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libstdc++: Fix regression in std::_Construct (PR 94831) 

By trying to reuse the existing std::_Construct function as a wrapper
for std::construct_at I introduced regressions, because changing
std::_Construct to return non-void made it ill-formed for array types.

The solution is to revert _Construct to its former state, and change
allocator_traits::construct to explicitly call construct_at instead.
This decouples all the existing callers of _Construct from the new
construct_at requirements.

	PR libstdc++/94831
	* include/bits/alloc_traits.h (_S_construct): Restore placement
	new-expression for C++11/14/17 and call std::construct_at directly
	for C++20.
	* include/bits/stl_construct.h (_Construct): Revert to non-constexpr
	function returning void.
	* testsuite/20_util/specialized_algorithms/
	uninitialized_value_construct/94831.cc: New test.
	* testsuite/23_containers/vector/cons/94831.cc: New test.
This commit is contained in:
Jonathan Wakely 2020-04-28 23:26:21 +01:00
parent 50714f45ee
commit 162c40a4c1
5 changed files with 84 additions and 14 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
libstdc++-v3/ChangeLog
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@ -1,3 +1,15 @@
2020-04-28 Jonathan Wakely <jwakely@redhat.com>
PR libstdc++/94831
* include/bits/alloc_traits.h (_S_construct): Restore placement
new-expression for C++11/14/17 and call std::construct_at directly
for C++20.
* include/bits/stl_construct.h (_Construct): Revert to non-constexpr
function returning void.
* testsuite/20_util/specialized_algorithms/
uninitialized_value_construct/94831.cc: New test.
* testsuite/23_containers/vector/cons/94831.cc: New test.
2020-04-28 Patrick Palka <ppalka@redhat.com>
LWG 3433 subrange::advance(n) has UB when n < 0

8
libstdc++-v3/include/bits/alloc_traits.h
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@ -253,7 +253,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_S_construct(_Alloc&, _Tp* __p, _Args&&... __args)
noexcept(noexcept(::new((void*)__p)
_Tp(std::forward<_Args>(__args)...)))
{ std::_Construct(__p, std::forward<_Args>(__args)...); }
{
#if __cplusplus <= 201703L
::new((void*)__p) _Tp(std::forward<_Args>(__args)...);
#else
std::construct_at(__p, std::forward<_Args>(__args)...);
#endif
}
template<typename _Alloc2, typename _Tp>
static _GLIBCXX14_CONSTEXPR auto

20
libstdc++-v3/include/bits/stl_construct.h
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@ -65,9 +65,9 @@
* std::destroy_n, and the C++20 function std::construct_at.
* It also provides std::_Construct, std::_Destroy,and std::_Destroy_n functions
* which are defined in all standard modes and so can be used in C++98-14 code.
* The _Construct and _Destroy functions will dispatch to construct_at and
* destroy_at during constant evaluation, because calls to those functions are
* intercepted by the compiler to allow use in constant expressions.
* The _Destroy functions will dispatch to destroy_at during constant
* evaluation, because calls to that function are intercepted by the compiler
* to allow use in constant expressions.
*/
namespace std _GLIBCXX_VISIBILITY(default)
@ -104,23 +104,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
*/
#if __cplusplus >= 201103L
template<typename _Tp, typename... _Args>
constexpr _Tp*
inline void
_Construct(_Tp* __p, _Args&&... __args)
{
#if __cplusplus > 201703L
return std::construct_at(__p, std::forward<_Args>(__args)...);
#else
return ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...);
#endif
}
{ ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...); }
#else
template<typename _T1, typename _T2>
inline _T1*
inline void
_Construct(_T1* __p, const _T2& __value)
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 402. wrong new expression in [some_]allocator::construct
return ::new(static_cast<void*>(__p)) _T1(__value);
::new(static_cast<void*>(__p)) _T1(__value);
}
#endif

29
libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_value_construct/94831.cc Normal file
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@ -0,0 +1,29 @@
// 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++17" }
// { dg-do compile { target c++17 } }
#include <memory>
void
test01()
{
// PR libstdc++/94831
float i[2];
std::uninitialized_value_construct(&i, &i + 1);
}

29
libstdc++-v3/testsuite/23_containers/vector/cons/94831.cc Normal file
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@ -0,0 +1,29 @@
// 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-do compile { target c++11 } }
#include <vector>
void
test01()
{
// PR libstdc++/94831.cc
// We allow this in C++11 and later as a GNU extension.
// FIXME: make it ill-formed when __STRICT_ANSI__ is defined.
std::vector<float[2]> v(1u);
}