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diff --git a/contrib/llvm-project/libcxx/include/__algorithm/nth_element.h b/contrib/llvm-project/libcxx/include/__algorithm/nth_element.h
new file mode 100644
index 000000000000..da748d7255ab
--- /dev/null
+++ b/contrib/llvm-project/libcxx/include/__algorithm/nth_element.h
@@ -0,0 +1,261 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_NTH_ELEMENT_H
+#define _LIBCPP___ALGORITHM_NTH_ELEMENT_H
+
+#include <__algorithm/comp.h>
+#include <__algorithm/comp_ref_type.h>
+#include <__algorithm/iterator_operations.h>
+#include <__algorithm/sort.h>
+#include <__assert>
+#include <__config>
+#include <__debug_utils/randomize_range.h>
+#include <__iterator/iterator_traits.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
+
+template <class _Compare, class _RandomAccessIterator>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool __nth_element_find_guard(
+    _RandomAccessIterator& __i, _RandomAccessIterator& __j, _RandomAccessIterator __m, _Compare __comp) {
+  // manually guard downward moving __j against __i
+  while (true) {
+    if (__i == --__j) {
+      return false;
+    }
+    if (__comp(*__j, *__m)) {
+      return true; // found guard for downward moving __j, now use unguarded partition
+    }
+  }
+}
+
+template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
+// NOLINTNEXTLINE(readability-function-cognitive-complexity)
+__nth_element(
+    _RandomAccessIterator __first, _RandomAccessIterator __nth, _RandomAccessIterator __last, _Compare __comp) {
+  using _Ops = _IterOps<_AlgPolicy>;
+
+  // _Compare is known to be a reference type
+  typedef typename iterator_traits<_RandomAccessIterator>::difference_type difference_type;
+  const difference_type __limit = 7;
+  while (true) {
+    if (__nth == __last)
+      return;
+    difference_type __len = __last - __first;
+    switch (__len) {
+    case 0:
+    case 1:
+      return;
+    case 2:
+      if (__comp(*--__last, *__first))
+        _Ops::iter_swap(__first, __last);
+      return;
+    case 3: {
+      _RandomAccessIterator __m = __first;
+      std::__sort3<_AlgPolicy, _Compare>(__first, ++__m, --__last, __comp);
+      return;
+    }
+    }
+    if (__len <= __limit) {
+      std::__selection_sort<_AlgPolicy, _Compare>(__first, __last, __comp);
+      return;
+    }
+    // __len > __limit >= 3
+    _RandomAccessIterator __m   = __first + __len / 2;
+    _RandomAccessIterator __lm1 = __last;
+    unsigned __n_swaps          = std::__sort3<_AlgPolicy, _Compare>(__first, __m, --__lm1, __comp);
+    // *__m is median
+    // partition [__first, __m) < *__m and *__m <= [__m, __last)
+    // (this inhibits tossing elements equivalent to __m around unnecessarily)
+    _RandomAccessIterator __i = __first;
+    _RandomAccessIterator __j = __lm1;
+    // j points beyond range to be tested, *__lm1 is known to be <= *__m
+    // The search going up is known to be guarded but the search coming down isn't.
+    // Prime the downward search with a guard.
+    if (!__comp(*__i, *__m)) // if *__first == *__m
+    {
+      // *__first == *__m, *__first doesn't go in first part
+      if (std::__nth_element_find_guard<_Compare>(__i, __j, __m, __comp)) {
+        _Ops::iter_swap(__i, __j);
+        ++__n_swaps;
+      } else {
+        // *__first == *__m, *__m <= all other elements
+        // Partition instead into [__first, __i) == *__first and *__first < [__i, __last)
+        ++__i; // __first + 1
+        __j = __last;
+        if (!__comp(*__first, *--__j)) { // we need a guard if *__first == *(__last-1)
+          while (true) {
+            if (__i == __j) {
+              return; // [__first, __last) all equivalent elements
+            } else if (__comp(*__first, *__i)) {
+              _Ops::iter_swap(__i, __j);
+              ++__n_swaps;
+              ++__i;
+              break;
+            }
+            ++__i;
+          }
+        }
+        // [__first, __i) == *__first and *__first < [__j, __last) and __j == __last - 1
+        if (__i == __j) {
+          return;
+        }
+        while (true) {
+          while (!__comp(*__first, *__i)) {
+            ++__i;
+            _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+                __i != __last,
+                "Would read out of bounds, does your comparator satisfy the strict-weak ordering requirement?");
+          }
+          do {
+            _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+                __j != __first,
+                "Would read out of bounds, does your comparator satisfy the strict-weak ordering requirement?");
+            --__j;
+          } while (__comp(*__first, *__j));
+          if (__i >= __j)
+            break;
+          _Ops::iter_swap(__i, __j);
+          ++__n_swaps;
+          ++__i;
+        }
+        // [__first, __i) == *__first and *__first < [__i, __last)
+        // The first part is sorted,
+        if (__nth < __i) {
+          return;
+        }
+        // __nth_element the second part
+        // std::__nth_element<_Compare>(__i, __nth, __last, __comp);
+        __first = __i;
+        continue;
+      }
+    }
+    ++__i;
+    // j points beyond range to be tested, *__lm1 is known to be <= *__m
+    // if not yet partitioned...
+    if (__i < __j) {
+      // known that *(__i - 1) < *__m
+      while (true) {
+        // __m still guards upward moving __i
+        while (__comp(*__i, *__m)) {
+          ++__i;
+          _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+              __i != __last,
+              "Would read out of bounds, does your comparator satisfy the strict-weak ordering requirement?");
+        }
+        // It is now known that a guard exists for downward moving __j
+        do {
+          _LIBCPP_ASSERT_VALID_ELEMENT_ACCESS(
+              __j != __first,
+              "Would read out of bounds, does your comparator satisfy the strict-weak ordering requirement?");
+          --__j;
+        } while (!__comp(*__j, *__m));
+        if (__i >= __j)
+          break;
+        _Ops::iter_swap(__i, __j);
+        ++__n_swaps;
+        // It is known that __m != __j
+        // If __m just moved, follow it
+        if (__m == __i)
+          __m = __j;
+        ++__i;
+      }
+    }
+    // [__first, __i) < *__m and *__m <= [__i, __last)
+    if (__i != __m && __comp(*__m, *__i)) {
+      _Ops::iter_swap(__i, __m);
+      ++__n_swaps;
+    }
+    // [__first, __i) < *__i and *__i <= [__i+1, __last)
+    if (__nth == __i)
+      return;
+    if (__n_swaps == 0) {
+      // We were given a perfectly partitioned sequence.  Coincidence?
+      if (__nth < __i) {
+        // Check for [__first, __i) already sorted
+        __j = __m = __first;
+        while (true) {
+          if (++__j == __i) {
+            // [__first, __i) sorted
+            return;
+          }
+          if (__comp(*__j, *__m)) {
+            // not yet sorted, so sort
+            break;
+          }
+          __m = __j;
+        }
+      } else {
+        // Check for [__i, __last) already sorted
+        __j = __m = __i;
+        while (true) {
+          if (++__j == __last) {
+            // [__i, __last) sorted
+            return;
+          }
+          if (__comp(*__j, *__m)) {
+            // not yet sorted, so sort
+            break;
+          }
+          __m = __j;
+        }
+      }
+    }
+    // __nth_element on range containing __nth
+    if (__nth < __i) {
+      // std::__nth_element<_Compare>(__first, __nth, __i, __comp);
+      __last = __i;
+    } else {
+      // std::__nth_element<_Compare>(__i+1, __nth, __last, __comp);
+      __first = ++__i;
+    }
+  }
+}
+
+template <class _AlgPolicy, class _RandomAccessIterator, class _Compare>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __nth_element_impl(
+    _RandomAccessIterator __first, _RandomAccessIterator __nth, _RandomAccessIterator __last, _Compare& __comp) {
+  if (__nth == __last)
+    return;
+
+  std::__debug_randomize_range<_AlgPolicy>(__first, __last);
+
+  std::__nth_element<_AlgPolicy, __comp_ref_type<_Compare> >(__first, __nth, __last, __comp);
+
+  std::__debug_randomize_range<_AlgPolicy>(__first, __nth);
+  if (__nth != __last) {
+    std::__debug_randomize_range<_AlgPolicy>(++__nth, __last);
+  }
+}
+
+template <class _RandomAccessIterator, class _Compare>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth, _RandomAccessIterator __last, _Compare __comp) {
+  std::__nth_element_impl<_ClassicAlgPolicy>(std::move(__first), std::move(__nth), std::move(__last), __comp);
+}
+
+template <class _RandomAccessIterator>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
+nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth, _RandomAccessIterator __last) {
+  std::nth_element(std::move(__first), std::move(__nth), std::move(__last), __less<>());
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_NTH_ELEMENT_H