diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index 7da664e6d02..0b4c3be8b78 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -61,6 +61,7 @@
 #![feature(refcell_replace_swap)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(specialization)]
 #![feature(unboxed_closures)]
 #![feature(trace_macros)]
diff --git a/src/librustc/middle/cstore.rs b/src/librustc/middle/cstore.rs
index add9b621596..41334a37dbe 100644
--- a/src/librustc/middle/cstore.rs
+++ b/src/librustc/middle/cstore.rs
@@ -401,7 +401,7 @@ pub fn used_crates(tcx: TyCtxt, prefer: LinkagePreference)
         .collect::<Vec<_>>();
     let mut ordering = tcx.postorder_cnums(LOCAL_CRATE);
     Lrc::make_mut(&mut ordering).reverse();
-    libs.sort_by_key(|&(a, _)| {
+    libs.sort_by_cached_key(|&(a, _)| {
         ordering.iter().position(|x| *x == a)
     });
     libs
diff --git a/src/librustc_mir/lib.rs b/src/librustc_mir/lib.rs
index 8762e7550cd..2fe64f492dd 100644
--- a/src/librustc_mir/lib.rs
+++ b/src/librustc_mir/lib.rs
@@ -17,6 +17,7 @@ Rust MIR: a lowered representation of Rust. Also: an experiment!
 #![deny(warnings)]
 
 #![feature(slice_patterns)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(from_ref)]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
diff --git a/src/librustc_mir/monomorphize/partitioning.rs b/src/librustc_mir/monomorphize/partitioning.rs
index da4cb4ec789..17d1156617d 100644
--- a/src/librustc_mir/monomorphize/partitioning.rs
+++ b/src/librustc_mir/monomorphize/partitioning.rs
@@ -509,7 +509,7 @@ fn merge_codegen_units<'tcx>(initial_partitioning: &mut PreInliningPartitioning<
     // Merge the two smallest codegen units until the target size is reached.
     while codegen_units.len() > target_cgu_count {
         // Sort small cgus to the back
-        codegen_units.sort_by_key(|cgu| usize::MAX - cgu.size_estimate());
+        codegen_units.sort_by_cached_key(|cgu| usize::MAX - cgu.size_estimate());
         let mut smallest = codegen_units.pop().unwrap();
         let second_smallest = codegen_units.last_mut().unwrap();
 
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index 2bf17cd1317..c1a7f20feff 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -14,6 +14,7 @@
 #![deny(warnings)]
 
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 
 #[macro_use]
 extern crate log;
@@ -3341,7 +3342,9 @@ impl<'a> Resolver<'a> {
                         let is_mod = |def| match def { Def::Mod(..) => true, _ => false };
                         let mut candidates =
                             self.lookup_import_candidates(name, TypeNS, is_mod);
-                        candidates.sort_by_key(|c| (c.path.segments.len(), c.path.to_string()));
+                        candidates.sort_by_cached_key(|c| {
+                            (c.path.segments.len(), c.path.to_string())
+                        });
                         if let Some(candidate) = candidates.get(0) {
                             format!("Did you mean `{}`?", candidate.path)
                         } else {
@@ -3579,7 +3582,7 @@ impl<'a> Resolver<'a> {
 
         let name = path[path.len() - 1].name;
         // Make sure error reporting is deterministic.
-        names.sort_by_key(|name| name.as_str());
+        names.sort_by_cached_key(|name| name.as_str());
         match find_best_match_for_name(names.iter(), &name.as_str(), None) {
             Some(found) if found != name => Some(found),
             _ => None,
diff --git a/src/librustc_trans/base.rs b/src/librustc_trans/base.rs
index 0329264a312..3e60af6ef22 100644
--- a/src/librustc_trans/base.rs
+++ b/src/librustc_trans/base.rs
@@ -830,7 +830,7 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     // a bit more efficiently.
     let codegen_units = {
         let mut codegen_units = codegen_units;
-        codegen_units.sort_by_key(|cgu| usize::MAX - cgu.size_estimate());
+        codegen_units.sort_by_cached_key(|cgu| usize::MAX - cgu.size_estimate());
         codegen_units
     };
 
diff --git a/src/librustc_trans/lib.rs b/src/librustc_trans/lib.rs
index 344f959c141..73c676021ec 100644
--- a/src/librustc_trans/lib.rs
+++ b/src/librustc_trans/lib.rs
@@ -27,6 +27,7 @@
 #![feature(libc)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(optin_builtin_traits)]
 #![feature(inclusive_range_fields)]
 #![feature(underscore_lifetimes)]
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index fa2022e8cc9..de570956622 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -799,7 +799,7 @@ impl<'a, 'gcx, 'tcx> ProbeContext<'a, 'gcx, 'tcx> {
             .collect();
 
         // sort them by the name so we have a stable result
-        names.sort_by_key(|n| n.as_str());
+        names.sort_by_cached_key(|n| n.as_str());
         names
     }
 
diff --git a/src/librustc_typeck/lib.rs b/src/librustc_typeck/lib.rs
index 6f71db998bd..2ead5e9d913 100644
--- a/src/librustc_typeck/lib.rs
+++ b/src/librustc_typeck/lib.rs
@@ -82,6 +82,7 @@ This API is completely unstable and subject to change.
 #![feature(refcell_replace_swap)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
+#![feature(slice_sort_by_cached_key)]
 #![feature(dyn_trait)]
 
 #[macro_use] extern crate log;