Default to nullptr, and assign __hash during construction

Author: vinay-deshmukh

libcxx/include/__hash_table

@@ -167,8 +167,8 @@ public:
 #endif
 
   template <class _Alloc, class... _Args>
-  _LIBCPP_HIDE_FROM_ABI explicit __hash_node(__next_pointer __next, size_t __hash, _Alloc& __na, _Args&&... __args)
-      : _Base(__next), __hash_(__hash) {
+  _LIBCPP_HIDE_FROM_ABI explicit __hash_node(size_t __hash, _Alloc& __na, _Args&&... __args)
+      : _Base(nullptr), __hash_(__hash) {
     allocator_traits<_Alloc>::construct(__na, std::addressof(__get_value()), std::forward<_Args>(__args)...);
   }
 
@@ -1884,11 +1884,10 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__construct_node(_Args&&... __args) {
   // We don't use the allocator's construct() method to construct the node itself since the
   // Cpp17FooInsertable named requirements don't require the allocator's construct() method
   // to work on anything other than the value_type.
-  std::__construct_at(std::addressof(*__h), /* next = */ nullptr, /* hash = */ 0, __na, std::forward<_Args>(__args)...);
+  std::__construct_at(std::addressof(*__h), /* hash = */ hash_function()(__h->__get_value()), __na, std::forward<_Args>(__args)...);
 
   __h.get_deleter().__value_constructed = true;
 
-  __h->__hash_ = hash_function()(__h->__get_value());
   return __h;
 }
 
@@ -1900,7 +1899,7 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__construct_node_hash(size_t __hash, _
   __node_allocator& __na = __node_alloc();
   __node_holder __h(__node_traits::allocate(__na, 1), _Dp(__na));
   std::__construct_at(
-      std::addressof(*__h), /* next = */ nullptr, /* hash = */ __hash, __na, std::forward<_Args>(__args)...);
+      std::addressof(*__h), /* hash = */ __hash, __na, std::forward<_Args>(__args)...);
   __h.get_deleter().__value_constructed = true;
   return __h;
 }