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libstdc++: Ignore cv-quals when std::allocator<void> constructs

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When I added the std::allocator_traits<std::allocator<void>>
specialization it broke code like this:

  std::allocate_shared<const int>(std::allocator<void>());

The problem is that allocator_traits<allocator<void>>::construct(a, p)
now uses std::_Construct(p), which only does a static_cast<void*>(p) and
so fails if the pointer has cv-quals.

This changes std::_Construct (and the related std::_Construct_novalue)
to use a C-style cast to (void*) which matches the effects of the
"voidify" helper in the C++20 standard.

libstdc++-v3/ChangeLog:

	* include/bits/stl_construct.h (_Construct, _Construct_novalue):
	Also cast away cv-qualifiers when converting pointer to void.
	* testsuite/20_util/allocator/void.cc: Test construct function
	with cv-qualified types.
This commit is contained in:
Jonathan Wakely 2022-01-13 21:59:13 +00:00
parent d67ba1dce9
commit fc6f1128ae
2 changed files with 17 additions and 2 deletions
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4
libstdc++-v3/include/bits/stl_construct.h
View File

@ -116,7 +116,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
return;
}
#endif
::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...);
::new((void*)__p) _Tp(std::forward<_Args>(__args)...);
}
#else
template<typename _T1, typename _T2>
@ -132,7 +132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _T1>
inline void
_Construct_novalue(_T1* __p)
{ ::new(static_cast<void*>(__p)) _T1; }
{ ::new((void*)__p) _T1; }
template<typename _ForwardIterator>
_GLIBCXX20_CONSTEXPR void

15
libstdc++-v3/testsuite/20_util/allocator/void.cc
View File

@ -87,8 +87,23 @@ static_assert( std::is_same<std::allocator<void>::const_pointer, const void*>(),
"const_pointer is const void*" );
#endif // C++20
void
test02()
{
std::allocator<void> av;
int* p = std::allocator<int>().allocate(1);
const int* c = p;
std::allocator_traits<std::allocator<void>>::construct(av, c, 0);
volatile int* v = p;
std::allocator_traits<std::allocator<void>>::construct(av, v, 0);
const volatile int* cv = p;
std::allocator_traits<std::allocator<void>>::construct(av, cv, 0);
std::allocator<int>().deallocate(p, 1);
}
int
main()
{
test01();
test02();
}