# Adds a class definition inside `flatten_mclass_hierarchy_cache` without
        # null check. The caller must have initialized the cache.
        protected fun unsafe_update_hierarchy_cache(mclassdef: MClassDef)
        do
                var hierarchy = self.flatten_mclass_hierarchy_cache.as(not null)
                # Update the cache
                var c = mclassdef.mclass
                hierarchy.add_node(c)
                for s in mclassdef.supertypes do
                        hierarchy.add_edge(c, s.mclass)
                end
        end