nit: cache crate-hash for next time

diff --git a/src/librustc_incremental/persist/hash.rs b/src/librustc_incremental/persist/hash.rs
index c36b9ed0d26a3246eb6f596c0be85408fdc1fa19..b729f25b873d4f05ec8df2b45e7239c4cb02fa7f 100644 (file)
--- a/src/librustc_incremental/persist/hash.rs
+++ b/src/librustc_incremental/persist/hash.rs
@@ -86,6 +86,11 @@ fn metadata_hash(&mut self, def_id: DefId) -> u64 {
             // krate; in that case, we just use the krate's overall hash
             if let Some(&hash) = self.crate_hashes.get(&def_id.krate) {
                 debug!("metadata_hash: def_id={:?} crate_hash={:?}", def_id, hash);
+
+                // micro-"optimization": avoid a cache miss if we ask
+                // for metadata from this particular def-id again.
+                self.item_metadata_hashes.insert(def_id, hash.as_u64());
+
                 return hash.as_u64();
             }