[PATCH] libstdc++: constexpr flat_map and flat_multimap

Yuao Ma addr2line@gmail.com
Tue Jan 6 15:57:11 GMT 2026


Hi Jonathan,

Happy New Year!

Could you take a final look before we merge this patch?


On 12/19/2025 11:34 PM, Yuao Ma wrote:
> On Thu, Dec 18, 2025 at 11:15 PM Patrick Palka <ppalka@redhat.com> wrote:
>>
>> On Fri, 12 Dec 2025, Yuao Ma wrote:
>>
>>> Hi all,
>>>
>>> This patch is a follow-up to r16-6026-gbf9dd44a97400e. It makes
>>> flat_map and flat_multimap constexpr as part of P3372R3.
>>> Tested on x86_64-linux. OK for trunk?
>>>
>>> Yuao
>>>
>>>  From c2a1c42266bdd87c97868735514b621cec3e30bd Mon Sep 17 00:00:00 2001
>>> From: Yuao Ma <c8ef@outlook.com>
>>> Date: Fri, 12 Dec 2025 19:26:01 +0800
>>> Subject: [PATCH] libstdc++: constexpr flat_map and flat_multimap
>>>
>>> This patch makes flat_map and flat_multimap constexpr as part of P3372R3.
>>>
>>> libstdc++-v3/ChangeLog:
>>>
>>>        * include/bits/version.def: Add FTM.
>>>        * include/bits/version.h: Regenerate.
>>>        * include/std/flat_map: Add constexpr.
>>>        * testsuite/23_containers/flat_map/1.cc: Add constexpr test.
>>>        * testsuite/23_containers/flat_multimap/1.cc: Add constexpr test.
>>
>> LGTM
>>
>
> Thanks for the review!
>
> Hi Jonathan,
> Could you take a look at this patch when you have a moment? I’ve
> rebased it against the latest trunk and verified it in both debug and
> release modes. Everything seems to be working correctly now.
>
>>> ---
>>>   libstdc++-v3/include/bits/version.def         |   8 +
>>>   libstdc++-v3/include/bits/version.h           |  10 ++
>>>   libstdc++-v3/include/std/flat_map             | 157 +++++++++++++++++-
>>>   .../testsuite/23_containers/flat_map/1.cc     |  43 ++++-
>>>   .../23_containers/flat_multimap/1.cc          |  42 ++++-
>>>   5 files changed, 245 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>>> index 5b95db19ac6..f97276d80f2 100644
>>> --- a/libstdc++-v3/include/bits/version.def
>>> +++ b/libstdc++-v3/include/bits/version.def
>>> @@ -1351,6 +1351,14 @@ ftms = {
>>>     };
>>>   };
>>>
>>> +ftms = {
>>> +  name = constexpr_flat_map;
>>> +  values = {
>>> +    v = 202502;
>>> +    cxxmin = 26;
>>> +  };
>>> +};
>>> +
>>>   ftms = {
>>>     name = constexpr_flat_set;
>>>     values = {
>>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>>> index eee9890a72b..97b37e9a62b 100644
>>> --- a/libstdc++-v3/include/bits/version.h
>>> +++ b/libstdc++-v3/include/bits/version.h
>>> @@ -1496,6 +1496,16 @@
>>>   #endif /* !defined(__cpp_lib_constexpr_dynamic_alloc) */
>>>   #undef __glibcxx_want_constexpr_dynamic_alloc
>>>
>>> +#if !defined(__cpp_lib_constexpr_flat_map)
>>> +# if (__cplusplus >  202302L)
>>> +#  define __glibcxx_constexpr_flat_map 202502L
>>> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_flat_map)
>>> +#   define __cpp_lib_constexpr_flat_map 202502L
>>> +#  endif
>>> +# endif
>>> +#endif /* !defined(__cpp_lib_constexpr_flat_map) */
>>> +#undef __glibcxx_want_constexpr_flat_map
>>> +
>>>   #if !defined(__cpp_lib_constexpr_flat_set)
>>>   # if (__cplusplus >  202302L)
>>>   #  define __glibcxx_constexpr_flat_set 202502L
>>> diff --git a/libstdc++-v3/include/std/flat_map b/libstdc++-v3/include/std/flat_map
>>> index 637c3b7fe0d..e270735a87b 100644
>>> --- a/libstdc++-v3/include/std/flat_map
>>> +++ b/libstdc++-v3/include/std/flat_map
>>> @@ -33,6 +33,7 @@
>>>   #pragma GCC system_header
>>>   #endif
>>>
>>> +#define __glibcxx_want_constexpr_flat_map
>>>   #define __glibcxx_want_flat_map
>>>   #include <bits/version.h>
>>>
>>> @@ -108,9 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         class value_compare
>>>         {
>>>        [[no_unique_address]] key_compare _M_comp;
>>> +     _GLIBCXX26_CONSTEXPR
>>>        value_compare(key_compare __c) : _M_comp(__c) { }
>>>
>>>         public:
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        operator()(const_reference __x, const_reference __y) const
>>>        { return _M_comp(__x.first, __y.first); }
>>> @@ -129,10 +132,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        containers* _M_cont;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _ClearGuard(containers& __cont)
>>>        : _M_cont(std::__addressof(__cont))
>>>        { }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        ~_ClearGuard()
>>>        {
>>>          if (_M_cont)
>>> @@ -142,24 +147,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>            }
>>>        }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_disable()
>>>        { _M_cont = nullptr; }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _ClearGuard
>>>         _M_make_clear_guard()
>>>         { return _ClearGuard{this->_M_cont}; }
>>>
>>>       public:
>>>         // constructors
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl() : _Flat_map_impl(key_compare()) { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         explicit
>>>         _Flat_map_impl(const key_compare& __comp)
>>>         : _M_cont(), _M_comp(__comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -169,6 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        _M_sort_uniq();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t,
>>>                     key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>> @@ -180,12 +191,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>>        : _M_cont(), _M_comp(__comp)
>>>        { insert(__first, __last); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>> @@ -193,20 +206,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { insert(__s, __first, __last); }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare())
>>>        { }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp)
>>>        : _Flat_map_impl(__comp)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>>         : _Flat_map_impl(__il.begin(), __il.end(), __comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t __s,
>>>                     initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -216,12 +233,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         // constructors with allocators
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        explicit
>>>        _Flat_map_impl(const _Alloc& __a)
>>>        : _Flat_map_impl(key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_compare& __comp, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a)),
>>> @@ -229,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const _Alloc& __a)
>>> @@ -236,6 +256,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const key_compare& __comp,
>>> @@ -249,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -257,6 +279,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -271,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const _Derived& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a, __x._M_cont.keys),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a, __x._M_cont.values)),
>>> @@ -278,6 +302,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_Derived&& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>
>>>                  (__a, std::move(__x._M_cont.keys)),
>>> @@ -288,6 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(std::move(__first), std::move(__last), key_compare(), __a)
>>> @@ -295,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -303,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>> @@ -311,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>> @@ -320,6 +349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare(), __a)
>>> @@ -327,18 +357,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__comp, __a)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__il, key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -346,6 +379,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>> @@ -353,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>> @@ -360,6 +395,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        : _Flat_map_impl(__s, __il.begin(), __il.end(), __comp, __a)
>>>        { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Derived&
>>>         operator=(initializer_list<value_type> __il)
>>>         {
>>> @@ -369,64 +405,79 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         // iterators
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         begin() noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         begin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         end() noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         end() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rbegin() noexcept
>>>         { return reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rbegin() const noexcept
>>>         { return const_reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rend() noexcept
>>>         { return reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rend() const noexcept
>>>         { return const_reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cbegin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cend() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crbegin() const noexcept
>>>         { return const_reverse_iterator(cend()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crend() const noexcept
>>>         { return const_reverse_iterator(cbegin()); }
>>>
>>>         // capacity
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         empty() const noexcept
>>>         { return _M_cont.keys.empty(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         size() const noexcept
>>>         { return _M_cont.keys.size(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         max_size() const noexcept
>>>         { return std::min<size_type>(keys().max_size(), values().max_size()); }
>>> @@ -436,6 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // modifiers
>>>         template<typename _Key2, typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        _M_try_emplace(optional<const_iterator> __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -491,6 +543,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<value_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        emplace(_Args&&... __args)
>>>        {
>>> @@ -503,6 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        emplace_hint(const_iterator __position, _Args&&... __args)
>>>        {
>>> @@ -510,36 +564,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return _M_try_emplace(__position, std::move(__p.first), std::move(__p.second)).first;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(const value_type& __x)
>>>         { return emplace(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(value_type&& __x)
>>>         { return emplace(std::move(__x)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, const value_type& __x)
>>>         { return emplace_hint(__position, __x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, value_type&& __x)
>>>         { return emplace_hint(__position, std::move(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        insert(_Arg&& __x)
>>>        { return emplace(std::forward<_Arg>(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert(const_iterator __position, _Arg&& __x)
>>>        { return emplace_hint(__position, std::forward<_Arg>(__x)); }
>>>
>>>       private:
>>>         template<typename _Iter, typename _Sent>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_insert(_Iter __first, _Sent __last)
>>>        {
>>> @@ -577,11 +638,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>       public:
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(_InputIterator __first, _InputIterator __last)
>>>        { _M_insert(std::move(__first), std::move(__last)); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(__sorted_t, _InputIterator __first, _InputIterator __last)
>>>        {
>>> @@ -590,18 +653,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert_range(_Rg&& __rg)
>>>        { _M_insert(ranges::begin(__rg), ranges::end(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(initializer_list<value_type> __il)
>>>         { insert(__il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(__sorted_t __s, initializer_list<value_type> __il)
>>>         { insert(__s, __il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         containers
>>>         extract() &&
>>>         {
>>> @@ -609,6 +676,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return {std::move(_M_cont.keys), std::move(_M_cont.values)};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont)
>>>         {
>>> @@ -622,10 +690,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // try_emplace and insert_or_assign defined directly in class flat_map only.
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(iterator __position)
>>>         { return erase(static_cast<const_iterator>(__position)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __position)
>>>         {
>>> @@ -637,6 +707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         erase(const key_type& __x)
>>>         { return erase<const key_type&>(__x); }
>>> @@ -646,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          || (__transparent_comparator<_Compare>
>>>              && !is_convertible_v<_Key2, iterator>
>>>              && !is_convertible_v<_Key2, const_iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        erase(_Key2&& __x)
>>>        {
>>> @@ -655,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return __n;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __first, const_iterator __last)
>>>         {
>>> @@ -667,6 +740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         swap(_Derived& __y) noexcept
>>>         {
>>> @@ -675,6 +749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        ranges::swap(_M_cont.values, __y._M_cont.values);
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         clear() noexcept
>>>         {
>>> @@ -684,32 +759,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // observers
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         key_compare
>>>         key_comp() const
>>>         { return _M_comp; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         value_compare
>>>         value_comp() const
>>>         { return value_compare(_M_comp); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const key_container_type&
>>>         keys() const noexcept
>>>         { return _M_cont.keys; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_container_type&
>>>         values() const noexcept
>>>         { return _M_cont.values; }
>>>
>>>         // map operations
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         find(const key_type& __x)
>>>         { return find<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         find(const key_type& __x) const
>>>         { return find<key_type>(__x); }
>>> @@ -717,6 +798,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        find(const _Key2& __x)
>>>        {
>>> @@ -730,6 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        find(const _Key2& __x) const
>>>        {
>>> @@ -741,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         count(const key_type& __x) const
>>>         { return count<key_type>(__x); }
>>> @@ -748,6 +832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        count(const _Key2& __x) const
>>>        {
>>> @@ -761,6 +846,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         contains(const key_type& __x) const
>>>         { return contains<key_type>(__x); }
>>> @@ -768,16 +854,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        contains(const _Key2& __x) const
>>>        { return find(__x) != cend(); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         lower_bound(const key_type& __x)
>>>         { return lower_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         lower_bound(const key_type& __x) const
>>>         { return lower_bound<key_type>(__x); }
>>> @@ -785,6 +874,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        lower_bound(const _Key2& __x)
>>>        {
>>> @@ -796,6 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        lower_bound(const _Key2& __x) const
>>>        {
>>> @@ -805,11 +896,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         upper_bound(const key_type& __x)
>>>         { return upper_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         upper_bound(const key_type& __x) const
>>>         { return upper_bound<key_type>(__x); }
>>> @@ -817,6 +910,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        upper_bound(const _Key2& __x)
>>>        {
>>> @@ -828,6 +922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        upper_bound(const _Key2& __x) const
>>>        {
>>> @@ -837,11 +932,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<iterator, iterator>
>>>         equal_range(const key_type& __x)
>>>         { return equal_range<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<const_iterator, const_iterator>
>>>         equal_range(const key_type& __x) const
>>>         { return equal_range<key_type>(__x); }
>>> @@ -849,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, iterator>
>>>        equal_range(const _Key2& __x)
>>>        {
>>> @@ -861,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<const_iterator, const_iterator>
>>>        equal_range(const _Key2& __x) const
>>>        {
>>> @@ -871,7 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Derived& __x, const _Derived& __y)
>>>         {
>>>        return __x._M_cont.keys == __y._M_cont.keys
>>> @@ -880,7 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Up = value_type>
>>>        [[nodiscard]]
>>> -     friend __detail::__synth3way_t<_Up>
>>> +     friend _GLIBCXX26_CONSTEXPR __detail::__synth3way_t<_Up>
>>>        operator<=>(const _Derived& __x, const _Derived& __y)
>>>        {
>>>          return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
>>> @@ -888,11 +987,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                                        __detail::__synth3way);
>>>        }
>>>
>>> -      friend void
>>> +      friend _GLIBCXX26_CONSTEXPR void
>>>         swap(_Derived& __x, _Derived& __y) noexcept
>>>         { return __x.swap(__y); }
>>>
>>>         template<typename _Predicate>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        _M_erase_if(_Predicate __pred)
>>>        {
>>> @@ -912,6 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         containers _M_cont;
>>>         [[no_unique_address]] _Compare _M_comp;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_sort_uniq()
>>>         {
>>> @@ -921,13 +1022,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          _M_unique();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_unique() requires (!_Multi)
>>>         {
>>>        struct __key_equiv
>>>        {
>>> +       _GLIBCXX26_CONSTEXPR
>>>          __key_equiv(key_compare __c) : _M_comp(__c) { }
>>>
>>> +       _GLIBCXX26_CONSTEXPR
>>>          bool
>>>          operator()(const_reference __x, const_reference __y) const
>>>          { return !_M_comp(__x.first, __y.first) && !_M_comp(__y.first, __x.first); }
>>> @@ -958,12 +1062,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                     ranges::__maybe_const_t<_Const, mapped_type>&>;
>>>         using difference_type   = ptrdiff_t;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator() = default;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Iterator<!_Const> __it) requires _Const
>>>         : _M_cont(__it._M_cont), _M_index(__it._M_index)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator*() const noexcept
>>>         {
>>> @@ -975,19 +1082,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        reference __p;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const reference*
>>>        operator->() const noexcept
>>>        { return std::__addressof(__p); }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pointer
>>>         operator->() const
>>>         { return pointer{operator*()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator[](difference_type __n) const noexcept
>>>         { return *(*this + __n); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator++() noexcept
>>>         {
>>> @@ -995,6 +1106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator--() noexcept
>>>         {
>>> @@ -1002,6 +1114,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator++(int) noexcept
>>>         {
>>> @@ -1010,6 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator--(int) noexcept
>>>         {
>>> @@ -1018,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator+=(difference_type __n) noexcept
>>>         {
>>> @@ -1025,6 +1140,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator-=(difference_type __n) noexcept
>>>         {
>>> @@ -1036,45 +1152,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         friend _Flat_map_impl;
>>>         friend _Iterator<!_Const>;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires (!_Const)
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(const _Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires _Const
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(difference_type __n, _Iterator __it) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator-(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it -= __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend difference_type
>>> +      friend _GLIBCXX26_CONSTEXPR difference_type
>>>         operator-(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>>        return __x._M_index - __y._M_index;
>>>         }
>>>
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1082,7 +1200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __x._M_index == __y._M_index;
>>>         }
>>>
>>> -      friend strong_ordering
>>> +      friend _GLIBCXX26_CONSTEXPR strong_ordering
>>>         operator<=>(const _Iterator& __x, const _Iterator& __y)
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1146,30 +1264,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         using _Impl::max_size;
>>>
>>>         // element access
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](const key_type& __x)
>>>         { return try_emplace(__x).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](key_type&& __x)
>>>         { return try_emplace(std::move(__x)).first->second; }
>>>
>>>         template<typename _Key2>
>>>        requires __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        operator[](_Key2&& __x)
>>>        { return try_emplace(std::forward<_Key2>(__x)).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         at(const key_type& __x)
>>>         { return at<key_type>(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_type&
>>>         at(const key_type& __x) const
>>>         { return at<key_type>(__x); }
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        at(const _Key2& __x)
>>>        {
>>> @@ -1181,6 +1305,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const mapped_type&
>>>        at(const _Key2& __x) const
>>>        {
>>> @@ -1203,12 +1328,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(nullopt, __k, std::forward<_Args>(__args)...); }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1222,6 +1349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<mapped_type, _Args...>
>>>          && (!is_convertible_v<_Key2&&, const_iterator>)
>>>          && (!is_convertible_v<_Key2&&, iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(_Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1231,12 +1359,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(__hint, __k, std::forward<_Args>(__args)...).first; }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1248,6 +1378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        requires __transparent_comparator<_Compare>
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1258,6 +1389,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(const key_type& __k, _Mapped&& __obj)
>>>        { return insert_or_assign<const key_type&, _Mapped>(__k, std::forward<_Mapped>(__obj)); }
>>> @@ -1265,6 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1277,6 +1410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(_Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1290,6 +1424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, const key_type& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1300,6 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1312,6 +1448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, _Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1422,6 +1559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> @@ -1590,6 +1728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> index 5bcda3464f1..04c2101aab1 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> @@ -17,7 +17,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -76,6 +76,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -127,6 +128,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(20,42) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -158,6 +160,7 @@ test02()
>>>     VERIFY( m.count(3) == 1 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -186,6 +189,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -218,6 +222,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -227,6 +232,7 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, -4, -5}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -243,6 +249,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -254,6 +261,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test08()
>>>   {
>>> @@ -263,6 +271,7 @@ test08()
>>>     m[k] = 0;
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -274,8 +283,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -290,3 +299,31 @@ main()
>>>     test08();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test08();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> index f143f3acd1b..00644c14061 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> @@ -11,7 +11,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -74,6 +74,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -111,6 +112,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(12,3) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -137,6 +139,7 @@ test02()
>>>     VERIFY( m.count(3) == 2 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -165,6 +168,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -197,6 +201,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -205,6 +210,8 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::keys, (int[]){1, 2, 3, 3, 4, 5}) );
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, 3, -4, -5}) );
>>>   }
>>> +
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -221,6 +228,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -232,6 +240,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -243,8 +252,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -258,3 +267,30 @@ main()
>>>     test07();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> --
>>> 2.52.0
>>>
>>>  From c2a1c42266bdd87c97868735514b621cec3e30bd Mon Sep 17 00:00:00 2001
>>> From: Yuao Ma <c8ef@outlook.com>
>>> Date: Fri, 12 Dec 2025 19:26:01 +0800
>>> Subject: [PATCH] libstdc++: constexpr flat_map and flat_multimap
>>>
>>> This patch makes flat_map and flat_multimap constexpr as part of P3372R3.
>>>
>>> libstdc++-v3/ChangeLog:
>>>
>>>        * include/bits/version.def: Add FTM.
>>>        * include/bits/version.h: Regenerate.
>>>        * include/std/flat_map: Add constexpr.
>>>        * testsuite/23_containers/flat_map/1.cc: Add constexpr test.
>>>        * testsuite/23_containers/flat_multimap/1.cc: Add constexpr test.
>>> ---
>>>   libstdc++-v3/include/bits/version.def         |   8 +
>>>   libstdc++-v3/include/bits/version.h           |  10 ++
>>>   libstdc++-v3/include/std/flat_map             | 157 +++++++++++++++++-
>>>   .../testsuite/23_containers/flat_map/1.cc     |  43 ++++-
>>>   .../23_containers/flat_multimap/1.cc          |  42 ++++-
>>>   5 files changed, 245 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>>> index 5b95db19ac6..f97276d80f2 100644
>>> --- a/libstdc++-v3/include/bits/version.def
>>> +++ b/libstdc++-v3/include/bits/version.def
>>> @@ -1351,6 +1351,14 @@ ftms = {
>>>     };
>>>   };
>>>
>>> +ftms = {
>>> +  name = constexpr_flat_map;
>>> +  values = {
>>> +    v = 202502;
>>> +    cxxmin = 26;
>>> +  };
>>> +};
>>> +
>>>   ftms = {
>>>     name = constexpr_flat_set;
>>>     values = {
>>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>>> index eee9890a72b..97b37e9a62b 100644
>>> --- a/libstdc++-v3/include/bits/version.h
>>> +++ b/libstdc++-v3/include/bits/version.h
>>> @@ -1496,6 +1496,16 @@
>>>   #endif /* !defined(__cpp_lib_constexpr_dynamic_alloc) */
>>>   #undef __glibcxx_want_constexpr_dynamic_alloc
>>>
>>> +#if !defined(__cpp_lib_constexpr_flat_map)
>>> +# if (__cplusplus >  202302L)
>>> +#  define __glibcxx_constexpr_flat_map 202502L
>>> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_flat_map)
>>> +#   define __cpp_lib_constexpr_flat_map 202502L
>>> +#  endif
>>> +# endif
>>> +#endif /* !defined(__cpp_lib_constexpr_flat_map) */
>>> +#undef __glibcxx_want_constexpr_flat_map
>>> +
>>>   #if !defined(__cpp_lib_constexpr_flat_set)
>>>   # if (__cplusplus >  202302L)
>>>   #  define __glibcxx_constexpr_flat_set 202502L
>>> diff --git a/libstdc++-v3/include/std/flat_map b/libstdc++-v3/include/std/flat_map
>>> index 637c3b7fe0d..e270735a87b 100644
>>> --- a/libstdc++-v3/include/std/flat_map
>>> +++ b/libstdc++-v3/include/std/flat_map
>>> @@ -33,6 +33,7 @@
>>>   #pragma GCC system_header
>>>   #endif
>>>
>>> +#define __glibcxx_want_constexpr_flat_map
>>>   #define __glibcxx_want_flat_map
>>>   #include <bits/version.h>
>>>
>>> @@ -108,9 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         class value_compare
>>>         {
>>>        [[no_unique_address]] key_compare _M_comp;
>>> +     _GLIBCXX26_CONSTEXPR
>>>        value_compare(key_compare __c) : _M_comp(__c) { }
>>>
>>>         public:
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        operator()(const_reference __x, const_reference __y) const
>>>        { return _M_comp(__x.first, __y.first); }
>>> @@ -129,10 +132,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        containers* _M_cont;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _ClearGuard(containers& __cont)
>>>        : _M_cont(std::__addressof(__cont))
>>>        { }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        ~_ClearGuard()
>>>        {
>>>          if (_M_cont)
>>> @@ -142,24 +147,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>            }
>>>        }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_disable()
>>>        { _M_cont = nullptr; }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _ClearGuard
>>>         _M_make_clear_guard()
>>>         { return _ClearGuard{this->_M_cont}; }
>>>
>>>       public:
>>>         // constructors
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl() : _Flat_map_impl(key_compare()) { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         explicit
>>>         _Flat_map_impl(const key_compare& __comp)
>>>         : _M_cont(), _M_comp(__comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -169,6 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        _M_sort_uniq();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t,
>>>                     key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>> @@ -180,12 +191,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>>        : _M_cont(), _M_comp(__comp)
>>>        { insert(__first, __last); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>> @@ -193,20 +206,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { insert(__s, __first, __last); }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare())
>>>        { }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp)
>>>        : _Flat_map_impl(__comp)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>>         : _Flat_map_impl(__il.begin(), __il.end(), __comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t __s,
>>>                     initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -216,12 +233,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         // constructors with allocators
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        explicit
>>>        _Flat_map_impl(const _Alloc& __a)
>>>        : _Flat_map_impl(key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_compare& __comp, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a)),
>>> @@ -229,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const _Alloc& __a)
>>> @@ -236,6 +256,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const key_compare& __comp,
>>> @@ -249,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -257,6 +279,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -271,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const _Derived& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a, __x._M_cont.keys),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a, __x._M_cont.values)),
>>> @@ -278,6 +302,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_Derived&& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>
>>>                  (__a, std::move(__x._M_cont.keys)),
>>> @@ -288,6 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(std::move(__first), std::move(__last), key_compare(), __a)
>>> @@ -295,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -303,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>> @@ -311,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>> @@ -320,6 +349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare(), __a)
>>> @@ -327,18 +357,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__comp, __a)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__il, key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -346,6 +379,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>> @@ -353,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>> @@ -360,6 +395,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        : _Flat_map_impl(__s, __il.begin(), __il.end(), __comp, __a)
>>>        { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Derived&
>>>         operator=(initializer_list<value_type> __il)
>>>         {
>>> @@ -369,64 +405,79 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         // iterators
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         begin() noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         begin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         end() noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         end() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rbegin() noexcept
>>>         { return reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rbegin() const noexcept
>>>         { return const_reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rend() noexcept
>>>         { return reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rend() const noexcept
>>>         { return const_reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cbegin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cend() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crbegin() const noexcept
>>>         { return const_reverse_iterator(cend()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crend() const noexcept
>>>         { return const_reverse_iterator(cbegin()); }
>>>
>>>         // capacity
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         empty() const noexcept
>>>         { return _M_cont.keys.empty(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         size() const noexcept
>>>         { return _M_cont.keys.size(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         max_size() const noexcept
>>>         { return std::min<size_type>(keys().max_size(), values().max_size()); }
>>> @@ -436,6 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // modifiers
>>>         template<typename _Key2, typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        _M_try_emplace(optional<const_iterator> __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -491,6 +543,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<value_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        emplace(_Args&&... __args)
>>>        {
>>> @@ -503,6 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        emplace_hint(const_iterator __position, _Args&&... __args)
>>>        {
>>> @@ -510,36 +564,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return _M_try_emplace(__position, std::move(__p.first), std::move(__p.second)).first;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(const value_type& __x)
>>>         { return emplace(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(value_type&& __x)
>>>         { return emplace(std::move(__x)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, const value_type& __x)
>>>         { return emplace_hint(__position, __x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, value_type&& __x)
>>>         { return emplace_hint(__position, std::move(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        insert(_Arg&& __x)
>>>        { return emplace(std::forward<_Arg>(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert(const_iterator __position, _Arg&& __x)
>>>        { return emplace_hint(__position, std::forward<_Arg>(__x)); }
>>>
>>>       private:
>>>         template<typename _Iter, typename _Sent>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_insert(_Iter __first, _Sent __last)
>>>        {
>>> @@ -577,11 +638,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>       public:
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(_InputIterator __first, _InputIterator __last)
>>>        { _M_insert(std::move(__first), std::move(__last)); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(__sorted_t, _InputIterator __first, _InputIterator __last)
>>>        {
>>> @@ -590,18 +653,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert_range(_Rg&& __rg)
>>>        { _M_insert(ranges::begin(__rg), ranges::end(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(initializer_list<value_type> __il)
>>>         { insert(__il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(__sorted_t __s, initializer_list<value_type> __il)
>>>         { insert(__s, __il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         containers
>>>         extract() &&
>>>         {
>>> @@ -609,6 +676,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return {std::move(_M_cont.keys), std::move(_M_cont.values)};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont)
>>>         {
>>> @@ -622,10 +690,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // try_emplace and insert_or_assign defined directly in class flat_map only.
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(iterator __position)
>>>         { return erase(static_cast<const_iterator>(__position)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __position)
>>>         {
>>> @@ -637,6 +707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         erase(const key_type& __x)
>>>         { return erase<const key_type&>(__x); }
>>> @@ -646,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          || (__transparent_comparator<_Compare>
>>>              && !is_convertible_v<_Key2, iterator>
>>>              && !is_convertible_v<_Key2, const_iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        erase(_Key2&& __x)
>>>        {
>>> @@ -655,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return __n;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __first, const_iterator __last)
>>>         {
>>> @@ -667,6 +740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         swap(_Derived& __y) noexcept
>>>         {
>>> @@ -675,6 +749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        ranges::swap(_M_cont.values, __y._M_cont.values);
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         clear() noexcept
>>>         {
>>> @@ -684,32 +759,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // observers
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         key_compare
>>>         key_comp() const
>>>         { return _M_comp; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         value_compare
>>>         value_comp() const
>>>         { return value_compare(_M_comp); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const key_container_type&
>>>         keys() const noexcept
>>>         { return _M_cont.keys; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_container_type&
>>>         values() const noexcept
>>>         { return _M_cont.values; }
>>>
>>>         // map operations
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         find(const key_type& __x)
>>>         { return find<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         find(const key_type& __x) const
>>>         { return find<key_type>(__x); }
>>> @@ -717,6 +798,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        find(const _Key2& __x)
>>>        {
>>> @@ -730,6 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        find(const _Key2& __x) const
>>>        {
>>> @@ -741,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         count(const key_type& __x) const
>>>         { return count<key_type>(__x); }
>>> @@ -748,6 +832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        count(const _Key2& __x) const
>>>        {
>>> @@ -761,6 +846,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         contains(const key_type& __x) const
>>>         { return contains<key_type>(__x); }
>>> @@ -768,16 +854,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        contains(const _Key2& __x) const
>>>        { return find(__x) != cend(); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         lower_bound(const key_type& __x)
>>>         { return lower_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         lower_bound(const key_type& __x) const
>>>         { return lower_bound<key_type>(__x); }
>>> @@ -785,6 +874,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        lower_bound(const _Key2& __x)
>>>        {
>>> @@ -796,6 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        lower_bound(const _Key2& __x) const
>>>        {
>>> @@ -805,11 +896,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         upper_bound(const key_type& __x)
>>>         { return upper_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         upper_bound(const key_type& __x) const
>>>         { return upper_bound<key_type>(__x); }
>>> @@ -817,6 +910,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        upper_bound(const _Key2& __x)
>>>        {
>>> @@ -828,6 +922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        upper_bound(const _Key2& __x) const
>>>        {
>>> @@ -837,11 +932,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<iterator, iterator>
>>>         equal_range(const key_type& __x)
>>>         { return equal_range<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<const_iterator, const_iterator>
>>>         equal_range(const key_type& __x) const
>>>         { return equal_range<key_type>(__x); }
>>> @@ -849,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, iterator>
>>>        equal_range(const _Key2& __x)
>>>        {
>>> @@ -861,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<const_iterator, const_iterator>
>>>        equal_range(const _Key2& __x) const
>>>        {
>>> @@ -871,7 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Derived& __x, const _Derived& __y)
>>>         {
>>>        return __x._M_cont.keys == __y._M_cont.keys
>>> @@ -880,7 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Up = value_type>
>>>        [[nodiscard]]
>>> -     friend __detail::__synth3way_t<_Up>
>>> +     friend _GLIBCXX26_CONSTEXPR __detail::__synth3way_t<_Up>
>>>        operator<=>(const _Derived& __x, const _Derived& __y)
>>>        {
>>>          return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
>>> @@ -888,11 +987,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                                        __detail::__synth3way);
>>>        }
>>>
>>> -      friend void
>>> +      friend _GLIBCXX26_CONSTEXPR void
>>>         swap(_Derived& __x, _Derived& __y) noexcept
>>>         { return __x.swap(__y); }
>>>
>>>         template<typename _Predicate>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        _M_erase_if(_Predicate __pred)
>>>        {
>>> @@ -912,6 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         containers _M_cont;
>>>         [[no_unique_address]] _Compare _M_comp;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_sort_uniq()
>>>         {
>>> @@ -921,13 +1022,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          _M_unique();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_unique() requires (!_Multi)
>>>         {
>>>        struct __key_equiv
>>>        {
>>> +       _GLIBCXX26_CONSTEXPR
>>>          __key_equiv(key_compare __c) : _M_comp(__c) { }
>>>
>>> +       _GLIBCXX26_CONSTEXPR
>>>          bool
>>>          operator()(const_reference __x, const_reference __y) const
>>>          { return !_M_comp(__x.first, __y.first) && !_M_comp(__y.first, __x.first); }
>>> @@ -958,12 +1062,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                     ranges::__maybe_const_t<_Const, mapped_type>&>;
>>>         using difference_type   = ptrdiff_t;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator() = default;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Iterator<!_Const> __it) requires _Const
>>>         : _M_cont(__it._M_cont), _M_index(__it._M_index)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator*() const noexcept
>>>         {
>>> @@ -975,19 +1082,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        reference __p;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const reference*
>>>        operator->() const noexcept
>>>        { return std::__addressof(__p); }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pointer
>>>         operator->() const
>>>         { return pointer{operator*()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator[](difference_type __n) const noexcept
>>>         { return *(*this + __n); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator++() noexcept
>>>         {
>>> @@ -995,6 +1106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator--() noexcept
>>>         {
>>> @@ -1002,6 +1114,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator++(int) noexcept
>>>         {
>>> @@ -1010,6 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator--(int) noexcept
>>>         {
>>> @@ -1018,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator+=(difference_type __n) noexcept
>>>         {
>>> @@ -1025,6 +1140,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator-=(difference_type __n) noexcept
>>>         {
>>> @@ -1036,45 +1152,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         friend _Flat_map_impl;
>>>         friend _Iterator<!_Const>;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires (!_Const)
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(const _Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires _Const
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(difference_type __n, _Iterator __it) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator-(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it -= __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend difference_type
>>> +      friend _GLIBCXX26_CONSTEXPR difference_type
>>>         operator-(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>>        return __x._M_index - __y._M_index;
>>>         }
>>>
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1082,7 +1200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __x._M_index == __y._M_index;
>>>         }
>>>
>>> -      friend strong_ordering
>>> +      friend _GLIBCXX26_CONSTEXPR strong_ordering
>>>         operator<=>(const _Iterator& __x, const _Iterator& __y)
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1146,30 +1264,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         using _Impl::max_size;
>>>
>>>         // element access
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](const key_type& __x)
>>>         { return try_emplace(__x).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](key_type&& __x)
>>>         { return try_emplace(std::move(__x)).first->second; }
>>>
>>>         template<typename _Key2>
>>>        requires __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        operator[](_Key2&& __x)
>>>        { return try_emplace(std::forward<_Key2>(__x)).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         at(const key_type& __x)
>>>         { return at<key_type>(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_type&
>>>         at(const key_type& __x) const
>>>         { return at<key_type>(__x); }
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        at(const _Key2& __x)
>>>        {
>>> @@ -1181,6 +1305,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const mapped_type&
>>>        at(const _Key2& __x) const
>>>        {
>>> @@ -1203,12 +1328,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(nullopt, __k, std::forward<_Args>(__args)...); }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1222,6 +1349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<mapped_type, _Args...>
>>>          && (!is_convertible_v<_Key2&&, const_iterator>)
>>>          && (!is_convertible_v<_Key2&&, iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(_Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1231,12 +1359,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(__hint, __k, std::forward<_Args>(__args)...).first; }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1248,6 +1378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        requires __transparent_comparator<_Compare>
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1258,6 +1389,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(const key_type& __k, _Mapped&& __obj)
>>>        { return insert_or_assign<const key_type&, _Mapped>(__k, std::forward<_Mapped>(__obj)); }
>>> @@ -1265,6 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1277,6 +1410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(_Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1290,6 +1424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, const key_type& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1300,6 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1312,6 +1448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, _Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1422,6 +1559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> @@ -1590,6 +1728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> index 5bcda3464f1..04c2101aab1 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> @@ -17,7 +17,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -76,6 +76,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -127,6 +128,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(20,42) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -158,6 +160,7 @@ test02()
>>>     VERIFY( m.count(3) == 1 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -186,6 +189,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -218,6 +222,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -227,6 +232,7 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, -4, -5}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -243,6 +249,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -254,6 +261,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test08()
>>>   {
>>> @@ -263,6 +271,7 @@ test08()
>>>     m[k] = 0;
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -274,8 +283,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -290,3 +299,31 @@ main()
>>>     test08();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test08();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> index f143f3acd1b..00644c14061 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> @@ -11,7 +11,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -74,6 +74,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -111,6 +112,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(12,3) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -137,6 +139,7 @@ test02()
>>>     VERIFY( m.count(3) == 2 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -165,6 +168,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -197,6 +201,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -205,6 +210,8 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::keys, (int[]){1, 2, 3, 3, 4, 5}) );
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, 3, -4, -5}) );
>>>   }
>>> +
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -221,6 +228,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -232,6 +240,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -243,8 +252,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -258,3 +267,30 @@ main()
>>>     test07();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> --
>>> 2.52.0
>>>
>>>  From c2a1c42266bdd87c97868735514b621cec3e30bd Mon Sep 17 00:00:00 2001
>>> From: Yuao Ma <c8ef@outlook.com>
>>> Date: Fri, 12 Dec 2025 19:26:01 +0800
>>> Subject: [PATCH] libstdc++: constexpr flat_map and flat_multimap
>>>
>>> This patch makes flat_map and flat_multimap constexpr as part of P3372R3.
>>>
>>> libstdc++-v3/ChangeLog:
>>>
>>>        * include/bits/version.def: Add FTM.
>>>        * include/bits/version.h: Regenerate.
>>>        * include/std/flat_map: Add constexpr.
>>>        * testsuite/23_containers/flat_map/1.cc: Add constexpr test.
>>>        * testsuite/23_containers/flat_multimap/1.cc: Add constexpr test.
>>> ---
>>>   libstdc++-v3/include/bits/version.def         |   8 +
>>>   libstdc++-v3/include/bits/version.h           |  10 ++
>>>   libstdc++-v3/include/std/flat_map             | 157 +++++++++++++++++-
>>>   .../testsuite/23_containers/flat_map/1.cc     |  43 ++++-
>>>   .../23_containers/flat_multimap/1.cc          |  42 ++++-
>>>   5 files changed, 245 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>>> index 5b95db19ac6..f97276d80f2 100644
>>> --- a/libstdc++-v3/include/bits/version.def
>>> +++ b/libstdc++-v3/include/bits/version.def
>>> @@ -1351,6 +1351,14 @@ ftms = {
>>>     };
>>>   };
>>>
>>> +ftms = {
>>> +  name = constexpr_flat_map;
>>> +  values = {
>>> +    v = 202502;
>>> +    cxxmin = 26;
>>> +  };
>>> +};
>>> +
>>>   ftms = {
>>>     name = constexpr_flat_set;
>>>     values = {
>>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>>> index eee9890a72b..97b37e9a62b 100644
>>> --- a/libstdc++-v3/include/bits/version.h
>>> +++ b/libstdc++-v3/include/bits/version.h
>>> @@ -1496,6 +1496,16 @@
>>>   #endif /* !defined(__cpp_lib_constexpr_dynamic_alloc) */
>>>   #undef __glibcxx_want_constexpr_dynamic_alloc
>>>
>>> +#if !defined(__cpp_lib_constexpr_flat_map)
>>> +# if (__cplusplus >  202302L)
>>> +#  define __glibcxx_constexpr_flat_map 202502L
>>> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_flat_map)
>>> +#   define __cpp_lib_constexpr_flat_map 202502L
>>> +#  endif
>>> +# endif
>>> +#endif /* !defined(__cpp_lib_constexpr_flat_map) */
>>> +#undef __glibcxx_want_constexpr_flat_map
>>> +
>>>   #if !defined(__cpp_lib_constexpr_flat_set)
>>>   # if (__cplusplus >  202302L)
>>>   #  define __glibcxx_constexpr_flat_set 202502L
>>> diff --git a/libstdc++-v3/include/std/flat_map b/libstdc++-v3/include/std/flat_map
>>> index 637c3b7fe0d..e270735a87b 100644
>>> --- a/libstdc++-v3/include/std/flat_map
>>> +++ b/libstdc++-v3/include/std/flat_map
>>> @@ -33,6 +33,7 @@
>>>   #pragma GCC system_header
>>>   #endif
>>>
>>> +#define __glibcxx_want_constexpr_flat_map
>>>   #define __glibcxx_want_flat_map
>>>   #include <bits/version.h>
>>>
>>> @@ -108,9 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         class value_compare
>>>         {
>>>        [[no_unique_address]] key_compare _M_comp;
>>> +     _GLIBCXX26_CONSTEXPR
>>>        value_compare(key_compare __c) : _M_comp(__c) { }
>>>
>>>         public:
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        operator()(const_reference __x, const_reference __y) const
>>>        { return _M_comp(__x.first, __y.first); }
>>> @@ -129,10 +132,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        containers* _M_cont;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _ClearGuard(containers& __cont)
>>>        : _M_cont(std::__addressof(__cont))
>>>        { }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        ~_ClearGuard()
>>>        {
>>>          if (_M_cont)
>>> @@ -142,24 +147,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>            }
>>>        }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_disable()
>>>        { _M_cont = nullptr; }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _ClearGuard
>>>         _M_make_clear_guard()
>>>         { return _ClearGuard{this->_M_cont}; }
>>>
>>>       public:
>>>         // constructors
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl() : _Flat_map_impl(key_compare()) { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         explicit
>>>         _Flat_map_impl(const key_compare& __comp)
>>>         : _M_cont(), _M_comp(__comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -169,6 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        _M_sort_uniq();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t,
>>>                     key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>> @@ -180,12 +191,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>>        : _M_cont(), _M_comp(__comp)
>>>        { insert(__first, __last); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>> @@ -193,20 +206,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { insert(__s, __first, __last); }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare())
>>>        { }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp)
>>>        : _Flat_map_impl(__comp)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>>         : _Flat_map_impl(__il.begin(), __il.end(), __comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t __s,
>>>                     initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -216,12 +233,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         // constructors with allocators
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        explicit
>>>        _Flat_map_impl(const _Alloc& __a)
>>>        : _Flat_map_impl(key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_compare& __comp, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a)),
>>> @@ -229,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const _Alloc& __a)
>>> @@ -236,6 +256,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const key_compare& __comp,
>>> @@ -249,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -257,6 +279,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -271,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const _Derived& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a, __x._M_cont.keys),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a, __x._M_cont.values)),
>>> @@ -278,6 +302,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_Derived&& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>
>>>                  (__a, std::move(__x._M_cont.keys)),
>>> @@ -288,6 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(std::move(__first), std::move(__last), key_compare(), __a)
>>> @@ -295,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -303,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>> @@ -311,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>> @@ -320,6 +349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare(), __a)
>>> @@ -327,18 +357,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__comp, __a)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__il, key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -346,6 +379,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>> @@ -353,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>> @@ -360,6 +395,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        : _Flat_map_impl(__s, __il.begin(), __il.end(), __comp, __a)
>>>        { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Derived&
>>>         operator=(initializer_list<value_type> __il)
>>>         {
>>> @@ -369,64 +405,79 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         // iterators
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         begin() noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         begin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         end() noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         end() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rbegin() noexcept
>>>         { return reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rbegin() const noexcept
>>>         { return const_reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rend() noexcept
>>>         { return reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rend() const noexcept
>>>         { return const_reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cbegin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cend() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crbegin() const noexcept
>>>         { return const_reverse_iterator(cend()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crend() const noexcept
>>>         { return const_reverse_iterator(cbegin()); }
>>>
>>>         // capacity
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         empty() const noexcept
>>>         { return _M_cont.keys.empty(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         size() const noexcept
>>>         { return _M_cont.keys.size(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         max_size() const noexcept
>>>         { return std::min<size_type>(keys().max_size(), values().max_size()); }
>>> @@ -436,6 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // modifiers
>>>         template<typename _Key2, typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        _M_try_emplace(optional<const_iterator> __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -491,6 +543,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<value_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        emplace(_Args&&... __args)
>>>        {
>>> @@ -503,6 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        emplace_hint(const_iterator __position, _Args&&... __args)
>>>        {
>>> @@ -510,36 +564,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return _M_try_emplace(__position, std::move(__p.first), std::move(__p.second)).first;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(const value_type& __x)
>>>         { return emplace(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(value_type&& __x)
>>>         { return emplace(std::move(__x)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, const value_type& __x)
>>>         { return emplace_hint(__position, __x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, value_type&& __x)
>>>         { return emplace_hint(__position, std::move(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        insert(_Arg&& __x)
>>>        { return emplace(std::forward<_Arg>(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert(const_iterator __position, _Arg&& __x)
>>>        { return emplace_hint(__position, std::forward<_Arg>(__x)); }
>>>
>>>       private:
>>>         template<typename _Iter, typename _Sent>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_insert(_Iter __first, _Sent __last)
>>>        {
>>> @@ -577,11 +638,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>       public:
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(_InputIterator __first, _InputIterator __last)
>>>        { _M_insert(std::move(__first), std::move(__last)); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(__sorted_t, _InputIterator __first, _InputIterator __last)
>>>        {
>>> @@ -590,18 +653,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert_range(_Rg&& __rg)
>>>        { _M_insert(ranges::begin(__rg), ranges::end(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(initializer_list<value_type> __il)
>>>         { insert(__il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(__sorted_t __s, initializer_list<value_type> __il)
>>>         { insert(__s, __il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         containers
>>>         extract() &&
>>>         {
>>> @@ -609,6 +676,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return {std::move(_M_cont.keys), std::move(_M_cont.values)};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont)
>>>         {
>>> @@ -622,10 +690,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // try_emplace and insert_or_assign defined directly in class flat_map only.
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(iterator __position)
>>>         { return erase(static_cast<const_iterator>(__position)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __position)
>>>         {
>>> @@ -637,6 +707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         erase(const key_type& __x)
>>>         { return erase<const key_type&>(__x); }
>>> @@ -646,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          || (__transparent_comparator<_Compare>
>>>              && !is_convertible_v<_Key2, iterator>
>>>              && !is_convertible_v<_Key2, const_iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        erase(_Key2&& __x)
>>>        {
>>> @@ -655,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return __n;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __first, const_iterator __last)
>>>         {
>>> @@ -667,6 +740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         swap(_Derived& __y) noexcept
>>>         {
>>> @@ -675,6 +749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        ranges::swap(_M_cont.values, __y._M_cont.values);
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         clear() noexcept
>>>         {
>>> @@ -684,32 +759,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // observers
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         key_compare
>>>         key_comp() const
>>>         { return _M_comp; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         value_compare
>>>         value_comp() const
>>>         { return value_compare(_M_comp); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const key_container_type&
>>>         keys() const noexcept
>>>         { return _M_cont.keys; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_container_type&
>>>         values() const noexcept
>>>         { return _M_cont.values; }
>>>
>>>         // map operations
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         find(const key_type& __x)
>>>         { return find<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         find(const key_type& __x) const
>>>         { return find<key_type>(__x); }
>>> @@ -717,6 +798,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        find(const _Key2& __x)
>>>        {
>>> @@ -730,6 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        find(const _Key2& __x) const
>>>        {
>>> @@ -741,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         count(const key_type& __x) const
>>>         { return count<key_type>(__x); }
>>> @@ -748,6 +832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        count(const _Key2& __x) const
>>>        {
>>> @@ -761,6 +846,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         contains(const key_type& __x) const
>>>         { return contains<key_type>(__x); }
>>> @@ -768,16 +854,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        contains(const _Key2& __x) const
>>>        { return find(__x) != cend(); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         lower_bound(const key_type& __x)
>>>         { return lower_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         lower_bound(const key_type& __x) const
>>>         { return lower_bound<key_type>(__x); }
>>> @@ -785,6 +874,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        lower_bound(const _Key2& __x)
>>>        {
>>> @@ -796,6 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        lower_bound(const _Key2& __x) const
>>>        {
>>> @@ -805,11 +896,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         upper_bound(const key_type& __x)
>>>         { return upper_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         upper_bound(const key_type& __x) const
>>>         { return upper_bound<key_type>(__x); }
>>> @@ -817,6 +910,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        upper_bound(const _Key2& __x)
>>>        {
>>> @@ -828,6 +922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        upper_bound(const _Key2& __x) const
>>>        {
>>> @@ -837,11 +932,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<iterator, iterator>
>>>         equal_range(const key_type& __x)
>>>         { return equal_range<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<const_iterator, const_iterator>
>>>         equal_range(const key_type& __x) const
>>>         { return equal_range<key_type>(__x); }
>>> @@ -849,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, iterator>
>>>        equal_range(const _Key2& __x)
>>>        {
>>> @@ -861,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<const_iterator, const_iterator>
>>>        equal_range(const _Key2& __x) const
>>>        {
>>> @@ -871,7 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Derived& __x, const _Derived& __y)
>>>         {
>>>        return __x._M_cont.keys == __y._M_cont.keys
>>> @@ -880,7 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Up = value_type>
>>>        [[nodiscard]]
>>> -     friend __detail::__synth3way_t<_Up>
>>> +     friend _GLIBCXX26_CONSTEXPR __detail::__synth3way_t<_Up>
>>>        operator<=>(const _Derived& __x, const _Derived& __y)
>>>        {
>>>          return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
>>> @@ -888,11 +987,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                                        __detail::__synth3way);
>>>        }
>>>
>>> -      friend void
>>> +      friend _GLIBCXX26_CONSTEXPR void
>>>         swap(_Derived& __x, _Derived& __y) noexcept
>>>         { return __x.swap(__y); }
>>>
>>>         template<typename _Predicate>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        _M_erase_if(_Predicate __pred)
>>>        {
>>> @@ -912,6 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         containers _M_cont;
>>>         [[no_unique_address]] _Compare _M_comp;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_sort_uniq()
>>>         {
>>> @@ -921,13 +1022,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          _M_unique();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_unique() requires (!_Multi)
>>>         {
>>>        struct __key_equiv
>>>        {
>>> +       _GLIBCXX26_CONSTEXPR
>>>          __key_equiv(key_compare __c) : _M_comp(__c) { }
>>>
>>> +       _GLIBCXX26_CONSTEXPR
>>>          bool
>>>          operator()(const_reference __x, const_reference __y) const
>>>          { return !_M_comp(__x.first, __y.first) && !_M_comp(__y.first, __x.first); }
>>> @@ -958,12 +1062,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                     ranges::__maybe_const_t<_Const, mapped_type>&>;
>>>         using difference_type   = ptrdiff_t;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator() = default;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Iterator<!_Const> __it) requires _Const
>>>         : _M_cont(__it._M_cont), _M_index(__it._M_index)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator*() const noexcept
>>>         {
>>> @@ -975,19 +1082,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        reference __p;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const reference*
>>>        operator->() const noexcept
>>>        { return std::__addressof(__p); }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pointer
>>>         operator->() const
>>>         { return pointer{operator*()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator[](difference_type __n) const noexcept
>>>         { return *(*this + __n); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator++() noexcept
>>>         {
>>> @@ -995,6 +1106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator--() noexcept
>>>         {
>>> @@ -1002,6 +1114,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator++(int) noexcept
>>>         {
>>> @@ -1010,6 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator--(int) noexcept
>>>         {
>>> @@ -1018,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator+=(difference_type __n) noexcept
>>>         {
>>> @@ -1025,6 +1140,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator-=(difference_type __n) noexcept
>>>         {
>>> @@ -1036,45 +1152,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         friend _Flat_map_impl;
>>>         friend _Iterator<!_Const>;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires (!_Const)
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(const _Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires _Const
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(difference_type __n, _Iterator __it) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator-(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it -= __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend difference_type
>>> +      friend _GLIBCXX26_CONSTEXPR difference_type
>>>         operator-(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>>        return __x._M_index - __y._M_index;
>>>         }
>>>
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1082,7 +1200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __x._M_index == __y._M_index;
>>>         }
>>>
>>> -      friend strong_ordering
>>> +      friend _GLIBCXX26_CONSTEXPR strong_ordering
>>>         operator<=>(const _Iterator& __x, const _Iterator& __y)
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1146,30 +1264,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         using _Impl::max_size;
>>>
>>>         // element access
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](const key_type& __x)
>>>         { return try_emplace(__x).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](key_type&& __x)
>>>         { return try_emplace(std::move(__x)).first->second; }
>>>
>>>         template<typename _Key2>
>>>        requires __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        operator[](_Key2&& __x)
>>>        { return try_emplace(std::forward<_Key2>(__x)).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         at(const key_type& __x)
>>>         { return at<key_type>(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_type&
>>>         at(const key_type& __x) const
>>>         { return at<key_type>(__x); }
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        at(const _Key2& __x)
>>>        {
>>> @@ -1181,6 +1305,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const mapped_type&
>>>        at(const _Key2& __x) const
>>>        {
>>> @@ -1203,12 +1328,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(nullopt, __k, std::forward<_Args>(__args)...); }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1222,6 +1349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<mapped_type, _Args...>
>>>          && (!is_convertible_v<_Key2&&, const_iterator>)
>>>          && (!is_convertible_v<_Key2&&, iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(_Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1231,12 +1359,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(__hint, __k, std::forward<_Args>(__args)...).first; }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1248,6 +1378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        requires __transparent_comparator<_Compare>
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1258,6 +1389,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(const key_type& __k, _Mapped&& __obj)
>>>        { return insert_or_assign<const key_type&, _Mapped>(__k, std::forward<_Mapped>(__obj)); }
>>> @@ -1265,6 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1277,6 +1410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(_Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1290,6 +1424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, const key_type& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1300,6 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1312,6 +1448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, _Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1422,6 +1559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> @@ -1590,6 +1728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> index 5bcda3464f1..04c2101aab1 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> @@ -17,7 +17,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -76,6 +76,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -127,6 +128,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(20,42) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -158,6 +160,7 @@ test02()
>>>     VERIFY( m.count(3) == 1 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -186,6 +189,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -218,6 +222,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -227,6 +232,7 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, -4, -5}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -243,6 +249,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -254,6 +261,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test08()
>>>   {
>>> @@ -263,6 +271,7 @@ test08()
>>>     m[k] = 0;
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -274,8 +283,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -290,3 +299,31 @@ main()
>>>     test08();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test08();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> index f143f3acd1b..00644c14061 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> @@ -11,7 +11,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -74,6 +74,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -111,6 +112,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(12,3) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -137,6 +139,7 @@ test02()
>>>     VERIFY( m.count(3) == 2 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -165,6 +168,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -197,6 +201,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -205,6 +210,8 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::keys, (int[]){1, 2, 3, 3, 4, 5}) );
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, 3, -4, -5}) );
>>>   }
>>> +
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -221,6 +228,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -232,6 +240,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -243,8 +252,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -258,3 +267,30 @@ main()
>>>     test07();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> --
>>> 2.52.0
>>>
>>>  From c2a1c42266bdd87c97868735514b621cec3e30bd Mon Sep 17 00:00:00 2001
>>> From: Yuao Ma <c8ef@outlook.com>
>>> Date: Fri, 12 Dec 2025 19:26:01 +0800
>>> Subject: [PATCH] libstdc++: constexpr flat_map and flat_multimap
>>>
>>> This patch makes flat_map and flat_multimap constexpr as part of P3372R3.
>>>
>>> libstdc++-v3/ChangeLog:
>>>
>>>        * include/bits/version.def: Add FTM.
>>>        * include/bits/version.h: Regenerate.
>>>        * include/std/flat_map: Add constexpr.
>>>        * testsuite/23_containers/flat_map/1.cc: Add constexpr test.
>>>        * testsuite/23_containers/flat_multimap/1.cc: Add constexpr test.
>>> ---
>>>   libstdc++-v3/include/bits/version.def         |   8 +
>>>   libstdc++-v3/include/bits/version.h           |  10 ++
>>>   libstdc++-v3/include/std/flat_map             | 157 +++++++++++++++++-
>>>   .../testsuite/23_containers/flat_map/1.cc     |  43 ++++-
>>>   .../23_containers/flat_multimap/1.cc          |  42 ++++-
>>>   5 files changed, 245 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>>> index 5b95db19ac6..f97276d80f2 100644
>>> --- a/libstdc++-v3/include/bits/version.def
>>> +++ b/libstdc++-v3/include/bits/version.def
>>> @@ -1351,6 +1351,14 @@ ftms = {
>>>     };
>>>   };
>>>
>>> +ftms = {
>>> +  name = constexpr_flat_map;
>>> +  values = {
>>> +    v = 202502;
>>> +    cxxmin = 26;
>>> +  };
>>> +};
>>> +
>>>   ftms = {
>>>     name = constexpr_flat_set;
>>>     values = {
>>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>>> index eee9890a72b..97b37e9a62b 100644
>>> --- a/libstdc++-v3/include/bits/version.h
>>> +++ b/libstdc++-v3/include/bits/version.h
>>> @@ -1496,6 +1496,16 @@
>>>   #endif /* !defined(__cpp_lib_constexpr_dynamic_alloc) */
>>>   #undef __glibcxx_want_constexpr_dynamic_alloc
>>>
>>> +#if !defined(__cpp_lib_constexpr_flat_map)
>>> +# if (__cplusplus >  202302L)
>>> +#  define __glibcxx_constexpr_flat_map 202502L
>>> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_flat_map)
>>> +#   define __cpp_lib_constexpr_flat_map 202502L
>>> +#  endif
>>> +# endif
>>> +#endif /* !defined(__cpp_lib_constexpr_flat_map) */
>>> +#undef __glibcxx_want_constexpr_flat_map
>>> +
>>>   #if !defined(__cpp_lib_constexpr_flat_set)
>>>   # if (__cplusplus >  202302L)
>>>   #  define __glibcxx_constexpr_flat_set 202502L
>>> diff --git a/libstdc++-v3/include/std/flat_map b/libstdc++-v3/include/std/flat_map
>>> index 637c3b7fe0d..e270735a87b 100644
>>> --- a/libstdc++-v3/include/std/flat_map
>>> +++ b/libstdc++-v3/include/std/flat_map
>>> @@ -33,6 +33,7 @@
>>>   #pragma GCC system_header
>>>   #endif
>>>
>>> +#define __glibcxx_want_constexpr_flat_map
>>>   #define __glibcxx_want_flat_map
>>>   #include <bits/version.h>
>>>
>>> @@ -108,9 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         class value_compare
>>>         {
>>>        [[no_unique_address]] key_compare _M_comp;
>>> +     _GLIBCXX26_CONSTEXPR
>>>        value_compare(key_compare __c) : _M_comp(__c) { }
>>>
>>>         public:
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        operator()(const_reference __x, const_reference __y) const
>>>        { return _M_comp(__x.first, __y.first); }
>>> @@ -129,10 +132,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        containers* _M_cont;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _ClearGuard(containers& __cont)
>>>        : _M_cont(std::__addressof(__cont))
>>>        { }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        ~_ClearGuard()
>>>        {
>>>          if (_M_cont)
>>> @@ -142,24 +147,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>            }
>>>        }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_disable()
>>>        { _M_cont = nullptr; }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _ClearGuard
>>>         _M_make_clear_guard()
>>>         { return _ClearGuard{this->_M_cont}; }
>>>
>>>       public:
>>>         // constructors
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl() : _Flat_map_impl(key_compare()) { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         explicit
>>>         _Flat_map_impl(const key_compare& __comp)
>>>         : _M_cont(), _M_comp(__comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -169,6 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        _M_sort_uniq();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t,
>>>                     key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>> @@ -180,12 +191,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>>        : _M_cont(), _M_comp(__comp)
>>>        { insert(__first, __last); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>> @@ -193,20 +206,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { insert(__s, __first, __last); }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare())
>>>        { }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp)
>>>        : _Flat_map_impl(__comp)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>>         : _Flat_map_impl(__il.begin(), __il.end(), __comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t __s,
>>>                     initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -216,12 +233,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         // constructors with allocators
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        explicit
>>>        _Flat_map_impl(const _Alloc& __a)
>>>        : _Flat_map_impl(key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_compare& __comp, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a)),
>>> @@ -229,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const _Alloc& __a)
>>> @@ -236,6 +256,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const key_compare& __comp,
>>> @@ -249,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -257,6 +279,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -271,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const _Derived& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a, __x._M_cont.keys),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a, __x._M_cont.values)),
>>> @@ -278,6 +302,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_Derived&& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>
>>>                  (__a, std::move(__x._M_cont.keys)),
>>> @@ -288,6 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(std::move(__first), std::move(__last), key_compare(), __a)
>>> @@ -295,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -303,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>> @@ -311,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>> @@ -320,6 +349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare(), __a)
>>> @@ -327,18 +357,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__comp, __a)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__il, key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -346,6 +379,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>> @@ -353,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>> @@ -360,6 +395,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        : _Flat_map_impl(__s, __il.begin(), __il.end(), __comp, __a)
>>>        { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Derived&
>>>         operator=(initializer_list<value_type> __il)
>>>         {
>>> @@ -369,64 +405,79 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         // iterators
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         begin() noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         begin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         end() noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         end() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rbegin() noexcept
>>>         { return reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rbegin() const noexcept
>>>         { return const_reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rend() noexcept
>>>         { return reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rend() const noexcept
>>>         { return const_reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cbegin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cend() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crbegin() const noexcept
>>>         { return const_reverse_iterator(cend()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crend() const noexcept
>>>         { return const_reverse_iterator(cbegin()); }
>>>
>>>         // capacity
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         empty() const noexcept
>>>         { return _M_cont.keys.empty(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         size() const noexcept
>>>         { return _M_cont.keys.size(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         max_size() const noexcept
>>>         { return std::min<size_type>(keys().max_size(), values().max_size()); }
>>> @@ -436,6 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // modifiers
>>>         template<typename _Key2, typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        _M_try_emplace(optional<const_iterator> __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -491,6 +543,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<value_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        emplace(_Args&&... __args)
>>>        {
>>> @@ -503,6 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        emplace_hint(const_iterator __position, _Args&&... __args)
>>>        {
>>> @@ -510,36 +564,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return _M_try_emplace(__position, std::move(__p.first), std::move(__p.second)).first;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(const value_type& __x)
>>>         { return emplace(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(value_type&& __x)
>>>         { return emplace(std::move(__x)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, const value_type& __x)
>>>         { return emplace_hint(__position, __x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, value_type&& __x)
>>>         { return emplace_hint(__position, std::move(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        insert(_Arg&& __x)
>>>        { return emplace(std::forward<_Arg>(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert(const_iterator __position, _Arg&& __x)
>>>        { return emplace_hint(__position, std::forward<_Arg>(__x)); }
>>>
>>>       private:
>>>         template<typename _Iter, typename _Sent>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_insert(_Iter __first, _Sent __last)
>>>        {
>>> @@ -577,11 +638,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>       public:
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(_InputIterator __first, _InputIterator __last)
>>>        { _M_insert(std::move(__first), std::move(__last)); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(__sorted_t, _InputIterator __first, _InputIterator __last)
>>>        {
>>> @@ -590,18 +653,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert_range(_Rg&& __rg)
>>>        { _M_insert(ranges::begin(__rg), ranges::end(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(initializer_list<value_type> __il)
>>>         { insert(__il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(__sorted_t __s, initializer_list<value_type> __il)
>>>         { insert(__s, __il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         containers
>>>         extract() &&
>>>         {
>>> @@ -609,6 +676,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return {std::move(_M_cont.keys), std::move(_M_cont.values)};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont)
>>>         {
>>> @@ -622,10 +690,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // try_emplace and insert_or_assign defined directly in class flat_map only.
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(iterator __position)
>>>         { return erase(static_cast<const_iterator>(__position)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __position)
>>>         {
>>> @@ -637,6 +707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         erase(const key_type& __x)
>>>         { return erase<const key_type&>(__x); }
>>> @@ -646,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          || (__transparent_comparator<_Compare>
>>>              && !is_convertible_v<_Key2, iterator>
>>>              && !is_convertible_v<_Key2, const_iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        erase(_Key2&& __x)
>>>        {
>>> @@ -655,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return __n;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __first, const_iterator __last)
>>>         {
>>> @@ -667,6 +740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         swap(_Derived& __y) noexcept
>>>         {
>>> @@ -675,6 +749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        ranges::swap(_M_cont.values, __y._M_cont.values);
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         clear() noexcept
>>>         {
>>> @@ -684,32 +759,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // observers
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         key_compare
>>>         key_comp() const
>>>         { return _M_comp; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         value_compare
>>>         value_comp() const
>>>         { return value_compare(_M_comp); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const key_container_type&
>>>         keys() const noexcept
>>>         { return _M_cont.keys; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_container_type&
>>>         values() const noexcept
>>>         { return _M_cont.values; }
>>>
>>>         // map operations
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         find(const key_type& __x)
>>>         { return find<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         find(const key_type& __x) const
>>>         { return find<key_type>(__x); }
>>> @@ -717,6 +798,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        find(const _Key2& __x)
>>>        {
>>> @@ -730,6 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        find(const _Key2& __x) const
>>>        {
>>> @@ -741,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         count(const key_type& __x) const
>>>         { return count<key_type>(__x); }
>>> @@ -748,6 +832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        count(const _Key2& __x) const
>>>        {
>>> @@ -761,6 +846,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         contains(const key_type& __x) const
>>>         { return contains<key_type>(__x); }
>>> @@ -768,16 +854,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        contains(const _Key2& __x) const
>>>        { return find(__x) != cend(); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         lower_bound(const key_type& __x)
>>>         { return lower_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         lower_bound(const key_type& __x) const
>>>         { return lower_bound<key_type>(__x); }
>>> @@ -785,6 +874,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        lower_bound(const _Key2& __x)
>>>        {
>>> @@ -796,6 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        lower_bound(const _Key2& __x) const
>>>        {
>>> @@ -805,11 +896,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         upper_bound(const key_type& __x)
>>>         { return upper_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         upper_bound(const key_type& __x) const
>>>         { return upper_bound<key_type>(__x); }
>>> @@ -817,6 +910,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        upper_bound(const _Key2& __x)
>>>        {
>>> @@ -828,6 +922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        upper_bound(const _Key2& __x) const
>>>        {
>>> @@ -837,11 +932,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<iterator, iterator>
>>>         equal_range(const key_type& __x)
>>>         { return equal_range<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<const_iterator, const_iterator>
>>>         equal_range(const key_type& __x) const
>>>         { return equal_range<key_type>(__x); }
>>> @@ -849,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, iterator>
>>>        equal_range(const _Key2& __x)
>>>        {
>>> @@ -861,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<const_iterator, const_iterator>
>>>        equal_range(const _Key2& __x) const
>>>        {
>>> @@ -871,7 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Derived& __x, const _Derived& __y)
>>>         {
>>>        return __x._M_cont.keys == __y._M_cont.keys
>>> @@ -880,7 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Up = value_type>
>>>        [[nodiscard]]
>>> -     friend __detail::__synth3way_t<_Up>
>>> +     friend _GLIBCXX26_CONSTEXPR __detail::__synth3way_t<_Up>
>>>        operator<=>(const _Derived& __x, const _Derived& __y)
>>>        {
>>>          return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
>>> @@ -888,11 +987,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                                        __detail::__synth3way);
>>>        }
>>>
>>> -      friend void
>>> +      friend _GLIBCXX26_CONSTEXPR void
>>>         swap(_Derived& __x, _Derived& __y) noexcept
>>>         { return __x.swap(__y); }
>>>
>>>         template<typename _Predicate>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        _M_erase_if(_Predicate __pred)
>>>        {
>>> @@ -912,6 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         containers _M_cont;
>>>         [[no_unique_address]] _Compare _M_comp;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_sort_uniq()
>>>         {
>>> @@ -921,13 +1022,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          _M_unique();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_unique() requires (!_Multi)
>>>         {
>>>        struct __key_equiv
>>>        {
>>> +       _GLIBCXX26_CONSTEXPR
>>>          __key_equiv(key_compare __c) : _M_comp(__c) { }
>>>
>>> +       _GLIBCXX26_CONSTEXPR
>>>          bool
>>>          operator()(const_reference __x, const_reference __y) const
>>>          { return !_M_comp(__x.first, __y.first) && !_M_comp(__y.first, __x.first); }
>>> @@ -958,12 +1062,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                     ranges::__maybe_const_t<_Const, mapped_type>&>;
>>>         using difference_type   = ptrdiff_t;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator() = default;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Iterator<!_Const> __it) requires _Const
>>>         : _M_cont(__it._M_cont), _M_index(__it._M_index)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator*() const noexcept
>>>         {
>>> @@ -975,19 +1082,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        reference __p;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const reference*
>>>        operator->() const noexcept
>>>        { return std::__addressof(__p); }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pointer
>>>         operator->() const
>>>         { return pointer{operator*()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator[](difference_type __n) const noexcept
>>>         { return *(*this + __n); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator++() noexcept
>>>         {
>>> @@ -995,6 +1106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator--() noexcept
>>>         {
>>> @@ -1002,6 +1114,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator++(int) noexcept
>>>         {
>>> @@ -1010,6 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator--(int) noexcept
>>>         {
>>> @@ -1018,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator+=(difference_type __n) noexcept
>>>         {
>>> @@ -1025,6 +1140,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator-=(difference_type __n) noexcept
>>>         {
>>> @@ -1036,45 +1152,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         friend _Flat_map_impl;
>>>         friend _Iterator<!_Const>;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires (!_Const)
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(const _Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires _Const
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(difference_type __n, _Iterator __it) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator-(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it -= __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend difference_type
>>> +      friend _GLIBCXX26_CONSTEXPR difference_type
>>>         operator-(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>>        return __x._M_index - __y._M_index;
>>>         }
>>>
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1082,7 +1200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __x._M_index == __y._M_index;
>>>         }
>>>
>>> -      friend strong_ordering
>>> +      friend _GLIBCXX26_CONSTEXPR strong_ordering
>>>         operator<=>(const _Iterator& __x, const _Iterator& __y)
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1146,30 +1264,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         using _Impl::max_size;
>>>
>>>         // element access
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](const key_type& __x)
>>>         { return try_emplace(__x).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](key_type&& __x)
>>>         { return try_emplace(std::move(__x)).first->second; }
>>>
>>>         template<typename _Key2>
>>>        requires __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        operator[](_Key2&& __x)
>>>        { return try_emplace(std::forward<_Key2>(__x)).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         at(const key_type& __x)
>>>         { return at<key_type>(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_type&
>>>         at(const key_type& __x) const
>>>         { return at<key_type>(__x); }
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        at(const _Key2& __x)
>>>        {
>>> @@ -1181,6 +1305,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const mapped_type&
>>>        at(const _Key2& __x) const
>>>        {
>>> @@ -1203,12 +1328,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(nullopt, __k, std::forward<_Args>(__args)...); }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1222,6 +1349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<mapped_type, _Args...>
>>>          && (!is_convertible_v<_Key2&&, const_iterator>)
>>>          && (!is_convertible_v<_Key2&&, iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(_Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1231,12 +1359,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(__hint, __k, std::forward<_Args>(__args)...).first; }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1248,6 +1378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        requires __transparent_comparator<_Compare>
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1258,6 +1389,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(const key_type& __k, _Mapped&& __obj)
>>>        { return insert_or_assign<const key_type&, _Mapped>(__k, std::forward<_Mapped>(__obj)); }
>>> @@ -1265,6 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1277,6 +1410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(_Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1290,6 +1424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, const key_type& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1300,6 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1312,6 +1448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, _Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1422,6 +1559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> @@ -1590,6 +1728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> index 5bcda3464f1..04c2101aab1 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> @@ -17,7 +17,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -76,6 +76,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -127,6 +128,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(20,42) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -158,6 +160,7 @@ test02()
>>>     VERIFY( m.count(3) == 1 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -186,6 +189,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -218,6 +222,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -227,6 +232,7 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, -4, -5}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -243,6 +249,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -254,6 +261,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test08()
>>>   {
>>> @@ -263,6 +271,7 @@ test08()
>>>     m[k] = 0;
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -274,8 +283,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -290,3 +299,31 @@ main()
>>>     test08();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test08();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> index f143f3acd1b..00644c14061 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> @@ -11,7 +11,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -74,6 +74,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -111,6 +112,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(12,3) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -137,6 +139,7 @@ test02()
>>>     VERIFY( m.count(3) == 2 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -165,6 +168,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -197,6 +201,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -205,6 +210,8 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::keys, (int[]){1, 2, 3, 3, 4, 5}) );
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, 3, -4, -5}) );
>>>   }
>>> +
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -221,6 +228,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -232,6 +240,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -243,8 +252,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -258,3 +267,30 @@ main()
>>>     test07();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> --
>>> 2.52.0
>>>
>>>  From c2a1c42266bdd87c97868735514b621cec3e30bd Mon Sep 17 00:00:00 2001
>>> From: Yuao Ma <c8ef@outlook.com>
>>> Date: Fri, 12 Dec 2025 19:26:01 +0800
>>> Subject: [PATCH] libstdc++: constexpr flat_map and flat_multimap
>>>
>>> This patch makes flat_map and flat_multimap constexpr as part of P3372R3.
>>>
>>> libstdc++-v3/ChangeLog:
>>>
>>>        * include/bits/version.def: Add FTM.
>>>        * include/bits/version.h: Regenerate.
>>>        * include/std/flat_map: Add constexpr.
>>>        * testsuite/23_containers/flat_map/1.cc: Add constexpr test.
>>>        * testsuite/23_containers/flat_multimap/1.cc: Add constexpr test.
>>> ---
>>>   libstdc++-v3/include/bits/version.def         |   8 +
>>>   libstdc++-v3/include/bits/version.h           |  10 ++
>>>   libstdc++-v3/include/std/flat_map             | 157 +++++++++++++++++-
>>>   .../testsuite/23_containers/flat_map/1.cc     |  43 ++++-
>>>   .../23_containers/flat_multimap/1.cc          |  42 ++++-
>>>   5 files changed, 245 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>>> index 5b95db19ac6..f97276d80f2 100644
>>> --- a/libstdc++-v3/include/bits/version.def
>>> +++ b/libstdc++-v3/include/bits/version.def
>>> @@ -1351,6 +1351,14 @@ ftms = {
>>>     };
>>>   };
>>>
>>> +ftms = {
>>> +  name = constexpr_flat_map;
>>> +  values = {
>>> +    v = 202502;
>>> +    cxxmin = 26;
>>> +  };
>>> +};
>>> +
>>>   ftms = {
>>>     name = constexpr_flat_set;
>>>     values = {
>>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>>> index eee9890a72b..97b37e9a62b 100644
>>> --- a/libstdc++-v3/include/bits/version.h
>>> +++ b/libstdc++-v3/include/bits/version.h
>>> @@ -1496,6 +1496,16 @@
>>>   #endif /* !defined(__cpp_lib_constexpr_dynamic_alloc) */
>>>   #undef __glibcxx_want_constexpr_dynamic_alloc
>>>
>>> +#if !defined(__cpp_lib_constexpr_flat_map)
>>> +# if (__cplusplus >  202302L)
>>> +#  define __glibcxx_constexpr_flat_map 202502L
>>> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_flat_map)
>>> +#   define __cpp_lib_constexpr_flat_map 202502L
>>> +#  endif
>>> +# endif
>>> +#endif /* !defined(__cpp_lib_constexpr_flat_map) */
>>> +#undef __glibcxx_want_constexpr_flat_map
>>> +
>>>   #if !defined(__cpp_lib_constexpr_flat_set)
>>>   # if (__cplusplus >  202302L)
>>>   #  define __glibcxx_constexpr_flat_set 202502L
>>> diff --git a/libstdc++-v3/include/std/flat_map b/libstdc++-v3/include/std/flat_map
>>> index 637c3b7fe0d..e270735a87b 100644
>>> --- a/libstdc++-v3/include/std/flat_map
>>> +++ b/libstdc++-v3/include/std/flat_map
>>> @@ -33,6 +33,7 @@
>>>   #pragma GCC system_header
>>>   #endif
>>>
>>> +#define __glibcxx_want_constexpr_flat_map
>>>   #define __glibcxx_want_flat_map
>>>   #include <bits/version.h>
>>>
>>> @@ -108,9 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         class value_compare
>>>         {
>>>        [[no_unique_address]] key_compare _M_comp;
>>> +     _GLIBCXX26_CONSTEXPR
>>>        value_compare(key_compare __c) : _M_comp(__c) { }
>>>
>>>         public:
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        operator()(const_reference __x, const_reference __y) const
>>>        { return _M_comp(__x.first, __y.first); }
>>> @@ -129,10 +132,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        containers* _M_cont;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _ClearGuard(containers& __cont)
>>>        : _M_cont(std::__addressof(__cont))
>>>        { }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        ~_ClearGuard()
>>>        {
>>>          if (_M_cont)
>>> @@ -142,24 +147,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>            }
>>>        }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_disable()
>>>        { _M_cont = nullptr; }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _ClearGuard
>>>         _M_make_clear_guard()
>>>         { return _ClearGuard{this->_M_cont}; }
>>>
>>>       public:
>>>         // constructors
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl() : _Flat_map_impl(key_compare()) { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         explicit
>>>         _Flat_map_impl(const key_compare& __comp)
>>>         : _M_cont(), _M_comp(__comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -169,6 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        _M_sort_uniq();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t,
>>>                     key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>> @@ -180,12 +191,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>>        : _M_cont(), _M_comp(__comp)
>>>        { insert(__first, __last); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>> @@ -193,20 +206,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { insert(__s, __first, __last); }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare())
>>>        { }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp)
>>>        : _Flat_map_impl(__comp)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>>         : _Flat_map_impl(__il.begin(), __il.end(), __comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t __s,
>>>                     initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -216,12 +233,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         // constructors with allocators
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        explicit
>>>        _Flat_map_impl(const _Alloc& __a)
>>>        : _Flat_map_impl(key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_compare& __comp, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a)),
>>> @@ -229,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const _Alloc& __a)
>>> @@ -236,6 +256,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const key_compare& __comp,
>>> @@ -249,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -257,6 +279,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -271,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const _Derived& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a, __x._M_cont.keys),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a, __x._M_cont.values)),
>>> @@ -278,6 +302,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_Derived&& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>
>>>                  (__a, std::move(__x._M_cont.keys)),
>>> @@ -288,6 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(std::move(__first), std::move(__last), key_compare(), __a)
>>> @@ -295,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -303,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>> @@ -311,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>> @@ -320,6 +349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare(), __a)
>>> @@ -327,18 +357,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__comp, __a)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__il, key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -346,6 +379,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>> @@ -353,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>> @@ -360,6 +395,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        : _Flat_map_impl(__s, __il.begin(), __il.end(), __comp, __a)
>>>        { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Derived&
>>>         operator=(initializer_list<value_type> __il)
>>>         {
>>> @@ -369,64 +405,79 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         // iterators
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         begin() noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         begin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         end() noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         end() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rbegin() noexcept
>>>         { return reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rbegin() const noexcept
>>>         { return const_reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rend() noexcept
>>>         { return reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rend() const noexcept
>>>         { return const_reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cbegin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cend() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crbegin() const noexcept
>>>         { return const_reverse_iterator(cend()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crend() const noexcept
>>>         { return const_reverse_iterator(cbegin()); }
>>>
>>>         // capacity
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         empty() const noexcept
>>>         { return _M_cont.keys.empty(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         size() const noexcept
>>>         { return _M_cont.keys.size(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         max_size() const noexcept
>>>         { return std::min<size_type>(keys().max_size(), values().max_size()); }
>>> @@ -436,6 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // modifiers
>>>         template<typename _Key2, typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        _M_try_emplace(optional<const_iterator> __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -491,6 +543,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<value_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        emplace(_Args&&... __args)
>>>        {
>>> @@ -503,6 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        emplace_hint(const_iterator __position, _Args&&... __args)
>>>        {
>>> @@ -510,36 +564,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return _M_try_emplace(__position, std::move(__p.first), std::move(__p.second)).first;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(const value_type& __x)
>>>         { return emplace(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(value_type&& __x)
>>>         { return emplace(std::move(__x)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, const value_type& __x)
>>>         { return emplace_hint(__position, __x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, value_type&& __x)
>>>         { return emplace_hint(__position, std::move(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        insert(_Arg&& __x)
>>>        { return emplace(std::forward<_Arg>(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert(const_iterator __position, _Arg&& __x)
>>>        { return emplace_hint(__position, std::forward<_Arg>(__x)); }
>>>
>>>       private:
>>>         template<typename _Iter, typename _Sent>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_insert(_Iter __first, _Sent __last)
>>>        {
>>> @@ -577,11 +638,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>       public:
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(_InputIterator __first, _InputIterator __last)
>>>        { _M_insert(std::move(__first), std::move(__last)); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(__sorted_t, _InputIterator __first, _InputIterator __last)
>>>        {
>>> @@ -590,18 +653,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert_range(_Rg&& __rg)
>>>        { _M_insert(ranges::begin(__rg), ranges::end(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(initializer_list<value_type> __il)
>>>         { insert(__il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(__sorted_t __s, initializer_list<value_type> __il)
>>>         { insert(__s, __il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         containers
>>>         extract() &&
>>>         {
>>> @@ -609,6 +676,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return {std::move(_M_cont.keys), std::move(_M_cont.values)};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont)
>>>         {
>>> @@ -622,10 +690,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // try_emplace and insert_or_assign defined directly in class flat_map only.
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(iterator __position)
>>>         { return erase(static_cast<const_iterator>(__position)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __position)
>>>         {
>>> @@ -637,6 +707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         erase(const key_type& __x)
>>>         { return erase<const key_type&>(__x); }
>>> @@ -646,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          || (__transparent_comparator<_Compare>
>>>              && !is_convertible_v<_Key2, iterator>
>>>              && !is_convertible_v<_Key2, const_iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        erase(_Key2&& __x)
>>>        {
>>> @@ -655,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return __n;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __first, const_iterator __last)
>>>         {
>>> @@ -667,6 +740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         swap(_Derived& __y) noexcept
>>>         {
>>> @@ -675,6 +749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        ranges::swap(_M_cont.values, __y._M_cont.values);
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         clear() noexcept
>>>         {
>>> @@ -684,32 +759,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // observers
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         key_compare
>>>         key_comp() const
>>>         { return _M_comp; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         value_compare
>>>         value_comp() const
>>>         { return value_compare(_M_comp); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const key_container_type&
>>>         keys() const noexcept
>>>         { return _M_cont.keys; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_container_type&
>>>         values() const noexcept
>>>         { return _M_cont.values; }
>>>
>>>         // map operations
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         find(const key_type& __x)
>>>         { return find<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         find(const key_type& __x) const
>>>         { return find<key_type>(__x); }
>>> @@ -717,6 +798,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        find(const _Key2& __x)
>>>        {
>>> @@ -730,6 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        find(const _Key2& __x) const
>>>        {
>>> @@ -741,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         count(const key_type& __x) const
>>>         { return count<key_type>(__x); }
>>> @@ -748,6 +832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        count(const _Key2& __x) const
>>>        {
>>> @@ -761,6 +846,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         contains(const key_type& __x) const
>>>         { return contains<key_type>(__x); }
>>> @@ -768,16 +854,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        contains(const _Key2& __x) const
>>>        { return find(__x) != cend(); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         lower_bound(const key_type& __x)
>>>         { return lower_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         lower_bound(const key_type& __x) const
>>>         { return lower_bound<key_type>(__x); }
>>> @@ -785,6 +874,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        lower_bound(const _Key2& __x)
>>>        {
>>> @@ -796,6 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        lower_bound(const _Key2& __x) const
>>>        {
>>> @@ -805,11 +896,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         upper_bound(const key_type& __x)
>>>         { return upper_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         upper_bound(const key_type& __x) const
>>>         { return upper_bound<key_type>(__x); }
>>> @@ -817,6 +910,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        upper_bound(const _Key2& __x)
>>>        {
>>> @@ -828,6 +922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        upper_bound(const _Key2& __x) const
>>>        {
>>> @@ -837,11 +932,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<iterator, iterator>
>>>         equal_range(const key_type& __x)
>>>         { return equal_range<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<const_iterator, const_iterator>
>>>         equal_range(const key_type& __x) const
>>>         { return equal_range<key_type>(__x); }
>>> @@ -849,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, iterator>
>>>        equal_range(const _Key2& __x)
>>>        {
>>> @@ -861,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<const_iterator, const_iterator>
>>>        equal_range(const _Key2& __x) const
>>>        {
>>> @@ -871,7 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Derived& __x, const _Derived& __y)
>>>         {
>>>        return __x._M_cont.keys == __y._M_cont.keys
>>> @@ -880,7 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Up = value_type>
>>>        [[nodiscard]]
>>> -     friend __detail::__synth3way_t<_Up>
>>> +     friend _GLIBCXX26_CONSTEXPR __detail::__synth3way_t<_Up>
>>>        operator<=>(const _Derived& __x, const _Derived& __y)
>>>        {
>>>          return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
>>> @@ -888,11 +987,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                                        __detail::__synth3way);
>>>        }
>>>
>>> -      friend void
>>> +      friend _GLIBCXX26_CONSTEXPR void
>>>         swap(_Derived& __x, _Derived& __y) noexcept
>>>         { return __x.swap(__y); }
>>>
>>>         template<typename _Predicate>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        _M_erase_if(_Predicate __pred)
>>>        {
>>> @@ -912,6 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         containers _M_cont;
>>>         [[no_unique_address]] _Compare _M_comp;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_sort_uniq()
>>>         {
>>> @@ -921,13 +1022,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          _M_unique();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_unique() requires (!_Multi)
>>>         {
>>>        struct __key_equiv
>>>        {
>>> +       _GLIBCXX26_CONSTEXPR
>>>          __key_equiv(key_compare __c) : _M_comp(__c) { }
>>>
>>> +       _GLIBCXX26_CONSTEXPR
>>>          bool
>>>          operator()(const_reference __x, const_reference __y) const
>>>          { return !_M_comp(__x.first, __y.first) && !_M_comp(__y.first, __x.first); }
>>> @@ -958,12 +1062,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                     ranges::__maybe_const_t<_Const, mapped_type>&>;
>>>         using difference_type   = ptrdiff_t;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator() = default;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Iterator<!_Const> __it) requires _Const
>>>         : _M_cont(__it._M_cont), _M_index(__it._M_index)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator*() const noexcept
>>>         {
>>> @@ -975,19 +1082,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        reference __p;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const reference*
>>>        operator->() const noexcept
>>>        { return std::__addressof(__p); }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pointer
>>>         operator->() const
>>>         { return pointer{operator*()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator[](difference_type __n) const noexcept
>>>         { return *(*this + __n); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator++() noexcept
>>>         {
>>> @@ -995,6 +1106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator--() noexcept
>>>         {
>>> @@ -1002,6 +1114,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator++(int) noexcept
>>>         {
>>> @@ -1010,6 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator--(int) noexcept
>>>         {
>>> @@ -1018,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator+=(difference_type __n) noexcept
>>>         {
>>> @@ -1025,6 +1140,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator-=(difference_type __n) noexcept
>>>         {
>>> @@ -1036,45 +1152,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         friend _Flat_map_impl;
>>>         friend _Iterator<!_Const>;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires (!_Const)
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(const _Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires _Const
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(difference_type __n, _Iterator __it) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator-(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it -= __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend difference_type
>>> +      friend _GLIBCXX26_CONSTEXPR difference_type
>>>         operator-(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>>        return __x._M_index - __y._M_index;
>>>         }
>>>
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1082,7 +1200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __x._M_index == __y._M_index;
>>>         }
>>>
>>> -      friend strong_ordering
>>> +      friend _GLIBCXX26_CONSTEXPR strong_ordering
>>>         operator<=>(const _Iterator& __x, const _Iterator& __y)
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1146,30 +1264,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         using _Impl::max_size;
>>>
>>>         // element access
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](const key_type& __x)
>>>         { return try_emplace(__x).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](key_type&& __x)
>>>         { return try_emplace(std::move(__x)).first->second; }
>>>
>>>         template<typename _Key2>
>>>        requires __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        operator[](_Key2&& __x)
>>>        { return try_emplace(std::forward<_Key2>(__x)).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         at(const key_type& __x)
>>>         { return at<key_type>(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_type&
>>>         at(const key_type& __x) const
>>>         { return at<key_type>(__x); }
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        at(const _Key2& __x)
>>>        {
>>> @@ -1181,6 +1305,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const mapped_type&
>>>        at(const _Key2& __x) const
>>>        {
>>> @@ -1203,12 +1328,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(nullopt, __k, std::forward<_Args>(__args)...); }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1222,6 +1349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<mapped_type, _Args...>
>>>          && (!is_convertible_v<_Key2&&, const_iterator>)
>>>          && (!is_convertible_v<_Key2&&, iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(_Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1231,12 +1359,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(__hint, __k, std::forward<_Args>(__args)...).first; }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1248,6 +1378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        requires __transparent_comparator<_Compare>
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1258,6 +1389,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(const key_type& __k, _Mapped&& __obj)
>>>        { return insert_or_assign<const key_type&, _Mapped>(__k, std::forward<_Mapped>(__obj)); }
>>> @@ -1265,6 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1277,6 +1410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(_Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1290,6 +1424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, const key_type& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1300,6 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1312,6 +1448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, _Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1422,6 +1559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> @@ -1590,6 +1728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> index 5bcda3464f1..04c2101aab1 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> @@ -17,7 +17,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -76,6 +76,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -127,6 +128,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(20,42) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -158,6 +160,7 @@ test02()
>>>     VERIFY( m.count(3) == 1 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -186,6 +189,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -218,6 +222,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -227,6 +232,7 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, -4, -5}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -243,6 +249,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -254,6 +261,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test08()
>>>   {
>>> @@ -263,6 +271,7 @@ test08()
>>>     m[k] = 0;
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -274,8 +283,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -290,3 +299,31 @@ main()
>>>     test08();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test08();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> index f143f3acd1b..00644c14061 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> @@ -11,7 +11,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -74,6 +74,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -111,6 +112,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(12,3) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -137,6 +139,7 @@ test02()
>>>     VERIFY( m.count(3) == 2 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -165,6 +168,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -197,6 +201,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -205,6 +210,8 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::keys, (int[]){1, 2, 3, 3, 4, 5}) );
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, 3, -4, -5}) );
>>>   }
>>> +
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -221,6 +228,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -232,6 +240,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -243,8 +252,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -258,3 +267,30 @@ main()
>>>     test07();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> --
>>> 2.52.0
>>>
>>>  From c2a1c42266bdd87c97868735514b621cec3e30bd Mon Sep 17 00:00:00 2001
>>> From: Yuao Ma <c8ef@outlook.com>
>>> Date: Fri, 12 Dec 2025 19:26:01 +0800
>>> Subject: [PATCH] libstdc++: constexpr flat_map and flat_multimap
>>>
>>> This patch makes flat_map and flat_multimap constexpr as part of P3372R3.
>>>
>>> libstdc++-v3/ChangeLog:
>>>
>>>        * include/bits/version.def: Add FTM.
>>>        * include/bits/version.h: Regenerate.
>>>        * include/std/flat_map: Add constexpr.
>>>        * testsuite/23_containers/flat_map/1.cc: Add constexpr test.
>>>        * testsuite/23_containers/flat_multimap/1.cc: Add constexpr test.
>>> ---
>>>   libstdc++-v3/include/bits/version.def         |   8 +
>>>   libstdc++-v3/include/bits/version.h           |  10 ++
>>>   libstdc++-v3/include/std/flat_map             | 157 +++++++++++++++++-
>>>   .../testsuite/23_containers/flat_map/1.cc     |  43 ++++-
>>>   .../23_containers/flat_multimap/1.cc          |  42 ++++-
>>>   5 files changed, 245 insertions(+), 15 deletions(-)
>>>
>>> diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
>>> index 5b95db19ac6..f97276d80f2 100644
>>> --- a/libstdc++-v3/include/bits/version.def
>>> +++ b/libstdc++-v3/include/bits/version.def
>>> @@ -1351,6 +1351,14 @@ ftms = {
>>>     };
>>>   };
>>>
>>> +ftms = {
>>> +  name = constexpr_flat_map;
>>> +  values = {
>>> +    v = 202502;
>>> +    cxxmin = 26;
>>> +  };
>>> +};
>>> +
>>>   ftms = {
>>>     name = constexpr_flat_set;
>>>     values = {
>>> diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
>>> index eee9890a72b..97b37e9a62b 100644
>>> --- a/libstdc++-v3/include/bits/version.h
>>> +++ b/libstdc++-v3/include/bits/version.h
>>> @@ -1496,6 +1496,16 @@
>>>   #endif /* !defined(__cpp_lib_constexpr_dynamic_alloc) */
>>>   #undef __glibcxx_want_constexpr_dynamic_alloc
>>>
>>> +#if !defined(__cpp_lib_constexpr_flat_map)
>>> +# if (__cplusplus >  202302L)
>>> +#  define __glibcxx_constexpr_flat_map 202502L
>>> +#  if defined(__glibcxx_want_all) || defined(__glibcxx_want_constexpr_flat_map)
>>> +#   define __cpp_lib_constexpr_flat_map 202502L
>>> +#  endif
>>> +# endif
>>> +#endif /* !defined(__cpp_lib_constexpr_flat_map) */
>>> +#undef __glibcxx_want_constexpr_flat_map
>>> +
>>>   #if !defined(__cpp_lib_constexpr_flat_set)
>>>   # if (__cplusplus >  202302L)
>>>   #  define __glibcxx_constexpr_flat_set 202502L
>>> diff --git a/libstdc++-v3/include/std/flat_map b/libstdc++-v3/include/std/flat_map
>>> index 637c3b7fe0d..e270735a87b 100644
>>> --- a/libstdc++-v3/include/std/flat_map
>>> +++ b/libstdc++-v3/include/std/flat_map
>>> @@ -33,6 +33,7 @@
>>>   #pragma GCC system_header
>>>   #endif
>>>
>>> +#define __glibcxx_want_constexpr_flat_map
>>>   #define __glibcxx_want_flat_map
>>>   #include <bits/version.h>
>>>
>>> @@ -108,9 +109,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         class value_compare
>>>         {
>>>        [[no_unique_address]] key_compare _M_comp;
>>> +     _GLIBCXX26_CONSTEXPR
>>>        value_compare(key_compare __c) : _M_comp(__c) { }
>>>
>>>         public:
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        operator()(const_reference __x, const_reference __y) const
>>>        { return _M_comp(__x.first, __y.first); }
>>> @@ -129,10 +132,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        containers* _M_cont;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _ClearGuard(containers& __cont)
>>>        : _M_cont(std::__addressof(__cont))
>>>        { }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        ~_ClearGuard()
>>>        {
>>>          if (_M_cont)
>>> @@ -142,24 +147,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>            }
>>>        }
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_disable()
>>>        { _M_cont = nullptr; }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _ClearGuard
>>>         _M_make_clear_guard()
>>>         { return _ClearGuard{this->_M_cont}; }
>>>
>>>       public:
>>>         // constructors
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl() : _Flat_map_impl(key_compare()) { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         explicit
>>>         _Flat_map_impl(const key_compare& __comp)
>>>         : _M_cont(), _M_comp(__comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -169,6 +179,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        _M_sort_uniq();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t,
>>>                     key_container_type __key_cont,
>>>                     mapped_container_type __mapped_cont,
>>> @@ -180,12 +191,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>>        : _M_cont(), _M_comp(__comp)
>>>        { insert(__first, __last); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp = key_compare())
>>> @@ -193,20 +206,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { insert(__s, __first, __last); }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare())
>>>        { }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp)
>>>        : _Flat_map_impl(__comp)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>>         : _Flat_map_impl(__il.begin(), __il.end(), __comp)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Flat_map_impl(__sorted_t __s,
>>>                     initializer_list<value_type> __il,
>>>                     const key_compare& __comp = key_compare())
>>> @@ -216,12 +233,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         // constructors with allocators
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        explicit
>>>        _Flat_map_impl(const _Alloc& __a)
>>>        : _Flat_map_impl(key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_compare& __comp, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a)),
>>> @@ -229,6 +248,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const _Alloc& __a)
>>> @@ -236,6 +256,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>>                       const key_compare& __comp,
>>> @@ -249,6 +270,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -257,6 +279,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t,
>>>                       const key_container_type& __key_cont,
>>>                       const mapped_container_type& __mapped_cont,
>>> @@ -271,6 +294,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(const _Derived& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>(__a, __x._M_cont.keys),
>>>                  std::make_obj_using_allocator<mapped_container_type>(__a, __x._M_cont.values)),
>>> @@ -278,6 +302,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_Derived&& __x, const _Alloc& __a)
>>>        : _M_cont(std::make_obj_using_allocator<key_container_type>
>>>                  (__a, std::move(__x._M_cont.keys)),
>>> @@ -288,6 +313,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(std::move(__first), std::move(__last), key_compare(), __a)
>>> @@ -295,6 +321,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(_InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -303,6 +330,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const _Alloc& __a)
>>> @@ -311,6 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__has_input_iter_cat _InputIterator,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       _InputIterator __first, _InputIterator __last,
>>>                       const key_compare& __comp,
>>> @@ -320,6 +349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(from_range, std::forward<_Rg>(__rg), key_compare(), __a)
>>> @@ -327,18 +357,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg,
>>>               __allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(from_range_t, _Rg&& __rg, const key_compare& __comp,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__comp, __a)
>>>        { insert_range(std::forward<_Rg>(__rg)); }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>>        : _Flat_map_impl(__il, key_compare(), __a)
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>>                       const _Alloc& __a)
>>> @@ -346,6 +379,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const _Alloc& __a)
>>> @@ -353,6 +387,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        { }
>>>
>>>         template<__allocator_for<key_container_type, mapped_container_type> _Alloc>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        _Flat_map_impl(__sorted_t __s,
>>>                       initializer_list<value_type> __il,
>>>                       const key_compare& __comp,
>>> @@ -360,6 +395,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        : _Flat_map_impl(__s, __il.begin(), __il.end(), __comp, __a)
>>>        { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Derived&
>>>         operator=(initializer_list<value_type> __il)
>>>         {
>>> @@ -369,64 +405,79 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         }
>>>
>>>         // iterators
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         begin() noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         begin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         end() noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         end() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rbegin() noexcept
>>>         { return reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rbegin() const noexcept
>>>         { return const_reverse_iterator(end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reverse_iterator
>>>         rend() noexcept
>>>         { return reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         rend() const noexcept
>>>         { return const_reverse_iterator(begin()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cbegin() const noexcept
>>>         { return {this, _M_cont.keys.cbegin()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         cend() const noexcept
>>>         { return {this, _M_cont.keys.cend()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crbegin() const noexcept
>>>         { return const_reverse_iterator(cend()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_reverse_iterator
>>>         crend() const noexcept
>>>         { return const_reverse_iterator(cbegin()); }
>>>
>>>         // capacity
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         empty() const noexcept
>>>         { return _M_cont.keys.empty(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         size() const noexcept
>>>         { return _M_cont.keys.size(); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         max_size() const noexcept
>>>         { return std::min<size_type>(keys().max_size(), values().max_size()); }
>>> @@ -436,6 +487,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // modifiers
>>>         template<typename _Key2, typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        _M_try_emplace(optional<const_iterator> __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -491,6 +543,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<value_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        emplace(_Args&&... __args)
>>>        {
>>> @@ -503,6 +556,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<typename... _Args>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        emplace_hint(const_iterator __position, _Args&&... __args)
>>>        {
>>> @@ -510,36 +564,43 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return _M_try_emplace(__position, std::move(__p.first), std::move(__p.second)).first;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(const value_type& __x)
>>>         { return emplace(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         __emplace_result_t
>>>         insert(value_type&& __x)
>>>         { return emplace(std::move(__x)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, const value_type& __x)
>>>         { return emplace_hint(__position, __x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         insert(const_iterator __position, value_type&& __x)
>>>         { return emplace_hint(__position, std::move(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        __emplace_result_t
>>>        insert(_Arg&& __x)
>>>        { return emplace(std::forward<_Arg>(__x)); }
>>>
>>>         template<typename _Arg>
>>>        requires is_constructible_v<value_type, _Arg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert(const_iterator __position, _Arg&& __x)
>>>        { return emplace_hint(__position, std::forward<_Arg>(__x)); }
>>>
>>>       private:
>>>         template<typename _Iter, typename _Sent>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        _M_insert(_Iter __first, _Sent __last)
>>>        {
>>> @@ -577,11 +638,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>       public:
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(_InputIterator __first, _InputIterator __last)
>>>        { _M_insert(std::move(__first), std::move(__last)); }
>>>
>>>         template<__has_input_iter_cat _InputIterator>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert(__sorted_t, _InputIterator __first, _InputIterator __last)
>>>        {
>>> @@ -590,18 +653,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         template<__detail::__container_compatible_range<value_type> _Rg>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        void
>>>        insert_range(_Rg&& __rg)
>>>        { _M_insert(ranges::begin(__rg), ranges::end(__rg)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(initializer_list<value_type> __il)
>>>         { insert(__il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         insert(__sorted_t __s, initializer_list<value_type> __il)
>>>         { insert(__s, __il.begin(), __il.end()); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         containers
>>>         extract() &&
>>>         {
>>> @@ -609,6 +676,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return {std::move(_M_cont.keys), std::move(_M_cont.values)};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont)
>>>         {
>>> @@ -622,10 +690,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // try_emplace and insert_or_assign defined directly in class flat_map only.
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(iterator __position)
>>>         { return erase(static_cast<const_iterator>(__position)); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __position)
>>>         {
>>> @@ -637,6 +707,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         erase(const key_type& __x)
>>>         { return erase<const key_type&>(__x); }
>>> @@ -646,6 +717,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          || (__transparent_comparator<_Compare>
>>>              && !is_convertible_v<_Key2, iterator>
>>>              && !is_convertible_v<_Key2, const_iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        erase(_Key2&& __x)
>>>        {
>>> @@ -655,6 +727,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          return __n;
>>>        }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         erase(const_iterator __first, const_iterator __last)
>>>         {
>>> @@ -667,6 +740,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return iterator{this, __it};
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         swap(_Derived& __y) noexcept
>>>         {
>>> @@ -675,6 +749,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        ranges::swap(_M_cont.values, __y._M_cont.values);
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         clear() noexcept
>>>         {
>>> @@ -684,32 +759,38 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         // observers
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         key_compare
>>>         key_comp() const
>>>         { return _M_comp; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         value_compare
>>>         value_comp() const
>>>         { return value_compare(_M_comp); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const key_container_type&
>>>         keys() const noexcept
>>>         { return _M_cont.keys; }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_container_type&
>>>         values() const noexcept
>>>         { return _M_cont.values; }
>>>
>>>         // map operations
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         find(const key_type& __x)
>>>         { return find<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         find(const key_type& __x) const
>>>         { return find<key_type>(__x); }
>>> @@ -717,6 +798,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        find(const _Key2& __x)
>>>        {
>>> @@ -730,6 +812,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        find(const _Key2& __x) const
>>>        {
>>> @@ -741,6 +824,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         size_type
>>>         count(const key_type& __x) const
>>>         { return count<key_type>(__x); }
>>> @@ -748,6 +832,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        count(const _Key2& __x) const
>>>        {
>>> @@ -761,6 +846,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         bool
>>>         contains(const key_type& __x) const
>>>         { return contains<key_type>(__x); }
>>> @@ -768,16 +854,19 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        bool
>>>        contains(const _Key2& __x) const
>>>        { return find(__x) != cend(); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         lower_bound(const key_type& __x)
>>>         { return lower_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         lower_bound(const key_type& __x) const
>>>         { return lower_bound<key_type>(__x); }
>>> @@ -785,6 +874,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        lower_bound(const _Key2& __x)
>>>        {
>>> @@ -796,6 +886,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        lower_bound(const _Key2& __x) const
>>>        {
>>> @@ -805,11 +896,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         iterator
>>>         upper_bound(const key_type& __x)
>>>         { return upper_bound<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const_iterator
>>>         upper_bound(const key_type& __x) const
>>>         { return upper_bound<key_type>(__x); }
>>> @@ -817,6 +910,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        upper_bound(const _Key2& __x)
>>>        {
>>> @@ -828,6 +922,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const_iterator
>>>        upper_bound(const _Key2& __x) const
>>>        {
>>> @@ -837,11 +932,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<iterator, iterator>
>>>         equal_range(const key_type& __x)
>>>         { return equal_range<key_type>(__x); }
>>>
>>>         [[nodiscard]]
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pair<const_iterator, const_iterator>
>>>         equal_range(const key_type& __x) const
>>>         { return equal_range<key_type>(__x); }
>>> @@ -849,6 +946,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, iterator>
>>>        equal_range(const _Key2& __x)
>>>        {
>>> @@ -861,6 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>>        [[nodiscard]]
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<const_iterator, const_iterator>
>>>        equal_range(const _Key2& __x) const
>>>        {
>>> @@ -871,7 +970,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        }
>>>
>>>         [[nodiscard]]
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Derived& __x, const _Derived& __y)
>>>         {
>>>        return __x._M_cont.keys == __y._M_cont.keys
>>> @@ -880,7 +979,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Up = value_type>
>>>        [[nodiscard]]
>>> -     friend __detail::__synth3way_t<_Up>
>>> +     friend _GLIBCXX26_CONSTEXPR __detail::__synth3way_t<_Up>
>>>        operator<=>(const _Derived& __x, const _Derived& __y)
>>>        {
>>>          return std::lexicographical_compare_three_way(__x.begin(), __x.end(),
>>> @@ -888,11 +987,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                                        __detail::__synth3way);
>>>        }
>>>
>>> -      friend void
>>> +      friend _GLIBCXX26_CONSTEXPR void
>>>         swap(_Derived& __x, _Derived& __y) noexcept
>>>         { return __x.swap(__y); }
>>>
>>>         template<typename _Predicate>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        size_type
>>>        _M_erase_if(_Predicate __pred)
>>>        {
>>> @@ -912,6 +1012,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         containers _M_cont;
>>>         [[no_unique_address]] _Compare _M_comp;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_sort_uniq()
>>>         {
>>> @@ -921,13 +1022,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          _M_unique();
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         void
>>>         _M_unique() requires (!_Multi)
>>>         {
>>>        struct __key_equiv
>>>        {
>>> +       _GLIBCXX26_CONSTEXPR
>>>          __key_equiv(key_compare __c) : _M_comp(__c) { }
>>>
>>> +       _GLIBCXX26_CONSTEXPR
>>>          bool
>>>          operator()(const_reference __x, const_reference __y) const
>>>          { return !_M_comp(__x.first, __y.first) && !_M_comp(__y.first, __x.first); }
>>> @@ -958,12 +1062,15 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>                                     ranges::__maybe_const_t<_Const, mapped_type>&>;
>>>         using difference_type   = ptrdiff_t;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator() = default;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Iterator<!_Const> __it) requires _Const
>>>         : _M_cont(__it._M_cont), _M_index(__it._M_index)
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator*() const noexcept
>>>         {
>>> @@ -975,19 +1082,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         {
>>>        reference __p;
>>>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const reference*
>>>        operator->() const noexcept
>>>        { return std::__addressof(__p); }
>>>         };
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         pointer
>>>         operator->() const
>>>         { return pointer{operator*()}; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         reference
>>>         operator[](difference_type __n) const noexcept
>>>         { return *(*this + __n); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator++() noexcept
>>>         {
>>> @@ -995,6 +1106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator--() noexcept
>>>         {
>>> @@ -1002,6 +1114,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator++(int) noexcept
>>>         {
>>> @@ -1010,6 +1123,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator
>>>         operator--(int) noexcept
>>>         {
>>> @@ -1018,6 +1132,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __tmp;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator+=(difference_type __n) noexcept
>>>         {
>>> @@ -1025,6 +1140,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return *this;
>>>         }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator&
>>>         operator-=(difference_type __n) noexcept
>>>         {
>>> @@ -1036,45 +1152,47 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         friend _Flat_map_impl;
>>>         friend _Iterator<!_Const>;
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(_Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires (!_Const)
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         _Iterator(const _Flat_map_impl* __fm, typename key_container_type::const_iterator __it)
>>>         requires _Const
>>>         : _M_cont(std::__addressof(__fm->_M_cont)), _M_index(__it - __fm->keys().cbegin())
>>>         { }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator+(difference_type __n, _Iterator __it) noexcept
>>>         {
>>>        __it += __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend _Iterator
>>> +      friend _GLIBCXX26_CONSTEXPR _Iterator
>>>         operator-(_Iterator __it, difference_type __n) noexcept
>>>         {
>>>        __it -= __n;
>>>        return __it;
>>>         }
>>>
>>> -      friend difference_type
>>> +      friend _GLIBCXX26_CONSTEXPR difference_type
>>>         operator-(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>>        return __x._M_index - __y._M_index;
>>>         }
>>>
>>> -      friend bool
>>> +      friend _GLIBCXX26_CONSTEXPR bool
>>>         operator==(const _Iterator& __x, const _Iterator& __y) noexcept
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1082,7 +1200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        return __x._M_index == __y._M_index;
>>>         }
>>>
>>> -      friend strong_ordering
>>> +      friend _GLIBCXX26_CONSTEXPR strong_ordering
>>>         operator<=>(const _Iterator& __x, const _Iterator& __y)
>>>         {
>>>        __glibcxx_assert(__x._M_cont == __y._M_cont);
>>> @@ -1146,30 +1264,36 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         using _Impl::max_size;
>>>
>>>         // element access
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](const key_type& __x)
>>>         { return try_emplace(__x).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         operator[](key_type&& __x)
>>>         { return try_emplace(std::move(__x)).first->second; }
>>>
>>>         template<typename _Key2>
>>>        requires __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        operator[](_Key2&& __x)
>>>        { return try_emplace(std::forward<_Key2>(__x)).first->second; }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         mapped_type&
>>>         at(const key_type& __x)
>>>         { return at<key_type>(__x); }
>>>
>>> +      _GLIBCXX26_CONSTEXPR
>>>         const mapped_type&
>>>         at(const key_type& __x) const
>>>         { return at<key_type>(__x); }
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        mapped_type&
>>>        at(const _Key2& __x)
>>>        {
>>> @@ -1181,6 +1305,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename _Key2>
>>>        requires same_as<_Key2, _Key> || __transparent_comparator<_Compare>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        const mapped_type&
>>>        at(const _Key2& __x) const
>>>        {
>>> @@ -1203,12 +1328,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(nullopt, __k, std::forward<_Args>(__args)...); }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1222,6 +1349,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<mapped_type, _Args...>
>>>          && (!is_convertible_v<_Key2&&, const_iterator>)
>>>          && (!is_convertible_v<_Key2&&, iterator>)
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        try_emplace(_Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1231,12 +1359,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, const key_type& __k, _Args&&... __args)
>>>        { return _Impl::_M_try_emplace(__hint, __k, std::forward<_Args>(__args)...).first; }
>>>
>>>         template<typename... _Args>
>>>        requires is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, key_type&& __k, _Args&&... __args)
>>>        {
>>> @@ -1248,6 +1378,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>        requires __transparent_comparator<_Compare>
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_constructible_v<mapped_type, _Args...>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        try_emplace(const_iterator __hint, _Key2&& __k, _Args&&... __args)
>>>        {
>>> @@ -1258,6 +1389,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(const key_type& __k, _Mapped&& __obj)
>>>        { return insert_or_assign<const key_type&, _Mapped>(__k, std::forward<_Mapped>(__obj)); }
>>> @@ -1265,6 +1397,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1277,6 +1410,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        pair<iterator, bool>
>>>        insert_or_assign(_Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1290,6 +1424,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, const key_type& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1300,6 +1435,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>         template<typename _Mapped>
>>>        requires is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, key_type&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1312,6 +1448,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>          && is_constructible_v<key_type, _Key2>
>>>          && is_assignable_v<mapped_type&, _Mapped>
>>>          && is_constructible_v<mapped_type, _Mapped>
>>> +     _GLIBCXX26_CONSTEXPR
>>>        iterator
>>>        insert_or_assign(const_iterator __hint, _Key2&& __k, _Mapped&& __obj)
>>>        {
>>> @@ -1422,6 +1559,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> @@ -1590,6 +1728,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>
>>>     template<typename _Key, typename _Tp, typename _Compare,
>>>           typename _KeyContainer, typename _MappedContainer, typename _Predicate>
>>> +    _GLIBCXX26_CONSTEXPR
>>>       typename flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
>>>       erase_if(flat_multimap<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __c,
>>>             _Predicate __pred)
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> index 5bcda3464f1..04c2101aab1 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_map/1.cc
>>> @@ -17,7 +17,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -76,6 +76,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -127,6 +128,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(20,42) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -158,6 +160,7 @@ test02()
>>>     VERIFY( m.count(3) == 1 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -186,6 +189,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -218,6 +222,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -227,6 +232,7 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, -4, -5}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -243,6 +249,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -254,6 +261,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test08()
>>>   {
>>> @@ -263,6 +271,7 @@ test08()
>>>     m[k] = 0;
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -274,8 +283,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -290,3 +299,31 @@ main()
>>>     test08();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test08();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> diff --git a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> index f143f3acd1b..00644c14061 100644
>>> --- a/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> +++ b/libstdc++-v3/testsuite/23_containers/flat_multimap/1.cc
>>> @@ -11,7 +11,7 @@
>>>
>>>   struct Gt {
>>>     template<typename T, typename U>
>>> -  bool operator()(T const& l, U const & r) const
>>> +  constexpr bool operator()(T const& l, U const & r) const
>>>     { return l > r; }
>>>   };
>>>
>>> @@ -74,6 +74,7 @@ test_deduction_guide()
>>>   }
>>>
>>>   template<template<typename> class KeyContainer, template<typename> class MappedContainer>
>>> +constexpr
>>>   void
>>>   test01()
>>>   {
>>> @@ -111,6 +112,7 @@ test01()
>>>     VERIFY( m.end()[-1] == std::pair(12,3) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test02()
>>>   {
>>> @@ -137,6 +139,7 @@ test02()
>>>     VERIFY( m.count(3) == 2 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test03()
>>>   {
>>> @@ -165,6 +168,7 @@ test03()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int, int>[]){{5, 6}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test04()
>>>   {
>>> @@ -197,6 +201,7 @@ test04()
>>>     VERIFY( m5.values().get_allocator().get_personality() == 44 );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test05()
>>>   {
>>> @@ -205,6 +210,8 @@ test05()
>>>     VERIFY( std::ranges::equal(m | std::views::keys, (int[]){1, 2, 3, 3, 4, 5}) );
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){-1, -2, -3, 3, -4, -5}) );
>>>   }
>>> +
>>> +constexpr
>>>   void
>>>   test06()
>>>   {
>>> @@ -221,6 +228,7 @@ test06()
>>>     VERIFY( std::ranges::equal(m | std::views::values, (int[]){2, 3, 4, 5, 6}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test07()
>>>   {
>>> @@ -232,6 +240,7 @@ test07()
>>>     VERIFY( std::ranges::equal(m, (std::pair<int,int>[]){{3,4},{3,3}}) );
>>>   }
>>>
>>> +constexpr
>>>   void
>>>   test09()
>>>   {
>>> @@ -243,8 +252,8 @@ test09()
>>>     using value_type = std::pair<int, int>;
>>>   }
>>>
>>> -int
>>> -main()
>>> +void
>>> +test()
>>>   {
>>>     test01<std::vector, std::vector>();
>>>     test01<std::deque, std::deque>();
>>> @@ -258,3 +267,30 @@ main()
>>>     test07();
>>>     test09();
>>>   }
>>> +
>>> +constexpr
>>> +bool
>>> +test_constexpr()
>>> +{
>>> +  test01<std::vector, std::vector>();
>>> +  test02();
>>> +  test03();
>>> +  test04();
>>> +  test05();
>>> +  test06();
>>> +  test07();
>>> +  test09();
>>> +  return true;
>>> +}
>>> +
>>> +int
>>> +main()
>>> +{
>>> +  test();
>>> +#if __cplusplus > 202302L
>>> +  static_assert(test_constexpr());
>>> +#if __cpp_lib_constexpr_flat_map != 202502L
>>> +#error "Feature-test macro __cpp_lib_constexpr_flat_map has wrong value in <flat_map>"
>>> +#endif
>>> +#endif
>>> +}
>>> --
>>> 2.52.0
>>>
>>


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