Speed up plug_leaks

src/librustc/infer/higher_ranked/mod.rs

@@ -749,13 +749,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
     pub fn plug_leaks<T>(&self,
                          skol_map: SkolemizationMap<'tcx>,
                          snapshot: &CombinedSnapshot,
-                         value: &T) -> T
+                         value: T) -> T
         where T : TypeFoldable<'tcx>
     {
         debug!("plug_leaks(skol_map={:?}, value={:?})",
                skol_map,
                value);
 
+        if skol_map.is_empty() {
+            return value;
+        }
+
         // Compute a mapping from the "taint set" of each skolemized
         // region back to the `ty::BoundRegion` that it originally
         // represented. Because `leak_check` passed, we know that
@@ -775,7 +779,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
 
         // Remove any instantiated type variables from `value`; those can hide
         // references to regions from the `fold_regions` code below.
-        let value = self.resolve_type_vars_if_possible(value);
+        let value = self.resolve_type_vars_if_possible(&value);
 
         // Map any skolemization byproducts back to a late-bound
         // region. Put that late-bound region at whatever the outermost
@@ -813,9 +817,6 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             }
         });
 
-        debug!("plug_leaks: result={:?}",
-               result);
-
         self.pop_skolemized(skol_map, snapshot);
 
         debug!("plug_leaks: result={:?}", result);

src/librustc/traits/project.rs

@@ -171,7 +171,7 @@ pub fn poly_project_and_unify_type<'cx, 'gcx, 'tcx>(
             Ok(result) => {
                 let span = obligation.cause.span;
                 match infcx.leak_check(false, span, &skol_map, snapshot) {
-                    Ok(()) => Ok(infcx.plug_leaks(skol_map, snapshot, &result)),
+                    Ok(()) => Ok(infcx.plug_leaks(skol_map, snapshot, result)),
                     Err(e) => Err(MismatchedProjectionTypes { err: e }),
                 }
             }

src/librustc/traits/select.rs

@@ -1980,7 +1980,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                                                   normalized_ty,
                                                   &[]);
                 obligations.push(skol_obligation);
-                this.infcx().plug_leaks(skol_map, snapshot, &obligations)
+                this.infcx().plug_leaks(skol_map, snapshot, obligations)
             })
         }).collect()
     }
@@ -2899,7 +2899,7 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                     predicate: predicate.value
                 }))
         }).collect();
-        self.infcx().plug_leaks(skol_map, snapshot, &predicates)
+        self.infcx().plug_leaks(skol_map, snapshot, predicates)
     }
 }