[libcxx-commits] [libcxx] [libc++] Remove UB from `std::map` by updating `std::__tree_node` construction (PR #153908)

[Vinay Deshmukh via libcxx-commits]

================
@@ -1874,16 +1879,13 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__construct_node(_Args&&... __args) {
   __node_allocator& __na = __node_alloc();
   __node_holder __h(__node_traits::allocate(__na, 1), _Dp(__na));
 
-  // Begin the lifetime of the node itself. Note that this doesn't begin the lifetime of the value
-  // held inside the node, since we need to use the allocator's construct() method for that.
+  // Begin the lifetime of the node itself and the value_type contained within.
   //
   // 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);
+  std::__construct_at(std::addressof(*__h), /* next = */ nullptr, /* hash = */ 0, __na, std::forward<_Args>(__args)...);
----------------
vinay-deshmukh wrote:

`nullptr` was used in all instances, but the `hash = ` arg can be 0 or a variable for the second occurrence, so that is still a constructor arg.

one more thing, for the second instance this was `0`, but then in the next line, it was being reassigned with a variable, so I changed that to be assigned through the constructor arg.

https://github.com/llvm/llvm-project/pull/153908