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[libc++] NFC: Move unwrap_iter to its own header

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This re-applies 9968896cd6, which was reverted in b13edf6e90 because
it broke the build.

Differential Revision: https://reviews.llvm.org/D103369
This commit is contained in:
Louis Dionne
2021-05-31 12:08:05 -04:00
parent bd20756d2c
commit 924ea3bb53
4 changed files with 92 additions and 59 deletions
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60
libcxx/include/algorithm
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@@ -645,6 +645,7 @@ template <class BidirectionalIterator, class Compare>
*/
#include <__algorithm/unwrap_iter.h>
#include <__config>
#include <__bits> // __libcpp_clz
#include <cstddef>
@@ -1639,65 +1640,6 @@ search_n(_ForwardIterator __first, _ForwardIterator __last, _Size __count, const
__value_, __equal_to<__v, _Tp>());
}
// __unwrap_iter, __rewrap_iter
// The job of __unwrap_iter is to lower contiguous iterators (such as
// vector<T>::iterator) into pointers, to reduce the number of template
// instantiations and to enable pointer-based optimizations e.g. in std::copy.
// For iterators that are not contiguous, it must be a no-op.
// In debug mode, we don't do this.
//
// __unwrap_iter is non-constexpr for user-defined iterators whose
// `to_address` and/or `operator->` is non-constexpr. This is okay; but we
// try to avoid doing __unwrap_iter in constant-evaluated contexts anyway.
//
// Some algorithms (e.g. std::copy, but not std::sort) need to convert an
// "unwrapped" result back into a contiguous iterator. Since contiguous iterators
// are random-access, we can do this portably using iterator arithmetic; this
// is the job of __rewrap_iter.
template <class _Iter, bool = __is_cpp17_contiguous_iterator<_Iter>::value>
struct __unwrap_iter_impl {
static _LIBCPP_CONSTEXPR _Iter
__apply(_Iter __i) _NOEXCEPT {
return __i;
}
};
#if _LIBCPP_DEBUG_LEVEL < 2
template <class _Iter>
struct __unwrap_iter_impl<_Iter, true> {
static _LIBCPP_CONSTEXPR decltype(_VSTD::__to_address(declval<_Iter>()))
__apply(_Iter __i) _NOEXCEPT {
return _VSTD::__to_address(__i);
}
};
#endif // _LIBCPP_DEBUG_LEVEL < 2
template<class _Iter, class _Impl = __unwrap_iter_impl<_Iter> >
inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR
decltype(_Impl::__apply(declval<_Iter>()))
__unwrap_iter(_Iter __i) _NOEXCEPT
{
return _Impl::__apply(__i);
}
template<class _OrigIter>
_OrigIter __rewrap_iter(_OrigIter, _OrigIter __result)
{
return __result;
}
template<class _OrigIter, class _UnwrappedIter>
_OrigIter __rewrap_iter(_OrigIter __first, _UnwrappedIter __result)
{
// Precondition: __result is reachable from __first
// Precondition: _OrigIter is a contiguous iterator
return __first + (__result - _VSTD::__unwrap_iter(__first));
}
// copy
template <class _InputIterator, class _OutputIterator>