diff --git a/src/librustc_middle/ty/fold.rs b/src/librustc_middle/ty/fold.rs
index a3d611a1325..7b23460eb6e 100644
--- a/src/librustc_middle/ty/fold.rs
+++ b/src/librustc_middle/ty/fold.rs
@@ -263,20 +263,6 @@ where
 // Region folder
 
 impl<'tcx> TyCtxt<'tcx> {
-    /// Collects the free and escaping regions in `value` into `region_set`. Returns
-    /// whether any late-bound regions were skipped
-    pub fn collect_regions<T>(self, value: &T, region_set: &mut FxHashSet<ty::Region<'tcx>>) -> bool
-    where
-        T: TypeFoldable<'tcx>,
-    {
-        let mut have_bound_regions = false;
-        self.fold_regions(value, &mut have_bound_regions, |r, d| {
-            region_set.insert(self.mk_region(r.shifted_out_to_binder(d)));
-            r
-        });
-        have_bound_regions
-    }
-
     /// Folds the escaping and free regions in `value` using `f`, and
     /// sets `skipped_regions` to true if any late-bound region was found
     /// and skipped.
diff --git a/src/librustc_middle/ty/mod.rs b/src/librustc_middle/ty/mod.rs
index 79fa13b0b4a..48bc90526af 100644
--- a/src/librustc_middle/ty/mod.rs
+++ b/src/librustc_middle/ty/mod.rs
@@ -1518,77 +1518,7 @@ impl<'tcx> ToPredicate<'tcx> for PolyProjectionPredicate<'tcx> {
     }
 }
 
-// A custom iterator used by `Predicate::walk_tys`.
-enum WalkTysIter<'tcx, I, J, K>
-where
-    I: Iterator<Item = Ty<'tcx>>,
-    J: Iterator<Item = Ty<'tcx>>,
-    K: Iterator<Item = Ty<'tcx>>,
-{
-    None,
-    One(Ty<'tcx>),
-    Two(Ty<'tcx>, Ty<'tcx>),
-    Types(I),
-    InputTypes(J),
-    ProjectionTypes(K),
-}
-
-impl<'tcx, I, J, K> Iterator for WalkTysIter<'tcx, I, J, K>
-where
-    I: Iterator<Item = Ty<'tcx>>,
-    J: Iterator<Item = Ty<'tcx>>,
-    K: Iterator<Item = Ty<'tcx>>,
-{
-    type Item = Ty<'tcx>;
-
-    fn next(&mut self) -> Option<Ty<'tcx>> {
-        match *self {
-            WalkTysIter::None => None,
-            WalkTysIter::One(item) => {
-                *self = WalkTysIter::None;
-                Some(item)
-            }
-            WalkTysIter::Two(item1, item2) => {
-                *self = WalkTysIter::One(item2);
-                Some(item1)
-            }
-            WalkTysIter::Types(ref mut iter) => iter.next(),
-            WalkTysIter::InputTypes(ref mut iter) => iter.next(),
-            WalkTysIter::ProjectionTypes(ref mut iter) => iter.next(),
-        }
-    }
-}
-
 impl<'tcx> Predicate<'tcx> {
-    /// Iterates over the types in this predicate. Note that in all
-    /// cases this is skipping over a binder, so late-bound regions
-    /// with depth 0 are bound by the predicate.
-    pub fn walk_tys(&'a self) -> impl Iterator<Item = Ty<'tcx>> + 'a {
-        match *self {
-            ty::Predicate::Trait(ref data, _) => {
-                WalkTysIter::InputTypes(data.skip_binder().input_types())
-            }
-            ty::Predicate::Subtype(binder) => {
-                let SubtypePredicate { a, b, a_is_expected: _ } = binder.skip_binder();
-                WalkTysIter::Two(a, b)
-            }
-            ty::Predicate::TypeOutlives(binder) => WalkTysIter::One(binder.skip_binder().0),
-            ty::Predicate::RegionOutlives(..) => WalkTysIter::None,
-            ty::Predicate::Projection(ref data) => {
-                let inner = data.skip_binder();
-                WalkTysIter::ProjectionTypes(
-                    inner.projection_ty.substs.types().chain(Some(inner.ty)),
-                )
-            }
-            ty::Predicate::WellFormed(data) => WalkTysIter::One(data),
-            ty::Predicate::ObjectSafe(_trait_def_id) => WalkTysIter::None,
-            ty::Predicate::ClosureKind(_closure_def_id, closure_substs, _kind) => {
-                WalkTysIter::Types(closure_substs.types())
-            }
-            ty::Predicate::ConstEvaluatable(_, substs) => WalkTysIter::Types(substs.types()),
-        }
-    }
-
     pub fn to_opt_poly_trait_ref(&self) -> Option<PolyTraitRef<'tcx>> {
         match *self {
             Predicate::Trait(ref t, _) => Some(t.to_poly_trait_ref()),
diff --git a/src/librustdoc/clean/auto_trait.rs b/src/librustdoc/clean/auto_trait.rs
index 73df844a91b..eb8aec708a6 100644
--- a/src/librustdoc/clean/auto_trait.rs
+++ b/src/librustdoc/clean/auto_trait.rs
@@ -315,25 +315,28 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
         tcx: TyCtxt<'tcx>,
         pred: ty::Predicate<'tcx>,
     ) -> FxHashSet<GenericParamDef> {
-        pred.walk_tys()
-            .flat_map(|t| {
-                let mut regions = FxHashSet::default();
-                tcx.collect_regions(&t, &mut regions);
+        let regions = match pred {
+            ty::Predicate::Trait(poly_trait_pred, _) => {
+                tcx.collect_referenced_late_bound_regions(&poly_trait_pred)
+            }
+            ty::Predicate::Projection(poly_proj_pred) => {
+                tcx.collect_referenced_late_bound_regions(&poly_proj_pred)
+            }
+            _ => return FxHashSet::default(),
+        };
 
-                regions.into_iter().flat_map(|r| {
-                    match r {
-                        // We only care about late bound regions, as we need to add them
-                        // to the 'for<>' section
-                        &ty::ReLateBound(_, ty::BoundRegion::BrNamed(_, name)) => {
-                            Some(GenericParamDef {
-                                name: name.to_string(),
-                                kind: GenericParamDefKind::Lifetime,
-                            })
-                        }
-                        &ty::ReVar(_) | &ty::ReEarlyBound(_) | &ty::ReStatic => None,
-                        _ => panic!("Unexpected region type {:?}", r),
-                    }
-                })
+        regions
+            .into_iter()
+            .filter_map(|br| {
+                match br {
+                    // We only care about named late bound regions, as we need to add them
+                    // to the 'for<>' section
+                    ty::BrNamed(_, name) => Some(GenericParamDef {
+                        name: name.to_string(),
+                        kind: GenericParamDefKind::Lifetime,
+                    }),
+                    _ => None,
+                }
             })
             .collect()
     }