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
37template <class _From, class _To>
38struct __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
49template <class _From, class _To>
50struct __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
60template <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
69template <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
82template <class _F1, class _F2>
83struct __overload : _F1, _F2 {
84  using _F1::operator();
85  using _F2::operator();
86};
87
88template <class _InIter, class _Sent, class _OutIter, class = void>
89struct __can_rewrap : false_type {};
90
91template <class _InIter, class _Sent, class _OutIter>
92struct __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
99template <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
112template <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
122template <class _IterOps, class _InValue, class _OutIter, class = void>
123struct __can_copy_without_conversion : false_type {};
124
125template <class _IterOps, class _InValue, class _OutIter>
126struct __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
132template <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