Add 'unlikely' annotation to branch in crate DepNodeIndex caching.

src/librustc_metadata/decoder.rs

@@ -1372,7 +1372,7 @@ impl<'a, 'tcx> CrateMetadata {
     pub(super) fn get_crate_dep_node_index(&self, tcx: TyCtxt<'tcx>) -> DepNodeIndex {
         let mut dep_node_index = self.dep_node_index.load();
 
-        if dep_node_index == DepNodeIndex::INVALID {
+        if unlikely!(dep_node_index == DepNodeIndex::INVALID) {
             // We have not cached the DepNodeIndex for this upstream crate yet,
             // so use the dep-graph to find it out and cache it.
             // Note that multiple threads can enter this block concurrently.

src/librustc_metadata/lib.rs

@@ -1,6 +1,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![feature(box_patterns)]
+#![feature(core_intrinsics)]
 #![feature(crate_visibility_modifier)]
 #![feature(drain_filter)]
 #![feature(in_band_lifetimes)]
@@ -11,6 +12,7 @@
 #![feature(rustc_private)]
 #![feature(slice_patterns)]
 #![feature(specialization)]
+#![feature(stmt_expr_attributes)]
 
 #![recursion_limit="256"]