[libcxx-commits] [libcxx] [libc++] constexpr flat_map (PR #137453)

via libcxx-commits libcxx-commits at lists.llvm.org
Sat Apr 26 03:06:10 PDT 2025


https://github.com/huixie90 created https://github.com/llvm/llvm-project/pull/137453

None

>From 360224cf3b9b19013bda4cc2aaad49c840dcd3e9 Mon Sep 17 00:00:00 2001
From: Hui Xie <hui.xie1990 at gmail.com>
Date: Sat, 26 Apr 2025 11:05:21 +0100
Subject: [PATCH] [libc++] constexpr flat_map

---
 libcxx/include/__flat_map/flat_map.h          | 391 +++++++++++-------
 .../include/__flat_map/key_value_iterator.h   |  58 ++-
 libcxx/include/__flat_map/utils.h             |   4 +-
 libcxx/test/std/containers/Emplaceable.h      |  16 +-
 .../flat.map/flat.map.access/at.pass.cpp      |  41 +-
 .../flat.map.access/at_transparent.pass.cpp   |  40 +-
 .../flat.map.access/index_key.pass.cpp        |  25 +-
 .../flat.map.access/index_rv_key.pass.cpp     |  23 +-
 .../index_transparent.pass.cpp                |  25 +-
 .../flat.map/flat.map.capacity/empty.pass.cpp |  22 +-
 .../flat.map.capacity/max_size.pass.cpp       |  12 +-
 .../flat.map/flat.map.capacity/size.pass.cpp  |  23 +-
 .../flat.map/flat.map.cons/alloc.pass.cpp     |  46 ++-
 .../assign_initializer_list.pass.cpp          |  22 +-
 .../flat.map/flat.map.cons/compare.pass.cpp   | 108 +++--
 .../flat.map.cons/containers.pass.cpp         | 153 ++++---
 .../flat.map/flat.map.cons/copy.pass.cpp      |  32 +-
 .../flat.map.cons/copy_alloc.pass.cpp         |  58 ++-
 .../flat.map.cons/copy_assign.pass.cpp        |  35 +-
 .../flat.map/flat.map.cons/default.pass.cpp   |  40 +-
 .../flat.map.cons/default_noexcept.pass.cpp   |  16 +-
 .../flat.map.cons/dtor_noexcept.pass.cpp      |  41 +-
 .../flat.map.cons/initializer_list.pass.cpp   | 159 +++----
 .../flat.map/flat.map.cons/iter_iter.pass.cpp | 189 ++++++---
 .../flat.map/flat.map.cons/move.pass.cpp      |  35 +-
 .../flat.map.cons/move_alloc.pass.cpp         |  64 ++-
 .../flat.map.cons/move_assign.pass.cpp        |  31 +-
 .../flat.map.cons/move_assign_clears.pass.cpp |  43 +-
 ... => move_assign_noexcept.compile.pass.cpp} |   4 +-
 .../flat.map/flat.map.cons/range.pass.cpp     | 241 +++++++----
 .../flat.map.cons/sorted_container.pass.cpp   | 118 +++---
 .../sorted_initializer_list.pass.cpp          | 164 ++++----
 .../flat.map.cons/sorted_iter_iter.pass.cpp   | 127 ++++--
 .../flat.map.erasure/erase_if.pass.cpp        |  28 +-
 .../flat.map.iterators/iterator.pass.cpp      |  20 +-
 .../iterator_comparison.pass.cpp              |  20 +-
 .../reverse_iterator.pass.cpp                 | 100 +++--
 .../flat.map.modifiers/clear.pass.cpp         |  20 +-
 .../flat.map.modifiers/emplace.pass.cpp       |  26 +-
 .../flat.map.modifiers/emplace_hint.pass.cpp  |  27 +-
 .../flat.map.modifiers/erase_iter.pass.cpp    |  23 +-
 .../erase_iter_iter.pass.cpp                  |  24 +-
 .../flat.map.modifiers/erase_key.pass.cpp     |  23 +-
 .../erase_key_transparent.pass.cpp            |  33 +-
 .../flat.map.modifiers/extract.pass.cpp       |  23 +-
 .../flat.map.modifiers/insert_cv.pass.cpp     |  23 +-
 .../insert_initializer_list.pass.cpp          |  39 +-
 .../insert_iter_cv.pass.cpp                   |  23 +-
 .../insert_iter_iter.pass.cpp                 |  50 ++-
 .../insert_iter_rv.pass.cpp                   |  26 +-
 .../insert_or_assign.pass.cpp                 |  24 +-
 .../insert_or_assign_transparent.pass.cpp     |  52 ++-
 .../flat.map.modifiers/insert_range.pass.cpp  |  27 +-
 .../flat.map.modifiers/insert_rv.pass.cpp     |  24 +-
 .../insert_sorted_initializer_list.pass.cpp   |  39 +-
 .../insert_sorted_iter_iter.pass.cpp          |  22 +-
 .../insert_transparent.pass.cpp               | 159 +++----
 .../flat.map.modifiers/replace.pass.cpp       |  23 +-
 .../flat.map.modifiers/swap_free.pass.cpp     |  20 +-
 .../flat.map.modifiers/swap_member.pass.cpp   |  20 +-
 .../flat.map.modifiers/try_emplace.pass.cpp   |  94 +++--
 .../try_emplace_transparent.pass.cpp          |  54 ++-
 .../flat.map/flat.map.observers/comp.pass.cpp |  17 +-
 .../flat.map.observers/keys_values.pass.cpp   |  20 +-
 .../flat.map.operations/contains.pass.cpp     |  20 +-
 .../contains_transparent.pass.cpp             |  21 +-
 .../flat.map.operations/count.pass.cpp        |  20 +-
 .../count_transparent.pass.cpp                |  20 +-
 .../flat.map.operations/equal_range.pass.cpp  |  20 +-
 .../equal_range_transparent.pass.cpp          |  20 +-
 .../flat.map.operations/find.pass.cpp         |  20 +-
 .../find_transparent.pass.cpp                 |  20 +-
 .../flat.map.operations/lower_bound.pass.cpp  |  20 +-
 .../lower_bound_transparent.pass.cpp          |  20 +-
 .../flat.map.operations/upper_bound.pass.cpp  |  20 +-
 .../upper_bound_transparent.pass.cpp          |  20 +-
 .../container.adaptors/flat.map/helpers.h     |  11 +-
 .../flat.map/incomplete_type.pass.cpp         |  17 +-
 .../flat.map/op_compare.pass.cpp              |  23 +-
 .../container.adaptors/flat_helpers.h         |  37 +-
 libcxx/test/std/containers/test_compare.h     |  18 +-
 libcxx/test/support/MinSequenceContainer.h    |  41 +-
 82 files changed, 2695 insertions(+), 1222 deletions(-)
 rename libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/{move_assign_noexcept.pass.cpp => move_assign_noexcept.compile.pass.cpp} (99%)

diff --git a/libcxx/include/__flat_map/flat_map.h b/libcxx/include/__flat_map/flat_map.h
index f5abfd0985280..452938595b7d4 100644
--- a/libcxx/include/__flat_map/flat_map.h
+++ b/libcxx/include/__flat_map/flat_map.h
@@ -115,11 +115,12 @@ class flat_map {
   class value_compare {
   private:
     key_compare __comp_;
-    _LIBCPP_HIDE_FROM_ABI value_compare(key_compare __c) : __comp_(__c) {}
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare(key_compare __c) : __comp_(__c) {}
     friend flat_map;
 
   public:
-    _LIBCPP_HIDE_FROM_ABI bool operator()(const_reference __x, const_reference __y) const {
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool
+    operator()(const_reference __x, const_reference __y) const {
       return __comp_(__x.first, __y.first);
     }
   };
@@ -138,14 +139,14 @@ class flat_map {
 
 public:
   // [flat.map.cons], construct/copy/destroy
-  _LIBCPP_HIDE_FROM_ABI flat_map() noexcept(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map() noexcept(
       is_nothrow_default_constructible_v<_KeyContainer> && is_nothrow_default_constructible_v<_MappedContainer> &&
       is_nothrow_default_constructible_v<_Compare>)
       : __containers_(), __compare_() {}
 
   _LIBCPP_HIDE_FROM_ABI flat_map(const flat_map&) = default;
 
-  _LIBCPP_HIDE_FROM_ABI flat_map(flat_map&& __other) noexcept(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(flat_map&& __other) noexcept(
       is_nothrow_move_constructible_v<_KeyContainer> && is_nothrow_move_constructible_v<_MappedContainer> &&
       is_nothrow_move_constructible_v<_Compare>)
 #  if _LIBCPP_HAS_EXCEPTIONS
@@ -166,7 +167,7 @@ class flat_map {
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(const flat_map& __other, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(const flat_map& __other, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_tag{},
                  __alloc,
                  __other.__containers_.keys,
@@ -175,7 +176,7 @@ class flat_map {
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(flat_map&& __other, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(flat_map&& __other, const _Allocator& __alloc)
 #  if _LIBCPP_HAS_EXCEPTIONS
       try
 #  endif // _LIBCPP_HAS_EXCEPTIONS
@@ -192,7 +193,7 @@ class flat_map {
 #  endif // _LIBCPP_HAS_EXCEPTIONS
   }
 
-  _LIBCPP_HIDE_FROM_ABI flat_map(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(
       key_container_type __key_cont, mapped_container_type __mapped_cont, const key_compare& __comp = key_compare())
       : __containers_{.keys = std::move(__key_cont), .values = std::move(__mapped_cont)}, __compare_(__comp) {
     _LIBCPP_ASSERT_VALID_INPUT_RANGE(__containers_.keys.size() == __containers_.values.size(),
@@ -202,7 +203,7 @@ class flat_map {
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(const key_container_type& __key_cont, const mapped_container_type& __mapped_cont, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_tag{}, __alloc, __key_cont, __mapped_cont) {
     _LIBCPP_ASSERT_VALID_INPUT_RANGE(__containers_.keys.size() == __containers_.values.size(),
@@ -212,7 +213,7 @@ class flat_map {
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(const key_container_type& __key_cont,
            const mapped_container_type& __mapped_cont,
            const key_compare& __comp,
@@ -223,7 +224,7 @@ class flat_map {
     __sort_and_unique();
   }
 
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(sorted_unique_t,
            key_container_type __key_cont,
            mapped_container_type __mapped_cont,
@@ -237,7 +238,7 @@ class flat_map {
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(sorted_unique_t,
            const key_container_type& __key_cont,
            const mapped_container_type& __mapped_cont,
@@ -251,12 +252,12 @@ class flat_map {
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
-  flat_map(sorted_unique_t,
-           const key_container_type& __key_cont,
-           const mapped_container_type& __mapped_cont,
-           const key_compare& __comp,
-           const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(
+      sorted_unique_t,
+      const key_container_type& __key_cont,
+      const mapped_container_type& __mapped_cont,
+      const key_compare& __comp,
+      const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_tag{}, __alloc, __key_cont, __mapped_cont, __comp) {
     _LIBCPP_ASSERT_VALID_INPUT_RANGE(__containers_.keys.size() == __containers_.values.size(),
                                      "flat_map keys and mapped containers have different size");
@@ -264,21 +265,22 @@ class flat_map {
         __is_sorted_and_unique(__containers_.keys), "Either the key container is not sorted or it contains duplicates");
   }
 
-  _LIBCPP_HIDE_FROM_ABI explicit flat_map(const key_compare& __comp) : __containers_(), __compare_(__comp) {}
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit flat_map(const key_compare& __comp)
+      : __containers_(), __compare_(__comp) {}
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(const key_compare& __comp, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(const key_compare& __comp, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc, __comp) {}
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI explicit flat_map(const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 explicit flat_map(const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc) {}
 
   template <class _InputIterator>
     requires __has_input_iterator_category<_InputIterator>::value
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(_InputIterator __first, _InputIterator __last, const key_compare& __comp = key_compare())
       : __containers_(), __compare_(__comp) {
     insert(__first, __last);
@@ -286,7 +288,7 @@ class flat_map {
 
   template <class _InputIterator, class _Allocator>
     requires(__has_input_iterator_category<_InputIterator>::value && __allocator_ctor_constraint<_Allocator>)
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(_InputIterator __first, _InputIterator __last, const key_compare& __comp, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc, __comp) {
     insert(__first, __last);
@@ -294,99 +296,105 @@ class flat_map {
 
   template <class _InputIterator, class _Allocator>
     requires(__has_input_iterator_category<_InputIterator>::value && __allocator_ctor_constraint<_Allocator>)
-  _LIBCPP_HIDE_FROM_ABI flat_map(_InputIterator __first, _InputIterator __last, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  flat_map(_InputIterator __first, _InputIterator __last, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc) {
     insert(__first, __last);
   }
 
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI flat_map(from_range_t __fr, _Range&& __rg)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(from_range_t __fr, _Range&& __rg)
       : flat_map(__fr, std::forward<_Range>(__rg), key_compare()) {}
 
   template <_ContainerCompatibleRange<value_type> _Range, class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(from_range_t, _Range&& __rg, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(from_range_t, _Range&& __rg, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc) {
     insert_range(std::forward<_Range>(__rg));
   }
 
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI flat_map(from_range_t, _Range&& __rg, const key_compare& __comp) : flat_map(__comp) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(from_range_t, _Range&& __rg, const key_compare& __comp)
+      : flat_map(__comp) {
     insert_range(std::forward<_Range>(__rg));
   }
 
   template <_ContainerCompatibleRange<value_type> _Range, class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(from_range_t, _Range&& __rg, const key_compare& __comp, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  flat_map(from_range_t, _Range&& __rg, const key_compare& __comp, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc, __comp) {
     insert_range(std::forward<_Range>(__rg));
   }
 
   template <class _InputIterator>
     requires __has_input_iterator_category<_InputIterator>::value
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(sorted_unique_t, _InputIterator __first, _InputIterator __last, const key_compare& __comp = key_compare())
       : __containers_(), __compare_(__comp) {
     insert(sorted_unique, __first, __last);
   }
   template <class _InputIterator, class _Allocator>
     requires(__has_input_iterator_category<_InputIterator>::value && __allocator_ctor_constraint<_Allocator>)
-  _LIBCPP_HIDE_FROM_ABI
-  flat_map(sorted_unique_t,
-           _InputIterator __first,
-           _InputIterator __last,
-           const key_compare& __comp,
-           const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(
+      sorted_unique_t,
+      _InputIterator __first,
+      _InputIterator __last,
+      const key_compare& __comp,
+      const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc, __comp) {
     insert(sorted_unique, __first, __last);
   }
 
   template <class _InputIterator, class _Allocator>
     requires(__has_input_iterator_category<_InputIterator>::value && __allocator_ctor_constraint<_Allocator>)
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(sorted_unique_t, _InputIterator __first, _InputIterator __last, const _Allocator& __alloc)
       : flat_map(__ctor_uses_allocator_empty_tag{}, __alloc) {
     insert(sorted_unique, __first, __last);
   }
 
-  _LIBCPP_HIDE_FROM_ABI flat_map(initializer_list<value_type> __il, const key_compare& __comp = key_compare())
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  flat_map(initializer_list<value_type> __il, const key_compare& __comp = key_compare())
       : flat_map(__il.begin(), __il.end(), __comp) {}
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(initializer_list<value_type> __il, const key_compare& __comp, const _Allocator& __alloc)
       : flat_map(__il.begin(), __il.end(), __comp, __alloc) {}
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(initializer_list<value_type> __il, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  flat_map(initializer_list<value_type> __il, const _Allocator& __alloc)
       : flat_map(__il.begin(), __il.end(), __alloc) {}
 
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(sorted_unique_t, initializer_list<value_type> __il, const key_compare& __comp = key_compare())
       : flat_map(sorted_unique, __il.begin(), __il.end(), __comp) {}
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
   flat_map(sorted_unique_t, initializer_list<value_type> __il, const key_compare& __comp, const _Allocator& __alloc)
       : flat_map(sorted_unique, __il.begin(), __il.end(), __comp, __alloc) {}
 
   template <class _Allocator>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(sorted_unique_t, initializer_list<value_type> __il, const _Allocator& __alloc)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  flat_map(sorted_unique_t, initializer_list<value_type> __il, const _Allocator& __alloc)
       : flat_map(sorted_unique, __il.begin(), __il.end(), __alloc) {}
 
-  _LIBCPP_HIDE_FROM_ABI flat_map& operator=(initializer_list<value_type> __il) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map& operator=(initializer_list<value_type> __il) {
     clear();
     insert(__il);
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI flat_map& operator=(const flat_map&) = default;
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map& operator=(const flat_map&) = default;
 
-  _LIBCPP_HIDE_FROM_ABI flat_map& operator=(flat_map&& __other) noexcept(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map& operator=(flat_map&& __other) noexcept(
       is_nothrow_move_assignable_v<_KeyContainer> && is_nothrow_move_assignable_v<_MappedContainer> &&
       is_nothrow_move_assignable_v<_Compare>) {
     // No matter what happens, we always want to clear the other container before returning
@@ -403,49 +411,65 @@ class flat_map {
   }
 
   // iterators
-  _LIBCPP_HIDE_FROM_ABI iterator begin() noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator begin() noexcept {
     return iterator(__containers_.keys.begin(), __containers_.values.begin());
   }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator begin() const noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator begin() const noexcept {
     return const_iterator(__containers_.keys.begin(), __containers_.values.begin());
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator end() noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator end() noexcept {
     return iterator(__containers_.keys.end(), __containers_.values.end());
   }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator end() const noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator end() const noexcept {
     return const_iterator(__containers_.keys.end(), __containers_.values.end());
   }
 
-  _LIBCPP_HIDE_FROM_ABI reverse_iterator rbegin() noexcept { return reverse_iterator(end()); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rbegin() const noexcept { return const_reverse_iterator(end()); }
-  _LIBCPP_HIDE_FROM_ABI reverse_iterator rend() noexcept { return reverse_iterator(begin()); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator rend() const noexcept { return const_reverse_iterator(begin()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rbegin() noexcept {
+    return reverse_iterator(end());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rbegin() const noexcept {
+    return const_reverse_iterator(end());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 reverse_iterator rend() noexcept {
+    return reverse_iterator(begin());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator rend() const noexcept {
+    return const_reverse_iterator(begin());
+  }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator cbegin() const noexcept { return begin(); }
-  _LIBCPP_HIDE_FROM_ABI const_iterator cend() const noexcept { return end(); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator(end()); }
-  _LIBCPP_HIDE_FROM_ABI const_reverse_iterator crend() const noexcept { return const_reverse_iterator(begin()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cbegin() const noexcept { return begin(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator cend() const noexcept { return end(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crbegin() const noexcept {
+    return const_reverse_iterator(end());
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_reverse_iterator crend() const noexcept {
+    return const_reverse_iterator(begin());
+  }
 
   // [flat.map.capacity], capacity
-  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI bool empty() const noexcept { return __containers_.keys.empty(); }
+  [[nodiscard]] _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool empty() const noexcept {
+    return __containers_.keys.empty();
+  }
 
-  _LIBCPP_HIDE_FROM_ABI size_type size() const noexcept { return __containers_.keys.size(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type size() const noexcept {
+    return __containers_.keys.size();
+  }
 
-  _LIBCPP_HIDE_FROM_ABI size_type max_size() const noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type max_size() const noexcept {
     return std::min<size_type>(__containers_.keys.max_size(), __containers_.values.max_size());
   }
 
   // [flat.map.access], element access
-  _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](const key_type& __x)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](const key_type& __x)
     requires is_constructible_v<mapped_type>
   {
     return try_emplace(__x).first->second;
   }
 
-  _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](key_type&& __x)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](key_type&& __x)
     requires is_constructible_v<mapped_type>
   {
     return try_emplace(std::move(__x)).first->second;
@@ -454,11 +478,11 @@ class flat_map {
   template <class _Kp>
     requires(__is_compare_transparent && is_constructible_v<key_type, _Kp> && is_constructible_v<mapped_type> &&
              !is_convertible_v<_Kp &&, const_iterator> && !is_convertible_v<_Kp &&, iterator>)
-  _LIBCPP_HIDE_FROM_ABI mapped_type& operator[](_Kp&& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& operator[](_Kp&& __x) {
     return try_emplace(std::forward<_Kp>(__x)).first->second;
   }
 
-  _LIBCPP_HIDE_FROM_ABI mapped_type& at(const key_type& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& at(const key_type& __x) {
     auto __it = find(__x);
     if (__it == end()) {
       std::__throw_out_of_range("flat_map::at(const key_type&): Key does not exist");
@@ -466,7 +490,7 @@ class flat_map {
     return __it->second;
   }
 
-  _LIBCPP_HIDE_FROM_ABI const mapped_type& at(const key_type& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const mapped_type& at(const key_type& __x) const {
     auto __it = find(__x);
     if (__it == end()) {
       std::__throw_out_of_range("flat_map::at(const key_type&) const: Key does not exist");
@@ -476,7 +500,7 @@ class flat_map {
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI mapped_type& at(const _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 mapped_type& at(const _Kp& __x) {
     auto __it = find(__x);
     if (__it == end()) {
       std::__throw_out_of_range("flat_map::at(const K&): Key does not exist");
@@ -486,7 +510,7 @@ class flat_map {
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI const mapped_type& at(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const mapped_type& at(const _Kp& __x) const {
     auto __it = find(__x);
     if (__it == end()) {
       std::__throw_out_of_range("flat_map::at(const K&) const: Key does not exist");
@@ -497,45 +521,49 @@ class flat_map {
   // [flat.map.modifiers], modifiers
   template <class... _Args>
     requires is_constructible_v<pair<key_type, mapped_type>, _Args...>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> emplace(_Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> emplace(_Args&&... __args) {
     std::pair<key_type, mapped_type> __pair(std::forward<_Args>(__args)...);
     return __try_emplace(std::move(__pair.first), std::move(__pair.second));
   }
 
   template <class... _Args>
     requires is_constructible_v<pair<key_type, mapped_type>, _Args...>
-  _LIBCPP_HIDE_FROM_ABI iterator emplace_hint(const_iterator __hint, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator emplace_hint(const_iterator __hint, _Args&&... __args) {
     std::pair<key_type, mapped_type> __pair(std::forward<_Args>(__args)...);
     return __try_emplace_hint(__hint, std::move(__pair.first), std::move(__pair.second)).first;
   }
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert(const value_type& __x) { return emplace(__x); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert(const value_type& __x) {
+    return emplace(__x);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert(value_type&& __x) { return emplace(std::move(__x)); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert(value_type&& __x) {
+    return emplace(std::move(__x));
+  }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __hint, const value_type& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __hint, const value_type& __x) {
     return emplace_hint(__hint, __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __hint, value_type&& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __hint, value_type&& __x) {
     return emplace_hint(__hint, std::move(__x));
   }
 
   template <class _PairLike>
     requires is_constructible_v<pair<key_type, mapped_type>, _PairLike>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert(_PairLike&& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> insert(_PairLike&& __x) {
     return emplace(std::forward<_PairLike>(__x));
   }
 
   template <class _PairLike>
     requires is_constructible_v<pair<key_type, mapped_type>, _PairLike>
-  _LIBCPP_HIDE_FROM_ABI iterator insert(const_iterator __hint, _PairLike&& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator insert(const_iterator __hint, _PairLike&& __x) {
     return emplace_hint(__hint, std::forward<_PairLike>(__x));
   }
 
   template <class _InputIterator>
     requires __has_input_iterator_category<_InputIterator>::value
-  _LIBCPP_HIDE_FROM_ABI void insert(_InputIterator __first, _InputIterator __last) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(_InputIterator __first, _InputIterator __last) {
     if constexpr (sized_sentinel_for<_InputIterator, _InputIterator>) {
       __reserve(__last - __first);
     }
@@ -544,7 +572,8 @@ class flat_map {
 
   template <class _InputIterator>
     requires __has_input_iterator_category<_InputIterator>::value
-  _LIBCPP_HIDE_FROM_ABI void insert(sorted_unique_t, _InputIterator __first, _InputIterator __last) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  insert(sorted_unique_t, _InputIterator __first, _InputIterator __last) {
     if constexpr (sized_sentinel_for<_InputIterator, _InputIterator>) {
       __reserve(__last - __first);
     }
@@ -553,7 +582,7 @@ class flat_map {
   }
 
   template <_ContainerCompatibleRange<value_type> _Range>
-  _LIBCPP_HIDE_FROM_ABI void insert_range(_Range&& __range) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert_range(_Range&& __range) {
     if constexpr (ranges::sized_range<_Range>) {
       __reserve(ranges::size(__range));
     }
@@ -561,19 +590,22 @@ class flat_map {
     __append_sort_merge_unique</*WasSorted = */ false>(ranges::begin(__range), ranges::end(__range));
   }
 
-  _LIBCPP_HIDE_FROM_ABI void insert(initializer_list<value_type> __il) { insert(__il.begin(), __il.end()); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(initializer_list<value_type> __il) {
+    insert(__il.begin(), __il.end());
+  }
 
-  _LIBCPP_HIDE_FROM_ABI void insert(sorted_unique_t, initializer_list<value_type> __il) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void insert(sorted_unique_t, initializer_list<value_type> __il) {
     insert(sorted_unique, __il.begin(), __il.end());
   }
 
-  _LIBCPP_HIDE_FROM_ABI containers extract() && {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 containers extract() && {
     auto __guard = std::__make_scope_guard([&]() noexcept { clear() /* noexcept */; });
     auto __ret   = std::move(__containers_);
     return __ret;
   }
 
-  _LIBCPP_HIDE_FROM_ABI void replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  replace(key_container_type&& __key_cont, mapped_container_type&& __mapped_cont) {
     _LIBCPP_ASSERT_VALID_INPUT_RANGE(
         __key_cont.size() == __mapped_cont.size(), "flat_map keys and mapped containers have different size");
 
@@ -587,13 +619,15 @@ class flat_map {
 
   template <class... _Args>
     requires is_constructible_v<mapped_type, _Args...>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> try_emplace(const key_type& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  try_emplace(const key_type& __key, _Args&&... __args) {
     return __try_emplace(__key, std::forward<_Args>(__args)...);
   }
 
   template <class... _Args>
     requires is_constructible_v<mapped_type, _Args...>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> try_emplace(key_type&& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  try_emplace(key_type&& __key, _Args&&... __args) {
     return __try_emplace(std::move(__key), std::forward<_Args>(__args)...);
   }
 
@@ -601,75 +635,84 @@ class flat_map {
     requires(__is_compare_transparent && is_constructible_v<key_type, _Kp> &&
              is_constructible_v<mapped_type, _Args...> && !is_convertible_v<_Kp &&, const_iterator> &&
              !is_convertible_v<_Kp &&, iterator>)
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> try_emplace(_Kp&& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool> try_emplace(_Kp&& __key, _Args&&... __args) {
     return __try_emplace(std::forward<_Kp>(__key), std::forward<_Args>(__args)...);
   }
 
   template <class... _Args>
     requires is_constructible_v<mapped_type, _Args...>
-  _LIBCPP_HIDE_FROM_ABI iterator try_emplace(const_iterator __hint, const key_type& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  try_emplace(const_iterator __hint, const key_type& __key, _Args&&... __args) {
     return __try_emplace_hint(__hint, __key, std::forward<_Args>(__args)...).first;
   }
 
   template <class... _Args>
     requires is_constructible_v<mapped_type, _Args...>
-  _LIBCPP_HIDE_FROM_ABI iterator try_emplace(const_iterator __hint, key_type&& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  try_emplace(const_iterator __hint, key_type&& __key, _Args&&... __args) {
     return __try_emplace_hint(__hint, std::move(__key), std::forward<_Args>(__args)...).first;
   }
 
   template <class _Kp, class... _Args>
     requires __is_compare_transparent && is_constructible_v<key_type, _Kp> && is_constructible_v<mapped_type, _Args...>
-  _LIBCPP_HIDE_FROM_ABI iterator try_emplace(const_iterator __hint, _Kp&& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  try_emplace(const_iterator __hint, _Kp&& __key, _Args&&... __args) {
     return __try_emplace_hint(__hint, std::forward<_Kp>(__key), std::forward<_Args>(__args)...).first;
   }
 
   template <class _Mapped>
     requires is_assignable_v<mapped_type&, _Mapped> && is_constructible_v<mapped_type, _Mapped>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(const key_type& __key, _Mapped&& __obj) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  insert_or_assign(const key_type& __key, _Mapped&& __obj) {
     return __insert_or_assign(__key, std::forward<_Mapped>(__obj));
   }
 
   template <class _Mapped>
     requires is_assignable_v<mapped_type&, _Mapped> && is_constructible_v<mapped_type, _Mapped>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(key_type&& __key, _Mapped&& __obj) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  insert_or_assign(key_type&& __key, _Mapped&& __obj) {
     return __insert_or_assign(std::move(__key), std::forward<_Mapped>(__obj));
   }
 
   template <class _Kp, class _Mapped>
     requires __is_compare_transparent && is_constructible_v<key_type, _Kp> && is_assignable_v<mapped_type&, _Mapped> &&
              is_constructible_v<mapped_type, _Mapped>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> insert_or_assign(_Kp&& __key, _Mapped&& __obj) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  insert_or_assign(_Kp&& __key, _Mapped&& __obj) {
     return __insert_or_assign(std::forward<_Kp>(__key), std::forward<_Mapped>(__obj));
   }
 
   template <class _Mapped>
     requires is_assignable_v<mapped_type&, _Mapped> && is_constructible_v<mapped_type, _Mapped>
-  _LIBCPP_HIDE_FROM_ABI iterator insert_or_assign(const_iterator __hint, const key_type& __key, _Mapped&& __obj) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  insert_or_assign(const_iterator __hint, const key_type& __key, _Mapped&& __obj) {
     return __insert_or_assign(__hint, __key, std::forward<_Mapped>(__obj));
   }
 
   template <class _Mapped>
     requires is_assignable_v<mapped_type&, _Mapped> && is_constructible_v<mapped_type, _Mapped>
-  _LIBCPP_HIDE_FROM_ABI iterator insert_or_assign(const_iterator __hint, key_type&& __key, _Mapped&& __obj) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  insert_or_assign(const_iterator __hint, key_type&& __key, _Mapped&& __obj) {
     return __insert_or_assign(__hint, std::move(__key), std::forward<_Mapped>(__obj));
   }
 
   template <class _Kp, class _Mapped>
     requires __is_compare_transparent && is_constructible_v<key_type, _Kp> && is_assignable_v<mapped_type&, _Mapped> &&
              is_constructible_v<mapped_type, _Mapped>
-  _LIBCPP_HIDE_FROM_ABI iterator insert_or_assign(const_iterator __hint, _Kp&& __key, _Mapped&& __obj) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  insert_or_assign(const_iterator __hint, _Kp&& __key, _Mapped&& __obj) {
     return __insert_or_assign(__hint, std::forward<_Kp>(__key), std::forward<_Mapped>(__obj));
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator erase(iterator __position) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(iterator __position) {
     return __erase(__position.__key_iter_, __position.__mapped_iter_);
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __position) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(const_iterator __position) {
     return __erase(__position.__key_iter_, __position.__mapped_iter_);
   }
 
-  _LIBCPP_HIDE_FROM_ABI size_type erase(const key_type& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type erase(const key_type& __x) {
     auto __iter = find(__x);
     if (__iter != end()) {
       erase(__iter);
@@ -681,14 +724,14 @@ class flat_map {
   template <class _Kp>
     requires(__is_compare_transparent && !is_convertible_v<_Kp &&, iterator> &&
              !is_convertible_v<_Kp &&, const_iterator>)
-  _LIBCPP_HIDE_FROM_ABI size_type erase(_Kp&& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type erase(_Kp&& __x) {
     auto [__first, __last] = equal_range(__x);
     auto __res             = __last - __first;
     erase(__first, __last);
     return __res;
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator erase(const_iterator __first, const_iterator __last) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator erase(const_iterator __first, const_iterator __last) {
     auto __on_failure = std::__make_exception_guard([&]() noexcept { clear() /* noexcept */; });
     auto __key_it     = __containers_.keys.erase(__first.__key_iter_, __last.__key_iter_);
     auto __mapped_it  = __containers_.values.erase(__first.__mapped_iter_, __last.__mapped_iter_);
@@ -696,7 +739,7 @@ class flat_map {
     return iterator(std::move(__key_it), std::move(__mapped_it));
   }
 
-  _LIBCPP_HIDE_FROM_ABI void swap(flat_map& __y) noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void swap(flat_map& __y) noexcept {
     // warning: The spec has unconditional noexcept, which means that
     // if any of the following functions throw an exception,
     // std::terminate will be called.
@@ -706,133 +749,156 @@ class flat_map {
     ranges::swap(__containers_.values, __y.__containers_.values);
   }
 
-  _LIBCPP_HIDE_FROM_ABI void clear() noexcept {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void clear() noexcept {
     __containers_.keys.clear();
     __containers_.values.clear();
   }
 
   // observers
-  _LIBCPP_HIDE_FROM_ABI key_compare key_comp() const { return __compare_; }
-  _LIBCPP_HIDE_FROM_ABI value_compare value_comp() const { return value_compare(__compare_); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 key_compare key_comp() const { return __compare_; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 value_compare value_comp() const {
+    return value_compare(__compare_);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI const key_container_type& keys() const noexcept { return __containers_.keys; }
-  _LIBCPP_HIDE_FROM_ABI const mapped_container_type& values() const noexcept { return __containers_.values; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const key_container_type& keys() const noexcept {
+    return __containers_.keys;
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const mapped_container_type& values() const noexcept {
+    return __containers_.values;
+  }
 
   // map operations
-  _LIBCPP_HIDE_FROM_ABI iterator find(const key_type& __x) { return __find_impl(*this, __x); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const key_type& __x) {
+    return __find_impl(*this, __x);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator find(const key_type& __x) const { return __find_impl(*this, __x); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const key_type& __x) const {
+    return __find_impl(*this, __x);
+  }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI iterator find(const _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator find(const _Kp& __x) {
     return __find_impl(*this, __x);
   }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI const_iterator find(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator find(const _Kp& __x) const {
     return __find_impl(*this, __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI size_type count(const key_type& __x) const { return contains(__x) ? 1 : 0; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const key_type& __x) const {
+    return contains(__x) ? 1 : 0;
+  }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI size_type count(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 size_type count(const _Kp& __x) const {
     return contains(__x) ? 1 : 0;
   }
 
-  _LIBCPP_HIDE_FROM_ABI bool contains(const key_type& __x) const { return find(__x) != end(); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const key_type& __x) const {
+    return find(__x) != end();
+  }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI bool contains(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool contains(const _Kp& __x) const {
     return find(__x) != end();
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const key_type& __x) { return __lower_bound<iterator>(*this, __x); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const key_type& __x) {
+    return __lower_bound<iterator>(*this, __x);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const key_type& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const key_type& __x) const {
     return __lower_bound<const_iterator>(*this, __x);
   }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI iterator lower_bound(const _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator lower_bound(const _Kp& __x) {
     return __lower_bound<iterator>(*this, __x);
   }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI const_iterator lower_bound(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator lower_bound(const _Kp& __x) const {
     return __lower_bound<const_iterator>(*this, __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const key_type& __x) { return __upper_bound<iterator>(*this, __x); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const key_type& __x) {
+    return __upper_bound<iterator>(*this, __x);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const key_type& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const key_type& __x) const {
     return __upper_bound<const_iterator>(*this, __x);
   }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI iterator upper_bound(const _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator upper_bound(const _Kp& __x) {
     return __upper_bound<iterator>(*this, __x);
   }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI const_iterator upper_bound(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 const_iterator upper_bound(const _Kp& __x) const {
     return __upper_bound<const_iterator>(*this, __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const key_type& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator> equal_range(const key_type& __x) {
     return __equal_range_impl(*this, __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const key_type& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
+  equal_range(const key_type& __x) const {
     return __equal_range_impl(*this, __x);
   }
 
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, iterator> equal_range(const _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, iterator> equal_range(const _Kp& __x) {
     return __equal_range_impl(*this, __x);
   }
   template <class _Kp>
     requires __is_compare_transparent
-  _LIBCPP_HIDE_FROM_ABI pair<const_iterator, const_iterator> equal_range(const _Kp& __x) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<const_iterator, const_iterator>
+  equal_range(const _Kp& __x) const {
     return __equal_range_impl(*this, __x);
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI bool operator==(const flat_map& __x, const flat_map& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool operator==(const flat_map& __x, const flat_map& __y) {
     return ranges::equal(__x, __y);
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI auto operator<=>(const flat_map& __x, const flat_map& __y) {
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 auto
+  operator<=>(const flat_map& __x, const flat_map& __y) {
     return std::lexicographical_compare_three_way(
         __x.begin(), __x.end(), __y.begin(), __y.end(), std::__synth_three_way);
   }
 
-  friend _LIBCPP_HIDE_FROM_ABI void swap(flat_map& __x, flat_map& __y) noexcept { __x.swap(__y); }
+  friend _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void swap(flat_map& __x, flat_map& __y) noexcept {
+    __x.swap(__y);
+  }
 
 private:
   struct __ctor_uses_allocator_tag {
-    explicit _LIBCPP_HIDE_FROM_ABI __ctor_uses_allocator_tag() = default;
+    explicit _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __ctor_uses_allocator_tag() = default;
   };
   struct __ctor_uses_allocator_empty_tag {
-    explicit _LIBCPP_HIDE_FROM_ABI __ctor_uses_allocator_empty_tag() = default;
+    explicit _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __ctor_uses_allocator_empty_tag() = default;
   };
 
   template <class _Allocator, class _KeyCont, class _MappedCont, class... _CompArg>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI
-  flat_map(__ctor_uses_allocator_tag,
-           const _Allocator& __alloc,
-           _KeyCont&& __key_cont,
-           _MappedCont&& __mapped_cont,
-           _CompArg&&... __comp)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 flat_map(
+      __ctor_uses_allocator_tag,
+      const _Allocator& __alloc,
+      _KeyCont&& __key_cont,
+      _MappedCont&& __mapped_cont,
+      _CompArg&&... __comp)
       : __containers_{.keys = std::make_obj_using_allocator<key_container_type>(
                           __alloc, std::forward<_KeyCont>(__key_cont)),
                       .values = std::make_obj_using_allocator<mapped_container_type>(
@@ -841,12 +907,13 @@ class flat_map {
 
   template <class _Allocator, class... _CompArg>
     requires __allocator_ctor_constraint<_Allocator>
-  _LIBCPP_HIDE_FROM_ABI flat_map(__ctor_uses_allocator_empty_tag, const _Allocator& __alloc, _CompArg&&... __comp)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  flat_map(__ctor_uses_allocator_empty_tag, const _Allocator& __alloc, _CompArg&&... __comp)
       : __containers_{.keys   = std::make_obj_using_allocator<key_container_type>(__alloc),
                       .values = std::make_obj_using_allocator<mapped_container_type>(__alloc)},
         __compare_(std::forward<_CompArg>(__comp)...) {}
 
-  _LIBCPP_HIDE_FROM_ABI bool __is_sorted_and_unique(auto&& __key_container) const {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool __is_sorted_and_unique(auto&& __key_container) const {
     auto __greater_or_equal_to = [this](const auto& __x, const auto& __y) { return !__compare_(__x, __y); };
     return ranges::adjacent_find(__key_container, __greater_or_equal_to) == ranges::end(__key_container);
   }
@@ -854,7 +921,7 @@ class flat_map {
   // This function is only used in constructors. So there is not exception handling in this function.
   // If the function exits via an exception, there will be no flat_map object constructed, thus, there
   // is no invariant state to preserve
-  _LIBCPP_HIDE_FROM_ABI void __sort_and_unique() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __sort_and_unique() {
     auto __zv = ranges::views::zip(__containers_.keys, __containers_.values);
     ranges::sort(__zv, __compare_, [](const auto& __p) -> decltype(auto) { return std::get<0>(__p); });
     auto __dup_start = ranges::unique(__zv, __key_equiv(__compare_)).begin();
@@ -864,7 +931,8 @@ class flat_map {
   }
 
   template <bool _WasSorted, class _InputIterator, class _Sentinel>
-  _LIBCPP_HIDE_FROM_ABI void __append_sort_merge_unique(_InputIterator __first, _Sentinel __last) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void
+  __append_sort_merge_unique(_InputIterator __first, _Sentinel __last) {
     auto __on_failure        = std::__make_exception_guard([&]() noexcept { clear() /* noexcept */; });
     size_t __num_of_appended = __flat_map_utils::__append(*this, std::move(__first), std::move(__last));
     if (__num_of_appended != 0) {
@@ -892,7 +960,7 @@ class flat_map {
   }
 
   template <class _Self, class _Kp>
-  _LIBCPP_HIDE_FROM_ABI static auto __find_impl(_Self&& __self, const _Kp& __key) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static auto __find_impl(_Self&& __self, const _Kp& __key) {
     auto __it   = __self.lower_bound(__key);
     auto __last = __self.end();
     if (__it == __last || __self.__compare_(__key, __it->first)) {
@@ -902,7 +970,7 @@ class flat_map {
   }
 
   template <class _Self, class _Kp>
-  _LIBCPP_HIDE_FROM_ABI static auto __key_equal_range(_Self&& __self, const _Kp& __key) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static auto __key_equal_range(_Self&& __self, const _Kp& __key) {
     auto __it   = ranges::lower_bound(__self.__containers_.keys, __key, __self.__compare_);
     auto __last = __self.__containers_.keys.end();
     if (__it == __last || __self.__compare_(__key, *__it)) {
@@ -912,7 +980,7 @@ class flat_map {
   }
 
   template <class _Self, class _Kp>
-  _LIBCPP_HIDE_FROM_ABI static auto __equal_range_impl(_Self&& __self, const _Kp& __key) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static auto __equal_range_impl(_Self&& __self, const _Kp& __key) {
     auto [__key_first, __key_last] = __key_equal_range(__self, __key);
 
     const auto __make_mapped_iter = [&](const auto& __key_iter) {
@@ -927,17 +995,18 @@ class flat_map {
   }
 
   template <class _Res, class _Self, class _Kp>
-  _LIBCPP_HIDE_FROM_ABI static _Res __lower_bound(_Self&& __self, _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static _Res __lower_bound(_Self&& __self, _Kp& __x) {
     return __binary_search<_Res>(__self, ranges::lower_bound, __x);
   }
 
   template <class _Res, class _Self, class _Kp>
-  _LIBCPP_HIDE_FROM_ABI static _Res __upper_bound(_Self&& __self, _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static _Res __upper_bound(_Self&& __self, _Kp& __x) {
     return __binary_search<_Res>(__self, ranges::upper_bound, __x);
   }
 
   template <class _Res, class _Self, class _Fn, class _Kp>
-  _LIBCPP_HIDE_FROM_ABI static _Res __binary_search(_Self&& __self, _Fn __search_fn, _Kp& __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static _Res
+  __binary_search(_Self&& __self, _Fn __search_fn, _Kp& __x) {
     auto __key_iter = __search_fn(__self.__containers_.keys, __x, __self.__compare_);
     auto __mapped_iter =
         __self.__containers_.values.begin() +
@@ -948,7 +1017,8 @@ class flat_map {
   }
 
   template <class _KeyArg, class... _MArgs>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __try_emplace(_KeyArg&& __key, _MArgs&&... __mapped_args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  __try_emplace(_KeyArg&& __key, _MArgs&&... __mapped_args) {
     auto __key_it    = ranges::lower_bound(__containers_.keys, __key, __compare_);
     auto __mapped_it = __containers_.values.begin() + ranges::distance(__containers_.keys.begin(), __key_it);
 
@@ -967,7 +1037,7 @@ class flat_map {
   }
 
   template <class _Kp>
-  _LIBCPP_HIDE_FROM_ABI bool __is_hint_correct(const_iterator __hint, _Kp&& __key) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool __is_hint_correct(const_iterator __hint, _Kp&& __key) {
     if (__hint != cbegin() && !__compare_((__hint - 1)->first, __key)) {
       return false;
     }
@@ -978,7 +1048,8 @@ class flat_map {
   }
 
   template <class _Kp, class... _Args>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __try_emplace_hint(const_iterator __hint, _Kp&& __key, _Args&&... __args) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  __try_emplace_hint(const_iterator __hint, _Kp&& __key, _Args&&... __args) {
     if (__is_hint_correct(__hint, __key)) {
       if (__hint == cend() || __compare_(__key, __hint->first)) {
         return {__flat_map_utils::__emplace_exact_pos(
@@ -999,7 +1070,8 @@ class flat_map {
   }
 
   template <class _Kp, class _Mapped>
-  _LIBCPP_HIDE_FROM_ABI pair<iterator, bool> __insert_or_assign(_Kp&& __key, _Mapped&& __mapped) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 pair<iterator, bool>
+  __insert_or_assign(_Kp&& __key, _Mapped&& __mapped) {
     auto __r = try_emplace(std::forward<_Kp>(__key), std::forward<_Mapped>(__mapped));
     if (!__r.second) {
       __r.first->second = std::forward<_Mapped>(__mapped);
@@ -1008,7 +1080,8 @@ class flat_map {
   }
 
   template <class _Kp, class _Mapped>
-  _LIBCPP_HIDE_FROM_ABI iterator __insert_or_assign(const_iterator __hint, _Kp&& __key, _Mapped&& __mapped) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  __insert_or_assign(const_iterator __hint, _Kp&& __key, _Mapped&& __mapped) {
     auto __r = __try_emplace_hint(__hint, std::forward<_Kp>(__key), std::forward<_Mapped>(__mapped));
     if (!__r.second) {
       __r.first->second = std::forward<_Mapped>(__mapped);
@@ -1016,7 +1089,7 @@ class flat_map {
     return __r.first;
   }
 
-  _LIBCPP_HIDE_FROM_ABI void __reserve(size_t __size) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 void __reserve(size_t __size) {
     if constexpr (requires { __containers_.keys.reserve(__size); }) {
       __containers_.keys.reserve(__size);
     }
@@ -1027,7 +1100,8 @@ class flat_map {
   }
 
   template <class _KIter, class _MIter>
-  _LIBCPP_HIDE_FROM_ABI iterator __erase(_KIter __key_iter_to_remove, _MIter __mapped_iter_to_remove) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 iterator
+  __erase(_KIter __key_iter_to_remove, _MIter __mapped_iter_to_remove) {
     auto __on_failure  = std::__make_exception_guard([&]() noexcept { clear() /* noexcept */; });
     auto __key_iter    = __containers_.keys.erase(__key_iter_to_remove);
     auto __mapped_iter = __containers_.values.erase(__mapped_iter_to_remove);
@@ -1037,7 +1111,8 @@ class flat_map {
 
   template <class _Key2, class _Tp2, class _Compare2, class _KeyContainer2, class _MappedContainer2, class _Predicate>
   friend typename flat_map<_Key2, _Tp2, _Compare2, _KeyContainer2, _MappedContainer2>::size_type
-  erase_if(flat_map<_Key2, _Tp2, _Compare2, _KeyContainer2, _MappedContainer2>&, _Predicate);
+      _LIBCPP_CONSTEXPR_SINCE_CXX26
+      erase_if(flat_map<_Key2, _Tp2, _Compare2, _KeyContainer2, _MappedContainer2>&, _Predicate);
 
   friend __flat_map_utils;
 
@@ -1045,8 +1120,9 @@ class flat_map {
   _LIBCPP_NO_UNIQUE_ADDRESS key_compare __compare_;
 
   struct __key_equiv {
-    _LIBCPP_HIDE_FROM_ABI __key_equiv(key_compare __c) : __comp_(__c) {}
-    _LIBCPP_HIDE_FROM_ABI bool operator()(const_reference __x, const_reference __y) const {
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_equiv(key_compare __c) : __comp_(__c) {}
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 bool
+    operator()(const_reference __x, const_reference __y) const {
       return !__comp_(std::get<0>(__x), std::get<0>(__y)) && !__comp_(std::get<0>(__y), std::get<0>(__x));
     }
     key_compare __comp_;
@@ -1169,8 +1245,9 @@ struct uses_allocator<flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContai
     : bool_constant<uses_allocator_v<_KeyContainer, _Allocator> && uses_allocator_v<_MappedContainer, _Allocator>> {};
 
 template <class _Key, class _Tp, class _Compare, class _KeyContainer, class _MappedContainer, class _Predicate>
-_LIBCPP_HIDE_FROM_ABI typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
-erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __flat_map, _Predicate __pred) {
+_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+    typename flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>::size_type
+    erase_if(flat_map<_Key, _Tp, _Compare, _KeyContainer, _MappedContainer>& __flat_map, _Predicate __pred) {
   auto __zv     = ranges::views::zip(__flat_map.__containers_.keys, __flat_map.__containers_.values);
   auto __first  = __zv.begin();
   auto __last   = __zv.end();
diff --git a/libcxx/include/__flat_map/key_value_iterator.h b/libcxx/include/__flat_map/key_value_iterator.h
index 3ebb653deb197..f163dfc28706d 100644
--- a/libcxx/include/__flat_map/key_value_iterator.h
+++ b/libcxx/include/__flat_map/key_value_iterator.h
@@ -46,7 +46,7 @@ struct __key_value_iterator {
 
   struct __arrow_proxy {
     __reference __ref_;
-    _LIBCPP_HIDE_FROM_ABI __reference* operator->() { return std::addressof(__ref_); }
+    _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __reference* operator->() { return std::addressof(__ref_); }
   };
 
   __key_iterator __key_iter_;
@@ -69,99 +69,113 @@ struct __key_value_iterator {
 
   _LIBCPP_HIDE_FROM_ABI __key_value_iterator() = default;
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator(__key_value_iterator<_Owner, _KeyContainer, _MappedContainer, !_Const> __i)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  __key_value_iterator(__key_value_iterator<_Owner, _KeyContainer, _MappedContainer, !_Const> __i)
     requires _Const && convertible_to<typename _KeyContainer::iterator, __key_iterator> &&
                  convertible_to<typename _MappedContainer::iterator, __mapped_iterator>
       : __key_iter_(std::move(__i.__key_iter_)), __mapped_iter_(std::move(__i.__mapped_iter_)) {}
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator(__key_iterator __key_iter, __mapped_iterator __mapped_iter)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26
+  __key_value_iterator(__key_iterator __key_iter, __mapped_iterator __mapped_iter)
       : __key_iter_(std::move(__key_iter)), __mapped_iter_(std::move(__mapped_iter)) {}
 
-  _LIBCPP_HIDE_FROM_ABI __reference operator*() const { return __reference(*__key_iter_, *__mapped_iter_); }
-  _LIBCPP_HIDE_FROM_ABI __arrow_proxy operator->() const { return __arrow_proxy{**this}; }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __reference operator*() const {
+    return __reference(*__key_iter_, *__mapped_iter_);
+  }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __arrow_proxy operator->() const { return __arrow_proxy{**this}; }
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator& operator++() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_value_iterator& operator++() {
     ++__key_iter_;
     ++__mapped_iter_;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator operator++(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_value_iterator operator++(int) {
     __key_value_iterator __tmp(*this);
     ++*this;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator& operator--() {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_value_iterator& operator--() {
     --__key_iter_;
     --__mapped_iter_;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator operator--(int) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_value_iterator operator--(int) {
     __key_value_iterator __tmp(*this);
     --*this;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator& operator+=(difference_type __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_value_iterator& operator+=(difference_type __x) {
     __key_iter_ += __x;
     __mapped_iter_ += __x;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __key_value_iterator& operator-=(difference_type __x) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __key_value_iterator& operator-=(difference_type __x) {
     __key_iter_ -= __x;
     __mapped_iter_ -= __x;
     return *this;
   }
 
-  _LIBCPP_HIDE_FROM_ABI __reference operator[](difference_type __n) const { return *(*this + __n); }
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 __reference operator[](difference_type __n) const {
+    return *(*this + __n);
+  }
 
-  _LIBCPP_HIDE_FROM_ABI friend constexpr bool
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend bool
   operator==(const __key_value_iterator& __x, const __key_value_iterator& __y) {
     return __x.__key_iter_ == __y.__key_iter_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator<(const __key_value_iterator& __x, const __key_value_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend bool
+  operator<(const __key_value_iterator& __x, const __key_value_iterator& __y) {
     return __x.__key_iter_ < __y.__key_iter_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator>(const __key_value_iterator& __x, const __key_value_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend bool
+  operator>(const __key_value_iterator& __x, const __key_value_iterator& __y) {
     return __y < __x;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator<=(const __key_value_iterator& __x, const __key_value_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend bool
+  operator<=(const __key_value_iterator& __x, const __key_value_iterator& __y) {
     return !(__y < __x);
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend bool operator>=(const __key_value_iterator& __x, const __key_value_iterator& __y) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend bool
+  operator>=(const __key_value_iterator& __x, const __key_value_iterator& __y) {
     return !(__x < __y);
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend auto operator<=>(const __key_value_iterator& __x, const __key_value_iterator& __y)
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend auto
+  operator<=>(const __key_value_iterator& __x, const __key_value_iterator& __y)
     requires three_way_comparable<__key_iterator>
   {
     return __x.__key_iter_ <=> __y.__key_iter_;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend __key_value_iterator operator+(const __key_value_iterator& __i, difference_type __n) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend __key_value_iterator
+  operator+(const __key_value_iterator& __i, difference_type __n) {
     auto __tmp = __i;
     __tmp += __n;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend __key_value_iterator operator+(difference_type __n, const __key_value_iterator& __i) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend __key_value_iterator
+  operator+(difference_type __n, const __key_value_iterator& __i) {
     return __i + __n;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend __key_value_iterator operator-(const __key_value_iterator& __i, difference_type __n) {
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend __key_value_iterator
+  operator-(const __key_value_iterator& __i, difference_type __n) {
     auto __tmp = __i;
     __tmp -= __n;
     return __tmp;
   }
 
-  _LIBCPP_HIDE_FROM_ABI friend difference_type
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 friend difference_type
   operator-(const __key_value_iterator& __x, const __key_value_iterator& __y) {
     return difference_type(__x.__key_iter_ - __y.__key_iter_);
   }
diff --git a/libcxx/include/__flat_map/utils.h b/libcxx/include/__flat_map/utils.h
index acb7dca7ffe96..27687ae8de3bc 100644
--- a/libcxx/include/__flat_map/utils.h
+++ b/libcxx/include/__flat_map/utils.h
@@ -35,7 +35,7 @@ struct __flat_map_utils {
   // roll back the changes it made to the map. If it cannot roll back the changes, it will
   // clear the map.
   template <class _Map, class _IterK, class _IterM, class _KeyArg, class... _MArgs>
-  _LIBCPP_HIDE_FROM_ABI static typename _Map::iterator __emplace_exact_pos(
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static typename _Map::iterator __emplace_exact_pos(
       _Map& __map, _IterK&& __it_key, _IterM&& __it_mapped, _KeyArg&& __key, _MArgs&&... __mapped_args) {
     auto __on_key_failed = std::__make_exception_guard([&]() noexcept {
       using _KeyContainer = typename _Map::key_container_type;
@@ -82,7 +82,7 @@ struct __flat_map_utils {
   // TODO: We could optimize this, see
   // https://github.com/llvm/llvm-project/issues/108624
   template <class _Map, class _InputIterator, class _Sentinel>
-  _LIBCPP_HIDE_FROM_ABI static typename _Map::size_type
+  _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX26 static typename _Map::size_type
   __append(_Map& __map, _InputIterator __first, _Sentinel __last) {
     typename _Map::size_type __num_appended = 0;
     for (; __first != __last; ++__first) {
diff --git a/libcxx/test/std/containers/Emplaceable.h b/libcxx/test/std/containers/Emplaceable.h
index afc4e2e38b0eb..48d8eab0a9a09 100644
--- a/libcxx/test/std/containers/Emplaceable.h
+++ b/libcxx/test/std/containers/Emplaceable.h
@@ -22,13 +22,13 @@ class Emplaceable {
   double double_;
 
 public:
-  Emplaceable() : int_(0), double_(0) {}
-  Emplaceable(int i, double d) : int_(i), double_(d) {}
-  Emplaceable(Emplaceable&& x) : int_(x.int_), double_(x.double_) {
+  TEST_CONSTEXPR Emplaceable() : int_(0), double_(0) {}
+  TEST_CONSTEXPR Emplaceable(int i, double d) : int_(i), double_(d) {}
+  TEST_CONSTEXPR Emplaceable(Emplaceable&& x) : int_(x.int_), double_(x.double_) {
     x.int_    = 0;
     x.double_ = 0;
   }
-  Emplaceable& operator=(Emplaceable&& x) {
+  TEST_CONSTEXPR Emplaceable& operator=(Emplaceable&& x) {
     int_      = x.int_;
     x.int_    = 0;
     double_   = x.double_;
@@ -36,10 +36,12 @@ class Emplaceable {
     return *this;
   }
 
-  bool operator==(const Emplaceable& x) const { return int_ == x.int_ && double_ == x.double_; }
-  bool operator<(const Emplaceable& x) const { return int_ < x.int_ || (int_ == x.int_ && double_ < x.double_); }
+  TEST_CONSTEXPR bool operator==(const Emplaceable& x) const { return int_ == x.int_ && double_ == x.double_; }
+  TEST_CONSTEXPR bool operator<(const Emplaceable& x) const {
+    return int_ < x.int_ || (int_ == x.int_ && double_ < x.double_);
+  }
 
-  int get() const { return int_; }
+  TEST_CONSTEXPR int get() const { return int_; }
 };
 
 template <>
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at.pass.cpp
index d30055bf1701c..bb4dd6453dd94 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at.pass.cpp
@@ -18,6 +18,7 @@
 #include <flat_map>
 #include <functional>
 #include <stdexcept>
+#include <type_traits>
 #include <vector>
 
 #include "MinSequenceContainer.h"
@@ -25,7 +26,7 @@
 #include "test_macros.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using P = std::pair<int, double>;
   P ar[]  = {
       P(1, 1.5),
@@ -49,10 +50,12 @@ void test() {
     assert(m.at(4) == 4.5);
     assert(m.at(5) == 5.5);
 #ifndef TEST_HAS_NO_EXCEPTIONS
-    try {
-      TEST_IGNORE_NODISCARD m.at(6);
-      assert(false);
-    } catch (std::out_of_range&) {
+    if (!std::is_constant_evaluated()) {
+      try {
+        TEST_IGNORE_NODISCARD m.at(6);
+        assert(false);
+      } catch (std::out_of_range&) {
+      }
     }
 #endif
     assert(m.at(7) == 7.5);
@@ -70,10 +73,12 @@ void test() {
     assert(m.at(4) == 4.5);
     assert(m.at(5) == 5.5);
 #ifndef TEST_HAS_NO_EXCEPTIONS
-    try {
-      TEST_IGNORE_NODISCARD m.at(6);
-      assert(false);
-    } catch (std::out_of_range&) {
+    if (!std::is_constant_evaluated()) {
+      try {
+        TEST_IGNORE_NODISCARD m.at(6);
+        assert(false);
+      } catch (std::out_of_range&) {
+      }
     }
 #endif
     assert(m.at(7) == 7.5);
@@ -82,11 +87,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
index 456f12e0c0d29..7aa69b5ab5184 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/at_transparent.pass.cpp
@@ -35,7 +35,7 @@ static_assert(!CanAt<NonTransparentMap>);
 static_assert(!CanAt<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using P = std::pair<int, double>;
   P ar[]  = {
       P(1, 1.5),
@@ -60,10 +60,12 @@ void test() {
     assert(m.at(Transparent<int>{4}) == 4.5);
     assert(m.at(Transparent<int>{5}) == 5.5);
 #ifndef TEST_HAS_NO_EXCEPTIONS
-    try {
-      TEST_IGNORE_NODISCARD m.at(Transparent<int>{6});
-      assert(false);
-    } catch (std::out_of_range&) {
+    if (!std::is_constant_evaluated()) {
+      try {
+        TEST_IGNORE_NODISCARD m.at(Transparent<int>{6});
+        assert(false);
+      } catch (std::out_of_range&) {
+      }
     }
 #endif
     assert(m.at(Transparent<int>{7}) == 7.5);
@@ -81,10 +83,12 @@ void test() {
     assert(m.at(Transparent<int>{4}) == 4.5);
     assert(m.at(Transparent<int>{5}) == 5.5);
 #ifndef TEST_HAS_NO_EXCEPTIONS
-    try {
-      TEST_IGNORE_NODISCARD m.at(Transparent<int>{6});
-      assert(false);
-    } catch (std::out_of_range&) {
+    if (!std::is_constant_evaluated()) {
+      try {
+        TEST_IGNORE_NODISCARD m.at(Transparent<int>{6});
+        assert(false);
+      } catch (std::out_of_range&) {
+      }
     }
 #endif
     assert(m.at(Transparent<int>{7}) == 7.5);
@@ -93,9 +97,14 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
   {
@@ -107,5 +116,14 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_key.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_key.pass.cpp
index ea2f5d800878a..a7d613de399ed 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_key.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_key.pass.cpp
@@ -16,6 +16,7 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
 #include "MinSequenceContainer.h"
@@ -31,7 +32,7 @@ static_assert(CanIndex<std::flat_map<int, double>, const int&>);
 static_assert(!CanIndex<std::flat_map<int, NoDefaultCtr>, const int&>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using P = std::pair<int, double>;
   P ar[]  = {
       P(1, 1.5),
@@ -58,13 +59,18 @@ void test() {
   assert(m.size() == 8);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto index_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap                             = std::decay_t<decltype(m)>;
       const typename FlatMap::key_type key      = key_arg;
@@ -73,5 +79,16 @@ int main(int, char**) {
     };
     test_emplace_exception_guarantee(index_func);
   }
+
+  return true;
+}
+
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_rv_key.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_rv_key.pass.cpp
index faacc3cfe8f96..4843e7c63b15c 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_rv_key.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_rv_key.pass.cpp
@@ -16,6 +16,7 @@
 #include <deque>
 #include <functional>
 #include <cassert>
+#include <type_traits>
 
 #include "MinSequenceContainer.h"
 #include "../helpers.h"
@@ -31,7 +32,7 @@ static_assert(CanIndex<std::flat_map<int, double>, int&&>);
 static_assert(!CanIndex<std::flat_map<int, NoDefaultCtr>, int&&>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   {
     std::flat_map<MoveOnly, double, std::less<MoveOnly>, KeyContainer, ValueContainer> m;
     ASSERT_SAME_TYPE(decltype(m[MoveOnly{}]), double&);
@@ -49,13 +50,18 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<MoveOnly>, std::vector<double>>();
-  test<std::deque<MoveOnly>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<MoveOnly>, std::vector<double>>();
+  }
   test<MinSequenceContainer<MoveOnly>, MinSequenceContainer<double>>();
   test<std::vector<MoveOnly, min_allocator<MoveOnly>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto index_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap                             = std::decay_t<decltype(m)>;
       typename FlatMap::key_type key            = key_arg;
@@ -64,5 +70,14 @@ int main(int, char**) {
     };
     test_emplace_exception_guarantee(index_func);
   }
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp
index 24c08464f3158..ab9309d194ed1 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.access/index_transparent.pass.cpp
@@ -50,7 +50,7 @@ static_assert(!CanIndex<TransparentMap, TransparentMap::iterator>);
 static_assert(!CanIndex<TransparentMap, TransparentMap::const_iterator>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using P = std::pair<int, double>;
   P ar[]  = {
       P(1, 1.5),
@@ -81,11 +81,17 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
+
   {
     bool transparent_used = false;
     TransparentComparator c(transparent_used);
@@ -94,7 +100,8 @@ int main(int, char**) {
     m[ConvertibleTransparent<int>{3}];
     assert(transparent_used);
   }
-  {
+
+  if (!std::is_constant_evaluated()) {
     auto index_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap                             = std::decay_t<decltype(m)>;
       using Key                                 = typename FlatMap::key_type;
@@ -103,5 +110,15 @@ int main(int, char**) {
     };
     test_emplace_exception_guarantee(index_func);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/empty.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/empty.pass.cpp
index 05efe063c1e17..8027cab4b4260 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/empty.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/empty.pass.cpp
@@ -24,10 +24,10 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
-  using M     = std::flat_multimap<Key, Value, std::less<int>, KeyContainer, ValueContainer>;
+  using M     = std::flat_map<Key, Value, std::less<int>, KeyContainer, ValueContainer>;
   M m;
   ASSERT_SAME_TYPE(decltype(m.empty()), bool);
   ASSERT_NOEXCEPT(m.empty());
@@ -39,11 +39,25 @@ void test() {
   assert(m.empty());
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/max_size.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/max_size.pass.cpp
index 87acdfd2cf625..ee01f8eb1dfe4 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/max_size.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/max_size.pass.cpp
@@ -24,7 +24,7 @@
 #include "test_allocator.h"
 #include "test_macros.h"
 
-int main(int, char**) {
+constexpr bool test() {
   {
     using A1 = limited_allocator<int, 10>;
     using A2 = limited_allocator<int, 20>;
@@ -72,5 +72,15 @@ int main(int, char**) {
     assert(c.max_size() <= max_dist);
     assert(c.max_size() <= alloc_max_size(std::allocator<char>()));
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/size.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/size.pass.cpp
index 957a860450091..08cfb0e9da062 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/size.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.capacity/size.pass.cpp
@@ -16,6 +16,7 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
 #include "MinSequenceContainer.h"
@@ -23,7 +24,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using M = std::flat_map<int, char, std::less<int>, KeyContainer, ValueContainer>;
   {
     const M m = {{1, 'a'}, {1, 'b'}, {4, 'd'}, {5, 'e'}, {5, 'h'}};
@@ -45,7 +46,7 @@ void test() {
   }
   {
     M m;
-    std::size_t s = 1000000;
+    std::size_t s = std::is_constant_evaluated() ? 100 : 1000000;
     for (auto i = 0u; i < s; ++i) {
       m.emplace(i, 'a');
     }
@@ -55,11 +56,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/alloc.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/alloc.pass.cpp
index 3f8d2ed332d6b..54dbe2309c43c 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/alloc.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/alloc.pass.cpp
@@ -14,6 +14,7 @@
 //   explicit flat_map(const Allocator& a);
 
 #include <cassert>
+#include <deque>
 #include <flat_map>
 #include <functional>
 #include <vector>
@@ -22,7 +23,23 @@
 #include "test_allocator.h"
 #include "../../../test_compare.h"
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
+  using A = test_allocator<short>;
+  using M =
+      std::flat_map<int,
+                    long,
+                    std::less<int>,
+                    KeyContainer<int, test_allocator<int>>,
+                    ValueContainer<long, test_allocator<long>>>;
+  M m(A(0, 5));
+  assert(m.empty());
+  assert(m.begin() == m.end());
+  assert(m.keys().get_allocator().get_id() == 5);
+  assert(m.values().get_allocator().get_id() == 5);
+}
+
+constexpr bool test() {
   {
     // The constructors in this subclause shall not participate in overload
     // resolution unless uses_allocator_v<key_container_type, Alloc> is true
@@ -53,20 +70,23 @@ int main(int, char**) {
     static_assert(std::is_constructible_v<M, test_allocator<int>>);
     static_assert(!std::is_convertible_v<test_allocator<int>, M>);
   }
+
+  test<std::vector, std::vector>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
   {
-    using A = test_allocator<short>;
-    using M =
-        std::flat_map<int,
-                      long,
-                      std::less<int>,
-                      std::vector<int, test_allocator<int>>,
-                      std::vector<long, test_allocator<long>>>;
-    M m(A(0, 5));
-    assert(m.empty());
-    assert(m.begin() == m.end());
-    assert(m.keys().get_allocator().get_id() == 5);
-    assert(m.values().get_allocator().get_id() == 5);
+    test<std::deque, std::deque>();
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/assign_initializer_list.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/assign_initializer_list.pass.cpp
index 06bde71e79941..fd0d8c34fc7bd 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/assign_initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/assign_initializer_list.pass.cpp
@@ -26,7 +26,7 @@
 #include "test_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -36,7 +36,6 @@ void test() {
     m                              = {{3, 0}, {1, 0}, {2, 0}, {2, 1}, {3, 1}, {4, 0}, {3, 2}, {5, 0}, {6, 0}, {5, 1}};
     std::pair<int, int> expected[] = {{1, 0}, {2, 0}, {3, 0}, {4, 0}, {5, 0}, {6, 0}};
     assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
   }
   {
     M m = {{10, 1}, {8, 1}};
@@ -47,13 +46,28 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
+
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/compare.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/compare.pass.cpp
index 40a1710f55e42..56c4699c32177 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/compare.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/compare.pass.cpp
@@ -20,48 +20,52 @@
 #include <type_traits>
 #include <vector>
 
+#include "MinSequenceContainer.h"
+#include "min_allocator.h"
 #include "test_macros.h"
 #include "../../../test_compare.h"
 #include "test_allocator.h"
 
-int main(int, char**) {
+// explicit flat_map(const key_compare& comp);
+template <class KeyContainer, class ValueContainer>
+constexpr void test_compare() {
+  using Key   = typename KeyContainer::value_type;
+  using Value = typename ValueContainer::value_type;
   {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+    // The one-argument ctor is explicit.
+    using C = test_less<Key>;
+    static_assert(std::is_constructible_v<std::flat_map<Key, Value, C>, C>);
+    static_assert(!std::is_convertible_v<C, std::flat_map<Key, Value, C>>);
 
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = other_allocator<int>;
-    using M1 = std::flat_map<int, int, C, std::vector<int, A1>, std::vector<int, A1>>;
-    using M2 = std::flat_map<int, int, C, std::vector<int, A1>, std::vector<int, A2>>;
-    using M3 = std::flat_map<int, int, C, std::vector<int, A2>, std::vector<int, A1>>;
-    static_assert(std::is_constructible_v<M1, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, const C&, const A2&>);
+    static_assert(std::is_constructible_v<std::flat_map<Key, Value>, std::less<Key>>);
+    static_assert(!std::is_convertible_v<std::less<Key>, std::flat_map<Key, Value>>);
   }
   {
-    using C = test_less<int>;
-    auto m  = std::flat_map<int, char*, C>(C(3));
+    using C = test_less<Key>;
+    auto m  = std::flat_map<Key, Value, C>(C(3));
     assert(m.empty());
     assert(m.begin() == m.end());
     assert(m.key_comp() == C(3));
   }
-  {
-    // The one-argument ctor is explicit.
-    using C = test_less<int>;
-    static_assert(std::is_constructible_v<std::flat_map<int, char*, C>, C>);
-    static_assert(!std::is_convertible_v<C, std::flat_map<int, char*, C>>);
+}
 
-    static_assert(std::is_constructible_v<std::flat_map<int, char*>, std::less<int>>);
-    static_assert(!std::is_convertible_v<std::less<int>, std::flat_map<int, char*>>);
+// template <class Alloc>
+//   flat_map(const key_compare& comp, const Alloc& a);
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test_compare_alloc() {
+  {
+    // If an allocator is given, it must be usable by both containers.
+    using A = test_allocator<int>;
+    using M = std::flat_map<int, int, std::less<>, KeyContainer<int>, ValueContainer<int, A>>;
+    static_assert(std::is_constructible_v<M, std::less<>>);
+    static_assert(!std::is_constructible_v<M, std::less<>, std::allocator<int>>);
+    static_assert(!std::is_constructible_v<M, std::less<>, A>);
   }
   {
     using C  = test_less<int>;
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    auto m   = std::flat_map<int, short, C, std::vector<int, A1>, std::vector<short, A2>>(C(4), A1(5));
+    auto m   = std::flat_map<int, short, C, KeyContainer<int, A1>, ValueContainer<short, A2>>(C(4), A1(5));
     assert(m.empty());
     assert(m.begin() == m.end());
     assert(m.key_comp() == C(4));
@@ -70,24 +74,60 @@ int main(int, char**) {
   }
   {
     // explicit(false)
-    using C                                                                    = test_less<int>;
-    using A1                                                                   = test_allocator<int>;
-    using A2                                                                   = test_allocator<short>;
-    std::flat_map<int, short, C, std::deque<int, A1>, std::deque<short, A2>> m = {C(4), A1(5)};
+    using C                                                                          = test_less<int>;
+    using A1                                                                         = test_allocator<int>;
+    using A2                                                                         = test_allocator<short>;
+    std::flat_map<int, short, C, KeyContainer<int, A1>, ValueContainer<short, A2>> m = {C(4), A1(5)};
     assert(m.empty());
     assert(m.begin() == m.end());
     assert(m.key_comp() == C(4));
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
+}
+
+constexpr bool test() {
   {
-    // If an allocator is given, it must be usable by both containers.
-    using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<>, std::vector<int>, std::vector<int, A>>;
-    static_assert(std::is_constructible_v<M, std::less<>>);
-    static_assert(!std::is_constructible_v<M, std::less<>, std::allocator<int>>);
-    static_assert(!std::is_constructible_v<M, std::less<>, A>);
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = other_allocator<int>;
+    using M1 = std::flat_map<int, int, C, std::vector<int, A1>, std::vector<int, A1>>;
+    using M2 = std::flat_map<int, int, C, std::vector<int, A1>, std::vector<int, A2>>;
+    using M3 = std::flat_map<int, int, C, std::vector<int, A2>, std::vector<int, A1>>;
+    static_assert(std::is_constructible_v<M1, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, const C&, const A2&>);
+  }
+
+  test_compare<std::vector<int>, std::vector<int>>();
+  test_compare<std::vector<int>, std::vector<double>>();
+  test_compare<MinSequenceContainer<int>, MinSequenceContainer<double>>();
+  test_compare<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
+  test_compare<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
+
+  test_compare_alloc<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test_compare<std::deque<int>, std::vector<double>>();
+    test_compare_alloc<std::deque, std::deque>();
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/containers.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/containers.pass.cpp
index 812e2c3e4f02a..560abf5151b6f 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/containers.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/containers.pass.cpp
@@ -30,49 +30,34 @@
 #include "test_allocator.h"
 #include "test_iterators.h"
 #include "test_macros.h"
+#include "../helpers.h"
 #include "../../../test_compare.h"
 
 struct P {
   int first;
   int second;
   template <class T, class U>
-  bool operator==(const std::pair<T, U>& rhs) const {
+  constexpr bool operator==(const std::pair<T, U>& rhs) const {
     return MoveOnly(first) == rhs.first && MoveOnly(second) == rhs.second;
   }
 };
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = other_allocator<int>;
-    using V1 = std::vector<int, A1>;
-    using V2 = std::vector<int, A2>;
-    using M1 = std::flat_map<int, int, C, V1, V1>;
-    using M2 = std::flat_map<int, int, C, V1, V2>;
-    using M3 = std::flat_map<int, int, C, V2, V1>;
-    static_assert(std::is_constructible_v<M1, const V1&, const V1&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, const V1&, const V1&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, const V1&, const V2&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, const V2&, const V1&, const A2&>);
-
-    static_assert(std::is_constructible_v<M1, const V1&, const V1&, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, const V1&, const V1&, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, const V1&, const V2&, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, const V2&, const V1&, const C&, const A2&>);
-  }
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     // flat_map(key_container_type , mapped_container_type)
-    using M              = std::flat_map<int, char>;
-    std::vector<int> ks  = {1, 1, 1, 2, 2, 3, 2, 3, 3};
-    std::vector<char> vs = {1, 2, 3, 4, 5, 6, 7, 8, 9};
-    auto m               = M(ks, vs);
-    assert((m.keys() == std::vector<int>{1, 2, 3}));
-    LIBCPP_ASSERT((m.values() == std::vector<char>{1, 4, 6}));
+    using M                  = std::flat_map<int, short, std::less<int>, KeyContainer<int>, ValueContainer<short>>;
+    KeyContainer<int> ks     = {1, 1, 1, 2, 2, 3, 2, 3, 3};
+    ValueContainer<short> vs = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+    auto m                   = M(ks, vs);
+    assert((m.keys() == KeyContainer<int>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
 
     // explicit(false)
     M m2 = {ks, vs};
@@ -81,15 +66,21 @@ int main(int, char**) {
     m = M(std::move(ks), std::move(vs));
     assert(ks.empty()); // it was moved-from
     assert(vs.empty()); // it was moved-from
-    assert((m.keys() == std::vector<int>{1, 2, 3}));
-    LIBCPP_ASSERT((m.values() == std::vector<char>{1, 4, 6}));
+    assert((m.keys() == KeyContainer<int>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
   }
   {
     // flat_map(key_container_type , mapped_container_type)
     // move-only
     P expected[] = {{3, 2}, {2, 1}, {1, 3}};
-    using Ks     = std::deque<int, min_allocator<int>>;
-    using Vs     = std::vector<MoveOnly, min_allocator<MoveOnly>>;
+    using Ks     = KeyContainer<int, min_allocator<int>>;
+    using Vs     = ValueContainer<MoveOnly, min_allocator<MoveOnly>>;
     using M      = std::flat_map<int, MoveOnly, std::greater<int>, Ks, Vs>;
     Ks ks        = {1, 3, 2};
     Vs vs;
@@ -105,9 +96,9 @@ int main(int, char**) {
     // flat_map(key_container_type , mapped_container_type)
     // container's allocators are used
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<int>, std::vector<int, A>, std::deque<int, A>>;
-    auto ks = std::vector<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(5));
-    auto vs = std::deque<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(6));
+    using M = std::flat_map<int, int, std::less<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
+    auto ks = KeyContainer<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(5));
+    auto vs = ValueContainer<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(6));
     auto m  = M(std::move(ks), std::move(vs));
     assert(ks.empty()); // it was moved-from
     assert(vs.empty()); // it was moved-from
@@ -117,13 +108,19 @@ int main(int, char**) {
   }
   {
     // flat_map(key_container_type , mapped_container_type, key_compare)
-    using C              = test_less<int>;
-    using M              = std::flat_map<int, char, C>;
-    std::vector<int> ks  = {1, 1, 1, 2, 2, 3, 2, 3, 3};
-    std::vector<char> vs = {1, 2, 3, 4, 5, 6, 7, 8, 9};
-    auto m               = M(ks, vs, C(4));
-    assert((m.keys() == std::vector<int>{1, 2, 3}));
-    LIBCPP_ASSERT((m.values() == std::vector<char>{1, 4, 6}));
+    using C                 = test_less<int>;
+    using M                 = std::flat_map<int, char, C, KeyContainer<int>, ValueContainer<char>>;
+    KeyContainer<int> ks    = {1, 1, 1, 2, 2, 3, 2, 3, 3};
+    ValueContainer<char> vs = {1, 2, 3, 4, 5, 6, 7, 8, 9};
+    auto m                  = M(ks, vs, C(4));
+    assert((m.keys() == KeyContainer<int>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<char>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.key_comp() == C(4));
 
     // explicit(false)
@@ -134,9 +131,9 @@ int main(int, char**) {
   {
     // flat_map(key_container_type , mapped_container_type, const Allocator&)
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<int>, std::vector<int, A>, std::deque<int, A>>;
-    auto ks = std::vector<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(5));
-    auto vs = std::deque<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(6));
+    using M = std::flat_map<int, int, std::less<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
+    auto ks = KeyContainer<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(5));
+    auto vs = ValueContainer<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(6));
     auto m  = M(ks, vs, A(4)); // replaces the allocators
     assert(!ks.empty());       // it was an lvalue above
     assert(!vs.empty());       // it was an lvalue above
@@ -148,9 +145,9 @@ int main(int, char**) {
     // flat_map(key_container_type , mapped_container_type, const Allocator&)
     // explicit(false)
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<int>, std::vector<int, A>, std::deque<int, A>>;
-    auto ks = std::vector<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(5));
-    auto vs = std::deque<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(6));
+    using M = std::flat_map<int, int, std::less<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
+    auto ks = KeyContainer<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(5));
+    auto vs = ValueContainer<int, A>({1, 1, 1, 2, 2, 3, 2, 3, 3}, A(6));
     M m     = {ks, vs, A(4)}; // implicit ctor
     assert(!ks.empty());      // it was an lvalue above
     assert(!vs.empty());      // it was an lvalue above
@@ -158,6 +155,7 @@ int main(int, char**) {
     assert(m.keys().get_allocator() == A(4));
     assert(m.values().get_allocator() == A(4));
   }
+
   {
     // flat_map(key_container_type , mapped_container_type, key_compare, const Allocator&)
     using C                = test_less<int>;
@@ -167,7 +165,13 @@ int main(int, char**) {
     std::vector<int, A> vs = {1, 2, 3, 4, 5, 6, 7, 8, 9};
     auto m                 = M(ks, vs, C(4), A(5));
     assert((m.keys() == std::vector<int, A>{1, 2, 3}));
-    LIBCPP_ASSERT((m.values() == std::vector<int, A>{1, 4, 6}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<int>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.key_comp() == C(4));
     assert(m.keys().get_allocator() == A(5));
     assert(m.values().get_allocator() == A(5));
@@ -179,6 +183,51 @@ int main(int, char**) {
     assert(m2.keys().get_allocator() == A(5));
     assert(m2.values().get_allocator() == A(5));
   }
+}
+
+bool constexpr test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = other_allocator<int>;
+    using V1 = std::vector<int, A1>;
+    using V2 = std::vector<int, A2>;
+    using M1 = std::flat_map<int, int, C, V1, V1>;
+    using M2 = std::flat_map<int, int, C, V1, V2>;
+    using M3 = std::flat_map<int, int, C, V2, V1>;
+    static_assert(std::is_constructible_v<M1, const V1&, const V1&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, const V1&, const V1&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, const V1&, const V2&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, const V2&, const V1&, const A2&>);
+
+    static_assert(std::is_constructible_v<M1, const V1&, const V1&, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, const V1&, const V1&, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, const V1&, const V2&, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, const V2&, const V1&, const C&, const A2&>);
+  }
+
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::vector>();
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy.pass.cpp
index fcd0415088c1c..70fc3f7734bfd 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy.pass.cpp
@@ -13,6 +13,7 @@
 // flat_map(const flat_map& m);
 
 #include <cassert>
+#include <deque>
 #include <flat_map>
 #include <vector>
 
@@ -20,11 +21,12 @@
 #include "../../../test_compare.h"
 #include "test_allocator.h"
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     using C = test_less<int>;
-    std::vector<int, test_allocator<int>> ks({1, 3, 5}, test_allocator<int>(6));
-    std::vector<char, test_allocator<char>> vs({2, 2, 1}, test_allocator<char>(7));
+    KeyContainer<int, test_allocator<int>> ks({1, 3, 5}, test_allocator<int>(6));
+    ValueContainer<char, test_allocator<char>> vs({2, 2, 1}, test_allocator<char>(7));
     using M = std::flat_map<int, char, C, decltype(ks), decltype(vs)>;
     auto mo = M(ks, vs, C(5));
     auto m  = mo;
@@ -44,8 +46,8 @@ int main(int, char**) {
   }
   {
     using C  = test_less<int>;
-    using Ks = std::vector<int, other_allocator<int>>;
-    using Vs = std::vector<char, other_allocator<char>>;
+    using Ks = KeyContainer<int, other_allocator<int>>;
+    using Vs = ValueContainer<char, other_allocator<char>>;
     auto ks  = Ks({1, 3, 5}, other_allocator<int>(6));
     auto vs  = Vs({2, 2, 1}, other_allocator<char>(7));
     using M  = std::flat_map<int, char, C, Ks, Vs>;
@@ -65,6 +67,26 @@ int main(int, char**) {
     assert(mo.keys().get_allocator() == other_allocator<int>(6));
     assert(mo.values().get_allocator() == other_allocator<char>(7));
   }
+}
+
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_alloc.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_alloc.pass.cpp
index cbda6ea853268..377b99a8cffb8 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_alloc.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_alloc.pass.cpp
@@ -22,7 +22,30 @@
 #include "../../../test_compare.h"
 #include "test_allocator.h"
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
+  using C = test_less<int>;
+  KeyContainer<int, test_allocator<int>> ks({1, 3, 5}, test_allocator<int>(6));
+  ValueContainer<char, test_allocator<char>> vs({2, 2, 1}, test_allocator<char>(7));
+  using M = std::flat_map<int, char, C, decltype(ks), decltype(vs)>;
+  auto mo = M(ks, vs, C(5));
+  auto m  = M(mo, test_allocator<int>(3));
+
+  assert(m.key_comp() == C(5));
+  assert(m.keys() == ks);
+  assert(m.values() == vs);
+  assert(m.keys().get_allocator() == test_allocator<int>(3));
+  assert(m.values().get_allocator() == test_allocator<char>(3));
+
+  // mo is unchanged
+  assert(mo.key_comp() == C(5));
+  assert(mo.keys() == ks);
+  assert(mo.values() == vs);
+  assert(mo.keys().get_allocator() == test_allocator<int>(6));
+  assert(mo.values().get_allocator() == test_allocator<char>(7));
+}
+
+constexpr bool test() {
   {
     // The constructors in this subclause shall not participate in overload
     // resolution unless uses_allocator_v<key_container_type, Alloc> is true
@@ -41,27 +64,24 @@ int main(int, char**) {
     static_assert(!std::is_constructible_v<M2, const M2&, const A2&>);
     static_assert(!std::is_constructible_v<M3, const M3&, const A2&>);
   }
-  {
-    using C = test_less<int>;
-    std::vector<int, test_allocator<int>> ks({1, 3, 5}, test_allocator<int>(6));
-    std::vector<char, test_allocator<char>> vs({2, 2, 1}, test_allocator<char>(7));
-    using M = std::flat_map<int, char, C, decltype(ks), decltype(vs)>;
-    auto mo = M(ks, vs, C(5));
-    auto m  = M(mo, test_allocator<int>(3));
 
-    assert(m.key_comp() == C(5));
-    assert(m.keys() == ks);
-    assert(m.values() == vs);
-    assert(m.keys().get_allocator() == test_allocator<int>(3));
-    assert(m.values().get_allocator() == test_allocator<char>(3));
+  test<std::vector, std::vector>();
 
-    // mo is unchanged
-    assert(mo.key_comp() == C(5));
-    assert(mo.keys() == ks);
-    assert(mo.values() == vs);
-    assert(mo.keys().get_allocator() == test_allocator<int>(6));
-    assert(mo.values().get_allocator() == test_allocator<char>(7));
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_assign.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_assign.pass.cpp
index 4f9797d5bf810..f0c8d8c2ccb98 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_assign.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/copy_assign.pass.cpp
@@ -15,18 +15,20 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
 #include "test_macros.h"
 #include "../../../test_compare.h"
 #include "test_allocator.h"
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     // test_allocator is not propagated
     using C = test_less<int>;
-    std::vector<int, test_allocator<int>> ks({1, 3, 5}, test_allocator<int>(6));
-    std::vector<char, test_allocator<char>> vs({2, 2, 1}, test_allocator<char>(7));
+    KeyContainer<int, test_allocator<int>> ks({1, 3, 5}, test_allocator<int>(6));
+    ValueContainer<char, test_allocator<char>> vs({2, 2, 1}, test_allocator<char>(7));
     using M = std::flat_map<int, char, C, decltype(ks), decltype(vs)>;
     auto mo = M(ks, vs, C(5));
     auto m  = M({{3, 3}, {4, 4}, {5, 5}}, C(3), test_allocator<int>(2));
@@ -48,8 +50,8 @@ int main(int, char**) {
   {
     // other_allocator is propagated
     using C  = test_less<int>;
-    using Ks = std::vector<int, other_allocator<int>>;
-    using Vs = std::vector<char, other_allocator<char>>;
+    using Ks = KeyContainer<int, other_allocator<int>>;
+    using Vs = ValueContainer<char, other_allocator<char>>;
     auto ks  = Ks({1, 3, 5}, other_allocator<int>(6));
     auto vs  = Vs({2, 2, 1}, other_allocator<char>(7));
     using M  = std::flat_map<int, char, C, Ks, Vs>;
@@ -70,7 +72,7 @@ int main(int, char**) {
     assert(mo.keys().get_allocator() == other_allocator<int>(6));
     assert(mo.values().get_allocator() == other_allocator<char>(7));
   }
-  {
+  if (!std::is_constant_evaluated()) {
     // comparator is copied and invariant is preserved
     using M = std::flat_map<int, int, std::function<bool(int, int)>>;
     M mo    = M({{1, 2}, {3, 4}}, std::less<int>());
@@ -88,5 +90,26 @@ int main(int, char**) {
     m       = static_cast<const M&>(m);
     assert((m == M{{1, 2}, {3, 4}}));
   }
+}
+
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default.pass.cpp
index c5b94896b9293..bcf5f95ff9dcb 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default.pass.cpp
@@ -24,23 +24,24 @@
 #include "test_allocator.h"
 
 struct DefaultCtableComp {
-  explicit DefaultCtableComp() { default_constructed_ = true; }
-  bool operator()(int, int) const { return false; }
+  constexpr explicit DefaultCtableComp() { default_constructed_ = true; }
+  constexpr bool operator()(int, int) const { return false; }
   bool default_constructed_ = false;
 };
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
-    std::flat_map<int, char*> m;
+    std::flat_map<int, char*, std::less<int>, KeyContainer<int>, ValueContainer<char*>> m;
     assert(m.empty());
   }
   {
     // explicit(false)
-    std::flat_map<int, char*> m = {};
+    std::flat_map<int, char*, std::less<int>, KeyContainer<int>, ValueContainer<char*>> m = {};
     assert(m.empty());
   }
   {
-    std::flat_map<int, char*, DefaultCtableComp, std::deque<int, min_allocator<int>>> m;
+    std::flat_map<int, char*, DefaultCtableComp, KeyContainer<int, min_allocator<int>>> m;
     assert(m.empty());
     assert(m.begin() == m.end());
     assert(m.key_comp().default_constructed_);
@@ -49,13 +50,13 @@ int main(int, char**) {
     using A1 = explicit_allocator<int>;
     using A2 = explicit_allocator<char*>;
     {
-      std::flat_map<int, char*, DefaultCtableComp, std::vector<int, A1>, std::vector<char*, A2>> m;
+      std::flat_map<int, char*, DefaultCtableComp, KeyContainer<int, A1>, ValueContainer<char*, A2>> m;
       assert(m.empty());
       assert(m.key_comp().default_constructed_);
     }
     {
       A1 a1;
-      std::flat_map<int, int, DefaultCtableComp, std::vector<int, A1>, std::vector<int, A1>> m(a1);
+      std::flat_map<int, int, DefaultCtableComp, KeyContainer<int, A1>, ValueContainer<int, A1>> m(a1);
       assert(m.empty());
       assert(m.key_comp().default_constructed_);
     }
@@ -63,10 +64,31 @@ int main(int, char**) {
   {
     // If an allocator is given, it must be usable by both containers.
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<>, std::vector<int>, std::vector<int, A>>;
+    using M = std::flat_map<int, int, std::less<>, KeyContainer<int>, ValueContainer<int, A>>;
     static_assert(std::is_constructible_v<M>);
     static_assert(!std::is_constructible_v<M, std::allocator<int>>);
     static_assert(!std::is_constructible_v<M, A>);
   }
+}
+
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default_noexcept.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default_noexcept.pass.cpp
index 790dfa4a02ed5..9fb6785a7cf1a 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default_noexcept.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/default_noexcept.pass.cpp
@@ -28,11 +28,11 @@
 #include "test_allocator.h"
 
 struct ThrowingCtorComp {
-  ThrowingCtorComp() noexcept(false) {}
-  bool operator()(const auto&, const auto&) const { return false; }
+  constexpr ThrowingCtorComp() noexcept(false) {}
+  constexpr bool operator()(const auto&, const auto&) const { return false; }
 };
 
-int main(int, char**) {
+constexpr bool test() {
 #if defined(_LIBCPP_VERSION)
   {
     using C = std::flat_map<MoveOnly, MoveOnly>;
@@ -55,5 +55,15 @@ int main(int, char**) {
     static_assert(!std::is_nothrow_default_constructible_v<C>);
     C c;
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/dtor_noexcept.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/dtor_noexcept.pass.cpp
index 1570b0fa14888..ea89e6a68281c 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/dtor_noexcept.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/dtor_noexcept.pass.cpp
@@ -23,35 +23,58 @@
 #include "test_allocator.h"
 
 struct ThrowingDtorComp {
-  bool operator()(const auto&, const auto&) const;
-  ~ThrowingDtorComp() noexcept(false) {}
+  constexpr bool operator()(const auto&, const auto&) const;
+  constexpr ~ThrowingDtorComp() noexcept(false) {}
 };
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
-    using C = std::flat_map<MoveOnly, MoveOnly>;
+    using C = std::flat_map<MoveOnly, MoveOnly, std::less<MoveOnly>, KeyContainer<MoveOnly>, ValueContainer<MoveOnly>>;
     static_assert(std::is_nothrow_destructible_v<C>);
     C c;
   }
   {
-    using V = std::vector<MoveOnly, test_allocator<MoveOnly>>;
-    using C = std::flat_map<MoveOnly, MoveOnly, std::less<MoveOnly>, V, V>;
+    using V  = KeyContainer<MoveOnly, test_allocator<MoveOnly>>;
+    using V2 = ValueContainer<MoveOnly, test_allocator<MoveOnly>>;
+    using C  = std::flat_map<MoveOnly, MoveOnly, std::less<MoveOnly>, V, V2>;
     static_assert(std::is_nothrow_destructible_v<C>);
     C c;
   }
   {
-    using V = std::deque<MoveOnly, other_allocator<MoveOnly>>;
-    using C = std::flat_map<MoveOnly, MoveOnly, std::greater<MoveOnly>, V, V>;
+    using V  = KeyContainer<MoveOnly, test_allocator<MoveOnly>>;
+    using V2 = ValueContainer<MoveOnly, test_allocator<MoveOnly>>;
+    using C  = std::flat_map<MoveOnly, MoveOnly, std::greater<MoveOnly>, V, V2>;
     static_assert(std::is_nothrow_destructible_v<C>);
     C c;
   }
 #if defined(_LIBCPP_VERSION)
   {
-    using C = std::flat_map<MoveOnly, MoveOnly, ThrowingDtorComp>;
+    using C = std::flat_map<MoveOnly, MoveOnly, ThrowingDtorComp, KeyContainer<MoveOnly>, ValueContainer<MoveOnly>>;
     static_assert(!std::is_nothrow_destructible_v<C>);
     C c;
   }
 #endif // _LIBCPP_VERSION
+}
+
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/initializer_list.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/initializer_list.pass.cpp
index 7a22746845d00..ae56de816245b 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/initializer_list.pass.cpp
@@ -30,58 +30,13 @@
 #include "../../../test_compare.h"
 
 struct DefaultCtableComp {
-  explicit DefaultCtableComp() { default_constructed_ = true; }
-  bool operator()(int, int) const { return false; }
+  constexpr explicit DefaultCtableComp() { default_constructed_ = true; }
+  constexpr bool operator()(int, int) const { return false; }
   bool default_constructed_ = false;
 };
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = other_allocator<int>;
-    using V1 = std::vector<int, A1>;
-    using V2 = std::vector<int, A2>;
-    using M1 = std::flat_map<int, int, C, V1, V1>;
-    using M2 = std::flat_map<int, int, C, V1, V2>;
-    using M3 = std::flat_map<int, int, C, V2, V1>;
-    using IL = std::initializer_list<std::pair<int, int>>;
-    static_assert(std::is_constructible_v<M1, IL, const A1&>);
-    static_assert(!std::is_constructible_v<M1, IL, const A2&>);
-    static_assert(!std::is_constructible_v<M2, IL, const A2&>);
-    static_assert(!std::is_constructible_v<M3, IL, const A2&>);
-
-    static_assert(std::is_constructible_v<M1, IL, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, IL, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, IL, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, IL, const C&, const A2&>);
-  }
-
-  {
-    // initializer_list<value_type> needs to match exactly
-    using M = std::flat_map<int, short>;
-    using C = typename M::key_compare;
-    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>>);
-    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>, C>);
-    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>, C, std::allocator<int>>);
-    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>, std::allocator<int>>);
-    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>>);
-    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>, C>);
-    static_assert(
-        !std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>, C, std::allocator<int>>);
-    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>, std::allocator<int>>);
-    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>>);
-    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>, C>);
-    static_assert(
-        !std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>, C, std::allocator<int>>);
-    static_assert(
-        !std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>, std::allocator<int>>);
-  }
-
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   std::pair<int, short> expected[] = {{1, 1}, {2, 2}, {3, 3}, {5, 2}};
   {
     // flat_map(initializer_list<value_type>);
@@ -99,29 +54,27 @@ int main(int, char**) {
   }
   {
     // flat_map(initializer_list<value_type>);
-    using M = std::flat_map<int, short, std::greater<int>, std::deque<int, min_allocator<int>>>;
+    using M = std::flat_map<int, short, std::greater<int>, KeyContainer<int, min_allocator<int>>>;
     M m     = {{5, 2}, {2, 2}, {2, 2}, {3, 3}, {1, 1}, {3, 3}};
     assert(std::equal(m.rbegin(), m.rend(), expected, expected + 4));
   }
   {
+    // flat_map(initializer_list<value_type>);
+    // different comparator
     using A = explicit_allocator<int>;
-    {
-      // flat_map(initializer_list<value_type>);
-      // different comparator
-      using M = std::flat_map<int, int, DefaultCtableComp, std::vector<int, A>, std::deque<int, A>>;
-      M m     = {{1, 1}, {2, 2}, {3, 3}};
-      assert(m.size() == 1);
-      assert(m.begin()->first == m.begin()->second);
-      LIBCPP_ASSERT(*m.begin() == std::make_pair(1, 1));
-      assert(m.key_comp().default_constructed_);
-    }
-    {
-      // flat_map(initializer_list<value_type>, const Allocator&);
-      using M = std::flat_map<int, int, std::greater<int>, std::deque<int, A>, std::vector<int, A>>;
-      A a;
-      M m({{5, 2}, {2, 2}, {2, 2}, {3, 3}, {1, 1}, {3, 3}}, a);
-      assert(std::equal(m.rbegin(), m.rend(), expected, expected + 4));
-    }
+    using M = std::flat_map<int, int, DefaultCtableComp, KeyContainer<int, A>, ValueContainer<int, A>>;
+    M m     = {{1, 1}, {2, 2}, {3, 3}};
+    assert(m.size() == 1);
+    assert(m.begin()->first == m.begin()->second);
+    assert(m.key_comp().default_constructed_);
+  }
+  {
+    // flat_map(initializer_list<value_type>, const Allocator&);
+    using A = explicit_allocator<int>;
+    using M = std::flat_map<int, int, std::greater<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
+    A a;
+    M m({{5, 2}, {2, 2}, {2, 2}, {3, 3}, {1, 1}, {3, 3}}, a);
+    assert(std::equal(m.rbegin(), m.rend(), expected, expected + 4));
   }
   {
     // flat_map(initializer_list<value_type>, const key_compare&);
@@ -136,10 +89,10 @@ int main(int, char**) {
     assert(m2 == m);
     assert(m2.key_comp() == C(10));
   }
-  {
+  if (!std::is_constant_evaluated()) {
     // flat_map(initializer_list<value_type>, const key_compare&);
     // Sorting uses the comparator that was passed in
-    using M = std::flat_map<int, short, std::function<bool(int, int)>, std::deque<int, min_allocator<int>>>;
+    using M = std::flat_map<int, short, std::function<bool(int, int)>, KeyContainer<int, min_allocator<int>>>;
     auto m  = M({{5, 2}, {2, 2}, {2, 2}, {3, 3}, {1, 1}, {3, 3}}, std::greater<int>());
     assert(std::equal(m.rbegin(), m.rend(), expected, expected + 4));
     assert(m.key_comp()(2, 1) == true);
@@ -147,11 +100,77 @@ int main(int, char**) {
   {
     // flat_map(initializer_list<value_type> il, const key_compare& comp, const Alloc& a);
     using A = explicit_allocator<int>;
-    using M = std::flat_map<int, int, std::greater<int>, std::deque<int, A>, std::vector<int, A>>;
+    using M = std::flat_map<int, int, std::greater<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
     A a;
     M m({{5, 2}, {2, 2}, {2, 2}, {3, 3}, {1, 1}, {3, 3}}, {}, a);
     assert(std::equal(m.rbegin(), m.rend(), expected, expected + 4));
   }
+}
+
+constexpr bool test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = other_allocator<int>;
+    using V1 = std::vector<int, A1>;
+    using V2 = std::vector<int, A2>;
+    using M1 = std::flat_map<int, int, C, V1, V1>;
+    using M2 = std::flat_map<int, int, C, V1, V2>;
+    using M3 = std::flat_map<int, int, C, V2, V1>;
+    using IL = std::initializer_list<std::pair<int, int>>;
+    static_assert(std::is_constructible_v<M1, IL, const A1&>);
+    static_assert(!std::is_constructible_v<M1, IL, const A2&>);
+    static_assert(!std::is_constructible_v<M2, IL, const A2&>);
+    static_assert(!std::is_constructible_v<M3, IL, const A2&>);
+
+    static_assert(std::is_constructible_v<M1, IL, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, IL, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, IL, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, IL, const C&, const A2&>);
+  }
+
+  {
+    // initializer_list<value_type> needs to match exactly
+    using M = std::flat_map<int, short>;
+    using C = typename M::key_compare;
+    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>>);
+    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>, C>);
+    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>, C, std::allocator<int>>);
+    static_assert(std::is_constructible_v<M, std::initializer_list<std::pair<int, short>>, std::allocator<int>>);
+    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>>);
+    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>, C>);
+    static_assert(
+        !std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>, C, std::allocator<int>>);
+    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, short>>, std::allocator<int>>);
+    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>>);
+    static_assert(!std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>, C>);
+    static_assert(
+        !std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>, C, std::allocator<int>>);
+    static_assert(
+        !std::is_constructible_v<M, std::initializer_list<std::pair<const int, const short>>, std::allocator<int>>);
+  }
+
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/iter_iter.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/iter_iter.pass.cpp
index 7c0c487969943..812553ea0fa68 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/iter_iter.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/iter_iter.pass.cpp
@@ -22,51 +22,35 @@
 #include <flat_map>
 #include <functional>
 #include <vector>
+#include <ranges>
 
+#include "MinSequenceContainer.h"
 #include "min_allocator.h"
 #include "test_allocator.h"
 #include "test_iterators.h"
 #include "test_macros.h"
+#include "../helpers.h"
 #include "../../../test_compare.h"
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-
-    using C     = test_less<int>;
-    using A1    = test_allocator<int>;
-    using A2    = other_allocator<int>;
-    using V1    = std::vector<int, A1>;
-    using V2    = std::vector<int, A2>;
-    using M1    = std::flat_map<int, int, C, V1, V1>;
-    using M2    = std::flat_map<int, int, C, V1, V2>;
-    using M3    = std::flat_map<int, int, C, V2, V1>;
-    using Iter1 = typename M1::iterator;
-    using Iter2 = typename M2::iterator;
-    using Iter3 = typename M3::iterator;
-    static_assert(std::is_constructible_v<M1, Iter1, Iter1, const A1&>);
-    static_assert(!std::is_constructible_v<M1, Iter1, Iter1, const A2&>);
-    static_assert(!std::is_constructible_v<M2, Iter2, Iter2, const A2&>);
-    static_assert(!std::is_constructible_v<M3, Iter3, Iter3, const A2&>);
-
-    static_assert(std::is_constructible_v<M1, Iter1, Iter1, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, Iter1, Iter1, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, Iter2, Iter2, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, Iter3, Iter3, const C&, const A2&>);
-  }
-
-  using P      = std::pair<int, short>;
-  P ar[]       = {{1, 1}, {1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {2, 7}, {3, 8}, {3, 9}};
-  P expected[] = {{1, 1}, {2, 4}, {3, 6}};
+template <class KeyContainer, class ValueContainer>
+constexpr void test() {
+  using Key   = typename KeyContainer::value_type;
+  using Value = typename ValueContainer::value_type;
+  using P     = std::pair<Key, Value>;
+  P ar[]      = {{1, 1}, {1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {2, 7}, {3, 8}, {3, 9}};
   {
     // flat_map(InputIterator , InputIterator)
     // cpp17_input_iterator
-    using M = std::flat_map<int, short>;
+    using M = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
     auto m  = M(cpp17_input_iterator<const P*>(ar), cpp17_input_iterator<const P*>(ar + 9));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
 
     // explicit(false)
     M m2 = {cpp17_input_iterator<const P*>(ar), cpp17_input_iterator<const P*>(ar + 9)};
@@ -75,25 +59,37 @@ int main(int, char**) {
   {
     // flat_map(InputIterator , InputIterator)
     // greater
-    using M = std::flat_map<int, short, std::greater<int>, std::deque<int, min_allocator<int>>, std::deque<short>>;
+    using M = std::flat_map<Key, Value, std::greater<Key>, KeyContainer, ValueContainer>;
     auto m  = M(cpp17_input_iterator<const P*>(ar), cpp17_input_iterator<const P*>(ar + 9));
-    assert((m.keys() == std::deque<int, min_allocator<int>>{3, 2, 1}));
-    LIBCPP_ASSERT((m.values() == std::deque<short>{6, 4, 1}));
+    assert(std::ranges::equal(m.keys(), KeyContainer{3, 2, 1}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {6, 8, 9},
+            {4, 5, 7},
+            {1, 2, 3},
+        });
   }
   {
     // flat_map(InputIterator , InputIterator)
     // Test when the operands are of array type (also contiguous iterator type)
-    using M = std::flat_map<int, short, std::greater<int>, std::vector<int, min_allocator<int>>>;
+    using M = std::flat_map<Key, Value, std::greater<Key>, KeyContainer, ValueContainer>;
     auto m  = M(ar, ar);
     assert(m.empty());
   }
   {
     // flat_map(InputIterator , InputIterator, const key_compare&)
-    using C = test_less<int>;
-    using M = std::flat_map<int, short, C, std::vector<int>, std::deque<short>>;
+    using C = test_less<Key>;
+    using M = std::flat_map<Key, Value, C, KeyContainer, ValueContainer>;
     auto m  = M(ar, ar + 9, C(3));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.key_comp() == C(3));
 
     // explicit(false)
@@ -101,14 +97,27 @@ int main(int, char**) {
     assert(m2 == m);
     assert(m2.key_comp() == C(3));
   }
+}
+
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test_alloc() {
+  using P      = std::pair<int, short>;
+  P ar[]       = {{1, 1}, {1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {2, 7}, {3, 8}, {3, 9}};
+
   {
     // flat_map(InputIterator , InputIterator, const Allocator&)
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, std::less<int>, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     auto m   = M(ar, ar + 9, A1(5));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
@@ -117,10 +126,16 @@ int main(int, char**) {
     // explicit(false)
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, std::less<int>, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     M m      = {ar, ar + 9, A1(5)}; // implicit ctor
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
@@ -129,10 +144,16 @@ int main(int, char**) {
     using C  = test_less<int>;
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, C, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, C, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     auto m   = M(ar, ar + 9, C(3), A1(5));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.key_comp() == C(3));
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
@@ -142,13 +163,73 @@ int main(int, char**) {
     // explicit(false)
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, std::less<int>, std::deque<int, A1>, std::vector<short, A2>>;
+    using M  = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     M m      = {ar, ar + 9, {}, A2(5)}; // implicit ctor
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
+}
+
+constexpr bool test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C     = test_less<int>;
+    using A1    = test_allocator<int>;
+    using A2    = other_allocator<int>;
+    using V1    = std::vector<int, A1>;
+    using V2    = std::vector<int, A2>;
+    using M1    = std::flat_map<int, int, C, V1, V1>;
+    using M2    = std::flat_map<int, int, C, V1, V2>;
+    using M3    = std::flat_map<int, int, C, V2, V1>;
+    using Iter1 = typename M1::iterator;
+    using Iter2 = typename M2::iterator;
+    using Iter3 = typename M3::iterator;
+    static_assert(std::is_constructible_v<M1, Iter1, Iter1, const A1&>);
+    static_assert(!std::is_constructible_v<M1, Iter1, Iter1, const A2&>);
+    static_assert(!std::is_constructible_v<M2, Iter2, Iter2, const A2&>);
+    static_assert(!std::is_constructible_v<M3, Iter3, Iter3, const A2&>);
+
+    static_assert(std::is_constructible_v<M1, Iter1, Iter1, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, Iter1, Iter1, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, Iter2, Iter2, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, Iter3, Iter3, const C&, const A2&>);
+  }
+
+  test<std::vector<int>, std::vector<int>>();
+  test<std::vector<int>, std::vector<double>>();
+  test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
+
+  test_alloc<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+    test_alloc<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move.pass.cpp
index 955d3156064aa..091f727730321 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move.pass.cpp
@@ -16,6 +16,7 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -25,11 +26,12 @@
 #include "test_allocator.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     using C = test_less<int>;
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, C, std::vector<int, A>, std::deque<int, A>>;
+    using M = std::flat_map<int, int, C, KeyContainer<int, A>, ValueContainer<int, A>>;
     M mo    = M({{1, 1}, {2, 2}, {3, 1}}, C(5), A(7));
     M m     = std::move(mo);
     assert((m == M{{1, 1}, {2, 2}, {3, 1}}));
@@ -45,7 +47,7 @@ int main(int, char**) {
   {
     using C = test_less<int>;
     using A = min_allocator<int>;
-    using M = std::flat_map<int, int, C, std::vector<int, A>, std::deque<int, A>>;
+    using M = std::flat_map<int, int, C, KeyContainer<int, A>, ValueContainer<int, A>>;
     M mo    = M({{1, 1}, {2, 2}, {3, 1}}, C(5), A());
     M m     = std::move(mo);
     assert((m == M{{1, 1}, {2, 2}, {3, 1}}));
@@ -58,9 +60,9 @@ int main(int, char**) {
     assert(m.keys().get_allocator() == A());
     assert(m.values().get_allocator() == A());
   }
-  {
+  if (!std::is_constant_evaluated()) {
     // A moved-from flat_map maintains its class invariant in the presence of moved-from comparators.
-    using M = std::flat_map<int, int, std::function<bool(int, int)>>;
+    using M = std::flat_map<int, int, std::function<bool(int, int)>, KeyContainer<int>, ValueContainer<int>>;
     M mo    = M({{1, 1}, {2, 2}, {3, 1}}, std::less<int>());
     M m     = std::move(mo);
     assert(m.size() == 3);
@@ -75,7 +77,7 @@ int main(int, char**) {
   }
   {
     // moved-from object maintains invariant if one of underlying container does not clear after move
-    using M = std::flat_map<int, int, std::less<>, std::vector<int>, CopyOnlyVector<int>>;
+    using M = std::flat_map<int, int, std::less<>, KeyContainer<int>, CopyOnlyVector<int>>;
     M m1    = M({1, 2, 3}, {1, 2, 3});
     M m2    = std::move(m1);
     assert(m2.size() == 3);
@@ -84,5 +86,26 @@ int main(int, char**) {
     LIBCPP_ASSERT(m1.keys().size() == 0);
     LIBCPP_ASSERT(m1.values().size() == 0);
   }
+}
+
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_alloc.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_alloc.pass.cpp
index 93a3976422520..caec240ccee3b 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_alloc.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_alloc.pass.cpp
@@ -24,30 +24,13 @@
 #include "../../../test_compare.h"
 #include "test_allocator.h"
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = other_allocator<int>;
-    using V1 = std::vector<int, A1>;
-    using V2 = std::vector<int, A2>;
-    using M1 = std::flat_map<int, int, C, V1, V1>;
-    using M2 = std::flat_map<int, int, C, V1, V2>;
-    using M3 = std::flat_map<int, int, C, V2, V1>;
-    static_assert(std::is_constructible_v<M1, M1&&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, M1&&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, M2&&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, M3&&, const A2&>);
-  }
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     std::pair<int, int> expected[] = {{1, 1}, {2, 2}, {3, 1}};
     using C                        = test_less<int>;
     using A                        = test_allocator<int>;
-    using M                        = std::flat_map<int, int, C, std::vector<int, A>, std::deque<int, A>>;
+    using M                        = std::flat_map<int, int, C, KeyContainer<int, A>, ValueContainer<int, A>>;
     auto mo                        = M(expected, expected + 3, C(5), A(7));
     auto m                         = M(std::move(mo), A(3));
 
@@ -68,7 +51,7 @@ int main(int, char**) {
   }
   {
     // moved-from object maintains invariant if one of underlying container does not clear after move
-    using M = std::flat_map<int, int, std::less<>, std::vector<int>, CopyOnlyVector<int>>;
+    using M = std::flat_map<int, int, std::less<>, KeyContainer<int>, CopyOnlyVector<int>>;
     M m1    = M({1, 2, 3}, {1, 2, 3});
     M m2(std::move(m1), std::allocator<int>{});
     assert(m2.size() == 3);
@@ -77,6 +60,45 @@ int main(int, char**) {
     LIBCPP_ASSERT(m1.keys().size() == 0);
     LIBCPP_ASSERT(m1.values().size() == 0);
   }
+}
+
+constexpr bool test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = other_allocator<int>;
+    using V1 = std::vector<int, A1>;
+    using V2 = std::vector<int, A2>;
+    using M1 = std::flat_map<int, int, C, V1, V1>;
+    using M2 = std::flat_map<int, int, C, V1, V2>;
+    using M3 = std::flat_map<int, int, C, V2, V1>;
+    static_assert(std::is_constructible_v<M1, M1&&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, M1&&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, M2&&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, M3&&, const A2&>);
+  }
+
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign.pass.cpp
index a94c442c695dd..aa2eadf2f06e2 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign.pass.cpp
@@ -26,12 +26,13 @@
 #include "test_allocator.h"
 #include "min_allocator.h"
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     using C  = test_less<int>;
     using A1 = test_allocator<int>;
     using A2 = test_allocator<char>;
-    using M  = std::flat_map<int, char, C, std::vector<int, A1>, std::vector<char, A2>>;
+    using M  = std::flat_map<int, char, C, KeyContainer<int, A1>, ValueContainer<char, A2>>;
     M mo     = M({{1, 1}, {2, 3}, {3, 2}}, C(5), A1(7));
     M m      = M({}, C(3), A1(7));
     m        = std::move(mo);
@@ -46,7 +47,7 @@ int main(int, char**) {
     using C  = test_less<int>;
     using A1 = other_allocator<int>;
     using A2 = other_allocator<char>;
-    using M  = std::flat_map<int, char, C, std::deque<int, A1>, std::deque<char, A2>>;
+    using M  = std::flat_map<int, char, C, KeyContainer<int, A1>, ValueContainer<char, A2>>;
     M mo     = M({{4, 5}, {5, 4}}, C(5), A1(7));
     M m      = M({{1, 1}, {2, 2}, {3, 3}, {4, 4}}, C(3), A1(7));
     m        = std::move(mo);
@@ -59,7 +60,7 @@ int main(int, char**) {
   }
   {
     using A = min_allocator<int>;
-    using M = std::flat_map<int, int, std::greater<int>, std::vector<int, A>, std::vector<int, A>>;
+    using M = std::flat_map<int, int, std::greater<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
     M mo    = M({{5, 1}, {4, 2}, {3, 3}}, A());
     M m     = M({{4, 4}, {3, 3}, {2, 2}, {1, 1}}, A());
     m       = std::move(mo);
@@ -69,6 +70,26 @@ int main(int, char**) {
     assert(vs.get_allocator() == A());
     assert(mo.empty());
   }
+}
 
-  return 0;
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
 }
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
+  return 0;
+}
\ No newline at end of file
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_clears.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_clears.pass.cpp
index f28d52dd4e463..ddedb0c015706 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_clears.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_clears.pass.cpp
@@ -16,6 +16,7 @@
 #include <algorithm>
 #include <cassert>
 #include <compare>
+#include <deque>
 #include <flat_map>
 #include <functional>
 #include <utility>
@@ -27,9 +28,9 @@
 struct MoveNegates {
   int value_    = 0;
   MoveNegates() = default;
-  MoveNegates(int v) : value_(v) {}
-  MoveNegates(MoveNegates&& rhs) : value_(rhs.value_) { rhs.value_ = -rhs.value_; }
-  MoveNegates& operator=(MoveNegates&& rhs) {
+  constexpr MoveNegates(int v) : value_(v) {}
+  constexpr MoveNegates(MoveNegates&& rhs) : value_(rhs.value_) { rhs.value_ = -rhs.value_; }
+  constexpr MoveNegates& operator=(MoveNegates&& rhs) {
     value_     = rhs.value_;
     rhs.value_ = -rhs.value_;
     return *this;
@@ -41,9 +42,9 @@ struct MoveNegates {
 struct MoveClears {
   int value_   = 0;
   MoveClears() = default;
-  MoveClears(int v) : value_(v) {}
-  MoveClears(MoveClears&& rhs) : value_(rhs.value_) { rhs.value_ = 0; }
-  MoveClears& operator=(MoveClears&& rhs) {
+  constexpr MoveClears(int v) : value_(v) {}
+  constexpr MoveClears(MoveClears&& rhs) : value_(rhs.value_) { rhs.value_ = 0; }
+  constexpr MoveClears& operator=(MoveClears&& rhs) {
     value_     = rhs.value_;
     rhs.value_ = 0;
     return *this;
@@ -52,11 +53,12 @@ struct MoveClears {
   auto operator<=>(const MoveClears&) const = default;
 };
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   auto value_eq = [](auto&& p, auto&& q) { return p.first == q.first; };
   {
     const std::pair<int, int> expected[] = {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}, {6, 6}, {7, 7}, {8, 8}};
-    using M = std::flat_map<MoveNegates, int, std::less<MoveNegates>, std::vector<MoveNegates>>;
+    using M = std::flat_map<MoveNegates, int, std::less<MoveNegates>, KeyContainer<MoveNegates>, ValueContainer<int>>;
     M m     = M(expected, expected + 8);
     M m2    = M(expected, expected + 3);
 
@@ -73,7 +75,7 @@ int main(int, char**) {
   }
   {
     const std::pair<int, int> expected[] = {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}, {6, 6}, {7, 7}, {8, 8}};
-    using M = std::flat_map<MoveClears, int, std::less<MoveClears>, std::vector<MoveClears>>;
+    using M = std::flat_map<MoveClears, int, std::less<MoveClears>, KeyContainer<MoveClears>, ValueContainer<int>>;
     M m     = M(expected, expected + 8);
     M m2    = M(expected, expected + 3);
 
@@ -90,7 +92,7 @@ int main(int, char**) {
   }
   {
     // moved-from object maintains invariant if one of underlying container does not clear after move
-    using M = std::flat_map<int, int, std::less<>, std::vector<int>, CopyOnlyVector<int>>;
+    using M = std::flat_map<int, int, std::less<>, KeyContainer<int>, CopyOnlyVector<int>>;
     M m1    = M({1, 2, 3}, {1, 2, 3});
     M m2    = M({1, 2}, {1, 2});
     m2      = std::move(m1);
@@ -100,5 +102,26 @@ int main(int, char**) {
     LIBCPP_ASSERT(m1.keys().size() == 0);
     LIBCPP_ASSERT(m1.values().size() == 0);
   }
+}
+
+constexpr bool test() {
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_noexcept.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_noexcept.compile.pass.cpp
similarity index 99%
rename from libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_noexcept.pass.cpp
rename to libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_noexcept.compile.pass.cpp
index 665b763e6c4f7..18d332cf27b5b 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_noexcept.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/move_assign_noexcept.compile.pass.cpp
@@ -49,7 +49,7 @@ struct MoveThrowsComp {
   bool operator()(const auto&, const auto&) const;
 };
 
-int main(int, char**) {
+void test() {
   {
     using C = std::flat_map<int, int>;
     LIBCPP_STATIC_ASSERT(std::is_nothrow_move_assignable_v<C>);
@@ -105,6 +105,4 @@ int main(int, char**) {
     using C = std::flat_map<int, int, std::less<int>, std::vector<int>, std::pmr::vector<int>>;
     static_assert(!std::is_nothrow_move_assignable_v<C>);
   }
-
-  return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/range.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/range.pass.cpp
index 282cc71f31994..ae447f62b57d4 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/range.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/range.pass.cpp
@@ -27,9 +27,11 @@
 #include <vector>
 
 #include "min_allocator.h"
+#include "MinSequenceContainer.h"
 #include "test_allocator.h"
 #include "test_iterators.h"
 #include "test_macros.h"
+#include "../helpers.h"
 #include "../../../test_compare.h"
 
 // test constraint container-compatible-range
@@ -66,70 +68,28 @@ static_assert(std::is_constructible_v<Map,
 static_assert(!std::is_constructible_v<Map, std::from_range_t, RangeOf<int>, std::less<int>, std::allocator<int>>);
 static_assert(!std::is_constructible_v<Map, std::from_range_t, RangeOf<double>, std::less<int>, std::allocator<int>>);
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = other_allocator<int>;
-    using V1 = std::vector<int, A1>;
-    using V2 = std::vector<int, A2>;
-    using M1 = std::flat_map<int, int, C, V1, V1>;
-    using M2 = std::flat_map<int, int, C, V1, V2>;
-    using M3 = std::flat_map<int, int, C, V2, V1>;
-    static_assert(std::is_constructible_v<M1, std::from_range_t, M1, const A1&>);
-    static_assert(!std::is_constructible_v<M1, std::from_range_t, M1, const A2&>);
-    static_assert(!std::is_constructible_v<M2, std::from_range_t, M2, const A2&>);
-    static_assert(!std::is_constructible_v<M3, std::from_range_t, M3, const A2&>);
-
-    static_assert(std::is_constructible_v<M1, std::from_range_t, M1, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, std::from_range_t, M1, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, std::from_range_t, M2, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, std::from_range_t, M3, const C&, const A2&>);
-  }
-  {
-    // container-compatible-range
-    using C           = test_less<int>;
-    using A1          = test_allocator<int>;
-    using A2          = test_allocator<std::string>;
-    using M           = std::flat_map<int, std::string, C, std::vector<int, A1>, std::vector<std::string, A2>>;
-    using Pair        = std::pair<int, std::string>;
-    using PairLike    = std::tuple<int, std::string>;
-    using NonPairLike = int;
-
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&>);
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&>);
-    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&>);
-
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&, const C&>);
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&, const C&>);
-    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&, const C&>);
-
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&, const A1&>);
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&, const A1&>);
-    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&, const A1&>);
-
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&, const C&, const A1&>);
-    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&, const C&, const A1&>);
-  }
-
-  using P      = std::pair<int, short>;
-  P ar[]       = {{1, 1}, {1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {2, 7}, {3, 8}, {3, 9}};
-  P expected[] = {{1, 1}, {2, 4}, {3, 6}};
+template <class KeyContainer, class ValueContainer>
+constexpr void test() {
+  using Key   = typename KeyContainer::value_type;
+  using Value = typename ValueContainer::value_type;
+  using P     = std::pair<Key, Value>;
+  P ar[]      = {{1, 1}, {1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {2, 7}, {3, 8}, {3, 9}};
   {
     // flat_map(from_range_t, R&&)
     // input_range && !common
-    using M    = std::flat_map<int, short>;
+    using M    = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
     using Iter = cpp20_input_iterator<const P*>;
     using Sent = sentinel_wrapper<Iter>;
     using R    = std::ranges::subrange<Iter, Sent>;
     auto m     = M(std::from_range, R(Iter(ar), Sent(Iter(ar + 9))));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
 
     // explicit(false)
     M m2 = {std::from_range, R(Iter(ar), Sent(Iter(ar + 9)))};
@@ -138,31 +98,49 @@ int main(int, char**) {
   {
     // flat_map(from_range_t, R&&)
     // greater
-    using M    = std::flat_map<int, short, std::greater<int>, std::deque<int, min_allocator<int>>, std::deque<short>>;
+    using M    = std::flat_map<Key, Value, std::greater<int>, KeyContainer, ValueContainer>;
     using Iter = cpp20_input_iterator<const P*>;
     using Sent = sentinel_wrapper<Iter>;
     using R    = std::ranges::subrange<Iter, Sent>;
     auto m     = M(std::from_range, R(Iter(ar), Sent(Iter(ar + 9))));
-    assert((m.keys() == std::deque<int, min_allocator<int>>{3, 2, 1}));
-    LIBCPP_ASSERT((m.values() == std::deque<short>{6, 4, 1}));
+    assert(std::ranges::equal(m.keys(), KeyContainer{3, 2, 1}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {6, 8, 9},
+            {4, 5, 7},
+            {1, 2, 3},
+        });
   }
   {
     // flat_map(from_range_t, R&&)
     // contiguous range
-    using M = std::flat_map<int, short>;
+    using M = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
     using R = std::ranges::subrange<const P*>;
     auto m  = M(std::from_range, R(ar, ar + 9));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
   }
   {
     // flat_map(from_range_t, R&&, const key_compare&)
     using C = test_less<int>;
-    using M = std::flat_map<int, short, C, std::vector<int>, std::deque<short>>;
+    using M = std::flat_map<Key, Value, C, KeyContainer, ValueContainer>;
     using R = std::ranges::subrange<const P*>;
     auto m  = M(std::from_range, R(ar, ar + 9), C(3));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<Value>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.key_comp() == C(3));
 
     // explicit(false)
@@ -170,15 +148,27 @@ int main(int, char**) {
     assert(m2 == m);
     assert(m2.key_comp() == C(3));
   }
+}
+
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test_alloc() {
+  using P = std::pair<int, short>;
+  P ar[]  = {{1, 1}, {1, 2}, {1, 3}, {2, 4}, {2, 5}, {3, 6}, {2, 7}, {3, 8}, {3, 9}};
   {
     // flat_map(from_range_t, R&&, const Allocator&)
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, std::less<int>, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     using R  = std::ranges::subrange<const P*>;
     auto m   = M(std::from_range, R(ar, ar + 9), A1(5));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
@@ -187,11 +177,17 @@ int main(int, char**) {
     // explicit(false)
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, std::less<int>, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     using R  = std::ranges::subrange<const P*>;
     M m      = {std::from_range, R(ar, ar + 9), A1(5)}; // implicit ctor
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
@@ -200,11 +196,17 @@ int main(int, char**) {
     using C  = test_less<int>;
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, C, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, C, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     using R  = std::ranges::subrange<const P*>;
     auto m   = M(std::from_range, R(ar, ar + 9), C(3), A1(5));
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.key_comp() == C(3));
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
@@ -214,14 +216,97 @@ int main(int, char**) {
     // explicit(false)
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, std::less<int>, std::deque<int, A1>, std::vector<short, A2>>;
+    using M  = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     using R  = std::ranges::subrange<const P*>;
     M m      = {std::from_range, R(ar, ar + 9), {}, A2(5)}; // implicit ctor
-    assert(std::ranges::equal(m.keys(), expected | std::views::elements<0>));
-    LIBCPP_ASSERT(std::ranges::equal(m, expected));
+    assert(std::ranges::equal(m.keys(), KeyContainer<int, A1>{1, 2, 3}));
+    check_possible_values(
+        m.values(),
+        std::vector<std::vector<short>>{
+            {1, 2, 3},
+            {4, 5, 7},
+            {6, 8, 9},
+        });
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
+}
+
+constexpr bool test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = other_allocator<int>;
+    using V1 = std::vector<int, A1>;
+    using V2 = std::vector<int, A2>;
+    using M1 = std::flat_map<int, int, C, V1, V1>;
+    using M2 = std::flat_map<int, int, C, V1, V2>;
+    using M3 = std::flat_map<int, int, C, V2, V1>;
+    static_assert(std::is_constructible_v<M1, std::from_range_t, M1, const A1&>);
+    static_assert(!std::is_constructible_v<M1, std::from_range_t, M1, const A2&>);
+    static_assert(!std::is_constructible_v<M2, std::from_range_t, M2, const A2&>);
+    static_assert(!std::is_constructible_v<M3, std::from_range_t, M3, const A2&>);
+
+    static_assert(std::is_constructible_v<M1, std::from_range_t, M1, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, std::from_range_t, M1, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, std::from_range_t, M2, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, std::from_range_t, M3, const C&, const A2&>);
+  }
+  {
+    // container-compatible-range
+    using C           = test_less<int>;
+    using A1          = test_allocator<int>;
+    using A2          = test_allocator<std::string>;
+    using M           = std::flat_map<int, std::string, C, std::vector<int, A1>, std::vector<std::string, A2>>;
+    using Pair        = std::pair<int, std::string>;
+    using PairLike    = std::tuple<int, std::string>;
+    using NonPairLike = int;
+
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&>);
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&>);
+    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&>);
+
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&, const C&>);
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&, const C&>);
+    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&, const C&>);
+
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&, const A1&>);
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&, const A1&>);
+    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&, const A1&>);
+
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<Pair>&, const C&, const A1&>);
+    static_assert(std::is_constructible_v<M, std::from_range_t, std::vector<PairLike>&, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M, std::from_range_t, std::vector<NonPairLike>&, const C&, const A1&>);
+  }
+
+  test<std::vector<int>, std::vector<int>>();
+  test<std::vector<int>, std::vector<double>>();
+  test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
+
+  test_alloc<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+    test_alloc<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_container.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_container.pass.cpp
index 3c8868f2ff424..698f667c896ab 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_container.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_container.pass.cpp
@@ -31,39 +31,18 @@
 #include "test_allocator.h"
 #include "test_iterators.h"
 #include "test_macros.h"
+#include "../helpers.h"
 #include "../../../test_compare.h"
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = other_allocator<int>;
-    using V1 = std::vector<int, A1>;
-    using V2 = std::vector<int, A2>;
-    using M1 = std::flat_map<int, int, C, V1, V1>;
-    using M2 = std::flat_map<int, int, C, V1, V2>;
-    using M3 = std::flat_map<int, int, C, V2, V1>;
-    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, const V1&, const V2&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, const V2&, const V1&, const A2&>);
-
-    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, const V1&, const V2&, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, const V2&, const V1&, const C&, const A2&>);
-  }
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
   {
     // flat_map(sorted_unique_t, key_container_type , mapped_container_type)
-    using M              = std::flat_map<int, char>;
-    std::vector<int> ks  = {1, 2, 4, 10};
-    std::vector<char> vs = {4, 3, 2, 1};
-    auto ks2             = ks;
-    auto vs2             = vs;
+    using M                 = std::flat_map<int, char, std::less<int>, KeyContainer<int>, ValueContainer<char>>;
+    KeyContainer<int> ks    = {1, 2, 4, 10};
+    ValueContainer<char> vs = {4, 3, 2, 1};
+    auto ks2                = ks;
+    auto vs2                = vs;
 
     auto m = M(std::sorted_unique, ks, vs);
     assert((m == M{{1, 4}, {2, 3}, {4, 2}, {10, 1}}));
@@ -79,8 +58,8 @@ int main(int, char**) {
   {
     // flat_map(sorted_unique_t, key_container_type , mapped_container_type)
     // non-default container, comparator and allocator type
-    using Ks = std::deque<int, min_allocator<int>>;
-    using Vs = std::deque<char, min_allocator<char>>;
+    using Ks = KeyContainer<int, min_allocator<int>>;
+    using Vs = ValueContainer<char, min_allocator<char>>;
     using M  = std::flat_map<int, char, std::greater<int>, Ks, Vs>;
     Ks ks    = {10, 4, 2, 1};
     Vs vs    = {1, 2, 3, 4};
@@ -95,9 +74,9 @@ int main(int, char**) {
     // flat_map(sorted_unique_t, key_container_type , mapped_container_type)
     // allocator copied into the containers
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<int>, std::vector<int, A>, std::deque<int, A>>;
-    auto ks = std::vector<int, A>({1, 2, 4, 10}, A(4));
-    auto vs = std::deque<int, A>({4, 3, 2, 1}, A(5));
+    using M = std::flat_map<int, int, std::less<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
+    auto ks = KeyContainer<int, A>({1, 2, 4, 10}, A(4));
+    auto vs = ValueContainer<int, A>({4, 3, 2, 1}, A(5));
     auto m  = M(std::sorted_unique, std::move(ks), std::move(vs));
     assert(ks.empty()); // it was moved-from
     assert(vs.empty()); // it was moved-from
@@ -107,10 +86,10 @@ int main(int, char**) {
   }
   {
     // flat_map(sorted_unique_t, key_container_type , mapped_container_type, key_compare)
-    using C              = test_less<int>;
-    using M              = std::flat_map<int, char, C>;
-    std::vector<int> ks  = {1, 2, 4, 10};
-    std::vector<char> vs = {4, 3, 2, 1};
+    using C                 = test_less<int>;
+    using M                 = std::flat_map<int, char, C, KeyContainer<int>, ValueContainer<char>>;
+    KeyContainer<int> ks    = {1, 2, 4, 10};
+    ValueContainer<char> vs = {4, 3, 2, 1};
 
     auto m = M(std::sorted_unique, ks, vs, C(4));
     assert((m == M{{1, 4}, {2, 3}, {4, 2}, {10, 1}}));
@@ -123,12 +102,12 @@ int main(int, char**) {
   }
   {
     // flat_map(sorted_unique_t, key_container_type , mapped_container_type, key_compare, const Allocator&)
-    using C                = test_less<int>;
-    using A                = test_allocator<int>;
-    using M                = std::flat_map<int, int, C, std::vector<int, A>, std::vector<int, A>>;
-    std::vector<int, A> ks = {1, 2, 4, 10};
-    std::vector<int, A> vs = {4, 3, 2, 1};
-    auto m                 = M(std::sorted_unique, ks, vs, C(4), A(5));
+    using C                   = test_less<int>;
+    using A                   = test_allocator<int>;
+    using M                   = std::flat_map<int, int, C, KeyContainer<int, A>, ValueContainer<int, A>>;
+    KeyContainer<int, A> ks   = {1, 2, 4, 10};
+    ValueContainer<int, A> vs = {4, 3, 2, 1};
+    auto m                    = M(std::sorted_unique, ks, vs, C(4), A(5));
     assert((m == M{{1, 4}, {2, 3}, {4, 2}, {10, 1}}));
     assert(m.key_comp() == C(4));
     assert(m.keys().get_allocator() == A(5));
@@ -144,9 +123,9 @@ int main(int, char**) {
   {
     // flat_map(sorted_unique_t, key_container_type , mapped_container_type, const Allocator&)
     using A = test_allocator<int>;
-    using M = std::flat_map<int, int, std::less<int>, std::vector<int, A>, std::deque<int, A>>;
-    auto ks = std::vector<int, A>({1, 2, 4, 10}, A(4));
-    auto vs = std::deque<int, A>({4, 3, 2, 1}, A(5));
+    using M = std::flat_map<int, int, std::less<int>, KeyContainer<int, A>, ValueContainer<int, A>>;
+    auto ks = KeyContainer<int, A>({1, 2, 4, 10}, A(4));
+    auto vs = ValueContainer<int, A>({4, 3, 2, 1}, A(5));
     auto m  = M(std::sorted_unique, ks, vs, A(6)); // replaces the allocators
     assert(!ks.empty());                           // it was an lvalue above
     assert(!vs.empty());                           // it was an lvalue above
@@ -160,6 +139,51 @@ int main(int, char**) {
     assert(m2.keys().get_allocator() == A(6));
     assert(m2.values().get_allocator() == A(6));
   }
+}
+
+constexpr bool test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = other_allocator<int>;
+    using V1 = std::vector<int, A1>;
+    using V2 = std::vector<int, A2>;
+    using M1 = std::flat_map<int, int, C, V1, V1>;
+    using M2 = std::flat_map<int, int, C, V1, V2>;
+    using M3 = std::flat_map<int, int, C, V2, V1>;
+    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, const V1&, const V2&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, const V2&, const V1&, const A2&>);
+
+    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, const V1&, const V1&, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, const V1&, const V2&, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, const V2&, const V1&, const C&, const A2&>);
+  }
+
+  test<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque, std::vector>();
+    test<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_initializer_list.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_initializer_list.pass.cpp
index 26452472ba201..8f00e04f84d12 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_initializer_list.pass.cpp
@@ -22,6 +22,7 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
 #include "min_allocator.h"
@@ -31,13 +32,87 @@
 #include "../../../test_compare.h"
 
 template <class T, class U>
-std::initializer_list<std::pair<T, U>> il = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
+constexpr std::initializer_list<std::pair<T, U>> il = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
 
-const auto il1 = il<int, int>;
-const auto il2 = il<int, short>;
-const auto il3 = il<short, int>;
+constexpr auto il1 = il<int, int>;
+constexpr auto il2 = il<int, short>;
+constexpr auto il3 = il<short, int>;
 
-int main(int, char**) {
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test() {
+  {
+    // flat_map(sorted_unique_t, initializer_list<value_type>);
+    using M       = std::flat_map<int, int, std::less<int>, KeyContainer<int>, ValueContainer<int>>;
+    auto m        = M(std::sorted_unique, il1);
+    auto expected = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
+    assert(m == expected);
+
+    // explicit(false)
+    M m2 = {std::sorted_unique, il1};
+    assert(m2 == m);
+  }
+  if (!std::is_constant_evaluated()) {
+    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&);
+    using M = std::flat_map<int, int, std::function<bool(int, int)>, KeyContainer<int>, ValueContainer<int>>;
+    auto m  = M(std::sorted_unique, il1, std::less<int>());
+    assert(m == M({{1, 1}, {2, 2}, {4, 4}, {5, 5}}, std::less<>()));
+    assert(m.key_comp()(1, 2) == true);
+
+    // explicit(false)
+    M m2 = {std::sorted_unique, il1, std::less<int>()};
+    assert(m2 == m);
+  }
+  {
+    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&);
+    // greater
+    using M = std::flat_map<int, int, std::greater<int>, KeyContainer<int, min_allocator<int>>, ValueContainer<int>>;
+    std::initializer_list<std::pair<int, int>> il4{{5, 5}, {4, 4}, {2, 2}, {1, 1}};
+    auto m = M(std::sorted_unique, il4, std::greater<int>());
+    assert((m == M{{5, 5}, {4, 4}, {2, 2}, {1, 1}}));
+  }
+  {
+    // flat_map(sorted_unique_t, initializer_list<value_type>,  const Allocator&)
+    using A1      = test_allocator<int>;
+    using A2      = test_allocator<short>;
+    using M       = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
+    auto m        = M(std::sorted_unique, il2, A1(5));
+    auto expected = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
+    assert(m == expected);
+    assert(m.keys().get_allocator() == A1(5));
+    assert(m.values().get_allocator() == A2(5));
+
+    // explicit(false)
+    M m2 = {std::sorted_unique, il2, A1(5)};
+    assert(m2 == m);
+    assert(m2.keys().get_allocator() == A1(5));
+    assert(m2.values().get_allocator() == A2(5));
+  }
+  {
+    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&, const Allocator&);
+    using C  = test_less<int>;
+    using A1 = test_allocator<int>;
+    using A2 = test_allocator<short>;
+    using M  = std::flat_map<int, short, C, KeyContainer<int, A1>, ValueContainer<short, A2>>;
+    auto m   = M(std::sorted_unique, il2, C(3), A1(5));
+    assert((m == M{{1, 1}, {2, 2}, {4, 4}, {5, 5}}));
+    assert(m.key_comp() == C(3));
+    assert(m.keys().get_allocator() == A1(5));
+    assert(m.values().get_allocator() == A2(5));
+  }
+  {
+    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&, const Allocator&);
+    // explicit(false)
+    using A1 = test_allocator<short>;
+    using A2 = test_allocator<int>;
+    using M  = std::flat_map<short, int, std::less<int>, KeyContainer<short, A1>, ValueContainer<int, A2>>;
+    M m      = {std::sorted_unique, il3, {}, A1(5)}; // implicit ctor
+    assert((m == M{{1, 1}, {2, 2}, {4, 4}, {5, 5}}));
+    assert(m.keys().get_allocator() == A1(5));
+    assert(m.values().get_allocator() == A2(5));
+  }
+}
+
+constexpr bool test() {
   {
     // The constructors in this subclause shall not participate in overload
     // resolution unless uses_allocator_v<key_container_type, Alloc> is true
@@ -104,76 +179,23 @@ int main(int, char**) {
                                            std::allocator<int>>);
   }
 
-  {
-    // flat_map(sorted_unique_t, initializer_list<value_type>);
-    using M       = std::flat_map<int, int>;
-    auto m        = M(std::sorted_unique, il1);
-    auto expected = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    assert(m == expected);
-
-    // explicit(false)
-    M m2 = {std::sorted_unique, il1};
-    assert(m2 == m);
-  }
-  {
-    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&);
-    using M = std::flat_map<int, int, std::function<bool(int, int)>>;
-    auto m  = M(std::sorted_unique, il1, std::less<int>());
-    assert(m == M({{1, 1}, {2, 2}, {4, 4}, {5, 5}}, std::less<>()));
-    assert(m.key_comp()(1, 2) == true);
+  test<std::vector, std::vector>();
 
-    // explicit(false)
-    M m2 = {std::sorted_unique, il1, std::less<int>()};
-    assert(m2 == m);
-  }
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
   {
-    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&);
-    // greater
-    using M = std::flat_map<int, int, std::greater<int>, std::deque<int, min_allocator<int>>, std::vector<int>>;
-    std::initializer_list<std::pair<int, int>> il4{{5, 5}, {4, 4}, {2, 2}, {1, 1}};
-    auto m = M(std::sorted_unique, il4, std::greater<int>());
-    assert((m == M{{5, 5}, {4, 4}, {2, 2}, {1, 1}}));
+    test<std::deque, std::deque>();
   }
-  {
-    // flat_map(sorted_unique_t, initializer_list<value_type>,  const Allocator&)
-    using A1      = test_allocator<int>;
-    using A2      = test_allocator<short>;
-    using M       = std::flat_map<int, short, std::less<int>, std::vector<int, A1>, std::deque<short, A2>>;
-    auto m        = M(std::sorted_unique, il2, A1(5));
-    auto expected = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    assert(m == expected);
-    assert(m.keys().get_allocator() == A1(5));
-    assert(m.values().get_allocator() == A2(5));
 
-    // explicit(false)
-    M m2 = {std::sorted_unique, il2, A1(5)};
-    assert(m2 == m);
-    assert(m2.keys().get_allocator() == A1(5));
-    assert(m2.values().get_allocator() == A2(5));
-  }
-  {
-    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&, const Allocator&);
-    using C  = test_less<int>;
-    using A1 = test_allocator<int>;
-    using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, C, std::vector<int, A1>, std::deque<short, A2>>;
-    auto m   = M(std::sorted_unique, il2, C(3), A1(5));
-    assert((m == M{{1, 1}, {2, 2}, {4, 4}, {5, 5}}));
-    assert(m.key_comp() == C(3));
-    assert(m.keys().get_allocator() == A1(5));
-    assert(m.values().get_allocator() == A2(5));
-  }
-  {
-    // flat_map(sorted_unique_t, initializer_list<value_type>, const key_compare&, const Allocator&);
-    // explicit(false)
-    using A1 = test_allocator<short>;
-    using A2 = test_allocator<int>;
-    using M  = std::flat_map<short, int, std::less<int>, std::deque<short, A1>, std::vector<int, A2>>;
-    M m      = {std::sorted_unique, il3, {}, A1(5)}; // implicit ctor
-    assert((m == M{{1, 1}, {2, 2}, {4, 4}, {5, 5}}));
-    assert(m.keys().get_allocator() == A1(5));
-    assert(m.values().get_allocator() == A2(5));
-  }
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_iter_iter.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_iter_iter.pass.cpp
index 8eb7547e917cc..710d45ed36f72 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_iter_iter.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.cons/sorted_iter_iter.pass.cpp
@@ -20,45 +20,26 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
+#include "MinSequenceContainer.h"
 #include "min_allocator.h"
 #include "test_allocator.h"
 #include "test_iterators.h"
 #include "test_macros.h"
 #include "../../../test_compare.h"
 
-int main(int, char**) {
-  {
-    // The constructors in this subclause shall not participate in overload
-    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
-    // and uses_allocator_v<mapped_container_type, Alloc> is true.
-    using C     = test_less<int>;
-    using A1    = test_allocator<int>;
-    using A2    = other_allocator<int>;
-    using V1    = std::vector<int, A1>;
-    using V2    = std::vector<int, A2>;
-    using M1    = std::flat_map<int, int, C, V1, V1>;
-    using M2    = std::flat_map<int, int, C, V1, V2>;
-    using M3    = std::flat_map<int, int, C, V2, V1>;
-    using Iter1 = typename M1::iterator;
-    using Iter2 = typename M2::iterator;
-    using Iter3 = typename M3::iterator;
-    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const A1&>);
-    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const A2&>);
-    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, Iter2, Iter2, const A2&>);
-    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, Iter3, Iter3, const A2&>);
+template <class KeyContainer, class ValueContainer>
+constexpr void test() {
+  using Key   = typename KeyContainer::value_type;
+  using Value = typename ValueContainer::value_type;
 
-    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const C&, const A1&>);
-    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, Iter2, Iter2, const C&, const A2&>);
-    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, Iter3, Iter3, const C&, const A2&>);
-  }
   {
     // flat_map(sorted_unique_t, InputIterator, InputIterator);
     // cpp17_input_iterator
-    using M       = std::flat_map<int, int>;
-    using P       = std::pair<int, int>;
+    using M       = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
+    using P       = std::pair<Key, Value>;
     P ar[]        = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
     auto m        = M(std::sorted_unique, cpp17_input_iterator<const P*>(ar), cpp17_input_iterator<const P*>(ar + 4));
     auto expected = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
@@ -71,18 +52,19 @@ int main(int, char**) {
   {
     // flat_map(sorted_unique_t, InputIterator, InputIterator);
     // contiguous iterator
-    using C = test_less<int>;
-    using M = std::flat_map<int, int, C, std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>;
-    std::pair<int, int> ar[] = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    auto m                   = M(std::sorted_unique, ar, ar + 4);
-    auto expected            = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
+    using C       = test_less<Key>;
+    using P       = std::pair<Key, Value>;
+    using M       = std::flat_map<Key, Value, C, KeyContainer, ValueContainer>;
+    P ar[]        = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
+    auto m        = M(std::sorted_unique, ar, ar + 4);
+    auto expected = M{{1, 1}, {2, 2}, {4, 4}, {5, 5}};
     assert(m == expected);
   }
-  {
+  if (!std::is_constant_evaluated()) {
     // flat_map(sorted_unique_t, InputIterator, InputIterator, const key_compare&);
     // cpp_17_input_iterator
-    using M = std::flat_map<int, int, std::function<bool(int, int)>>;
-    using P = std::pair<int, int>;
+    using M = std::flat_map<Key, Value, std::function<bool(Key, Value)>>;
+    using P = std::pair<Key, Value>;
     P ar[]  = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
     auto m  = M(std::sorted_unique,
                cpp17_input_iterator<const P*>(ar),
@@ -101,8 +83,8 @@ int main(int, char**) {
   {
     // flat_map(sorted_unique_t, InputIterator, InputIterator, const key_compare&);
     // greater
-    using M = std::flat_map<int, int, std::greater<int>, std::deque<int, min_allocator<int>>, std::vector<int>>;
-    using P = std::pair<int, int>;
+    using M = std::flat_map<Key, Value, std::greater<int>, KeyContainer, ValueContainer>;
+    using P = std::pair<Key, Value>;
     P ar[]  = {{5, 5}, {4, 4}, {2, 2}, {1, 1}};
     auto m  = M(std::sorted_unique,
                cpp17_input_iterator<const P*>(ar),
@@ -113,18 +95,22 @@ int main(int, char**) {
   {
     // flat_map(sorted_unique_t, InputIterator, InputIterator, const key_compare&);
     // contiguous iterator
-    using C = test_less<int>;
-    using M = std::flat_map<int, int, C, std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>;
-    std::pair<int, int> ar[1] = {{42, 42}};
-    auto m                    = M(std::sorted_unique, ar, ar, C(5));
+    using C                     = test_less<Key>;
+    using M                     = std::flat_map<Key, Value, C, KeyContainer, ValueContainer>;
+    std::pair<Key, Value> ar[1] = {{42, 42}};
+    auto m                      = M(std::sorted_unique, ar, ar, C(5));
     assert(m.empty());
     assert(m.key_comp() == C(5));
   }
+}
+
+template <template <class...> class KeyContainer, template <class...> class ValueContainer>
+constexpr void test_alloc() {
   {
     // flat_map(sorted_unique_t, InputIterator , InputIterator, const Allocator&)
     using A1      = test_allocator<int>;
     using A2      = test_allocator<short>;
-    using M       = std::flat_map<int, short, std::less<int>, std::vector<int, A1>, std::deque<short, A2>>;
+    using M       = std::flat_map<int, short, std::less<int>, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     using P       = std::pair<int, int>;
     P ar[]        = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
     auto m        = M(std::sorted_unique, ar, ar + 4, A1(5));
@@ -144,7 +130,7 @@ int main(int, char**) {
     using C  = test_less<int>;
     using A1 = test_allocator<int>;
     using A2 = test_allocator<short>;
-    using M  = std::flat_map<int, short, C, std::vector<int, A1>, std::deque<short, A2>>;
+    using M  = std::flat_map<int, short, C, KeyContainer<int, A1>, ValueContainer<short, A2>>;
     using P  = std::pair<int, int>;
     P ar[]   = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
     auto m   = M(std::sorted_unique, ar, ar + 4, C(3), A1(5));
@@ -158,7 +144,7 @@ int main(int, char**) {
     // explicit(false)
     using A1 = test_allocator<short>;
     using A2 = test_allocator<int>;
-    using M  = std::flat_map<short, int, std::less<int>, std::deque<short, A1>, std::vector<int, A2>>;
+    using M  = std::flat_map<short, int, std::less<int>, KeyContainer<short, A1>, ValueContainer<int, A2>>;
     using P  = std::pair<int, int>;
     P ar[]   = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
     M m      = {std::sorted_unique, ar, ar + 4, {}, A1(5)}; // implicit ctor
@@ -166,6 +152,59 @@ int main(int, char**) {
     assert(m.keys().get_allocator() == A1(5));
     assert(m.values().get_allocator() == A2(5));
   }
+}
+
+constexpr bool test() {
+  {
+    // The constructors in this subclause shall not participate in overload
+    // resolution unless uses_allocator_v<key_container_type, Alloc> is true
+    // and uses_allocator_v<mapped_container_type, Alloc> is true.
+    using C     = test_less<int>;
+    using A1    = test_allocator<int>;
+    using A2    = other_allocator<int>;
+    using V1    = std::vector<int, A1>;
+    using V2    = std::vector<int, A2>;
+    using M1    = std::flat_map<int, int, C, V1, V1>;
+    using M2    = std::flat_map<int, int, C, V1, V2>;
+    using M3    = std::flat_map<int, int, C, V2, V1>;
+    using Iter1 = typename M1::iterator;
+    using Iter2 = typename M2::iterator;
+    using Iter3 = typename M3::iterator;
+    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const A1&>);
+    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const A2&>);
+    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, Iter2, Iter2, const A2&>);
+    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, Iter3, Iter3, const A2&>);
+
+    static_assert(std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const C&, const A1&>);
+    static_assert(!std::is_constructible_v<M1, std::sorted_unique_t, Iter1, Iter1, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M2, std::sorted_unique_t, Iter2, Iter2, const C&, const A2&>);
+    static_assert(!std::is_constructible_v<M3, std::sorted_unique_t, Iter3, Iter3, const C&, const A2&>);
+  }
+
+  test<std::vector<int>, std::vector<int>>();
+  test<std::vector<int>, std::vector<double>>();
+  test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
+
+  test_alloc<std::vector, std::vector>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+    test_alloc<std::deque, std::deque>();
+  }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.erasure/erase_if.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.erasure/erase_if.pass.cpp
index fb0563eec5376..07ed235ce7edc 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.erasure/erase_if.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.erasure/erase_if.pass.cpp
@@ -32,7 +32,7 @@ static_assert(HasStdErase<std::vector<int>>);
 static_assert(!HasStdErase<std::flat_map<int, int>>);
 
 template <class M>
-M make(std::initializer_list<int> vals) {
+constexpr M make(std::initializer_list<int> vals) {
   M ret;
   for (int v : vals)
     ret[static_cast<typename M::key_type>(v)] = static_cast<typename M::mapped_type>(v + 10);
@@ -40,8 +40,8 @@ M make(std::initializer_list<int> vals) {
 }
 
 template <class M, class Pred>
-void test0(
-    std::initializer_list<int> vals, Pred p, std::initializer_list<int> expected, std::size_t expected_erased_count) {
+constexpr void
+test0(std::initializer_list<int> vals, Pred p, std::initializer_list<int> expected, std::size_t expected_erased_count) {
   M s = make<M>(vals);
   ASSERT_SAME_TYPE(typename M::size_type, decltype(std::erase_if(s, p)));
   assert(expected_erased_count == std::erase_if(s, p));
@@ -49,7 +49,7 @@ void test0(
 }
 
 template <class S>
-void test() {
+constexpr void test() {
   // Test all the plausible signatures for this predicate.
   auto is1   = [](typename S::const_reference v) { return v.first == 1; };
   auto is2   = [](typename S::value_type v) { return v.first == 2; };
@@ -76,7 +76,7 @@ void test() {
   test0<S>({1, 2, 3}, False, {1, 2, 3}, 0);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::flat_map<int, char>>();
   test<std::flat_map<int,
                      char,
@@ -84,10 +84,24 @@ int main(int, char**) {
                      std::vector<int, min_allocator<int>>,
                      std::vector<char, min_allocator<char>>>>();
   test<std::flat_map<int, char, std::greater<int>, std::vector<int, test_allocator<int>>>>();
-  test<std::flat_map<int, char, std::less<int>, std::deque<int, min_allocator<int>>>>();
-  test<std::flat_map<int, char, std::greater<int>, std::deque<int, test_allocator<int>>>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::flat_map<int, char, std::less<int>, std::deque<int, min_allocator<int>>>>();
+    test<std::flat_map<int, char, std::greater<int>, std::deque<int, test_allocator<int>>>>();
+  }
   test<std::flat_map<long, int>>();
   test<std::flat_map<double, int>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator.pass.cpp
index b63ce6b19ee16..1585c0c4a3215 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator.pass.cpp
@@ -30,7 +30,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -70,9 +70,14 @@ void test() {
   assert(i == m.begin());
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
@@ -92,5 +97,14 @@ int main(int, char**) {
     assert(!(cii != ii1));
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator_comparison.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator_comparison.pass.cpp
index 1975d0ed86cc8..8cca1d4b3d5ec 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator_comparison.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/iterator_comparison.pass.cpp
@@ -24,7 +24,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -145,11 +145,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/reverse_iterator.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/reverse_iterator.pass.cpp
index b4d76aac119a3..0c6c6d6c595f1 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/reverse_iterator.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.iterators/reverse_iterator.pass.cpp
@@ -25,48 +25,64 @@
 
 #include <iterator>
 
+#include "MinSequenceContainer.h"
 #include "test_macros.h"
+#include "min_allocator.h"
 
-int main(int, char**) {
+template <class KeyContainer, class ValueContainer>
+constexpr void test() {
+  using Key   = typename KeyContainer::value_type;
+  using Value = typename ValueContainer::value_type;
+  using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
+  M m         = {{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}};
+  const M& cm = m;
+  ASSERT_SAME_TYPE(decltype(m.rbegin()), typename M::reverse_iterator);
+  ASSERT_SAME_TYPE(decltype(m.crbegin()), typename M::const_reverse_iterator);
+  ASSERT_SAME_TYPE(decltype(cm.rbegin()), typename M::const_reverse_iterator);
+  ASSERT_SAME_TYPE(decltype(m.rend()), typename M::reverse_iterator);
+  ASSERT_SAME_TYPE(decltype(m.crend()), typename M::const_reverse_iterator);
+  ASSERT_SAME_TYPE(decltype(cm.rend()), typename M::const_reverse_iterator);
+  static_assert(noexcept(m.rbegin()));
+  static_assert(noexcept(cm.rbegin()));
+  static_assert(noexcept(m.crbegin()));
+  static_assert(noexcept(m.rend()));
+  static_assert(noexcept(cm.rend()));
+  static_assert(noexcept(m.crend()));
+  assert(m.size() == 4);
+  assert(std::distance(m.rbegin(), m.rend()) == 4);
+  assert(std::distance(cm.rbegin(), cm.rend()) == 4);
+  assert(std::distance(m.crbegin(), m.crend()) == 4);
+  assert(std::distance(cm.crbegin(), cm.crend()) == 4);
+  typename M::reverse_iterator i; // default-construct
+  ASSERT_SAME_TYPE(decltype(i->first), const int&);
+  ASSERT_SAME_TYPE(decltype(i->second), char&);
+  i                                    = m.rbegin(); // move-assignment
+  typename M::const_reverse_iterator k = i;          // converting constructor
+  assert(i == k);                                    // comparison
+  for (int j = 4; j >= 1; --j, ++i) {                // pre-increment
+    assert(i->first == j);                           // operator->
+    assert(i->second == 'a' + j - 1);
+  }
+  assert(i == m.rend());
+  for (int j = 1; j <= 4; ++j) {
+    --i; // pre-decrement
+    assert((*i).first == j);
+    assert((*i).second == 'a' + j - 1);
+  }
+  assert(i == m.rbegin());
+}
+
+constexpr bool test() {
+  test<std::vector<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
   {
-    using M     = std::flat_map<int, char, std::less<int>, std::deque<int>, std::deque<char>>;
-    M m         = {{1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'}};
-    const M& cm = m;
-    ASSERT_SAME_TYPE(decltype(m.rbegin()), M::reverse_iterator);
-    ASSERT_SAME_TYPE(decltype(m.crbegin()), M::const_reverse_iterator);
-    ASSERT_SAME_TYPE(decltype(cm.rbegin()), M::const_reverse_iterator);
-    ASSERT_SAME_TYPE(decltype(m.rend()), M::reverse_iterator);
-    ASSERT_SAME_TYPE(decltype(m.crend()), M::const_reverse_iterator);
-    ASSERT_SAME_TYPE(decltype(cm.rend()), M::const_reverse_iterator);
-    static_assert(noexcept(m.rbegin()));
-    static_assert(noexcept(cm.rbegin()));
-    static_assert(noexcept(m.crbegin()));
-    static_assert(noexcept(m.rend()));
-    static_assert(noexcept(cm.rend()));
-    static_assert(noexcept(m.crend()));
-    assert(m.size() == 4);
-    assert(std::distance(m.rbegin(), m.rend()) == 4);
-    assert(std::distance(cm.rbegin(), cm.rend()) == 4);
-    assert(std::distance(m.crbegin(), m.crend()) == 4);
-    assert(std::distance(cm.crbegin(), cm.crend()) == 4);
-    M::reverse_iterator i; // default-construct
-    ASSERT_SAME_TYPE(decltype(i->first), const int&);
-    ASSERT_SAME_TYPE(decltype(i->second), char&);
-    i                           = m.rbegin(); // move-assignment
-    M::const_reverse_iterator k = i;          // converting constructor
-    assert(i == k);                           // comparison
-    for (int j = 4; j >= 1; --j, ++i) {       // pre-increment
-      assert(i->first == j);                  // operator->
-      assert(i->second == 'a' + j - 1);
-    }
-    assert(i == m.rend());
-    for (int j = 1; j <= 4; ++j) {
-      --i; // pre-decrement
-      assert((*i).first == j);
-      assert((*i).second == 'a' + j - 1);
-    }
-    assert(i == m.rbegin());
+    test<std::deque<int>, std::vector<char>>();
   }
+  test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
+  test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
+
   {
     // N3644 testing
     using C = std::flat_map<int, char>;
@@ -82,6 +98,14 @@ int main(int, char**) {
     assert(!(ii1 != cii));
     assert(!(cii != ii1));
   }
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
 
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/clear.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/clear.pass.cpp
index 30271eb55660b..0ba5bba99f7bc 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/clear.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/clear.pass.cpp
@@ -39,7 +39,7 @@ static_assert(
 #endif
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -52,13 +52,27 @@ void test() {
   assert(m.size() == 0);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace.pass.cpp
index a54fcad639280..784ea49eac11d 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace.pass.cpp
@@ -18,6 +18,7 @@
 #include <deque>
 #include <tuple>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
 #include "MinSequenceContainer.h"
@@ -39,7 +40,7 @@ static_assert(!CanEmplace<Map, Emplaceable>);
 static_assert(!CanEmplace<Map, int, double>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -117,7 +118,7 @@ void test() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test_emplaceable() {
+constexpr void test_emplaceable() {
   using M = std::flat_map<int, Emplaceable, std::less<int>, KeyContainer, ValueContainer>;
   using R = std::pair<typename M::iterator, bool>;
 
@@ -143,23 +144,38 @@ void test_emplaceable() {
   assert(m.begin()->second == Emplaceable(2, 3.5));
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
   test_emplaceable<std::vector<int>, std::vector<Emplaceable>>();
-  test_emplaceable<std::deque<int>, std::vector<Emplaceable>>();
   test_emplaceable<MinSequenceContainer<int>, MinSequenceContainer<Emplaceable>>();
   test_emplaceable<std::vector<int, min_allocator<int>>, std::vector<Emplaceable, min_allocator<Emplaceable>>>();
 
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
   {
+    test<std::deque<int>, std::vector<double>>();
+    test_emplaceable<std::deque<int>, std::vector<Emplaceable>>();
+  }
+
+  if (!std::is_constant_evaluated()) {
     auto emplace_func = [](auto& m, auto key_arg, auto value_arg) {
       m.emplace(std::piecewise_construct, std::tuple(key_arg), std::tuple(value_arg));
     };
     test_emplace_exception_guarantee(emplace_func);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace_hint.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace_hint.pass.cpp
index 77c022a6de92b..ebcf36be1735c 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace_hint.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/emplace_hint.pass.cpp
@@ -17,6 +17,7 @@
 #include <cassert>
 #include <deque>
 #include <functional>
+#include <type_traits>
 #include <vector>
 
 #include "MinSequenceContainer.h"
@@ -42,7 +43,7 @@ static_assert(!CanEmplaceHint<Map, int, double>);
 #endif
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -139,7 +140,7 @@ void test() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test_emplaceable() {
+constexpr void test_emplaceable() {
   using M = std::flat_map<int, Emplaceable, std::less<int>, KeyContainer, ValueContainer>;
   using R = M::iterator;
 
@@ -162,23 +163,37 @@ void test_emplaceable() {
   assert(m.begin()->second == Emplaceable(2, 3.5));
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+    test_emplaceable<std::deque<int>, std::vector<Emplaceable>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
   test_emplaceable<std::vector<int>, std::vector<Emplaceable>>();
-  test_emplaceable<std::deque<int>, std::vector<Emplaceable>>();
   test_emplaceable<MinSequenceContainer<int>, MinSequenceContainer<Emplaceable>>();
   test_emplaceable<std::vector<int, min_allocator<int>>, std::vector<Emplaceable, min_allocator<Emplaceable>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto emplace_func = [](auto& m, auto key_arg, auto value_arg) {
       m.emplace_hint(m.begin(), std::piecewise_construct, std::tuple(key_arg), std::tuple(value_arg));
     };
     test_emplace_exception_guarantee(emplace_func);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter.pass.cpp
index 914e8b676a656..e368ae9663e9d 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter.pass.cpp
@@ -18,6 +18,7 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -27,7 +28,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -136,16 +137,30 @@ void test() {
   assert(i8 == m.end());
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto erase_function = [](auto& m, auto) { m.erase(m.begin() + 2); };
     test_erase_exception_guarantee(erase_function);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter_iter.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter_iter.pass.cpp
index 0bc9208294029..7abf1e1db2e57 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter_iter.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_iter_iter.pass.cpp
@@ -17,6 +17,7 @@
 #include <deque>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -26,7 +27,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -95,15 +96,30 @@ void test() {
   assert(i4 == m.end());
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto erase_function = [](auto& m, auto) { m.erase(m.begin(), m.begin() + 2); };
     test_erase_exception_guarantee(erase_function);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key.pass.cpp
index ef57b1cb5512d..8a004a77827b9 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key.pass.cpp
@@ -26,7 +26,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer, class Compare = std::less<>>
-void test() {
+constexpr void test() {
   using M = std::flat_map<int, char, Compare, KeyContainer, ValueContainer>;
 
   auto make = [](std::initializer_list<int> il) {
@@ -70,14 +70,20 @@ void test() {
   assert(m.empty());
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
   test<std::vector<int>, std::vector<char>, std::greater<>>();
-  test<std::deque<int>, std::vector<char>>();
+
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto erase_function = [](auto& m, auto key_arg) {
       using Map = std::decay_t<decltype(m)>;
       using Key = typename Map::key_type;
@@ -87,5 +93,14 @@ int main(int, char**) {
     test_erase_exception_guarantee(erase_function);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp
index 3ba30757bf2c7..5320b1eed8137 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/erase_key_transparent.pass.cpp
@@ -38,9 +38,9 @@ static_assert(!CanErase<const NonTransparentMap>);
 
 template <class Key, class It>
 struct HeterogeneousKey {
-  explicit HeterogeneousKey(Key key, It it) : key_(key), it_(it) {}
-  operator It() && { return it_; }
-  auto operator<=>(Key key) const { return key_ <=> key; }
+  constexpr explicit HeterogeneousKey(Key key, It it) : key_(key), it_(it) {}
+  constexpr operator It() && { return it_; }
+  constexpr auto operator<=>(Key key) const { return key_ <=> key; }
   friend bool operator<(const HeterogeneousKey&, const HeterogeneousKey&) {
     assert(false);
     return false;
@@ -50,7 +50,7 @@ struct HeterogeneousKey {
 };
 
 template <class KeyContainer, class ValueContainer>
-void test_simple() {
+constexpr void test_simple() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -71,7 +71,7 @@ void test_simple() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test_transparent_comparator() {
+constexpr void test_transparent_comparator() {
   using M = std::flat_map<std::string, int, TransparentComparator, KeyContainer, ValueContainer>;
   M m     = {{"alpha", 1}, {"beta", 2}, {"epsilon", 3}, {"eta", 4}, {"gamma", 5}};
   ASSERT_SAME_TYPE(decltype(m.erase(Transparent<std::string>{"abc"})), typename M::size_type);
@@ -87,18 +87,24 @@ void test_transparent_comparator() {
   assert(m == expected);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test_simple<std::vector<int>, std::vector<double>>();
-  test_simple<std::deque<int>, std::vector<double>>();
   test_simple<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test_simple<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
   test_transparent_comparator<std::vector<std::string>, std::vector<int>>();
-  test_transparent_comparator<std::deque<std::string>, std::vector<int>>();
   test_transparent_comparator<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test_transparent_comparator<std::vector<std::string, min_allocator<std::string>>,
                               std::vector<int, min_allocator<int>>>();
 
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test_simple<std::deque<int>, std::vector<double>>();
+    test_transparent_comparator<std::deque<std::string>, std::vector<int>>();
+  }
+
   {
     // P2077's HeterogeneousKey example
     using M                           = std::flat_map<int, int, std::less<>>;
@@ -131,7 +137,7 @@ int main(int, char**) {
     assert(n == 1);
     assert(transparent_used);
   }
-  {
+  if (!std::is_constant_evaluated()) {
     auto erase_transparent = [](auto& m, auto key_arg) {
       using Map = std::decay_t<decltype(m)>;
       using Key = typename Map::key_type;
@@ -140,5 +146,14 @@ int main(int, char**) {
     test_erase_exception_guarantee(erase_transparent);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/extract.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/extract.pass.cpp
index d8e4ce94efb9e..30219df3d60ba 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/extract.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/extract.pass.cpp
@@ -33,7 +33,7 @@ static_assert(!CanExtract<std::flat_map<int, int> const&>);
 static_assert(!CanExtract<std::flat_map<int, int> const&&>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using M = std::flat_map<int, int, std::less<int>, KeyContainer, ValueContainer>;
   M m     = M({1, 2, 3}, {4, 5, 6});
 
@@ -49,9 +49,14 @@ void test() {
   LIBCPP_ASSERT(m.values().size() == 0);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
-  test<std::deque<int>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<int>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<int>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
   {
@@ -67,7 +72,7 @@ int main(int, char**) {
     LIBCPP_ASSERT(m.values().size() == 0);
   }
 
-  {
+  if (!std::is_constant_evaluated()) {
 #ifndef TEST_HAS_NO_EXCEPTIONS
     using KeyContainer   = std::vector<int>;
     using ValueContainer = ThrowOnMoveContainer<int>;
@@ -87,5 +92,15 @@ int main(int, char**) {
     }
 #endif
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_cv.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_cv.pass.cpp
index 7e667c4e4877b..93e263ed33d2f 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_cv.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_cv.pass.cpp
@@ -23,7 +23,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -64,13 +64,18 @@ void test() {
   assert(r.first->second == 3.5);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap    = std::decay_t<decltype(m)>;
       using value_type = typename FlatMap::value_type;
@@ -79,5 +84,15 @@ int main(int, char**) {
     };
     test_emplace_exception_guarantee(insert_func);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_initializer_list.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_initializer_list.pass.cpp
index 32be3ab8a95b3..1a49e30584df0 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_initializer_list.pass.cpp
@@ -12,10 +12,12 @@
 
 // void insert(initializer_list<value_type> il);
 
+#include <algorithm>
 #include <flat_map>
 #include <cassert>
 #include <functional>
 #include <deque>
+#include <type_traits>
 
 #include "MinSequenceContainer.h"
 #include "../helpers.h"
@@ -23,7 +25,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -42,20 +44,29 @@ void test() {
       {2, 2},
   });
   assert(m.size() == 4);
-  assert(std::distance(m.begin(), m.end()) == 4);
-  assert(*m.begin() == V(1, 1));
-  assert(*std::next(m.begin()) == V(2, 1));
-  assert(*std::next(m.begin(), 2) == V(3, 1));
-  assert(*std::next(m.begin(), 3) == V(4, 1));
+  assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3, 4}));
+  check_possible_values(
+      m.values(),
+      std::vector<std::vector<Value>>{
+          {1, 1.5, 2},
+          {1, 1.5, 2},
+          {1, 1.5, 2},
+          {1, 1.5, 2},
+      });
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, const auto& newValues) {
       using FlatMap                        = std::decay_t<decltype(m)>;
       using value_type                     = typename FlatMap::value_type;
@@ -64,5 +75,15 @@ int main(int, char**) {
     };
     test_insert_range_exception_guarantee(insert_func);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_cv.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_cv.pass.cpp
index 4bbe0628317dc..f0fd5622ddefe 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_cv.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_cv.pass.cpp
@@ -23,7 +23,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -60,13 +60,18 @@ void test() {
   assert(r->second == 3.5);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap    = std::decay_t<decltype(m)>;
       using value_type = typename FlatMap::value_type;
@@ -75,5 +80,15 @@ int main(int, char**) {
     };
     test_emplace_exception_guarantee(insert_func);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_iter.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_iter.pass.cpp
index 8455b19475fe4..2b6e5fafc555e 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_iter.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_iter.pass.cpp
@@ -37,7 +37,7 @@ static_assert(!CanInsert<Map, int, int>);
 static_assert(!CanInsert<Map, cpp20_input_iterator<Pair*>, cpp20_input_iterator<Pair*>>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using P = std::pair<int, double>;
   using M = std::flat_map<int, double, std::less<int>, KeyContainer, ValueContainer>;
 
@@ -67,23 +67,57 @@ void test() {
   M m;
   m.insert(cpp17_input_iterator<P*>(ar1), cpp17_input_iterator<P*>(ar1 + sizeof(ar1) / sizeof(ar1[0])));
   assert(m.size() == 3);
-  M expected{{1, 1}, {2, 1}, {3, 1}};
-  assert(m == expected);
+
+  assert(std::ranges::equal(m.keys(), KeyContainer{1, 2, 3}));
+  check_possible_values(
+      m.values(),
+      std::vector<std::vector<double>>{
+          {1, 1.5, 2},
+          {1, 1.5, 2},
+          {1, 1.5, 2},
+      });
+
+  auto m_copy = m;
 
   m.insert(cpp17_input_iterator<P*>(ar2), cpp17_input_iterator<P*>(ar2 + sizeof(ar2) / sizeof(ar2[0])));
   assert(m.size() == 5);
-  M expected2{{0, 1}, {1, 1}, {2, 1}, {3, 1}, {4, 1}};
-  assert(m == expected2);
+
+  assert(std::ranges::equal(m.keys(), KeyContainer{0, 1, 2, 3, 4}));
+  check_possible_values(
+      m.values(),
+      std::vector<std::vector<double>>{
+          {1, 1.5, 2},
+          {m_copy[1]},
+          {m_copy[2]},
+          {m_copy[3]},
+          {1, 1.5, 2},
+      });
 }
-int main(int, char**) {
+
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, const auto& newValues) { m.insert(newValues.begin(), newValues.end()); };
     test_insert_range_exception_guarantee(insert_func);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_rv.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_rv.pass.cpp
index 034941b55eb80..afd0345fd5988 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_rv.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_iter_rv.pass.cpp
@@ -22,7 +22,7 @@
 #include "test_macros.h"
 
 template <class Container, class Pair>
-void do_insert_iter_rv_test() {
+constexpr void do_insert_iter_rv_test() {
   using M = Container;
   using P = Pair;
   using R = typename M::iterator;
@@ -53,7 +53,7 @@ void do_insert_iter_rv_test() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -64,17 +64,22 @@ void test() {
   do_insert_iter_rv_test<M, CP>();
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
   test<std::vector<int>, std::vector<MoveOnly>>();
-  test<std::deque<int>, std::deque<double>>();
-  test<std::deque<int>, std::deque<MoveOnly>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::deque<double>>();
+    test<std::deque<int>, std::deque<MoveOnly>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<MinSequenceContainer<int>, MinSequenceContainer<MoveOnly>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
   test<std::vector<int, min_allocator<int>>, std::vector<MoveOnly, min_allocator<MoveOnly>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap    = std::decay_t<decltype(m)>;
       using value_type = typename FlatMap::value_type;
@@ -84,5 +89,14 @@ int main(int, char**) {
     test_emplace_exception_guarantee(insert_func);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign.pass.cpp
index 398a7a1a4052e..a93c86d85d07d 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign.pass.cpp
@@ -78,7 +78,7 @@ static_assert(!CanInsertOrAssignIter<std::flat_map<int, ConstructFrom<V>>, int&&
 static_assert(!CanInsertOrAssignIter<std::flat_map<int, AssignFrom<V>>, int&&, V>);
 
 template <class KeyContainer, class ValueContainer>
-void test_cv_key() {
+constexpr void test_cv_key() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -194,7 +194,7 @@ void test_cv_key() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test_rv_key() {
+constexpr void test_rv_key() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -311,16 +311,30 @@ void test_rv_key() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test_cv_key<std::vector<int>, std::vector<Moveable>>();
-  test_cv_key<std::deque<int>, std::vector<Moveable>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test_cv_key<std::deque<int>, std::vector<Moveable>>();
+    test_rv_key<std::deque<Moveable>, std::vector<Moveable>>();
+  }
   test_cv_key<MinSequenceContainer<int>, MinSequenceContainer<Moveable>>();
   test_cv_key<std::vector<int, min_allocator<int>>, std::vector<Moveable, min_allocator<Moveable>>>();
 
   test_rv_key<std::vector<Moveable>, std::vector<Moveable>>();
-  test_rv_key<std::deque<Moveable>, std::vector<Moveable>>();
   test_rv_key<MinSequenceContainer<Moveable>, MinSequenceContainer<Moveable>>();
   test_rv_key<std::vector<Moveable, min_allocator<Moveable>>, std::vector<Moveable, min_allocator<Moveable>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp
index 636c4edfe551d..23e913769cf30 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_or_assign_transparent.pass.cpp
@@ -94,7 +94,7 @@ static_assert(
     !CanInsertOrAssignIter<std::flat_map<int, AssignFrom<V>, TransparentComparator>, ConvertibleTransparent<int>, V>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -212,9 +212,14 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<Moveable>>();
-  test<std::deque<int>, std::vector<Moveable>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<Moveable>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<Moveable>>();
   test<std::vector<int, min_allocator<int>>, std::vector<Moveable, min_allocator<Moveable>>>();
 
@@ -237,23 +242,34 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
-  {
-    auto insert_or_assign = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      m.insert_or_assign(ConvertibleTransparent<Key>{key_arg}, value_arg);
-    };
-    test_emplace_exception_guarantee(insert_or_assign);
-  }
+  if (!std::is_constant_evaluated()) {
+    {
+      auto insert_or_assign = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        m.insert_or_assign(ConvertibleTransparent<Key>{key_arg}, value_arg);
+      };
+      test_emplace_exception_guarantee(insert_or_assign);
+    }
 
-  {
-    auto insert_or_assign_iter = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      m.insert_or_assign(m.begin(), ConvertibleTransparent<Key>{key_arg}, value_arg);
-    };
-    test_emplace_exception_guarantee(insert_or_assign_iter);
+    {
+      auto insert_or_assign_iter = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        m.insert_or_assign(m.begin(), ConvertibleTransparent<Key>{key_arg}, value_arg);
+      };
+      test_emplace_exception_guarantee(insert_or_assign_iter);
+    }
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_range.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_range.pass.cpp
index a2e64431a3c25..7339f58eaffdc 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_range.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_range.pass.cpp
@@ -39,7 +39,7 @@ static_assert(!CanInsertRange<Map, std::ranges::subrange<int*>>);
 static_assert(!CanInsertRange<Map, std::ranges::subrange<double*>>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
 
@@ -68,7 +68,7 @@ void test() {
   {
     // The "uniquing" part uses the comparator, not operator==.
     struct ModTen {
-      bool operator()(int a, int b) const { return (a % 10) < (b % 10); }
+      constexpr bool operator()(int a, int b) const { return (a % 10) < (b % 10); }
     };
     using P = std::pair<int, int>;
     using M = std::flat_map<Key, Value, ModTen, KeyContainer, ValueContainer>;
@@ -79,9 +79,14 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
-  test<std::deque<int>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<int>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<int>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
   {
@@ -95,15 +100,25 @@ int main(int, char**) {
   {
     // The element type of the range doesn't need to be std::pair (P2767).
     std::pair<int, int> pa[] = {{3, 3}, {1, 1}, {4, 4}, {1, 1}, {5, 5}};
-    std::deque<std::reference_wrapper<std::pair<int, int>>> a(pa, pa + 5);
+    std::vector<std::reference_wrapper<std::pair<int, int>>> a(pa, pa + 5);
     std::flat_map<int, int> m;
     m.insert_range(a);
     std::pair<int, int> expected[] = {{1, 1}, {3, 3}, {4, 4}, {5, 5}};
     assert(std::ranges::equal(m, expected));
   }
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, const auto& newValues) { m.insert_range(newValues); };
     test_insert_range_exception_guarantee(insert_func);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_rv.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_rv.pass.cpp
index 9ea7a6a636666..60af8b654e57a 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_rv.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_rv.pass.cpp
@@ -25,7 +25,7 @@
 #include "../helpers.h"
 
 template <class Container, class Pair>
-void do_insert_rv_test() {
+constexpr void do_insert_rv_test() {
   using M = Container;
   using P = Pair;
   using R = std::pair<typename M::iterator, bool>;
@@ -60,7 +60,7 @@ void do_insert_rv_test() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -72,9 +72,14 @@ void test() {
   do_insert_rv_test<M, CP>();
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<MoveOnly>>();
-  test<std::deque<int>, std::vector<MoveOnly>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<MoveOnly>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<MoveOnly>>();
   test<std::vector<int, min_allocator<int>>, std::vector<MoveOnly, min_allocator<MoveOnly>>>();
 
@@ -110,7 +115,7 @@ int main(int, char**) {
     assert(r.first->first == 3);
     assert(r.first->second == 3);
   }
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, auto key_arg, auto value_arg) {
       using FlatMap    = std::decay_t<decltype(m)>;
       using value_type = typename FlatMap::value_type;
@@ -120,5 +125,14 @@ int main(int, char**) {
     test_emplace_exception_guarantee(insert_func);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_initializer_list.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_initializer_list.pass.cpp
index 08d2caf349879..e0692ffe40fea 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_initializer_list.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_initializer_list.pass.cpp
@@ -23,7 +23,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -39,20 +39,34 @@ void test() {
            });
   assert(m.size() == 5);
   assert(std::distance(m.begin(), m.end()) == 5);
+
   assert(*m.begin() == V(0, 1));
-  assert(*std::next(m.begin()) == V(1, 1));
-  assert(*std::next(m.begin(), 2) == V(2, 1));
-  assert(*std::next(m.begin(), 3) == V(3, 1));
-  assert(*std::next(m.begin(), 4) == V(4, 1));
+  auto v1 = *std::next(m.begin());
+  assert(v1.first == 1);
+  assert(v1.second == 1 || v1.second == 1.5 || v1.second == 2);
+  auto v2 = *std::next(m.begin(), 2);
+  assert(v2.first == 2);
+  assert(v2.second == 1);
+  auto v3 = *std::next(m.begin(), 3);
+  assert(v3.first == 3);
+  assert(v3.second == 1 || v3.second == 1.5 || v3.second == 2);
+  auto v4 = *std::next(m.begin(), 4);
+  assert(v4.first == 4);
+  assert(v4.second == 1);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, const auto& newValues) {
       using FlatMap                        = std::decay_t<decltype(m)>;
       using value_type                     = typename FlatMap::value_type;
@@ -62,5 +76,14 @@ int main(int, char**) {
     test_insert_range_exception_guarantee(insert_func);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_iter_iter.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_iter_iter.pass.cpp
index 18a3b571a4199..61ffb689af367 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_iter_iter.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_sorted_iter_iter.pass.cpp
@@ -37,7 +37,7 @@ static_assert(!CanInsert<Map, std::sorted_unique_t, int, int>);
 static_assert(!CanInsert<Map, std::sorted_unique_t, cpp20_input_iterator<Pair*>, cpp20_input_iterator<Pair*>>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -69,18 +69,32 @@ void test() {
   assert(m == expected2);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
     auto insert_func = [](auto& m, const auto& newValues) {
       m.insert(std::sorted_unique, newValues.begin(), newValues.end());
     };
     test_insert_range_exception_guarantee(insert_func);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp
index 75cabb70630f3..ecc5c54075e60 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/insert_transparent.pass.cpp
@@ -41,98 +41,42 @@ static_assert(CanInsert<Map, Iter, std::tuple<short, double>&&>);
 static_assert(!CanInsert<Map, int>);
 static_assert(!CanInsert<Map, Iter, int>);
 
-static int expensive_comparisons = 0;
-static int cheap_comparisons     = 0;
-
-struct CompareCounter {
-  int i_ = 0;
-  CompareCounter(int i) : i_(i) {}
-  friend auto operator<=>(const CompareCounter& x, const CompareCounter& y) {
-    expensive_comparisons += 1;
-    return x.i_ <=> y.i_;
-  }
-  bool operator==(const CompareCounter&) const = default;
-  friend auto operator<=>(const CompareCounter& x, int y) {
-    cheap_comparisons += 1;
-    return x.i_ <=> y;
-  }
-};
+constexpr bool test() {
+  {
+    // template<class K> pair<iterator, bool> insert(P&& x);
+    bool transparent_used = false;
+    TransparentComparator c(transparent_used);
+    using M = std::flat_map<int, int, TransparentComparator>;
+    M m(std::sorted_unique, {{1, 1}, {2, 2}, {4, 4}}, c);
+    assert(!transparent_used);
 
-template <class KeyContainer, class ValueContainer>
-void test() {
-  using Key   = typename KeyContainer::value_type;
-  using Value = typename ValueContainer::value_type;
-  using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
+    std::same_as<std::pair<typename M::iterator, bool>> decltype(auto) res =
+        m.insert(std::pair(ConvertibleTransparent<int>{3}, 3));
 
-  const std::pair<int, int> expected[] = {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}};
-  {
-    // insert(P&&)
+    assert(res.second);
+    assert(res.first->first == 3);
+    assert(res.first->second == 3);
     //   Unlike flat_set, here we can't use key_compare to compare value_type versus P,
     //   so we must eagerly convert to value_type.
-    M m                   = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    expensive_comparisons = 0;
-    cheap_comparisons     = 0;
-    std::same_as<std::pair<typename M::iterator, bool>> auto p =
-        m.insert(std::make_pair(3, 3)); // conversion happens first
-    assert(expensive_comparisons >= 2);
-    assert(cheap_comparisons == 0);
-    assert(p == std::make_pair(m.begin() + 2, true));
-    assert(std::ranges::equal(m, expected));
-  }
-  {
-    // insert(const_iterator, P&&)
-    M m                                        = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    expensive_comparisons                      = 0;
-    cheap_comparisons                          = 0;
-    std::same_as<typename M::iterator> auto it = m.insert(m.begin(), std::make_pair(3, 3));
-    assert(expensive_comparisons >= 2);
-    assert(cheap_comparisons == 0);
-    assert(it == m.begin() + 2);
-    assert(std::ranges::equal(m, expected));
-  }
-  {
-    // insert(value_type&&)
-    M m                   = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    expensive_comparisons = 0;
-    cheap_comparisons     = 0;
-    std::same_as<std::pair<typename M::iterator, bool>> auto p =
-        m.insert(std::make_pair(3, 3)); // conversion happens last
-    assert(expensive_comparisons >= 2);
-    assert(cheap_comparisons == 0);
-    assert(p == std::make_pair(m.begin() + 2, true));
-    assert(std::ranges::equal(m, expected));
-  }
-  {
-    // insert(const_iterator, value_type&&)
-    M m                                        = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    expensive_comparisons                      = 0;
-    cheap_comparisons                          = 0;
-    std::same_as<typename M::iterator> auto it = m.insert(m.begin(), std::make_pair(3, 3));
-    assert(expensive_comparisons >= 2);
-    assert(cheap_comparisons == 0);
-    assert(it == m.begin() + 2);
-    assert(std::ranges::equal(m, expected));
+    assert(!transparent_used);
   }
   {
-    // emplace(Args&&...)
-    M m                   = {{1, 1}, {2, 2}, {4, 4}, {5, 5}};
-    expensive_comparisons = 0;
-    cheap_comparisons     = 0;
-    std::same_as<std::pair<typename M::iterator, bool>> auto p =
-        m.emplace(std::make_pair(3, 3)); // conversion happens first
-    assert(expensive_comparisons >= 2);
-    assert(cheap_comparisons == 0);
-    assert(p == std::make_pair(m.begin() + 2, true));
-    assert(std::ranges::equal(m, expected));
-  }
-}
+    // template<class K> iterator insert(const_iterator hint, P&& x);
+    bool transparent_used = false;
+    TransparentComparator c(transparent_used);
+    using M = std::flat_map<int, int, TransparentComparator>;
+    M m(std::sorted_unique, {{1, 1}, {2, 2}, {4, 4}}, c);
+    assert(!transparent_used);
 
-int main(int, char**) {
-  test<std::vector<CompareCounter>, std::vector<double>>();
-  test<std::deque<CompareCounter>, std::vector<double>>();
-  test<MinSequenceContainer<CompareCounter>, MinSequenceContainer<double>>();
-  test<std::vector<CompareCounter, min_allocator<CompareCounter>>, std::vector<double, min_allocator<double>>>();
+    std::same_as<typename M::iterator> decltype(auto) res =
+        m.insert(m.begin(), std::pair(ConvertibleTransparent<int>{3}, 3));
 
+    assert(res->first == 3);
+    assert(res->second == 3);
+    //   Unlike flat_set, here we can't use key_compare to compare value_type versus P,
+    //   so we must eagerly convert to value_type.
+    assert(!transparent_used);
+  }
   {
     // no ambiguity between insert(pos, P&&) and insert(first, last)
     using M = std::flat_map<int, int>;
@@ -145,23 +89,36 @@ int main(int, char**) {
     ASSERT_SAME_TYPE(decltype(m.insert(m.begin(), Evil())), M::iterator);
     ASSERT_SAME_TYPE(decltype(m.insert(m.begin(), m.end())), void);
   }
-  {
-    auto insert_func = [](auto& m, auto key_arg, auto value_arg) {
-      using FlatMap    = std::decay_t<decltype(m)>;
-      using tuple_type = std::tuple<typename FlatMap::key_type, typename FlatMap::mapped_type>;
-      tuple_type t(key_arg, value_arg);
-      m.insert(t);
-    };
-    test_emplace_exception_guarantee(insert_func);
-  }
-  {
-    auto insert_func_iter = [](auto& m, auto key_arg, auto value_arg) {
-      using FlatMap    = std::decay_t<decltype(m)>;
-      using tuple_type = std::tuple<typename FlatMap::key_type, typename FlatMap::mapped_type>;
-      tuple_type t(key_arg, value_arg);
-      m.insert(m.begin(), t);
-    };
-    test_emplace_exception_guarantee(insert_func_iter);
+
+  if (!std::is_constant_evaluated()) {
+    {
+      auto insert_func = [](auto& m, auto key_arg, auto value_arg) {
+        using FlatMap    = std::decay_t<decltype(m)>;
+        using tuple_type = std::tuple<typename FlatMap::key_type, typename FlatMap::mapped_type>;
+        tuple_type t(key_arg, value_arg);
+        m.insert(t);
+      };
+      test_emplace_exception_guarantee(insert_func);
+    }
+    {
+      auto insert_func_iter = [](auto& m, auto key_arg, auto value_arg) {
+        using FlatMap    = std::decay_t<decltype(m)>;
+        using tuple_type = std::tuple<typename FlatMap::key_type, typename FlatMap::mapped_type>;
+        tuple_type t(key_arg, value_arg);
+        m.insert(m.begin(), t);
+      };
+      test_emplace_exception_guarantee(insert_func_iter);
+    }
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/replace.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/replace.pass.cpp
index 5ca811d761520..2c10725903e4d 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/replace.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/replace.pass.cpp
@@ -33,7 +33,7 @@ static_assert(!CanReplace<Map, std::vector<int>, const std::vector<int>&>);
 static_assert(!CanReplace<Map, const std::vector<int>&, const std::vector<int>&>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -49,13 +49,18 @@ void test() {
   assert(std::ranges::equal(m.values(), expected_values));
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
-  {
+  if (!std::is_constant_evaluated()) {
 #ifndef TEST_HAS_NO_EXCEPTIONS
     using KeyContainer   = std::vector<int>;
     using ValueContainer = ThrowOnMoveContainer<int>;
@@ -76,5 +81,15 @@ int main(int, char**) {
     }
 #endif
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_free.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_free.pass.cpp
index 98c60c1488cf5..163e74c349479 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_free.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_free.pass.cpp
@@ -39,7 +39,7 @@ static_assert(
 #endif
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -87,11 +87,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_member.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_member.pass.cpp
index d2d8f5673edeb..e65a3c1970f85 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_member.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/swap_member.pass.cpp
@@ -38,7 +38,7 @@ static_assert(
 #endif
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -85,11 +85,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<double>>();
-  test<std::deque<int>, std::vector<double>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<double>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<double>>();
   test<std::vector<int, min_allocator<int>>, std::vector<double, min_allocator<double>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace.pass.cpp
index 4be2fe1c4333e..ee6e53d378026 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace.pass.cpp
@@ -63,7 +63,7 @@ static_assert(!CanTryEmplace<Map, Iter, Emplaceable, const Emplaceable&>);
 static_assert(!CanTryEmplace<Map, Iter, Emplaceable, int>);
 
 template <class KeyContainer, class ValueContainer>
-void test_ck() {
+constexpr void test_ck() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -101,7 +101,7 @@ void test_ck() {
     assert(r3.first->second.get() == 5); // value
 
     Moveable mv3(-1, 3.0);
-    std::same_as<R> decltype(auto) r4 = m.try_emplace(117, std::move(mv2));
+    std::same_as<R> decltype(auto) r4 = m.try_emplace(117, std::move(mv3));
     assert(m.size() == 13);
     assert(r4.second);                    // was inserted
     assert(mv2.moved());                  // was moved from
@@ -135,7 +135,7 @@ void test_ck() {
 }
 
 template <class KeyContainer, class ValueContainer>
-void test_rk() {
+constexpr void test_rk() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -193,54 +193,70 @@ void test_rk() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test_ck<std::vector<int>, std::vector<Moveable>>();
-  test_ck<std::deque<int>, std::vector<Moveable>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test_ck<std::deque<int>, std::vector<Moveable>>();
+    test_rk<std::deque<Moveable>, std::vector<Moveable>>();
+  }
   test_ck<MinSequenceContainer<int>, MinSequenceContainer<Moveable>>();
   test_ck<std::vector<int, min_allocator<int>>, std::vector<Moveable, min_allocator<Moveable>>>();
 
   test_rk<std::vector<Moveable>, std::vector<Moveable>>();
-  test_rk<std::deque<Moveable>, std::vector<Moveable>>();
   test_rk<MinSequenceContainer<Moveable>, MinSequenceContainer<Moveable>>();
   test_rk<std::vector<Moveable, min_allocator<Moveable>>, std::vector<Moveable, min_allocator<Moveable>>>();
 
-  {
-    auto try_emplace_ck = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      const Key key{key_arg};
-      m.try_emplace(key, value_arg);
-    };
-    test_emplace_exception_guarantee(try_emplace_ck);
-  }
+  if (!std::is_constant_evaluated()) {
+    {
+      auto try_emplace_ck = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        const Key key{key_arg};
+        m.try_emplace(key, value_arg);
+      };
+      test_emplace_exception_guarantee(try_emplace_ck);
+    }
 
-  {
-    auto try_emplace_rk = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      m.try_emplace(Key{key_arg}, value_arg);
-    };
-    test_emplace_exception_guarantee(try_emplace_rk);
-  }
+    {
+      auto try_emplace_rk = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        m.try_emplace(Key{key_arg}, value_arg);
+      };
+      test_emplace_exception_guarantee(try_emplace_rk);
+    }
 
-  {
-    auto try_emplace_iter_ck = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      const Key key{key_arg};
-      m.try_emplace(m.begin(), key, value_arg);
-    };
-    test_emplace_exception_guarantee(try_emplace_iter_ck);
-  }
+    {
+      auto try_emplace_iter_ck = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        const Key key{key_arg};
+        m.try_emplace(m.begin(), key, value_arg);
+      };
+      test_emplace_exception_guarantee(try_emplace_iter_ck);
+    }
 
-  {
-    auto try_emplace_iter_rk = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      m.try_emplace(m.begin(), Key{key_arg}, value_arg);
-    };
-    test_emplace_exception_guarantee(try_emplace_iter_rk);
+    {
+      auto try_emplace_iter_rk = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        m.try_emplace(m.begin(), Key{key_arg}, value_arg);
+      };
+      test_emplace_exception_guarantee(try_emplace_iter_rk);
+    }
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp
index 21fda43780967..abea83f956269 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.modifiers/try_emplace_transparent.pass.cpp
@@ -65,7 +65,7 @@ static_assert(!CanTryEmplace<NonTransparentMap, TransparentMapConstIter, NonConv
 static_assert(!CanTryEmplace<TransparentMap, TransparentMapConstIter, ConvertibleTransparent<int>, int>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -103,7 +103,7 @@ void test() {
     assert(r3.first->second.get() == 5); // value
 
     Moveable mv3(-1, 3.0);
-    std::same_as<R> decltype(auto) r4 = m.try_emplace(ConvertibleTransparent<int>{117}, std::move(mv2));
+    std::same_as<R> decltype(auto) r4 = m.try_emplace(ConvertibleTransparent<int>{117}, std::move(mv3));
     assert(m.size() == 13);
     assert(r4.second);                    // was inserted
     assert(mv2.moved());                  // was moved from
@@ -136,9 +136,14 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<Moveable>>();
-  test<std::deque<int>, std::vector<Moveable>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<Moveable>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<Moveable>>();
   test<std::vector<int, min_allocator<int>>, std::vector<Moveable, min_allocator<Moveable>>>();
 
@@ -160,23 +165,34 @@ int main(int, char**) {
     assert(p->second == 3);
     assert(transparent_used);
   }
-  {
-    auto try_emplace = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      m.try_emplace(ConvertibleTransparent<Key>{key_arg}, value_arg);
-    };
-    test_emplace_exception_guarantee(try_emplace);
-  }
+  if (!std::is_constant_evaluated()) {
+    {
+      auto try_emplace = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        m.try_emplace(ConvertibleTransparent<Key>{key_arg}, value_arg);
+      };
+      test_emplace_exception_guarantee(try_emplace);
+    }
 
-  {
-    auto try_emplace_iter = [](auto& m, auto key_arg, auto value_arg) {
-      using M   = std::decay_t<decltype(m)>;
-      using Key = typename M::key_type;
-      m.try_emplace(m.begin(), ConvertibleTransparent<Key>{key_arg}, value_arg);
-    };
-    test_emplace_exception_guarantee(try_emplace_iter);
+    {
+      auto try_emplace_iter = [](auto& m, auto key_arg, auto value_arg) {
+        using M   = std::decay_t<decltype(m)>;
+        using Key = typename M::key_type;
+        m.try_emplace(m.begin(), ConvertibleTransparent<Key>{key_arg}, value_arg);
+      };
+      test_emplace_exception_guarantee(try_emplace_iter);
+    }
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/comp.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/comp.pass.cpp
index d86224952dee4..f85b7a08a464e 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/comp.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/comp.pass.cpp
@@ -16,12 +16,13 @@
 #include <cassert>
 #include <flat_map>
 #include <functional>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
 #include "test_macros.h"
 
-int main(int, char**) {
+constexpr bool test() {
   {
     using M    = std::flat_map<int, char>;
     using Comp = std::less<int>; // the default
@@ -38,7 +39,7 @@ int main(int, char**) {
     assert(vc({1, '2'}, {2, '1'}));
     assert(!vc({2, '1'}, {1, '2'}));
   }
-  {
+  if (!std::is_constant_evaluated()) {
     using Comp = std::function<bool(int, int)>;
     using M    = std::flat_map<int, int, Comp>;
     Comp comp  = std::greater<int>();
@@ -72,7 +73,7 @@ int main(int, char**) {
     assert(vc({1, 2}, {2, 1}));
     assert(!vc({2, 1}, {1, 2}));
   }
-  {
+  if (!std::is_constant_evaluated()) {
     using Comp = std::function<bool(const std::vector<int>&, const std::vector<int>&)>;
     using M    = std::flat_map<std::vector<int>, int, Comp>;
     Comp comp  = [i = 1](const auto& x, const auto& y) { return x[i] < y[i]; };
@@ -92,5 +93,15 @@ int main(int, char**) {
     assert(!vc(b, a));
     assert(!vc(c, b));
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/keys_values.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/keys_values.pass.cpp
index 84d8f8344aaa6..dae2adf2b1e08 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/keys_values.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.observers/keys_values.pass.cpp
@@ -28,7 +28,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -47,11 +47,25 @@ void test() {
   assert(std::ranges::equal(values, expected_values));
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains.pass.cpp
index 208d6138fa683..9b72aace59fc0 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains.pass.cpp
@@ -23,7 +23,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   {
@@ -60,11 +60,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
-  test<std::deque<int>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<int>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<int>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp
index 0493538ab6dad..b47141be8bdaa 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/contains_transparent.pass.cpp
@@ -34,7 +34,7 @@ static_assert(!CanContains<NonTransparentMap>);
 static_assert(!CanContains<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -52,9 +52,14 @@ void test() {
   assert(m.contains(Transparent<std::string>{"g"}) == false);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<std::string>, std::vector<int>>();
-  test<std::deque<std::string>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<std::string>, std::vector<int>>();
+  }
   test<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test<std::vector<std::string, min_allocator<std::string>>, std::vector<int, min_allocator<int>>>();
 
@@ -67,5 +72,15 @@ int main(int, char**) {
     assert(b);
     assert(transparent_used);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count.pass.cpp
index db675854d5e98..a79880ad26d28 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count.pass.cpp
@@ -23,7 +23,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
 
@@ -59,11 +59,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
-  test<std::deque<int>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<int>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<int>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp
index cd195ff1fa8b4..6a63351941324 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/count_transparent.pass.cpp
@@ -34,7 +34,7 @@ static_assert(!CanCount<NonTransparentMap>);
 static_assert(!CanCount<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -52,9 +52,14 @@ void test() {
   assert(m.count(Transparent<std::string>{"g"}) == 0);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<std::string>, std::vector<int>>();
-  test<std::deque<std::string>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<std::string>, std::vector<int>>();
+  }
   test<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test<std::vector<std::string, min_allocator<std::string>>, std::vector<int, min_allocator<int>>>();
 
@@ -68,5 +73,14 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range.pass.cpp
index 8fa73d2a2eb51..e09516226e084 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range.pass.cpp
@@ -24,7 +24,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   {
@@ -68,11 +68,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp
index 0198f433bdc4f..910d4ce8c9e90 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/equal_range_transparent.pass.cpp
@@ -35,7 +35,7 @@ static_assert(!CanEqualRange<NonTransparentMap>);
 static_assert(!CanEqualRange<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -80,9 +80,14 @@ void test() {
   test_not_found(cm, "zzz", 5);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<std::string>, std::vector<int>>();
-  test<std::deque<std::string>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<std::string>, std::vector<int>>();
+  }
   test<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test<std::vector<std::string, min_allocator<std::string>>, std::vector<int, min_allocator<int>>>();
 
@@ -96,5 +101,14 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find.pass.cpp
index 9fae407c7d8f7..67e2f9213a1b6 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find.pass.cpp
@@ -25,7 +25,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, std::less<Key>, KeyContainer, ValueContainer>;
@@ -45,11 +45,25 @@ void test() {
   assert(std::as_const(m).find(9) == m.end());
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp
index 291577a89fc8f..e85194a15b394 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/find_transparent.pass.cpp
@@ -35,7 +35,7 @@ static_assert(!CanFind<NonTransparentMap>);
 static_assert(!CanFind<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -68,9 +68,14 @@ void test() {
   test_find(cm, "zzz", 5);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<std::string>, std::vector<int>>();
-  test<std::deque<std::string>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<std::string>, std::vector<int>>();
+  }
   test<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test<std::vector<std::string, min_allocator<std::string>>, std::vector<int, min_allocator<int>>>();
 
@@ -84,5 +89,14 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound.pass.cpp
index b5491f3b22674..cc7622ce556e7 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound.pass.cpp
@@ -24,7 +24,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   {
@@ -61,11 +61,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound_transparent.pass.cpp
index 6a923c197e91e..bd0316245620e 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/lower_bound_transparent.pass.cpp
@@ -35,7 +35,7 @@ static_assert(!CanLowerBound<NonTransparentMap>);
 static_assert(!CanLowerBound<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -75,9 +75,14 @@ void test() {
   test_lower_bound(cm, "zzz", 5);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<std::string>, std::vector<int>>();
-  test<std::deque<std::string>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<std::string>, std::vector<int>>();
+  }
   test<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test<std::vector<std::string, min_allocator<std::string>>, std::vector<int, min_allocator<int>>>();
 
@@ -91,5 +96,14 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound.pass.cpp
index 775e53286d629..13eb3b1d941b4 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound.pass.cpp
@@ -24,7 +24,7 @@
 #include "min_allocator.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   {
@@ -62,11 +62,25 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<char>>();
-  test<std::deque<int>, std::vector<char>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::vector<char>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<char>>();
   test<std::vector<int, min_allocator<int>>, std::vector<char, min_allocator<char>>>();
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound_transparent.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound_transparent.pass.cpp
index 4e83f920835df..110f9e8c151e8 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound_transparent.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/flat.map.operations/upper_bound_transparent.pass.cpp
@@ -35,7 +35,7 @@ static_assert(!CanUpperBound<NonTransparentMap>);
 static_assert(!CanUpperBound<const NonTransparentMap>);
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
   using M     = std::flat_map<Key, Value, TransparentComparator, KeyContainer, ValueContainer>;
@@ -75,9 +75,14 @@ void test() {
   test_upper_bound(cm, "zzz", 5);
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<std::string>, std::vector<int>>();
-  test<std::deque<std::string>, std::vector<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<std::string>, std::vector<int>>();
+  }
   test<MinSequenceContainer<std::string>, MinSequenceContainer<int>>();
   test<std::vector<std::string, min_allocator<std::string>>, std::vector<int, min_allocator<int>>>();
   {
@@ -90,5 +95,14 @@ int main(int, char**) {
     assert(transparent_used);
   }
 
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/helpers.h b/libcxx/test/std/containers/container.adaptors/flat.map/helpers.h
index b6b8fa061c840..932f330db829e 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/helpers.h
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/helpers.h
@@ -14,13 +14,14 @@
 #include <string>
 #include <vector>
 #include <flat_map>
+#include <ranges>
 
 #include "../flat_helpers.h"
 #include "test_allocator.h"
 #include "test_macros.h"
 
 template <class... Args>
-void check_invariant(const std::flat_map<Args...>& m) {
+constexpr void check_invariant(const std::flat_map<Args...>& m) {
   assert(m.keys().size() == m.values().size());
   const auto& keys = m.keys();
   assert(std::is_sorted(keys.begin(), keys.end(), m.key_comp()));
@@ -31,6 +32,14 @@ void check_invariant(const std::flat_map<Args...>& m) {
   assert(std::adjacent_find(keys.begin(), keys.end(), key_equal) == keys.end());
 }
 
+constexpr void check_possible_values(const auto& actual, const auto& expected) {
+  assert(std::ranges::size(actual) == std::ranges::size(expected));
+
+  for (const auto& [actual_value, possible_values] : std::views::zip(actual, expected)) {
+    assert(std::ranges::find(possible_values, actual_value) != std::ranges::end(possible_values));
+  }
+}
+
 template <class F>
 void test_emplace_exception_guarantee([[maybe_unused]] F&& emplace_function) {
 #ifndef TEST_HAS_NO_EXCEPTIONS
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/incomplete_type.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/incomplete_type.pass.cpp
index 76461951f0d3d..80f4af4be44bc 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/incomplete_type.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/incomplete_type.pass.cpp
@@ -16,6 +16,8 @@
 #include <flat_map>
 #include <vector>
 
+#include "test_macros.h"
+
 struct A {
   using Map = std::flat_map<A, A>;
   int data;
@@ -25,9 +27,20 @@ struct A {
 };
 
 // Implement the operator< required in order to instantiate flat_map<A, X>
-bool operator<(A const& L, A const& R) { return L.data < R.data; }
+constexpr bool operator<(A const& L, A const& R) { return L.data < R.data; }
 
-int main(int, char**) {
+
+constexpr bool test() {
   A a;
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat.map/op_compare.pass.cpp b/libcxx/test/std/containers/container.adaptors/flat.map/op_compare.pass.cpp
index fffe711580704..5d3110215c46a 100644
--- a/libcxx/test/std/containers/container.adaptors/flat.map/op_compare.pass.cpp
+++ b/libcxx/test/std/containers/container.adaptors/flat.map/op_compare.pass.cpp
@@ -31,7 +31,7 @@
 #include "test_container_comparisons.h"
 
 template <class KeyContainer, class ValueContainer>
-void test() {
+constexpr void test() {
   using Key   = typename KeyContainer::value_type;
   using Value = typename ValueContainer::value_type;
 
@@ -70,9 +70,14 @@ void test() {
   }
 }
 
-int main(int, char**) {
+constexpr bool test() {
   test<std::vector<int>, std::vector<int>>();
-  test<std::deque<int>, std::deque<int>>();
+#ifndef __cpp_lib_constexpr_deque
+  if (!std::is_constant_evaluated())
+#endif
+  {
+    test<std::deque<int>, std::deque<int>>();
+  }
   test<MinSequenceContainer<int>, MinSequenceContainer<int>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
   test<std::vector<int, min_allocator<int>>, std::vector<int, min_allocator<int>>>();
@@ -98,7 +103,7 @@ int main(int, char**) {
   {
     // Comparisons use value_type's native operators, not the comparator
     struct StrongComp {
-      bool operator()(double a, double b) const { return std::strong_order(a, b) < 0; }
+      constexpr bool operator()(double a, double b) const { return std::strong_order(a, b) < 0; }
     };
     using C = std::flat_map<double, double, StrongComp>;
     C s1    = {{1, 1}};
@@ -114,5 +119,15 @@ int main(int, char**) {
     assert(s1 != s2);
     assert((s1 <=> s2) == std::partial_ordering::unordered);
   }
+
+  return true;
+}
+
+int main(int, char**) {
+  test();
+#if TEST_STD_VER >= 26
+  static_assert(test());
+#endif
+
   return 0;
 }
diff --git a/libcxx/test/std/containers/container.adaptors/flat_helpers.h b/libcxx/test/std/containers/container.adaptors/flat_helpers.h
index 9cd408ef960a9..6db7ec6abba0b 100644
--- a/libcxx/test/std/containers/container.adaptors/flat_helpers.h
+++ b/libcxx/test/std/containers/container.adaptors/flat_helpers.h
@@ -18,18 +18,19 @@ struct CopyOnlyVector : std::vector<T> {
   using std::vector<T>::vector;
 
   CopyOnlyVector(const CopyOnlyVector&) = default;
-  CopyOnlyVector(CopyOnlyVector&& other) : CopyOnlyVector(other) {}
-  CopyOnlyVector(CopyOnlyVector&& other, std::vector<T>::allocator_type alloc) : CopyOnlyVector(other, alloc) {}
+  constexpr CopyOnlyVector(CopyOnlyVector&& other) : CopyOnlyVector(other) {}
+  constexpr CopyOnlyVector(CopyOnlyVector&& other, std::vector<T>::allocator_type alloc)
+      : CopyOnlyVector(other, alloc) {}
 
-  CopyOnlyVector& operator=(const CopyOnlyVector&) = default;
-  CopyOnlyVector& operator=(CopyOnlyVector& other) { return this->operator=(other); }
+  constexpr CopyOnlyVector& operator=(const CopyOnlyVector&) = default;
+  constexpr CopyOnlyVector& operator=(CopyOnlyVector& other) { return this->operator=(other); }
 };
 
 template <class T, bool ConvertibleToT = false>
 struct Transparent {
   T t;
 
-  explicit operator T() const
+  TEST_CONSTEXPR explicit operator T() const
     requires ConvertibleToT
   {
     return t;
@@ -50,10 +51,10 @@ struct TransparentComparator {
 
   bool* transparent_used  = nullptr;
   TransparentComparator() = default;
-  TransparentComparator(bool& used) : transparent_used(&used) {}
+  TEST_CONSTEXPR TransparentComparator(bool& used) : transparent_used(&used) {}
 
   template <class T, bool Convertible>
-  bool operator()(const T& t, const Transparent<T, Convertible>& transparent) const {
+  TEST_CONSTEXPR bool operator()(const T& t, const Transparent<T, Convertible>& transparent) const {
     if (transparent_used != nullptr) {
       *transparent_used = true;
     }
@@ -61,7 +62,7 @@ struct TransparentComparator {
   }
 
   template <class T, bool Convertible>
-  bool operator()(const Transparent<T, Convertible>& transparent, const T& t) const {
+  TEST_CONSTEXPR bool operator()(const Transparent<T, Convertible>& transparent, const T& t) const {
     if (transparent_used != nullptr) {
       *transparent_used = true;
     }
@@ -69,7 +70,7 @@ struct TransparentComparator {
   }
 
   template <class T>
-  bool operator()(const T& t1, const T& t2) const {
+  TEST_CONSTEXPR bool operator()(const T& t1, const T& t2) const {
     return t1 < t2;
   }
 };
@@ -94,13 +95,13 @@ class Moveable {
   double double_;
 
 public:
-  Moveable() : int_(0), double_(0) {}
-  Moveable(int i, double d) : int_(i), double_(d) {}
-  Moveable(Moveable&& x) : int_(x.int_), double_(x.double_) {
+  TEST_CONSTEXPR Moveable() : int_(0), double_(0) {}
+  TEST_CONSTEXPR Moveable(int i, double d) : int_(i), double_(d) {}
+  TEST_CONSTEXPR Moveable(Moveable&& x) : int_(x.int_), double_(x.double_) {
     x.int_    = -1;
     x.double_ = -1;
   }
-  Moveable& operator=(Moveable&& x) {
+  TEST_CONSTEXPR Moveable& operator=(Moveable&& x) {
     int_      = x.int_;
     x.int_    = -1;
     double_   = x.double_;
@@ -110,11 +111,13 @@ class Moveable {
 
   Moveable(const Moveable&)            = delete;
   Moveable& operator=(const Moveable&) = delete;
-  bool operator==(const Moveable& x) const { return int_ == x.int_ && double_ == x.double_; }
-  bool operator<(const Moveable& x) const { return int_ < x.int_ || (int_ == x.int_ && double_ < x.double_); }
+  TEST_CONSTEXPR bool operator==(const Moveable& x) const { return int_ == x.int_ && double_ == x.double_; }
+  TEST_CONSTEXPR bool operator<(const Moveable& x) const {
+    return int_ < x.int_ || (int_ == x.int_ && double_ < x.double_);
+  }
 
-  int get() const { return int_; }
-  bool moved() const { return int_ == -1; }
+  TEST_CONSTEXPR int get() const { return int_; }
+  TEST_CONSTEXPR bool moved() const { return int_ == -1; }
 };
 
 #ifndef TEST_HAS_NO_EXCEPTIONS
diff --git a/libcxx/test/std/containers/test_compare.h b/libcxx/test/std/containers/test_compare.h
index 18e0b27dc954d..070f15869a4a3 100644
--- a/libcxx/test/std/containers/test_compare.h
+++ b/libcxx/test/std/containers/test_compare.h
@@ -9,22 +9,24 @@
 #ifndef TEST_COMPARE_H
 #define TEST_COMPARE_H
 
+#include "test_macros.h"
+
 template <class T>
 struct test_equal_to {
   int data_;
-  explicit test_equal_to() : data_(0) {}
-  explicit test_equal_to(int data) : data_(data) {}
-  bool operator()(const T& a, const T& b) const { return a == b; }
-  friend bool operator==(const test_equal_to& a, const test_equal_to& b) { return a.data_ == b.data_; }
+  TEST_CONSTEXPR explicit test_equal_to() : data_(0) {}
+  TEST_CONSTEXPR explicit test_equal_to(int data) : data_(data) {}
+  TEST_CONSTEXPR bool operator()(const T& a, const T& b) const { return a == b; }
+  TEST_CONSTEXPR friend bool operator==(const test_equal_to& a, const test_equal_to& b) { return a.data_ == b.data_; }
 };
 
 template <class T>
 struct test_less {
   int data_;
-  explicit test_less() : data_(0) {}
-  explicit test_less(int data) : data_(data) {}
-  bool operator()(const T& a, const T& b) const { return a < b; }
-  friend bool operator==(const test_less& a, const test_less& b) { return a.data_ == b.data_; }
+  TEST_CONSTEXPR explicit test_less() : data_(0) {}
+  TEST_CONSTEXPR explicit test_less(int data) : data_(data) {}
+  TEST_CONSTEXPR bool operator()(const T& a, const T& b) const { return a < b; }
+  TEST_CONSTEXPR friend bool operator==(const test_less& a, const test_less& b) { return a.data_ == b.data_; }
 };
 
 #endif // TEST_COMPARE_H
diff --git a/libcxx/test/support/MinSequenceContainer.h b/libcxx/test/support/MinSequenceContainer.h
index 7fee4dd0fbdc1..a399146159278 100644
--- a/libcxx/test/support/MinSequenceContainer.h
+++ b/libcxx/test/support/MinSequenceContainer.h
@@ -13,6 +13,7 @@
 #include <vector>
 
 #include "test_iterators.h"
+#include "test_macros.h"
 
 template <class T, class Iterator = random_access_iterator<T*>, class ConstIterator = random_access_iterator<const T*>>
 struct MinSequenceContainer {
@@ -24,42 +25,46 @@ struct MinSequenceContainer {
 
   explicit MinSequenceContainer() = default;
   template <class It>
-  explicit MinSequenceContainer(It first, It last) : data_(first, last) {}
-  MinSequenceContainer(std::initializer_list<T> il) : data_(il) {}
-  iterator begin() { return iterator(data_.data()); }
-  const_iterator begin() const { return const_iterator(data_.data()); }
-  const_iterator cbegin() const { return const_iterator(data_.data()); }
-  iterator end() { return begin() + size(); }
-  const_iterator end() const { return begin() + size(); }
-  size_type size() const { return static_cast<size_type>(data_.size()); }
-  bool empty() const { return data_.empty(); }
-
-  void clear() { data_.clear(); }
+  TEST_CONSTEXPR_CXX23 explicit MinSequenceContainer(It first, It last) : data_(first, last) {}
+  TEST_CONSTEXPR_CXX23 MinSequenceContainer(std::initializer_list<T> il) : data_(il) {}
+  TEST_CONSTEXPR_CXX23 iterator begin() { return iterator(data_.data()); }
+  TEST_CONSTEXPR_CXX23 const_iterator begin() const { return const_iterator(data_.data()); }
+  TEST_CONSTEXPR_CXX23 const_iterator cbegin() const { return const_iterator(data_.data()); }
+  TEST_CONSTEXPR_CXX23 iterator end() { return begin() + size(); }
+  TEST_CONSTEXPR_CXX23 const_iterator end() const { return begin() + size(); }
+  TEST_CONSTEXPR_CXX23 size_type size() const { return static_cast<size_type>(data_.size()); }
+  TEST_CONSTEXPR_CXX23 bool empty() const { return data_.empty(); }
+
+  TEST_CONSTEXPR_CXX23 void clear() { data_.clear(); }
 
   template <class It>
-  iterator insert(const_iterator p, It first, It last) {
+  TEST_CONSTEXPR_CXX23 iterator insert(const_iterator p, It first, It last) {
     return from_vector_iterator(data_.insert(to_vector_iterator(p), first, last));
   }
 
-  iterator insert(const_iterator p, T value) {
+  TEST_CONSTEXPR_CXX23 iterator insert(const_iterator p, T value) {
     return from_vector_iterator(data_.insert(to_vector_iterator(p), std::move(value)));
   }
 
-  iterator erase(const_iterator first, const_iterator last) {
+  TEST_CONSTEXPR_CXX23 iterator erase(const_iterator first, const_iterator last) {
     return from_vector_iterator(data_.erase(to_vector_iterator(first), to_vector_iterator(last)));
   }
 
-  iterator erase(const_iterator iter) { return from_vector_iterator(data_.erase(to_vector_iterator(iter))); }
+  TEST_CONSTEXPR_CXX23 iterator erase(const_iterator iter) {
+    return from_vector_iterator(data_.erase(to_vector_iterator(iter)));
+  }
 
   template <class... Args>
-  iterator emplace(const_iterator pos, Args&&... args) {
+  TEST_CONSTEXPR_CXX23 iterator emplace(const_iterator pos, Args&&... args) {
     return from_vector_iterator(data_.emplace(to_vector_iterator(pos), std::forward<Args>(args)...));
   }
 
 private:
-  std::vector<T>::const_iterator to_vector_iterator(const_iterator cit) const { return cit - cbegin() + data_.begin(); }
+  TEST_CONSTEXPR_CXX23 std::vector<T>::const_iterator to_vector_iterator(const_iterator cit) const {
+    return cit - cbegin() + data_.begin();
+  }
 
-  iterator from_vector_iterator(std::vector<T>::iterator it) { return it - data_.begin() + begin(); }
+  TEST_CONSTEXPR_CXX23 iterator from_vector_iterator(std::vector<T>::iterator it) { return it - data_.begin() + begin(); }
 
   std::vector<T> data_;
 };



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