diff --git a/src/librustc_mir/borrow_check/mod.rs b/src/librustc_mir/borrow_check/mod.rs
index d3ab7df817b..a3ee49651ba 100644
--- a/src/librustc_mir/borrow_check/mod.rs
+++ b/src/librustc_mir/borrow_check/mod.rs
@@ -209,7 +209,7 @@ fn do_mir_borrowck<'a, 'tcx>(
         nll_errors,
     } = nll::compute_regions(
         infcx,
-        def_id.to_def_id(),
+        def_id,
         free_regions,
         body,
         &promoted,
diff --git a/src/librustc_mir/borrow_check/nll.rs b/src/librustc_mir/borrow_check/nll.rs
index 29636a06709..b820b79c47f 100644
--- a/src/librustc_mir/borrow_check/nll.rs
+++ b/src/librustc_mir/borrow_check/nll.rs
@@ -2,7 +2,7 @@
 
 use rustc_data_structures::fx::FxHashMap;
 use rustc_errors::Diagnostic;
-use rustc_hir::def_id::DefId;
+use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_index::vec::IndexVec;
 use rustc_infer::infer::InferCtxt;
 use rustc_middle::mir::{
@@ -157,7 +157,7 @@ fn populate_polonius_move_facts(
 /// This may result in errors being reported.
 pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     infcx: &InferCtxt<'cx, 'tcx>,
-    def_id: DefId,
+    def_id: LocalDefId,
     universal_regions: UniversalRegions<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexVec<Promoted, Body<'tcx>>,
@@ -272,7 +272,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
     // Dump facts if requested.
     let polonius_output = all_facts.and_then(|all_facts| {
         if infcx.tcx.sess.opts.debugging_opts.nll_facts {
-            let def_path = infcx.tcx.def_path(def_id);
+            let def_path = infcx.tcx.def_path(def_id.to_def_id());
             let dir_path =
                 PathBuf::from("nll-facts").join(def_path.to_filename_friendly_no_crate());
             all_facts.write_to_dir(dir_path, location_table).unwrap();
@@ -292,7 +292,7 @@ pub(in crate::borrow_check) fn compute_regions<'cx, 'tcx>(
 
     // Solve the region constraints.
     let (closure_region_requirements, nll_errors) =
-        regioncx.solve(infcx, &body, def_id, polonius_output.clone());
+        regioncx.solve(infcx, &body, def_id.to_def_id(), polonius_output.clone());
 
     if !nll_errors.is_empty() {
         // Suppress unhelpful extra errors in `infer_opaque_types`.
diff --git a/src/librustc_mir/borrow_check/type_check/input_output.rs b/src/librustc_mir/borrow_check/type_check/input_output.rs
index 894a997ea7a..edd2dc3c2de 100644
--- a/src/librustc_mir/borrow_check/type_check/input_output.rs
+++ b/src/librustc_mir/borrow_check/type_check/input_output.rs
@@ -33,35 +33,37 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         //
         // e.g., `|x: FxHashMap<_, &'static u32>| ...`
         let user_provided_sig;
-        if !self.tcx().is_closure(self.mir_def_id) {
+        if !self.tcx().is_closure(self.mir_def_id.to_def_id()) {
             user_provided_sig = None;
         } else {
-            let typeck_tables = self.tcx().typeck_tables_of(self.mir_def_id.expect_local());
-            user_provided_sig = match typeck_tables.user_provided_sigs.get(&self.mir_def_id) {
-                None => None,
-                Some(user_provided_poly_sig) => {
-                    // Instantiate the canonicalized variables from
-                    // user-provided signature (e.g., the `_` in the code
-                    // above) with fresh variables.
-                    let (poly_sig, _) = self.infcx.instantiate_canonical_with_fresh_inference_vars(
-                        body.span,
-                        &user_provided_poly_sig,
-                    );
-
-                    // Replace the bound items in the fn sig with fresh
-                    // variables, so that they represent the view from
-                    // "inside" the closure.
-                    Some(
-                        self.infcx
-                            .replace_bound_vars_with_fresh_vars(
+            let typeck_tables = self.tcx().typeck_tables_of(self.mir_def_id);
+            user_provided_sig =
+                match typeck_tables.user_provided_sigs.get(&self.mir_def_id.to_def_id()) {
+                    None => None,
+                    Some(user_provided_poly_sig) => {
+                        // Instantiate the canonicalized variables from
+                        // user-provided signature (e.g., the `_` in the code
+                        // above) with fresh variables.
+                        let (poly_sig, _) =
+                            self.infcx.instantiate_canonical_with_fresh_inference_vars(
                                 body.span,
-                                LateBoundRegionConversionTime::FnCall,
-                                &poly_sig,
-                            )
-                            .0,
-                    )
+                                &user_provided_poly_sig,
+                            );
+
+                        // Replace the bound items in the fn sig with fresh
+                        // variables, so that they represent the view from
+                        // "inside" the closure.
+                        Some(
+                            self.infcx
+                                .replace_bound_vars_with_fresh_vars(
+                                    body.span,
+                                    LateBoundRegionConversionTime::FnCall,
+                                    &poly_sig,
+                                )
+                                .0,
+                        )
+                    }
                 }
-            }
         };
 
         debug!(
@@ -120,7 +122,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
         if let Err(terr) = self.eq_opaque_type_and_type(
             mir_output_ty,
             normalized_output_ty,
-            self.mir_def_id,
+            self.mir_def_id.to_def_id(),
             Locations::All(output_span),
             ConstraintCategory::BoringNoLocation,
         ) {
@@ -143,7 +145,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             if let Err(err) = self.eq_opaque_type_and_type(
                 mir_output_ty,
                 user_provided_output_ty,
-                self.mir_def_id,
+                self.mir_def_id.to_def_id(),
                 Locations::All(output_span),
                 ConstraintCategory::BoringNoLocation,
             ) {
diff --git a/src/librustc_mir/borrow_check/type_check/mod.rs b/src/librustc_mir/borrow_check/type_check/mod.rs
index ee8a4358147..9282a0a06b4 100644
--- a/src/librustc_mir/borrow_check/type_check/mod.rs
+++ b/src/librustc_mir/borrow_check/type_check/mod.rs
@@ -108,26 +108,22 @@ mod relate_tys;
 ///
 /// - `infcx` -- inference context to use
 /// - `param_env` -- parameter environment to use for trait solving
-/// - `mir` -- MIR to type-check
-/// - `mir_def_id` -- DefId from which the MIR is derived (must be local)
-/// - `region_bound_pairs` -- the implied outlives obligations between type parameters
-///   and lifetimes (e.g., `&'a T` implies `T: 'a`)
-/// - `implicit_region_bound` -- a region which all generic parameters are assumed
-///   to outlive; should represent the fn body
-/// - `input_tys` -- fully liberated, but **not** normalized, expected types of the arguments;
-///   the types of the input parameters found in the MIR itself will be equated with these
-/// - `output_ty` -- fully liberated, but **not** normalized, expected return type;
-///   the type for the RETURN_PLACE will be equated with this
-/// - `liveness` -- results of a liveness computation on the MIR; used to create liveness
-///   constraints for the regions in the types of variables
+/// - `body` -- MIR body to type-check
+/// - `promoted` -- map of promoted constants within `body`
+/// - `mir_def_id` -- `LocalDefId` from which the MIR is derived
+/// - `universal_regions` -- the universal regions from `body`s function signature
+/// - `location_table` -- MIR location map of `body`
+/// - `borrow_set` -- information about borrows occurring in `body`
+/// - `all_facts` -- when using Polonius, this is the generated set of Polonius facts
 /// - `flow_inits` -- results of a maybe-init dataflow analysis
 /// - `move_data` -- move-data constructed when performing the maybe-init dataflow analysis
+/// - `elements` -- MIR region map
 pub(crate) fn type_check<'mir, 'tcx>(
     infcx: &InferCtxt<'_, 'tcx>,
     param_env: ty::ParamEnv<'tcx>,
     body: &Body<'tcx>,
     promoted: &IndexVec<Promoted, Body<'tcx>>,
-    mir_def_id: DefId,
+    mir_def_id: LocalDefId,
     universal_regions: &Rc<UniversalRegions<'tcx>>,
     location_table: &LocationTable,
     borrow_set: &BorrowSet<'tcx>,
@@ -191,7 +187,7 @@ pub(crate) fn type_check<'mir, 'tcx>(
 
 fn type_check_internal<'a, 'tcx, R>(
     infcx: &'a InferCtxt<'a, 'tcx>,
-    mir_def_id: DefId,
+    mir_def_id: LocalDefId,
     param_env: ty::ParamEnv<'tcx>,
     body: &'a Body<'tcx>,
     promoted: &'a IndexVec<Promoted, Body<'tcx>>,
@@ -271,7 +267,7 @@ struct TypeVerifier<'a, 'b, 'tcx> {
     body: &'b Body<'tcx>,
     promoted: &'b IndexVec<Promoted, Body<'tcx>>,
     last_span: Span,
-    mir_def_id: DefId,
+    mir_def_id: LocalDefId,
     errors_reported: bool,
 }
 
@@ -815,7 +811,7 @@ struct TypeChecker<'a, 'tcx> {
     /// User type annotations are shared between the main MIR and the MIR of
     /// all of the promoted items.
     user_type_annotations: &'a CanonicalUserTypeAnnotations<'tcx>,
-    mir_def_id: DefId,
+    mir_def_id: LocalDefId,
     region_bound_pairs: &'a RegionBoundPairs<'tcx>,
     implicit_region_bound: ty::Region<'tcx>,
     reported_errors: FxHashSet<(Ty<'tcx>, Span)>,
@@ -963,7 +959,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
     fn new(
         infcx: &'a InferCtxt<'a, 'tcx>,
         body: &'a Body<'tcx>,
-        mir_def_id: DefId,
+        mir_def_id: LocalDefId,
         param_env: ty::ParamEnv<'tcx>,
         region_bound_pairs: &'a RegionBoundPairs<'tcx>,
         implicit_region_bound: ty::Region<'tcx>,
@@ -1142,7 +1138,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                 // When you have `let x: impl Foo = ...` in a closure,
                 // the resulting inferend values are stored with the
                 // def-id of the base function.
-                let parent_def_id = self.tcx().closure_base_def_id(self.mir_def_id);
+                let parent_def_id = self.tcx().closure_base_def_id(self.mir_def_id.to_def_id());
                 return self.eq_opaque_type_and_type(sub, sup, parent_def_id, locations, category);
             } else {
                 return Err(terr);
@@ -1994,7 +1990,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                         if !self.infcx.type_is_copy_modulo_regions(self.param_env, ty, span) {
                             let ccx = ConstCx::new_with_param_env(
                                 tcx,
-                                self.mir_def_id.expect_local(),
+                                self.mir_def_id,
                                 body,
                                 self.param_env,
                             );
@@ -2010,9 +2006,7 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
                                 &traits::Obligation::new(
                                     ObligationCause::new(
                                         span,
-                                        self.tcx()
-                                            .hir()
-                                            .local_def_id_to_hir_id(self.mir_def_id.expect_local()),
+                                        self.tcx().hir().local_def_id_to_hir_id(self.mir_def_id),
                                         traits::ObligationCauseCode::RepeatVec(should_suggest),
                                     ),
                                     self.param_env,