'Add a reference from code to this memory data.
:param int irsb_addr: Address of the basic block.
:param int stmt_idx: ID of the statement referencing this data entry.
:param int insn_addr: Address of the instruction referencing this data entry.
:return: None'

def add_ref(self, irsb_addr, stmt_idx, insn_addr):

    ref = (irsb_addr, stmt_idx, insn_addr)
    if (ref not in self.refs):
        self.refs.add(ref)
