libcxx/include/__memory/allocator.h

   1 // -*- C++ -*-
   2 //===----------------------------------------------------------------------===//
   3 //
   4 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   5 // See https://llvm.org/LICENSE.txt for license information.
   6 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   7 //
   8 //===----------------------------------------------------------------------===//
   9
  10 #ifndef _LIBCPP___MEMORY_ALLOCATOR_H
  11 #define _LIBCPP___MEMORY_ALLOCATOR_H
  12
  13 #include <__config>
  14 #include <__cstddef/ptrdiff_t.h>
  15 #include <__memory/addressof.h>
  16 #include <__memory/allocate_at_least.h>
  17 #include <__memory/allocator_traits.h>
  18 #include <__type_traits/is_const.h>
  19 #include <__type_traits/is_constant_evaluated.h>
  20 #include <__type_traits/is_same.h>
  21 #include <__type_traits/is_void.h>
  22 #include <__type_traits/is_volatile.h>
  23 #include <__utility/forward.h>
  24 #include <new>
  25
  26 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
  27 #  pragma GCC system_header
  28 #endif
  29
  30 _LIBCPP_BEGIN_NAMESPACE_STD
  31
  32 template <class _Tp>
  33 class allocator;
  34
  35 #if _LIBCPP_STD_VER <= 17
  36 // These specializations shouldn't be marked _LIBCPP_DEPRECATED_IN_CXX17.
  37 // Specializing allocator<void> is deprecated, but not using it.
  38 template <>
  39 class _LIBCPP_TEMPLATE_VIS allocator<void> {
  40 public:
  41   _LIBCPP_DEPRECATED_IN_CXX17 typedef void* pointer;
  42   _LIBCPP_DEPRECATED_IN_CXX17 typedef const void* const_pointer;
  43   _LIBCPP_DEPRECATED_IN_CXX17 typedef void value_type;
  44
  45   template <class _Up>
  46   struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {
  47     typedef allocator<_Up> other;
  48   };
  49 };
  50 #endif // _LIBCPP_STD_VER <= 17
  51
  52 // This class provides a non-trivial default constructor to the class that derives from it
  53 // if the condition is satisfied.
  54 //
  55 // The second template parameter exists to allow giving a unique type to __non_trivial_if,
  56 // which makes it possible to avoid breaking the ABI when making this a base class of an
  57 // existing class. Without that, imagine we have classes D1 and D2, both of which used to
  58 // have no base classes, but which now derive from __non_trivial_if. The layout of a class
  59 // that inherits from both D1 and D2 will change because the two __non_trivial_if base
  60 // classes are not allowed to share the same address.
  61 //
  62 // By making those __non_trivial_if base classes unique, we work around this problem and
  63 // it is safe to start deriving from __non_trivial_if in existing classes.
  64 template <bool _Cond, class _Unique>
  65 struct __non_trivial_if {};
  66
  67 template <class _Unique>
  68 struct __non_trivial_if<true, _Unique> {
  69   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR __non_trivial_if() _NOEXCEPT {}
  70 };
  71
  72 // allocator
  73 //
  74 // Note: For ABI compatibility between C++20 and previous standards, we make
  75 //       allocator<void> trivial in C++20.
  76
  77 template <class _Tp>
  78 class _LIBCPP_TEMPLATE_VIS allocator : private __non_trivial_if<!is_void<_Tp>::value, allocator<_Tp> > {
  79   static_assert(!is_const<_Tp>::value, "std::allocator does not support const types");
  80   static_assert(!is_volatile<_Tp>::value, "std::allocator does not support volatile types");
  81
  82 public:
  83   typedef size_t size_type;
  84   typedef ptrdiff_t difference_type;
  85   typedef _Tp value_type;
  86   typedef true_type propagate_on_container_move_assignment;
  87 #if _LIBCPP_STD_VER <= 23 || defined(_LIBCPP_ENABLE_CXX26_REMOVED_ALLOCATOR_MEMBERS)
  88   _LIBCPP_DEPRECATED_IN_CXX23 typedef true_type is_always_equal;
  89 #endif
  90
  91   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 allocator() _NOEXCEPT = default;
  92
  93   template <class _Up>
  94   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 allocator(const allocator<_Up>&) _NOEXCEPT {}
  95
  96   [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _Tp* allocate(size_t __n) {
  97     static_assert(sizeof(_Tp) >= 0, "cannot allocate memory for an incomplete type");
  98     if (__n > allocator_traits<allocator>::max_size(*this))
  99       __throw_bad_array_new_length();
 100     if (__libcpp_is_constant_evaluated()) {
 101       return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
 102     } else {
 103       return static_cast<_Tp*>(std::__libcpp_allocate(__n * sizeof(_Tp), _LIBCPP_ALIGNOF(_Tp)));
 104     }
 105   }
 106
 107 #if _LIBCPP_STD_VER >= 23
 108   [[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr allocation_result<_Tp*> allocate_at_least(size_t __n) {
 109     static_assert(sizeof(_Tp) >= 0, "cannot allocate memory for an incomplete type");
 110     return {allocate(__n), __n};
 111   }
 112 #endif
 113
 114   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void deallocate(_Tp* __p, size_t __n) _NOEXCEPT {
 115     if (__libcpp_is_constant_evaluated()) {
 116       ::operator delete(__p);
 117     } else {
 118       std::__libcpp_deallocate((void*)__p, __n * sizeof(_Tp), _LIBCPP_ALIGNOF(_Tp));
 119     }
 120   }
 121
 122   // C++20 Removed members
 123 #if _LIBCPP_STD_VER <= 17
 124   _LIBCPP_DEPRECATED_IN_CXX17 typedef _Tp* pointer;
 125   _LIBCPP_DEPRECATED_IN_CXX17 typedef const _Tp* const_pointer;
 126   _LIBCPP_DEPRECATED_IN_CXX17 typedef _Tp& reference;
 127   _LIBCPP_DEPRECATED_IN_CXX17 typedef const _Tp& const_reference;
 128
 129   template <class _Up>
 130   struct _LIBCPP_DEPRECATED_IN_CXX17 rebind {
 131     typedef allocator<_Up> other;
 132   };
 133
 134   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI pointer address(reference __x) const _NOEXCEPT {
 135     return std::addressof(__x);
 136   }
 137   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI const_pointer address(const_reference __x) const _NOEXCEPT {
 138     return std::addressof(__x);
 139   }
 140
 141   [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_DEPRECATED_IN_CXX17 _Tp* allocate(size_t __n, const void*) {
 142     return allocate(__n);
 143   }
 144
 145   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
 146     return size_type(~0) / sizeof(_Tp);
 147   }
 148
 149   template <class _Up, class... _Args>
 150   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI void construct(_Up* __p, _Args&&... __args) {
 151     ::new ((void*)__p) _Up(std::forward<_Args>(__args)...);
 152   }
 153
 154   _LIBCPP_DEPRECATED_IN_CXX17 _LIBCPP_HIDE_FROM_ABI void destroy(pointer __p) { __p->~_Tp(); }
 155 #endif
 156 };
 157
 158 template <class _Tp, class _Up>
 159 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 160 operator==(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {
 161   return true;
 162 }
 163
 164 #if _LIBCPP_STD_VER <= 17
 165
 166 template <class _Tp, class _Up>
 167 inline _LIBCPP_HIDE_FROM_ABI bool operator!=(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {
 168   return false;
 169 }
 170
 171 #endif
 172
 173 _LIBCPP_END_NAMESPACE_STD
 174
 175 #endif // _LIBCPP___MEMORY_ALLOCATOR_H