In PCTRIE_INSERT_LOOKUP_{G,L}E, there is a test - if two pointers are equal, replace one with a new value. The pointers can never be equal; one points to a struct pctrie_node and the other is the (void*) cast of a pointer to a field within a struct pctrie_node. So the tests and assignments can be removed with no effect.
If the assignments were made under some other conditions, they would only move the neighbor pointer one level up the tree, undoing the benefits of a neighbor update near the end of pctrie_insert_lookup_compount.