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