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 <__type_traits/enable_if.h>
19 #include <__type_traits/is_always_bitcastable.h>
20 #include <__type_traits/is_constant_evaluated.h>
21 #include <__type_traits/is_copy_constructible.h>
22 #include <__type_traits/is_trivially_assignable.h>
23 #include <__type_traits/is_trivially_copyable.h>
24 #include <__type_traits/is_volatile.h>
25 #include <__utility/move.h>
26 #include <__utility/pair.h>
27 #include <cstddef>
28
29 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
30 # pragma GCC system_header
31 #endif
32
33 _LIBCPP_BEGIN_NAMESPACE_STD
34
35 // Type traits.
36
37 template <class _From, class _To>
38 struct __can_lower_copy_assignment_to_memmove {
39 static const bool value =
40 // If the types are always bitcastable, it's valid to do a bitwise copy between them.
41 __is_always_bitcastable<_From, _To>::value &&
42 // Reject conversions that wouldn't be performed by the regular built-in assignment (e.g. between arrays).
43 is_trivially_assignable<_To&, const _From&>::value &&
44 // `memmove` doesn't accept `volatile` pointers, make sure the optimization SFINAEs away in that case.
45 !is_volatile<_From>::value &&
46 !is_volatile<_To>::value;
47 };
48
49 template <class _From, class _To>
50 struct __can_lower_move_assignment_to_memmove {
51 static const bool value =
52 __is_always_bitcastable<_From, _To>::value &&
53 is_trivially_assignable<_To&, _From&&>::value &&
54 !is_volatile<_From>::value &&
55 !is_volatile<_To>::value;
56 };
57
58 // `memmove` algorithms implementation.
59
60 template <class _In, class _Out>
61 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
__copy_trivial_impl(_In * __first,_In * __last,_Out * __result)62 __copy_trivial_impl(_In* __first, _In* __last, _Out* __result) {
63 const size_t __n = static_cast<size_t>(__last - __first);
64 ::__builtin_memmove(__result, __first, __n * sizeof(_Out));
65
66 return std::make_pair(__last, __result + __n);
67 }
68
69 template <class _In, class _Out>
70 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
__copy_backward_trivial_impl(_In * __first,_In * __last,_Out * __result)71 __copy_backward_trivial_impl(_In* __first, _In* __last, _Out* __result) {
72 const size_t __n = static_cast<size_t>(__last - __first);
73 __result -= __n;
74
75 ::__builtin_memmove(__result, __first, __n * sizeof(_Out));
76
77 return std::make_pair(__last, __result);
78 }
79
80 // Iterator unwrapping and dispatching to the correct overload.
81
82 template <class _F1, class _F2>
83 struct __overload : _F1, _F2 {
84 using _F1::operator();
85 using _F2::operator();
86 };
87
88 template <class _InIter, class _Sent, class _OutIter, class = void>
89 struct __can_rewrap : false_type {};
90
91 template <class _InIter, class _Sent, class _OutIter>
92 struct __can_rewrap<_InIter,
93 _Sent,
94 _OutIter,
95 // Note that sentinels are always copy-constructible.
96 __enable_if_t< is_copy_constructible<_InIter>::value &&
97 is_copy_constructible<_OutIter>::value > > : true_type {};
98
99 template <class _Algorithm,
100 class _InIter,
101 class _Sent,
102 class _OutIter,
103 __enable_if_t<__can_rewrap<_InIter, _Sent, _OutIter>::value, int> = 0>
104 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
105 __unwrap_and_dispatch(_InIter __first, _Sent __last, _OutIter __out_first) {
106 auto __range = std::__unwrap_range(__first, std::move(__last));
107 auto __result = _Algorithm()(std::move(__range.first), std::move(__range.second), std::__unwrap_iter(__out_first));
108 return std::make_pair(std::__rewrap_range<_Sent>(std::move(__first), std::move(__result.first)),
109 std::__rewrap_iter(std::move(__out_first), std::move(__result.second)));
110 }
111
112 template <class _Algorithm,
113 class _InIter,
114 class _Sent,
115 class _OutIter,
116 __enable_if_t<!__can_rewrap<_InIter, _Sent, _OutIter>::value, int> = 0>
117 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
118 __unwrap_and_dispatch(_InIter __first, _Sent __last, _OutIter __out_first) {
119 return _Algorithm()(std::move(__first), std::move(__last), std::move(__out_first));
120 }
121
122 template <class _IterOps, class _InValue, class _OutIter, class = void>
123 struct __can_copy_without_conversion : false_type {};
124
125 template <class _IterOps, class _InValue, class _OutIter>
126 struct __can_copy_without_conversion<
127 _IterOps,
128 _InValue,
129 _OutIter,
130 __enable_if_t<is_same<_InValue, typename _IterOps::template __value_type<_OutIter> >::value> > : true_type {};
131
132 template <class _AlgPolicy,
133 class _NaiveAlgorithm,
134 class _OptimizedAlgorithm,
135 class _InIter,
136 class _Sent,
137 class _OutIter>
138 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
139 __dispatch_copy_or_move(_InIter __first, _Sent __last, _OutIter __out_first) {
140 #ifdef _LIBCPP_COMPILER_GCC
141 // GCC doesn't support `__builtin_memmove` during constant evaluation.
142 if (__libcpp_is_constant_evaluated()) {
143 return std::__unwrap_and_dispatch<_NaiveAlgorithm>(std::move(__first), std::move(__last), std::move(__out_first));
144 }
145 #else
146 // In Clang, `__builtin_memmove` only supports fully trivially copyable types (just having trivial copy assignment is
147 // insufficient). Also, conversions are not supported.
148 if (__libcpp_is_constant_evaluated()) {
149 using _InValue = typename _IterOps<_AlgPolicy>::template __value_type<_InIter>;
150 if (!is_trivially_copyable<_InValue>::value ||
151 !__can_copy_without_conversion<_IterOps<_AlgPolicy>, _InValue, _OutIter>::value) {
152 return std::__unwrap_and_dispatch<_NaiveAlgorithm>(std::move(__first), std::move(__last), std::move(__out_first));
153 }
154 }
155 #endif // _LIBCPP_COMPILER_GCC
156
157 using _Algorithm = __overload<_NaiveAlgorithm, _OptimizedAlgorithm>;
158 return std::__unwrap_and_dispatch<_Algorithm>(std::move(__first), std::move(__last), std::move(__out_first));
159 }
160
161 _LIBCPP_END_NAMESPACE_STD
162
163 #endif // _LIBCPP___ALGORITHM_COPY_MOVE_COMMON_H
164