rustc: Preallocate when building the dep graph

src/librustc/dep_graph/query.rs

@@ -22,11 +22,10 @@ impl DepGraphQuery {
     pub fn new(nodes: &[DepNode],
                edges: &[(DepNode, DepNode)])
                -> DepGraphQuery {
-        let mut graph = Graph::new();
+        let mut graph = Graph::with_capacity(nodes.len(), edges.len());
         let mut indices = FxHashMap();
         for node in nodes {
-            indices.insert(node.clone(), graph.next_node_index());
-            graph.add_node(node.clone());
+            indices.insert(node.clone(), graph.add_node(node.clone()));
         }
 
         for &(ref source, ref target) in edges {

src/librustc_data_structures/graph/mod.rs

@@ -114,6 +114,13 @@ impl<N: Debug, E: Debug> Graph<N, E> {
         }
     }
 
+    pub fn with_capacity(nodes: usize, edges: usize) -> Graph<N, E> {
+        Graph {
+            nodes: SnapshotVec::with_capacity(nodes),
+            edges: SnapshotVec::with_capacity(edges),
+        }
+    }
+
     // # Simple accessors
 
     #[inline]

src/librustc_data_structures/snapshot_vec.rs

@@ -66,6 +66,13 @@ impl<D: SnapshotVecDelegate> SnapshotVec<D> {
         }
     }
 
+    pub fn with_capacity(n: usize) -> SnapshotVec<D> {
+        SnapshotVec {
+            values: Vec::with_capacity(n),
+            undo_log: Vec::new(),
+        }
+    }
+
     fn in_snapshot(&self) -> bool {
         !self.undo_log.is_empty()
     }