4 files changed, 23 insertions, 36 deletions
diff --git a/libcxx/include/__iterator/concepts.h b/libcxx/include/__iterator/concepts.h
index f386887..3b43920 100644
--- a/libcxx/include/__iterator/concepts.h
+++ b/libcxx/include/__iterator/concepts.h
@@ -117,15 +117,12 @@ template <class _Tp>
 concept __signed_integer_like = signed_integral<_Tp>;
 
 template <class _Ip>
-concept weakly_incrementable =
-    // TODO: remove this once the clang bug is fixed (https://llvm.org/PR48173).
-    !same_as<_Ip, bool> && // Currently, clang does not handle bool correctly.
-    movable<_Ip> && requires(_Ip __i) {
-      typename iter_difference_t<_Ip>;
-      requires __signed_integer_like<iter_difference_t<_Ip>>;
-      { ++__i } -> same_as<_Ip&>; // not required to be equality-preserving
-      __i++;                      // not required to be equality-preserving
-    };
+concept weakly_incrementable = movable<_Ip> && requires(_Ip __i) {
+  typename iter_difference_t<_Ip>;
+  requires __signed_integer_like<iter_difference_t<_Ip>>;
+  { ++__i } -> same_as<_Ip&>; // not required to be equality-preserving
+  __i++;                      // not required to be equality-preserving
+};
 
 // [iterator.concept.inc]
 template <class _Ip>
diff --git a/libcxx/include/__iterator/distance.h b/libcxx/include/__iterator/distance.h
index 9be9db0..1a9fbf2 100644
--- a/libcxx/include/__iterator/distance.h
+++ b/libcxx/include/__iterator/distance.h
@@ -11,6 +11,7 @@
 #define _LIBCPP___ITERATOR_DISTANCE_H
 
 #include <__algorithm/for_each_segment.h>
+#include <__concepts/same_as.h>
 #include <__config>
 #include <__iterator/concepts.h>
 #include <__iterator/incrementable_traits.h>
@@ -41,35 +42,29 @@ template <class _Iter>
 using __iter_distance_t _LIBCPP_NODEBUG = typename iterator_traits<_Iter>::difference_type;
 #endif
 
-template <class _InputIter, class _Sent>
-inline _LIBCPP_HIDE_FROM_ABI
-_LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_InputIter> __distance(_InputIter __first, _Sent __last) {
-  __iter_distance_t<_InputIter> __r(0);
-  for (; __first != __last; ++__first)
-    ++__r;
-  return __r;
-}
-
 template <class _RandIter, __enable_if_t<__has_random_access_iterator_category<_RandIter>::value, int> = 0>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_RandIter>
 __distance(_RandIter __first, _RandIter __last) {
   return __last - __first;
 }
 
+template <class _InputIter, class _Sent>
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_InputIter>
+__distance(_InputIter __first, _Sent __last) {
+  __iter_distance_t<_InputIter> __r(0);
 #if _LIBCPP_STD_VER >= 20
-template <class _SegmentedIter,
-          __enable_if_t<!__has_random_access_iterator_category<_SegmentedIter>::value &&
-                            __is_segmented_iterator_v<_SegmentedIter>,
-                        int> = 0>
-inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 __iter_distance_t<_SegmentedIter>
-__distance(_SegmentedIter __first, _SegmentedIter __last) {
-  __iter_distance_t<_SegmentedIter> __r(0);
-  std::__for_each_segment(__first, __last, [&__r](auto __lfirst, auto __llast) {
-    __r += std::__distance(__lfirst, __llast);
-  });
+  if constexpr (same_as<_InputIter, _Sent> && __is_segmented_iterator_v<_InputIter>) {
+    std::__for_each_segment(__first, __last, [&__r](auto __lfirst, auto __llast) {
+      __r += std::__distance(__lfirst, __llast);
+    });
+  } else
+#endif
+  {
+    for (; __first != __last; ++__first)
+      ++__r;
+  }
   return __r;
 }
-#endif // _LIBCPP_STD_VER >= 20
 
 template <class _InputIter>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 typename iterator_traits<_InputIter>::difference_type
diff --git a/libcxx/include/__iterator/segmented_iterator.h b/libcxx/include/__iterator/segmented_iterator.h
index 5df9737..dc56a74 100644
--- a/libcxx/include/__iterator/segmented_iterator.h
+++ b/libcxx/include/__iterator/segmented_iterator.h
@@ -75,11 +75,6 @@ inline const bool __has_specialization_v<_Tp, sizeof(_Tp) * 0> = true;
 template <class _Iterator>
 inline const bool __is_segmented_iterator_v = __has_specialization_v<__segmented_iterator_traits<_Iterator> >;
 
-template <class _SegmentedIterator>
-struct __has_random_access_local_iterator
-    : __has_random_access_iterator_category<
-          typename __segmented_iterator_traits< _SegmentedIterator >::__local_iterator > {};
-
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___SEGMENTED_ITERATOR_H
diff --git a/libcxx/include/__iterator/wrap_iter.h b/libcxx/include/__iterator/wrap_iter.h
index d18d968..98745f6 100644
--- a/libcxx/include/__iterator/wrap_iter.h
+++ b/libcxx/include/__iterator/wrap_iter.h
@@ -117,8 +117,8 @@ private:
   friend class span;
   template <class _Tp, size_t _Size>
   friend struct array;
-  template <class _Tp>
-  friend class optional;
+  template <class _Tp, class>
+  friend struct __optional_iterator;
 };
 
 template <class _Iter1>