1 files changed, 85 insertions, 0 deletions
diff --git a/contrib/llvm-project/libcxx/include/__algorithm/unwrap_iter.h b/contrib/llvm-project/libcxx/include/__algorithm/unwrap_iter.h
new file mode 100644
index 000000000000..50d815c97088
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+++ b/contrib/llvm-project/libcxx/include/__algorithm/unwrap_iter.h
@@ -0,0 +1,85 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_UNWRAP_ITER_H
+#define _LIBCPP___ALGORITHM_UNWRAP_ITER_H
+
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__memory/pointer_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_copy_constructible.h>
+#include <__utility/declval.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// TODO: Change the name of __unwrap_iter_impl to something more appropriate
+// The job of __unwrap_iter is to remove iterator wrappers (like reverse_iterator or __wrap_iter),
+// to reduce the number of template instantiations and to enable pointer-based optimizations e.g. in std::copy.
+//
+// Some algorithms (e.g. std::copy, but not std::sort) need to convert an
+// "unwrapped" result back into the original iterator type. Doing that is the job of __rewrap_iter.
+
+// Default case - we can't unwrap anything
+template <class _Iter, bool = __libcpp_is_contiguous_iterator<_Iter>::value>
+struct __unwrap_iter_impl {
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __rewrap(_Iter, _Iter __iter) { return __iter; }
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __unwrap(_Iter __i) _NOEXCEPT { return __i; }
+};
+
+// TODO(hardening): make sure that the following unwrapping doesn't unexpectedly turn hardened iterators into raw
+// pointers.
+
+// It's a contiguous iterator, so we can use a raw pointer instead
+template <class _Iter>
+struct __unwrap_iter_impl<_Iter, true> {
+  using _ToAddressT = decltype(std::__to_address(std::declval<_Iter>()));
+
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Iter __rewrap(_Iter __orig_iter, _ToAddressT __unwrapped_iter) {
+    return __orig_iter + (__unwrapped_iter - std::__to_address(__orig_iter));
+  }
+
+  static _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ToAddressT __unwrap(_Iter __i) _NOEXCEPT {
+    return std::__to_address(__i);
+  }
+};
+
+template <class _Iter,
+          class _Impl                                             = __unwrap_iter_impl<_Iter>,
+          __enable_if_t<is_copy_constructible<_Iter>::value, int> = 0>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 decltype(_Impl::__unwrap(std::declval<_Iter>()))
+__unwrap_iter(_Iter __i) _NOEXCEPT {
+  return _Impl::__unwrap(__i);
+}
+
+// Allow input_iterators to be passed to __unwrap_iter (but not __rewrap_iter)
+#if _LIBCPP_STD_VER >= 20
+template <class _Iter, __enable_if_t<!is_copy_constructible<_Iter>::value, int> = 0>
+inline _LIBCPP_HIDE_FROM_ABI constexpr _Iter __unwrap_iter(_Iter __i) noexcept {
+  return __i;
+}
+#endif
+
+template <class _OrigIter, class _Iter, class _Impl = __unwrap_iter_impl<_OrigIter> >
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _OrigIter __rewrap_iter(_OrigIter __orig_iter, _Iter __iter) _NOEXCEPT {
+  return _Impl::__rewrap(std::move(__orig_iter), std::move(__iter));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_UNWRAP_ITER_H