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libstdc++: Fix missing members in std::allocator<void> 

The changes in 75c6a925da were slightly
incorrect, because the converting constructor should be noexcept, and
the POCMA and is_always_equal traits should still be present in C++20.
This fixes it, and slightly refactors the preprocessor conditions and
order of members. Also add comments explaining things.

The non-standard construct and destroy members added for PR 78052 can be
private if allocator_traits<allocator<void>> is made a friend.

libstdc++-v3/ChangeLog:

	* include/bits/allocator.h (allocator<void>) [C++20]: Add
	missing noexcept to constructor. Restore missing POCMA and
	is_always_equal_traits.
	[C++17]: Make construct and destroy members private and
	declare allocator_traits as a friend.
	* include/bits/memoryfwd.h (allocator_traits): Declare.
	* include/ext/malloc_allocator.h (malloc_allocator::allocate):
	Add nodiscard attribute. Add static assertion for LWG 3307.
	* include/ext/new_allocator.h (new_allocator::allocate): Add
	static assertion for LWG 3307.
	* testsuite/20_util/allocator/void.cc: Check that converting
	constructor is noexcept. Check for propagation traits and
	size_type and difference_type. Check that pointer and
	const_pointer are gone in C++20.
This commit is contained in:
Jonathan Wakely 2021-05-11 15:01:01 +01:00
parent 5ea40269a7
commit 5e3a1ea3d8
5 changed files with 88 additions and 19 deletions
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44
libstdc++-v3/include/bits/allocator.h
View File

@ -60,6 +60,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
* @{
*/
// Since C++20 the primary template should be used for allocator<void>,
// but then it would have a non-trivial default ctor and dtor, which
// would be an ABI change. So C++20 still uses the allocator<void> explicit
// specialization, with the historical ABI properties, but with the same
// members that are present in the primary template.
#if ! _GLIBCXX_INLINE_VERSION
/// allocator<void> specialization.
template<>
class allocator<void>
@ -68,28 +75,40 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
typedef void value_type;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
#if __cplusplus <= 201703L
// These were removed for C++20.
typedef void* pointer;
typedef const void* const_pointer;
template<typename _Tp1>
struct rebind
{ typedef allocator<_Tp1> other; };
#else
allocator() = default;
#endif
template<typename _Up>
constexpr
allocator(const allocator<_Up>&) { }
#endif // ! C++20
#if __cplusplus >= 201103L && __cplusplus <= 201703L
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 2103. std::allocator propagate_on_container_move_assignment
typedef true_type propagate_on_container_move_assignment;
typedef true_type is_always_equal;
#if __cplusplus >= 202002L
allocator() = default;
template<typename _Up>
constexpr
allocator(const allocator<_Up>&) noexcept { }
// No allocate member because it's ill-formed by LWG 3307.
// No deallocate member because it would be undefined to call it
// with any pointer which wasn't obtained from allocate.
#else // ! C++20
private:
// This uses construct and destroy in C++11/14/17 modes.
friend allocator_traits<allocator<void>>;
template<typename _Up, typename... _Args>
void
construct(_Up* __p, _Args&&... __args)
@ -101,11 +120,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
destroy(_Up* __p)
noexcept(std::is_nothrow_destructible<_Up>::value)
{ __p->~_Up(); }
#endif // C++11 to C++17
#endif // C++17
#endif // C++11
};
#endif // ! _GLIBCXX_INLINE_VERSION
/**
* @brief The @a standard allocator, as per [20.4].
* @brief The @a standard allocator, as per C++03 [20.4.1].
*
* See https://gcc.gnu.org/onlinedocs/libstdc++/manual/memory.html#std.util.memory.allocator
* for further details.
@ -119,7 +141,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
typedef _Tp value_type;
typedef size_t size_type;
typedef ptrdiff_t difference_type;
#if __cplusplus <= 201703L
// These were removed for C++20.
typedef _Tp* pointer;
typedef const _Tp* const_pointer;
typedef _Tp& reference;

7
libstdc++-v3/include/bits/memoryfwd.h
View File

@ -63,15 +63,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename>
class allocator;
#if __cplusplus <= 201703L
template<>
class allocator<void>;
#endif
#if __cplusplus >= 201103L
/// Declare uses_allocator so it can be specialized in \<queue\> etc.
/// Declare uses_allocator so it can be specialized in `<queue>` etc.
template<typename, typename>
struct uses_allocator;
template<typename>
struct allocator_traits;
#endif
/// @} group memory

8
libstdc++-v3/include/ext/malloc_allocator.h
View File

@ -99,9 +99,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// NB: __n is permitted to be 0. The C++ standard says nothing
// about what the return value is when __n == 0.
_Tp*
_GLIBCXX_NODISCARD _Tp*
allocate(size_type __n, const void* = 0)
{
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3308. std::allocator<void>().allocate(n)
static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
#endif
if (__builtin_expect(__n > this->_M_max_size(), false))
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS

8
libstdc++-v3/include/ext/new_allocator.h
View File

@ -42,7 +42,7 @@ namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
_GLIBCXX_BEGIN_NAMESPACE_VERSION
/**
* @brief An allocator that uses global new, as per [20.4].
* @brief An allocator that uses global new, as per C++03 [20.4.1].
* @ingroup allocators
*
* This is precisely the allocator defined in the C++ Standard.
@ -102,6 +102,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX_NODISCARD _Tp*
allocate(size_type __n, const void* = static_cast<const void*>(0))
{
#if __cplusplus >= 201103L
// _GLIBCXX_RESOLVE_LIB_DEFECTS
// 3308. std::allocator<void>().allocate(n)
static_assert(sizeof(_Tp) != 0, "cannot allocate incomplete types");
#endif
if (__builtin_expect(__n > this->_M_max_size(), false))
{
// _GLIBCXX_RESOLVE_LIB_DEFECTS

40
libstdc++-v3/testsuite/20_util/allocator/void.cc
View File

@ -33,6 +33,18 @@ test01()
std::allocator_traits<alloc_type>::destroy(a, &i);
}
static_assert( std::allocator<void>::propagate_on_container_move_assignment(),
"POCMA trait should always be present" );
static_assert( std::allocator<void>::is_always_equal(),
"is_always_equal trait should always be present" );
static_assert(
std::is_same<std::allocator<void>::size_type, std::size_t>(),
"size_type is size_t" );
static_assert(
std::is_same<std::allocator<void>::difference_type, std::ptrdiff_t>(),
"size_type is size_t" );
// These properties are formally unspecified, but have always been true for
// the libstdc++ definition of allocator<void>.
static_assert(
@ -48,12 +60,32 @@ static_assert(
std::is_trivially_destructible<std::allocator<void>>::value,
"explicit specialization has trivial destructor");
#if __cplusplus > 201703L
#if __cplusplus >= 202002L
// C++20 removes the allocator<void> explicit specialization, so it can now be
// constructed using the converting constructor from other specializations.
static_assert( std::is_constructible_v<std::allocator<void>,
std::allocator<int>> );
#endif
static_assert( std::is_nothrow_constructible_v<std::allocator<void>,
std::allocator<int>> );
template<typename T>
concept has_pointer = requires { typename T::pointer; };
template<typename T>
concept has_const_pointer = requires { typename T::const_pointer; };
template<typename T>
concept has_size_type = requires { typename T::size_type; };
template<typename T>
concept has_difference_type = requires { typename T::difference_type; };
// These were removed for C++20
static_assert( ! has_pointer<std::allocator<void>> );
static_assert( ! has_const_pointer<std::allocator<void>> );
#else
static_assert(
std::is_same<std::allocator<void>::pointer, void*>(),
"pointer is void*" );
static_assert( std::is_same<std::allocator<void>::const_pointer, const void*>(),
"const_pointer is const void*" );
#endif // C++20
int
main()