This rewrites ranges::construct_at in terms of std::construct_at so that we can piggy back on the compiler's existing support for recognizing placement new within std::construct_at during constexpr evaluation instead of having to additionally teach the compiler about ranges::construct_at.
While we're here, we should also make ranges::construct_at conditionally noexcept like std::construct_at. Tested on x86_64-pc-linux-gnu, does this look OK for trunk? libstdc++-v3/ChangeLog: PR libstdc++/95788 * include/bits/ranges_uninitialized.h: (__construct_at_fn::operator()): Just call std::construct_at. Declare it conditionally noexcept. * testsuite/20_util/specialized_algorithms/construct_at/95788.cc: New test. --- .../include/bits/ranges_uninitialized.h | 6 +-- .../construct_at/95788.cc | 40 +++++++++++++++++++ 2 files changed, 42 insertions(+), 4 deletions(-) create mode 100644 libstdc++-v3/testsuite/20_util/specialized_algorithms/construct_at/95788.cc diff --git a/libstdc++-v3/include/bits/ranges_uninitialized.h b/libstdc++-v3/include/bits/ranges_uninitialized.h index d758078fc03..def086508fb 100644 --- a/libstdc++-v3/include/bits/ranges_uninitialized.h +++ b/libstdc++-v3/include/bits/ranges_uninitialized.h @@ -496,10 +496,8 @@ namespace ranges requires requires { ::new (declval<void*>()) _Tp(declval<_Args>()...); } constexpr _Tp* operator()(_Tp* __location, _Args&&... __args) const - { - return ::new (__detail::__voidify(*__location)) - _Tp(std::forward<_Args>(__args)...); - } + noexcept(noexcept(std::construct_at(__location, declval<_Args>()...))) + { return std::construct_at(__location, std::forward<_Args>(__args)...); } }; inline constexpr __construct_at_fn construct_at{}; diff --git a/libstdc++-v3/testsuite/20_util/specialized_algorithms/construct_at/95788.cc b/libstdc++-v3/testsuite/20_util/specialized_algorithms/construct_at/95788.cc new file mode 100644 index 00000000000..aeb04de1ea3 --- /dev/null +++ b/libstdc++-v3/testsuite/20_util/specialized_algorithms/construct_at/95788.cc @@ -0,0 +1,40 @@ +// 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 <memory> + +constexpr bool test01() +{ + const int sz{1}; + int* data{std::allocator<int>{}.allocate(sz)}; + static_assert(noexcept(std::ranges::construct_at(data, 42))); + std::ranges::construct_at(data, 42); + if (*data != 42) + return false; + std::ranges::destroy_at(data); + std::allocator<int>{}.deallocate(data, sz); + return true; +} + +static_assert(test01()); + +struct S { S(); }; +S *p; +static_assert(!noexcept(std::ranges::construct_at(p))); -- 2.28.0.651.g306ee63a70