libcxx: update to LLVM 17

release/17.x branch, commit 8f4dd44097c9ae25dd203d5ac87f3b48f854bba8

This adds the flag `-D_LIBCPP_PSTL_CPU_BACKEND_SERIAL`. A future
enhancement could possibly pass something different if there is a
compelling parallel implementation. That libdispatch one might be worth
looking into.

lib/libcxx/include/__algorithm/adjacent_find.h

@@ -20,6 +20,9 @@
 #  pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Iter, class _Sent, class _BinaryPredicate>
@@ -50,4 +53,6 @@ adjacent_find(_ForwardIterator __first, _ForwardIterator __last) {
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_ADJACENT_FIND_H

lib/libcxx/include/__algorithm/all_of.h

@@ -19,7 +19,7 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator, class _Predicate>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 all_of(_InputIterator __first, _InputIterator __last, _Predicate __pred) {
   for (; __first != __last; ++__first)
     if (!__pred(*__first))

lib/libcxx/include/__algorithm/binary_search.h

@@ -37,8 +37,7 @@ _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 bool
 binary_search(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value)
 {
-    return std::binary_search(__first, __last, __value,
+    return std::binary_search(__first, __last, __value, __less<>());
-                              __less<typename iterator_traits<_ForwardIterator>::value_type, _Tp>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/clamp.h

@@ -19,14 +19,14 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 14
+#if _LIBCPP_STD_VER >= 17
 template<class _Tp, class _Compare>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY constexpr
 const _Tp&
 clamp(const _Tp& __v, const _Tp& __lo, const _Tp& __hi, _Compare __comp)
 {
-    _LIBCPP_ASSERT(!__comp(__hi, __lo), "Bad bounds passed to std::clamp");
+    _LIBCPP_ASSERT_UNCATEGORIZED(!__comp(__hi, __lo), "Bad bounds passed to std::clamp");
     return __comp(__v, __lo) ? __lo : __comp(__hi, __v) ? __hi : __v;
 
 }
@@ -37,7 +37,7 @@ _LIBCPP_INLINE_VISIBILITY constexpr
 const _Tp&
 clamp(const _Tp& __v, const _Tp& __lo, const _Tp& __hi)
 {
-    return _VSTD::clamp(__v, __lo, __hi, __less<_Tp>());
+    return _VSTD::clamp(__v, __lo, __hi, __less<>());
 }
 #endif
 

lib/libcxx/include/__algorithm/comp.h

@@ -10,6 +10,8 @@
 #define _LIBCPP___ALGORITHM_COMP_H
 
 #include <__config>
+#include <__type_traits/integral_constant.h>
+#include <__type_traits/predicate_traits.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -24,41 +26,20 @@ struct __equal_to {
   }
 };
 
-template <class _T1, class _T2 = _T1>
+template <class _Lhs, class _Rhs>
-struct __less
+struct __is_trivial_equality_predicate<__equal_to, _Lhs, _Rhs> : true_type {};
-{
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
-    bool operator()(const _T1& __x, const _T1& __y) const {return __x < __y;}
 
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+// The definition is required because __less is part of the ABI, but it's empty
-    bool operator()(const _T1& __x, const _T2& __y) const {return __x < __y;}
+// because all comparisons should be transparent.
+template <class _T1 = void, class _T2 = _T1>
+struct __less {};
 
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+template <>
-    bool operator()(const _T2& __x, const _T1& __y) const {return __x < __y;}
+struct __less<void, void> {
-
+  template <class _Tp, class _Up>
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 bool operator()(const _Tp& __lhs, const _Up& __rhs) const {
-    bool operator()(const _T2& __x, const _T2& __y) const {return __x < __y;}
+    return __lhs < __rhs;
-};
+  }
-
-template <class _T1>
-struct __less<_T1, _T1>
-{
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
-    bool operator()(const _T1& __x, const _T1& __y) const {return __x < __y;}
-};
-
-template <class _T1>
-struct __less<const _T1, _T1>
-{
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
-    bool operator()(const _T1& __x, const _T1& __y) const {return __x < __y;}
-};
-
-template <class _T1>
-struct __less<_T1, const _T1>
-{
-    _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
-    bool operator()(const _T1& __x, const _T1& __y) const {return __x < __y;}
 };
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/comp_ref_type.h

@@ -9,8 +9,8 @@
 #ifndef _LIBCPP___ALGORITHM_COMP_REF_TYPE_H
 #define _LIBCPP___ALGORITHM_COMP_REF_TYPE_H
 
+#include <__assert>
 #include <__config>
-#include <__debug>
 #include <__utility/declval.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
@@ -23,11 +23,10 @@ template <class _Compare>
 struct __debug_less
 {
     _Compare &__comp_;
-    _LIBCPP_CONSTEXPR_SINCE_CXX14
+    _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI __debug_less(_Compare& __c) : __comp_(__c) {}
-    __debug_less(_Compare& __c) : __comp_(__c) {}
 
     template <class _Tp, class _Up>
-    _LIBCPP_CONSTEXPR_SINCE_CXX14
+    _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI
     bool operator()(const _Tp& __x,  const _Up& __y)
     {
         bool __r = __comp_(__x, __y);
@@ -37,7 +36,7 @@ struct __debug_less
     }
 
     template <class _Tp, class _Up>
-    _LIBCPP_CONSTEXPR_SINCE_CXX14
+    _LIBCPP_CONSTEXPR_SINCE_CXX14 _LIBCPP_HIDE_FROM_ABI
     bool operator()(_Tp& __x,  _Up& __y)
     {
         bool __r = __comp_(__x, __y);
@@ -52,7 +51,7 @@ struct __debug_less
     decltype((void)std::declval<_Compare&>()(
         std::declval<_LHS &>(), std::declval<_RHS &>()))
     __do_compare_assert(int, _LHS & __l, _RHS & __r) {
-        _LIBCPP_DEBUG_ASSERT(!__comp_(__l, __r),
+        _LIBCPP_ASSERT_UNCATEGORIZED(!__comp_(__l, __r),
             "Comparator does not induce a strict weak ordering");
         (void)__l;
         (void)__r;
@@ -66,7 +65,7 @@ struct __debug_less
 
 // Pass the comparator by lvalue reference. Or in debug mode, using a
 // debugging wrapper that stores a reference.
-#ifdef _LIBCPP_ENABLE_DEBUG_MODE
+#if _LIBCPP_ENABLE_DEBUG_MODE
 template <class _Comp>
 using __comp_ref_type = __debug_less<_Comp>;
 #else

lib/libcxx/include/__algorithm/copy.h

@@ -10,6 +10,7 @@
 #define _LIBCPP___ALGORITHM_COPY_H
 
 #include <__algorithm/copy_move_common.h>
+#include <__algorithm/for_each_segment.h>
 #include <__algorithm/iterator_operations.h>
 #include <__algorithm/min.h>
 #include <__config>
@@ -44,36 +45,34 @@ struct __copy_loop {
     return std::make_pair(std::move(__first), std::move(__result));
   }
 
+  template <class _InIter, class _OutIter>
+  struct _CopySegment {
+    using _Traits = __segmented_iterator_traits<_InIter>;
+
+    _OutIter& __result_;
+
+    _LIBCPP_HIDE_FROM_ABI _CopySegment(_OutIter& __result) : __result_(__result) {}
+
+    _LIBCPP_HIDE_FROM_ABI void
+    operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+      __result_ = std::__copy<_AlgPolicy>(__lfirst, __llast, std::move(__result_)).second;
+    }
+  };
+
   template <class _InIter, class _OutIter, __enable_if_t<__is_segmented_iterator<_InIter>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
   operator()(_InIter __first, _InIter __last, _OutIter __result) const {
-    using _Traits = __segmented_iterator_traits<_InIter>;
+    std::__for_each_segment(__first, __last, _CopySegment<_InIter, _OutIter>(__result));
-    auto __sfirst = _Traits::__segment(__first);
-    auto __slast  = _Traits::__segment(__last);
-    if (__sfirst == __slast) {
-      auto __iters = std::__copy<_AlgPolicy>(_Traits::__local(__first), _Traits::__local(__last), std::move(__result));
-      return std::make_pair(__last, std::move(__iters.second));
-    }
-
-    __result = std::__copy<_AlgPolicy>(_Traits::__local(__first), _Traits::__end(__sfirst), std::move(__result)).second;
-    ++__sfirst;
-    while (__sfirst != __slast) {
-      __result =
-          std::__copy<_AlgPolicy>(_Traits::__begin(__sfirst), _Traits::__end(__sfirst), std::move(__result)).second;
-      ++__sfirst;
-    }
-    __result =
-        std::__copy<_AlgPolicy>(_Traits::__begin(__sfirst), _Traits::__local(__last), std::move(__result)).second;
     return std::make_pair(__last, std::move(__result));
   }
 
   template <class _InIter,
             class _OutIter,
-            __enable_if_t<__is_cpp17_random_access_iterator<_InIter>::value &&
+            __enable_if_t<__has_random_access_iterator_category<_InIter>::value &&
                               !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _InIter __last, _OutIter __result) {
+  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
     using _Traits = __segmented_iterator_traits<_OutIter>;
     using _DiffT  = typename common_type<__iter_diff_t<_InIter>, __iter_diff_t<_OutIter> >::type;
 
@@ -98,8 +97,7 @@ struct __copy_loop {
 
 struct __copy_trivial {
   // At this point, the iterators have been unwrapped so any `contiguous_iterator` has been unwrapped to a pointer.
-  template <class _In, class _Out,
+  template <class _In, class _Out, __enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
-            __enable_if_t<__can_lower_copy_assignment_to_memmove<_In, _Out>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
   operator()(_In* __first, _In* __last, _Out* __result) const {
     return std::__copy_trivial_impl(__first, __last, __result);

lib/libcxx/include/__algorithm/copy_backward.h

@@ -76,11 +76,11 @@ struct __copy_backward_loop {
 
   template <class _InIter,
             class _OutIter,
-            __enable_if_t<__is_cpp17_random_access_iterator<_InIter>::value &&
+            __enable_if_t<__has_random_access_iterator_category<_InIter>::value &&
                               !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _InIter __last, _OutIter __result) {
+  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
     using _Traits           = __segmented_iterator_traits<_OutIter>;
     auto __orig_last        = __last;
     auto __segment_iterator = _Traits::__segment(__result);

lib/libcxx/include/__algorithm/copy_move_common.h

@@ -15,6 +15,7 @@
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__memory/pointer_traits.h>
+#include <__string/constexpr_c_functions.h>
 #include <__type_traits/enable_if.h>
 #include <__type_traits/is_always_bitcastable.h>
 #include <__type_traits/is_constant_evaluated.h>
@@ -61,7 +62,8 @@ template <class _In, class _Out>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_In*, _Out*>
 __copy_trivial_impl(_In* __first, _In* __last, _Out* __result) {
   const size_t __n = static_cast<size_t>(__last - __first);
-  ::__builtin_memmove(__result, __first, __n * sizeof(_Out));
+
+  std::__constexpr_memmove(__result, __first, __element_count(__n));
 
   return std::make_pair(__last, __result + __n);
 }
@@ -72,7 +74,7 @@ __copy_backward_trivial_impl(_In* __first, _In* __last, _Out* __result) {
   const size_t __n = static_cast<size_t>(__last - __first);
   __result -= __n;
 
-  ::__builtin_memmove(__result, __first, __n * sizeof(_Out));
+  std::__constexpr_memmove(__result, __first, __element_count(__n));
 
   return std::make_pair(__last, __result);
 }
@@ -119,16 +121,6 @@ __unwrap_and_dispatch(_InIter __first, _Sent __last, _OutIter __out_first) {
   return _Algorithm()(std::move(__first), std::move(__last), std::move(__out_first));
 }
 
-template <class _IterOps, class _InValue, class _OutIter, class = void>
-struct __can_copy_without_conversion : false_type {};
-
-template <class _IterOps, class _InValue, class _OutIter>
-struct __can_copy_without_conversion<
-    _IterOps,
-    _InValue,
-    _OutIter,
-    __enable_if_t<is_same<_InValue, typename _IterOps::template __value_type<_OutIter> >::value> > : true_type {};
-
 template <class _AlgPolicy,
           class _NaiveAlgorithm,
           class _OptimizedAlgorithm,
@@ -137,23 +129,6 @@ template <class _AlgPolicy,
           class _OutIter>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX17 pair<_InIter, _OutIter>
 __dispatch_copy_or_move(_InIter __first, _Sent __last, _OutIter __out_first) {
-#ifdef _LIBCPP_COMPILER_GCC
-  // GCC doesn't support `__builtin_memmove` during constant evaluation.
-  if (__libcpp_is_constant_evaluated()) {
-    return std::__unwrap_and_dispatch<_NaiveAlgorithm>(std::move(__first), std::move(__last), std::move(__out_first));
-  }
-#else
-  // In Clang, `__builtin_memmove` only supports fully trivially copyable types (just having trivial copy assignment is
-  // insufficient). Also, conversions are not supported.
-  if (__libcpp_is_constant_evaluated()) {
-    using _InValue = typename _IterOps<_AlgPolicy>::template __value_type<_InIter>;
-    if (!is_trivially_copyable<_InValue>::value ||
-        !__can_copy_without_conversion<_IterOps<_AlgPolicy>, _InValue, _OutIter>::value) {
-      return std::__unwrap_and_dispatch<_NaiveAlgorithm>(std::move(__first), std::move(__last), std::move(__out_first));
-    }
-  }
-#endif // _LIBCPP_COMPILER_GCC
-
   using _Algorithm = __overload<_NaiveAlgorithm, _OptimizedAlgorithm>;
   return std::__unwrap_and_dispatch<_Algorithm>(std::move(__first), std::move(__last), std::move(__out_first));
 }

lib/libcxx/include/__algorithm/copy_n.h

@@ -12,8 +12,8 @@
 #include <__algorithm/copy.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
 #include <__utility/convert_to_integral.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -25,8 +25,8 @@ template<class _InputIterator, class _Size, class _OutputIterator>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename enable_if
 <
-    __is_cpp17_input_iterator<_InputIterator>::value &&
+    __has_input_iterator_category<_InputIterator>::value &&
-   !__is_cpp17_random_access_iterator<_InputIterator>::value,
+   !__has_random_access_iterator_category<_InputIterator>::value,
     _OutputIterator
 >::type
 copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result)
@@ -51,7 +51,7 @@ template<class _InputIterator, class _Size, class _OutputIterator>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 typename enable_if
 <
-    __is_cpp17_random_access_iterator<_InputIterator>::value,
+    __has_random_access_iterator_category<_InputIterator>::value,
     _OutputIterator
 >::type
 copy_n(_InputIterator __first, _Size __orig_n, _OutputIterator __result)

lib/libcxx/include/__algorithm/equal.h

@@ -11,9 +11,20 @@
 #define _LIBCPP___ALGORITHM_EQUAL_H
 
 #include <__algorithm/comp.h>
+#include <__algorithm/unwrap_iter.h>
 #include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
+#include <__string/constexpr_c_functions.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/integral_constant.h>
+#include <__type_traits/is_constant_evaluated.h>
+#include <__type_traits/is_equality_comparable.h>
+#include <__type_traits/is_volatile.h>
+#include <__type_traits/predicate_traits.h>
+#include <__utility/move.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -22,23 +33,42 @@
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_iter_impl(
-equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _BinaryPredicate __pred) {
+    _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _BinaryPredicate& __pred) {
   for (; __first1 != __last1; ++__first1, (void)++__first2)
     if (!__pred(*__first1, *__first2))
       return false;
   return true;
 }
 
+template <
+    class _Tp,
+    class _Up,
+    class _BinaryPredicate,
+    __enable_if_t<__is_trivial_equality_predicate<_BinaryPredicate, _Tp, _Up>::value && !is_volatile<_Tp>::value &&
+                      !is_volatile<_Up>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
+                  int> = 0>
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+__equal_iter_impl(_Tp* __first1, _Tp* __last1, _Up* __first2, _BinaryPredicate&) {
+  return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
+}
+
+template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _BinaryPredicate __pred) {
+  return std::__equal_iter_impl(
+      std::__unwrap_iter(__first1), std::__unwrap_iter(__last1), std::__unwrap_iter(__first2), __pred);
+}
+
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2) {
   return std::equal(__first1, __last1, __first2, __equal_to());
 }
 
-#if _LIBCPP_STD_VER > 11
+#if _LIBCPP_STD_VER >= 14
 template <class _BinaryPredicate, class _InputIterator1, class _InputIterator2>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 __equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2,
         _BinaryPredicate __pred, input_iterator_tag, input_iterator_tag) {
   for (; __first1 != __last1 && __first2 != __last2; ++__first1, (void)++__first2)
@@ -47,19 +77,52 @@ __equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __fir
   return __first1 == __last1 && __first2 == __last2;
 }
 
+template <class _Iter1, class _Sent1, class _Iter2, class _Sent2, class _Pred, class _Proj1, class _Proj2>
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_impl(
+    _Iter1 __first1, _Sent1 __last1, _Iter2 __first2, _Sent2 __last2, _Pred& __comp, _Proj1& __proj1, _Proj2& __proj2) {
+  while (__first1 != __last1 && __first2 != __last2) {
+    if (!std::__invoke(__comp, std::__invoke(__proj1, *__first1), std::__invoke(__proj2, *__first2)))
+      return false;
+    ++__first1;
+    ++__first2;
+  }
+  return __first1 == __last1 && __first2 == __last2;
+}
+
+template <class _Tp,
+          class _Up,
+          class _Pred,
+          class _Proj1,
+          class _Proj2,
+          __enable_if_t<__is_trivial_equality_predicate<_Pred, _Tp, _Up>::value && __is_identity<_Proj1>::value &&
+                            __is_identity<_Proj2>::value && !is_volatile<_Tp>::value && !is_volatile<_Up>::value &&
+                            __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value,
+                        int> = 0>
+_LIBCPP_NODISCARD inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool __equal_impl(
+    _Tp* __first1, _Tp* __last1, _Up* __first2, _Up*, _Pred&, _Proj1&, _Proj2&) {
+  return std::__constexpr_memcmp_equal(__first1, __first2, __element_count(__last1 - __first1));
+}
+
 template <class _BinaryPredicate, class _RandomAccessIterator1, class _RandomAccessIterator2>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 __equal(_RandomAccessIterator1 __first1, _RandomAccessIterator1 __last1, _RandomAccessIterator2 __first2,
         _RandomAccessIterator2 __last2, _BinaryPredicate __pred, random_access_iterator_tag,
         random_access_iterator_tag) {
   if (_VSTD::distance(__first1, __last1) != _VSTD::distance(__first2, __last2))
     return false;
-  return _VSTD::equal<_RandomAccessIterator1, _RandomAccessIterator2,
+  __identity __proj;
-                      _BinaryPredicate&>(__first1, __last1, __first2, __pred);
+  return std::__equal_impl(
+      std::__unwrap_iter(__first1),
+      std::__unwrap_iter(__last1),
+      std::__unwrap_iter(__first2),
+      std::__unwrap_iter(__last2),
+      __pred,
+      __proj,
+      __proj);
 }
 
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2,
       _BinaryPredicate __pred) {
   return _VSTD::__equal<_BinaryPredicate&>(
@@ -68,7 +131,7 @@ equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first
 }
 
 template <class _InputIterator1, class _InputIterator2>
-_LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
+_LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 equal(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
   return std::__equal(
       __first1,

lib/libcxx/include/__algorithm/equal_range.h

@@ -50,7 +50,7 @@ __equal_range(_Iter __first, _Sent __last, const _Tp& __value, _Compare&& __comp
     } else {
       _Iter __mp1 = __mid;
       return pair<_Iter, _Iter>(
-          std::__lower_bound_impl<_AlgPolicy>(__first, __mid, __value, __comp, __proj),
+          std::__lower_bound<_AlgPolicy>(__first, __mid, __value, __comp, __proj),
           std::__upper_bound<_AlgPolicy>(++__mp1, __end, __value, __comp, __proj));
     }
   }
@@ -75,11 +75,7 @@ equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __valu
 template <class _ForwardIterator, class _Tp>
 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_ForwardIterator, _ForwardIterator>
 equal_range(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
-  return std::equal_range(
+  return std::equal_range(std::move(__first), std::move(__last), __value, __less<>());
-      std::move(__first),
-      std::move(__last),
-      __value,
-      __less<typename iterator_traits<_ForwardIterator>::value_type, _Tp>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/fill.h

@@ -12,7 +12,6 @@
 #include <__algorithm/fill_n.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

lib/libcxx/include/__algorithm/fill_n.h

@@ -12,7 +12,6 @@
 #include <__config>
 #include <__iterator/iterator_traits.h>
 #include <__utility/convert_to_integral.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

lib/libcxx/include/__algorithm/find.h

@@ -10,7 +10,16 @@
 #ifndef _LIBCPP___ALGORITHM_FIND_H
 #define _LIBCPP___ALGORITHM_FIND_H
 
+#include <__algorithm/unwrap_iter.h>
 #include <__config>
+#include <__functional/identity.h>
+#include <__functional/invoke.h>
+#include <__string/constexpr_c_functions.h>
+#include <__type_traits/is_same.h>
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+#  include <cwchar>
+#endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -18,13 +27,49 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
+template <class _Iter, class _Sent, class _Tp, class _Proj>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Iter
+__find_impl(_Iter __first, _Sent __last, const _Tp& __value, _Proj& __proj) {
+  for (; __first != __last; ++__first)
+    if (std::__invoke(__proj, *__first) == __value)
+      break;
+  return __first;
+}
+
+template <class _Tp,
+          class _Up,
+          class _Proj,
+          __enable_if_t<__is_identity<_Proj>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value &&
+                            sizeof(_Tp) == 1,
+                        int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*
+__find_impl(_Tp* __first, _Tp* __last, const _Up& __value, _Proj&) {
+  if (auto __ret = std::__constexpr_memchr(__first, __value, __last - __first))
+    return __ret;
+  return __last;
+}
+
+#ifndef _LIBCPP_HAS_NO_WIDE_CHARACTERS
+template <class _Tp,
+          class _Up,
+          class _Proj,
+          __enable_if_t<__is_identity<_Proj>::value && __libcpp_is_trivially_equality_comparable<_Tp, _Up>::value &&
+                            sizeof(_Tp) == sizeof(wchar_t) && _LIBCPP_ALIGNOF(_Tp) >= _LIBCPP_ALIGNOF(wchar_t),
+                        int> = 0>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _Tp*
+__find_impl(_Tp* __first, _Tp* __last, const _Up& __value, _Proj&) {
+  if (auto __ret = std::__constexpr_wmemchr(__first, __value, __last - __first))
+    return __ret;
+  return __last;
+}
+#endif // _LIBCPP_HAS_NO_WIDE_CHARACTERS
+
 template <class _InputIterator, class _Tp>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator
 find(_InputIterator __first, _InputIterator __last, const _Tp& __value) {
-  for (; __first != __last; ++__first)
+  __identity __proj;
-    if (*__first == __value)
+  return std::__rewrap_iter(
-      break;
+      __first, std::__find_impl(std::__unwrap_iter(__first), std::__unwrap_iter(__last), __value, __proj));
-  return __first;
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/find_end.h

@@ -15,12 +15,12 @@
 #include <__algorithm/search.h>
 #include <__config>
 #include <__functional/identity.h>
+#include <__functional/invoke.h>
 #include <__iterator/advance.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/next.h>
 #include <__iterator/reverse_iterator.h>
 #include <__utility/pair.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

lib/libcxx/include/__algorithm/for_each_n.h

@@ -12,7 +12,6 @@
 
 #include <__config>
 #include <__utility/convert_to_integral.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -20,7 +19,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 14
+#if _LIBCPP_STD_VER >= 17
 
 template <class _InputIterator, class _Size, class _Function>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20 _InputIterator for_each_n(_InputIterator __first,

lib/libcxx/include/__algorithm/for_each_segment.h

@@ -0,0 +1,53 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_FOR_EACH_SEGMENT_H
+#define _LIBCPP___ALGORITHM_FOR_EACH_SEGMENT_H
+
+#include <__config>
+#include <__iterator/segmented_iterator.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// __for_each_segment is a utility function for optimizing iterating over segmented iterators linearly.
+// __first and __last are expected to be a segmented range. __func is expected to take a range of local iterators.
+// Anything that is returned from __func is ignored.
+
+template <class _SegmentedIterator, class _Functor>
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 void
+__for_each_segment(_SegmentedIterator __first, _SegmentedIterator __last, _Functor __func) {
+  using _Traits = __segmented_iterator_traits<_SegmentedIterator>;
+
+  auto __sfirst = _Traits::__segment(__first);
+  auto __slast  = _Traits::__segment(__last);
+
+  // We are in a single segment, so we might not be at the beginning or end
+  if (__sfirst == __slast) {
+    __func(_Traits::__local(__first), _Traits::__local(__last));
+    return;
+  }
+
+  // We have more than one segment. Iterate over the first segment, since we might not start at the beginning
+  __func(_Traits::__local(__first), _Traits::__end(__sfirst));
+  ++__sfirst;
+  // iterate over the segments which are guaranteed to be completely in the range
+  while (__sfirst != __slast) {
+    __func(_Traits::__begin(__sfirst), _Traits::__end(__sfirst));
+    ++__sfirst;
+  }
+  // iterate over the last segment
+  __func(_Traits::__begin(__sfirst), _Traits::__local(__last));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___ALGORITHM_FOR_EACH_SEGMENT_H

lib/libcxx/include/__algorithm/generate_n.h

@@ -11,7 +11,6 @@
 
 #include <__config>
 #include <__utility/convert_to_integral.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

lib/libcxx/include/__algorithm/half_positive.h

@@ -10,7 +10,9 @@
 #define _LIBCPP___ALGORITHM_HALF_POSITIVE_H
 
 #include <__config>
-#include <type_traits>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_integral.h>
+#include <__type_traits/make_unsigned.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

lib/libcxx/include/__algorithm/in_found_result.h

@@ -18,7 +18,7 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -44,6 +44,6 @@ struct in_found_result {
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_IN_FOUND_RESULT_H

lib/libcxx/include/__algorithm/in_fun_result.h

@@ -20,7 +20,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 template <class _InIter1, class _Func1>
@@ -42,7 +42,7 @@ struct in_fun_result {
 };
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

lib/libcxx/include/__algorithm/in_in_out_result.h

@@ -20,7 +20,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 
@@ -49,7 +49,7 @@ struct in_in_out_result {
 
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

lib/libcxx/include/__algorithm/in_in_result.h

@@ -20,7 +20,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 
@@ -46,7 +46,7 @@ struct in_in_result {
 
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

lib/libcxx/include/__algorithm/in_out_out_result.h

@@ -20,7 +20,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 template <class _InIter1, class _OutIter1, class _OutIter2>
@@ -47,7 +47,7 @@ struct in_out_out_result {
 };
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

lib/libcxx/include/__algorithm/in_out_result.h

@@ -18,9 +18,12 @@
 #  pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 
@@ -46,8 +49,10 @@ struct in_out_result {
 
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_IN_OUT_RESULT_H

lib/libcxx/include/__algorithm/includes.h

@@ -61,13 +61,7 @@ _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 template <class _InputIterator1, class _InputIterator2>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 bool
 includes(_InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
-  return std::includes(
+  return std::includes(std::move(__first1), std::move(__last1), std::move(__first2), std::move(__last2), __less<>());
-      std::move(__first1),
-      std::move(__last1),
-      std::move(__first2),
-      std::move(__last2),
-      __less<typename iterator_traits<_InputIterator1>::value_type,
-             typename iterator_traits<_InputIterator2>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/inplace_merge.h

@@ -246,8 +246,7 @@ inline _LIBCPP_HIDE_FROM_ABI
 void
 inplace_merge(_BidirectionalIterator __first, _BidirectionalIterator __middle, _BidirectionalIterator __last)
 {
-    std::inplace_merge(std::move(__first), std::move(__middle), std::move(__last),
+    std::inplace_merge(std::move(__first), std::move(__middle), std::move(__last), __less<>());
-                        __less<typename iterator_traits<_BidirectionalIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/is_heap.h

@@ -36,7 +36,7 @@ _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 bool
 is_heap(_RandomAccessIterator __first, _RandomAccessIterator __last)
 {
-    return _VSTD::is_heap(__first, __last, __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
+    return _VSTD::is_heap(__first, __last, __less<>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/is_heap_until.h

@@ -58,7 +58,7 @@ template<class _RandomAccessIterator>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _RandomAccessIterator
 is_heap_until(_RandomAccessIterator __first, _RandomAccessIterator __last)
 {
-    return _VSTD::__is_heap_until(__first, __last, __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
+    return _VSTD::__is_heap_until(__first, __last, __less<>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/is_permutation.h

@@ -19,19 +19,22 @@
 #include <__iterator/distance.h>
 #include <__iterator/iterator_traits.h>
 #include <__iterator/next.h>
+#include <__type_traits/is_callable.h>
 #include <__utility/move.h>
-#include <type_traits>
 
 #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 _Iter1, class _Sent1, class _Iter2, class _Sent2, class = void>
 struct _ConstTimeDistance : false_type {};
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 template <class _Iter1, class _Sent1, class _Iter2, class _Sent2>
 struct _ConstTimeDistance<_Iter1, _Sent1, _Iter2, _Sent2, __enable_if_t<
@@ -47,7 +50,7 @@ struct _ConstTimeDistance<_Iter1, _Iter1, _Iter2, _Iter2, __enable_if_t<
     is_same<typename iterator_traits<_Iter2>::iterator_category, random_access_iterator_tag>::value
 > > : true_type {};
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 // Internal functions
 
@@ -202,7 +205,7 @@ is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIt
   return std::is_permutation(__first1, __last1, __first2, __equal_to());
 }
 
-#if _LIBCPP_STD_VER > 11
+#if _LIBCPP_STD_VER >= 14
 
 // 2+2 iterators
 template <class _ForwardIterator1, class _ForwardIterator2>
@@ -231,8 +234,10 @@ is_permutation(_ForwardIterator1 __first1, _ForwardIterator1 __last1, _ForwardIt
       __pred, __identity(), __identity());
 }
 
-#endif // _LIBCPP_STD_VER > 11
+#endif // _LIBCPP_STD_VER >= 14
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_IS_PERMUTATION_H

lib/libcxx/include/__algorithm/is_sorted.h

@@ -36,7 +36,7 @@ _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 bool
 is_sorted(_ForwardIterator __first, _ForwardIterator __last)
 {
-    return _VSTD::is_sorted(__first, __last, __less<typename iterator_traits<_ForwardIterator>::value_type>());
+    return _VSTD::is_sorted(__first, __last, __less<>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/is_sorted_until.h

@@ -48,7 +48,7 @@ template<class _ForwardIterator>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _ForwardIterator
 is_sorted_until(_ForwardIterator __first, _ForwardIterator __last)
 {
-    return _VSTD::is_sorted_until(__first, __last, __less<typename iterator_traits<_ForwardIterator>::value_type>());
+    return _VSTD::is_sorted_until(__first, __last, __less<>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/iterator_operations.h

@@ -33,11 +33,14 @@
 #  pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _AlgPolicy> struct _IterOps;
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 struct _RangeAlgPolicy {};
 
 template <>
@@ -172,4 +175,6 @@ struct _IterOps<_ClassicAlgPolicy> {
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_ITERATOR_OPERATIONS_H

lib/libcxx/include/__algorithm/lexicographical_compare.h

@@ -52,9 +52,7 @@ bool
 lexicographical_compare(_InputIterator1 __first1, _InputIterator1 __last1,
                         _InputIterator2 __first2, _InputIterator2 __last2)
 {
-    return _VSTD::lexicographical_compare(__first1, __last1, __first2, __last2,
+    return _VSTD::lexicographical_compare(__first1, __last1, __first2, __last2, __less<>());
-                                         __less<typename iterator_traits<_InputIterator1>::value_type,
-                                                typename iterator_traits<_InputIterator2>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/lexicographical_compare_three_way.h

@@ -0,0 +1,125 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_LEXICOGRAPHICAL_COMPARE_THREE_WAY_H
+#define _LIBCPP___ALGORITHM_LEXICOGRAPHICAL_COMPARE_THREE_WAY_H
+
+#include <__algorithm/min.h>
+#include <__algorithm/three_way_comp_ref_type.h>
+#include <__compare/compare_three_way.h>
+#include <__compare/ordering.h>
+#include <__concepts/arithmetic.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/common_type.h>
+#include <__type_traits/is_copy_constructible.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
+
+#if _LIBCPP_STD_VER >= 20
+
+// Fast path for random access iterators which computes the number of loop iterations up-front and
+// then skips the iterator comparisons inside the loop.
+template <class _InputIterator1, class _InputIterator2, class _Cmp>
+_LIBCPP_HIDE_FROM_ABI constexpr auto __lexicographical_compare_three_way_fast_path(
+    _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2, _Cmp& __comp)
+    -> decltype(__comp(*__first1, *__first2)) {
+  static_assert(
+      signed_integral<__iter_diff_t<_InputIterator1>>, "Using a non-integral difference_type is undefined behavior.");
+  static_assert(
+      signed_integral<__iter_diff_t<_InputIterator2>>, "Using a non-integral difference_type is undefined behavior.");
+
+  using _Len1   = __iter_diff_t<_InputIterator1>;
+  using _Len2   = __iter_diff_t<_InputIterator2>;
+  using _Common = common_type_t<_Len1, _Len2>;
+
+  _Len1 __len1      = __last1 - __first1;
+  _Len2 __len2      = __last2 - __first2;
+  _Common __min_len = std::min<_Common>(__len1, __len2);
+
+  for (_Common __i = 0; __i < __min_len; ++__i) {
+    auto __c = __comp(*__first1, *__first2);
+    if (__c != 0) {
+      return __c;
+    }
+    ++__first1;
+    ++__first2;
+  }
+
+  return __len1 <=> __len2;
+}
+
+// Unoptimized implementation which compares the iterators against the end in every loop iteration
+template <class _InputIterator1, class _InputIterator2, class _Cmp>
+_LIBCPP_HIDE_FROM_ABI constexpr auto __lexicographical_compare_three_way_slow_path(
+    _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2, _Cmp& __comp)
+    -> decltype(__comp(*__first1, *__first2)) {
+  while (true) {
+    bool __exhausted1 = __first1 == __last1;
+    bool __exhausted2 = __first2 == __last2;
+
+    if (__exhausted1 || __exhausted2) {
+      if (!__exhausted1)
+        return strong_ordering::greater;
+      if (!__exhausted2)
+        return strong_ordering::less;
+      return strong_ordering::equal;
+    }
+
+    auto __c = __comp(*__first1, *__first2);
+    if (__c != 0) {
+      return __c;
+    }
+
+    ++__first1;
+    ++__first2;
+  }
+}
+
+template <class _InputIterator1, class _InputIterator2, class _Cmp>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto lexicographical_compare_three_way(
+    _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2, _Cmp __comp)
+    -> decltype(__comp(*__first1, *__first2)) {
+  static_assert(__comparison_category<decltype(__comp(*__first1, *__first2))>,
+                "The comparator passed to lexicographical_compare_three_way must return a comparison category type.");
+  static_assert(std::is_copy_constructible_v<_InputIterator1>, "Iterators must be copy constructible.");
+  static_assert(std::is_copy_constructible_v<_InputIterator2>, "Iterators must be copy constructible.");
+  __three_way_comp_ref_type<_Cmp> __wrapped_comp_ref(__comp);
+  if constexpr (__has_random_access_iterator_category<_InputIterator1>::value &&
+                __has_random_access_iterator_category<_InputIterator2>::value) {
+    return std::__lexicographical_compare_three_way_fast_path(
+        std::move(__first1), std::move(__last1), std::move(__first2), std::move(__last2), __wrapped_comp_ref);
+  } else {
+    // Unoptimized implementation which compares the iterators against the end in every loop iteration
+    return std::__lexicographical_compare_three_way_slow_path(
+        std::move(__first1), std::move(__last1), std::move(__first2), std::move(__last2), __wrapped_comp_ref);
+  }
+}
+
+template <class _InputIterator1, class _InputIterator2>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr auto lexicographical_compare_three_way(
+    _InputIterator1 __first1, _InputIterator1 __last1, _InputIterator2 __first2, _InputIterator2 __last2) {
+  return std::lexicographical_compare_three_way(
+      std::move(__first1), std::move(__last1), std::move(__first2), std::move(__last2), std::compare_three_way());
+}
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_LEXICOGRAPHICAL_COMPARE_THREE_WAY_H

lib/libcxx/include/__algorithm/lower_bound.h

@@ -20,7 +20,6 @@
 #include <__iterator/iterator_traits.h>
 #include <__type_traits/is_callable.h>
 #include <__type_traits/remove_reference.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -30,7 +29,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _AlgPolicy, class _Iter, class _Sent, class _Type, class _Proj, class _Comp>
 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
-_Iter __lower_bound_impl(_Iter __first, _Sent __last, const _Type& __value, _Comp& __comp, _Proj& __proj) {
+_Iter __lower_bound(_Iter __first, _Sent __last, const _Type& __value, _Comp& __comp, _Proj& __proj) {
   auto __len = _IterOps<_AlgPolicy>::distance(__first, __last);
 
   while (__len != 0) {
@@ -53,14 +52,13 @@ _ForwardIterator lower_bound(_ForwardIterator __first, _ForwardIterator __last,
   static_assert(__is_callable<_Compare, decltype(*__first), const _Tp&>::value,
                 "The comparator has to be callable");
   auto __proj = std::__identity();
-  return std::__lower_bound_impl<_ClassicAlgPolicy>(__first, __last, __value, __comp, __proj);
+  return std::__lower_bound<_ClassicAlgPolicy>(__first, __last, __value, __comp, __proj);
 }
 
 template <class _ForwardIterator, class _Tp>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 _ForwardIterator lower_bound(_ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
-  return std::lower_bound(__first, __last, __value,
+  return std::lower_bound(__first, __last, __value, __less<>());
-                          __less<typename iterator_traits<_ForwardIterator>::value_type, _Tp>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/make_heap.h

@@ -21,6 +21,9 @@
 #  pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _AlgPolicy, class _Compare, class _RandomAccessIterator>
@@ -47,10 +50,11 @@ void make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Com
 template <class _RandomAccessIterator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 void make_heap(_RandomAccessIterator __first, _RandomAccessIterator __last) {
-  std::make_heap(std::move(__first), std::move(__last),
+  std::make_heap(std::move(__first), std::move(__last), __less<>());
-      __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_MAKE_HEAP_H

lib/libcxx/include/__algorithm/make_projected.h

@@ -32,13 +32,14 @@ struct _ProjectedPred {
   _Pred& __pred; // Can be a unary or a binary predicate.
   _Proj& __proj;
 
-  _LIBCPP_CONSTEXPR _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg) : __pred(__pred_arg), __proj(__proj_arg) {}
+  _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI _ProjectedPred(_Pred& __pred_arg, _Proj& __proj_arg)
+      : __pred(__pred_arg), __proj(__proj_arg) {}
 
   template <class _Tp>
   typename __invoke_of<_Pred&,
                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_Tp>()))
   >::type
-  _LIBCPP_CONSTEXPR operator()(_Tp&& __v) const {
+  _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI operator()(_Tp&& __v) const {
     return std::__invoke(__pred, std::__invoke(__proj, std::forward<_Tp>(__v)));
   }
 
@@ -47,7 +48,7 @@ struct _ProjectedPred {
                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T1>())),
                        decltype(std::__invoke(std::declval<_Proj&>(), std::declval<_T2>()))
   >::type
-  _LIBCPP_CONSTEXPR operator()(_T1&& __lhs, _T2&& __rhs) const {
+  _LIBCPP_CONSTEXPR _LIBCPP_HIDE_FROM_ABI operator()(_T1&& __lhs, _T2&& __rhs) const {
     return std::__invoke(__pred,
                       std::__invoke(__proj, std::forward<_T1>(__lhs)),
                       std::__invoke(__proj, std::forward<_T2>(__rhs)));
@@ -55,25 +56,12 @@ struct _ProjectedPred {
 
 };
 
-template <class _Pred, class _Proj, class = void>
+template <class _Pred,
-struct __can_use_pristine_comp : false_type {};
+          class _Proj,
-
+          __enable_if_t<!(!is_member_pointer<__decay_t<_Pred> >::value &&
-template <class _Pred, class _Proj>
+                            __is_identity<__decay_t<_Proj> >::value),
-struct __can_use_pristine_comp<_Pred, _Proj, __enable_if_t<
+                        int> = 0>
-    !is_member_pointer<typename decay<_Pred>::type>::value && (
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _ProjectedPred<_Pred, _Proj>
-#if _LIBCPP_STD_VER > 17
-      is_same<typename decay<_Proj>::type, identity>::value ||
-#endif
-      is_same<typename decay<_Proj>::type, __identity>::value
-    )
-> > : true_type {};
-
-template <class _Pred, class _Proj>
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static
-__enable_if_t<
-    !__can_use_pristine_comp<_Pred, _Proj>::value,
-    _ProjectedPred<_Pred, _Proj>
->
 __make_projected(_Pred& __pred, _Proj& __proj) {
   return _ProjectedPred<_Pred, _Proj>(__pred, __proj);
 }
@@ -81,28 +69,27 @@ __make_projected(_Pred& __pred, _Proj& __proj) {
 // Avoid creating the functor and just use the pristine comparator -- for certain algorithms, this would enable
 // optimizations that rely on the type of the comparator. Additionally, this results in less layers of indirection in
 // the call stack when the comparator is invoked, even in an unoptimized build.
-template <class _Pred, class _Proj>
+template <class _Pred,
-_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR static
+          class _Proj,
-__enable_if_t<
+          __enable_if_t<!is_member_pointer<__decay_t<_Pred> >::value &&
-    __can_use_pristine_comp<_Pred, _Proj>::value,
+                          __is_identity<__decay_t<_Proj> >::value,
-    _Pred&
+                        int> = 0>
->
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR _Pred& __make_projected(_Pred& __pred, _Proj&) {
-__make_projected(_Pred& __pred, _Proj&) {
   return __pred;
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
 template <class _Comp, class _Proj1, class _Proj2>
-_LIBCPP_HIDE_FROM_ABI constexpr static
+_LIBCPP_HIDE_FROM_ABI constexpr
 decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __proj2) {
-  if constexpr (same_as<decay_t<_Proj1>, identity> && same_as<decay_t<_Proj2>, identity> &&
+  if constexpr (__is_identity<decay_t<_Proj1>>::value && __is_identity<decay_t<_Proj2>>::value &&
                 !is_member_pointer_v<decay_t<_Comp>>) {
     // Avoid creating the lambda and just use the pristine comparator -- for certain algorithms, this would enable
     // optimizations that rely on the type of the comparator.
@@ -121,6 +108,6 @@ decltype(auto) __make_projected_comp(_Comp& __comp, _Proj1& __proj1, _Proj2& __p
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_MAKE_PROJECTED_H

lib/libcxx/include/__algorithm/max.h

@@ -28,7 +28,7 @@ template <class _Tp, class _Compare>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 const _Tp&
-max(const _Tp& __a, const _Tp& __b, _Compare __comp)
+max(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b, _Compare __comp)
 {
     return __comp(__a, __b) ? __b : __a;
 }
@@ -37,9 +37,9 @@ template <class _Tp>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 const _Tp&
-max(const _Tp& __a, const _Tp& __b)
+max(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b)
 {
-    return _VSTD::max(__a, __b, __less<_Tp>());
+    return _VSTD::max(__a, __b, __less<>());
 }
 
 #ifndef _LIBCPP_CXX03_LANG
@@ -59,7 +59,7 @@ _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 _Tp
 max(initializer_list<_Tp> __t)
 {
-    return *_VSTD::max_element(__t.begin(), __t.end(), __less<_Tp>());
+    return *_VSTD::max_element(__t.begin(), __t.end(), __less<>());
 }
 
 #endif // _LIBCPP_CXX03_LANG

lib/libcxx/include/__algorithm/max_element.h

@@ -24,7 +24,7 @@ template <class _Compare, class _ForwardIterator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 __max_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
 {
-    static_assert(__is_cpp17_forward_iterator<_ForwardIterator>::value,
+    static_assert(__has_forward_iterator_category<_ForwardIterator>::value,
         "std::max_element requires a ForwardIterator");
     if (__first != __last)
     {
@@ -48,8 +48,7 @@ template <class _ForwardIterator>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 max_element(_ForwardIterator __first, _ForwardIterator __last)
 {
-    return _VSTD::max_element(__first, __last,
+    return _VSTD::max_element(__first, __last, __less<>());
-              __less<typename iterator_traits<_ForwardIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/merge.h

@@ -60,9 +60,7 @@ _OutputIterator
 merge(_InputIterator1 __first1, _InputIterator1 __last1,
       _InputIterator2 __first2, _InputIterator2 __last2, _OutputIterator __result)
 {
-    typedef typename iterator_traits<_InputIterator1>::value_type __v1;
+    return _VSTD::merge(__first1, __last1, __first2, __last2, __result, __less<>());
-    typedef typename iterator_traits<_InputIterator2>::value_type __v2;
-    return _VSTD::merge(__first1, __last1, __first2, __last2, __result, __less<__v1, __v2>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/min.h

@@ -28,7 +28,7 @@ template <class _Tp, class _Compare>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 const _Tp&
-min(const _Tp& __a, const _Tp& __b, _Compare __comp)
+min(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b, _Compare __comp)
 {
     return __comp(__b, __a) ? __b : __a;
 }
@@ -37,9 +37,9 @@ template <class _Tp>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 const _Tp&
-min(const _Tp& __a, const _Tp& __b)
+min(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b)
 {
-    return _VSTD::min(__a, __b, __less<_Tp>());
+    return _VSTD::min(__a, __b, __less<>());
 }
 
 #ifndef _LIBCPP_CXX03_LANG
@@ -59,7 +59,7 @@ _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 _Tp
 min(initializer_list<_Tp> __t)
 {
-    return *_VSTD::min_element(__t.begin(), __t.end(), __less<_Tp>());
+    return *_VSTD::min_element(__t.begin(), __t.end(), __less<>());
 }
 
 #endif // _LIBCPP_CXX03_LANG

lib/libcxx/include/__algorithm/min_element.h

@@ -22,6 +22,9 @@
 #  pragma GCC system_header
 #endif
 
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 template <class _Comp, class _Iter, class _Sent, class _Proj>
@@ -49,7 +52,7 @@ template <class _ForwardIterator, class _Compare>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 min_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp)
 {
-  static_assert(__is_cpp17_forward_iterator<_ForwardIterator>::value,
+  static_assert(__has_forward_iterator_category<_ForwardIterator>::value,
       "std::min_element requires a ForwardIterator");
   static_assert(__is_callable<_Compare, decltype(*__first), decltype(*__first)>::value,
               "The comparator has to be callable");
@@ -61,10 +64,11 @@ template <class _ForwardIterator>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 _ForwardIterator
 min_element(_ForwardIterator __first, _ForwardIterator __last)
 {
-    return _VSTD::min_element(__first, __last,
+    return _VSTD::min_element(__first, __last, __less<>());
-              __less<typename iterator_traits<_ForwardIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_MIN_ELEMENT_H

lib/libcxx/include/__algorithm/min_max_result.h

@@ -23,7 +23,7 @@ _LIBCPP_PUSH_MACROS
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 
@@ -47,7 +47,7 @@ struct min_max_result {
 
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

lib/libcxx/include/__algorithm/minmax.h

@@ -27,7 +27,7 @@ template<class _Tp, class _Compare>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 pair<const _Tp&, const _Tp&>
-minmax(const _Tp& __a, const _Tp& __b, _Compare __comp)
+minmax(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b, _Compare __comp)
 {
     return __comp(__b, __a) ? pair<const _Tp&, const _Tp&>(__b, __a) :
                               pair<const _Tp&, const _Tp&>(__a, __b);
@@ -37,9 +37,9 @@ template<class _Tp>
 _LIBCPP_NODISCARD_EXT inline
 _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 pair<const _Tp&, const _Tp&>
-minmax(const _Tp& __a, const _Tp& __b)
+minmax(_LIBCPP_LIFETIMEBOUND const _Tp& __a, _LIBCPP_LIFETIMEBOUND const _Tp& __b)
 {
-    return std::minmax(__a, __b, __less<_Tp>());
+    return std::minmax(__a, __b, __less<>());
 }
 
 #ifndef _LIBCPP_CXX03_LANG
@@ -59,7 +59,7 @@ _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX14
 pair<_Tp, _Tp>
 minmax(initializer_list<_Tp> __t)
 {
-    return std::minmax(__t, __less<_Tp>());
+    return std::minmax(__t, __less<>());
 }
 
 #endif // _LIBCPP_CXX03_LANG

lib/libcxx/include/__algorithm/minmax_element.h

@@ -12,9 +12,10 @@
 #include <__algorithm/comp.h>
 #include <__config>
 #include <__functional/identity.h>
+#include <__functional/invoke.h>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/is_callable.h>
 #include <__utility/pair.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -82,7 +83,7 @@ template <class _ForwardIterator, class _Compare>
 _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 pair<_ForwardIterator, _ForwardIterator>
 minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __comp) {
-  static_assert(__is_cpp17_forward_iterator<_ForwardIterator>::value,
+  static_assert(__has_forward_iterator_category<_ForwardIterator>::value,
                 "std::minmax_element requires a ForwardIterator");
   static_assert(__is_callable<_Compare, decltype(*__first), decltype(*__first)>::value,
                 "The comparator has to be callable");
@@ -93,7 +94,7 @@ minmax_element(_ForwardIterator __first, _ForwardIterator __last, _Compare __com
 template <class _ForwardIterator>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 pair<_ForwardIterator, _ForwardIterator> minmax_element(_ForwardIterator __first, _ForwardIterator __last) {
-    return std::minmax_element(__first, __last, __less<typename iterator_traits<_ForwardIterator>::value_type>());
+    return std::minmax_element(__first, __last, __less<>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/mismatch.h

@@ -38,7 +38,7 @@ _LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY
   return std::mismatch(__first1, __last1, __first2, __equal_to());
 }
 
-#if _LIBCPP_STD_VER > 11
+#if _LIBCPP_STD_VER >= 14
 template <class _InputIterator1, class _InputIterator2, class _BinaryPredicate>
 _LIBCPP_NODISCARD_EXT inline _LIBCPP_INLINE_VISIBILITY
     _LIBCPP_CONSTEXPR_SINCE_CXX20 pair<_InputIterator1, _InputIterator2>

lib/libcxx/include/__algorithm/move.h

@@ -10,6 +10,7 @@
 #define _LIBCPP___ALGORITHM_MOVE_H
 
 #include <__algorithm/copy_move_common.h>
+#include <__algorithm/for_each_segment.h>
 #include <__algorithm/iterator_operations.h>
 #include <__algorithm/min.h>
 #include <__config>
@@ -45,36 +46,34 @@ struct __move_loop {
     return std::make_pair(std::move(__first), std::move(__result));
   }
 
+  template <class _InIter, class _OutIter>
+  struct _MoveSegment {
+    using _Traits = __segmented_iterator_traits<_InIter>;
+
+    _OutIter& __result_;
+
+    _LIBCPP_HIDE_FROM_ABI _MoveSegment(_OutIter& __result) : __result_(__result) {}
+
+    _LIBCPP_HIDE_FROM_ABI void
+    operator()(typename _Traits::__local_iterator __lfirst, typename _Traits::__local_iterator __llast) {
+      __result_ = std::__move<_AlgPolicy>(__lfirst, __llast, std::move(__result_)).second;
+    }
+  };
+
   template <class _InIter, class _OutIter, __enable_if_t<__is_segmented_iterator<_InIter>::value, int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
   operator()(_InIter __first, _InIter __last, _OutIter __result) const {
-    using _Traits = __segmented_iterator_traits<_InIter>;
+    std::__for_each_segment(__first, __last, _MoveSegment<_InIter, _OutIter>(__result));
-    auto __sfirst = _Traits::__segment(__first);
-    auto __slast  = _Traits::__segment(__last);
-    if (__sfirst == __slast) {
-      auto __iters = std::__move<_AlgPolicy>(_Traits::__local(__first), _Traits::__local(__last), std::move(__result));
-      return std::make_pair(__last, std::move(__iters.second));
-    }
-
-    __result = std::__move<_AlgPolicy>(_Traits::__local(__first), _Traits::__end(__sfirst), std::move(__result)).second;
-    ++__sfirst;
-    while (__sfirst != __slast) {
-      __result =
-          std::__move<_AlgPolicy>(_Traits::__begin(__sfirst), _Traits::__end(__sfirst), std::move(__result)).second;
-      ++__sfirst;
-    }
-    __result =
-        std::__move<_AlgPolicy>(_Traits::__begin(__sfirst), _Traits::__local(__last), std::move(__result)).second;
     return std::make_pair(__last, std::move(__result));
   }
 
   template <class _InIter,
             class _OutIter,
-            __enable_if_t<__is_cpp17_random_access_iterator<_InIter>::value &&
+            __enable_if_t<__has_random_access_iterator_category<_InIter>::value &&
                               !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _InIter __last, _OutIter __result) {
+  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
     using _Traits = __segmented_iterator_traits<_OutIter>;
     using _DiffT  = typename common_type<__iter_diff_t<_InIter>, __iter_diff_t<_OutIter> >::type;
 

lib/libcxx/include/__algorithm/move_backward.h

@@ -76,11 +76,11 @@ struct __move_backward_loop {
 
   template <class _InIter,
             class _OutIter,
-            __enable_if_t<__is_cpp17_random_access_iterator<_InIter>::value &&
+            __enable_if_t<__has_random_access_iterator_category<_InIter>::value &&
                               !__is_segmented_iterator<_InIter>::value && __is_segmented_iterator<_OutIter>::value,
                           int> = 0>
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14 pair<_InIter, _OutIter>
-  operator()(_InIter __first, _InIter __last, _OutIter __result) {
+  operator()(_InIter __first, _InIter __last, _OutIter __result) const {
     using _Traits = __segmented_iterator_traits<_OutIter>;
     using _DiffT  = typename common_type<__iter_diff_t<_InIter>, __iter_diff_t<_OutIter> >::type;
 

lib/libcxx/include/__algorithm/next_permutation.h

@@ -69,8 +69,7 @@ inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 bool
 next_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last)
 {
-    return _VSTD::next_permutation(__first, __last,
+    return _VSTD::next_permutation(__first, __last, __less<>());
-                                  __less<typename iterator_traits<_BidirectionalIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/nth_element.h

@@ -14,7 +14,6 @@
 #include <__algorithm/iterator_operations.h>
 #include <__algorithm/sort.h>
 #include <__config>
-#include <__debug>
 #include <__debug_utils/randomize_range.h>
 #include <__iterator/iterator_traits.h>
 #include <__utility/move.h>
@@ -249,8 +248,7 @@ void nth_element(_RandomAccessIterator __first, _RandomAccessIterator __nth, _Ra
 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<typename
+  std::nth_element(std::move(__first), std::move(__nth), std::move(__last), __less<>());
-      iterator_traits<_RandomAccessIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/partial_sort.h

@@ -16,11 +16,11 @@
 #include <__algorithm/sift_down.h>
 #include <__algorithm/sort_heap.h>
 #include <__config>
-#include <__debug>
 #include <__debug_utils/randomize_range.h>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/is_copy_assignable.h>
+#include <__type_traits/is_copy_constructible.h>
 #include <__utility/move.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
@@ -87,8 +87,7 @@ inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 void
 partial_sort(_RandomAccessIterator __first, _RandomAccessIterator __middle, _RandomAccessIterator __last)
 {
-    _VSTD::partial_sort(__first, __middle, __last,
+    _VSTD::partial_sort(__first, __middle, __last, __less<>());
-                        __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/partial_sort_copy.h

@@ -79,8 +79,7 @@ _RandomAccessIterator
 partial_sort_copy(_InputIterator __first, _InputIterator __last,
                   _RandomAccessIterator __result_first, _RandomAccessIterator __result_last)
 {
-    return _VSTD::partial_sort_copy(__first, __last, __result_first, __result_last,
+    return _VSTD::partial_sort_copy(__first, __last, __result_first, __result_last, __less<>());
-                                   __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/partition.h

@@ -14,7 +14,6 @@
 #include <__iterator/iterator_traits.h>
 #include <__utility/move.h>
 #include <__utility/pair.h>
-#include <type_traits>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header

lib/libcxx/include/__algorithm/pop_heap.h

@@ -17,20 +17,24 @@
 #include <__assert>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/is_copy_assignable.h>
+#include <__type_traits/is_copy_constructible.h>
 #include <__utility/move.h>
-#include <type_traits>
 
 #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 _AlgPolicy, class _Compare, class _RandomAccessIterator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX14
 void __pop_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Compare& __comp,
     typename iterator_traits<_RandomAccessIterator>::difference_type __len) {
-  _LIBCPP_ASSERT(__len > 0, "The heap given to pop_heap must be non-empty");
+  _LIBCPP_ASSERT_UNCATEGORIZED(__len > 0, "The heap given to pop_heap must be non-empty");
 
   __comp_ref_type<_Compare> __comp_ref = __comp;
 
@@ -64,10 +68,11 @@ void pop_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp
 template <class _RandomAccessIterator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 void pop_heap(_RandomAccessIterator __first, _RandomAccessIterator __last) {
-  std::pop_heap(std::move(__first), std::move(__last),
+  std::pop_heap(std::move(__first), std::move(__last), __less<>());
-      __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_POP_HEAP_H

lib/libcxx/include/__algorithm/prev_permutation.h

@@ -70,8 +70,7 @@ inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 bool
 prev_permutation(_BidirectionalIterator __first, _BidirectionalIterator __last)
 {
-    return _VSTD::prev_permutation(__first, __last,
+    return _VSTD::prev_permutation(__first, __last, __less<>());
-                                  __less<typename iterator_traits<_BidirectionalIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD

lib/libcxx/include/__algorithm/pstl_any_all_none_of.h

@@ -0,0 +1,100 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_ANY_ALL_NONE_OF_H
+#define _LIBCPP___ALGORITHM_PSTL_ANY_ALL_NONE_OF_H
+
+#include <__algorithm/pstl_find.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__iterator/cpp17_iterator_concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_any_of(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI bool
+any_of(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_any_of),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, _Predicate __g_pred) {
+        return std::find_if(__policy, __g_first, __g_last, __g_pred) != __g_last;
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+template <class>
+void __pstl_all_of(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Pred,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI bool
+all_of(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Pred __pred) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_all_of),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, _Pred __g_pred) {
+        return !std::any_of(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __value) {
+          return !__g_pred(__value);
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+template <class>
+void __pstl_none_of(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Pred,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI bool
+none_of(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Pred __pred) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_none_of),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, _Pred __g_pred) {
+        return !std::any_of(__policy, __g_first, __g_last, __g_pred);
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_ANY_ALL_NONE_OF_H

lib/libcxx/include/__algorithm/pstl_backend.h

@@ -0,0 +1,198 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKEND_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKEND_H
+
+#include <__algorithm/pstl_backends/cpu_backend.h>
+#include <__config>
+#include <execution>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+/*
+TODO: Documentation of how backends work
+
+A PSTL parallel backend is a tag type to which the following functions are associated, at minimum:
+
+  template <class _ExecutionPolicy, class _Iterator, class _Func>
+  void __pstl_for_each(_Backend, _ExecutionPolicy&&, _Iterator __first, _Iterator __last, _Func __f);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  _Iterator __pstl_find_if(_Backend, _Iterator __first, _Iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _RandomAccessIterator, class _Comp>
+  void __pstl_stable_sort(_Backend, _RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp);
+
+  template <class _ExecutionPolicy, class _InIterator, class _OutIterator, class _UnaryOperation>
+  _OutIterator __pstl_transform(_InIterator __first, _InIterator __last, _OutIterator __result, _UnaryOperation __op);
+
+  template <class _ExecutionPolicy, class _InIterator1, class _InIterator2, class _OutIterator, class _BinaryOperation>
+  _OutIterator __pstl_transform(_InIterator1 __first1,
+                                _InIterator1 __last1,
+                                _InIterator2 __first2,
+                                _OutIterator __result,
+                                _BinaryOperation __op);
+
+  template <class _ExecutionPolicy,
+            class _Iterator1,
+            class _Iterator2,
+            class _Tp,
+            class _BinaryOperation1,
+            class _BinaryOperation2>
+  _Tp __pstl_transform_reduce(_Backend,
+                              _Iterator1 __first1,
+                              _Iterator1 __last1,
+                              _Iterator2 __first2,
+                              _Iterator2 __last2,
+                              _Tp __init,
+                              _BinaryOperation1 __reduce,
+                              _BinaryOperation2 __transform);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Tp, class _BinaryOperation, class _UnaryOperation>
+  _Tp __pstl_transform_reduce(_Backend,
+                              _Iterator __first,
+                              _Iterator __last,
+                              _Tp __init,
+                              _BinaryOperation __reduce,
+                              _UnaryOperation __transform);
+
+// TODO: Complete this list
+
+The following functions are optional but can be provided. If provided, they are used by the corresponding
+algorithms, otherwise they are implemented in terms of other algorithms. If none of the optional algorithms are
+implemented, all the algorithms will eventually forward to the basis algorithms listed above:
+
+  template <class _ExecutionPolicy, class _Iterator, class _Size, class _Func>
+  void __pstl_for_each_n(_Backend, _Iterator __first, _Size __n, _Func __f);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  bool __pstl_any_of(_Backend, _Iterator __first, _iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  bool __pstl_all_of(_Backend, _Iterator __first, _iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  bool __pstl_none_of(_Backend, _Iterator __first, _iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Tp>
+  _Iterator __pstl_find(_Backend, _Iterator __first, _Iterator __last, const _Tp& __value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  _Iterator __pstl_find_if_not(_Backend, _Iterator __first, _Iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Tp>
+  void __pstl_fill(_Backend, _Iterator __first, _Iterator __last, const _Tp& __value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _SizeT, class _Tp>
+  void __pstl_fill_n(_Backend, _Iterator __first, _SizeT __n, const _Tp& __value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Generator>
+  void __pstl_generate(_Backend, _Iterator __first, _Iterator __last, _Generator __gen);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  void __pstl_is_partitioned(_Backend, _Iterator __first, _Iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Size, class _Generator>
+  void __pstl_generator_n(_Backend, _Iterator __first, _Size __n, _Generator __gen);
+
+  template <class _ExecutionPolicy, class _terator1, class _Iterator2, class _OutIterator, class _Comp>
+  _OutIterator __pstl_merge(_Backend,
+                            _Iterator1 __first1,
+                            _Iterator1 __last1,
+                            _Iterator2 __first2,
+                            _Iterator2 __last2,
+                            _OutIterator __result,
+                            _Comp __comp);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Tp, class _BinaryOperation>
+  _Tp __pstl_reduce(_Backend, _Iterator __first, _Iterator __last, _Tp __init, _BinaryOperation __op);
+
+  temlate <class _ExecutionPolicy, class _Iterator>
+  __iter_value_type<_Iterator> __pstl_reduce(_Backend, _Iterator __first, _Iterator __last);
+
+  template <class _ExecuitonPolicy, class _Iterator, class _Tp>
+  __iter_diff_t<_Iterator> __pstl_count(_Backend, _Iterator __first, _Iterator __last, const _Tp& __value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Predicate>
+  __iter_diff_t<_Iterator> __pstl_count_if(_Backend, _Iterator __first, _Iterator __last, _Predicate __pred);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Tp>
+  void __pstl_replace(_Backend, _Iterator __first, _Iterator __last, const _Tp& __old_value, const _Tp& __new_value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Pred, class _Tp>
+  void __pstl_replace_if(_Backend, _Iterator __first, _Iterator __last, _Pred __pred, const _Tp& __new_value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _OutIterator, class _Tp>
+  void __pstl_replace_copy(_Backend,
+                           _Iterator __first,
+                           _Iterator __last,
+                           _OutIterator __result,
+                           const _Tp& __old_value,
+                           const _Tp& __new_value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _OutIterator, class _Pred, class _Tp>
+  void __pstl_replace_copy_if(_Backend,
+                              _Iterator __first,
+                              _Iterator __last,
+                              _OutIterator __result,
+                              _Pred __pred,
+                              const _Tp& __new_value);
+
+  template <class _ExecutionPolicy, class _Iterator, class _Comp>
+  void __pstl_sort(_Backend, _Iterator __first, _Iterator __last, _Comp __comp);
+
+// TODO: Complete this list
+
+*/
+
+template <class _ExecutionPolicy>
+struct __select_backend;
+
+template <>
+struct __select_backend<std::execution::sequenced_policy> {
+  using type = __cpu_backend_tag;
+};
+
+#  if _LIBCPP_STD_VER >= 20
+template <>
+struct __select_backend<std::execution::unsequenced_policy> {
+  using type = __cpu_backend_tag;
+};
+#  endif
+
+#  if defined(_LIBCPP_PSTL_CPU_BACKEND_SERIAL) || defined(_LIBCPP_PSTL_CPU_BACKEND_THREAD) ||                          \
+      defined(_LIBCPP_PSTL_CPU_BACKEND_LIBDISPATCH)
+template <>
+struct __select_backend<std::execution::parallel_policy> {
+  using type = __cpu_backend_tag;
+};
+
+template <>
+struct __select_backend<std::execution::parallel_unsequenced_policy> {
+  using type = __cpu_backend_tag;
+};
+
+#  else
+
+// ...New vendors can add parallel backends here...
+
+#    error "Invalid choice of a PSTL parallel backend"
+#  endif
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKEND_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backend.h

@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKEND_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKEND_H
+
+#include <__config>
+
+/*
+
+  // _Functor takes a subrange for [__first, __last) that should be executed in serial
+  template <class _RandomAccessIterator, class _Functor>
+  void __parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Functor __func);
+
+  template <class _Iterator, class _UnaryOp, class _Tp, class _BinaryOp, class _Reduction>
+  _Tp __parallel_transform_reduce(_Iterator __first, _Iterator __last, _UnaryOp, _Tp __init, _BinaryOp, _Reduction);
+
+  // Cancel the execution of other jobs - they aren't needed anymore
+  void __cancel_execution();
+
+  template <class _RandomAccessIterator1,
+            class _RandomAccessIterator2,
+            class _RandomAccessIterator3,
+            class _Compare,
+            class _LeafMerge>
+  void __parallel_merge(
+      _RandomAccessIterator1 __first1,
+      _RandomAccessIterator1 __last1,
+      _RandomAccessIterator2 __first2,
+      _RandomAccessIterator2 __last2,
+      _RandomAccessIterator3 __outit,
+      _Compare __comp,
+      _LeafMerge __leaf_merge);
+
+  template <class _RandomAccessIterator, class _Comp, class _LeafSort>
+  void __parallel_stable_sort(_RandomAccessIterator __first,
+                              _RandomAccessIterator __last,
+                              _Comp __comp,
+                              _LeafSort __leaf_sort);
+
+  TODO: Document the parallel backend
+*/
+
+#include <__algorithm/pstl_backends/cpu_backends/any_of.h>
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__algorithm/pstl_backends/cpu_backends/fill.h>
+#include <__algorithm/pstl_backends/cpu_backends/find_if.h>
+#include <__algorithm/pstl_backends/cpu_backends/for_each.h>
+#include <__algorithm/pstl_backends/cpu_backends/merge.h>
+#include <__algorithm/pstl_backends/cpu_backends/stable_sort.h>
+#include <__algorithm/pstl_backends/cpu_backends/transform.h>
+#include <__algorithm/pstl_backends/cpu_backends/transform_reduce.h>
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKEND_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/any_of.h

@@ -0,0 +1,90 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKEND_ANY_OF_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKEND_ANY_OF_H
+
+#include <__algorithm/any_of.h>
+#include <__algorithm/find_if.h>
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__atomic/atomic.h>
+#include <__atomic/memory_order.h>
+#include <__config>
+#include <__functional/operations.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/pair.h>
+#include <__utility/terminate_on_exception.h>
+#include <cstdint>
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Index, class _Brick>
+_LIBCPP_HIDE_FROM_ABI bool __parallel_or(_Index __first, _Index __last, _Brick __f) {
+  std::atomic<bool> __found(false);
+  __par_backend::__parallel_for(__first, __last, [__f, &__found](_Index __i, _Index __j) {
+    if (!__found.load(std::memory_order_relaxed) && __f(__i, __j)) {
+      __found.store(true, std::memory_order_relaxed);
+      __par_backend::__cancel_execution();
+    }
+  });
+  return __found;
+}
+
+// TODO: check whether __simd_first() can be used here
+template <class _Index, class _DifferenceType, class _Pred>
+_LIBCPP_HIDE_FROM_ABI bool __simd_or(_Index __first, _DifferenceType __n, _Pred __pred) noexcept {
+  _DifferenceType __block_size = 4 < __n ? 4 : __n;
+  const _Index __last          = __first + __n;
+  while (__last != __first) {
+    int32_t __flag = 1;
+    _PSTL_PRAGMA_SIMD_REDUCTION(& : __flag)
+    for (_DifferenceType __i = 0; __i < __block_size; ++__i)
+      if (__pred(*(__first + __i)))
+        __flag = 0;
+    if (!__flag)
+      return true;
+
+    __first += __block_size;
+    if (__last - __first >= __block_size << 1) {
+      // Double the block _Size.  Any unnecessary iterations can be amortized against work done so far.
+      __block_size <<= 1;
+    } else {
+      __block_size = __last - __first;
+    }
+  }
+  return false;
+}
+
+template <class _ExecutionPolicy, class _ForwardIterator, class _Predicate>
+_LIBCPP_HIDE_FROM_ABI bool
+__pstl_any_of(__cpu_backend_tag, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator>::value) {
+    return std::__terminate_on_exception([&] {
+      return std::__parallel_or(
+          __first, __last, [&__pred](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {
+            return std::__pstl_any_of<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{}, __brick_first, __brick_last, __pred);
+          });
+    });
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator>::value) {
+    return std::__simd_or(__first, __last - __first, __pred);
+  } else {
+    return std::any_of(__first, __last, __pred);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKEND_ANY_OF_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/backend.h

@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKEND_BACKEND_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKEND_BACKEND_H
+
+#include <__config>
+#include <cstddef>
+
+#if defined(_LIBCPP_PSTL_CPU_BACKEND_SERIAL)
+#  include <__algorithm/pstl_backends/cpu_backends/serial.h>
+#elif defined(_LIBCPP_PSTL_CPU_BACKEND_THREAD)
+#  include <__algorithm/pstl_backends/cpu_backends/thread.h>
+#elif defined(_LIBCPP_PSTL_CPU_BACKEND_LIBDISPATCH)
+#  include <__algorithm/pstl_backends/cpu_backends/libdispatch.h>
+#else
+#  error "Invalid CPU backend choice"
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+struct __cpu_backend_tag {};
+
+inline constexpr size_t __lane_size = 64;
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKEND_BACKEND_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/fill.h

@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_FILL_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FILL_H
+
+#include <__algorithm/fill.h>
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Index, class _DifferenceType, class _Tp>
+_LIBCPP_HIDE_FROM_ABI _Index __simd_fill_n(_Index __first, _DifferenceType __n, const _Tp& __value) noexcept {
+  _PSTL_USE_NONTEMPORAL_STORES_IF_ALLOWED
+  _PSTL_PRAGMA_SIMD
+  for (_DifferenceType __i = 0; __i < __n; ++__i)
+    __first[__i] = __value;
+  return __first + __n;
+}
+
+template <class _ExecutionPolicy, class _ForwardIterator, class _Tp>
+_LIBCPP_HIDE_FROM_ABI void
+__pstl_fill(__cpu_backend_tag, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator>::value) {
+    std::__terminate_on_exception([&] {
+      __par_backend::__parallel_for(
+          __first, __last, [&__value](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {
+            std::__pstl_fill<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{}, __brick_first, __brick_last, __value);
+          });
+    });
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator>::value) {
+    std::__simd_fill_n(__first, __last - __first, __value);
+  } else {
+    std::fill(__first, __last, __value);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FILL_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/find_if.h

@@ -0,0 +1,123 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_FIND_IF_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FIND_IF_H
+
+#include <__algorithm/find_if.h>
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__atomic/atomic.h>
+#include <__config>
+#include <__functional/operations.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/pair.h>
+#include <__utility/terminate_on_exception.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Index, class _Brick, class _Compare>
+_LIBCPP_HIDE_FROM_ABI _Index
+__parallel_find(_Index __first, _Index __last, _Brick __f, _Compare __comp, bool __b_first) {
+  typedef typename std::iterator_traits<_Index>::difference_type _DifferenceType;
+  const _DifferenceType __n      = __last - __first;
+  _DifferenceType __initial_dist = __b_first ? __n : -1;
+  std::atomic<_DifferenceType> __extremum(__initial_dist);
+  // TODO: find out what is better here: parallel_for or parallel_reduce
+  __par_backend::__parallel_for(__first, __last, [__comp, __f, __first, &__extremum](_Index __i, _Index __j) {
+    // See "Reducing Contention Through Priority Updates", PPoPP '13, for discussion of
+    // why using a shared variable scales fairly well in this situation.
+    if (__comp(__i - __first, __extremum)) {
+      _Index __res = __f(__i, __j);
+      // If not '__last' returned then we found what we want so put this to extremum
+      if (__res != __j) {
+        const _DifferenceType __k = __res - __first;
+        for (_DifferenceType __old = __extremum; __comp(__k, __old); __old = __extremum) {
+          __extremum.compare_exchange_weak(__old, __k);
+        }
+      }
+    }
+  });
+  return __extremum != __initial_dist ? __first + __extremum : __last;
+}
+
+template <class _Index, class _DifferenceType, class _Compare>
+_LIBCPP_HIDE_FROM_ABI _Index
+__simd_first(_Index __first, _DifferenceType __begin, _DifferenceType __end, _Compare __comp) noexcept {
+  // Experiments show good block sizes like this
+  const _DifferenceType __block_size                        = 8;
+  alignas(__lane_size) _DifferenceType __lane[__block_size] = {0};
+  while (__end - __begin >= __block_size) {
+    _DifferenceType __found = 0;
+    _PSTL_PRAGMA_SIMD_REDUCTION(| : __found) for (_DifferenceType __i = __begin; __i < __begin + __block_size; ++__i) {
+      const _DifferenceType __t = __comp(__first, __i);
+      __lane[__i - __begin]     = __t;
+      __found |= __t;
+    }
+    if (__found) {
+      _DifferenceType __i;
+      // This will vectorize
+      for (__i = 0; __i < __block_size; ++__i) {
+        if (__lane[__i]) {
+          break;
+        }
+      }
+      return __first + __begin + __i;
+    }
+    __begin += __block_size;
+  }
+
+  // Keep remainder scalar
+  while (__begin != __end) {
+    if (__comp(__first, __begin)) {
+      return __first + __begin;
+    }
+    ++__begin;
+  }
+  return __first + __end;
+}
+
+template <class _ExecutionPolicy, class _ForwardIterator, class _Predicate>
+_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+__pstl_find_if(__cpu_backend_tag, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator>::value) {
+    return std::__terminate_on_exception([&] {
+      return std::__parallel_find(
+          __first,
+          __last,
+          [&__pred](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {
+            return std::__pstl_find_if<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{}, __brick_first, __brick_last, __pred);
+          },
+          less<>{},
+          true);
+    });
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator>::value) {
+    using __diff_t = __iter_diff_t<_ForwardIterator>;
+    return std::__simd_first(__first, __diff_t(0), __last - __first, [&__pred](_ForwardIterator __iter, __diff_t __i) {
+      return __pred(__iter[__i]);
+    });
+  } else {
+    return std::find_if(__first, __last, __pred);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_FIND_IF_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/for_each.h

@@ -0,0 +1,60 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKNEDS_FOR_EACH_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKNEDS_FOR_EACH_H
+
+#include <__algorithm/for_each.h>
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Iterator, class _DifferenceType, class _Function>
+_LIBCPP_HIDE_FROM_ABI _Iterator __simd_walk_1(_Iterator __first, _DifferenceType __n, _Function __f) noexcept {
+  _PSTL_PRAGMA_SIMD
+  for (_DifferenceType __i = 0; __i < __n; ++__i)
+    __f(__first[__i]);
+
+  return __first + __n;
+}
+
+template <class _ExecutionPolicy, class _ForwardIterator, class _Functor>
+_LIBCPP_HIDE_FROM_ABI void
+__pstl_for_each(__cpu_backend_tag, _ForwardIterator __first, _ForwardIterator __last, _Functor __func) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator>::value) {
+    std::__terminate_on_exception([&] {
+      std::__par_backend::__parallel_for(
+          __first, __last, [__func](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {
+            std::__pstl_for_each<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{}, __brick_first, __brick_last, __func);
+          });
+    });
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator>::value) {
+    std::__simd_walk_1(__first, __last - __first, __func);
+  } else {
+    std::for_each(__first, __last, __func);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKNEDS_FOR_EACH_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/libdispatch.h

@@ -0,0 +1,241 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H
+
+#include <__algorithm/lower_bound.h>
+#include <__algorithm/max.h>
+#include <__algorithm/upper_bound.h>
+#include <__atomic/atomic.h>
+#include <__config>
+#include <__exception/terminate.h>
+#include <__iterator/iterator_traits.h>
+#include <__iterator/move_iterator.h>
+#include <__memory/allocator.h>
+#include <__memory/construct_at.h>
+#include <__memory/unique_ptr.h>
+#include <__numeric/reduce.h>
+#include <__utility/exception_guard.h>
+#include <__utility/move.h>
+#include <__utility/pair.h>
+#include <__utility/terminate_on_exception.h>
+#include <cstddef>
+#include <new>
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace __par_backend {
+inline namespace __libdispatch {
+
+// ::dispatch_apply is marked as __attribute__((nothrow)) because it doesn't let exceptions propagate, and neither do
+// we.
+// TODO: Do we want to add [[_Clang::__callback__(__func, __context, __)]]?
+_LIBCPP_EXPORTED_FROM_ABI void
+__dispatch_apply(size_t __chunk_count, void* __context, void (*__func)(void* __context, size_t __chunk)) noexcept;
+
+template <class _Func>
+_LIBCPP_HIDE_FROM_ABI void __dispatch_apply(size_t __chunk_count, _Func __func) noexcept {
+  __libdispatch::__dispatch_apply(__chunk_count, &__func, [](void* __context, size_t __chunk) {
+    (*static_cast<_Func*>(__context))(__chunk);
+  });
+}
+
+struct __chunk_partitions {
+  ptrdiff_t __chunk_count_; // includes the first chunk
+  ptrdiff_t __chunk_size_;
+  ptrdiff_t __first_chunk_size_;
+};
+
+[[__gnu__::__const__]] _LIBCPP_EXPORTED_FROM_ABI __chunk_partitions __partition_chunks(ptrdiff_t __size);
+
+template <class _RandomAccessIterator, class _Functor>
+_LIBCPP_HIDE_FROM_ABI void
+__parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Functor __func) {
+  auto __partitions = __libdispatch::__partition_chunks(__last - __first);
+
+  // Perform the chunked execution.
+  __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
+    auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
+    auto __index =
+        __chunk == 0
+            ? 0
+            : (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
+    __func(__first + __index, __first + __index + __this_chunk_size);
+  });
+}
+
+template <class _RandomAccessIterator1, class _RandomAccessIterator2, class _RandomAccessIteratorOut>
+struct __merge_range {
+  __merge_range(_RandomAccessIterator1 __mid1, _RandomAccessIterator2 __mid2, _RandomAccessIteratorOut __result)
+      : __mid1_(__mid1), __mid2_(__mid2), __result_(__result) {}
+
+  _RandomAccessIterator1 __mid1_;
+  _RandomAccessIterator2 __mid2_;
+  _RandomAccessIteratorOut __result_;
+};
+
+template <typename _RandomAccessIterator1,
+          typename _RandomAccessIterator2,
+          typename _RandomAccessIterator3,
+          typename _Compare,
+          typename _LeafMerge>
+_LIBCPP_HIDE_FROM_ABI void __parallel_merge(
+    _RandomAccessIterator1 __first1,
+    _RandomAccessIterator1 __last1,
+    _RandomAccessIterator2 __first2,
+    _RandomAccessIterator2 __last2,
+    _RandomAccessIterator3 __result,
+    _Compare __comp,
+    _LeafMerge __leaf_merge) {
+  __chunk_partitions __partitions =
+      __libdispatch::__partition_chunks(std::max<ptrdiff_t>(__last1 - __first1, __last2 - __first2));
+
+  if (__partitions.__chunk_count_ == 0)
+    return;
+
+  if (__partitions.__chunk_count_ == 1) {
+    __leaf_merge(__first1, __last1, __first2, __last2, __result, __comp);
+    return;
+  }
+
+  using __merge_range_t = __merge_range<_RandomAccessIterator1, _RandomAccessIterator2, _RandomAccessIterator3>;
+  auto const __n_ranges = __partitions.__chunk_count_ + 1;
+
+  // TODO: use __uninitialized_buffer
+  auto __destroy = [=](__merge_range_t* __ptr) {
+    std::destroy_n(__ptr, __n_ranges);
+    std::allocator<__merge_range_t>().deallocate(__ptr, __n_ranges);
+  };
+  unique_ptr<__merge_range_t[], decltype(__destroy)> __ranges(
+      std::allocator<__merge_range_t>().allocate(__n_ranges), __destroy);
+
+  // TODO: Improve the case where the smaller range is merged into just a few (or even one) chunks of the larger case
+  std::__terminate_on_exception([&] {
+    __merge_range_t* __r = __ranges.get();
+    std::__construct_at(__r++, __first1, __first2, __result);
+
+    bool __iterate_first_range = __last1 - __first1 > __last2 - __first2;
+
+    auto __compute_chunk = [&](size_t __chunk_size) -> __merge_range_t {
+      auto [__mid1, __mid2] = [&] {
+        if (__iterate_first_range) {
+          auto __m1 = __first1 + __chunk_size;
+          auto __m2 = std::lower_bound(__first2, __last2, __m1[-1], __comp);
+          return std::make_pair(__m1, __m2);
+        } else {
+          auto __m2 = __first2 + __chunk_size;
+          auto __m1 = std::lower_bound(__first1, __last1, __m2[-1], __comp);
+          return std::make_pair(__m1, __m2);
+        }
+      }();
+
+      __result += (__mid1 - __first1) + (__mid2 - __first2);
+      __first1 = __mid1;
+      __first2 = __mid2;
+      return {std::move(__mid1), std::move(__mid2), __result};
+    };
+
+    // handle first chunk
+    std::__construct_at(__r++, __compute_chunk(__partitions.__first_chunk_size_));
+
+    // handle 2 -> N - 1 chunks
+    for (ptrdiff_t __i = 0; __i != __partitions.__chunk_count_ - 2; ++__i)
+      std::__construct_at(__r++, __compute_chunk(__partitions.__chunk_size_));
+
+    // handle last chunk
+    std::__construct_at(__r, __last1, __last2, __result);
+
+    __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __index) {
+      auto __first_iters = __ranges[__index];
+      auto __last_iters  = __ranges[__index + 1];
+      __leaf_merge(
+          __first_iters.__mid1_,
+          __last_iters.__mid1_,
+          __first_iters.__mid2_,
+          __last_iters.__mid2_,
+          __first_iters.__result_,
+          __comp);
+    });
+  });
+}
+
+template <class _RandomAccessIterator, class _Transform, class _Value, class _Combiner, class _Reduction>
+_LIBCPP_HIDE_FROM_ABI _Value __parallel_transform_reduce(
+    _RandomAccessIterator __first,
+    _RandomAccessIterator __last,
+    _Transform __transform,
+    _Value __init,
+    _Combiner __combiner,
+    _Reduction __reduction) {
+  if (__first == __last)
+    return __init;
+
+  auto __partitions = __libdispatch::__partition_chunks(__last - __first);
+
+  auto __destroy = [__count = __partitions.__chunk_count_](_Value* __ptr) {
+    std::destroy_n(__ptr, __count);
+    std::allocator<_Value>().deallocate(__ptr, __count);
+  };
+
+  // TODO: use __uninitialized_buffer
+  // TODO: allocate one element per worker instead of one element per chunk
+  unique_ptr<_Value[], decltype(__destroy)> __values(
+      std::allocator<_Value>().allocate(__partitions.__chunk_count_), __destroy);
+
+  // __dispatch_apply is noexcept
+  __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
+    auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
+    auto __index =
+        __chunk == 0
+            ? 0
+            : (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
+    if (__this_chunk_size != 1) {
+      std::__construct_at(
+          __values.get() + __chunk,
+          __reduction(__first + __index + 2,
+                      __first + __index + __this_chunk_size,
+                      __combiner(__transform(__first + __index), __transform(__first + __index + 1))));
+    } else {
+      std::__construct_at(__values.get() + __chunk, __transform(__first + __index));
+    }
+  });
+
+  return std::__terminate_on_exception([&] {
+    return std::reduce(
+        std::make_move_iterator(__values.get()),
+        std::make_move_iterator(__values.get() + __partitions.__chunk_count_),
+        std::move(__init),
+        __combiner);
+  });
+}
+
+// TODO: parallelize this
+template <class _RandomAccessIterator, class _Comp, class _LeafSort>
+_LIBCPP_HIDE_FROM_ABI void __parallel_stable_sort(
+    _RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp, _LeafSort __leaf_sort) {
+  __leaf_sort(__first, __last, __comp);
+}
+
+_LIBCPP_HIDE_FROM_ABI inline void __cancel_execution() {}
+
+} // namespace __libdispatch
+} // namespace __par_backend
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_LIBDISPATCH_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/merge.h

@@ -0,0 +1,79 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_MERGE_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_MERGE_H
+
+#include <__algorithm/merge.h>
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator1,
+          class _ForwardIterator2,
+          class _ForwardOutIterator,
+          class _Comp>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator __pstl_merge(
+    __cpu_backend_tag,
+    _ForwardIterator1 __first1,
+    _ForwardIterator1 __last1,
+    _ForwardIterator2 __first2,
+    _ForwardIterator2 __last2,
+    _ForwardOutIterator __result,
+    _Comp __comp) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator1>::value &&
+                __has_random_access_iterator_category<_ForwardIterator2>::value &&
+                __has_random_access_iterator_category<_ForwardOutIterator>::value) {
+    return std::__terminate_on_exception([&] {
+      __par_backend::__parallel_merge(
+          __first1,
+          __last1,
+          __first2,
+          __last2,
+          __result,
+          __comp,
+          [](_ForwardIterator1 __g_first1,
+             _ForwardIterator1 __g_last1,
+             _ForwardIterator2 __g_first2,
+             _ForwardIterator2 __g_last2,
+             _ForwardOutIterator __g_result,
+             _Comp __g_comp) {
+            return std::__pstl_merge<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{},
+                std::move(__g_first1),
+                std::move(__g_last1),
+                std::move(__g_first2),
+                std::move(__g_last2),
+                std::move(__g_result),
+                std::move(__g_comp));
+          });
+      return __result + (__last1 - __first1) + (__last2 - __first2);
+    });
+  } else {
+    return std::merge(__first1, __last1, __first2, __last2, __result, __comp);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_MERGE_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/serial.h

@@ -0,0 +1,72 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_SERIAL_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_SERIAL_H
+
+#include <__config>
+#include <__utility/move.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace __par_backend {
+inline namespace __serial_cpu_backend {
+
+template <class _RandomAccessIterator, class _Fp>
+_LIBCPP_HIDE_FROM_ABI void __parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Fp __f) {
+  __f(__first, __last);
+}
+
+template <class _Index, class _UnaryOp, class _Tp, class _BinaryOp, class _Reduce>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__parallel_transform_reduce(_Index __first, _Index __last, _UnaryOp, _Tp __init, _BinaryOp, _Reduce __reduce) {
+  return __reduce(std::move(__first), std::move(__last), std::move(__init));
+}
+
+template <class _RandomAccessIterator, class _Compare, class _LeafSort>
+_LIBCPP_HIDE_FROM_ABI void __parallel_stable_sort(
+    _RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp, _LeafSort __leaf_sort) {
+  __leaf_sort(__first, __last, __comp);
+}
+
+_LIBCPP_HIDE_FROM_ABI inline void __cancel_execution() {}
+
+template <class _RandomAccessIterator1,
+          class _RandomAccessIterator2,
+          class _RandomAccessIterator3,
+          class _Compare,
+          class _LeafMerge>
+_LIBCPP_HIDE_FROM_ABI void __parallel_merge(
+    _RandomAccessIterator1 __first1,
+    _RandomAccessIterator1 __last1,
+    _RandomAccessIterator2 __first2,
+    _RandomAccessIterator2 __last2,
+    _RandomAccessIterator3 __outit,
+    _Compare __comp,
+    _LeafMerge __leaf_merge) {
+  __leaf_merge(__first1, __last1, __first2, __last2, __outit, __comp);
+}
+
+// TODO: Complete this list
+
+} // namespace __serial_cpu_backend
+} // namespace __par_backend
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_SERIAL_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/stable_sort.h

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_STABLE_SORT_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_STABLE_SORT_H
+
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__algorithm/stable_sort.h>
+#include <__config>
+#include <__type_traits/is_execution_policy.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy, class _RandomAccessIterator, class _Comp>
+_LIBCPP_HIDE_FROM_ABI void
+__pstl_stable_sort(__cpu_backend_tag, _RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy>) {
+    std::__terminate_on_exception([&] {
+      __par_backend::__parallel_stable_sort(
+          __first, __last, __comp, [](_RandomAccessIterator __g_first, _RandomAccessIterator __g_last, _Comp __g_comp) {
+            std::stable_sort(__g_first, __g_last, __g_comp);
+          });
+    });
+  } else {
+    std::stable_sort(__first, __last, __comp);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_STABLE_SORT_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/thread.h

@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_THREAD_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_THREAD_H
+
+#include <__assert>
+#include <__config>
+#include <__utility/move.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_PUSH_MACROS
+#include <__undef_macros>
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+// This backend implementation is for testing purposes only and not meant for production use. This will be replaced
+// by a proper implementation once the PSTL implementation is somewhat stable.
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+namespace __par_backend {
+inline namespace __thread_cpu_backend {
+
+template <class _RandomAccessIterator, class _Fp>
+_LIBCPP_HIDE_FROM_ABI void __parallel_for(_RandomAccessIterator __first, _RandomAccessIterator __last, _Fp __f) {
+  __f(__first, __last);
+}
+
+template <class _Index, class _UnaryOp, class _Tp, class _BinaryOp, class _Reduce>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__parallel_transform_reduce(_Index __first, _Index __last, _UnaryOp, _Tp __init, _BinaryOp, _Reduce __reduce) {
+  return __reduce(std::move(__first), std::move(__last), std::move(__init));
+}
+
+template <class _RandomAccessIterator, class _Compare, class _LeafSort>
+_LIBCPP_HIDE_FROM_ABI void __parallel_stable_sort(
+    _RandomAccessIterator __first, _RandomAccessIterator __last, _Compare __comp, _LeafSort __leaf_sort) {
+  __leaf_sort(__first, __last, __comp);
+}
+
+_LIBCPP_HIDE_FROM_ABI inline void __cancel_execution() {}
+
+template <class _RandomAccessIterator1,
+          class _RandomAccessIterator2,
+          class _RandomAccessIterator3,
+          class _Compare,
+          class _LeafMerge>
+_LIBCPP_HIDE_FROM_ABI void __parallel_merge(
+    _RandomAccessIterator1 __first1,
+    _RandomAccessIterator1 __last1,
+    _RandomAccessIterator2 __first2,
+    _RandomAccessIterator2 __last2,
+    _RandomAccessIterator3 __outit,
+    _Compare __comp,
+    _LeafMerge __leaf_merge) {
+  __leaf_merge(__first1, __last1, __first2, __last2, __outit, __comp);
+}
+
+} // namespace __thread_cpu_backend
+} // namespace __par_backend
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_THREAD_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/transform.h

@@ -0,0 +1,132 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_TRANSFORM_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_TRANSFORM_H
+
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__algorithm/transform.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _Iterator1, class _DifferenceType, class _Iterator2, class _Function>
+_LIBCPP_HIDE_FROM_ABI _Iterator2
+__simd_walk_2(_Iterator1 __first1, _DifferenceType __n, _Iterator2 __first2, _Function __f) noexcept {
+  _PSTL_PRAGMA_SIMD
+  for (_DifferenceType __i = 0; __i < __n; ++__i)
+    __f(__first1[__i], __first2[__i]);
+  return __first2 + __n;
+}
+
+template <class _ExecutionPolicy, class _ForwardIterator, class _ForwardOutIterator, class _UnaryOperation>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator __pstl_transform(
+    __cpu_backend_tag,
+    _ForwardIterator __first,
+    _ForwardIterator __last,
+    _ForwardOutIterator __result,
+    _UnaryOperation __op) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator>::value &&
+                __has_random_access_iterator_category<_ForwardOutIterator>::value) {
+    std::__terminate_on_exception([&] {
+      std::__par_backend::__parallel_for(
+          __first, __last, [__op, __first, __result](_ForwardIterator __brick_first, _ForwardIterator __brick_last) {
+            return std::__pstl_transform<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{}, __brick_first, __brick_last, __result + (__brick_first - __first), __op);
+          });
+    });
+    return __result + (__last - __first);
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator>::value &&
+                       __has_random_access_iterator_category<_ForwardOutIterator>::value) {
+    return std::__simd_walk_2(
+        __first,
+        __last - __first,
+        __result,
+        [&](__iter_reference<_ForwardIterator> __in_value, __iter_reference<_ForwardOutIterator> __out_value) {
+          __out_value = __op(__in_value);
+        });
+  } else {
+    return std::transform(__first, __last, __result, __op);
+  }
+}
+
+template <class _Iterator1, class _DifferenceType, class _Iterator2, class _Iterator3, class _Function>
+_LIBCPP_HIDE_FROM_ABI _Iterator3 __simd_walk_3(
+    _Iterator1 __first1, _DifferenceType __n, _Iterator2 __first2, _Iterator3 __first3, _Function __f) noexcept {
+  _PSTL_PRAGMA_SIMD
+  for (_DifferenceType __i = 0; __i < __n; ++__i)
+    __f(__first1[__i], __first2[__i], __first3[__i]);
+  return __first3 + __n;
+}
+template <class _ExecutionPolicy,
+          class _ForwardIterator1,
+          class _ForwardIterator2,
+          class _ForwardOutIterator,
+          class _BinaryOperation,
+          enable_if_t<is_execution_policy_v<__remove_cvref_t<_ExecutionPolicy>>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator __pstl_transform(
+    __cpu_backend_tag,
+    _ForwardIterator1 __first1,
+    _ForwardIterator1 __last1,
+    _ForwardIterator2 __first2,
+    _ForwardOutIterator __result,
+    _BinaryOperation __op) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator1>::value &&
+                __has_random_access_iterator_category<_ForwardIterator2>::value &&
+                __has_random_access_iterator_category<_ForwardOutIterator>::value) {
+    std::__terminate_on_exception([&] {
+      std::__par_backend::__parallel_for(
+          __first1,
+          __last1,
+          [__op, __first1, __first2, __result](_ForwardIterator1 __brick_first, _ForwardIterator1 __brick_last) {
+            return std::__pstl_transform<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{},
+                __brick_first,
+                __brick_last,
+                __first2 + (__brick_first - __first1),
+                __result + (__brick_first - __first1),
+                __op);
+          });
+    });
+    return __result + (__last1 - __first1);
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator1>::value &&
+                       __has_random_access_iterator_category<_ForwardIterator2>::value &&
+                       __has_random_access_iterator_category<_ForwardOutIterator>::value) {
+    return std::__simd_walk_3(
+        __first1,
+        __last1 - __first1,
+        __first2,
+        __result,
+        [&](__iter_reference<_ForwardIterator1> __in1,
+            __iter_reference<_ForwardIterator2> __in2,
+            __iter_reference<_ForwardOutIterator> __out_value) { __out_value = __op(__in1, __in2); });
+  } else {
+    return std::transform(__first1, __last1, __first2, __result, __op);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_TRANSFORM_H

lib/libcxx/include/__algorithm/pstl_backends/cpu_backends/transform_reduce.h

@@ -0,0 +1,194 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_BACKENDS_CPU_BACKENDS_TRANSFORM_REDUCE_H
+#define _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_TRANSFORM_REDUCE_H
+
+#include <__algorithm/pstl_backends/cpu_backends/backend.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__numeric/transform_reduce.h>
+#include <__type_traits/is_arithmetic.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/operation_traits.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+#include <new>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <
+    typename _DifferenceType,
+    typename _Tp,
+    typename _BinaryOperation,
+    typename _UnaryOperation,
+    __enable_if_t<__is_trivial_plus_operation<_BinaryOperation, _Tp, _Tp>::value && is_arithmetic_v<_Tp>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__simd_transform_reduce(_DifferenceType __n, _Tp __init, _BinaryOperation, _UnaryOperation __f) noexcept {
+  _PSTL_PRAGMA_SIMD_REDUCTION(+ : __init)
+  for (_DifferenceType __i = 0; __i < __n; ++__i)
+    __init += __f(__i);
+  return __init;
+}
+
+template <
+    typename _Size,
+    typename _Tp,
+    typename _BinaryOperation,
+    typename _UnaryOperation,
+    __enable_if_t<!(__is_trivial_plus_operation<_BinaryOperation, _Tp, _Tp>::value && is_arithmetic_v<_Tp>), int> = 0>
+_LIBCPP_HIDE_FROM_ABI _Tp
+__simd_transform_reduce(_Size __n, _Tp __init, _BinaryOperation __binary_op, _UnaryOperation __f) noexcept {
+  const _Size __block_size = __lane_size / sizeof(_Tp);
+  if (__n > 2 * __block_size && __block_size > 1) {
+    alignas(__lane_size) char __lane_buffer[__lane_size];
+    _Tp* __lane = reinterpret_cast<_Tp*>(__lane_buffer);
+
+    // initializer
+    _PSTL_PRAGMA_SIMD
+    for (_Size __i = 0; __i < __block_size; ++__i) {
+      ::new (__lane + __i) _Tp(__binary_op(__f(__i), __f(__block_size + __i)));
+    }
+    // main loop
+    _Size __i                    = 2 * __block_size;
+    const _Size __last_iteration = __block_size * (__n / __block_size);
+    for (; __i < __last_iteration; __i += __block_size) {
+      _PSTL_PRAGMA_SIMD
+      for (_Size __j = 0; __j < __block_size; ++__j) {
+        __lane[__j] = __binary_op(std::move(__lane[__j]), __f(__i + __j));
+      }
+    }
+    // remainder
+    _PSTL_PRAGMA_SIMD
+    for (_Size __j = 0; __j < __n - __last_iteration; ++__j) {
+      __lane[__j] = __binary_op(std::move(__lane[__j]), __f(__last_iteration + __j));
+    }
+    // combiner
+    for (_Size __j = 0; __j < __block_size; ++__j) {
+      __init = __binary_op(std::move(__init), std::move(__lane[__j]));
+    }
+    // destroyer
+    _PSTL_PRAGMA_SIMD
+    for (_Size __j = 0; __j < __block_size; ++__j) {
+      __lane[__j].~_Tp();
+    }
+  } else {
+    for (_Size __i = 0; __i < __n; ++__i) {
+      __init = __binary_op(std::move(__init), __f(__i));
+    }
+  }
+  return __init;
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator1,
+          class _ForwardIterator2,
+          class _Tp,
+          class _BinaryOperation1,
+          class _BinaryOperation2>
+_LIBCPP_HIDE_FROM_ABI _Tp __pstl_transform_reduce(
+    __cpu_backend_tag,
+    _ForwardIterator1 __first1,
+    _ForwardIterator1 __last1,
+    _ForwardIterator2 __first2,
+    _Tp __init,
+    _BinaryOperation1 __reduce,
+    _BinaryOperation2 __transform) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator1>::value &&
+                __has_random_access_iterator_category<_ForwardIterator2>::value) {
+    return std::__terminate_on_exception([&] {
+      return __par_backend::__parallel_transform_reduce(
+          __first1,
+          std::move(__last1),
+          [__first1, __first2, __transform](_ForwardIterator1 __iter) {
+            return __transform(*__iter, *(__first2 + (__iter - __first1)));
+          },
+          std::move(__init),
+          std::move(__reduce),
+          [__first1, __first2, __reduce, __transform](
+              _ForwardIterator1 __brick_first, _ForwardIterator1 __brick_last, _Tp __brick_init) {
+            return std::__pstl_transform_reduce<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{},
+                __brick_first,
+                std::move(__brick_last),
+                __first2 + (__brick_first - __first1),
+                std::move(__brick_init),
+                std::move(__reduce),
+                std::move(__transform));
+          });
+    });
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator1>::value &&
+                       __has_random_access_iterator_category<_ForwardIterator2>::value) {
+    return std::__simd_transform_reduce(
+        __last1 - __first1, std::move(__init), std::move(__reduce), [&](__iter_diff_t<_ForwardIterator1> __i) {
+          return __transform(__first1[__i], __first2[__i]);
+        });
+  } else {
+    return std::transform_reduce(
+        std::move(__first1),
+        std::move(__last1),
+        std::move(__first2),
+        std::move(__init),
+        std::move(__reduce),
+        std::move(__transform));
+  }
+}
+
+template <class _ExecutionPolicy, class _ForwardIterator, class _Tp, class _BinaryOperation, class _UnaryOperation>
+_LIBCPP_HIDE_FROM_ABI _Tp __pstl_transform_reduce(
+    __cpu_backend_tag,
+    _ForwardIterator __first,
+    _ForwardIterator __last,
+    _Tp __init,
+    _BinaryOperation __reduce,
+    _UnaryOperation __transform) {
+  if constexpr (__is_parallel_execution_policy_v<_ExecutionPolicy> &&
+                __has_random_access_iterator_category<_ForwardIterator>::value) {
+    return std::__terminate_on_exception([&] {
+      return __par_backend::__parallel_transform_reduce(
+          std::move(__first),
+          std::move(__last),
+          [__transform](_ForwardIterator __iter) { return __transform(*__iter); },
+          std::move(__init),
+          __reduce,
+          [__transform, __reduce](auto __brick_first, auto __brick_last, _Tp __brick_init) {
+            return std::__pstl_transform_reduce<__remove_parallel_policy_t<_ExecutionPolicy>>(
+                __cpu_backend_tag{},
+                std::move(__brick_first),
+                std::move(__brick_last),
+                std::move(__brick_init),
+                std::move(__reduce),
+                std::move(__transform));
+          });
+    });
+  } else if constexpr (__is_unsequenced_execution_policy_v<_ExecutionPolicy> &&
+                       __has_random_access_iterator_category<_ForwardIterator>::value) {
+    return std::__simd_transform_reduce(
+        __last - __first,
+        std::move(__init),
+        std::move(__reduce),
+        [=, &__transform](__iter_diff_t<_ForwardIterator> __i) { return __transform(__first[__i]); });
+  } else {
+    return std::transform_reduce(
+        std::move(__first), std::move(__last), std::move(__init), std::move(__reduce), std::move(__transform));
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_BACKENDS_CPU_BACKENDS_TRANSFORM_REDUCE_H

lib/libcxx/include/__algorithm/pstl_copy.h

@@ -0,0 +1,59 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_COPY_H
+#define _LIBCPP___ALGORITHM_PSTL_COPY_H
+
+#include <__algorithm/copy_n.h>
+#include <__algorithm/pstl_transform.h>
+#include <__config>
+#include <__functional/identity.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_constant_evaluated.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/is_trivially_copyable.h>
+#include <__type_traits/remove_cvref.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+// TODO: Use the std::copy/move shenanigans to forward to std::memmove
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          enable_if_t<is_execution_policy_v<__remove_cvref_t<_ExecutionPolicy>>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator
+copy(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _ForwardOutIterator __result) {
+  return std::transform(__policy, __first, __last, __result, __identity());
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          class _Size,
+          enable_if_t<is_execution_policy_v<__remove_cvref_t<_ExecutionPolicy>>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator
+copy_n(_ExecutionPolicy&& __policy, _ForwardIterator __first, _Size __n, _ForwardOutIterator __result) {
+  if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value)
+    return std::copy(__policy, __first, __first + __n, __result);
+  else
+    return std::copy_n(__first, __n, __result);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_COPY_H

lib/libcxx/include/__algorithm/pstl_count.h

@@ -0,0 +1,89 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_COUNT_H
+#define _LIBCPP___ALGORITHM_PSTL_COUNT_H
+
+#include <__algorithm/count.h>
+#include <__algorithm/for_each.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_for_each.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__atomic/atomic.h>
+#include <__config>
+#include <__functional/operations.h>
+#include <__iterator/iterator_traits.h>
+#include <__numeric/pstl_transform_reduce.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_count_if(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI __iter_diff_t<_ForwardIterator>
+count_if(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  using __diff_t = __iter_diff_t<_ForwardIterator>;
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_count_if),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, _Predicate __g_pred) {
+        return std::transform_reduce(
+            __policy,
+            std::move(__g_first),
+            std::move(__g_last),
+            __diff_t(),
+            std::plus{},
+            [&](__iter_reference<_ForwardIterator> __element) -> bool { return __g_pred(__element); });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+template <class>
+void __pstl_count(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI __iter_diff_t<_ForwardIterator>
+count(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_count),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, const _Tp& __g_value) {
+        return std::count_if(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __v) {
+          return __v == __g_value;
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      __value);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_COUNT_H

lib/libcxx/include/__algorithm/pstl_fill.h

@@ -0,0 +1,84 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_FILL_H
+#define _LIBCPP___ALGORITHM_PSTL_FILL_H
+
+#include <__algorithm/fill_n.h>
+#include <__algorithm/pstl_for_each.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__iterator/cpp17_iterator_concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_fill(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+fill(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_fill),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, const _Tp& __g_value) {
+        std::for_each(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __element) {
+          __element = __g_value;
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      __value);
+}
+
+template <class>
+void __pstl_fill_n(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _SizeT,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+fill_n(_ExecutionPolicy&& __policy, _ForwardIterator __first, _SizeT __n, const _Tp& __value) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_fill_n),
+      [&](_ForwardIterator __g_first, _SizeT __g_n, const _Tp& __g_value) {
+        if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value)
+          std::fill(__policy, __g_first, __g_first + __g_n, __g_value);
+        else
+          std::fill_n(__g_first, __g_n, __g_value);
+      },
+      std::move(__first),
+      __n,
+      __value);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_FILL_H

lib/libcxx/include/__algorithm/pstl_find.h

@@ -0,0 +1,95 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_FIND_H
+#define _LIBCPP___ALGORITHM_PSTL_FIND_H
+
+#include <__algorithm/comp.h>
+#include <__algorithm/find.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__iterator/cpp17_iterator_concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+find_if(_ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  using _Backend = typename __select_backend<_RawPolicy>::type;
+  return std::__pstl_find_if<_RawPolicy>(_Backend{}, std::move(__first), std::move(__last), std::move(__pred));
+}
+
+template <class>
+void __pstl_find_if_not();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+find_if_not(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_find_if_not),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, _Predicate __g_pred) {
+        return std::find_if(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __value) {
+          return !__g_pred(__value);
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+template <class>
+void __pstl_find();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardIterator
+find(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, const _Tp& __value) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_find),
+      [&](_ForwardIterator __g_first, _ForwardIterator __g_last, const _Tp& __g_value) {
+        return std::find_if(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __element) {
+          return __element == __g_value;
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      __value);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_FIND_H

lib/libcxx/include/__algorithm/pstl_for_each.h

@@ -0,0 +1,76 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_FOR_EACH_H
+#define _LIBCPP___ALGORITHM_PSTL_FOR_EACH_H
+
+#include <__algorithm/for_each.h>
+#include <__algorithm/for_each_n.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__iterator/cpp17_iterator_concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__type_traits/void_t.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Function,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+for_each(_ExecutionPolicy&&, _ForwardIterator __first, _ForwardIterator __last, _Function __func) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  using _Backend = typename __select_backend<_RawPolicy>::type;
+  std::__pstl_for_each<_RawPolicy>(_Backend{}, std::move(__first), std::move(__last), std::move(__func));
+}
+
+template <class>
+void __pstl_for_each_n(); // declaration needed for the frontend dispatch below
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Size,
+          class _Function,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+for_each_n(_ExecutionPolicy&& __policy, _ForwardIterator __first, _Size __size, _Function __func) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_for_each_n),
+      [&](_ForwardIterator __g_first, _Size __g_size, _Function __g_func) {
+        if constexpr (__has_random_access_iterator_category<_ForwardIterator>::value) {
+          std::for_each(__policy, std::move(__g_first), __g_first + __g_size, std::move(__g_func));
+        } else {
+          std::for_each_n(std::move(__g_first), __g_size, std::move(__g_func));
+        }
+      },
+      __first,
+      __size,
+      std::move(__func));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_FOR_EACH_H

lib/libcxx/include/__algorithm/pstl_frontend_dispatch.h

@@ -0,0 +1,45 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_FRONTEND_DISPATCH
+#define _LIBCPP___ALGORITHM_PSTL_FRONTEND_DISPATCH
+
+#include <__config>
+#include <__type_traits/is_callable.h>
+#include <__utility/forward.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#  define _LIBCPP_PSTL_CUSTOMIZATION_POINT(name)                                                                       \
+    [](auto&&... __args) -> decltype(std::name<_RawPolicy>(typename __select_backend<_RawPolicy>::type{},              \
+                                                           std::forward<decltype(__args)>(__args)...)) {               \
+      return std::name<_RawPolicy>(                                                                                    \
+          typename __select_backend<_RawPolicy>::type{}, std::forward<decltype(__args)>(__args)...);                   \
+    }
+
+template <class _SpecializedImpl, class _GenericImpl, class... _Args>
+_LIBCPP_HIDE_FROM_ABI decltype(auto)
+__pstl_frontend_dispatch(_SpecializedImpl __specialized_impl, _GenericImpl __generic_impl, _Args&&... __args) {
+  if constexpr (__is_callable<_SpecializedImpl, _Args...>::value) {
+    return __specialized_impl(std::forward<_Args>(__args)...);
+  } else {
+    return __generic_impl(std::forward<_Args>(__args)...);
+  }
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_FRONTEND_DISPATCH

lib/libcxx/include/__algorithm/pstl_generate.h

@@ -0,0 +1,82 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_GENERATE_H
+#define _LIBCPP___ALGORITHM_PSTL_GENERATE_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_for_each.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__iterator/cpp17_iterator_concepts.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_generate();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Generator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+generate(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Generator __gen) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_generate),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _Generator __g_gen) {
+        std::for_each(
+            __policy, std::move(__g_first), std::move(__g_last), [&](__iter_reference<_ForwardIterator> __element) {
+              __element = __g_gen();
+            });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__gen));
+}
+
+template <class>
+void __pstl_generate_n();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Size,
+          class _Generator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+generate_n(_ExecutionPolicy&& __policy, _ForwardIterator __first, _Size __n, _Generator __gen) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_generate_n),
+      [&__policy](_ForwardIterator __g_first, _Size __g_n, _Generator __g_gen) {
+        std::for_each_n(__policy, std::move(__g_first), __g_n, [&](__iter_reference<_ForwardIterator> __element) {
+          __element = __g_gen();
+        });
+      },
+      std::move(__first),
+      __n,
+      std::move(__gen));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_GENERATE_H

lib/libcxx/include/__algorithm/pstl_is_partitioned.h

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_IS_PARITTIONED
+#define _LIBCPP___ALGORITHM_PSTL_IS_PARITTIONED
+
+#include <__algorithm/pstl_any_all_none_of.h>
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_find.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__config>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_is_partitioned();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Predicate,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI bool
+is_partitioned(_ExecutionPolicy&& __policy, _ForwardIterator __first, _ForwardIterator __last, _Predicate __pred) {
+  return std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_is_partitioned),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _Predicate __g_pred) {
+        __g_first = std::find_if_not(__policy, __g_first, __g_last, __g_pred);
+        if (__g_first == __g_last)
+          return true;
+        ++__g_first;
+        return std::none_of(__policy, __g_first, __g_last, __g_pred);
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_IS_PARITTIONED

lib/libcxx/include/__algorithm/pstl_merge.h

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_MERGE_H
+#define _LIBCPP___ALGORITHM_PSTL_MERGE_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__config>
+#include <__functional/operations.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator1,
+          class _ForwardIterator2,
+          class _ForwardOutIterator,
+          class _Comp                                         = std::less<>,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator
+merge(_ExecutionPolicy&&,
+      _ForwardIterator1 __first1,
+      _ForwardIterator1 __last1,
+      _ForwardIterator2 __first2,
+      _ForwardIterator2 __last2,
+      _ForwardOutIterator __result,
+      _Comp __comp = {}) {
+  using _Backend = typename __select_backend<_RawPolicy>::type;
+  return std::__pstl_merge<_RawPolicy>(
+      _Backend{},
+      std::move(__first1),
+      std::move(__last1),
+      std::move(__first2),
+      std::move(__last2),
+      std::move(__result),
+      std::move(__comp));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_MERGE_H

lib/libcxx/include/__algorithm/pstl_replace.h

@@ -0,0 +1,167 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_REPLACE_H
+#define _LIBCPP___ALGORITHM_PSTL_REPLACE_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_for_each.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__algorithm/pstl_transform.h>
+#include <__config>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_replace_if();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Pred,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+replace_if(_ExecutionPolicy&& __policy,
+           _ForwardIterator __first,
+           _ForwardIterator __last,
+           _Pred __pred,
+           const _Tp& __new_value) {
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_replace_if),
+      [&__policy](_ForwardIterator __g_first, _ForwardIterator __g_last, _Pred __g_pred, const _Tp& __g_new_value) {
+        std::for_each(__policy, __g_first, __g_last, [&](__iter_reference<_ForwardIterator> __element) {
+          if (__g_pred(__element))
+            __element = __g_new_value;
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__pred),
+      __new_value);
+}
+
+template <class>
+void __pstl_replace();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+replace(_ExecutionPolicy&& __policy,
+        _ForwardIterator __first,
+        _ForwardIterator __last,
+        const _Tp& __old_value,
+        const _Tp& __new_value) {
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_replace),
+      [&__policy](
+          _ForwardIterator __g_first, _ForwardIterator __g_last, const _Tp& __g_old_value, const _Tp& __g_new_value) {
+        std::replace_if(
+            __policy,
+            std::move(__g_first),
+            std::move(__g_last),
+            [&](__iter_reference<_ForwardIterator> __element) { return __element == __g_old_value; },
+            __g_new_value);
+      },
+      std::move(__first),
+      std::move(__last),
+      __old_value,
+      __new_value);
+}
+
+template <class>
+void __pstl_replace_copy_if();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          class _Pred,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void replace_copy_if(
+    _ExecutionPolicy&& __policy,
+    _ForwardIterator __first,
+    _ForwardIterator __last,
+    _ForwardOutIterator __result,
+    _Pred __pred,
+    const _Tp& __new_value) {
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_replace_copy_if),
+      [&__policy](_ForwardIterator __g_first,
+                  _ForwardIterator __g_last,
+                  _ForwardOutIterator __g_result,
+                  _Pred __g_pred,
+                  const _Tp& __g_new_value) {
+        std::transform(__policy, __g_first, __g_last, __g_result, [&](__iter_reference<_ForwardIterator> __element) {
+          return __g_pred(__element) ? __g_new_value : __element;
+        });
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__result),
+      std::move(__pred),
+      __new_value);
+}
+
+template <class>
+void __pstl_replace_copy();
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          class _Tp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void replace_copy(
+    _ExecutionPolicy&& __policy,
+    _ForwardIterator __first,
+    _ForwardIterator __last,
+    _ForwardOutIterator __result,
+    const _Tp& __old_value,
+    const _Tp& __new_value) {
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_replace_copy),
+      [&__policy](_ForwardIterator __g_first,
+                  _ForwardIterator __g_last,
+                  _ForwardOutIterator __g_result,
+                  const _Tp& __g_old_value,
+                  const _Tp& __g_new_value) {
+        return std::replace_copy_if(
+            __policy,
+            std::move(__g_first),
+            std::move(__g_last),
+            std::move(__g_result),
+            [&](__iter_reference<_ForwardIterator> __element) { return __element == __g_old_value; },
+            __g_new_value);
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__result),
+      __old_value,
+      __new_value);
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_REPLACE_H

lib/libcxx/include/__algorithm/pstl_sort.h

@@ -0,0 +1,63 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_SORT_H
+#define _LIBCPP___ALGORITHM_PSTL_SORT_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__algorithm/pstl_frontend_dispatch.h>
+#include <__algorithm/pstl_stable_sort.h>
+#include <__config>
+#include <__functional/operations.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/forward.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class>
+void __pstl_sort();
+
+template <class _ExecutionPolicy,
+          class _RandomAccessIterator,
+          class _Comp,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+sort(_ExecutionPolicy&& __policy, _RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp) {
+  std::__pstl_frontend_dispatch(
+      _LIBCPP_PSTL_CUSTOMIZATION_POINT(__pstl_sort),
+      [&__policy](_RandomAccessIterator __g_first, _RandomAccessIterator __g_last, _Comp __g_comp) {
+        std::stable_sort(__policy, std::move(__g_first), std::move(__g_last), std::move(__g_comp));
+      },
+      std::move(__first),
+      std::move(__last),
+      std::move(__comp));
+}
+
+template <class _ExecutionPolicy,
+          class _RandomAccessIterator,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+sort(_ExecutionPolicy&& __policy, _RandomAccessIterator __first, _RandomAccessIterator __last) {
+  std::sort(std::forward<_ExecutionPolicy>(__policy), std::move(__first), std::move(__last), less{});
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_SORT_H

lib/libcxx/include/__algorithm/pstl_stable_sort.h

@@ -0,0 +1,43 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_STABLE_SORT_H
+#define _LIBCPP___ALGORITHM_PSTL_STABLE_SORT_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__config>
+#include <__functional/operations.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy,
+          class _RandomAccessIterator,
+          class _Comp                                         = less<>,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI void
+stable_sort(_ExecutionPolicy&&, _RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp = {}) {
+  using _Backend = typename __select_backend<_RawPolicy>::type;
+  std::__pstl_stable_sort<_RawPolicy>(_Backend{}, std::move(__first), std::move(__last), std::move(__comp));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_STABLE_SORT_H

lib/libcxx/include/__algorithm/pstl_transform.h

@@ -0,0 +1,77 @@
+//===----------------------------------------------------------------------===//
+//
+// 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_PSTL_TRANSFORM_H
+#define _LIBCPP___ALGORITHM_PSTL_TRANSFORM_H
+
+#include <__algorithm/pstl_backend.h>
+#include <__config>
+#include <__iterator/cpp17_iterator_concepts.h>
+#include <__iterator/iterator_traits.h>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_execution_policy.h>
+#include <__type_traits/remove_cvref.h>
+#include <__utility/move.h>
+#include <__utility/terminate_on_exception.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+#if !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator,
+          class _ForwardOutIterator,
+          class _UnaryOperation,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator transform(
+    _ExecutionPolicy&&,
+    _ForwardIterator __first,
+    _ForwardIterator __last,
+    _ForwardOutIterator __result,
+    _UnaryOperation __op) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator);
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardOutIterator);
+  _LIBCPP_REQUIRE_CPP17_OUTPUT_ITERATOR(_ForwardOutIterator, decltype(__op(*__first)));
+  using _Backend = typename __select_backend<_RawPolicy>::type;
+  return std::__pstl_transform<_RawPolicy>(
+      _Backend{}, std::move(__first), std::move(__last), std::move(__result), std::move(__op));
+}
+
+template <class _ExecutionPolicy,
+          class _ForwardIterator1,
+          class _ForwardIterator2,
+          class _ForwardOutIterator,
+          class _BinaryOperation,
+          class _RawPolicy                                    = __remove_cvref_t<_ExecutionPolicy>,
+          enable_if_t<is_execution_policy_v<_RawPolicy>, int> = 0>
+_LIBCPP_HIDE_FROM_ABI _ForwardOutIterator transform(
+    _ExecutionPolicy&&,
+    _ForwardIterator1 __first1,
+    _ForwardIterator1 __last1,
+    _ForwardIterator2 __first2,
+    _ForwardOutIterator __result,
+    _BinaryOperation __op) {
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator1);
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardIterator2);
+  _LIBCPP_REQUIRE_CPP17_FORWARD_ITERATOR(_ForwardOutIterator);
+  _LIBCPP_REQUIRE_CPP17_OUTPUT_ITERATOR(_ForwardOutIterator, decltype(__op(*__first1, *__first2)));
+  using _Backend = typename __select_backend<_RawPolicy>::type;
+  return std::__pstl_transform<_RawPolicy>(
+      _Backend{}, std::move(__first1), std::move(__last1), std::move(__first2), std::move(__result), std::move(__op));
+}
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // !defined(_LIBCPP_HAS_NO_INCOMPLETE_PSTL) && _LIBCPP_STD_VER >= 17
+
+#endif // _LIBCPP___ALGORITHM_PSTL_TRANSFORM_H

lib/libcxx/include/__algorithm/push_heap.h

@@ -14,13 +14,17 @@
 #include <__algorithm/iterator_operations.h>
 #include <__config>
 #include <__iterator/iterator_traits.h>
+#include <__type_traits/is_copy_assignable.h>
+#include <__type_traits/is_copy_constructible.h>
 #include <__utility/move.h>
-#include <type_traits>
 
 #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 _AlgPolicy, class _Compare, class _RandomAccessIterator>
@@ -68,10 +72,11 @@ void push_heap(_RandomAccessIterator __first, _RandomAccessIterator __last, _Com
 template <class _RandomAccessIterator>
 inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20
 void push_heap(_RandomAccessIterator __first, _RandomAccessIterator __last) {
-  std::push_heap(std::move(__first), std::move(__last),
+  std::push_heap(std::move(__first), std::move(__last), __less<>());
-      __less<typename iterator_traits<_RandomAccessIterator>::value_type>());
 }
 
 _LIBCPP_END_NAMESPACE_STD
 
+_LIBCPP_POP_MACROS
+
 #endif // _LIBCPP___ALGORITHM_PUSH_HEAP_H

lib/libcxx/include/__algorithm/ranges_adjacent_find.h

@@ -24,17 +24,16 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 namespace __adjacent_find {
 struct __fn {
-
   template <class _Iter, class _Sent, class _Proj, class _Pred>
-  _LIBCPP_HIDE_FROM_ABI constexpr static
+  _LIBCPP_HIDE_FROM_ABI constexpr static _Iter
-  _Iter __adjacent_find_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
+  __adjacent_find_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
     if (__first == __last)
       return __first;
 
@@ -47,32 +46,33 @@ struct __fn {
     return __i;
   }
 
-  template <forward_iterator _Iter, sentinel_for<_Iter> _Sent,
+  template <forward_iterator _Iter,
-            class _Proj = identity,
+            sentinel_for<_Iter> _Sent,
+            class _Proj                                                                       = identity,
             indirect_binary_predicate<projected<_Iter, _Proj>, projected<_Iter, _Proj>> _Pred = ranges::equal_to>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr _Iter
-  _Iter operator()(_Iter __first, _Sent __last, _Pred __pred = {}, _Proj __proj = {}) const {
+  operator()(_Iter __first, _Sent __last, _Pred __pred = {}, _Proj __proj = {}) const {
     return __adjacent_find_impl(std::move(__first), std::move(__last), __pred, __proj);
   }
 
   template <forward_range _Range,
             class _Proj = identity,
-            indirect_binary_predicate<projected<iterator_t<_Range>, _Proj>,
+            indirect_binary_predicate<projected<iterator_t<_Range>, _Proj>, projected<iterator_t<_Range>, _Proj>>
-                                      projected<iterator_t<_Range>, _Proj>> _Pred = ranges::equal_to>
+                _Pred = ranges::equal_to>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range>
-  borrowed_iterator_t<_Range> operator()(_Range&& __range, _Pred __pred = {}, _Proj __proj = {}) const {
+  operator()(_Range&& __range, _Pred __pred = {}, _Proj __proj = {}) const {
     return __adjacent_find_impl(ranges::begin(__range), ranges::end(__range), __pred, __proj);
   }
 };
 } // namespace __adjacent_find
 
 inline namespace __cpo {
-  inline constexpr auto adjacent_find = __adjacent_find::__fn{};
+inline constexpr auto adjacent_find = __adjacent_find::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_ADJACENT_FIND_H

lib/libcxx/include/__algorithm/ranges_all_of.h

@@ -22,17 +22,15 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 namespace __all_of {
 struct __fn {
-
   template <class _Iter, class _Sent, class _Proj, class _Pred>
-  _LIBCPP_HIDE_FROM_ABI constexpr static
+  _LIBCPP_HIDE_FROM_ABI constexpr static bool __all_of_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
-  bool __all_of_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
     for (; __first != __last; ++__first) {
       if (!std::invoke(__pred, std::invoke(__proj, *__first)))
         return false;
@@ -40,29 +38,32 @@ struct __fn {
     return true;
   }
 
-  template <input_iterator _Iter, sentinel_for<_Iter> _Sent, class _Proj = identity,
+  template <input_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            class _Proj = identity,
             indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool
-  bool operator()(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {}) const {
+  operator()(_Iter __first, _Sent __last, _Pred __pred, _Proj __proj = {}) const {
     return __all_of_impl(std::move(__first), std::move(__last), __pred, __proj);
   }
 
-  template <input_range _Range, class _Proj = identity,
+  template <input_range _Range,
+            class _Proj = identity,
             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool
-  bool operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) const {
+  operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) const {
     return __all_of_impl(ranges::begin(__range), ranges::end(__range), __pred, __proj);
   }
 };
 } // namespace __all_of
 
 inline namespace __cpo {
-  inline constexpr auto all_of = __all_of::__fn{};
+inline constexpr auto all_of = __all_of::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_ALL_OF_H

lib/libcxx/include/__algorithm/ranges_any_of.h

@@ -22,17 +22,15 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 namespace __any_of {
 struct __fn {
-
   template <class _Iter, class _Sent, class _Proj, class _Pred>
-  _LIBCPP_HIDE_FROM_ABI constexpr static
+  _LIBCPP_HIDE_FROM_ABI constexpr static bool __any_of_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
-  bool __any_of_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
     for (; __first != __last; ++__first) {
       if (std::invoke(__pred, std::invoke(__proj, *__first)))
         return true;
@@ -40,29 +38,32 @@ struct __fn {
     return false;
   }
 
-  template <input_iterator _Iter, sentinel_for<_Iter> _Sent, class _Proj = identity,
+  template <input_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            class _Proj = identity,
             indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool
-  bool operator()(_Iter __first, _Sent __last, _Pred __pred = {}, _Proj __proj = {}) const {
+  operator()(_Iter __first, _Sent __last, _Pred __pred = {}, _Proj __proj = {}) const {
     return __any_of_impl(std::move(__first), std::move(__last), __pred, __proj);
   }
 
-  template <input_range _Range, class _Proj = identity,
+  template <input_range _Range,
+            class _Proj = identity,
             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool
-  bool operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) const {
+  operator()(_Range&& __range, _Pred __pred, _Proj __proj = {}) const {
     return __any_of_impl(ranges::begin(__range), ranges::end(__range), __pred, __proj);
   }
 };
 } // namespace __any_of
 
 inline namespace __cpo {
-  inline constexpr auto any_of = __any_of::__fn{};
+inline constexpr auto any_of = __any_of::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_ANY_OF_H

lib/libcxx/include/__algorithm/ranges_binary_search.h

@@ -24,40 +24,45 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 namespace __binary_search {
 struct __fn {
-  template <forward_iterator _Iter, sentinel_for<_Iter> _Sent, class _Type, class _Proj = identity,
+  template <forward_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            class _Type,
+            class _Proj                                                             = identity,
             indirect_strict_weak_order<const _Type*, projected<_Iter, _Proj>> _Comp = ranges::less>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool
-  bool operator()(_Iter __first, _Sent __last, const _Type& __value, _Comp __comp = {}, _Proj __proj = {}) const {
+  operator()(_Iter __first, _Sent __last, const _Type& __value, _Comp __comp = {}, _Proj __proj = {}) const {
-    auto __ret = std::__lower_bound_impl<_RangeAlgPolicy>(__first, __last, __value, __comp, __proj);
+    auto __ret = std::__lower_bound<_RangeAlgPolicy>(__first, __last, __value, __comp, __proj);
     return __ret != __last && !std::invoke(__comp, __value, std::invoke(__proj, *__ret));
   }
 
-  template <forward_range _Range, class _Type, class _Proj = identity,
+  template <forward_range _Range,
+            class _Type,
+            class _Proj                                                                          = identity,
             indirect_strict_weak_order<const _Type*, projected<iterator_t<_Range>, _Proj>> _Comp = ranges::less>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool
-  bool operator()(_Range&& __r, const _Type& __value, _Comp __comp = {}, _Proj __proj = {}) const {
+  operator()(_Range&& __r, const _Type& __value, _Comp __comp = {}, _Proj __proj = {}) const {
     auto __first = ranges::begin(__r);
-    auto __last = ranges::end(__r);
+    auto __last  = ranges::end(__r);
-    auto __ret = std::__lower_bound_impl<_RangeAlgPolicy>(__first, __last, __value, __comp, __proj);
+    auto __ret   = std::__lower_bound<_RangeAlgPolicy>(__first, __last, __value, __comp, __proj);
     return __ret != __last && !std::invoke(__comp, __value, std::invoke(__proj, *__ret));
   }
 };
 } // namespace __binary_search
 
 inline namespace __cpo {
-  inline constexpr auto binary_search = __binary_search::__fn{};
+inline constexpr auto binary_search = __binary_search::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_BINARY_SEARCH_H

lib/libcxx/include/__algorithm/ranges_clamp.h

@@ -22,25 +22,20 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 namespace __clamp {
 struct __fn {
-
   template <class _Type,
-            class _Proj = identity,
+            class _Proj                                                      = identity,
             indirect_strict_weak_order<projected<const _Type*, _Proj>> _Comp = ranges::less>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr const _Type& operator()(
-  const _Type& operator()(const _Type& __value,
+      const _Type& __value, const _Type& __low, const _Type& __high, _Comp __comp = {}, _Proj __proj = {}) const {
-                          const _Type& __low,
+    _LIBCPP_ASSERT_UNCATEGORIZED(!bool(std::invoke(__comp, std::invoke(__proj, __high), std::invoke(__proj, __low))),
-                          const _Type& __high,
+                                 "Bad bounds passed to std::ranges::clamp");
-                          _Comp __comp = {},
-                          _Proj __proj = {}) const {
-    _LIBCPP_ASSERT(!bool(std::invoke(__comp, std::invoke(__proj, __high), std::invoke(__proj, __low))),
-                   "Bad bounds passed to std::ranges::clamp");
 
     if (std::invoke(__comp, std::invoke(__proj, __value), std::invoke(__proj, __low)))
       return __low;
@@ -49,17 +44,16 @@ struct __fn {
     else
       return __value;
   }
-
 };
 } // namespace __clamp
 
 inline namespace __cpo {
-  inline constexpr auto clamp = __clamp::__fn{};
+inline constexpr auto clamp = __clamp::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_CLAMP_H

lib/libcxx/include/__algorithm/ranges_copy.h

@@ -25,7 +25,7 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -36,19 +36,18 @@ using copy_result = in_out_result<_InIter, _OutIter>;
 
 namespace __copy {
 struct __fn {
-
   template <input_iterator _InIter, sentinel_for<_InIter> _Sent, weakly_incrementable _OutIter>
     requires indirectly_copyable<_InIter, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_result<_InIter, _OutIter>
-  copy_result<_InIter, _OutIter> operator()(_InIter __first, _Sent __last, _OutIter __result) const {
+  operator()(_InIter __first, _Sent __last, _OutIter __result) const {
     auto __ret = std::__copy<_RangeAlgPolicy>(std::move(__first), std::move(__last), std::move(__result));
     return {std::move(__ret.first), std::move(__ret.second)};
   }
 
   template <input_range _Range, weakly_incrementable _OutIter>
     requires indirectly_copyable<iterator_t<_Range>, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_result<borrowed_iterator_t<_Range>, _OutIter>
-  copy_result<borrowed_iterator_t<_Range>, _OutIter> operator()(_Range&& __r, _OutIter __result) const {
+  operator()(_Range&& __r, _OutIter __result) const {
     auto __ret = std::__copy<_RangeAlgPolicy>(ranges::begin(__r), ranges::end(__r), std::move(__result));
     return {std::move(__ret.first), std::move(__ret.second)};
   }
@@ -56,12 +55,12 @@ struct __fn {
 } // namespace __copy
 
 inline namespace __cpo {
-  inline constexpr auto copy = __copy::__fn{};
+inline constexpr auto copy = __copy::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_COPY_H

lib/libcxx/include/__algorithm/ranges_copy_backward.h

@@ -23,30 +23,29 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
-template<class _Ip, class _Op>
+template <class _Ip, class _Op>
 using copy_backward_result = in_out_result<_Ip, _Op>;
 
 namespace __copy_backward {
 struct __fn {
-
   template <bidirectional_iterator _InIter1, sentinel_for<_InIter1> _Sent1, bidirectional_iterator _InIter2>
     requires indirectly_copyable<_InIter1, _InIter2>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_backward_result<_InIter1, _InIter2>
-  copy_backward_result<_InIter1, _InIter2> operator()(_InIter1 __first, _Sent1 __last, _InIter2 __result) const {
+  operator()(_InIter1 __first, _Sent1 __last, _InIter2 __result) const {
     auto __ret = std::__copy_backward<_RangeAlgPolicy>(std::move(__first), std::move(__last), std::move(__result));
     return {std::move(__ret.first), std::move(__ret.second)};
   }
 
   template <bidirectional_range _Range, bidirectional_iterator _Iter>
     requires indirectly_copyable<iterator_t<_Range>, _Iter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_backward_result<borrowed_iterator_t<_Range>, _Iter>
-  copy_backward_result<borrowed_iterator_t<_Range>, _Iter> operator()(_Range&& __r, _Iter __result) const {
+  operator()(_Range&& __r, _Iter __result) const {
     auto __ret = std::__copy_backward<_RangeAlgPolicy>(ranges::begin(__r), ranges::end(__r), std::move(__result));
     return {std::move(__ret.first), std::move(__ret.second)};
   }
@@ -54,12 +53,12 @@ struct __fn {
 } // namespace __copy_backward
 
 inline namespace __cpo {
-  inline constexpr auto copy_backward = __copy_backward::__fn{};
+inline constexpr auto copy_backward = __copy_backward::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_COPY_BACKWARD_H

lib/libcxx/include/__algorithm/ranges_copy_if.h

@@ -24,21 +24,19 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 
-template<class _Ip, class _Op>
+template <class _Ip, class _Op>
 using copy_if_result = in_out_result<_Ip, _Op>;
 
 namespace __copy_if {
 struct __fn {
-
   template <class _InIter, class _Sent, class _OutIter, class _Proj, class _Pred>
-  _LIBCPP_HIDE_FROM_ABI static constexpr
+  _LIBCPP_HIDE_FROM_ABI static constexpr copy_if_result<_InIter, _OutIter>
-  copy_if_result <_InIter, _OutIter>
   __copy_if_impl(_InIter __first, _Sent __last, _OutIter __result, _Pred& __pred, _Proj& __proj) {
     for (; __first != __last; ++__first) {
       if (std::invoke(__pred, std::invoke(__proj, *__first))) {
@@ -49,20 +47,23 @@ struct __fn {
     return {std::move(__first), std::move(__result)};
   }
 
-  template <input_iterator _Iter, sentinel_for<_Iter> _Sent, weakly_incrementable _OutIter, class _Proj = identity,
+  template <input_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            weakly_incrementable _OutIter,
+            class _Proj = identity,
             indirect_unary_predicate<projected<_Iter, _Proj>> _Pred>
     requires indirectly_copyable<_Iter, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_if_result<_Iter, _OutIter>
-  copy_if_result<_Iter, _OutIter>
   operator()(_Iter __first, _Sent __last, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
     return __copy_if_impl(std::move(__first), std::move(__last), std::move(__result), __pred, __proj);
   }
 
-  template <input_range _Range, weakly_incrementable _OutIter, class _Proj = identity,
+  template <input_range _Range,
+            weakly_incrementable _OutIter,
+            class _Proj = identity,
             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Pred>
     requires indirectly_copyable<iterator_t<_Range>, _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_if_result<borrowed_iterator_t<_Range>, _OutIter>
-  copy_if_result<borrowed_iterator_t<_Range>, _OutIter>
   operator()(_Range&& __r, _OutIter __result, _Pred __pred, _Proj __proj = {}) const {
     return __copy_if_impl(ranges::begin(__r), ranges::end(__r), std::move(__result), __pred, __proj);
   }
@@ -70,12 +71,12 @@ struct __fn {
 } // namespace __copy_if
 
 inline namespace __cpo {
-  inline constexpr auto copy_if = __copy_if::__fn{};
+inline constexpr auto copy_if = __copy_if::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_COPY_IF_H

lib/libcxx/include/__algorithm/ranges_copy_n.h

@@ -27,7 +27,7 @@
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 namespace ranges {
 
@@ -36,10 +36,9 @@ using copy_n_result = in_out_result<_Ip, _Op>;
 
 namespace __copy_n {
 struct __fn {
-
   template <class _InIter, class _DiffType, class _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr static
+  _LIBCPP_HIDE_FROM_ABI constexpr static copy_n_result<_InIter, _OutIter>
-  copy_n_result<_InIter, _OutIter> __go(_InIter __first, _DiffType __n, _OutIter __result) {
+  __go(_InIter __first, _DiffType __n, _OutIter __result) {
     while (__n != 0) {
       *__result = *__first;
       ++__first;
@@ -50,27 +49,27 @@ struct __fn {
   }
 
   template <random_access_iterator _InIter, class _DiffType, random_access_iterator _OutIter>
-  _LIBCPP_HIDE_FROM_ABI constexpr static
+  _LIBCPP_HIDE_FROM_ABI constexpr static copy_n_result<_InIter, _OutIter>
-  copy_n_result<_InIter, _OutIter> __go(_InIter __first, _DiffType __n, _OutIter __result) {
+  __go(_InIter __first, _DiffType __n, _OutIter __result) {
     auto __ret = std::__copy<_RangeAlgPolicy>(__first, __first + __n, __result);
     return {__ret.first, __ret.second};
   }
 
   template <input_iterator _Ip, weakly_incrementable _Op>
     requires indirectly_copyable<_Ip, _Op>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr copy_n_result<_Ip, _Op>
-  copy_n_result<_Ip, _Op> operator()(_Ip __first, iter_difference_t<_Ip> __n, _Op __result) const {
+  operator()(_Ip __first, iter_difference_t<_Ip> __n, _Op __result) const {
     return __go(std::move(__first), __n, std::move(__result));
   }
 };
 } // namespace __copy_n
 
 inline namespace __cpo {
-  inline constexpr auto copy_n = __copy_n::__fn{};
+inline constexpr auto copy_n = __copy_n::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 _LIBCPP_END_NAMESPACE_STD
 

lib/libcxx/include/__algorithm/ranges_count.h

@@ -25,7 +25,7 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -34,16 +34,16 @@ namespace __count {
 struct __fn {
   template <input_iterator _Iter, sentinel_for<_Iter> _Sent, class _Type, class _Proj = identity>
     requires indirect_binary_predicate<ranges::equal_to, projected<_Iter, _Proj>, const _Type*>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Iter>
-  iter_difference_t<_Iter> operator()(_Iter __first, _Sent __last, const _Type& __value, _Proj __proj = {}) const {
+  operator()(_Iter __first, _Sent __last, const _Type& __value, _Proj __proj = {}) const {
     auto __pred = [&](auto&& __e) { return __e == __value; };
     return ranges::__count_if_impl(std::move(__first), std::move(__last), __pred, __proj);
   }
 
   template <input_range _Range, class _Type, class _Proj = identity>
     requires indirect_binary_predicate<ranges::equal_to, projected<iterator_t<_Range>, _Proj>, const _Type*>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr range_difference_t<_Range>
-  range_difference_t<_Range> operator()(_Range&& __r, const _Type& __value, _Proj __proj = {}) const {
+  operator()(_Range&& __r, const _Type& __value, _Proj __proj = {}) const {
     auto __pred = [&](auto&& __e) { return __e == __value; };
     return ranges::__count_if_impl(ranges::begin(__r), ranges::end(__r), __pred, __proj);
   }
@@ -51,12 +51,12 @@ struct __fn {
 } // namespace __count
 
 inline namespace __cpo {
-  inline constexpr auto count = __count::__fn{};
+inline constexpr auto count = __count::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_COUNT_H

lib/libcxx/include/__algorithm/ranges_count_if.h

@@ -25,15 +25,14 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 template <class _Iter, class _Sent, class _Proj, class _Pred>
-_LIBCPP_HIDE_FROM_ABI constexpr
+_LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Iter>
-iter_difference_t<_Iter> __count_if_impl(_Iter __first, _Sent __last,
+__count_if_impl(_Iter __first, _Sent __last, _Pred& __pred, _Proj& __proj) {
-                                             _Pred& __pred, _Proj& __proj) {
   iter_difference_t<_Iter> __counter(0);
   for (; __first != __last; ++__first) {
     if (std::invoke(__pred, std::invoke(__proj, *__first)))
@@ -44,29 +43,32 @@ iter_difference_t<_Iter> __count_if_impl(_Iter __first, _Sent __last,
 
 namespace __count_if {
 struct __fn {
-  template <input_iterator _Iter, sentinel_for<_Iter> _Sent, class _Proj = identity,
+  template <input_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
+            class _Proj = identity,
             indirect_unary_predicate<projected<_Iter, _Proj>> _Predicate>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr iter_difference_t<_Iter>
-  iter_difference_t<_Iter> operator()(_Iter __first, _Sent __last, _Predicate __pred, _Proj __proj = {}) const {
+  operator()(_Iter __first, _Sent __last, _Predicate __pred, _Proj __proj = {}) const {
     return ranges::__count_if_impl(std::move(__first), std::move(__last), __pred, __proj);
   }
 
-  template <input_range _Range, class _Proj = identity,
+  template <input_range _Range,
+            class _Proj = identity,
             indirect_unary_predicate<projected<iterator_t<_Range>, _Proj>> _Predicate>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr range_difference_t<_Range>
-  range_difference_t<_Range> operator()(_Range&& __r, _Predicate __pred, _Proj __proj = {}) const {
+  operator()(_Range&& __r, _Predicate __pred, _Proj __proj = {}) const {
     return ranges::__count_if_impl(ranges::begin(__r), ranges::end(__r), __pred, __proj);
   }
 };
 } // namespace __count_if
 
 inline namespace __cpo {
-  inline constexpr auto count_if = __count_if::__fn{};
+inline constexpr auto count_if = __count_if::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_COUNT_IF_H

lib/libcxx/include/__algorithm/ranges_equal.h

@@ -9,6 +9,8 @@
 #ifndef _LIBCPP___ALGORITHM_RANGES_EQUAL_H
 #define _LIBCPP___ALGORITHM_RANGES_EQUAL_H
 
+#include <__algorithm/equal.h>
+#include <__algorithm/unwrap_range.h>
 #include <__config>
 #include <__functional/identity.h>
 #include <__functional/invoke.h>
@@ -24,92 +26,79 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace ranges {
 namespace __equal {
 struct __fn {
-private:
+  template <input_iterator _Iter1,
-  template <class _Iter1, class _Sent1,
+            sentinel_for<_Iter1> _Sent1,
-            class _Iter2, class _Sent2,
+            input_iterator _Iter2,
-            class _Pred,
+            sentinel_for<_Iter2> _Sent2,
-            class _Proj1,
+            class _Pred  = ranges::equal_to,
-            class _Proj2>
-  _LIBCPP_HIDE_FROM_ABI constexpr static
-  bool __equal_impl(_Iter1 __first1, _Sent1 __last1,
-                    _Iter2 __first2, _Sent2 __last2,
-                    _Pred& __pred,
-                    _Proj1& __proj1,
-                    _Proj2& __proj2) {
-    while (__first1 != __last1 && __first2 != __last2) {
-      if (!std::invoke(__pred, std::invoke(__proj1, *__first1), std::invoke(__proj2, *__first2)))
-        return false;
-      ++__first1;
-      ++__first2;
-    }
-    return __first1 == __last1 && __first2 == __last2;
-  }
-
-public:
-
-  template <input_iterator _Iter1, sentinel_for<_Iter1> _Sent1,
-            input_iterator _Iter2, sentinel_for<_Iter2> _Sent2,
-            class _Pred = ranges::equal_to,
             class _Proj1 = identity,
             class _Proj2 = identity>
     requires indirectly_comparable<_Iter1, _Iter2, _Pred, _Proj1, _Proj2>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(
-  bool operator()(_Iter1 __first1, _Sent1 __last1,
+      _Iter1 __first1,
-                  _Iter2 __first2, _Sent2 __last2,
+      _Sent1 __last1,
-                  _Pred __pred = {},
+      _Iter2 __first2,
-                  _Proj1 __proj1 = {},
+      _Sent2 __last2,
-                  _Proj2 __proj2 = {}) const {
+      _Pred __pred   = {},
+      _Proj1 __proj1 = {},
+      _Proj2 __proj2 = {}) const {
     if constexpr (sized_sentinel_for<_Sent1, _Iter1> && sized_sentinel_for<_Sent2, _Iter2>) {
       if (__last1 - __first1 != __last2 - __first2)
         return false;
     }
-    return __equal_impl(std::move(__first1), std::move(__last1),
+    auto __unwrapped1 = std::__unwrap_range(std::move(__first1), std::move(__last1));
-                        std::move(__first2), std::move(__last2),
+    auto __unwrapped2 = std::__unwrap_range(std::move(__first2), std::move(__last2));
-                        __pred,
+    return std::__equal_impl(
-                        __proj1,
+        std::move(__unwrapped1.first),
-                        __proj2);
+        std::move(__unwrapped1.second),
+        std::move(__unwrapped2.first),
+        std::move(__unwrapped2.second),
+        __pred,
+        __proj1,
+        __proj2);
   }
 
   template <input_range _Range1,
             input_range _Range2,
-            class _Pred = ranges::equal_to,
+            class _Pred  = ranges::equal_to,
             class _Proj1 = identity,
             class _Proj2 = identity>
     requires indirectly_comparable<iterator_t<_Range1>, iterator_t<_Range2>, _Pred, _Proj1, _Proj2>
-  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr bool operator()(
-  bool operator()(_Range1&& __range1,
+      _Range1&& __range1, _Range2&& __range2, _Pred __pred = {}, _Proj1 __proj1 = {}, _Proj2 __proj2 = {}) const {
-                  _Range2&& __range2,
-                  _Pred __pred = {},
-                  _Proj1 __proj1 = {},
-                  _Proj2 __proj2 = {}) const {
     if constexpr (sized_range<_Range1> && sized_range<_Range2>) {
       if (ranges::distance(__range1) != ranges::distance(__range2))
         return false;
     }
-    return __equal_impl(ranges::begin(__range1), ranges::end(__range1),
+    auto __unwrapped1 = std::__unwrap_range(ranges::begin(__range1), ranges::end(__range1));
-                        ranges::begin(__range2), ranges::end(__range2),
+    auto __unwrapped2 = std::__unwrap_range(ranges::begin(__range2), ranges::end(__range2));
-                        __pred,
+    return std::__equal_impl(
-                        __proj1,
+        std::move(__unwrapped1.first),
-                        __proj2);
+        std::move(__unwrapped1.second),
+        std::move(__unwrapped2.first),
+        std::move(__unwrapped2.second),
+        __pred,
+        __proj1,
+        __proj2);
     return false;
   }
 };
 } // namespace __equal
 
 inline namespace __cpo {
-  inline constexpr auto equal = __equal::__fn{};
+inline constexpr auto equal = __equal::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_EQUAL_H

lib/libcxx/include/__algorithm/ranges_equal_range.h

@@ -30,7 +30,7 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -38,28 +38,25 @@ namespace ranges {
 namespace __equal_range {
 
 struct __fn {
-  template <
+  template <forward_iterator _Iter,
-      forward_iterator _Iter,
+            sentinel_for<_Iter> _Sent,
-      sentinel_for<_Iter> _Sent,
+            class _Tp,
-      class _Tp,
+            class _Proj                                                           = identity,
-      class _Proj                                                           = identity,
+            indirect_strict_weak_order<const _Tp*, projected<_Iter, _Proj>> _Comp = ranges::less>
-      indirect_strict_weak_order<const _Tp*, projected<_Iter, _Proj>> _Comp = ranges::less>
   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr subrange<_Iter>
   operator()(_Iter __first, _Sent __last, const _Tp& __value, _Comp __comp = {}, _Proj __proj = {}) const {
-    auto __ret = std::__equal_range<_RangeAlgPolicy>(
+    auto __ret = std::__equal_range<_RangeAlgPolicy>(std::move(__first), std::move(__last), __value, __comp, __proj);
-        std::move(__first), std::move(__last), __value, __comp, __proj);
     return {std::move(__ret.first), std::move(__ret.second)};
   }
 
-  template <
+  template <forward_range _Range,
-      forward_range _Range,
+            class _Tp,
-      class _Tp,
+            class _Proj                                                                        = identity,
-      class _Proj                                                                        = identity,
+            indirect_strict_weak_order<const _Tp*, projected<iterator_t<_Range>, _Proj>> _Comp = ranges::less>
-      indirect_strict_weak_order<const _Tp*, projected<iterator_t<_Range>, _Proj>> _Comp = ranges::less>
   _LIBCPP_NODISCARD_EXT _LIBCPP_HIDE_FROM_ABI constexpr borrowed_subrange_t<_Range>
   operator()(_Range&& __range, const _Tp& __value, _Comp __comp = {}, _Proj __proj = {}) const {
-    auto __ret = std::__equal_range<_RangeAlgPolicy>(
+    auto __ret =
-        ranges::begin(__range), ranges::end(__range), __value, __comp, __proj);
+        std::__equal_range<_RangeAlgPolicy>(ranges::begin(__range), ranges::end(__range), __value, __comp, __proj);
     return {std::move(__ret.first), std::move(__ret.second)};
   }
 };
@@ -67,12 +64,12 @@ struct __fn {
 } // namespace __equal_range
 
 inline namespace __cpo {
-  inline constexpr auto equal_range = __equal_range::__fn{};
+inline constexpr auto equal_range = __equal_range::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_EQUAL_RANGE_H

lib/libcxx/include/__algorithm/ranges_fill.h

@@ -20,7 +20,7 @@
 #  pragma GCC system_header
 #endif
 
-#if _LIBCPP_STD_VER > 17
+#if _LIBCPP_STD_VER >= 20
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
@@ -28,9 +28,8 @@ namespace ranges {
 namespace __fill {
 struct __fn {
   template <class _Type, output_iterator<const _Type&> _Iter, sentinel_for<_Iter> _Sent>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr _Iter operator()(_Iter __first, _Sent __last, const _Type& __value) const {
-  _Iter operator()(_Iter __first, _Sent __last, const _Type& __value) const {
+    if constexpr (random_access_iterator<_Iter> && sized_sentinel_for<_Sent, _Iter>) {
-    if constexpr(random_access_iterator<_Iter> && sized_sentinel_for<_Sent, _Iter>) {
       return ranges::fill_n(__first, __last - __first, __value);
     } else {
       for (; __first != __last; ++__first)
@@ -40,20 +39,19 @@ struct __fn {
   }
 
   template <class _Type, output_range<const _Type&> _Range>
-  _LIBCPP_HIDE_FROM_ABI constexpr
+  _LIBCPP_HIDE_FROM_ABI constexpr borrowed_iterator_t<_Range> operator()(_Range&& __range, const _Type& __value) const {
-  borrowed_iterator_t<_Range> operator()(_Range&& __range, const _Type& __value) const {
     return (*this)(ranges::begin(__range), ranges::end(__range), __value);
   }
 };
 } // namespace __fill
 
 inline namespace __cpo {
-  inline constexpr auto fill = __fill::__fn{};
+inline constexpr auto fill = __fill::__fn{};
 } // namespace __cpo
 } // namespace ranges
 
 _LIBCPP_END_NAMESPACE_STD
 
-#endif // _LIBCPP_STD_VER > 17
+#endif // _LIBCPP_STD_VER >= 20
 
 #endif // _LIBCPP___ALGORITHM_RANGES_FILL_H