diff --git a/src/librustc/ich/hcx.rs b/src/librustc/ich/hcx.rs
index e60fdd62deb..a8e5db26ead 100644
--- a/src/librustc/ich/hcx.rs
+++ b/src/librustc/ich/hcx.rs
@@ -9,7 +9,6 @@ use crate::session::Session;
 
 use std::cmp::Ord;
 use std::hash as std_hash;
-use std::collections::HashMap;
 use std::cell::RefCell;
 
 use syntax::ast;
@@ -394,13 +393,12 @@ impl<'a> HashStable<StableHashingContext<'a>> for DelimSpan {
     }
 }
 
-pub fn hash_stable_trait_impls<'a, 'gcx, W, R>(
+pub fn hash_stable_trait_impls<'a, 'gcx, W>(
     hcx: &mut StableHashingContext<'a>,
     hasher: &mut StableHasher<W>,
     blanket_impls: &[DefId],
-    non_blanket_impls: &HashMap<fast_reject::SimplifiedType, Vec<DefId>, R>)
-    where W: StableHasherResult,
-          R: std_hash::BuildHasher,
+    non_blanket_impls: &FxHashMap<fast_reject::SimplifiedType, Vec<DefId>>)
+    where W: StableHasherResult
 {
     {
         let mut blanket_impls: SmallVec<[_; 8]> = blanket_impls
diff --git a/src/librustc/infer/error_reporting/mod.rs b/src/librustc/infer/error_reporting/mod.rs
index 2810b5a8e6a..19663161fe3 100644
--- a/src/librustc/infer/error_reporting/mod.rs
+++ b/src/librustc/infer/error_reporting/mod.rs
@@ -56,7 +56,7 @@ use crate::hir::Node;
 use crate::middle::region;
 use crate::traits::{ObligationCause, ObligationCauseCode};
 use crate::ty::error::TypeError;
-use crate::ty::{self, subst::{Subst, SubstsRef}, Region, Ty, TyCtxt, TyKind, TypeFoldable};
+use crate::ty::{self, subst::{Subst, SubstsRef}, Region, Ty, TyCtxt, TypeFoldable};
 use errors::{Applicability, DiagnosticBuilder, DiagnosticStyledString};
 use std::{cmp, fmt};
 use syntax_pos::{Pos, Span};
@@ -1094,14 +1094,14 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                 (_, false, _) => {
                     if let Some(exp_found) = exp_found {
                         let (def_id, ret_ty) = match exp_found.found.sty {
-                            TyKind::FnDef(def, _) => {
+                            ty::FnDef(def, _) => {
                                 (Some(def), Some(self.tcx.fn_sig(def).output()))
                             }
                             _ => (None, None),
                         };
 
                         let exp_is_struct = match exp_found.expected.sty {
-                            TyKind::Adt(def, _) => def.is_struct(),
+                            ty::Adt(def, _) => def.is_struct(),
                             _ => false,
                         };
 
@@ -1140,8 +1140,8 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         diag: &mut DiagnosticBuilder<'tcx>,
     ) {
         match (&exp_found.expected.sty, &exp_found.found.sty) {
-            (TyKind::Adt(exp_def, exp_substs), TyKind::Ref(_, found_ty, _)) => {
-                if let TyKind::Adt(found_def, found_substs) = found_ty.sty {
+            (ty::Adt(exp_def, exp_substs), ty::Ref(_, found_ty, _)) => {
+                if let ty::Adt(found_def, found_substs) = found_ty.sty {
                     let path_str = format!("{:?}", exp_def);
                     if exp_def == &found_def {
                         let opt_msg = "you can convert from `&Option<T>` to `Option<&T>` using \
@@ -1164,17 +1164,17 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
                             let mut show_suggestion = true;
                             for (exp_ty, found_ty) in exp_substs.types().zip(found_substs.types()) {
                                 match exp_ty.sty {
-                                    TyKind::Ref(_, exp_ty, _) => {
+                                    ty::Ref(_, exp_ty, _) => {
                                         match (&exp_ty.sty, &found_ty.sty) {
-                                            (_, TyKind::Param(_)) |
-                                            (_, TyKind::Infer(_)) |
-                                            (TyKind::Param(_), _) |
-                                            (TyKind::Infer(_), _) => {}
+                                            (_, ty::Param(_)) |
+                                            (_, ty::Infer(_)) |
+                                            (ty::Param(_), _) |
+                                            (ty::Infer(_), _) => {}
                                             _ if ty::TyS::same_type(exp_ty, found_ty) => {}
                                             _ => show_suggestion = false,
                                         };
                                     }
-                                    TyKind::Param(_) | TyKind::Infer(_) => {}
+                                    ty::Param(_) | ty::Infer(_) => {}
                                     _ => show_suggestion = false,
                                 }
                             }
diff --git a/src/librustc/lib.rs b/src/librustc/lib.rs
index b87343b43c9..0b75cb6c8a3 100644
--- a/src/librustc/lib.rs
+++ b/src/librustc/lib.rs
@@ -29,6 +29,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/")]
 
 #![deny(rust_2018_idioms)]
+#![cfg_attr(not(stage0), deny(internal))]
 #![allow(explicit_outlives_requirements)]
 
 #![feature(arbitrary_self_types)]
diff --git a/src/librustc/mir/tcx.rs b/src/librustc/mir/tcx.rs
index 0eb37f0ac9e..23be1bbf6c6 100644
--- a/src/librustc/mir/tcx.rs
+++ b/src/librustc/mir/tcx.rs
@@ -36,7 +36,7 @@ impl<'a, 'gcx, 'tcx> PlaceTy<'tcx> {
     pub fn field_ty(self, tcx: TyCtxt<'a, 'gcx, 'tcx>, f: &Field) -> Ty<'tcx>
     {
         let answer = match self.ty.sty {
-            ty::TyKind::Adt(adt_def, substs) => {
+            ty::Adt(adt_def, substs) => {
                 let variant_def = match self.variant_index {
                     None => adt_def.non_enum_variant(),
                     Some(variant_index) => {
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 102057c1380..7d47867cea1 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -1,3 +1,5 @@
+#![cfg_attr(not(stage0), allow(usage_of_ty_tykind))]
+
 pub use self::Variance::*;
 pub use self::AssociatedItemContainer::*;
 pub use self::BorrowKind::*;
diff --git a/src/librustc/util/common.rs b/src/librustc/util/common.rs
index 5622fe43436..26194176350 100644
--- a/src/librustc/util/common.rs
+++ b/src/librustc/util/common.rs
@@ -1,11 +1,10 @@
 #![allow(non_camel_case_types)]
 
-use rustc_data_structures::sync::Lock;
+use rustc_data_structures::{fx::FxHashMap, sync::Lock};
 
 use std::cell::{RefCell, Cell};
-use std::collections::HashMap;
 use std::fmt::Debug;
-use std::hash::{Hash, BuildHasher};
+use std::hash::Hash;
 use std::panic;
 use std::env;
 use std::time::{Duration, Instant};
@@ -341,8 +340,8 @@ pub trait MemoizationMap {
         where OP: FnOnce() -> Self::Value;
 }
 
-impl<K, V, S> MemoizationMap for RefCell<HashMap<K,V,S>>
-    where K: Hash+Eq+Clone, V: Clone, S: BuildHasher
+impl<K, V> MemoizationMap for RefCell<FxHashMap<K,V>>
+    where K: Hash+Eq+Clone, V: Clone
 {
     type Key = K;
     type Value = V;