On Fri, 13 Jun 2025 at 10:38, Daniel Krügler <daniel.krueg...@gmail.com> wrote:
>
> Am Fr., 13. Juni 2025 um 11:33 Uhr schrieb Jonathan Wakely
> <jwak...@redhat.com>:
>>
>> The std::uninitialized_{value,default}_construct{,_n} algorithms should
>> be able to create arrays, but that currently fails because when an
>> exception happens they clean up using std::_Destroy and in C++17 that
>> doesn't support destroying arrays. (For C++20 and later, std::destroy
>> does handle destroying arrays.)
>>
>> This commit adjusts the _UninitDestroyGuard RAII type used by those
>> algos so that in C++17 mode it recursively destroys each rank of an
>> array type, only using std::_Destroy for the last rank when it's
>> destroying non-array objects.
>>
>> libstdc++-v3/ChangeLog:
>>
>> PR libstdc++/120397
>> * include/bits/stl_uninitialized.h (_UninitDestroyGuard<I,void>):
>> Add new member function _S_destroy and call it from the
>> destructor (for C++17 only).
>> *
>> testsuite/20_util/specialized_algorithms/uninitialized_default_construct/120397.cc:
>> New test.
>> *
>> testsuite/20_util/specialized_algorithms/uninitialized_value_construct/120397.cc:
>> New test.
>> ---
>>
>> v2: Only define+use _S_destroy for C++17, at Tomasz's request.
>>
>> Tested x86_64-linux.
>>
>> libstdc++-v3/include/bits/stl_uninitialized.h | 21 +++++++++++++++++++
>> .../uninitialized_default_construct/120397.cc | 19 +++++++++++++++++
>> .../uninitialized_value_construct/120397.cc | 19 +++++++++++++++++
>> 3 files changed, 59 insertions(+)
>> create mode 100644
>> libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_default_construct/120397.cc
>> create mode 100644
>> libstdc++-v3/testsuite/20_util/specialized_algorithms/uninitialized_value_construct/120397.cc
>>
>> diff --git a/libstdc++-v3/include/bits/stl_uninitialized.h
>> b/libstdc++-v3/include/bits/stl_uninitialized.h
>> index bde787c2beaa..4b3f81604606 100644
>> --- a/libstdc++-v3/include/bits/stl_uninitialized.h
>> +++ b/libstdc++-v3/include/bits/stl_uninitialized.h
>> @@ -118,7 +118,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> ~_UninitDestroyGuard()
>> {
>> if (__builtin_expect(_M_cur != 0, 0))
>> +#if __cplusplus == 201703L
>> + // std::uninitialized_{value,default}{,_n} can construct array
>> types,
>> + // but std::_Destroy cannot handle them until C++20 (PR 120397).
>> + _S_destroy(_M_first, *_M_cur);
>> +#else
>> std::_Destroy(_M_first, *_M_cur);
>> +#endif
>> }
>>
>> _GLIBCXX20_CONSTEXPR
>> @@ -129,6 +135,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>
>> private:
>> _UninitDestroyGuard(const _UninitDestroyGuard&);
>> +
>> +#if __cplusplus == 201703L
>> + template<typename _Iter>
>> + _GLIBCXX20_CONSTEXPR
>
>
> Since this signature *only* targets C++17, what is the purpose of the
> _GLIBCXX20_CONSTEXPR ?
It's just a leftover from the previous patch, I'll remove it, thanks.
>
>>
>> + static void
>> + _S_destroy(_Iter __first, _Iter __last)
>> + {
>> + using _ValT = typename iterator_traits<_Iter>::value_type;
>> + if constexpr (is_array<_ValT>::value)
>> + for (; __first != __last; ++__first)
>> + _S_destroy(*__first, *__first + extent<_ValT>::value);
>> + else
>> + std::_Destroy(__first, __last);
>> + }
>> +#endif
>> };
>>
>
> - Daniel
>
>
