Auto merge of #55821 - ljedrz:cached_key_sorts, r=<try>

Use sort_by_cached_key when the key function is not trivial/free

I'm not 100% sure about `def_path_hash` (everything it does is inlined) but it seems like a good idea at least for the rest, as they are cloning.

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/borrow_check/mod.rs

@@ -341,7 +341,7 @@ fn do_mir_borrowck<'a, 'gcx, 'tcx>(
     }
 
     if !mbcx.errors_buffer.is_empty() {
-        mbcx.errors_buffer.sort_by_key(|diag| diag.span.primary_span());
+        mbcx.errors_buffer.sort_by_cached_key(|diag| diag.span.primary_span());
 
         if tcx.migrate_borrowck() {
             // When borrowck=migrate, check if AST-borrowck would

src/librustc_mir/monomorphize/partitioning.rs

@@ -585,7 +585,7 @@ fn merge_codegen_units<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>,
     // smallest into each other) we're sure to start off with a deterministic
     // order (sorted by name). This'll mean that if two cgus have the same size
     // the stable sort below will keep everything nice and deterministic.
-    codegen_units.sort_by_key(|cgu| cgu.name().clone());
+    codegen_units.sort_by_cached_key(|cgu| cgu.name().clone());
 
     // Merge the two smallest codegen units until the target size is reached.
     while codegen_units.len() > target_cgu_count {
@@ -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(" ");