1 files changed, 25 insertions, 17 deletions

diff --git a/contrib/llvm-project/libcxx/include/__algorithm/copy_backward.h b/contrib/llvm-project/libcxx/include/__algorithm/copy_backward.h
index dd43a91ffa87..26b8c4d791fd 100644
--- a/contrib/llvm-project/libcxx/include/__algorithm/copy_backward.h
+++ b/contrib/llvm-project/libcxx/include/__algorithm/copy_backward.h
@@ -10,10 +10,16 @@
 #define _LIBCPP___ALGORITHM_COPY_BACKWARD_H
 
 #include <__algorithm/copy.h>
+#include <__algorithm/iterator_operations.h>
+#include <__algorithm/ranges_copy.h>
 #include <__algorithm/unwrap_iter.h>
+#include <__concepts/same_as.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/reverse_iterator.h>
+#include <__ranges/subrange.h>
+#include <__utility/move.h>
+#include <__utility/pair.h>
 #include <cstring>
 #include <type_traits>
 
@@ -23,29 +29,31 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-template <class _Iter1, class _Sent1, class _Iter2>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
-pair<_Iter1, _Iter2> __copy_backward_impl(_Iter1 __first, _Sent1 __last, _Iter2 __result) {
-  auto __ret = std::__copy(reverse_iterator<_Iter1>(__last),
-                           reverse_iterator<_Sent1>(__first),
-                           reverse_iterator<_Iter2>(__result));
-  return pair<_Iter1, _Iter2>(__ret.first.base(), __ret.second.base());
+template <class _AlgPolicy, class _InputIterator, class _OutputIterator,
+          __enable_if_t<is_same<_AlgPolicy, _ClassicAlgPolicy>::value, int> = 0>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11 pair<_InputIterator, _OutputIterator>
+__copy_backward(_InputIterator __first, _InputIterator __last, _OutputIterator __result) {
+  auto __ret = std::__copy(
+      __unconstrained_reverse_iterator<_InputIterator>(__last),
+      __unconstrained_reverse_iterator<_InputIterator>(__first),
+      __unconstrained_reverse_iterator<_OutputIterator>(__result));
+  return pair<_InputIterator, _OutputIterator>(__ret.first.base(), __ret.second.base());
 }
 
-template <class _Iter1, class _Sent1, class _Iter2>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX11
-pair<_Iter1, _Iter2> __copy_backward(_Iter1 __first, _Sent1 __last, _Iter2 __result) {
-  auto __ret = std::__copy_backward_impl(std::__unwrap_iter(__first),
-                                         std::__unwrap_iter(__last),
-                                         std::__unwrap_iter(__result));
-  return pair<_Iter1, _Iter2>(std::__rewrap_iter(__first, __ret.first), std::__rewrap_iter(__result, __ret.second));
+#if _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
+template <class _AlgPolicy, class _Iter1, class _Sent1, class _Iter2,
+          __enable_if_t<is_same<_AlgPolicy, _RangeAlgPolicy>::value, int> = 0>
+_LIBCPP_HIDE_FROM_ABI constexpr pair<_Iter1, _Iter2> __copy_backward(_Iter1 __first, _Sent1 __last, _Iter2 __result) {
+  auto __reverse_range = std::__reverse_range(std::ranges::subrange(std::move(__first), std::move(__last)));
+  auto __ret           = ranges::copy(std::move(__reverse_range), std::make_reverse_iterator(__result));
+  return std::make_pair(__ret.in.base(), __ret.out.base());
 }
+#endif // _LIBCPP_STD_VER > 17 && !defined(_LIBCPP_HAS_NO_INCOMPLETE_RANGES)
 
 template <class _BidirectionalIterator1, class _BidirectionalIterator2>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17
-_BidirectionalIterator2
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_AFTER_CXX17 _BidirectionalIterator2
 copy_backward(_BidirectionalIterator1 __first, _BidirectionalIterator1 __last, _BidirectionalIterator2 __result) {
-  return std::__copy_backward(__first, __last, __result).second;
+  return std::__copy_backward<_ClassicAlgPolicy>(__first, __last, __result).second;
 }
 
 _LIBCPP_END_NAMESPACE_STD