[libcxx-commits] [libcxx] [libc++] Make map constexpr as part of P3372R3 (PR #134330)

Vinay Deshmukh via libcxx-commits libcxx-commits at lists.llvm.org
Sun Apr 6 11:25:14 PDT 2025


https://github.com/vinay-deshmukh updated https://github.com/llvm/llvm-project/pull/134330

>From 83583bb59845a52d7cbc6e1688ea6c809396c7e8 Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Thu, 3 Apr 2025 20:35:56 -0400
Subject: [PATCH 01/11] Apply initial _LIBCPP_CONSTEXPR_SINCE_CXX26

---
 libcxx/include/map | 238 ++++++++++++++++++++++++++++-----------------
 1 file changed, 150 insertions(+), 88 deletions(-)

diff --git a/libcxx/include/map b/libcxx/include/map
index e7e0c14e36999..3719efd6b6e73 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -989,10 +989,11 @@ public:
   protected:
     key_compare comp;
 
-    _LIBCPP_HIDE_FROM_ABI value_compare(key_compare __c) : comp(__c) {}
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare(key_compare __c) : comp(__c) {}
 
   public:
-    _LIBCPP_HIDE_FROM_ABI bool operator()(const value_type& __x, const value_type& __y) const {
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool
+    operator()(const value_type& __x, const value_type& __y) const {
       return comp(__x.first, __y.first);
     }
   };
@@ -1029,26 +1030,27 @@ public:
   template <class _Key2, class _Value2, class _Comp2, class _Alloc2>
   friend class _LIBCPP_TEMPLATE_VIS multimap;
 
-  _LIBCPP_HIDE_FROM_ABI map() _NOEXCEPT_(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map() _NOEXCEPT_(
       is_nothrow_default_constructible<allocator_type>::value&& is_nothrow_default_constructible<key_compare>::value&&
           is_nothrow_copy_constructible<key_compare>::value)
       : __tree_(__vc(key_compare())) {}
 
-  _LIBCPP_HIDE_FROM_ABI explicit map(const key_compare& __comp) _NOEXCEPT_(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit map(const key_compare& __comp) _NOEXCEPT_(
       is_nothrow_default_constructible<allocator_type>::value&& is_nothrow_copy_constructible<key_compare>::value)
       : __tree_(__vc(__comp)) {}
 
-  _LIBCPP_HIDE_FROM_ABI explicit map(const key_compare& __comp, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit map(const key_compare& __comp, const allocator_type& __a)
       : __tree_(__vc(__comp), typename __base::allocator_type(__a)) {}
 
   template <class _InputIterator>
-  _LIBCPP_HIDE_FROM_ABI map(_InputIterator __f, _InputIterator __l, const key_compare& __comp = key_compare())
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  map(_InputIterator __f, _InputIterator __l, const key_compare& __comp = key_compare())
       : __tree_(__vc(__comp)) {
     insert(__f, __l);
   }
 
   template <class _InputIterator>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   map(_InputIterator __f, _InputIterator __l, const key_compare& __comp, const allocator_type& __a)
       : __tree_(__vc(__comp), typename __base::allocator_type(__a)) {
     insert(__f, __l);
@@ -1056,7 +1058,7 @@ public:
 
 #  if _LIBCPP_STD_VER >= 23
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   map(from_range_t,
       _Range&& __range,
       const key_compare& __comp = key_compare(),
@@ -1068,19 +1070,22 @@ public:
 
 #  if _LIBCPP_STD_VER >= 14
   template <class _InputIterator>
-  _LIBCPP_HIDE_FROM_ABI map(_InputIterator __f, _InputIterator __l, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  map(_InputIterator __f, _InputIterator __l, const allocator_type& __a)
       : map(__f, __l, key_compare(), __a) {}
 #  endif
 
 #  if _LIBCPP_STD_VER >= 23
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI map(from_range_t, _Range&& __range, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map(from_range_t, _Range&& __range, const allocator_type& __a)
       : map(from_range, std::forward<_Range>(__range), key_compare(), __a) {}
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI map(const map& __m) : __tree_(__m.__tree_) { insert(__m.begin(), __m.end()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map(const map& __m) : __tree_(__m.__tree_) {
+    insert(__m.begin(), __m.end());
+  }
 
-  _LIBCPP_HIDE_FROM_ABI map& operator=(const map& __m) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map& operator=(const map& __m) {
 #  ifndef _LIBCPP_CXX03_LANG
     __tree_ = __m.__tree_;
 #  else
@@ -1096,32 +1101,36 @@ public:
 
 #  ifndef _LIBCPP_CXX03_LANG
 
-  _LIBCPP_HIDE_FROM_ABI map(map&& __m) noexcept(is_nothrow_move_constructible<__base>::value)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  map(map&& __m) noexcept(is_nothrow_move_constructible<__base>::value)
       : __tree_(std::move(__m.__tree_)) {}
 
-  _LIBCPP_HIDE_FROM_ABI map(map&& __m, const allocator_type& __a);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map(map&& __m, const allocator_type& __a);
 
-  _LIBCPP_HIDE_FROM_ABI map& operator=(map&& __m) noexcept(is_nothrow_move_assignable<__base>::value) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map&
+  operator=(map&& __m) noexcept(is_nothrow_move_assignable<__base>::value) {
     __tree_ = std::move(__m.__tree_);
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI map(initializer_list<value_type> __il, const key_compare& __comp = key_compare())
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  map(initializer_list<value_type> __il, const key_compare& __comp = key_compare())
       : __tree_(__vc(__comp)) {
     insert(__il.begin(), __il.end());
   }
 
-  _LIBCPP_HIDE_FROM_ABI map(initializer_list<value_type> __il, const key_compare& __comp, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  map(initializer_list<value_type> __il, const key_compare& __comp, const allocator_type& __a)
       : __tree_(__vc(__comp), typename __base::allocator_type(__a)) {
     insert(__il.begin(), __il.end());
   }
 
 #    if _LIBCPP_STD_VER >= 14
-  _LIBCPP_HIDE_FROM_ABI map(initializer_list<value_type> __il, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map(initializer_list<value_type> __il, const allocator_type& __a)
       : map(__il, key_compare(), __a) {}
 #    endif
 
-  _LIBCPP_HIDE_FROM_ABI map& operator=(initializer_list<value_type> __il) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map& operator=(initializer_list<value_type> __il) {
     __tree_.__assign_unique(__il.begin(), __il.end());
     return *this;
   }
@@ -1130,43 +1139,65 @@ public:
 
   _LIBCPP_HIDE_FROM_ABI explicit map(const allocator_type& __a) : __tree_(typename __base::allocator_type(__a)) {}
 
-  _LIBCPP_HIDE_FROM_ABI map(const map& __m, const allocator_type& __a)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 map(const map& __m, const allocator_type& __a)
       : __tree_(__m.__tree_.value_comp(), typename __base::allocator_type(__a)) {
     insert(__m.begin(), __m.end());
   }
 
-  _LIBCPP_HIDE_FROM_ABI ~map() { static_assert(sizeof(std::__diagnose_non_const_comparator<_Key, _Compare>()), ""); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 ~map() {
+    static_assert(sizeof(std::__diagnose_non_const_comparator<_Key, _Compare>()), "");
+  }
 
-  _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return __tree_.begin(); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return __tree_.begin(); }
-  _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return __tree_.end(); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return __tree_.end(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator begin() _NOEXCEPT { return __tree_.begin(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator begin() const _NOEXCEPT { return __tree_.begin(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator end() _NOEXCEPT { return __tree_.end(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator end() const _NOEXCEPT { return __tree_.end(); }
 
-  _LIBCPP_HIDE_FROM_ABI reverse_iterator rbegin() _NOEXCEPT { return reverse_iterator(end()); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rbegin() const _NOEXCEPT { return const_reverse_iterator(end()); }
-  _LIBCPP_HIDE_FROM_ABI reverse_iterator rend() _NOEXCEPT { return reverse_iterator(begin()); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rend() const _NOEXCEPT { return const_reverse_iterator(begin()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rbegin() _NOEXCEPT {
+    return reverse_iterator(end());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rbegin() const _NOEXCEPT {
+    return const_reverse_iterator(end());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rend() _NOEXCEPT {
+    return reverse_iterator(begin());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rend() const _NOEXCEPT {
+    return const_reverse_iterator(begin());
+  }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const _NOEXCEPT { return begin(); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator cend() const _NOEXCEPT { return end(); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crbegin() const _NOEXCEPT { return rbegin(); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crend() const _NOEXCEPT { return rend(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cbegin() const _NOEXCEPT { return begin(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cend() const _NOEXCEPT { return end(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crbegin() const _NOEXCEPT {
+    return rbegin();
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crend() const _NOEXCEPT { return rend(); }
 
-  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI bool empty() const _NOEXCEPT { return __tree_.size() == 0; }
-  _LIBCPP_HIDE_FROM_ABI size_type size() const _NOEXCEPT { return __tree_.size(); }
-  _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT { return __tree_.max_size(); }
+  [[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool empty() const _NOEXCEPT {
+    return __tree_.size() == 0;
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type size() const _NOEXCEPT { return __tree_.size(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type max_size() const _NOEXCEPT {
+    return __tree_.max_size();
+  }
 
-  _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](const key_type& __k);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](const key_type& __k);
 #  ifndef _LIBCPP_CXX03_LANG
-  _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __k);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](key_type&& __k);
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI mapped_type& at(const key_type& __k);
-  _LIBCPP_HIDE_FROM_ABI const mapped_type& at(const key_type& __k) const;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& at(const key_type& __k);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const mapped_type& at(const key_type& __k) const;
 
-  _LIBCPP_HIDE_FROM_ABI allocator_type get_allocator() const _NOEXCEPT { return allocator_type(__tree_.__alloc()); }
-  _LIBCPP_HIDE_FROM_ABI key_compare key_comp() const { return __tree_.value_comp().key_comp(); }
-  _LIBCPP_HIDE_FROM_ABI value_compare value_comp() const { return value_compare(__tree_.value_comp().key_comp()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 allocator_type get_allocator() const _NOEXCEPT {
+    return allocator_type(__tree_.__alloc());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 key_compare key_comp() const {
+    return __tree_.value_comp().key_comp();
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare value_comp() const {
+    return value_compare(__tree_.value_comp().key_comp());
+  }
 
 #  ifndef _LIBCPP_CXX03_LANG
   template <class... _Args>
@@ -1853,50 +1884,56 @@ public:
 #  ifndef _LIBCPP_CXX03_LANG
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator emplace(_Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator emplace(_Args&&... __args) {
     return __tree_.__emplace_multi(std::forward<_Args>(__args)...);
   }
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator emplace_hint(const_iterator __p, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator emplace_hint(const_iterator __p, _Args&&... __args) {
     return __tree_.__emplace_hint_multi(__p.__i_, std::forward<_Args>(__args)...);
   }
 
   template <class _Pp, __enable_if_t<is_constructible<value_type, _Pp>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator insert(_Pp&& __p) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(_Pp&& __p) {
     return __tree_.__insert_multi(std::forward<_Pp>(__p));
   }
 
   template <class _Pp, __enable_if_t<is_constructible<value_type, _Pp>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __pos, _Pp&& __p) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __pos, _Pp&& __p) {
     return __tree_.__insert_multi(__pos.__i_, std::forward<_Pp>(__p));
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(value_type&& __v) { return __tree_.__insert_multi(std::move(__v)); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(value_type&& __v) {
+    return __tree_.__insert_multi(std::move(__v));
+  }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, value_type&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __p, value_type&& __v) {
     return __tree_.__insert_multi(__p.__i_, std::move(__v));
   }
 
-  _LIBCPP_HIDE_FROM_ABI void insert(initializer_list<value_type> __il) { insert(__il.begin(), __il.end()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(initializer_list<value_type> __il) {
+    insert(__il.begin(), __il.end());
+  }
 
 #  endif // _LIBCPP_CXX03_LANG
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const value_type& __v) { return __tree_.__insert_multi(__v); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const value_type& __v) {
+    return __tree_.__insert_multi(__v);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, const value_type& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __p, const value_type& __v) {
     return __tree_.__insert_multi(__p.__i_, __v);
   }
 
   template <class _InputIterator>
-  _LIBCPP_HIDE_FROM_ABI void insert(_InputIterator __f, _InputIterator __l) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(_InputIterator __f, _InputIterator __l) {
     for (const_iterator __e = cend(); __f != __l; ++__f)
       __tree_.__insert_multi(__e.__i_, *__f);
   }
 
 #  if _LIBCPP_STD_VER >= 23
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI void insert_range(_Range&& __range) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert_range(_Range&& __range) {
     const_iterator __end = cend();
     for (auto&& __element : __range) {
       __tree_.__insert_multi(__end.__i_, std::forward<decltype(__element)>(__element));
@@ -1904,131 +1941,156 @@ public:
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __p) { return __tree_.erase(__p.__i_); }
-  _LIBCPP_HIDE_FROM_ABI iterator erase(iterator __p) { return __tree_.erase(__p.__i_); }
-  _LIBCPP_HIDE_FROM_ABI size_type erase(const key_type& __k) { return __tree_.__erase_multi(__k); }
-  _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __f, const_iterator __l) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(const_iterator __p) {
+    return __tree_.erase(__p.__i_);
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(iterator __p) { return __tree_.erase(__p.__i_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type erase(const key_type& __k) {
+    return __tree_.__erase_multi(__k);
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(const_iterator __f, const_iterator __l) {
     return __tree_.erase(__f.__i_, __l.__i_);
   }
 
 #  if _LIBCPP_STD_VER >= 17
-  _LIBCPP_HIDE_FROM_ABI iterator insert(node_type&& __nh) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(node_type&& __nh) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(__nh.empty() || __nh.get_allocator() == get_allocator(),
                                         "node_type with incompatible allocator passed to multimap::insert()");
     return __tree_.template __node_handle_insert_multi<node_type>(std::move(__nh));
   }
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __hint, node_type&& __nh) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __hint, node_type&& __nh) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(__nh.empty() || __nh.get_allocator() == get_allocator(),
                                         "node_type with incompatible allocator passed to multimap::insert()");
     return __tree_.template __node_handle_insert_multi<node_type>(__hint.__i_, std::move(__nh));
   }
-  _LIBCPP_HIDE_FROM_ABI node_type extract(key_type const& __key) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 node_type extract(key_type const& __key) {
     return __tree_.template __node_handle_extract<node_type>(__key);
   }
-  _LIBCPP_HIDE_FROM_ABI node_type extract(const_iterator __it) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 node_type extract(const_iterator __it) {
     return __tree_.template __node_handle_extract<node_type>(__it.__i_);
   }
   template <class _Compare2>
-  _LIBCPP_HIDE_FROM_ABI void merge(multimap<key_type, mapped_type, _Compare2, allocator_type>& __source) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  merge(multimap<key_type, mapped_type, _Compare2, allocator_type>& __source) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(
         __source.get_allocator() == get_allocator(), "merging container with incompatible allocator");
     return __tree_.__node_handle_merge_multi(__source.__tree_);
   }
   template <class _Compare2>
-  _LIBCPP_HIDE_FROM_ABI void merge(multimap<key_type, mapped_type, _Compare2, allocator_type>&& __source) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  merge(multimap<key_type, mapped_type, _Compare2, allocator_type>&& __source) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(
         __source.get_allocator() == get_allocator(), "merging container with incompatible allocator");
     return __tree_.__node_handle_merge_multi(__source.__tree_);
   }
   template <class _Compare2>
-  _LIBCPP_HIDE_FROM_ABI void merge(map<key_type, mapped_type, _Compare2, allocator_type>& __source) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  merge(map<key_type, mapped_type, _Compare2, allocator_type>& __source) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(
         __source.get_allocator() == get_allocator(), "merging container with incompatible allocator");
     return __tree_.__node_handle_merge_multi(__source.__tree_);
   }
   template <class _Compare2>
-  _LIBCPP_HIDE_FROM_ABI void merge(map<key_type, mapped_type, _Compare2, allocator_type>&& __source) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  merge(map<key_type, mapped_type, _Compare2, allocator_type>&& __source) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(
         __source.get_allocator() == get_allocator(), "merging container with incompatible allocator");
     return __tree_.__node_handle_merge_multi(__source.__tree_);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI void clear() _NOEXCEPT { __tree_.clear(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void clear() _NOEXCEPT { __tree_.clear(); }
 
-  _LIBCPP_HIDE_FROM_ABI void swap(multimap& __m) _NOEXCEPT_(__is_nothrow_swappable_v<__base>) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void swap(multimap& __m)
+      _NOEXCEPT_(__is_nothrow_swappable_v<__base>) {
     __tree_.swap(__m.__tree_);
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __k) { return __tree_.find(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __k) const { return __tree_.find(__k); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const key_type& __k) { return __tree_.find(__k); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const key_type& __k) const {
+    return __tree_.find(__k);
+  }
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator find(const _K2& __k) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const _K2& __k) {
     return __tree_.find(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI const_iterator find(const _K2& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const _K2& __k) const {
     return __tree_.find(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI size_type count(const key_type& __k) const { return __tree_.__count_multi(__k); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const key_type& __k) const {
+    return __tree_.__count_multi(__k);
+  }
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI size_type count(const _K2& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const _K2& __k) const {
     return __tree_.__count_multi(__k);
   }
 #  endif
 
 #  if _LIBCPP_STD_VER >= 20
-  _LIBCPP_HIDE_FROM_ABI bool contains(const key_type& __k) const { return find(__k) != end(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const key_type& __k) const {
+    return find(__k) != end();
+  }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI bool contains(const _K2& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const _K2& __k) const {
     return find(__k) != end();
   }
 #  endif // _LIBCPP_STD_VER >= 20
 
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __k) { return __tree_.lower_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __k) const { return __tree_.lower_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const key_type& __k) {
+    return __tree_.lower_bound(__k);
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const key_type& __k) const {
+    return __tree_.lower_bound(__k);
+  }
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _K2& __k) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const _K2& __k) {
     return __tree_.lower_bound(__k);
   }
 
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _K2& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const _K2& __k) const {
     return __tree_.lower_bound(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __k) { return __tree_.upper_bound(__k); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __k) const { return __tree_.upper_bound(__k); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const key_type& __k) {
+    return __tree_.upper_bound(__k);
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const key_type& __k) const {
+    return __tree_.upper_bound(__k);
+  }
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _K2& __k) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const _K2& __k) {
     return __tree_.upper_bound(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _K2& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const _K2& __k) const {
     return __tree_.upper_bound(__k);
   }
 #  endif
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const key_type& __k) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator> equal_range(const key_type& __k) {
     return __tree_.__equal_range_multi(__k);
   }
-  _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const key_type& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
+  equal_range(const key_type& __k) const {
     return __tree_.__equal_range_multi(__k);
   }
 #  if _LIBCPP_STD_VER >= 14
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const _K2& __k) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator> equal_range(const _K2& __k) {
     return __tree_.__equal_range_multi(__k);
   }
   template <typename _K2, enable_if_t<__is_transparent_v<_Compare, _K2>, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const _K2& __k) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
+  equal_range(const _K2& __k) const {
     return __tree_.__equal_range_multi(__k);
   }
 #  endif

>From 6560dd52ad94443674334585ef8d01f59032f59c Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Thu, 3 Apr 2025 20:37:35 -0400
Subject: [PATCH 02/11] Add feature test macro

---
 libcxx/docs/FeatureTestMacroTable.rst | 2 ++
 libcxx/include/version                | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/libcxx/docs/FeatureTestMacroTable.rst b/libcxx/docs/FeatureTestMacroTable.rst
index bbcc76b52f0a9..a72ddbdb3e67a 100644
--- a/libcxx/docs/FeatureTestMacroTable.rst
+++ b/libcxx/docs/FeatureTestMacroTable.rst
@@ -210,6 +210,8 @@ Status
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_iterator``                           ``201811L``
     ---------------------------------------------------------- -----------------
+    ``__cpp_lib_constexpr_map``                                ``202502L``
+    ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_memory``                             ``201811L``
     ---------------------------------------------------------- -----------------
     ``__cpp_lib_constexpr_numeric``                            ``201911L``
diff --git a/libcxx/include/version b/libcxx/include/version
index 83ae11dabd2bc..4f94be1ca14a8 100644
--- a/libcxx/include/version
+++ b/libcxx/include/version
@@ -69,6 +69,7 @@ __cpp_lib_constexpr_complex                             201711L <complex>
 __cpp_lib_constexpr_dynamic_alloc                       201907L <memory>
 __cpp_lib_constexpr_functional                          201907L <functional>
 __cpp_lib_constexpr_iterator                            201811L <iterator>
+__cpp_lib_constexpr_map                                 202502L <map>
 __cpp_lib_constexpr_memory                              202202L <memory>
                                                         201811L // C++20
 __cpp_lib_constexpr_new                                 202406L <new>
@@ -538,6 +539,7 @@ __cpp_lib_void_t                                        201411L <type_traits>
 # define __cpp_lib_bind_front                           202306L
 # define __cpp_lib_bitset                               202306L
 # undef  __cpp_lib_constexpr_algorithms
+# define __cpp_lib_constexpr_map                        202502L
 # define __cpp_lib_constexpr_algorithms                 202306L
 # if !defined(_LIBCPP_ABI_VCRUNTIME)
 #   define __cpp_lib_constexpr_new                      202406L

>From ce1a62f120212634daab4d844aec1e2ac343e4df Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Thu, 3 Apr 2025 21:20:23 -0400
Subject: [PATCH 03/11] one test to start with

---
 .../associative/map/map.cons/alloc.pass.cpp           | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/libcxx/test/std/containers/associative/map/map.cons/alloc.pass.cpp b/libcxx/test/std/containers/associative/map/map.cons/alloc.pass.cpp
index 52199204d7914..9b854659c38f9 100644
--- a/libcxx/test/std/containers/associative/map/map.cons/alloc.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.cons/alloc.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// explicit map(const allocator_type& a);
+// explicit map(const allocator_type& a); // constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -19,7 +19,7 @@
 #include "test_allocator.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::less<int> C;
     typedef test_allocator<std::pair<const int, double> > A;
@@ -46,6 +46,13 @@ int main(int, char**) {
     assert(m.get_allocator() == A());
   }
 #endif
+  return true;
+}
 
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }

>From a72b619c130bfd03f50f662556989cc217c73032 Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sat, 5 Apr 2025 02:00:35 -0400
Subject: [PATCH 04/11] start seeing constexpr failures for at.pass.cpp

---
 libcxx/include/__tree                         | 62 +++++++++---------
 libcxx/include/map                            | 64 +++++++++----------
 .../associative/map/map.access/at.pass.cpp    | 13 +++-
 3 files changed, 73 insertions(+), 66 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index 9d28381c8c2ce..ff57d63f15789 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -967,39 +967,39 @@ public:
   typedef __tree_iterator<value_type, __node_pointer, difference_type> iterator;
   typedef __tree_const_iterator<value_type, __node_pointer, difference_type> const_iterator;
 
-  _LIBCPP_HIDE_FROM_ABI explicit __tree(const value_compare& __comp) _NOEXCEPT_(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree(const value_compare& __comp) _NOEXCEPT_(
       is_nothrow_default_constructible<__node_allocator>::value&& is_nothrow_copy_constructible<value_compare>::value);
-  _LIBCPP_HIDE_FROM_ABI explicit __tree(const allocator_type& __a);
-  _LIBCPP_HIDE_FROM_ABI __tree(const value_compare& __comp, const allocator_type& __a);
-  _LIBCPP_HIDE_FROM_ABI __tree(const __tree& __t);
-  _LIBCPP_HIDE_FROM_ABI __tree& operator=(const __tree& __t);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree(const allocator_type& __a);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree(const value_compare& __comp, const allocator_type& __a);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree(const __tree& __t);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree& operator=(const __tree& __t);
   template <class _ForwardIterator>
-  _LIBCPP_HIDE_FROM_ABI void __assign_unique(_ForwardIterator __first, _ForwardIterator __last);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __assign_unique(_ForwardIterator __first, _ForwardIterator __last);
   template <class _InputIterator>
-  _LIBCPP_HIDE_FROM_ABI void __assign_multi(_InputIterator __first, _InputIterator __last);
-  _LIBCPP_HIDE_FROM_ABI __tree(__tree&& __t) _NOEXCEPT_(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __assign_multi(_InputIterator __first, _InputIterator __last);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree(__tree&& __t) _NOEXCEPT_(
       is_nothrow_move_constructible<__node_allocator>::value&& is_nothrow_move_constructible<value_compare>::value);
-  _LIBCPP_HIDE_FROM_ABI __tree(__tree&& __t, const allocator_type& __a);
-  _LIBCPP_HIDE_FROM_ABI __tree& operator=(__tree&& __t)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree(__tree&& __t, const allocator_type& __a);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree& operator=(__tree&& __t)
       _NOEXCEPT_(is_nothrow_move_assignable<value_compare>::value &&
                  ((__node_traits::propagate_on_container_move_assignment::value &&
                    is_nothrow_move_assignable<__node_allocator>::value) ||
                   allocator_traits<__node_allocator>::is_always_equal::value));
 
-  _LIBCPP_HIDE_FROM_ABI ~__tree();
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 ~__tree();
 
-  _LIBCPP_HIDE_FROM_ABI iterator begin() _NOEXCEPT { return iterator(__begin_node()); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator begin() const _NOEXCEPT { return const_iterator(__begin_node()); }
-  _LIBCPP_HIDE_FROM_ABI iterator end() _NOEXCEPT { return iterator(__end_node()); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator end() const _NOEXCEPT { return const_iterator(__end_node()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator begin() _NOEXCEPT { return iterator(__begin_node()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator begin() const _NOEXCEPT { return const_iterator(__begin_node()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator end() _NOEXCEPT { return iterator(__end_node()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator end() const _NOEXCEPT { return const_iterator(__end_node()); }
 
-  _LIBCPP_HIDE_FROM_ABI size_type max_size() const _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type max_size() const _NOEXCEPT {
     return std::min<size_type>(__node_traits::max_size(__node_alloc()), numeric_limits<difference_type >::max());
   }
 
-  _LIBCPP_HIDE_FROM_ABI void clear() _NOEXCEPT;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void clear() _NOEXCEPT;
 
-  _LIBCPP_HIDE_FROM_ABI void swap(__tree& __t)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void swap(__tree& __t)
 #if _LIBCPP_STD_VER <= 11
       _NOEXCEPT_(__is_nothrow_swappable_v<value_compare> &&
                  (!__node_traits::propagate_on_container_swap::value || __is_nothrow_swappable_v<__node_allocator>));
@@ -1315,20 +1315,20 @@ private:
 };
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::__tree(const value_compare& __comp) _NOEXCEPT_(
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__tree(const value_compare& __comp) _NOEXCEPT_(
     is_nothrow_default_constructible<__node_allocator>::value&& is_nothrow_copy_constructible<value_compare>::value)
     : __size_(0), __value_comp_(__comp) {
   __begin_node() = __end_node();
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::__tree(const allocator_type& __a)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__tree(const allocator_type& __a)
     : __begin_node_(__iter_pointer()), __node_alloc_(__node_allocator(__a)), __size_(0) {
   __begin_node() = __end_node();
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::__tree(const value_compare& __comp, const allocator_type& __a)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__tree(const value_compare& __comp, const allocator_type& __a)
     : __begin_node_(__iter_pointer()), __node_alloc_(__node_allocator(__a)), __size_(0), __value_comp_(__comp) {
   __begin_node() = __end_node();
 }
@@ -1375,7 +1375,7 @@ __tree<_Tp, _Compare, _Allocator>::_DetachedTreeCache::__detach_next(__node_poin
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=(const __tree& __t) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=(const __tree& __t) {
   if (this != std::addressof(__t)) {
     value_comp() = __t.value_comp();
     __copy_assign_alloc(__t);
@@ -1386,7 +1386,7 @@ __tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=(
 
 template <class _Tp, class _Compare, class _Allocator>
 template <class _ForwardIterator>
-void __tree<_Tp, _Compare, _Allocator>::__assign_unique(_ForwardIterator __first, _ForwardIterator __last) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree<_Tp, _Compare, _Allocator>::__assign_unique(_ForwardIterator __first, _ForwardIterator __last) {
   typedef iterator_traits<_ForwardIterator> _ITraits;
   typedef typename _ITraits::value_type _ItValueType;
   static_assert(is_same<_ItValueType, __container_value_type>::value,
@@ -1406,7 +1406,7 @@ void __tree<_Tp, _Compare, _Allocator>::__assign_unique(_ForwardIterator __first
 
 template <class _Tp, class _Compare, class _Allocator>
 template <class _InputIterator>
-void __tree<_Tp, _Compare, _Allocator>::__assign_multi(_InputIterator __first, _InputIterator __last) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree<_Tp, _Compare, _Allocator>::__assign_multi(_InputIterator __first, _InputIterator __last) {
   typedef iterator_traits<_InputIterator> _ITraits;
   typedef typename _ITraits::value_type _ItValueType;
   static_assert(
@@ -1426,7 +1426,7 @@ void __tree<_Tp, _Compare, _Allocator>::__assign_multi(_InputIterator __first, _
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::__tree(const __tree& __t)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__tree(const __tree& __t)
     : __begin_node_(__iter_pointer()),
       __node_alloc_(__node_traits::select_on_container_copy_construction(__t.__node_alloc())),
       __size_(0),
@@ -1435,7 +1435,7 @@ __tree<_Tp, _Compare, _Allocator>::__tree(const __tree& __t)
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::__tree(__tree&& __t) _NOEXCEPT_(
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__tree(__tree&& __t) _NOEXCEPT_(
     is_nothrow_move_constructible<__node_allocator>::value&& is_nothrow_move_constructible<value_compare>::value)
     : __begin_node_(std::move(__t.__begin_node_)),
       __end_node_(std::move(__t.__end_node_)),
@@ -1453,7 +1453,7 @@ __tree<_Tp, _Compare, _Allocator>::__tree(__tree&& __t) _NOEXCEPT_(
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::__tree(__tree&& __t, const allocator_type& __a)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__tree(__tree&& __t, const allocator_type& __a)
     : __node_alloc_(__node_allocator(__a)), __size_(0), __value_comp_(std::move(__t.value_comp())) {
   if (__a == __t.__alloc()) {
     if (__t.size() == 0)
@@ -1512,7 +1512,7 @@ void __tree<_Tp, _Compare, _Allocator>::__move_assign(__tree& __t, false_type) {
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=(__tree&& __t)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=(__tree&& __t)
     _NOEXCEPT_(is_nothrow_move_assignable<value_compare>::value &&
                ((__node_traits::propagate_on_container_move_assignment::value &&
                  is_nothrow_move_assignable<__node_allocator>::value) ||
@@ -1522,7 +1522,7 @@ __tree<_Tp, _Compare, _Allocator>& __tree<_Tp, _Compare, _Allocator>::operator=(
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-__tree<_Tp, _Compare, _Allocator>::~__tree() {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::~__tree() {
   static_assert(is_copy_constructible<value_compare>::value, "Comparator must be copy-constructible.");
   destroy(__root());
 }
@@ -1539,7 +1539,7 @@ void __tree<_Tp, _Compare, _Allocator>::destroy(__node_pointer __nd) _NOEXCEPT {
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-void __tree<_Tp, _Compare, _Allocator>::swap(__tree& __t)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree<_Tp, _Compare, _Allocator>::swap(__tree& __t)
 #if _LIBCPP_STD_VER <= 11
     _NOEXCEPT_(__is_nothrow_swappable_v<value_compare> &&
                (!__node_traits::propagate_on_container_swap::value || __is_nothrow_swappable_v<__node_allocator>))
@@ -1564,7 +1564,7 @@ void __tree<_Tp, _Compare, _Allocator>::swap(__tree& __t)
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-void __tree<_Tp, _Compare, _Allocator>::clear() _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree<_Tp, _Compare, _Allocator>::clear() _NOEXCEPT {
   destroy(__root());
   size()                = 0;
   __begin_node()        = __end_node();
diff --git a/libcxx/include/map b/libcxx/include/map
index 3719efd6b6e73..3ae485f1ce029 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -1201,54 +1201,54 @@ public:
 
 #  ifndef _LIBCPP_CXX03_LANG
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> emplace(_Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> emplace(_Args&&... __args) {
     return __tree_.__emplace_unique(std::forward<_Args>(__args)...);
   }
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator emplace_hint(const_iterator __p, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator emplace_hint(const_iterator __p, _Args&&... __args) {
     return __tree_.__emplace_hint_unique(__p.__i_, std::forward<_Args>(__args)...);
   }
 
   template <class _Pp, __enable_if_t<is_constructible<value_type, _Pp>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert(_Pp&& __p) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert(_Pp&& __p) {
     return __tree_.__insert_unique(std::forward<_Pp>(__p));
   }
 
   template <class _Pp, __enable_if_t<is_constructible<value_type, _Pp>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __pos, _Pp&& __p) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __pos, _Pp&& __p) {
     return __tree_.__insert_unique(__pos.__i_, std::forward<_Pp>(__p));
   }
 
 #  endif // _LIBCPP_CXX03_LANG
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert(const value_type& __v) { return __tree_.__insert_unique(__v); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert(const value_type& __v) { return __tree_.__insert_unique(__v); }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, const value_type& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __p, const value_type& __v) {
     return __tree_.__insert_unique(__p.__i_, __v);
   }
 
 #  ifndef _LIBCPP_CXX03_LANG
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert(value_type&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert(value_type&& __v) {
     return __tree_.__insert_unique(std::move(__v));
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __p, value_type&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __p, value_type&& __v) {
     return __tree_.__insert_unique(__p.__i_, std::move(__v));
   }
 
-  _LIBCPP_HIDE_FROM_ABI void insert(initializer_list<value_type> __il) { insert(__il.begin(), __il.end()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(initializer_list<value_type> __il) { insert(__il.begin(), __il.end()); }
 #  endif
 
   template <class _InputIterator>
-  _LIBCPP_HIDE_FROM_ABI void insert(_InputIterator __f, _InputIterator __l) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(_InputIterator __f, _InputIterator __l) {
     for (const_iterator __e = cend(); __f != __l; ++__f)
       insert(__e.__i_, *__f);
   }
 
 #  if _LIBCPP_STD_VER >= 23
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI void insert_range(_Range&& __range) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert_range(_Range&& __range) {
     const_iterator __end = cend();
     for (auto&& __element : __range) {
       insert(__end.__i_, std::forward<decltype(__element)>(__element));
@@ -1259,7 +1259,7 @@ public:
 #  if _LIBCPP_STD_VER >= 17
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> try_emplace(const key_type& __k, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> try_emplace(const key_type& __k, _Args&&... __args) {
     return __tree_.__emplace_unique_key_args(
         __k,
         std::piecewise_construct,
@@ -1268,7 +1268,7 @@ public:
   }
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> try_emplace(key_type&& __k, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> try_emplace(key_type&& __k, _Args&&... __args) {
     return __tree_.__emplace_unique_key_args(
         __k,
         std::piecewise_construct,
@@ -1277,7 +1277,7 @@ public:
   }
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator try_emplace(const_iterator __h, const key_type& __k, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator try_emplace(const_iterator __h, const key_type& __k, _Args&&... __args) {
     return __tree_
         .__emplace_hint_unique_key_args(
             __h.__i_,
@@ -1289,7 +1289,7 @@ public:
   }
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator try_emplace(const_iterator __h, key_type&& __k, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator try_emplace(const_iterator __h, key_type&& __k, _Args&&... __args) {
     return __tree_
         .__emplace_hint_unique_key_args(
             __h.__i_,
@@ -1301,7 +1301,7 @@ public:
   }
 
   template <class _Vp>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(const key_type& __k, _Vp&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert_or_assign(const key_type& __k, _Vp&& __v) {
     iterator __p = lower_bound(__k);
     if (__p != end() && !key_comp()(__k, __p->first)) {
       __p->second = std::forward<_Vp>(__v);
@@ -1311,7 +1311,7 @@ public:
   }
 
   template <class _Vp>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(key_type&& __k, _Vp&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert_or_assign(key_type&& __k, _Vp&& __v) {
     iterator __p = lower_bound(__k);
     if (__p != end() && !key_comp()(__k, __p->first)) {
       __p->second = std::forward<_Vp>(__v);
@@ -1321,7 +1321,7 @@ public:
   }
 
   template <class _Vp>
-  _LIBCPP_HIDE_FROM_ABI iterator insert_or_assign(const_iterator __h, const key_type& __k, _Vp&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert_or_assign(const_iterator __h, const key_type& __k, _Vp&& __v) {
     auto [__r, __inserted] = __tree_.__emplace_hint_unique_key_args(__h.__i_, __k, __k, std::forward<_Vp>(__v));
 
     if (!__inserted)
@@ -1331,7 +1331,7 @@ public:
   }
 
   template <class _Vp>
-  _LIBCPP_HIDE_FROM_ABI iterator insert_or_assign(const_iterator __h, key_type&& __k, _Vp&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert_or_assign(const_iterator __h, key_type&& __k, _Vp&& __v) {
     auto [__r, __inserted] =
         __tree_.__emplace_hint_unique_key_args(__h.__i_, __k, std::move(__k), std::forward<_Vp>(__v));
 
@@ -1343,26 +1343,26 @@ public:
 
 #  endif // _LIBCPP_STD_VER >= 17
 
-  _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __p) { return __tree_.erase(__p.__i_); }
-  _LIBCPP_HIDE_FROM_ABI iterator erase(iterator __p) { return __tree_.erase(__p.__i_); }
-  _LIBCPP_HIDE_FROM_ABI size_type erase(const key_type& __k) { return __tree_.__erase_unique(__k); }
-  _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __f, const_iterator __l) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(const_iterator __p) { return __tree_.erase(__p.__i_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(iterator __p) { return __tree_.erase(__p.__i_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type erase(const key_type& __k) { return __tree_.__erase_unique(__k); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(const_iterator __f, const_iterator __l) {
     return __tree_.erase(__f.__i_, __l.__i_);
   }
-  _LIBCPP_HIDE_FROM_ABI void clear() _NOEXCEPT { __tree_.clear(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void clear() _NOEXCEPT { __tree_.clear(); }
 
 #  if _LIBCPP_STD_VER >= 17
-  _LIBCPP_HIDE_FROM_ABI insert_return_type insert(node_type&& __nh) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 insert_return_type insert(node_type&& __nh) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(__nh.empty() || __nh.get_allocator() == get_allocator(),
                                         "node_type with incompatible allocator passed to map::insert()");
     return __tree_.template __node_handle_insert_unique< node_type, insert_return_type>(std::move(__nh));
   }
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __hint, node_type&& __nh) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __hint, node_type&& __nh) {
     _LIBCPP_ASSERT_COMPATIBLE_ALLOCATOR(__nh.empty() || __nh.get_allocator() == get_allocator(),
                                         "node_type with incompatible allocator passed to map::insert()");
     return __tree_.template __node_handle_insert_unique<node_type>(__hint.__i_, std::move(__nh));
   }
-  _LIBCPP_HIDE_FROM_ABI node_type extract(key_type const& __key) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 node_type extract(key_type const& __key) {
     return __tree_.template __node_handle_extract<node_type>(__key);
   }
   _LIBCPP_HIDE_FROM_ABI node_type extract(const_iterator __it) {
@@ -1537,7 +1537,7 @@ map(initializer_list<pair<_Key, _Tp>>,
 
 #  ifndef _LIBCPP_CXX03_LANG
 template <class _Key, class _Tp, class _Compare, class _Allocator>
-map<_Key, _Tp, _Compare, _Allocator>::map(map&& __m, const allocator_type& __a)
+_LIBCPP_CONSTEXPR_SINCE_CXX26 map<_Key, _Tp, _Compare, _Allocator>::map(map&& __m, const allocator_type& __a)
     : __tree_(std::move(__m.__tree_), typename __base::allocator_type(__a)) {
   if (__a != __m.get_allocator()) {
     const_iterator __e = cend();
@@ -1547,7 +1547,7 @@ map<_Key, _Tp, _Compare, _Allocator>::map(map&& __m, const allocator_type& __a)
 }
 
 template <class _Key, class _Tp, class _Compare, class _Allocator>
-_Tp& map<_Key, _Tp, _Compare, _Allocator>::operator[](const key_type& __k) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 _Tp& map<_Key, _Tp, _Compare, _Allocator>::operator[](const key_type& __k) {
   return __tree_
       .__emplace_unique_key_args(__k, std::piecewise_construct, std::forward_as_tuple(__k), std::forward_as_tuple())
       .first->__get_value()
@@ -1555,7 +1555,7 @@ _Tp& map<_Key, _Tp, _Compare, _Allocator>::operator[](const key_type& __k) {
 }
 
 template <class _Key, class _Tp, class _Compare, class _Allocator>
-_Tp& map<_Key, _Tp, _Compare, _Allocator>::operator[](key_type&& __k) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 _Tp& map<_Key, _Tp, _Compare, _Allocator>::operator[](key_type&& __k) {
   // TODO investigate this clang-tidy warning.
   // NOLINTBEGIN(bugprone-use-after-move)
   return __tree_
@@ -1596,7 +1596,7 @@ _Tp& map<_Key, _Tp, _Compare, _Allocator>::operator[](const key_type& __k) {
 #  endif // _LIBCPP_CXX03_LANG
 
 template <class _Key, class _Tp, class _Compare, class _Allocator>
-_Tp& map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 _Tp& map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k) {
   __parent_pointer __parent;
   __node_base_pointer& __child = __tree_.__find_equal(__parent, __k);
   if (__child == nullptr)
@@ -1605,7 +1605,7 @@ _Tp& map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k) {
 }
 
 template <class _Key, class _Tp, class _Compare, class _Allocator>
-const _Tp& map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k) const {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 const _Tp& map<_Key, _Tp, _Compare, _Allocator>::at(const key_type& __k) const {
   __parent_pointer __parent;
   __node_base_pointer __child = __tree_.__find_equal(__parent, __k);
   if (__child == nullptr)
diff --git a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
index cabc9f7eb1066..26a0ad1ff1613 100644
--- a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
@@ -10,8 +10,8 @@
 
 // class map
 
-//       mapped_type& at(const key_type& k);
-// const mapped_type& at(const key_type& k) const;
+//       mapped_type& at(const key_type& k); // constexpr since C++26
+// const mapped_type& at(const key_type& k) const; // constexpr since C++26
 
 #include <cassert>
 #include <map>
@@ -20,7 +20,7 @@
 #include "min_allocator.h"
 #include "test_macros.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::pair<const int, double> V;
     V ar[] = {
@@ -143,6 +143,13 @@ int main(int, char**) {
     assert(m.size() == 7);
   }
 #endif
+  return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }

>From c04441ebd9f2a7b685f2bead883c6efcfc8b2cba Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sat, 5 Apr 2025 02:25:01 -0400
Subject: [PATCH 05/11]  member call on object outside its lifetime is not
 allowed in a constant expression

---
 libcxx/include/__tree                         | 139 +++++++++---------
 libcxx/include/map                            |  56 +++----
 .../associative/map/map.access/empty.pass.cpp |  11 +-
 .../map/map.access/empty.verify.cpp           |  12 +-
 .../map/map.access/index_key.pass.cpp         |  11 +-
 .../map/map.access/index_rv_key.pass.cpp      |  11 +-
 .../map/map.access/index_tuple.pass.cpp       |  11 +-
 .../map/map.access/iterator.pass.cpp          |  33 +++--
 .../map/map.access/max_size.pass.cpp          |  11 +-
 .../associative/map/map.access/size.pass.cpp  |  11 +-
 .../map.cons/assign_initializer_list.pass.cpp |  17 ++-
 .../associative/map/map.cons/compare.pass.cpp |  11 +-
 .../map/map.cons/compare_alloc.pass.cpp       |  11 +-
 .../map/map.cons/copy_alloc.pass.cpp          |  11 +-
 14 files changed, 223 insertions(+), 133 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index ff57d63f15789..c966236e51842 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -509,10 +509,10 @@ struct __tree_key_value_types {
   typedef _Tp __container_value_type;
   static const bool __is_map = false;
 
-  _LIBCPP_HIDE_FROM_ABI static key_type const& __get_key(_Tp const& __v) { return __v; }
-  _LIBCPP_HIDE_FROM_ABI static __container_value_type const& __get_value(__node_value_type const& __v) { return __v; }
-  _LIBCPP_HIDE_FROM_ABI static __container_value_type* __get_ptr(__node_value_type& __n) { return std::addressof(__n); }
-  _LIBCPP_HIDE_FROM_ABI static __container_value_type&& __move(__node_value_type& __v) { return std::move(__v); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static key_type const& __get_key(_Tp const& __v) { return __v; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type const& __get_value(__node_value_type const& __v) { return __v; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type* __get_ptr(__node_value_type& __n) { return std::addressof(__n); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type&& __move(__node_value_type& __v) { return std::move(__v); }
 };
 
 template <class _Key, class _Tp>
@@ -524,25 +524,25 @@ struct __tree_key_value_types<__value_type<_Key, _Tp> > {
   typedef __container_value_type __map_value_type;
   static const bool __is_map = true;
 
-  _LIBCPP_HIDE_FROM_ABI static key_type const& __get_key(__node_value_type const& __t) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static key_type const& __get_key(__node_value_type const& __t) {
     return __t.__get_value().first;
   }
 
   template <class _Up, __enable_if_t<__is_same_uncvref<_Up, __container_value_type>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI static key_type const& __get_key(_Up& __t) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static key_type const& __get_key(_Up& __t) {
     return __t.first;
   }
 
-  _LIBCPP_HIDE_FROM_ABI static __container_value_type const& __get_value(__node_value_type const& __t) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type const& __get_value(__node_value_type const& __t) {
     return __t.__get_value();
   }
 
   template <class _Up, __enable_if_t<__is_same_uncvref<_Up, __container_value_type>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI static __container_value_type const& __get_value(_Up& __t) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type const& __get_value(_Up& __t) {
     return __t;
   }
 
-  _LIBCPP_HIDE_FROM_ABI static __container_value_type* __get_ptr(__node_value_type& __n) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type* __get_ptr(__node_value_type& __n) {
     return std::addressof(__n.__get_value());
   }
 
@@ -626,7 +626,7 @@ public:
   typedef _Pointer pointer;
   pointer __left_;
 
-  _LIBCPP_HIDE_FROM_ABI __tree_end_node() _NOEXCEPT : __left_() {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_end_node() _NOEXCEPT : __left_() {}
 };
 
 template <class _VoidPtr>
@@ -679,14 +679,14 @@ private:
 public:
   bool __value_constructed;
 
-  _LIBCPP_HIDE_FROM_ABI __tree_node_destructor(const __tree_node_destructor&) = default;
-  __tree_node_destructor& operator=(const __tree_node_destructor&)            = delete;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_node_destructor(const __tree_node_destructor&) = default;
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_node_destructor& operator=(const __tree_node_destructor&)            = delete;
 
-  _LIBCPP_HIDE_FROM_ABI explicit __tree_node_destructor(allocator_type& __na, bool __val = false) _NOEXCEPT
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree_node_destructor(allocator_type& __na, bool __val = false) _NOEXCEPT
       : __na_(__na),
         __value_constructed(__val) {}
 
-  _LIBCPP_HIDE_FROM_ABI void operator()(pointer __p) _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void operator()(pointer __p) _NOEXCEPT {
     if (__value_constructed)
       __alloc_traits::destroy(__na_, _NodeTypes::__get_ptr(__p->__value_));
     if (__p)
@@ -724,49 +724,49 @@ public:
   typedef value_type& reference;
   typedef typename _NodeTypes::__node_value_type_pointer pointer;
 
-  _LIBCPP_HIDE_FROM_ABI __tree_iterator() _NOEXCEPT
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_iterator() _NOEXCEPT
 #if _LIBCPP_STD_VER >= 14
       : __ptr_(nullptr)
 #endif
   {
   }
 
-  _LIBCPP_HIDE_FROM_ABI reference operator*() const { return __get_np()->__value_; }
-  _LIBCPP_HIDE_FROM_ABI pointer operator->() const { return pointer_traits<pointer>::pointer_to(__get_np()->__value_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reference operator*() const { return __get_np()->__value_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pointer operator->() const { return pointer_traits<pointer>::pointer_to(__get_np()->__value_); }
 
-  _LIBCPP_HIDE_FROM_ABI __tree_iterator& operator++() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_iterator& operator++() {
     __ptr_ = static_cast<__iter_pointer>(
         std::__tree_next_iter<__end_node_pointer>(static_cast<__node_base_pointer>(__ptr_)));
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI __tree_iterator operator++(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_iterator operator++(int) {
     __tree_iterator __t(*this);
     ++(*this);
     return __t;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __tree_iterator& operator--() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_iterator& operator--() {
     __ptr_ = static_cast<__iter_pointer>(
         std::__tree_prev_iter<__node_base_pointer>(static_cast<__end_node_pointer>(__ptr_)));
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI __tree_iterator operator--(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_iterator operator--(int) {
     __tree_iterator __t(*this);
     --(*this);
     return __t;
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI bool operator==(const __tree_iterator& __x, const __tree_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator==(const __tree_iterator& __x, const __tree_iterator& __y) {
     return __x.__ptr_ == __y.__ptr_;
   }
-  friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const __tree_iterator& __x, const __tree_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator!=(const __tree_iterator& __x, const __tree_iterator& __y) {
     return !(__x == __y);
   }
 
 private:
-  _LIBCPP_HIDE_FROM_ABI explicit __tree_iterator(__node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
-  _LIBCPP_HIDE_FROM_ABI explicit __tree_iterator(__end_node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
-  _LIBCPP_HIDE_FROM_ABI __node_pointer __get_np() const { return static_cast<__node_pointer>(__ptr_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree_iterator(__node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree_iterator(__end_node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_pointer __get_np() const { return static_cast<__node_pointer>(__ptr_); }
   template <class, class, class>
   friend class __tree;
   template <class, class, class>
@@ -801,7 +801,7 @@ public:
   typedef const value_type& reference;
   typedef typename _NodeTypes::__const_node_value_type_pointer pointer;
 
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator() _NOEXCEPT
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_const_iterator() _NOEXCEPT
 #if _LIBCPP_STD_VER >= 14
       : __ptr_(nullptr)
 #endif
@@ -812,46 +812,46 @@ private:
   typedef __tree_iterator<value_type, __node_pointer, difference_type> __non_const_iterator;
 
 public:
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator(__non_const_iterator __p) _NOEXCEPT : __ptr_(__p.__ptr_) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_const_iterator(__non_const_iterator __p) _NOEXCEPT : __ptr_(__p.__ptr_) {}
 
-  _LIBCPP_HIDE_FROM_ABI reference operator*() const { return __get_np()->__value_; }
-  _LIBCPP_HIDE_FROM_ABI pointer operator->() const { return pointer_traits<pointer>::pointer_to(__get_np()->__value_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reference operator*() const { return __get_np()->__value_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pointer operator->() const { return pointer_traits<pointer>::pointer_to(__get_np()->__value_); }
 
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator& operator++() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_const_iterator& operator++() {
     __ptr_ = static_cast<__iter_pointer>(
         std::__tree_next_iter<__end_node_pointer>(static_cast<__node_base_pointer>(__ptr_)));
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator operator++(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_const_iterator operator++(int) {
     __tree_const_iterator __t(*this);
     ++(*this);
     return __t;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator& operator--() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_const_iterator& operator--() {
     __ptr_ = static_cast<__iter_pointer>(
         std::__tree_prev_iter<__node_base_pointer>(static_cast<__end_node_pointer>(__ptr_)));
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __tree_const_iterator operator--(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_const_iterator operator--(int) {
     __tree_const_iterator __t(*this);
     --(*this);
     return __t;
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI bool operator==(const __tree_const_iterator& __x, const __tree_const_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator==(const __tree_const_iterator& __x, const __tree_const_iterator& __y) {
     return __x.__ptr_ == __y.__ptr_;
   }
-  friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const __tree_const_iterator& __x, const __tree_const_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator!=(const __tree_const_iterator& __x, const __tree_const_iterator& __y) {
     return !(__x == __y);
   }
 
 private:
-  _LIBCPP_HIDE_FROM_ABI explicit __tree_const_iterator(__node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
-  _LIBCPP_HIDE_FROM_ABI explicit __tree_const_iterator(__end_node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
-  _LIBCPP_HIDE_FROM_ABI __node_pointer __get_np() const { return static_cast<__node_pointer>(__ptr_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree_const_iterator(__node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit __tree_const_iterator(__end_node_pointer __p) _NOEXCEPT : __ptr_(__p) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_pointer __get_np() const { return static_cast<__node_pointer>(__ptr_); }
 
   template <class, class, class>
   friend class __tree;
@@ -930,19 +930,19 @@ private:
   _LIBCPP_COMPRESSED_PAIR(size_type, __size_, value_compare, __value_comp_);
 
 public:
-  _LIBCPP_HIDE_FROM_ABI __iter_pointer __end_node() _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __iter_pointer __end_node() _NOEXCEPT {
     return static_cast<__iter_pointer>(pointer_traits<__end_node_ptr>::pointer_to(__end_node_));
   }
-  _LIBCPP_HIDE_FROM_ABI __iter_pointer __end_node() const _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __iter_pointer __end_node() const _NOEXCEPT {
     return static_cast<__iter_pointer>(
         pointer_traits<__end_node_ptr>::pointer_to(const_cast<__end_node_t&>(__end_node_)));
   }
-  _LIBCPP_HIDE_FROM_ABI __node_allocator& __node_alloc() _NOEXCEPT { return __node_alloc_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_allocator& __node_alloc() _NOEXCEPT { return __node_alloc_; }
 
 private:
-  _LIBCPP_HIDE_FROM_ABI const __node_allocator& __node_alloc() const _NOEXCEPT { return __node_alloc_; }
-  _LIBCPP_HIDE_FROM_ABI __iter_pointer& __begin_node() _NOEXCEPT { return __begin_node_; }
-  _LIBCPP_HIDE_FROM_ABI const __iter_pointer& __begin_node() const _NOEXCEPT { return __begin_node_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const __node_allocator& __node_alloc() const _NOEXCEPT { return __node_alloc_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __iter_pointer& __begin_node() _NOEXCEPT { return __begin_node_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const __iter_pointer& __begin_node() const _NOEXCEPT { return __begin_node_; }
 
 public:
   _LIBCPP_HIDE_FROM_ABI allocator_type __alloc() const _NOEXCEPT { return allocator_type(__node_alloc()); }
@@ -1008,24 +1008,24 @@ public:
 #endif
 
   template <class _Key, class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __emplace_unique_key_args(_Key const&, _Args&&... __args);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __emplace_unique_key_args(_Key const&, _Args&&... __args);
   template <class _Key, class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __emplace_hint_unique_key_args(const_iterator, _Key const&, _Args&&...);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __emplace_hint_unique_key_args(const_iterator, _Key const&, _Args&&...);
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __emplace_unique_impl(_Args&&... __args);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __emplace_unique_impl(_Args&&... __args);
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator __emplace_hint_unique_impl(const_iterator __p, _Args&&... __args);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator __emplace_hint_unique_impl(const_iterator __p, _Args&&... __args);
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator __emplace_multi(_Args&&... __args);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator __emplace_multi(_Args&&... __args);
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI iterator __emplace_hint_multi(const_iterator __p, _Args&&... __args);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator __emplace_hint_multi(const_iterator __p, _Args&&... __args);
 
   template <class _Pp>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __emplace_unique(_Pp&& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __emplace_unique(_Pp&& __x) {
     return __emplace_unique_extract_key(std::forward<_Pp>(__x), __can_extract_key<_Pp, key_type>());
   }
 
@@ -1091,29 +1091,29 @@ public:
     return __emplace_hint_unique_key_args(__p, __x.first, std::forward<_Pp>(__x)).first;
   }
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __insert_unique(const __container_value_type& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __insert_unique(const __container_value_type& __v) {
     return __emplace_unique_key_args(_NodeTypes::__get_key(__v), __v);
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator __insert_unique(const_iterator __p, const __container_value_type& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator __insert_unique(const_iterator __p, const __container_value_type& __v) {
     return __emplace_hint_unique_key_args(__p, _NodeTypes::__get_key(__v), __v).first;
   }
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __insert_unique(__container_value_type&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __insert_unique(__container_value_type&& __v) {
     return __emplace_unique_key_args(_NodeTypes::__get_key(__v), std::move(__v));
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator __insert_unique(const_iterator __p, __container_value_type&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator __insert_unique(const_iterator __p, __container_value_type&& __v) {
     return __emplace_hint_unique_key_args(__p, _NodeTypes::__get_key(__v), std::move(__v)).first;
   }
 
   template <class _Vp, __enable_if_t<!is_same<__remove_const_ref_t<_Vp>, __container_value_type>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __insert_unique(_Vp&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> __insert_unique(_Vp&& __v) {
     return __emplace_unique(std::forward<_Vp>(__v));
   }
 
   template <class _Vp, __enable_if_t<!is_same<__remove_const_ref_t<_Vp>, __container_value_type>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI iterator __insert_unique(const_iterator __p, _Vp&& __v) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator __insert_unique(const_iterator __p, _Vp&& __v) {
     return __emplace_hint_unique(__p, std::forward<_Vp>(__v));
   }
 
@@ -1228,13 +1228,13 @@ public:
   // FIXME: Make this function const qualified. Unfortunately doing so
   // breaks existing code which uses non-const callable comparators.
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI __node_base_pointer& __find_equal(__parent_pointer& __parent, const _Key& __v);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_base_pointer& __find_equal(__parent_pointer& __parent, const _Key& __v);
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI __node_base_pointer& __find_equal(__parent_pointer& __parent, const _Key& __v) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_base_pointer& __find_equal(__parent_pointer& __parent, const _Key& __v) const {
     return const_cast<__tree*>(this)->__find_equal(__parent, __v);
   }
   template <class _Key>
-  _LIBCPP_HIDE_FROM_ABI __node_base_pointer&
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_base_pointer&
   __find_equal(const_iterator __hint, __parent_pointer& __parent, __node_base_pointer& __dummy, const _Key& __v);
 
   _LIBCPP_HIDE_FROM_ABI void __copy_assign_alloc(const __tree& __t) {
@@ -1255,7 +1255,7 @@ private:
   __find_leaf(const_iterator __hint, __parent_pointer& __parent, const key_type& __v);
 
   template <class... _Args>
-  _LIBCPP_HIDE_FROM_ABI __node_holder __construct_node(_Args&&... __args);
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_holder __construct_node(_Args&&... __args);
 
   // TODO: Make this _LIBCPP_HIDE_FROM_ABI
   _LIBCPP_HIDDEN void destroy(__node_pointer __nd) _NOEXCEPT;
@@ -1667,6 +1667,7 @@ __tree<_Tp, _Compare, _Allocator>::__find_leaf(const_iterator __hint, __parent_p
 // If __v exists, set parent to node of __v and return reference to node of __v
 template <class _Tp, class _Compare, class _Allocator>
 template <class _Key>
+_LIBCPP_CONSTEXPR_SINCE_CXX26 
 typename __tree<_Tp, _Compare, _Allocator>::__node_base_pointer&
 __tree<_Tp, _Compare, _Allocator>::__find_equal(__parent_pointer& __parent, const _Key& __v) {
   __node_pointer __nd           = __root();
@@ -1708,6 +1709,7 @@ __tree<_Tp, _Compare, _Allocator>::__find_equal(__parent_pointer& __parent, cons
 // If __v exists, set parent to node of __v and return reference to node of __v
 template <class _Tp, class _Compare, class _Allocator>
 template <class _Key>
+_LIBCPP_CONSTEXPR_SINCE_CXX26 
 typename __tree<_Tp, _Compare, _Allocator>::__node_base_pointer& __tree<_Tp, _Compare, _Allocator>::__find_equal(
     const_iterator __hint, __parent_pointer& __parent, __node_base_pointer& __dummy, const _Key& __v) {
   if (__hint == end() || value_comp()(__v, *__hint)) // check before
@@ -1766,7 +1768,7 @@ void __tree<_Tp, _Compare, _Allocator>::__insert_node_at(
 template <class _Tp, class _Compare, class _Allocator>
 template <class _Key, class... _Args>
 pair<typename __tree<_Tp, _Compare, _Allocator>::iterator, bool>
-__tree<_Tp, _Compare, _Allocator>::__emplace_unique_key_args(_Key const& __k, _Args&&... __args) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_unique_key_args(_Key const& __k, _Args&&... __args) {
   __parent_pointer __parent;
   __node_base_pointer& __child = __find_equal(__parent, __k);
   __node_pointer __r           = static_cast<__node_pointer>(__child);
@@ -1783,7 +1785,7 @@ __tree<_Tp, _Compare, _Allocator>::__emplace_unique_key_args(_Key const& __k, _A
 template <class _Tp, class _Compare, class _Allocator>
 template <class _Key, class... _Args>
 pair<typename __tree<_Tp, _Compare, _Allocator>::iterator, bool>
-__tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_key_args(
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_key_args(
     const_iterator __p, _Key const& __k, _Args&&... __args) {
   __parent_pointer __parent;
   __node_base_pointer __dummy;
@@ -1801,6 +1803,7 @@ __tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_key_args(
 
 template <class _Tp, class _Compare, class _Allocator>
 template <class... _Args>
+_LIBCPP_CONSTEXPR_SINCE_CXX26 
 typename __tree<_Tp, _Compare, _Allocator>::__node_holder
 __tree<_Tp, _Compare, _Allocator>::__construct_node(_Args&&... __args) {
   static_assert(!__is_tree_value_type<_Args...>::value, "Cannot construct from __value_type");
@@ -1814,7 +1817,7 @@ __tree<_Tp, _Compare, _Allocator>::__construct_node(_Args&&... __args) {
 template <class _Tp, class _Compare, class _Allocator>
 template <class... _Args>
 pair<typename __tree<_Tp, _Compare, _Allocator>::iterator, bool>
-__tree<_Tp, _Compare, _Allocator>::__emplace_unique_impl(_Args&&... __args) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_unique_impl(_Args&&... __args) {
   __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
   __parent_pointer __parent;
   __node_base_pointer& __child = __find_equal(__parent, __h->__value_);
@@ -1831,7 +1834,7 @@ __tree<_Tp, _Compare, _Allocator>::__emplace_unique_impl(_Args&&... __args) {
 template <class _Tp, class _Compare, class _Allocator>
 template <class... _Args>
 typename __tree<_Tp, _Compare, _Allocator>::iterator
-__tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_impl(const_iterator __p, _Args&&... __args) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_impl(const_iterator __p, _Args&&... __args) {
   __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
   __parent_pointer __parent;
   __node_base_pointer __dummy;
@@ -1847,7 +1850,7 @@ __tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_impl(const_iterator __p
 template <class _Tp, class _Compare, class _Allocator>
 template <class... _Args>
 typename __tree<_Tp, _Compare, _Allocator>::iterator
-__tree<_Tp, _Compare, _Allocator>::__emplace_multi(_Args&&... __args) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_multi(_Args&&... __args) {
   __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
   __parent_pointer __parent;
   __node_base_pointer& __child = __find_leaf_high(__parent, _NodeTypes::__get_key(__h->__value_));
@@ -1858,7 +1861,7 @@ __tree<_Tp, _Compare, _Allocator>::__emplace_multi(_Args&&... __args) {
 template <class _Tp, class _Compare, class _Allocator>
 template <class... _Args>
 typename __tree<_Tp, _Compare, _Allocator>::iterator
-__tree<_Tp, _Compare, _Allocator>::__emplace_hint_multi(const_iterator __p, _Args&&... __args) {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_hint_multi(const_iterator __p, _Args&&... __args) {
   __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
   __parent_pointer __parent;
   __node_base_pointer& __child = __find_leaf(__p, __parent, _NodeTypes::__get_key(__h->__value_));
diff --git a/libcxx/include/map b/libcxx/include/map
index 3ae485f1ce029..92891332c3a57 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -639,21 +639,21 @@ template <class _Key,
           bool = is_empty<_Compare>::value && !__libcpp_is_final<_Compare>::value>
 class __map_value_compare : private _Compare {
 public:
-  _LIBCPP_HIDE_FROM_ABI __map_value_compare() _NOEXCEPT_(is_nothrow_default_constructible<_Compare>::value)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_value_compare() _NOEXCEPT_(is_nothrow_default_constructible<_Compare>::value)
       : _Compare() {}
-  _LIBCPP_HIDE_FROM_ABI __map_value_compare(_Compare __c) _NOEXCEPT_(is_nothrow_copy_constructible<_Compare>::value)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_value_compare(_Compare __c) _NOEXCEPT_(is_nothrow_copy_constructible<_Compare>::value)
       : _Compare(__c) {}
-  _LIBCPP_HIDE_FROM_ABI const _Compare& key_comp() const _NOEXCEPT { return *this; }
-  _LIBCPP_HIDE_FROM_ABI bool operator()(const _CP& __x, const _CP& __y) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const _Compare& key_comp() const _NOEXCEPT { return *this; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator()(const _CP& __x, const _CP& __y) const {
     return static_cast<const _Compare&>(*this)(__x.__get_value().first, __y.__get_value().first);
   }
-  _LIBCPP_HIDE_FROM_ABI bool operator()(const _CP& __x, const _Key& __y) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator()(const _CP& __x, const _Key& __y) const {
     return static_cast<const _Compare&>(*this)(__x.__get_value().first, __y);
   }
-  _LIBCPP_HIDE_FROM_ABI bool operator()(const _Key& __x, const _CP& __y) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator()(const _Key& __x, const _CP& __y) const {
     return static_cast<const _Compare&>(*this)(__x, __y.__get_value().first);
   }
-  _LIBCPP_HIDE_FROM_ABI void swap(__map_value_compare& __y) _NOEXCEPT_(__is_nothrow_swappable_v<_Compare>) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void swap(__map_value_compare& __y) _NOEXCEPT_(__is_nothrow_swappable_v<_Compare>) {
     using std::swap;
     swap(static_cast<_Compare&>(*this), static_cast<_Compare&>(__y));
   }
@@ -868,37 +868,37 @@ public:
   typedef value_type& reference;
   typedef typename _NodeTypes::__map_value_type_pointer pointer;
 
-  _LIBCPP_HIDE_FROM_ABI __map_iterator() _NOEXCEPT {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_iterator() _NOEXCEPT {}
 
-  _LIBCPP_HIDE_FROM_ABI __map_iterator(_TreeIterator __i) _NOEXCEPT : __i_(__i) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_iterator(_TreeIterator __i) _NOEXCEPT : __i_(__i) {}
 
-  _LIBCPP_HIDE_FROM_ABI reference operator*() const { return __i_->__get_value(); }
-  _LIBCPP_HIDE_FROM_ABI pointer operator->() const { return pointer_traits<pointer>::pointer_to(__i_->__get_value()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reference operator*() const { return __i_->__get_value(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pointer operator->() const { return pointer_traits<pointer>::pointer_to(__i_->__get_value()); }
 
-  _LIBCPP_HIDE_FROM_ABI __map_iterator& operator++() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_iterator& operator++() {
     ++__i_;
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI __map_iterator operator++(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_iterator operator++(int) {
     __map_iterator __t(*this);
     ++(*this);
     return __t;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __map_iterator& operator--() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_iterator& operator--() {
     --__i_;
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI __map_iterator operator--(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_iterator operator--(int) {
     __map_iterator __t(*this);
     --(*this);
     return __t;
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI bool operator==(const __map_iterator& __x, const __map_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator==(const __map_iterator& __x, const __map_iterator& __y) {
     return __x.__i_ == __y.__i_;
   }
-  friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const __map_iterator& __x, const __map_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator!=(const __map_iterator& __x, const __map_iterator& __y) {
     return __x.__i_ != __y.__i_;
   }
 
@@ -924,39 +924,39 @@ public:
   typedef const value_type& reference;
   typedef typename _NodeTypes::__const_map_value_type_pointer pointer;
 
-  _LIBCPP_HIDE_FROM_ABI __map_const_iterator() _NOEXCEPT {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator() _NOEXCEPT {}
 
-  _LIBCPP_HIDE_FROM_ABI __map_const_iterator(_TreeIterator __i) _NOEXCEPT : __i_(__i) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator(_TreeIterator __i) _NOEXCEPT : __i_(__i) {}
   _LIBCPP_HIDE_FROM_ABI
-  __map_const_iterator(__map_iterator< typename _TreeIterator::__non_const_iterator> __i) _NOEXCEPT : __i_(__i.__i_) {}
+  _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator(__map_iterator< typename _TreeIterator::__non_const_iterator> __i) _NOEXCEPT : __i_(__i.__i_) {}
 
-  _LIBCPP_HIDE_FROM_ABI reference operator*() const { return __i_->__get_value(); }
-  _LIBCPP_HIDE_FROM_ABI pointer operator->() const { return pointer_traits<pointer>::pointer_to(__i_->__get_value()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reference operator*() const { return __i_->__get_value(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pointer operator->() const { return pointer_traits<pointer>::pointer_to(__i_->__get_value()); }
 
-  _LIBCPP_HIDE_FROM_ABI __map_const_iterator& operator++() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator& operator++() {
     ++__i_;
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI __map_const_iterator operator++(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator operator++(int) {
     __map_const_iterator __t(*this);
     ++(*this);
     return __t;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __map_const_iterator& operator--() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator& operator--() {
     --__i_;
     return *this;
   }
-  _LIBCPP_HIDE_FROM_ABI __map_const_iterator operator--(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __map_const_iterator operator--(int) {
     __map_const_iterator __t(*this);
     --(*this);
     return __t;
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI bool operator==(const __map_const_iterator& __x, const __map_const_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator==(const __map_const_iterator& __x, const __map_const_iterator& __y) {
     return __x.__i_ == __y.__i_;
   }
-  friend _LIBCPP_HIDE_FROM_ABI bool operator!=(const __map_const_iterator& __x, const __map_const_iterator& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator!=(const __map_const_iterator& __x, const __map_const_iterator& __y) {
     return __x.__i_ != __y.__i_;
   }
 
diff --git a/libcxx/test/std/containers/associative/map/map.access/empty.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/empty.pass.cpp
index 21118eca69693..247ac1895b4f3 100644
--- a/libcxx/test/std/containers/associative/map/map.access/empty.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/empty.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// bool empty() const;
+// bool empty() const;// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -18,7 +18,7 @@
 #include "test_macros.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::map<int, double> M;
     M m;
@@ -39,6 +39,13 @@ int main(int, char**) {
     assert(m.empty());
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/empty.verify.cpp b/libcxx/test/std/containers/associative/map/map.access/empty.verify.cpp
index f44411df0bb00..269add6089628 100644
--- a/libcxx/test/std/containers/associative/map/map.access/empty.verify.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/empty.verify.cpp
@@ -10,13 +10,21 @@
 
 // class map
 
-// bool empty() const noexcept;
+// bool empty() const noexcept;// constexpr since C++26
 
 // UNSUPPORTED: c++03, c++11, c++14, c++17
 
 #include <map>
 
-void f() {
+bool test() {
   std::map<int, int> c;
   c.empty(); // expected-warning {{ignoring return value of function declared with 'nodiscard' attribute}}
+  return true;
+}
+
+int main() {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/index_key.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/index_key.pass.cpp
index 58610c69ed3dc..8633d522947c5 100644
--- a/libcxx/test/std/containers/associative/map/map.access/index_key.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/index_key.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// mapped_type& operator[](const key_type& k);
+// mapped_type& operator[](const key_type& k);// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -23,7 +23,7 @@
 #  include "container_test_types.h"
 #endif
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::pair<const int, double> V;
     V ar[] = {
@@ -135,6 +135,13 @@ int main(int, char**) {
     assert(m.size() == 8);
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/index_rv_key.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/index_rv_key.pass.cpp
index d5d01b96a6988..f5ec0c73bd284 100644
--- a/libcxx/test/std/containers/associative/map/map.access/index_rv_key.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/index_rv_key.pass.cpp
@@ -12,7 +12,7 @@
 
 // class map
 
-// mapped_type& operator[](key_type&& k);
+// mapped_type& operator[](key_type&& k);// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -23,7 +23,7 @@
 #include "min_allocator.h"
 #include "container_test_types.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     std::map<MoveOnly, double> m;
     assert(m.size() == 0);
@@ -75,6 +75,13 @@ int main(int, char**) {
       }
     }
   }
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/index_tuple.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/index_tuple.pass.cpp
index 3f33cfd699151..565db2b6b7342 100644
--- a/libcxx/test/std/containers/associative/map/map.access/index_tuple.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/index_tuple.pass.cpp
@@ -12,16 +12,23 @@
 
 // class map
 
-// mapped_type& operator[](const key_type& k);
+// mapped_type& operator[](const key_type& k);// constexpr since C++26
 
 // https://llvm.org/PR16542
 
 #include <map>
 #include <tuple>
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   std::map<std::tuple<int, int>, std::size_t> m;
   m[std::make_tuple(2, 3)] = 7;
+return true;
+}
 
+int main(int, char**) {
+assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/iterator.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/iterator.pass.cpp
index bbad44c8edb30..20f8541213007 100644
--- a/libcxx/test/std/containers/associative/map/map.access/iterator.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/iterator.pass.cpp
@@ -10,20 +10,20 @@
 
 // class map
 
-//       iterator begin();
-// const_iterator begin() const;
-//       iterator end();
-// const_iterator end()   const;
+//       iterator begin();// constexpr since C++26
+// const_iterator begin() const;// constexpr since C++26
+//       iterator end();// constexpr since C++26
+// const_iterator end()   const;// constexpr since C++26
 //
-//       reverse_iterator rbegin();
-// const_reverse_iterator rbegin() const;
-//       reverse_iterator rend();
-// const_reverse_iterator rend()   const;
+//       reverse_iterator rbegin();// constexpr since C++26
+// const_reverse_iterator rbegin() const;// constexpr since C++26
+//       reverse_iterator rend();// constexpr since C++26
+// const_reverse_iterator rend()   const;// constexpr since C++26
 //
-// const_iterator         cbegin()  const;
-// const_iterator         cend()    const;
-// const_reverse_iterator crbegin() const;
-// const_reverse_iterator crend()   const;
+// const_iterator         cbegin()  const;// constexpr since C++26
+// const_iterator         cend()    const;// constexpr since C++26
+// const_reverse_iterator crbegin() const;// constexpr since C++26
+// const_reverse_iterator crend()   const;// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -32,7 +32,7 @@
 #include "test_macros.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::pair<const int, double> V;
     V ar[] = {V(1, 1),   V(1, 1.5), V(1, 2),   V(2, 1),   V(2, 1.5), V(2, 2),   V(3, 1),   V(3, 1.5),
@@ -156,6 +156,13 @@ int main(int, char**) {
     assert(!(cii != ii1));
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/max_size.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/max_size.pass.cpp
index 1a5d35c2579d8..3a552cebd1fb4 100644
--- a/libcxx/test/std/containers/associative/map/map.access/max_size.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/max_size.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// size_type max_size() const;
+// size_type max_size() const;// constexpr since C++26
 
 #include <cassert>
 #include <limits>
@@ -20,7 +20,7 @@
 #include "test_allocator.h"
 #include "test_macros.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   typedef std::pair<const int, int> KV;
   {
     typedef limited_allocator<KV, 10> A;
@@ -44,6 +44,13 @@ int main(int, char**) {
     assert(c.max_size() <= max_dist);
     assert(c.max_size() <= alloc_max_size(c.get_allocator()));
   }
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.access/size.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/size.pass.cpp
index 23914f6b8ed16..cfb3d6e9426df 100644
--- a/libcxx/test/std/containers/associative/map/map.access/size.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/size.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// size_type size() const;
+// size_type size() const;// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -18,7 +18,7 @@
 #include "test_macros.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::map<int, double> M;
     M m;
@@ -55,6 +55,13 @@ int main(int, char**) {
     assert(m.size() == 0);
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.cons/assign_initializer_list.pass.cpp b/libcxx/test/std/containers/associative/map/map.cons/assign_initializer_list.pass.cpp
index f237c9b56deee..9b1f9730591f3 100644
--- a/libcxx/test/std/containers/associative/map/map.cons/assign_initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.cons/assign_initializer_list.pass.cpp
@@ -12,7 +12,7 @@
 
 // class map
 
-// map& operator=(initializer_list<value_type> il);
+// map& operator=(initializer_list<value_type> il);// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -21,7 +21,7 @@
 #include "min_allocator.h"
 #include "test_allocator.h"
 
-void test_basic() {
+TEST_CONSTEXPR_CXX26 bool test_basic() {
   {
     typedef std::pair<const int, double> V;
     std::map<int, double> m = {
@@ -46,9 +46,10 @@ void test_basic() {
     assert(*std::next(m.begin()) == V(2, 1));
     assert(*std::next(m.begin(), 2) == V(3, 1));
   }
+  return true;
 }
 
-void duplicate_keys_test() {
+TEST_CONSTEXPR_CXX26 bool duplicate_keys_test() {
   test_allocator_statistics alloc_stats;
   typedef std::map<int, int, std::less<int>, test_allocator<std::pair<const int, int> > > Map;
   {
@@ -61,11 +62,19 @@ void duplicate_keys_test() {
     assert(s.begin()->first == 4);
   }
   LIBCPP_ASSERT(alloc_stats.alloc_count == 0);
+  return true;
 }
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   test_basic();
   duplicate_keys_test();
+return true;
+}
 
+int main(int, char**) {
+  assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.cons/compare.pass.cpp b/libcxx/test/std/containers/associative/map/map.cons/compare.pass.cpp
index bd27a2f4ddeb9..66696da0fd39f 100644
--- a/libcxx/test/std/containers/associative/map/map.cons/compare.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.cons/compare.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// explicit map(const key_compare& comp);
+// explicit map(const key_compare& comp);// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -19,7 +19,7 @@
 #include "../../../test_compare.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef test_less<int> C;
     const std::map<int, double, C> m(C(3));
@@ -36,6 +36,13 @@ int main(int, char**) {
     assert(m.key_comp() == C(3));
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.cons/compare_alloc.pass.cpp b/libcxx/test/std/containers/associative/map/map.cons/compare_alloc.pass.cpp
index 20f6a08db6a36..19b294573fc58 100644
--- a/libcxx/test/std/containers/associative/map/map.cons/compare_alloc.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.cons/compare_alloc.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// map(const key_compare& comp, const allocator_type& a);
+// map(const key_compare& comp, const allocator_type& a);// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -20,7 +20,7 @@
 #include "test_allocator.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef test_less<int> C;
     typedef test_allocator<std::pair<const int, double> > A;
@@ -50,6 +50,13 @@ int main(int, char**) {
     assert(m.get_allocator() == A{});
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }
diff --git a/libcxx/test/std/containers/associative/map/map.cons/copy_alloc.pass.cpp b/libcxx/test/std/containers/associative/map/map.cons/copy_alloc.pass.cpp
index aaf1be867b748..ffb99c9edd1f0 100644
--- a/libcxx/test/std/containers/associative/map/map.cons/copy_alloc.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.cons/copy_alloc.pass.cpp
@@ -10,7 +10,7 @@
 
 // class map
 
-// map(const map& m, const allocator_type& a);
+// map(const map& m, const allocator_type& a);// constexpr since C++26
 
 #include <map>
 #include <cassert>
@@ -20,7 +20,7 @@
 #include "test_allocator.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+TEST_CONSTEXPR_CXX26 bool test() {
   {
     typedef std::pair<const int, double> V;
     V ar[] = {
@@ -122,6 +122,13 @@ int main(int, char**) {
     assert(*std::next(mo.begin(), 2) == V(3, 1));
   }
 #endif
+return true;
+}
 
+int main(int, char**) {
+assert(test());
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
   return 0;
 }

>From ec9317e498e0f780a5e317ff1da6fe8874f0d104 Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sat, 5 Apr 2025 20:28:45 -0400
Subject: [PATCH 06/11] Move past member call on object past it's lifetime

---
 libcxx/include/__tree | 10 ++++++++--
 libcxx/include/map    | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index c966236e51842..d8c22cbcb2c4e 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -543,7 +543,11 @@ struct __tree_key_value_types<__value_type<_Key, _Tp> > {
   }
 
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static __container_value_type* __get_ptr(__node_value_type& __n) {
-    return std::addressof(__n.__get_value());
+    // __n's lifetime has not begun, so calling __get_value is wrong
+
+    // return std::addressof(__n.__get_value());
+
+    return __node_value_type::__get_address_of_value(__n);
   }
 
   _LIBCPP_HIDE_FROM_ABI static pair<key_type&&, mapped_type&&> __move(__node_value_type& __v) { return __v.__move(); }
@@ -658,6 +662,7 @@ public:
   __node_value_type __value_;
 
   _LIBCPP_HIDE_FROM_ABI _Tp& __get_value() { return __value_; }
+  // _LIBCPP_HIDE_FROM_ABI static _Tp& __get_value_static(__tree_node * foo) { return (foo->__value_); }
 
   ~__tree_node()                             = delete;
   __tree_node(__tree_node const&)            = delete;
@@ -1816,8 +1821,9 @@ __tree<_Tp, _Compare, _Allocator>::__construct_node(_Args&&... __args) {
 
 template <class _Tp, class _Compare, class _Allocator>
 template <class... _Args>
+_LIBCPP_CONSTEXPR_SINCE_CXX26 
 pair<typename __tree<_Tp, _Compare, _Allocator>::iterator, bool>
-_LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_unique_impl(_Args&&... __args) {
+__tree<_Tp, _Compare, _Allocator>::__emplace_unique_impl(_Args&&... __args) {
   __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
   __parent_pointer __parent;
   __node_base_pointer& __child = __find_equal(__parent, __h->__value_);
diff --git a/libcxx/include/map b/libcxx/include/map
index 92891332c3a57..5cefee5b0092d 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -790,6 +790,17 @@ public:
 #    endif
   }
 
+
+  /*
+  Use this helper when the lifetime of __v may not have begun,
+  so calling __v.__get_value() is not allowed
+  as per:
+  `note: member call on object outside its lifetime is not allowed in a constant expression`
+  */
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static value_type* __get_address_of_value(__value_type & __v) {
+    return std::addressof(__v.__cc_);
+  }
+
   _LIBCPP_HIDE_FROM_ABI __nc_ref_pair_type __ref() {
     value_type& __v = __get_value();
     return __nc_ref_pair_type(const_cast<key_type&>(__v.first), __v.second);
@@ -837,6 +848,13 @@ public:
   _LIBCPP_HIDE_FROM_ABI value_type& __get_value() { return __cc_; }
   _LIBCPP_HIDE_FROM_ABI const value_type& __get_value() const { return __cc_; }
 
+
+  // TODO: maybe needed
+  // _LIBCPP_HIDE_FROM_ABI static value_type* __get_address_of_value(__value_type const& __v) {
+  //   return std::addressof(__v.__cc_);
+  // }
+
+
   __value_type()                               = delete;
   __value_type(__value_type const&)            = delete;
   __value_type& operator=(__value_type const&) = delete;

>From cec33fbe71a41b45008e281d523146805eb6e37d Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sun, 6 Apr 2025 00:54:56 -0400
Subject: [PATCH 07/11] Add ctor to initialize __value_type and
 __tree_node_base, and the object of unique_ptr

---
 libcxx/include/__tree | 20 ++++++++++++++++++--
 libcxx/include/map    |  5 ++++-
 2 files changed, 22 insertions(+), 3 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index d8c22cbcb2c4e..f3d36c0b9db52 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -649,7 +649,10 @@ public:
 
   _LIBCPP_HIDE_FROM_ABI void __set_parent(pointer __p) { __parent_ = static_cast<__parent_pointer>(__p); }
 
-  ~__tree_node_base()                                  = delete;
+
+  // template <typename... Args> constexpr __tree_node_base(Args && ... args) =default;
+  __tree_node_base() = default;
+  ~__tree_node_base()                                  = default;
   __tree_node_base(__tree_node_base const&)            = delete;
   __tree_node_base& operator=(__tree_node_base const&) = delete;
 };
@@ -664,6 +667,10 @@ public:
   _LIBCPP_HIDE_FROM_ABI _Tp& __get_value() { return __value_; }
   // _LIBCPP_HIDE_FROM_ABI static _Tp& __get_value_static(__tree_node * foo) { return (foo->__value_); }
 
+
+  template <typename... Args> constexpr __tree_node(Args && ... args): __value_{std::forward<Args>(args)...} { }
+  // TODO: libcxx26
+  // _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree_node(__node_value_type &&  args): __value_{args} { }
   ~__tree_node()                             = delete;
   __tree_node(__tree_node const&)            = delete;
   __tree_node& operator=(__tree_node const&) = delete;
@@ -1814,7 +1821,16 @@ __tree<_Tp, _Compare, _Allocator>::__construct_node(_Args&&... __args) {
   static_assert(!__is_tree_value_type<_Args...>::value, "Cannot construct from __value_type");
   __node_allocator& __na = __node_alloc();
   __node_holder __h(__node_traits::allocate(__na, 1), _Dp(__na));
-  __node_traits::construct(__na, _NodeTypes::__get_ptr(__h->__value_), std::forward<_Args>(__args)...);
+  // std::__value_type<int, double>
+  // __h->__value_;
+// std::addresof(__h->__value_);
+
+  // __node_traits::construct(__na, std::addressof(__h->__value_), std::forward<_Args>(__args)...);
+  // *h is allocated as of yet, but not constructed
+  // TODO: -> remove (AFAIK, given only cc in  the following needs space: h, h->value and h->value->cc)
+  __node_traits::construct(__na, std::addressof(*__h), std::forward<_Args>(__args)...);
+
+  // __node_traits::construct(__na, _NodeTypes::__get_ptr(__h->__value_), std::forward<_Args>(__args)...);
   __h.get_deleter().__value_constructed = true;
   return __h;
 }
diff --git a/libcxx/include/map b/libcxx/include/map
index 5cefee5b0092d..e363d2ed84c79 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -827,8 +827,11 @@ public:
     return *this;
   }
 
+  // TODO: libcxx26
+  template <typename... Args> _LIBCPP_CONSTEXPR_SINCE_CXX26 __value_type(Args && ... args): __cc_{std::forward<Args>(args)...} { }
+  // constexpr __value_type(value_type && args): __cc_{args} { }
   __value_type()                    = delete;
-  ~__value_type()                   = delete;
+  ~__value_type()                   = default;
   __value_type(const __value_type&) = delete;
   __value_type(__value_type&&)      = delete;
 };

>From 0574be6138c0ac6777b9e267e815335a3a76a0f3 Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sun, 6 Apr 2025 10:00:53 -0400
Subject: [PATCH 08/11] construction works, at() fails due to
 throw_out_of_range

---
 libcxx/include/__tree    | 30 +++++++++++++++---------------
 libcxx/include/map       |  5 +++--
 libcxx/include/stdexcept |  6 +++---
 3 files changed, 21 insertions(+), 20 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index f3d36c0b9db52..2895364af3be3 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -98,7 +98,7 @@ __root, have a non-null __parent_ field.
 // Returns:  true if __x is a left child of its parent, else false
 // Precondition:  __x != nullptr.
 template <class _NodePtr>
-inline _LIBCPP_HIDE_FROM_ABI bool __tree_is_left_child(_NodePtr __x) _NOEXCEPT {
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool __tree_is_left_child(_NodePtr __x) _NOEXCEPT {
   return __x == __x->__parent_->__left_;
 }
 
@@ -164,7 +164,7 @@ inline _LIBCPP_HIDE_FROM_ABI _NodePtr __tree_min(_NodePtr __x) _NOEXCEPT {
 
 // Returns:  pointer to the right-most node under __x.
 template <class _NodePtr>
-inline _LIBCPP_HIDE_FROM_ABI _NodePtr __tree_max(_NodePtr __x) _NOEXCEPT {
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 _NodePtr __tree_max(_NodePtr __x) _NOEXCEPT {
   _LIBCPP_ASSERT_INTERNAL(__x != nullptr, "Root node shouldn't be null");
   while (__x->__right_ != nullptr)
     __x = __x->__right_;
@@ -195,7 +195,7 @@ inline _LIBCPP_HIDE_FROM_ABI _EndNodePtr __tree_next_iter(_NodePtr __x) _NOEXCEP
 // Returns:  pointer to the previous in-order node before __x.
 // Note: __x may be the end node.
 template <class _NodePtr, class _EndNodePtr>
-inline _LIBCPP_HIDE_FROM_ABI _NodePtr __tree_prev_iter(_EndNodePtr __x) _NOEXCEPT {
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 _NodePtr __tree_prev_iter(_EndNodePtr __x) _NOEXCEPT {
   _LIBCPP_ASSERT_INTERNAL(__x != nullptr, "node shouldn't be null");
   if (__x->__left_ != nullptr)
     return std::__tree_max(__x->__left_);
@@ -226,7 +226,7 @@ _LIBCPP_HIDE_FROM_ABI _NodePtr __tree_leaf(_NodePtr __x) _NOEXCEPT {
 // Effects:  Makes __x->__right_ the subtree root with __x as its left child
 //           while preserving in-order order.
 template <class _NodePtr>
-_LIBCPP_HIDE_FROM_ABI void __tree_left_rotate(_NodePtr __x) _NOEXCEPT {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree_left_rotate(_NodePtr __x) _NOEXCEPT {
   _LIBCPP_ASSERT_INTERNAL(__x != nullptr, "node shouldn't be null");
   _LIBCPP_ASSERT_INTERNAL(__x->__right_ != nullptr, "node should have a right child");
   _NodePtr __y  = __x->__right_;
@@ -269,7 +269,7 @@ _LIBCPP_HIDE_FROM_ABI void __tree_right_rotate(_NodePtr __x) _NOEXCEPT {
 // Postcondition: __tree_invariant(end_node->__left_) == true.  end_node->__left_
 //                may be different than the value passed in as __root.
 template <class _NodePtr>
-_LIBCPP_HIDE_FROM_ABI void __tree_balance_after_insert(_NodePtr __root, _NodePtr __x) _NOEXCEPT {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree_balance_after_insert(_NodePtr __root, _NodePtr __x) _NOEXCEPT {
   _LIBCPP_ASSERT_INTERNAL(__root != nullptr, "Root of the tree shouldn't be null");
   _LIBCPP_ASSERT_INTERNAL(__x != nullptr, "Can't attach null node to a leaf");
   __x->__is_black_ = __x == __root;
@@ -645,9 +645,9 @@ public:
   __parent_pointer __parent_;
   bool __is_black_;
 
-  _LIBCPP_HIDE_FROM_ABI pointer __parent_unsafe() const { return static_cast<pointer>(__parent_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pointer __parent_unsafe() const { return static_cast<pointer>(__parent_); }
 
-  _LIBCPP_HIDE_FROM_ABI void __set_parent(pointer __p) { __parent_ = static_cast<__parent_pointer>(__p); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __set_parent(pointer __p) { __parent_ = static_cast<__parent_pointer>(__p); }
 
 
   // template <typename... Args> constexpr __tree_node_base(Args && ... args) =default;
@@ -960,19 +960,19 @@ public:
   _LIBCPP_HIDE_FROM_ABI allocator_type __alloc() const _NOEXCEPT { return allocator_type(__node_alloc()); }
 
 private:
-  _LIBCPP_HIDE_FROM_ABI size_type& size() _NOEXCEPT { return __size_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type& size() _NOEXCEPT { return __size_; }
 
 public:
-  _LIBCPP_HIDE_FROM_ABI const size_type& size() const _NOEXCEPT { return __size_; }
-  _LIBCPP_HIDE_FROM_ABI value_compare& value_comp() _NOEXCEPT { return __value_comp_; }
-  _LIBCPP_HIDE_FROM_ABI const value_compare& value_comp() const _NOEXCEPT { return __value_comp_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const size_type& size() const _NOEXCEPT { return __size_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare& value_comp() _NOEXCEPT { return __value_comp_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const value_compare& value_comp() const _NOEXCEPT { return __value_comp_; }
 
 public:
-  _LIBCPP_HIDE_FROM_ABI __node_pointer __root() const _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_pointer __root() const _NOEXCEPT {
     return static_cast<__node_pointer>(__end_node()->__left_);
   }
 
-  _LIBCPP_HIDE_FROM_ABI __node_base_pointer* __root_ptr() const _NOEXCEPT {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_base_pointer* __root_ptr() const _NOEXCEPT {
     return std::addressof(__end_node()->__left_);
   }
 
@@ -1183,7 +1183,7 @@ public:
   template <class _Key>
   _LIBCPP_HIDE_FROM_ABI size_type __erase_multi(const _Key& __k);
 
-  _LIBCPP_HIDE_FROM_ABI void
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
   __insert_node_at(__parent_pointer __parent, __node_base_pointer& __child, __node_base_pointer __new_node) _NOEXCEPT;
 
   template <class _Key>
@@ -1764,7 +1764,7 @@ typename __tree<_Tp, _Compare, _Allocator>::__node_base_pointer& __tree<_Tp, _Co
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-void __tree<_Tp, _Compare, _Allocator>::__insert_node_at(
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree<_Tp, _Compare, _Allocator>::__insert_node_at(
     __parent_pointer __parent, __node_base_pointer& __child, __node_base_pointer __new_node) _NOEXCEPT {
   __new_node->__left_   = nullptr;
   __new_node->__right_  = nullptr;
diff --git a/libcxx/include/map b/libcxx/include/map
index e363d2ed84c79..3aaccf2e0f3d9 100644
--- a/libcxx/include/map
+++ b/libcxx/include/map
@@ -774,7 +774,7 @@ private:
   value_type __cc_;
 
 public:
-  _LIBCPP_HIDE_FROM_ABI value_type& __get_value() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_type& __get_value() {
 #    if _LIBCPP_STD_VER >= 17
     return *std::launder(std::addressof(__cc_));
 #    else
@@ -782,7 +782,7 @@ public:
 #    endif
   }
 
-  _LIBCPP_HIDE_FROM_ABI const value_type& __get_value() const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const value_type& __get_value() const {
 #    if _LIBCPP_STD_VER >= 17
     return *std::launder(std::addressof(__cc_));
 #    else
@@ -791,6 +791,7 @@ public:
   }
 
 
+  // TODO: possibly no longer needed
   /*
   Use this helper when the lifetime of __v may not have begun,
   so calling __v.__get_value() is not allowed
diff --git a/libcxx/include/stdexcept b/libcxx/include/stdexcept
index 85e11629bd6e3..29d5083ac1c31 100644
--- a/libcxx/include/stdexcept
+++ b/libcxx/include/stdexcept
@@ -161,8 +161,8 @@ public:
 
 class _LIBCPP_EXPORTED_FROM_ABI out_of_range : public logic_error {
 public:
-  _LIBCPP_HIDE_FROM_ABI explicit out_of_range(const string& __s) : logic_error(__s) {}
-  _LIBCPP_HIDE_FROM_ABI explicit out_of_range(const char* __s) : logic_error(__s) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit out_of_range(const string& __s) : logic_error(__s) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit out_of_range(const char* __s) : logic_error(__s) {}
 
 #  ifndef _LIBCPP_ABI_VCRUNTIME
   _LIBCPP_HIDE_FROM_ABI out_of_range(const out_of_range&) _NOEXCEPT            = default;
@@ -246,7 +246,7 @@ _LIBCPP_BEGIN_NAMESPACE_STD
 #  endif
 }
 
-[[__noreturn__]] inline _LIBCPP_HIDE_FROM_ABI void __throw_out_of_range(const char* __msg) {
+[[__noreturn__]] inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __throw_out_of_range(const char* __msg) {
 #  if _LIBCPP_HAS_EXCEPTIONS
   throw out_of_range(__msg);
 #  else

>From ed995a22d6d8608be504a01f52007d3866a0636c Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sun, 6 Apr 2025 10:14:21 -0400
Subject: [PATCH 09/11] can't intentionally throw in constexpr

---
 .../std/containers/associative/map/map.access/at.pass.cpp    | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
index 26a0ad1ff1613..130eefe990363 100644
--- a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
@@ -42,11 +42,16 @@ TEST_CONSTEXPR_CXX26 bool test() {
     assert(m.at(4) == 4.5);
     assert(m.at(5) == 5.5);
 #ifndef TEST_HAS_NO_EXCEPTIONS
+
+// throwing is not allowed in constexpr
+#if TEST_STD_VER < 26
     try {
       TEST_IGNORE_NODISCARD m.at(6);
       assert(false);
     } catch (std::out_of_range&) {
     }
+#endif
+
 #endif
     assert(m.at(7) == 7.5);
     assert(m.at(8) == 8.5);

>From e941811243219e2eb3637a0c5dc3ba078b9d63f4 Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sun, 6 Apr 2025 10:18:29 -0400
Subject: [PATCH 10/11] note: cast from 'void *' is not allowed in a constant
 expression because the pointed object type
 'std::__tree_node<std::__value_type<int, double>, min_pointer<void>>' is not
 similar to the target type 'std::__tree_node_base<min_pointer<void>>'

---
 libcxx/include/__tree                                         | 4 ++--
 .../std/containers/associative/map/map.access/at.pass.cpp     | 4 +++-
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index 2895364af3be3..cfdd1f6ca8f2b 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -1270,7 +1270,7 @@ private:
   _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __node_holder __construct_node(_Args&&... __args);
 
   // TODO: Make this _LIBCPP_HIDE_FROM_ABI
-  _LIBCPP_HIDDEN void destroy(__node_pointer __nd) _NOEXCEPT;
+  _LIBCPP_HIDDEN _LIBCPP_CONSTEXPR_SINCE_CXX26 void destroy(__node_pointer __nd) _NOEXCEPT;
 
   _LIBCPP_HIDE_FROM_ABI void __move_assign(__tree& __t, false_type);
   _LIBCPP_HIDE_FROM_ABI void __move_assign(__tree& __t, true_type) _NOEXCEPT_(
@@ -1540,7 +1540,7 @@ _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::~__tree() {
 }
 
 template <class _Tp, class _Compare, class _Allocator>
-void __tree<_Tp, _Compare, _Allocator>::destroy(__node_pointer __nd) _NOEXCEPT {
+_LIBCPP_CONSTEXPR_SINCE_CXX26 void __tree<_Tp, _Compare, _Allocator>::destroy(__node_pointer __nd) _NOEXCEPT {
   if (__nd != nullptr) {
     destroy(static_cast<__node_pointer>(__nd->__left_));
     destroy(static_cast<__node_pointer>(__nd->__right_));
diff --git a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
index 130eefe990363..3a761dd109410 100644
--- a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
@@ -75,13 +75,15 @@ TEST_CONSTEXPR_CXX26 bool test() {
     assert(m.at(3) == 3.5);
     assert(m.at(4) == 4.5);
     assert(m.at(5) == 5.5);
-#ifndef TEST_HAS_NO_EXCEPTIONS
+// throwing is not allowed in constexpr
+#if TEST_STD_VER < 26
     try {
       TEST_IGNORE_NODISCARD m.at(6);
       assert(false);
     } catch (std::out_of_range&) {
     }
 #endif
+
     assert(m.at(7) == 7.5);
     assert(m.at(8) == 8.5);
     assert(m.size() == 7);

>From def82612573b3b5fe13dac573e58f6dd12c8b347 Mon Sep 17 00:00:00 2001
From: Vinay Deshmukh <32487576+vinay-deshmukh at users.noreply.github.com>
Date: Sun, 6 Apr 2025 14:24:43 -0400
Subject: [PATCH 11/11] note: cast from 'void *' is not allowed in a constant
 expression because the pointed object type
 'std::__tree_node<std::__value_type<int, double>, min_pointer<void>>' is not
 similar to the target type 'std::__tree_node_base<min_pointer<void>>

---
 libcxx/include/__tree                         | 53 +++++++++++++++++++
 .../associative/map/map.access/at.pass.cpp    | 20 +++++++
 2 files changed, 73 insertions(+)

diff --git a/libcxx/include/__tree b/libcxx/include/__tree
index cfdd1f6ca8f2b..bcc0b58c464f2 100644
--- a/libcxx/include/__tree
+++ b/libcxx/include/__tree
@@ -1800,12 +1800,65 @@ pair<typename __tree<_Tp, _Compare, _Allocator>::iterator, bool>
 _LIBCPP_CONSTEXPR_SINCE_CXX26 __tree<_Tp, _Compare, _Allocator>::__emplace_hint_unique_key_args(
     const_iterator __p, _Key const& __k, _Args&&... __args) {
   __parent_pointer __parent;
+  // std::__tree_end_node<std::__tree_node_base<void *> *>
   __node_base_pointer __dummy;
+  // min_pointer<std::__tree_node_base<min_pointer<void>>>
+
   __node_base_pointer& __child = __find_equal(__p, __parent, __dummy, __k);
   __node_pointer __r           = static_cast<__node_pointer>(__child);
   bool __inserted              = false;
   if (__child == nullptr) {
     __node_holder __h = __construct_node(std::forward<_Args>(__args)...);
+    // std::unique_ptr<std::__tree_node<std::__value_type<int, double>, min_pointer<void>>, std::__tree_node_destructor<min_allocator<std::__tree_node<std::__value_type<int, double>, min_pointer<void>>>>>
+
+    // *h
+    // std::__tree_node<std::__value_type<int, double>, min_pointer<void>>
+    // (*__h).fooooo;
+    // std::__tree_node<std::__value_type<int, double>, min_pointer<void>>
+
+    // __h.get().foooooo;
+    // min_pointer<std::__tree_node<std::__value_type<int, double>, min_pointer<void>>>
+
+    // __node_base_pointer  = min_pointer<std::__tree_node_base<                                min_pointer<void>>>
+    // __h.get()            = min_pointer<std::__tree_node     <std::__value_type<int, double>, min_pointer<void>>>
+
+
+    // static_assert();
+
+    // __tree_node::__node_value_type = std::__value_type<int, double>
+
+    /*
+    without 233
+    no matching conversion for static_cast
+    from 'pointer' (aka
+      'min_pointer<std::__tree_node<std::__value_type<int, double>, min_pointer<void, std::integral_constant<unsigned long, 0>>>>'
+    ) 
+    to '__node_base_pointer' (aka 
+      'min_pointer<std::__tree_node_base<min_pointer<void, std::integral_constant<unsigned long, 0>>>, std::integral_constant<unsigned long, 0>>'
+    )
+    */
+
+
+
+
+    [[maybe_unused]] __node_base_pointer foo = static_cast<__node_base_pointer>(__h.get());
+    // [[maybe_unused]] __node_base_pointer foo2 = __node_base_pointer(__h.get());
+
+
+
+
+    /*
+    note:
+    cast from 'void *' is not allowed in a constant expression
+    because the pointed object type
+      'std::__tree_node<std::__value_type<int, double>, min_pointer<void>>'
+    is not similar to the target type
+      'std::__tree_node_base<min_pointer<void>>'
+    */
+
+// i believe this cast fails because the lifetime of __h.get() has not begun
+
+
     __insert_node_at(__parent, __child, static_cast<__node_base_pointer>(__h.get()));
     __r        = __h.release();
     __inserted = true;
diff --git a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
index 3a761dd109410..98235061da5c8 100644
--- a/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
+++ b/libcxx/test/std/containers/associative/map/map.access/at.pass.cpp
@@ -16,6 +16,7 @@
 #include <cassert>
 #include <map>
 #include <stdexcept>
+#include <type_traits>
 
 #include "min_allocator.h"
 #include "test_macros.h"
@@ -100,6 +101,25 @@ TEST_CONSTEXPR_CXX26 bool test() {
         V(7, 7.5),
         V(8, 8.5),
     };
+
+    // std::__tree_node<std::__value_type<int,double>, min_pointer<void>> d;
+    // std::__tree_node_base<min_pointer<void>> b  = d;
+    using Base = std::__tree_node_base<min_pointer<void>>;
+
+    using Derived = std::__tree_node<std::__value_type<int,double>, min_pointer<void>> ;
+    static_assert(std::is_base_of_v<Base, Derived>);
+
+
+    using BaseP = min_pointer<Base>;
+    using DerivedP = min_pointer<Derived>;
+    // static_assert(std::is_base_of_v<BaseP, DerivedP>);
+    DerivedP dp(nullptr);
+
+    BaseP bp =static_cast<BaseP>(dp); 
+    (void)bp;
+
+
+
     std::map<int, double, std::less<int>, min_allocator<V>> m(ar, ar + sizeof(ar) / sizeof(ar[0]));
     assert(m.size() == 7);
     assert(m.at(1) == 1.5);



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