Handle subtyping in inference through obligations

src/librustc/ich/impls_ty.rs

@@ -170,6 +170,7 @@ impl_stable_hash_for!(enum ty::Visibility {
 impl_stable_hash_for!(struct ty::TraitRef<'tcx> { def_id, substs });
 impl_stable_hash_for!(struct ty::TraitPredicate<'tcx> { trait_ref });
 impl_stable_hash_for!(tuple_struct ty::EquatePredicate<'tcx> { t1, t2 });
+impl_stable_hash_for!(struct ty::SubtypePredicate<'tcx> { a_is_expected, a, b });
 
 impl<'a, 'tcx, A, B> HashStable<StableHashingContext<'a, 'tcx>> for ty::OutlivesPredicate<A, B>
     where A: HashStable<StableHashingContext<'a, 'tcx>>,
@@ -200,6 +201,9 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a, 'tcx>> for ty::Predicate<'tcx
             ty::Predicate::Equate(ref pred) => {
                 pred.hash_stable(hcx, hasher);
             }
+            ty::Predicate::Subtype(ref pred) => {
+                pred.hash_stable(hcx, hasher);
+            }
             ty::Predicate::RegionOutlives(ref pred) => {
                 pred.hash_stable(hcx, hasher);
             }