Don't use Lock for heavily accessed CrateMetadata::cnum_map.

src/librustc_metadata/creader.rs

@@ -219,6 +219,8 @@ impl<'a> CrateLoader<'a> {
 
         let cnum_map = self.resolve_crate_deps(root, &crate_root, &metadata, cnum, span, dep_kind);
 
+        let dependencies: Vec<CrateNum> = cnum_map.iter().cloned().collect();
+
         let def_path_table = record_time(&self.sess.perf_stats.decode_def_path_tables_time, || {
             crate_root.def_path_table.decode((&metadata, self.sess))
         });
@@ -239,8 +241,9 @@ impl<'a> CrateLoader<'a> {
             }),
             root: crate_root,
             blob: metadata,
-            cnum_map: Lock::new(cnum_map),
+            cnum_map,
             cnum,
+            dependencies: Lock::new(dependencies),
             codemap_import_info: RwLock::new(vec![]),
             attribute_cache: Lock::new([Vec::new(), Vec::new()]),
             dep_kind: Lock::new(dep_kind),
@@ -392,7 +395,7 @@ impl<'a> CrateLoader<'a> {
 
         // Propagate the extern crate info to dependencies.
         extern_crate.direct = false;
-        for &dep_cnum in cmeta.cnum_map.borrow().iter() {
+        for &dep_cnum in cmeta.dependencies.borrow().iter() {
             self.update_extern_crate(dep_cnum, extern_crate, visited);
         }
     }
@@ -1040,7 +1043,7 @@ impl<'a> CrateLoader<'a> {
             }
 
             info!("injecting a dep from {} to {}", cnum, krate);
-            data.cnum_map.borrow_mut().push(krate);
+            data.dependencies.borrow_mut().push(krate);
         });
     }
 }

src/librustc_metadata/cstore.rs

@@ -64,8 +64,9 @@ pub struct CrateMetadata {
     pub extern_crate: Lock<Option<ExternCrate>>,
 
     pub blob: MetadataBlob,
-    pub cnum_map: Lock<CrateNumMap>,
+    pub cnum_map: CrateNumMap,
     pub cnum: CrateNum,
+    pub dependencies: Lock<Vec<CrateNum>>,
     pub codemap_import_info: RwLock<Vec<ImportedFileMap>>,
     pub attribute_cache: Lock<[Vec<Option<Lrc<[ast::Attribute]>>>; 2]>,
 
@@ -144,7 +145,7 @@ impl CStore {
         }
 
         let data = self.get_crate_data(krate);
-        for &dep in data.cnum_map.borrow().iter() {
+        for &dep in data.dependencies.borrow().iter() {
             if dep != krate {
                 self.push_dependencies_in_postorder(ordering, dep);
             }

src/librustc_metadata/decoder.rs

@@ -246,7 +246,7 @@ impl<'a, 'tcx: 'a> TyDecoder<'a, 'tcx> for DecodeContext<'a, 'tcx> {
         if cnum == LOCAL_CRATE {
             self.cdata().cnum
         } else {
-            self.cdata().cnum_map.borrow()[cnum]
+            self.cdata().cnum_map[cnum]
         }
     }
 }
@@ -932,7 +932,7 @@ impl<'a, 'tcx> CrateMetadata {
     // Translate a DefId from the current compilation environment to a DefId
     // for an external crate.
     fn reverse_translate_def_id(&self, did: DefId) -> Option<DefId> {
-        for (local, &global) in self.cnum_map.borrow().iter_enumerated() {
+        for (local, &global) in self.cnum_map.iter_enumerated() {
             if global == did.krate {
                 return Some(DefId {
                     krate: local,
@@ -1007,7 +1007,7 @@ impl<'a, 'tcx> CrateMetadata {
             .enumerate()
             .flat_map(|(i, link)| {
                 let cnum = CrateNum::new(i + 1);
-                link.map(|link| (self.cnum_map.borrow()[cnum], link))
+                link.map(|link| (self.cnum_map[cnum], link))
             })
             .collect()
     }