DrPoints (xref: #7685 ) showcases the use-case for a new iterator (hashtable_apply_to_all_key_payload_pairs_user_data()) over DynamoRIO's container hashtable_t that exposes the key and payload pair of every element.
This is necessary as we need to have access to both the basic block ID (key) and #executions (payload) once we reach the end of an instruction interval.