1 files changed, 34 insertions, 5 deletions
diff --git a/libcxx/include/__algorithm/swap_ranges.h b/libcxx/include/__algorithm/swap_ranges.h
index 0422265bb4be..5ce5ed8c8845 100644
--- a/libcxx/include/__algorithm/swap_ranges.h
+++ b/libcxx/include/__algorithm/swap_ranges.h
@@ -9,8 +9,10 @@
 #ifndef _LIBCPP___ALGORITHM_SWAP_RANGES_H
 #define _LIBCPP___ALGORITHM_SWAP_RANGES_H
 
+#include <__algorithm/iterator_operations.h>
 #include <__config>
-#include <__utility/swap.h>
+#include <__utility/move.h>
+#include <__utility/pair.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -18,12 +20,39 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+// 2+2 iterators: the shorter size will be used.
+template <class _AlgPolicy, class _ForwardIterator1, class _Sentinel1, class _ForwardIterator2, class _Sentinel2>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+pair<_ForwardIterator1, _ForwardIterator2>
+__swap_ranges(_ForwardIterator1 __first1, _Sentinel1 __last1, _ForwardIterator2 __first2, _Sentinel2 __last2) {
+  while (__first1 != __last1 && __first2 != __last2) {
+    _IterOps<_AlgPolicy>::iter_swap(__first1, __first2);
+    ++__first1;
+    ++__first2;
+  }
+
+  return pair<_ForwardIterator1, _ForwardIterator2>(std::move(__first1), std::move(__first2));
+}
+
+// 2+1 iterators: size2 >= size1.
+template <class _AlgPolicy, class _ForwardIterator1, class _Sentinel1, class _ForwardIterator2>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
+pair<_ForwardIterator1, _ForwardIterator2>
+__swap_ranges(_ForwardIterator1 __first1, _Sentinel1 __last1, _ForwardIterator2 __first2) {
+  while (__first1 != __last1) {
+    _IterOps<_AlgPolicy>::iter_swap(__first1, __first2);
+    ++__first1;
+    ++__first2;
+  }
+
+  return pair<_ForwardIterator1, _ForwardIterator2>(std::move(__first1), std::move(__first2));
+}
+
 template <class _ForwardIterator1, class _ForwardIterator2>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_AFTER_CXX17 _ForwardIterator2
+inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator2
 swap_ranges(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIterator2 __first2) {
-  for (; __first1 != __last1; ++__first1, (void)++__first2)
-    swap(*__first1, *__first2);
-  return __first2;
+  return std::__swap_ranges<_ClassicAlgPolicy>(
+      std::move(__first1), std::move(__last1), std::move(__first2)).second;
 }
 
 _LIBCPP_END_NAMESPACE_STD