Use sort_by_cached_key when key the function is not trivial/free

Author: ljedrz

src/librustc/middle/resolve_lifetime.rs

@@ -1573,7 +1573,7 @@ impl<'a, 'tcx> LifetimeContext<'a, 'tcx> {
             .collect();
 
         // ensure that we issue lints in a repeatable order
-        def_ids.sort_by_key(|&def_id| self.tcx.def_path_hash(def_id));
+        def_ids.sort_by_cached_key(|&def_id| self.tcx.def_path_hash(def_id));
 
         for def_id in def_ids {
             debug!(

src/librustc/traits/object_safety.rs

@@ -409,7 +409,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             .collect::<Vec<_>>();
 
         // existential predicates need to be in a specific order
-        associated_types.sort_by_key(|item| self.def_path_hash(item.def_id));
+        associated_types.sort_by_cached_key(|item| self.def_path_hash(item.def_id));
 
         let projection_predicates = associated_types.into_iter().map(|item| {
             ty::ExistentialPredicate::Projection(ty::ExistentialProjection {

src/librustc_mir/monomorphize/partitioning.rs

@@ -985,7 +985,7 @@ fn collect_and_partition_mono_items<'a, 'tcx>(
                 output.push_str(" @@");
                 let mut empty = Vec::new();
                 let cgus = item_to_cgus.get_mut(i).unwrap_or(&mut empty);
-                cgus.as_mut_slice().sort_by_key(|&(ref name, _)| name.clone());
+                cgus.as_mut_slice().sort_by_cached_key(|&(ref name, _)| name.clone());
                 cgus.dedup();
                 for &(ref cgu_name, (linkage, _)) in cgus.iter() {
                     output.push_str(" ");