-v3/include/bits/stl_algobase.h index efda15f816e..c6b7148b39c 100644 --- a/libstdc++-v3/include/bits/stl_algobase.h +++ b/libstdc++-v3/include/bits/stl_algobase.h @@ -95,7 +95,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION for(; __num > 0; --__num) { if constexpr (_IsMove) - *__dst = std::move(*__src); + // This const_cast looks unsafe, but we only use this function + // for trivially-copyable types, which means this assignment + // is trivial and so doesn't alter the source anyway. + // See PR 93872 for why it's needed. + *__dst = std::move(*const_cast<_Tp*>(__src)); else *__dst = *__src; ++__src; diff --git a/libstdc++-v3/testsuite/25_algorithms/move/93872.cc b/libstdc++-v3/testsuite/25_algorithms/move/93872.cc new file mode 100644 index 00000000000..c4dd43dfb64 --- /dev/null +++ b/libstdc++-v3/testsuite/25_algorithms/move/93872.cc @@ -0,0 +1,39 @@ +// 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/>. + +// { dg-options "-std=gnu++2a" } +// { dg-do compile { target c++2a } } + +#include <algorithm> + +struct X +{ + X() = default; + + X(const X&) = delete; + X& operator=(const X&) = delete; + + X(X&&) = default; + X& operator=(X&&) = default; +}; + +void +test01() +{ + X a[2], b[2]; + std::move(std::begin(a), std::end(a), std::begin(b)); +}
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