diff --git a/compiler/rustc_index/src/vec.rs b/compiler/rustc_index/src/vec.rs
index 88298150a79dc..b866c8b8433d9 100644
--- a/compiler/rustc_index/src/vec.rs
+++ b/compiler/rustc_index/src/vec.rs
@@ -208,6 +208,11 @@ impl<I: Idx, T> IndexVec<I, Option<T>> {
     pub fn remove(&mut self, index: I) -> Option<T> {
         self.get_mut(index)?.take()
     }
+
+    #[inline]
+    pub fn contains(&self, index: I) -> bool {
+        self.get(index).and_then(Option::as_ref).is_some()
+    }
 }
 
 impl<I: Idx, T: fmt::Debug> fmt::Debug for IndexVec<I, T> {
diff --git a/compiler/rustc_mir_transform/src/coroutine.rs b/compiler/rustc_mir_transform/src/coroutine.rs
index 05674792426f1..41c9c55cef595 100644
--- a/compiler/rustc_mir_transform/src/coroutine.rs
+++ b/compiler/rustc_mir_transform/src/coroutine.rs
@@ -58,7 +58,7 @@ use crate::deref_separator::deref_finder;
 use crate::errors;
 use crate::pass_manager as pm;
 use crate::simplify;
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::pluralize;
 use rustc_hir as hir;
 use rustc_hir::lang_items::LangItem;
@@ -236,8 +236,7 @@ struct TransformVisitor<'tcx> {
     discr_ty: Ty<'tcx>,
 
     // Mapping from Local to (type of local, coroutine struct index)
-    // FIXME(eddyb) This should use `IndexVec<Local, Option<_>>`.
-    remap: FxHashMap<Local, (Ty<'tcx>, VariantIdx, FieldIdx)>,
+    remap: IndexVec<Local, Option<(Ty<'tcx>, VariantIdx, FieldIdx)>>,
 
     // A map from a suspension point in a block to the locals which have live storage at that point
     storage_liveness: IndexVec<BasicBlock, Option<BitSet<Local>>>,
@@ -485,7 +484,7 @@ impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
     }
 
     fn visit_local(&mut self, local: &mut Local, _: PlaceContext, _: Location) {
-        assert_eq!(self.remap.get(local), None);
+        assert!(!self.remap.contains(*local));
     }
 
     fn visit_place(
@@ -495,7 +494,7 @@ impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
         _location: Location,
     ) {
         // Replace an Local in the remap with a coroutine struct access
-        if let Some(&(ty, variant_index, idx)) = self.remap.get(&place.local) {
+        if let Some(&Some((ty, variant_index, idx))) = self.remap.get(place.local) {
             replace_base(place, self.make_field(variant_index, idx, ty), self.tcx);
         }
     }
@@ -504,7 +503,7 @@ impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
         // Remove StorageLive and StorageDead statements for remapped locals
         data.retain_statements(|s| match s.kind {
             StatementKind::StorageLive(l) | StatementKind::StorageDead(l) => {
-                !self.remap.contains_key(&l)
+                !self.remap.contains(l)
             }
             _ => true,
         });
@@ -529,13 +528,9 @@ impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
 
                 // The resume arg target location might itself be remapped if its base local is
                 // live across a yield.
-                let resume_arg =
-                    if let Some(&(ty, variant, idx)) = self.remap.get(&resume_arg.local) {
-                        replace_base(&mut resume_arg, self.make_field(variant, idx, ty), self.tcx);
-                        resume_arg
-                    } else {
-                        resume_arg
-                    };
+                if let Some(&Some((ty, variant, idx))) = self.remap.get(resume_arg.local) {
+                    replace_base(&mut resume_arg, self.make_field(variant, idx, ty), self.tcx);
+                }
 
                 let storage_liveness: GrowableBitSet<Local> =
                     self.storage_liveness[block].clone().unwrap().into();
@@ -543,7 +538,7 @@ impl<'tcx> MutVisitor<'tcx> for TransformVisitor<'tcx> {
                 for i in 0..self.always_live_locals.domain_size() {
                     let l = Local::new(i);
                     let needs_storage_dead = storage_liveness.contains(l)
-                        && !self.remap.contains_key(&l)
+                        && !self.remap.contains(l)
                         && !self.always_live_locals.contains(l);
                     if needs_storage_dead {
                         data.statements
@@ -1037,7 +1032,7 @@ fn compute_layout<'tcx>(
     liveness: LivenessInfo,
     body: &Body<'tcx>,
 ) -> (
-    FxHashMap<Local, (Ty<'tcx>, VariantIdx, FieldIdx)>,
+    IndexVec<Local, Option<(Ty<'tcx>, VariantIdx, FieldIdx)>>,
     CoroutineLayout<'tcx>,
     IndexVec<BasicBlock, Option<BitSet<Local>>>,
 ) {
@@ -1098,7 +1093,7 @@ fn compute_layout<'tcx>(
     // Create a map from local indices to coroutine struct indices.
     let mut variant_fields: IndexVec<VariantIdx, IndexVec<FieldIdx, CoroutineSavedLocal>> =
         iter::repeat(IndexVec::new()).take(RESERVED_VARIANTS).collect();
-    let mut remap = FxHashMap::default();
+    let mut remap = IndexVec::from_elem_n(None, saved_locals.domain_size());
     for (suspension_point_idx, live_locals) in live_locals_at_suspension_points.iter().enumerate() {
         let variant_index = VariantIdx::from(RESERVED_VARIANTS + suspension_point_idx);
         let mut fields = IndexVec::new();
@@ -1109,7 +1104,7 @@ fn compute_layout<'tcx>(
             // around inside coroutines, so it doesn't matter which variant
             // index we access them by.
             let idx = FieldIdx::from_usize(idx);
-            remap.entry(locals[saved_local]).or_insert((tys[saved_local].ty, variant_index, idx));
+            remap[locals[saved_local]] = Some((tys[saved_local].ty, variant_index, idx));
         }
         variant_fields.push(fields);
         variant_source_info.push(source_info_at_suspension_points[suspension_point_idx]);
@@ -1121,7 +1116,9 @@ fn compute_layout<'tcx>(
     for var in &body.var_debug_info {
         let VarDebugInfoContents::Place(place) = &var.value else { continue };
         let Some(local) = place.as_local() else { continue };
-        let Some(&(_, variant, field)) = remap.get(&local) else { continue };
+        let Some(&Some((_, variant, field))) = remap.get(local) else {
+            continue;
+        };
 
         let saved_local = variant_fields[variant][field];
         field_names.get_or_insert_with(saved_local, || var.name);
@@ -1524,7 +1521,7 @@ fn create_cases<'tcx>(
                 for i in 0..(body.local_decls.len()) {
                     let l = Local::new(i);
                     let needs_storage_live = point.storage_liveness.contains(l)
-                        && !transform.remap.contains_key(&l)
+                        && !transform.remap.contains(l)
                         && !transform.always_live_locals.contains(l);
                     if needs_storage_live {
                         statements