avoid extra clone

Author: nikomatsakis

src/librustc/dep_graph/raii.rs

@@ -14,20 +14,20 @@ use super::thread::{DepGraphThreadData, DepMessage};
 
 pub struct DepTask<'graph> {
     data: &'graph DepGraphThreadData,
-    key: DepNode<DefId>,
+    key: Option<DepNode<DefId>>,
 }
 
 impl<'graph> DepTask<'graph> {
     pub fn new(data: &'graph DepGraphThreadData, key: DepNode<DefId>)
                -> DepTask<'graph> {
         data.enqueue(DepMessage::PushTask(key.clone()));
-        DepTask { data: data, key: key }
+        DepTask { data: data, key: Some(key) }
     }
 }
 
 impl<'graph> Drop for DepTask<'graph> {
     fn drop(&mut self) {
-        self.data.enqueue(DepMessage::PopTask(self.key.clone()));
+        self.data.enqueue(DepMessage::PopTask(self.key.take().unwrap()));
     }
 }