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368faacac7
This commit reverts 5aaefa51 (and also partly 7f285f48e77 and b6d75682f9, which were related to the original commit). As landed, 5aaefa51 had unintended consequences on some downstream bots and didn't have proper coverage upstream due to a few subtle things. Implementing this is something we should do in libc++, however we'll first need to address a few issues listed in https://reviews.llvm.org/D106124#3349710. Differential Revision: https://reviews.llvm.org/D120683
85 lines
2.7 KiB
C++
85 lines
2.7 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_UNWRAP_ITER_H
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#define _LIBCPP___ALGORITHM_UNWRAP_ITER_H
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#include <__config>
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#include <__memory/pointer_traits.h>
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#include <iterator>
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#include <type_traits>
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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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// The job of __unwrap_iter is to lower contiguous iterators (such as
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// vector<T>::iterator) into pointers, to reduce the number of template
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// instantiations and to enable pointer-based optimizations e.g. in std::copy.
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// For iterators that are not contiguous, it must be a no-op.
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// In debug mode, we don't do this.
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//
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// __unwrap_iter is non-constexpr for user-defined iterators whose
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// `to_address` and/or `operator->` is non-constexpr. This is okay; but we
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// try to avoid doing __unwrap_iter in constant-evaluated contexts anyway.
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//
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// Some algorithms (e.g. std::copy, but not std::sort) need to convert an
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// "unwrapped" result back into a contiguous iterator. Since contiguous iterators
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// are random-access, we can do this portably using iterator arithmetic; this
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// is the job of __rewrap_iter.
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template <class _Iter, bool = __is_cpp17_contiguous_iterator<_Iter>::value>
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struct __unwrap_iter_impl {
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static _LIBCPP_CONSTEXPR _Iter
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__apply(_Iter __i) _NOEXCEPT {
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return __i;
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}
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};
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#if _LIBCPP_DEBUG_LEVEL < 2
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template <class _Iter>
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struct __unwrap_iter_impl<_Iter, true> {
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static _LIBCPP_CONSTEXPR decltype(_VSTD::__to_address(declval<_Iter>()))
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__apply(_Iter __i) _NOEXCEPT {
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return _VSTD::__to_address(__i);
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}
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};
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#endif // _LIBCPP_DEBUG_LEVEL < 2
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template<class _Iter, class _Impl = __unwrap_iter_impl<_Iter> >
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inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
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decltype(_Impl::__apply(declval<_Iter>()))
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__unwrap_iter(_Iter __i) _NOEXCEPT
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{
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return _Impl::__apply(__i);
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}
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template<class _OrigIter>
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_LIBCPP_HIDE_FROM_ABI
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_OrigIter __rewrap_iter(_OrigIter, _OrigIter __result)
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{
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return __result;
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}
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template<class _OrigIter, class _UnwrappedIter>
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_LIBCPP_HIDE_FROM_ABI
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_OrigIter __rewrap_iter(_OrigIter __first, _UnwrappedIter __result)
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{
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// Precondition: __result is reachable from __first
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// Precondition: _OrigIter is a contiguous iterator
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return __first + (__result - _VSTD::__unwrap_iter(__first));
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}
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_LIBCPP_END_NAMESPACE_STD
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#endif // _LIBCPP___ALGORITHM_UNWRAP_ITER_H
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