Konstantin Varlamov 005916de58 [libc++][ranges]Refactor copy{,_backward} and move{,_backward}
Instead of using `reverse_iterator`, share the optimization between the 4 algorithms. The key observation here that `memmove` applies to both `copy` and `move` identically, and to their `_backward` versions very similarly. All algorithms now follow the same pattern along the lines of:
```
if constexpr (can_memmove<InIter, OutIter>) {
  memmove(first, last, out);
} else {
  naive_implementation(first, last, out);
}
```
A follow-up will delete `unconstrained_reverse_iterator`.

This patch removes duplication and divergence between `std::copy`, `std::move` and `std::move_backward`. It also improves testing:
- the test for whether the optimization is used only applied to `std::copy` and, more importantly, was essentially a no-op because it would still pass if the optimization was not used;
- there were no tests to make sure the optimization is not used when the effect would be visible.

Differential Revision: https://reviews.llvm.org/D130695
2022-10-01 17:35:12 -07:00

68 lines
2.6 KiB
C++

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
#ifndef _LIBCPP___ALGORITHM_MOVE_H
#define _LIBCPP___ALGORITHM_MOVE_H
#include <__algorithm/copy_move_common.h>
#include <__algorithm/iterator_operations.h>
#include <__config>
#include <__utility/move.h>
#include <__utility/pair.h>
#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
# pragma GCC system_header
#endif
_LIBCPP_BEGIN_NAMESPACE_STD
template <class _AlgPolicy>
struct __move_loop {
template <class _InIter, class _Sent, class _OutIter>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
operator()(_InIter __first, _Sent __last, _OutIter __result) const {
while (__first != __last) {
*__result = _IterOps<_AlgPolicy>::__iter_move(__first);
++__first;
++__result;
}
return std::make_pair(std::move(__first), std::move(__result));
}
};
struct __move_trivial {
// At this point, the iterators have been unwrapped so any `contiguous_iterator` has been unwrapped to a pointer.
template <class _In, class _Out, __enable_if_t< is_trivially_assignable<_Out&, _In&&>::value, int > = 0>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
operator()(_In* __first, _In* __last, _Out* __result) const {
return std::__copy_trivial_impl(__first, __last, __result);
}
};
template <class _AlgPolicy, class _InIter, class _Sent, class _OutIter>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
pair<_InIter, _OutIter>
__move(_InIter __first, _Sent __last, _OutIter __result) {
return std::__dispatch_copy_or_move<_AlgPolicy, __move_loop<_AlgPolicy>, __move_trivial>(
std::move(__first), std::move(__last), std::move(__result));
}
template <class _InputIterator, class _OutputIterator>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
_OutputIterator move(_InputIterator __first, _InputIterator __last, _OutputIterator __result) {
static_assert(is_copy_constructible<_InputIterator>::value, "Iterators has to be copy constructible.");
static_assert(is_copy_constructible<_OutputIterator>::value, "The output iterator has to be copy constructible.");
return std::__move<_ClassicAlgPolicy>(
std::move(__first), std::move(__last), std::move(__result)).second;
}
_LIBCPP_END_NAMESPACE_STD
#endif // _LIBCPP___ALGORITHM_MOVE_H