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*>
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*>
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