do not access inherited_impls map directly

src/librustc/middle/dead.rs

@@ -475,9 +475,9 @@ impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
         // This is done to handle the case where, for example, the static
         // method of a private type is used, but the type itself is never
         // called directly.
-        if let Some(impl_list) =
+        let def_id = self.tcx.hir.local_def_id(id);
-                self.tcx.maps.inherent_impls.borrow().get(&self.tcx.hir.local_def_id(id)) {
+        let inherent_impls = self.tcx.inherent_impls(def_id);
-            for &impl_did in impl_list.iter() {
+        for &impl_did in inherent_impls.iter() {
             for &item_did in &self.tcx.associated_item_def_ids(impl_did)[..] {
                 if let Some(item_node_id) = self.tcx.hir.as_local_node_id(item_did) {
                     if self.live_symbols.contains(&item_node_id) {
@@ -486,7 +486,6 @@ impl<'a, 'tcx> DeadVisitor<'a, 'tcx> {
                 }
             }
         }
-        }
         false
     }
 

src/librustc_metadata/encoder.rs

@@ -626,16 +626,16 @@ impl<'a, 'b: 'a, 'tcx: 'b> EntryBuilder<'a, 'b, 'tcx> {
     // Encodes the inherent implementations of a structure, enumeration, or trait.
     fn encode_inherent_implementations(&mut self, def_id: DefId) -> LazySeq<DefIndex> {
         debug!("EntryBuilder::encode_inherent_implementations({:?})", def_id);
-        match self.tcx.maps.inherent_impls.borrow().get(&def_id) {
+        let implementations = self.tcx.inherent_impls(def_id);
-            None => LazySeq::empty(),
+        if implementations.is_empty() {
-            Some(implementations) => {
+            LazySeq::empty()
+        } else {
             self.lazy_seq(implementations.iter().map(|&def_id| {
                 assert!(def_id.is_local());
                 def_id.index
             }))
         }
     }
-    }
 
     fn encode_stability(&mut self, def_id: DefId) -> Option<Lazy<attr::Stability>> {
         debug!("EntryBuilder::encode_stability({:?})", def_id);

src/librustc_typeck/coherence/inherent_impls.rs

@@ -66,11 +66,15 @@ pub fn inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     //
     // [the plan]: https://github.com/rust-lang/rust-roadmap/issues/4
 
+    thread_local! {
+        static EMPTY_DEF_ID_VEC: Rc<Vec<DefId>> = Rc::new(vec![])
+    }
+
     let result = tcx.dep_graph.with_ignore(|| {
         let crate_map = tcx.crate_inherent_impls(ty_def_id.krate);
         match crate_map.inherent_impls.get(&ty_def_id) {
             Some(v) => v.clone(),
-            None => Rc::new(vec![]),
+            None => EMPTY_DEF_ID_VEC.with(|v| v.clone())
         }
     });