[libc++] Require fancy pointer to be correctly convertible

Author: philnik777

libcxx/include/__hash_table

@@ -96,7 +96,7 @@ struct __hash_node_base {
   __next_pointer __next_;
 
   _LIBCPP_HIDE_FROM_ABI __next_pointer __ptr() _NOEXCEPT {
-    return static_cast<__next_pointer>(pointer_traits<__node_base_pointer>::pointer_to(*this));
+    return pointer_traits<__node_base_pointer>::pointer_to(*this);
   }
 
   _LIBCPP_HIDE_FROM_ABI __node_pointer __upcast() _NOEXCEPT {
@@ -1499,9 +1499,9 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__node_insert_multi(const_iterator __p
     while (__pp->__next_ != __np)
       __pp = __pp->__next_;
     __cp->__next_ = __np;
-    __pp->__next_ = static_cast<__next_pointer>(__cp);
+    __pp->__next_ = __cp;
     ++size();
-    return iterator(static_cast<__next_pointer>(__cp));
+    return iterator(__cp);
   }
   return __node_insert_multi(__cp);
 }
@@ -1547,9 +1547,9 @@ __hash_table<_Tp, _Hash, _Equal, _Alloc>::__emplace_unique_key_args(_Key const&
         __bucket_list_[std::__constrain_hash(__h->__next_->__hash(), __bc)] = __h.get()->__ptr();
     } else {
       __h->__next_  = __pn->__next_;
-      __pn->__next_ = static_cast<__next_pointer>(__h.get());
+      __pn->__next_ = __h.get();
     }
-    __nd = static_cast<__next_pointer>(__h.release());
+    __nd = __h.release();
     // increment size
     ++size();
     __inserted = true;

libcxx/include/__memory/pointer_traits.h

@@ -252,18 +252,6 @@ concept __resettable_smart_pointer_with_args = requires(_Smart __s, _Pointer __p
 
 #endif
 
-// This function ensures safe conversions between fancy pointers at compile-time, where we avoid casts from/to
-// `__void_pointer` by obtaining the underlying raw pointer from the fancy pointer using `std::to_address`,
-// then dereferencing it to retrieve the pointed-to object, and finally constructing the target fancy pointer
-// to that object using the `std::pointer_traits<>::pinter_to` function.
-template <class _PtrTo, class _PtrFrom>
-_LIBCPP_CONSTEXPR_SINCE_CXX20 _LIBCPP_HIDE_FROM_ABI _PtrTo __static_fancy_pointer_cast(const _PtrFrom& __p) {
-  using __ptr_traits   = pointer_traits<_PtrTo>;
-  using __element_type = typename __ptr_traits::element_type;
-  return __p ? __ptr_traits::pointer_to(*static_cast<__element_type*>(std::addressof(*__p)))
-             : static_cast<_PtrTo>(nullptr);
-}
-
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS