libcxx/include/__algorithm/copy_move_common.h

   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