diff --git a/libstdc++-v3/include/bits/hashtable.h b/libstdc++-v3/include/bits/hashtable.h
index cd3e1ac297c..e8e51714d72 100644
--- a/libstdc++-v3/include/bits/hashtable.h
+++ b/libstdc++-v3/include/bits/hashtable.h
@@ -48,7 +48,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     using __cache_default
       =  __not_<__and_<// Do not cache for fast hasher.
 		       __is_fast_hash<_Hash>,
-		       // Mandatory to have erase not throwing.
+		       // Mandatory for the rehash process.
 		       __is_nothrow_invocable<const _Hash&, const _Tp&>>>;
 
   // Helper to conditionally delete the default constructor.
@@ -481,7 +481,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Ht, typename _NodeGenerator>
 	void
-	_M_assign(_Ht&&, const _NodeGenerator&);
+	_M_assign(_Ht&&, _NodeGenerator&);
 
       void
       _M_move_assign(_Hashtable&&, true_type);
@@ -919,7 +919,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Kt, typename _Arg, typename _NodeGenerator>
 	std::pair<iterator, bool>
-	_M_insert_unique(_Kt&&, _Arg&&, const _NodeGenerator&);
+	_M_insert_unique(_Kt&&, _Arg&&, _NodeGenerator&);
 
       template<typename _Kt>
 	static __conditional_t<
@@ -939,7 +939,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Arg, typename _NodeGenerator>
 	std::pair<iterator, bool>
-	_M_insert_unique_aux(_Arg&& __arg, const _NodeGenerator& __node_gen)
+	_M_insert_unique_aux(_Arg&& __arg, _NodeGenerator& __node_gen)
 	{
 	  return _M_insert_unique(
 	    _S_forward_key(_ExtractKey{}(std::forward<_Arg>(__arg))),
@@ -948,7 +948,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Arg, typename _NodeGenerator>
 	std::pair<iterator, bool>
-	_M_insert(_Arg&& __arg, const _NodeGenerator& __node_gen,
+	_M_insert(_Arg&& __arg, _NodeGenerator& __node_gen,
 		  true_type /* __uks */)
 	{
 	  using __to_value
@@ -959,7 +959,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       template<typename _Arg, typename _NodeGenerator>
 	iterator
-	_M_insert(_Arg&& __arg, const _NodeGenerator& __node_gen,
+	_M_insert(_Arg&& __arg, _NodeGenerator& __node_gen,
 		  false_type __uks)
 	{
 	  using __to_value
@@ -972,7 +972,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Arg, typename _NodeGenerator>
 	iterator
 	_M_insert(const_iterator, _Arg&& __arg,
-		  const _NodeGenerator& __node_gen, true_type __uks)
+		  _NodeGenerator& __node_gen, true_type __uks)
 	{
 	  return
 	    _M_insert(std::forward<_Arg>(__arg), __node_gen, __uks).first;
@@ -982,7 +982,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       template<typename _Arg, typename _NodeGenerator>
 	iterator
 	_M_insert(const_iterator, _Arg&&,
-		  const _NodeGenerator&, false_type __uks);
+		  _NodeGenerator&, false_type __uks);
 
       size_type
       _M_erase(true_type __uks, const key_type&);
@@ -1414,7 +1414,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       void
       _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 		 _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
-      _M_assign(_Ht&& __ht, const _NodeGenerator& __node_gen)
+      _M_assign(_Ht&& __ht, _NodeGenerator& __node_gen)
       {
 	__buckets_ptr __buckets = nullptr;
 	if (!_M_buckets)
@@ -1656,8 +1656,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     ~_Hashtable() noexcept
     {
       // Getting a bucket index from a node shall not throw because it is used
-      // in methods (erase, swap...) that shall not throw. Need a complete
-      // type to check this, so do it in the destructor not at class scope.
+      // during the rehash process. This static_assert purpose is limited to usage
+      // of _Hashtable with _Hashtable_traits requesting non-cached hash code.
+      // Need a complete type to check this, so do it in the destructor not at
+      // class scope.
       static_assert(noexcept(declval<const __hash_code_base_access&>()
 			._M_bucket_index(declval<const __node_value_type&>(),
 					 (std::size_t)0)),
@@ -2313,7 +2315,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 		 _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
       _M_insert_unique(_Kt&& __k, _Arg&& __v,
-		       const _NodeGenerator& __node_gen)
+		       _NodeGenerator& __node_gen)
       -> pair<iterator, bool>
       {
 	const size_type __size = size();
@@ -2351,7 +2353,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       _Hashtable<_Key, _Value, _Alloc, _ExtractKey, _Equal,
 		 _Hash, _RangeHash, _Unused, _RehashPolicy, _Traits>::
       _M_insert(const_iterator __hint, _Arg&& __v,
-		const _NodeGenerator& __node_gen,
+		_NodeGenerator& __node_gen,
 		false_type /* __uks */)
       -> iterator
       {
diff --git a/libstdc++-v3/include/bits/hashtable_policy.h b/libstdc++-v3/include/bits/hashtable_policy.h
index 26def24f24e..1c121667ef0 100644
--- a/libstdc++-v3/include/bits/hashtable_policy.h
+++ b/libstdc++-v3/include/bits/hashtable_policy.h
@@ -155,7 +155,7 @@ namespace __detail
     {
       template<typename _Kt, typename _Arg, typename _NodeGenerator>
 	static auto
-	_S_build(_Kt&& __k, _Arg&& __arg, const _NodeGenerator& __node_gen)
+	_S_build(_Kt&& __k, _Arg&& __arg, _NodeGenerator& __node_gen)
 	-> typename _NodeGenerator::__node_ptr
 	{
 	  return __node_gen(std::forward<_Kt>(__k),
@@ -168,7 +168,7 @@ namespace __detail
     {
       template<typename _Kt, typename _Arg, typename _NodeGenerator>
 	static auto
-	_S_build(_Kt&& __k, _Arg&&, const _NodeGenerator& __node_gen)
+	_S_build(_Kt&& __k, _Arg&&, _NodeGenerator& __node_gen)
 	-> typename _NodeGenerator::__node_ptr
 	{ return __node_gen(std::forward<_Kt>(__k)); }
     };
@@ -212,7 +212,7 @@ namespace __detail
 
       template<typename... _Args>
 	__node_ptr
-	operator()(_Args&&... __args) const
+	operator()(_Args&&... __args)
 	{
 	  if (!_M_nodes)
 	    return _M_h._M_allocate_node(std::forward<_Args>(__args)...);
@@ -230,7 +230,7 @@ namespace __detail
 	}
 
     private:
-      mutable __node_ptr _M_nodes;
+      __node_ptr _M_nodes;
       __hashtable_alloc& _M_h;
     };
 
@@ -555,6 +555,7 @@ namespace __detail
     { return _M_max_load_factor; }
 
     // Return a bucket size no smaller than n.
+    // TODO: 'const' qualifier is kept for abi compatibility reason.
     std::size_t
     _M_next_bkt(std::size_t __n) const;
 
@@ -567,6 +568,7 @@ namespace __detail
     // and __n_ins is number of elements to be inserted.  Do we need to
     // increase bucket count?  If so, return make_pair(true, n), where n
     // is the new bucket count.  If not, return make_pair(false, 0).
+    // TODO: 'const' qualifier is kept for abi compatibility reason.
     std::pair<bool, std::size_t>
     _M_need_rehash(std::size_t __n_bkt, std::size_t __n_elt,
 		   std::size_t __n_ins) const;
@@ -588,6 +590,8 @@ namespace __detail
     static const std::size_t _S_growth_factor = 2;
 
     float		_M_max_load_factor;
+
+    // TODO: 'mutable' kept for abi compatibility reason.
     mutable std::size_t	_M_next_resize;
   };
 
@@ -931,12 +935,12 @@ namespace __detail
       template<typename _InputIterator, typename _NodeGetter>
 	void
 	_M_insert_range(_InputIterator __first, _InputIterator __last,
-			const _NodeGetter&, true_type __uks);
+			_NodeGetter&, true_type __uks);
 
       template<typename _InputIterator, typename _NodeGetter>
 	void
 	_M_insert_range(_InputIterator __first, _InputIterator __last,
-			const _NodeGetter&, false_type __uks);
+			_NodeGetter&, false_type __uks);
 
     public:
       using iterator = _Node_iterator<_Value, __constant_iterators::value,
@@ -1012,7 +1016,7 @@ namespace __detail
 		   _Hash, _RangeHash, _Unused,
 		   _RehashPolicy, _Traits>::
       _M_insert_range(_InputIterator __first, _InputIterator __last,
-		      const _NodeGetter& __node_gen, true_type __uks)
+		      _NodeGetter& __node_gen, true_type __uks)
       {
 	__hashtable& __h = _M_conjure_hashtable();
 	for (; __first != __last; ++__first)
@@ -1029,7 +1033,7 @@ namespace __detail
 		   _Hash, _RangeHash, _Unused,
 		   _RehashPolicy, _Traits>::
       _M_insert_range(_InputIterator __first, _InputIterator __last,
-		      const _NodeGetter& __node_gen, false_type __uks)
+		      _NodeGetter& __node_gen, false_type __uks)
       {
 	using __rehash_guard_t = typename __hashtable::__rehash_guard_t;
 	using __pair_type = std::pair<bool, std::size_t>;
@@ -1359,9 +1363,7 @@ namespace __detail
       std::size_t
       _M_bucket_index(const _Hash_node_value<_Value, false>& __n,
 		      std::size_t __bkt_count) const
-	noexcept( noexcept(declval<const _Hash&>()(declval<const _Key&>()))
-		  && noexcept(declval<const _RangeHash&>()((__hash_code)0,
-							   (std::size_t)0)) )
+      noexcept( noexcept(declval<const _Hash&>()(declval<const _Key&>())) )
       {
 	return _RangeHash{}(_M_hash_code(_ExtractKey{}(__n._M_v())),
 			    __bkt_count);
@@ -1369,9 +1371,7 @@ namespace __detail
 
       std::size_t
       _M_bucket_index(const _Hash_node_value<_Value, true>& __n,
-		      std::size_t __bkt_count) const
-	noexcept( noexcept(declval<const _RangeHash&>()((__hash_code)0,
-							(std::size_t)0)) )
+		      std::size_t __bkt_count) const noexcept
       { return _RangeHash{}(__n._M_hash_code, __bkt_count); }
 
       void