Rollup merge of rust-lang#50598 - whitfin:unnecessary-mut-borrow, r=michaelwoerister

Remove unnecessary mutable borrow and resizing in DepGraph::serialize

I might be mistaken, but I noticed this whilst in this file for something else. It appears that this mutable borrow is unnecessary and since it's locking it should be removed. The resizing looks redundant since nothing additional is added to the fingerprints in this function, so that can also be removed.

Author: alexcrichton

src/librustc/dep_graph/graph.rs

@@ -523,15 +523,9 @@ impl DepGraph {
     }
 
     pub fn serialize(&self) -> SerializedDepGraph {
-        let mut fingerprints = self.fingerprints.borrow_mut();
         let current_dep_graph = self.data.as_ref().unwrap().current.borrow();
 
-        // Make sure we don't run out of bounds below.
-        if current_dep_graph.nodes.len() > fingerprints.len() {
-            fingerprints.resize(current_dep_graph.nodes.len(), Fingerprint::ZERO);
-        }
-
-        let fingerprints = fingerprints.clone().convert_index_type();
+        let fingerprints = self.fingerprints.borrow().clone().convert_index_type();
         let nodes = current_dep_graph.nodes.clone().convert_index_type();
 
         let total_edge_count: usize = current_dep_graph.edges.iter()