Upgrade to 2022-era LLVM LIBCXX

third_party/libcxx/__compare/common_comparison_category.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___COMPARE_COMMON_COMPARISON_CATEGORY_H
+#define _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H
+
+#include <__compare/ordering.h>
+#include <__config>
+#include <__type_traits/is_same.h>
+#include <cstddef>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+namespace __comp_detail {
+
+enum _ClassifyCompCategory : unsigned {
+  _None,
+  _PartialOrd,
+  _WeakOrd,
+  _StrongOrd,
+  _CCC_Size
+};
+
+template <class _Tp>
+_LIBCPP_HIDE_FROM_ABI
+constexpr _ClassifyCompCategory __type_to_enum() noexcept {
+  if (is_same_v<_Tp, partial_ordering>)
+    return _PartialOrd;
+  if (is_same_v<_Tp, weak_ordering>)
+    return _WeakOrd;
+  if (is_same_v<_Tp, strong_ordering>)
+    return _StrongOrd;
+  return _None;
+}
+
+template <size_t _Size>
+_LIBCPP_HIDE_FROM_ABI
+constexpr _ClassifyCompCategory
+__compute_comp_type(const _ClassifyCompCategory (&__types)[_Size]) {
+  int __seen[_CCC_Size] = {};
+  for (auto __type : __types)
+    ++__seen[__type];
+  if (__seen[_None])
+    return _None;
+  if (__seen[_PartialOrd])
+    return _PartialOrd;
+  if (__seen[_WeakOrd])
+    return _WeakOrd;
+  return _StrongOrd;
+}
+
+template <class ..._Ts, bool _False = false>
+_LIBCPP_HIDE_FROM_ABI
+constexpr auto __get_comp_type() {
+  using _CCC = _ClassifyCompCategory;
+  constexpr _CCC __type_kinds[] = {_StrongOrd, __type_to_enum<_Ts>()...};
+  constexpr _CCC __cat = __comp_detail::__compute_comp_type(__type_kinds);
+  if constexpr (__cat == _None)
+    return void();
+  else if constexpr (__cat == _PartialOrd)
+    return partial_ordering::equivalent;
+  else if constexpr (__cat == _WeakOrd)
+    return weak_ordering::equivalent;
+  else if constexpr (__cat == _StrongOrd)
+    return strong_ordering::equivalent;
+  else
+    static_assert(_False, "unhandled case");
+}
+} // namespace __comp_detail
+
+// [cmp.common], common comparison category type
+template<class... _Ts>
+struct _LIBCPP_TEMPLATE_VIS common_comparison_category {
+  using type = decltype(__comp_detail::__get_comp_type<_Ts...>());
+};
+
+template<class... _Ts>
+using common_comparison_category_t = typename common_comparison_category<_Ts...>::type;
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMMON_COMPARISON_CATEGORY_H

third_party/libcxx/__compare/compare_partial_order_fallback.h

@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_COMPARE_PARTIAL_ORDER_FALLBACK
+#define _LIBCPP___COMPARE_COMPARE_PARTIAL_ORDER_FALLBACK
+
+#include <__compare/ordering.h>
+#include <__compare/partial_order.h>
+#include <__config>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_same.h>
+#include <__utility/forward.h>
+#include <__utility/priority_tag.h>
+
+#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [cmp.alg]
+namespace __compare_partial_order_fallback {
+    struct __fn {
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>)
+            noexcept(noexcept(_VSTD::partial_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            -> decltype(      _VSTD::partial_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))
+            { return          _VSTD::partial_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)); }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
+            noexcept(noexcept(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? partial_ordering::equivalent :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? partial_ordering::less :
+                              _VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t) ? partial_ordering::greater :
+                              partial_ordering::unordered))
+            -> decltype(      _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? partial_ordering::equivalent :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? partial_ordering::less :
+                              _VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t) ? partial_ordering::greater :
+                              partial_ordering::unordered)
+        {
+            return            _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? partial_ordering::equivalent :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? partial_ordering::less :
+                              _VSTD::forward<_Up>(__u) < _VSTD::forward<_Tp>(__t) ? partial_ordering::greater :
+                              partial_ordering::unordered;
+        }
+
+        template<class _Tp, class _Up>
+        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
+            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>())))
+            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>()))
+            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>()); }
+    };
+} // namespace __compare_partial_order_fallback
+
+inline namespace __cpo {
+    inline constexpr auto compare_partial_order_fallback = __compare_partial_order_fallback::__fn{};
+} // namespace __cpo
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMPARE_PARTIAL_ORDER_FALLBACK

third_party/libcxx/__compare/compare_strong_order_fallback.h

@@ -0,0 +1,71 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_COMPARE_STRONG_ORDER_FALLBACK
+#define _LIBCPP___COMPARE_COMPARE_STRONG_ORDER_FALLBACK
+
+#include <__compare/ordering.h>
+#include <__compare/strong_order.h>
+#include <__config>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_same.h>
+#include <__utility/forward.h>
+#include <__utility/priority_tag.h>
+
+#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [cmp.alg]
+namespace __compare_strong_order_fallback {
+    struct __fn {
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>)
+            noexcept(noexcept(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            -> decltype(      _VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))
+            { return          _VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)); }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
+            noexcept(noexcept(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? strong_ordering::equal :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? strong_ordering::less :
+                              strong_ordering::greater))
+            -> decltype(      _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? strong_ordering::equal :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? strong_ordering::less :
+                              strong_ordering::greater)
+        {
+            return            _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? strong_ordering::equal :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? strong_ordering::less :
+                              strong_ordering::greater;
+        }
+
+        template<class _Tp, class _Up>
+        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
+            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>())))
+            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>()))
+            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>()); }
+    };
+} // namespace __compare_strong_order_fallback
+
+inline namespace __cpo {
+    inline constexpr auto compare_strong_order_fallback = __compare_strong_order_fallback::__fn{};
+} // namespace __cpo
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMPARE_STRONG_ORDER_FALLBACK

third_party/libcxx/__compare/compare_three_way.h

@@ -0,0 +1,41 @@
+// -*- 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___COMPARE_COMPARE_THREE_WAY_H
+#define _LIBCPP___COMPARE_COMPARE_THREE_WAY_H
+
+#include <__compare/three_way_comparable.h>
+#include <__config>
+#include <__utility/forward.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+struct _LIBCPP_TEMPLATE_VIS compare_three_way
+{
+    template<class _T1, class _T2>
+        requires three_way_comparable_with<_T1, _T2>
+    constexpr _LIBCPP_HIDE_FROM_ABI
+    auto operator()(_T1&& __t, _T2&& __u) const
+        noexcept(noexcept(_VSTD::forward<_T1>(__t) <=> _VSTD::forward<_T2>(__u)))
+        { return          _VSTD::forward<_T1>(__t) <=> _VSTD::forward<_T2>(__u); }
+
+    using is_transparent = void;
+};
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMPARE_THREE_WAY_H

third_party/libcxx/__compare/compare_three_way_result.h

@@ -0,0 +1,44 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_COMPARE_THREE_WAY_RESULT_H
+#define _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H
+
+#include <__config>
+#include <__type_traits/make_const_lvalue_ref.h>
+#include <__utility/declval.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template<class, class, class>
+struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result { };
+
+template<class _Tp, class _Up>
+struct _LIBCPP_HIDE_FROM_ABI __compare_three_way_result<_Tp, _Up, decltype(
+  std::declval<__make_const_lvalue_ref<_Tp>>() <=> std::declval<__make_const_lvalue_ref<_Up>>(), void()
+)> {
+    using type = decltype(std::declval<__make_const_lvalue_ref<_Tp>>() <=> std::declval<__make_const_lvalue_ref<_Up>>());
+};
+
+template<class _Tp, class _Up = _Tp>
+struct _LIBCPP_TEMPLATE_VIS compare_three_way_result : __compare_three_way_result<_Tp, _Up, void> { };
+
+template<class _Tp, class _Up = _Tp>
+using compare_three_way_result_t = typename compare_three_way_result<_Tp, _Up>::type;
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMPARE_THREE_WAY_RESULT_H

third_party/libcxx/__compare/compare_weak_order_fallback.h

@@ -0,0 +1,71 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_COMPARE_WEAK_ORDER_FALLBACK
+#define _LIBCPP___COMPARE_COMPARE_WEAK_ORDER_FALLBACK
+
+#include <__compare/ordering.h>
+#include <__compare/weak_order.h>
+#include <__config>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_same.h>
+#include <__utility/forward.h>
+#include <__utility/priority_tag.h>
+
+#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [cmp.alg]
+namespace __compare_weak_order_fallback {
+    struct __fn {
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>)
+            noexcept(noexcept(_VSTD::weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            -> decltype(      _VSTD::weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))
+            { return          _VSTD::weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)); }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
+            noexcept(noexcept(_VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? weak_ordering::equivalent :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? weak_ordering::less :
+                              weak_ordering::greater))
+            -> decltype(      _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? weak_ordering::equivalent :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? weak_ordering::less :
+                              weak_ordering::greater)
+        {
+            return            _VSTD::forward<_Tp>(__t) == _VSTD::forward<_Up>(__u) ? weak_ordering::equivalent :
+                              _VSTD::forward<_Tp>(__t) < _VSTD::forward<_Up>(__u) ? weak_ordering::less :
+                              weak_ordering::greater;
+        }
+
+        template<class _Tp, class _Up>
+        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
+            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>())))
+            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>()))
+            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<1>()); }
+    };
+} // namespace __compare_weak_order_fallback
+
+inline namespace __cpo {
+    inline constexpr auto compare_weak_order_fallback = __compare_weak_order_fallback::__fn{};
+} // namespace __cpo
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_COMPARE_WEAK_ORDER_FALLBACK

third_party/libcxx/__compare/is_eq.h

@@ -0,0 +1,34 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_IS_EQ_H
+#define _LIBCPP___COMPARE_IS_EQ_H
+
+#include <__compare/ordering.h>
+#include <__config>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool is_eq(partial_ordering __c) noexcept { return __c == 0; }
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool is_neq(partial_ordering __c) noexcept { return __c != 0; }
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool is_lt(partial_ordering __c) noexcept { return __c < 0; }
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool is_lteq(partial_ordering __c) noexcept { return __c <= 0; }
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool is_gt(partial_ordering __c) noexcept { return __c > 0; }
+_LIBCPP_HIDE_FROM_ABI inline constexpr bool is_gteq(partial_ordering __c) noexcept { return __c >= 0; }
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_IS_EQ_H

third_party/libcxx/__compare/ordering.h

@@ -0,0 +1,326 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_ORDERING_H
+#define _LIBCPP___COMPARE_ORDERING_H
+
+#include <__config>
+#include <__type_traits/enable_if.h>
+#include <__type_traits/is_same.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// exposition only
+enum class _LIBCPP_ENUM_VIS _OrdResult : signed char {
+  __less = -1,
+  __equiv = 0,
+  __greater = 1
+};
+
+enum class _LIBCPP_ENUM_VIS _NCmpResult : signed char {
+  __unordered = -127
+};
+
+class partial_ordering;
+class weak_ordering;
+class strong_ordering;
+
+template<class _Tp, class... _Args>
+inline constexpr bool __one_of_v = (is_same_v<_Tp, _Args> || ...);
+
+struct _CmpUnspecifiedParam {
+  _LIBCPP_HIDE_FROM_ABI constexpr
+  _CmpUnspecifiedParam(int _CmpUnspecifiedParam::*) noexcept {}
+
+  template<class _Tp, class = enable_if_t<!__one_of_v<_Tp, int, partial_ordering, weak_ordering, strong_ordering>>>
+  _CmpUnspecifiedParam(_Tp) = delete;
+};
+
+class partial_ordering {
+  using _ValueT = signed char;
+
+  _LIBCPP_HIDE_FROM_ABI
+  explicit constexpr partial_ordering(_OrdResult __v) noexcept
+      : __value_(_ValueT(__v)) {}
+
+  _LIBCPP_HIDE_FROM_ABI
+  explicit constexpr partial_ordering(_NCmpResult __v) noexcept
+      : __value_(_ValueT(__v)) {}
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr bool __is_ordered() const noexcept {
+    return __value_ != _ValueT(_NCmpResult::__unordered);
+  }
+public:
+  // valid values
+  static const partial_ordering less;
+  static const partial_ordering equivalent;
+  static const partial_ordering greater;
+  static const partial_ordering unordered;
+
+  // comparisons
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator==(partial_ordering, partial_ordering) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator==(partial_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__is_ordered() && __v.__value_ == 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator< (partial_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__is_ordered() && __v.__value_ < 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator<=(partial_ordering __v, _CmpUnspecifiedParam) noexcept  {
+    return __v.__is_ordered() && __v.__value_ <= 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator> (partial_ordering __v, _CmpUnspecifiedParam) noexcept  {
+    return __v.__is_ordered() && __v.__value_ > 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator>=(partial_ordering __v, _CmpUnspecifiedParam) noexcept  {
+    return __v.__is_ordered() && __v.__value_ >= 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator< (_CmpUnspecifiedParam, partial_ordering __v) noexcept  {
+    return __v.__is_ordered() && 0 < __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator<=(_CmpUnspecifiedParam, partial_ordering __v) noexcept  {
+    return __v.__is_ordered() && 0 <= __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator> (_CmpUnspecifiedParam, partial_ordering __v) noexcept  {
+    return __v.__is_ordered() && 0 > __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator>=(_CmpUnspecifiedParam, partial_ordering __v) noexcept  {
+    return __v.__is_ordered() && 0 >= __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr partial_ordering operator<=>(partial_ordering __v, _CmpUnspecifiedParam) noexcept  {
+    return __v;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr partial_ordering operator<=>(_CmpUnspecifiedParam, partial_ordering __v) noexcept  {
+    return __v < 0 ? partial_ordering::greater : (__v > 0 ? partial_ordering::less : __v);
+  }
+private:
+  _ValueT __value_;
+};
+
+inline constexpr partial_ordering partial_ordering::less(_OrdResult::__less);
+inline constexpr partial_ordering partial_ordering::equivalent(_OrdResult::__equiv);
+inline constexpr partial_ordering partial_ordering::greater(_OrdResult::__greater);
+inline constexpr partial_ordering partial_ordering::unordered(_NCmpResult ::__unordered);
+
+class weak_ordering {
+  using _ValueT = signed char;
+
+  _LIBCPP_HIDE_FROM_ABI
+  explicit constexpr weak_ordering(_OrdResult __v) noexcept : __value_(_ValueT(__v)) {}
+
+public:
+  static const weak_ordering less;
+  static const weak_ordering equivalent;
+  static const weak_ordering greater;
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr operator partial_ordering() const noexcept {
+    return __value_ == 0 ? partial_ordering::equivalent
+        : (__value_ < 0 ? partial_ordering::less : partial_ordering::greater);
+  }
+
+  // comparisons
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator==(weak_ordering, weak_ordering) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator==(weak_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ == 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator< (weak_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ < 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator<=(weak_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ <= 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator> (weak_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ > 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator>=(weak_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ >= 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator< (_CmpUnspecifiedParam, weak_ordering __v) noexcept {
+    return 0 < __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator<=(_CmpUnspecifiedParam, weak_ordering __v) noexcept {
+    return 0 <= __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator> (_CmpUnspecifiedParam, weak_ordering __v) noexcept {
+    return 0 > __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator>=(_CmpUnspecifiedParam, weak_ordering __v) noexcept {
+    return 0 >= __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr weak_ordering operator<=>(weak_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr weak_ordering operator<=>(_CmpUnspecifiedParam, weak_ordering __v) noexcept {
+    return __v < 0 ? weak_ordering::greater : (__v > 0 ? weak_ordering::less : __v);
+  }
+
+private:
+  _ValueT __value_;
+};
+
+inline constexpr weak_ordering weak_ordering::less(_OrdResult::__less);
+inline constexpr weak_ordering weak_ordering::equivalent(_OrdResult::__equiv);
+inline constexpr weak_ordering weak_ordering::greater(_OrdResult::__greater);
+
+class strong_ordering {
+  using _ValueT = signed char;
+
+  _LIBCPP_HIDE_FROM_ABI
+  explicit constexpr strong_ordering(_OrdResult __v) noexcept : __value_(_ValueT(__v)) {}
+
+public:
+  static const strong_ordering less;
+  static const strong_ordering equal;
+  static const strong_ordering equivalent;
+  static const strong_ordering greater;
+
+  // conversions
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr operator partial_ordering() const noexcept {
+    return __value_ == 0 ? partial_ordering::equivalent
+        : (__value_ < 0 ? partial_ordering::less : partial_ordering::greater);
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  constexpr operator weak_ordering() const noexcept {
+    return __value_ == 0 ? weak_ordering::equivalent
+        : (__value_ < 0 ? weak_ordering::less : weak_ordering::greater);
+  }
+
+  // comparisons
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator==(strong_ordering, strong_ordering) noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator==(strong_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ == 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator< (strong_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ < 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator<=(strong_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ <= 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator> (strong_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ > 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator>=(strong_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v.__value_ >= 0;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator< (_CmpUnspecifiedParam, strong_ordering __v) noexcept {
+    return 0 < __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator<=(_CmpUnspecifiedParam, strong_ordering __v) noexcept {
+    return 0 <= __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator> (_CmpUnspecifiedParam, strong_ordering __v) noexcept {
+    return 0 > __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr bool operator>=(_CmpUnspecifiedParam, strong_ordering __v) noexcept {
+    return 0 >= __v.__value_;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr strong_ordering operator<=>(strong_ordering __v, _CmpUnspecifiedParam) noexcept {
+    return __v;
+  }
+
+  _LIBCPP_HIDE_FROM_ABI
+  friend constexpr strong_ordering operator<=>(_CmpUnspecifiedParam, strong_ordering __v) noexcept {
+    return __v < 0 ? strong_ordering::greater : (__v > 0 ? strong_ordering::less : __v);
+  }
+
+private:
+  _ValueT __value_;
+};
+
+inline constexpr strong_ordering strong_ordering::less(_OrdResult::__less);
+inline constexpr strong_ordering strong_ordering::equal(_OrdResult::__equiv);
+inline constexpr strong_ordering strong_ordering::equivalent(_OrdResult::__equiv);
+inline constexpr strong_ordering strong_ordering::greater(_OrdResult::__greater);
+
+/// [cmp.categories.pre]/1
+/// The types partial_ordering, weak_ordering, and strong_ordering are
+/// collectively termed the comparison category types.
+template <class _Tp>
+concept __comparison_category = __one_of_v<_Tp, partial_ordering, weak_ordering, strong_ordering>;
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_ORDERING_H

third_party/libcxx/__compare/partial_order.h

@@ -0,0 +1,74 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_PARTIAL_ORDER
+#define _LIBCPP___COMPARE_PARTIAL_ORDER
+
+#include <__compare/compare_three_way.h>
+#include <__compare/ordering.h>
+#include <__compare/weak_order.h>
+#include <__config>
+#include <__type_traits/decay.h>
+#include <__type_traits/is_same.h>
+#include <__utility/forward.h>
+#include <__utility/priority_tag.h>
+
+#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [cmp.alg]
+namespace __partial_order {
+    struct __fn {
+    // NOLINTBEGIN(libcpp-robust-against-adl) partial_order should use ADL, but only here
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<2>)
+            noexcept(noexcept(partial_ordering(partial_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      partial_ordering(partial_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          partial_ordering(partial_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+    // NOLINTEND(libcpp-robust-against-adl)
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>)
+            noexcept(noexcept(partial_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      partial_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          partial_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
+            noexcept(noexcept(partial_ordering(_VSTD::weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      partial_ordering(_VSTD::weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          partial_ordering(_VSTD::weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+
+        template<class _Tp, class _Up>
+        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
+            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>())))
+            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()))
+            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()); }
+    };
+} // namespace __partial_order
+
+inline namespace __cpo {
+    inline constexpr auto partial_order = __partial_order::__fn{};
+} // namespace __cpo
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_PARTIAL_ORDER

third_party/libcxx/__compare/strong_order.h

@@ -0,0 +1,139 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_STRONG_ORDER
+#define _LIBCPP___COMPARE_STRONG_ORDER
+
+#include <__bit/bit_cast.h>
+#include <__compare/compare_three_way.h>
+#include <__compare/ordering.h>
+#include <__config>
+#include <__type_traits/conditional.h>
+#include <__type_traits/decay.h>
+#include <__utility/forward.h>
+#include <__utility/priority_tag.h>
+#include <cmath>
+#include <cstdint>
+#include <limits>
+
+#ifndef _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
+
+// [cmp.alg]
+namespace __strong_order {
+    struct __fn {
+    // NOLINTBEGIN(libcpp-robust-against-adl) strong_order should use ADL, but only here
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<2>)
+            noexcept(noexcept(strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          strong_ordering(strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+    // NOLINTEND(libcpp-robust-against-adl)
+
+        template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
+            requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
+        _LIBCPP_HIDE_FROM_ABI static constexpr strong_ordering
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>) noexcept
+        {
+            if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int32_t)) {
+                int32_t __rx = _VSTD::bit_cast<int32_t>(__t);
+                int32_t __ry = _VSTD::bit_cast<int32_t>(__u);
+                __rx = (__rx < 0) ? (numeric_limits<int32_t>::min() - __rx - 1) : __rx;
+                __ry = (__ry < 0) ? (numeric_limits<int32_t>::min() - __ry - 1) : __ry;
+                return (__rx <=> __ry);
+            } else if constexpr (numeric_limits<_Dp>::is_iec559 && sizeof(_Dp) == sizeof(int64_t)) {
+                int64_t __rx = _VSTD::bit_cast<int64_t>(__t);
+                int64_t __ry = _VSTD::bit_cast<int64_t>(__u);
+                __rx = (__rx < 0) ? (numeric_limits<int64_t>::min() - __rx - 1) : __rx;
+                __ry = (__ry < 0) ? (numeric_limits<int64_t>::min() - __ry - 1) : __ry;
+                return (__rx <=> __ry);
+            } else if (__t < __u) {
+                return strong_ordering::less;
+            } else if (__t > __u) {
+                return strong_ordering::greater;
+            } else if (__t == __u) {
+                if constexpr (numeric_limits<_Dp>::radix == 2) {
+                    return _VSTD::signbit(__u) <=> _VSTD::signbit(__t);
+                } else {
+                    // This is bullet 3 of the IEEE754 algorithm, relevant
+                    // only for decimal floating-point;
+                    // see https://stackoverflow.com/questions/69068075/
+                    if (__t == 0 || _VSTD::isinf(__t)) {
+                        return _VSTD::signbit(__u) <=> _VSTD::signbit(__t);
+                    } else {
+                        int __texp, __uexp;
+                        (void)_VSTD::frexp(__t, &__texp);
+                        (void)_VSTD::frexp(__u, &__uexp);
+                        return (__t < 0) ? (__texp <=> __uexp) : (__uexp <=> __texp);
+                    }
+                }
+            } else {
+                // They're unordered, so one of them must be a NAN.
+                // The order is -QNAN, -SNAN, numbers, +SNAN, +QNAN.
+                bool __t_is_nan = _VSTD::isnan(__t);
+                bool __u_is_nan = _VSTD::isnan(__u);
+                bool __t_is_negative = _VSTD::signbit(__t);
+                bool __u_is_negative = _VSTD::signbit(__u);
+                using _IntType = conditional_t<
+                    sizeof(__t) == sizeof(int32_t), int32_t, conditional_t<
+                    sizeof(__t) == sizeof(int64_t), int64_t, void>
+                >;
+                if constexpr (is_same_v<_IntType, void>) {
+                    static_assert(sizeof(_Dp) == 0, "std::strong_order is unimplemented for this floating-point type");
+                } else if (__t_is_nan && __u_is_nan) {
+                    // Order by sign bit, then by "payload bits" (we'll just use bit_cast).
+                    if (__t_is_negative != __u_is_negative) {
+                        return (__u_is_negative <=> __t_is_negative);
+                    } else {
+                        return _VSTD::bit_cast<_IntType>(__t) <=> _VSTD::bit_cast<_IntType>(__u);
+                    }
+                } else if (__t_is_nan) {
+                    return __t_is_negative ? strong_ordering::less : strong_ordering::greater;
+                } else {
+                    return __u_is_negative ? strong_ordering::greater : strong_ordering::less;
+                }
+            }
+        }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
+            noexcept(noexcept(strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          strong_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+
+        template<class _Tp, class _Up>
+        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
+            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>())))
+            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()))
+            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<2>()); }
+    };
+} // namespace __strong_order
+
+inline namespace __cpo {
+    inline constexpr auto strong_order = __strong_order::__fn{};
+} // namespace __cpo
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+_LIBCPP_POP_MACROS
+
+#endif // _LIBCPP___COMPARE_STRONG_ORDER

third_party/libcxx/__compare/synth_three_way.h

@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_SYNTH_THREE_WAY_H
+#define _LIBCPP___COMPARE_SYNTH_THREE_WAY_H
+
+#include <__compare/ordering.h>
+#include <__compare/three_way_comparable.h>
+#include <__concepts/boolean_testable.h>
+#include <__config>
+#include <__utility/declval.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [expos.only.func]
+
+// TODO MODULES restore the lamba to match the Standard.
+// See https://github.com/llvm/llvm-project/issues/57222
+//_LIBCPP_HIDE_FROM_ABI inline constexpr auto __synth_three_way =
+//  []<class _Tp, class _Up>(const _Tp& __t, const _Up& __u)
+template <class _Tp, class _Up>
+_LIBCPP_HIDE_FROM_ABI constexpr auto __synth_three_way(const _Tp& __t, const _Up& __u)
+  requires requires {
+    { __t < __u } -> __boolean_testable;
+    { __u < __t } -> __boolean_testable;
+  }
+{
+  if constexpr (three_way_comparable_with<_Tp, _Up>) {
+    return __t <=> __u;
+  } else {
+    if (__t < __u)
+      return weak_ordering::less;
+    if (__u < __t)
+      return weak_ordering::greater;
+    return weak_ordering::equivalent;
+  }
+}
+
+template <class _Tp, class _Up = _Tp>
+using __synth_three_way_result = decltype(std::__synth_three_way(std::declval<_Tp&>(), std::declval<_Up&>()));
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_SYNTH_THREE_WAY_H

third_party/libcxx/__compare/three_way_comparable.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___COMPARE_THREE_WAY_COMPARABLE_H
+#define _LIBCPP___COMPARE_THREE_WAY_COMPARABLE_H
+
+#include <__compare/common_comparison_category.h>
+#include <__compare/ordering.h>
+#include <__concepts/common_reference_with.h>
+#include <__concepts/equality_comparable.h>
+#include <__concepts/same_as.h>
+#include <__concepts/totally_ordered.h>
+#include <__config>
+#include <__type_traits/common_reference.h>
+#include <__type_traits/make_const_lvalue_ref.h>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+template<class _Tp, class _Cat>
+concept __compares_as =
+  same_as<common_comparison_category_t<_Tp, _Cat>, _Cat>;
+
+template<class _Tp, class _Cat = partial_ordering>
+concept three_way_comparable =
+  __weakly_equality_comparable_with<_Tp, _Tp> &&
+  __partially_ordered_with<_Tp, _Tp> &&
+  requires(__make_const_lvalue_ref<_Tp> __a, __make_const_lvalue_ref<_Tp> __b) {
+    { __a <=> __b } -> __compares_as<_Cat>;
+  };
+
+template<class _Tp, class _Up, class _Cat = partial_ordering>
+concept three_way_comparable_with =
+  three_way_comparable<_Tp, _Cat> &&
+  three_way_comparable<_Up, _Cat> &&
+  common_reference_with<__make_const_lvalue_ref<_Tp>, __make_const_lvalue_ref<_Up>> &&
+  three_way_comparable<common_reference_t<__make_const_lvalue_ref<_Tp>, __make_const_lvalue_ref<_Up>>, _Cat> &&
+  __weakly_equality_comparable_with<_Tp, _Up> &&
+  __partially_ordered_with<_Tp, _Up> &&
+  requires(__make_const_lvalue_ref<_Tp> __t, __make_const_lvalue_ref<_Up> __u) {
+    { __t <=> __u } -> __compares_as<_Cat>;
+    { __u <=> __t } -> __compares_as<_Cat>;
+  };
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_THREE_WAY_COMPARABLE_H

third_party/libcxx/__compare/weak_order.h

@@ -0,0 +1,102 @@
+//===----------------------------------------------------------------------===//
+//
+// 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___COMPARE_WEAK_ORDER
+#define _LIBCPP___COMPARE_WEAK_ORDER
+
+#include <__compare/compare_three_way.h>
+#include <__compare/ordering.h>
+#include <__compare/strong_order.h>
+#include <__config>
+#include <__type_traits/decay.h>
+#include <__utility/forward.h>
+#include <__utility/priority_tag.h>
+#include <cmath>
+
+#ifndef _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20
+
+// [cmp.alg]
+namespace __weak_order {
+    struct __fn {
+    // NOLINTBEGIN(libcpp-robust-against-adl) weak_order should use ADL, but only here
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<3>)
+            noexcept(noexcept(weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          weak_ordering(weak_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+    // NOLINTEND(libcpp-robust-against-adl)
+
+        template<class _Tp, class _Up, class _Dp = decay_t<_Tp>>
+            requires is_same_v<_Dp, decay_t<_Up>> && is_floating_point_v<_Dp>
+        _LIBCPP_HIDE_FROM_ABI static constexpr weak_ordering
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<2>) noexcept
+        {
+            partial_ordering __po = (__t <=> __u);
+            if (__po == partial_ordering::less) {
+                return weak_ordering::less;
+            } else if (__po == partial_ordering::equivalent) {
+                return weak_ordering::equivalent;
+            } else if (__po == partial_ordering::greater) {
+                return weak_ordering::greater;
+            } else {
+                // Otherwise, at least one of them is a NaN.
+                bool __t_is_nan = _VSTD::isnan(__t);
+                bool __u_is_nan = _VSTD::isnan(__u);
+                bool __t_is_negative = _VSTD::signbit(__t);
+                bool __u_is_negative = _VSTD::signbit(__u);
+                if (__t_is_nan && __u_is_nan) {
+                    return (__u_is_negative <=> __t_is_negative);
+                } else if (__t_is_nan) {
+                    return __t_is_negative ? weak_ordering::less : weak_ordering::greater;
+                } else {
+                    return __u_is_negative ? weak_ordering::greater : weak_ordering::less;
+                }
+            }
+        }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<1>)
+            noexcept(noexcept(weak_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      weak_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          weak_ordering(compare_three_way()(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+
+        template<class _Tp, class _Up>
+            requires is_same_v<decay_t<_Tp>, decay_t<_Up>>
+        _LIBCPP_HIDE_FROM_ABI static constexpr auto
+        __go(_Tp&& __t, _Up&& __u, __priority_tag<0>)
+            noexcept(noexcept(weak_ordering(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u)))))
+            -> decltype(      weak_ordering(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))))
+            { return          weak_ordering(_VSTD::strong_order(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u))); }
+
+        template<class _Tp, class _Up>
+        _LIBCPP_HIDE_FROM_ABI constexpr auto operator()(_Tp&& __t, _Up&& __u) const
+            noexcept(noexcept(__go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<3>())))
+            -> decltype(      __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<3>()))
+            { return          __go(_VSTD::forward<_Tp>(__t), _VSTD::forward<_Up>(__u), __priority_tag<3>()); }
+    };
+} // namespace __weak_order
+
+inline namespace __cpo {
+    inline constexpr auto weak_order = __weak_order::__fn{};
+} // namespace __cpo
+
+#endif // _LIBCPP_STD_VER >= 20
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP___COMPARE_WEAK_ORDER