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005916de58
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
73 lines
2.9 KiB
C++
73 lines
2.9 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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#ifndef _LIBCPP___ALGORITHM_COPY_BACKWARD_H
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#define _LIBCPP___ALGORITHM_COPY_BACKWARD_H
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#include <__algorithm/copy_move_common.h>
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#include <__algorithm/iterator_operations.h>
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#include <__config>
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#include <__utility/move.h>
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#include <__utility/pair.h>
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#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
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# pragma GCC system_header
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#endif
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_LIBCPP_BEGIN_NAMESPACE_STD
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template <class _AlgPolicy>
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struct __copy_backward_loop {
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template <class _InIter, class _Sent, class _OutIter>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
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operator()(_InIter __first, _Sent __last, _OutIter __result) const {
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auto __last_iter = _IterOps<_AlgPolicy>::next(__first, __last);
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auto __original_last_iter = __last_iter;
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while (__first != __last_iter) {
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*--__result = *--__last_iter;
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}
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return std::make_pair(std::move(__original_last_iter), std::move(__result));
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}
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};
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struct __copy_backward_trivial {
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// At this point, the iterators have been unwrapped so any `contiguous_iterator` has been unwrapped to a pointer.
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template <class _In, class _Out, __enable_if_t< is_trivially_assignable<_Out&, _In&>::value, int > = 0>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
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operator()(_In* __first, _In* __last, _Out* __result) const {
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return std::__copy_backward_trivial_impl(__first, __last, __result);
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}
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};
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template <class _AlgPolicy, class _BidirectionalIterator1, class _Sentinel, class _BidirectionalIterator2>
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_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
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pair<_BidirectionalIterator1, _BidirectionalIterator2>
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__copy_backward(_BidirectionalIterator1 __first, _Sentinel __last, _BidirectionalIterator2 __result) {
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return std::__dispatch_copy_or_move<_AlgPolicy, __copy_backward_loop<_AlgPolicy>, __copy_backward_trivial>(
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std::move(__first), std::move(__last), std::move(__result));
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}
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template <class _BidirectionalIterator1, class _BidirectionalIterator2>
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inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
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_BidirectionalIterator2
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copy_backward(_BidirectionalIterator1 __first, _BidirectionalIterator1 __last,
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_BidirectionalIterator2 __result)
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{
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static_assert(std::is_copy_constructible<_BidirectionalIterator1>::value &&
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std::is_copy_constructible<_BidirectionalIterator1>::value, "Iterators must be copy constructible.");
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return std::__copy_backward<_ClassicAlgPolicy>(
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std::move(__first), std::move(__last), std::move(__result)).second;
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ALGORITHM_COPY_BACKWARD_H
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