add_node only adds to def use map if not already present

hercules_opt/src/editor.rs

@@ -457,7 +457,7 @@ impl<'a, 'b> FunctionEdit<'a, 'b> {
     pub fn add_node(&mut self, node: Node) -> NodeID {
         let id = NodeID::new(self.num_node_ids());
         // Added nodes need to have an entry in the def-use map.
-        self.updated_def_use.insert(id, HashSet::new());
+        self.updated_def_use.entry(id).or_insert(HashSet::new());
         // Added nodes use other nodes, and we need to update their def-use
         // entries.
         for u in get_uses(&node).as_ref() {