1 //===----------------------------------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
9 #ifndef _LIBCPP___ALGORITHM_COPY_MOVE_COMMON_H
10 #define _LIBCPP___ALGORITHM_COPY_MOVE_COMMON_H
11 
12 #include <__algorithm/iterator_operations.h>
13 #include <__algorithm/unwrap_iter.h>
14 #include <__algorithm/unwrap_range.h>
15 #include <__config>
16 #include <__iterator/iterator_traits.h>
17 #include <__memory/pointer_traits.h>
18 #include <__string/constexpr_c_functions.h>
19 #include <__type_traits/enable_if.h>
20 #include <__type_traits/is_always_bitcastable.h>
21 #include <__type_traits/is_constant_evaluated.h>
22 #include <__type_traits/is_copy_constructible.h>
23 #include <__type_traits/is_trivially_assignable.h>
24 #include <__type_traits/is_trivially_copyable.h>
25 #include <__type_traits/is_volatile.h>
26 #include <__utility/move.h>
27 #include <__utility/pair.h>
28 #include <cstddef>
29 
30 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
31 #  pragma GCC system_header
32 #endif
33 
34 _LIBCPP_BEGIN_NAMESPACE_STD
35 
36 // Type traits.
37 
38 template <class _From, class _To>
39 struct __can_lower_copy_assignment_to_memmove {
40   static const bool value =
41     // If the types are always bitcastable, it's valid to do a bitwise copy between them.
42     __is_always_bitcastable<_From, _To>::value &&
43     // Reject conversions that wouldn't be performed by the regular built-in assignment (e.g. between arrays).
44     is_trivially_assignable<_To&, const _From&>::value &&
45     // `memmove` doesn't accept `volatile` pointers, make sure the optimization SFINAEs away in that case.
46     !is_volatile<_From>::value &&
47     !is_volatile<_To>::value;
48 };
49 
50 template <class _From, class _To>
51 struct __can_lower_move_assignment_to_memmove {
52   static const bool value =
53     __is_always_bitcastable<_From, _To>::value &&
54     is_trivially_assignable<_To&, _From&&>::value &&
55     !is_volatile<_From>::value &&
56     !is_volatile<_To>::value;
57 };
58 
59 // `memmove` algorithms implementation.
60 
61 template <class _In, class _Out>
62 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
63 __copy_trivial_impl(_In* __first, _In* __last, _Out* __result) {
64   const size_t __n = static_cast<size_t>(__last - __first);
65 
66   std::__constexpr_memmove(__result, __first, __element_count(__n));
67 
68   return std::make_pair(__last, __result + __n);
69 }
70 
71 template <class _In, class _Out>
72 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
73 __copy_backward_trivial_impl(_In* __first, _In* __last, _Out* __result) {
74   const size_t __n = static_cast<size_t>(__last - __first);
75   __result -= __n;
76 
77   std::__constexpr_memmove(__result, __first, __element_count(__n));
78 
79   return std::make_pair(__last, __result);
80 }
81 
82 // Iterator unwrapping and dispatching to the correct overload.
83 
84 template <class _F1, class _F2>
85 struct __overload : _F1, _F2 {
86   using _F1::operator();
87   using _F2::operator();
88 };
89 
90 template <class _InIter, class _Sent, class _OutIter, class = void>
91 struct __can_rewrap : false_type {};
92 
93 template <class _InIter, class _Sent, class _OutIter>
94 struct __can_rewrap<_InIter,
95                     _Sent,
96                     _OutIter,
97                     // Note that sentinels are always copy-constructible.
98                     __enable_if_t< is_copy_constructible<_InIter>::value &&
99                                    is_copy_constructible<_OutIter>::value > > : true_type {};
100 
101 template <class _Algorithm,
102           class _InIter,
103           class _Sent,
104           class _OutIter,
105           __enable_if_t<__can_rewrap<_InIter, _Sent, _OutIter>::value, int> = 0>
106 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
107 __unwrap_and_dispatch(_InIter __first, _Sent __last, _OutIter __out_first) {
108   auto __range  = std::__unwrap_range(__first, std::move(__last));
109   auto __result = _Algorithm()(std::move(__range.first), std::move(__range.second), std::__unwrap_iter(__out_first));
110   return std::make_pair(std::__rewrap_range<_Sent>(std::move(__first), std::move(__result.first)),
111                                  std::__rewrap_iter(std::move(__out_first), std::move(__result.second)));
112 }
113 
114 template <class _Algorithm,
115           class _InIter,
116           class _Sent,
117           class _OutIter,
118           __enable_if_t<!__can_rewrap<_InIter, _Sent, _OutIter>::value, int> = 0>
119 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
120 __unwrap_and_dispatch(_InIter __first, _Sent __last, _OutIter __out_first) {
121   return _Algorithm()(std::move(__first), std::move(__last), std::move(__out_first));
122 }
123 
124 template <class _AlgPolicy,
125           class _NaiveAlgorithm,
126           class _OptimizedAlgorithm,
127           class _InIter,
128           class _Sent,
129           class _OutIter>
130 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
131 __dispatch_copy_or_move(_InIter __first, _Sent __last, _OutIter __out_first) {
132   using _Algorithm = __overload<_NaiveAlgorithm, _OptimizedAlgorithm>;
133   return std::__unwrap_and_dispatch<_Algorithm>(std::move(__first), std::move(__last), std::move(__out_first));
134 }
135 
136 _LIBCPP_END_NAMESPACE_STD
137 
138 #endif // _LIBCPP___ALGORITHM_COPY_MOVE_COMMON_H
139