diff --git a/src/librustc_hir/hir.rs b/src/librustc_hir/hir.rs
index bed2044c70855..e1fe80ec08d8d 100644
--- a/src/librustc_hir/hir.rs
+++ b/src/librustc_hir/hir.rs
@@ -12,6 +12,7 @@ use rustc_ast::node_id::NodeMap;
 use rustc_ast::util::parser::ExprPrecedence;
 use rustc_data_structures::sync::{par_for_each_in, Send, Sync};
 use rustc_macros::HashStable_Generic;
+use rustc_span::def_id::LocalDefId;
 use rustc_span::source_map::{SourceMap, Spanned};
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::{MultiSpan, Span, DUMMY_SP};
@@ -2651,25 +2652,11 @@ pub type CaptureModeMap = NodeMap<CaptureBy>;
 // has length > 0 if the trait is found through an chain of imports, starting with the
 // import/use statement in the scope where the trait is used.
 #[derive(Clone, Debug)]
-pub struct TraitCandidate<ID = HirId> {
+pub struct TraitCandidate {
     pub def_id: DefId,
-    pub import_ids: SmallVec<[ID; 1]>,
+    pub import_ids: SmallVec<[LocalDefId; 1]>,
 }
 
-impl<ID> TraitCandidate<ID> {
-    pub fn map_import_ids<F, T>(self, f: F) -> TraitCandidate<T>
-    where
-        F: Fn(ID) -> T,
-    {
-        let TraitCandidate { def_id, import_ids } = self;
-        let import_ids = import_ids.into_iter().map(f).collect();
-        TraitCandidate { def_id, import_ids }
-    }
-}
-
-// Trait method resolution
-pub type TraitMap<ID = HirId> = NodeMap<Vec<TraitCandidate<ID>>>;
-
 #[derive(Copy, Clone, Debug, HashStable_Generic)]
 pub enum Node<'hir> {
     Param(&'hir Param<'hir>),
diff --git a/src/librustc_middle/arena.rs b/src/librustc_middle/arena.rs
index 454e7adf99f0c..4f1889aeb162a 100644
--- a/src/librustc_middle/arena.rs
+++ b/src/librustc_middle/arena.rs
@@ -115,6 +115,7 @@ macro_rules! arena_types {
 
             // This is used to decode the &'tcx [Span] for InlineAsm's line_spans.
             [decode] span: rustc_span::Span, rustc_span::Span;
+            [decode] used_trait_imports: rustc_data_structures::fx::FxHashSet<rustc_hir::def_id::LocalDefId>, rustc_data_structures::fx::FxHashSet<rustc_hir::def_id::LocalDefId>;
         ], $tcx);
     )
 }
diff --git a/src/librustc_middle/ich/impls_hir.rs b/src/librustc_middle/ich/impls_hir.rs
index f668cc99754f4..78b9167ddd967 100644
--- a/src/librustc_middle/ich/impls_hir.rs
+++ b/src/librustc_middle/ich/impls_hir.rs
@@ -210,16 +210,15 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::TraitCandidate {
 }
 
 impl<'a> ToStableHashKey<StableHashingContext<'a>> for hir::TraitCandidate {
-    type KeyType = (DefPathHash, SmallVec<[(DefPathHash, hir::ItemLocalId); 1]>);
+    type KeyType = (DefPathHash, SmallVec<[DefPathHash; 1]>);
 
     fn to_stable_hash_key(&self, hcx: &StableHashingContext<'a>) -> Self::KeyType {
         let hir::TraitCandidate { def_id, import_ids } = self;
 
-        let import_keys = import_ids
-            .iter()
-            .map(|hir_id| (hcx.local_def_path_hash(hir_id.owner), hir_id.local_id))
-            .collect();
-        (hcx.def_path_hash(*def_id), import_keys)
+        (
+            hcx.def_path_hash(*def_id),
+            import_ids.iter().map(|def_id| hcx.local_def_path_hash(*def_id)).collect(),
+        )
     }
 }
 
diff --git a/src/librustc_middle/query/mod.rs b/src/librustc_middle/query/mod.rs
index 3b6d54a1bc1ee..b3751beede25a 100644
--- a/src/librustc_middle/query/mod.rs
+++ b/src/librustc_middle/query/mod.rs
@@ -526,7 +526,7 @@ rustc_queries! {
     }
 
     Other {
-        query used_trait_imports(key: LocalDefId) -> &'tcx DefIdSet {
+        query used_trait_imports(key: LocalDefId) -> &'tcx FxHashSet<LocalDefId> {
             desc { |tcx| "used_trait_imports `{}`", tcx.def_path_str(key.to_def_id()) }
             cache_on_disk_if { true }
         }
diff --git a/src/librustc_middle/ty/context.rs b/src/librustc_middle/ty/context.rs
index a12e510d30e72..4f8803f3e7f91 100644
--- a/src/librustc_middle/ty/context.rs
+++ b/src/librustc_middle/ty/context.rs
@@ -36,7 +36,7 @@ use rustc_data_structures::sync::{self, Lock, Lrc, WorkerLocal};
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::definitions::{DefPathHash, Definitions};
 use rustc_hir::lang_items::{self, PanicLocationLangItem};
 use rustc_hir::{HirId, ItemKind, ItemLocalId, ItemLocalMap, ItemLocalSet, Node, TraitCandidate};
@@ -408,7 +408,7 @@ pub struct TypeckTables<'tcx> {
     /// This is used for warning unused imports. During type
     /// checking, this `Lrc` should not be cloned: it must have a ref-count
     /// of 1 so that we can insert things into the set mutably.
-    pub used_trait_imports: Lrc<DefIdSet>,
+    pub used_trait_imports: Lrc<FxHashSet<LocalDefId>>,
 
     /// If any errors occurred while type-checking this body,
     /// this field will be set to `Some(ErrorReported)`.
diff --git a/src/librustc_middle/ty/mod.rs b/src/librustc_middle/ty/mod.rs
index db34018dedbd4..7c7f7d5c1c7e4 100644
--- a/src/librustc_middle/ty/mod.rs
+++ b/src/librustc_middle/ty/mod.rs
@@ -121,7 +121,7 @@ pub struct ResolverOutputs {
     pub definitions: rustc_hir::definitions::Definitions,
     pub cstore: Box<CrateStoreDyn>,
     pub extern_crate_map: FxHashMap<LocalDefId, CrateNum>,
-    pub trait_map: FxHashMap<hir::HirId, Vec<hir::TraitCandidate<hir::HirId>>>,
+    pub trait_map: FxHashMap<hir::HirId, Vec<hir::TraitCandidate>>,
     pub maybe_unused_trait_imports: FxHashSet<LocalDefId>,
     pub maybe_unused_extern_crates: Vec<(LocalDefId, Span)>,
     pub export_map: ExportMap<LocalDefId>,
diff --git a/src/librustc_resolve/late.rs b/src/librustc_resolve/late.rs
index 7166fef2d1395..61f20df8cc6c0 100644
--- a/src/librustc_resolve/late.rs
+++ b/src/librustc_resolve/late.rs
@@ -24,6 +24,7 @@ use rustc_hir::def_id::{DefId, CRATE_DEF_INDEX};
 use rustc_hir::TraitCandidate;
 use rustc_middle::{bug, span_bug};
 use rustc_session::lint;
+use rustc_span::def_id::LocalDefId;
 use rustc_span::symbol::{kw, sym, Ident, Symbol};
 use rustc_span::Span;
 use smallvec::{smallvec, SmallVec};
@@ -2188,7 +2189,7 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         &mut self,
         mut ident: Ident,
         ns: Namespace,
-    ) -> Vec<TraitCandidate<NodeId>> {
+    ) -> Vec<TraitCandidate> {
         debug!("(getting traits containing item) looking for '{}'", ident.name);
 
         let mut found_traits = Vec::new();
@@ -2233,7 +2234,7 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         ident: Ident,
         ns: Namespace,
         module: Module<'a>,
-        found_traits: &mut Vec<TraitCandidate<NodeId>>,
+        found_traits: &mut Vec<TraitCandidate>,
     ) {
         assert!(ns == TypeNS || ns == ValueNS);
         let mut traits = module.traits.borrow_mut();
@@ -2292,13 +2293,13 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         &mut self,
         mut kind: &NameBindingKind<'_>,
         trait_name: Ident,
-    ) -> SmallVec<[NodeId; 1]> {
+    ) -> SmallVec<[LocalDefId; 1]> {
         let mut import_ids = smallvec![];
         while let NameBindingKind::Import { import, binding, .. } = kind {
             let id = self.r.definitions.local_def_id(import.id);
             self.r.maybe_unused_trait_imports.insert(id);
             self.r.add_to_glob_map(&import, trait_name);
-            import_ids.push(import.id);
+            import_ids.push(id);
             kind = &binding.kind;
         }
         import_ids
diff --git a/src/librustc_resolve/lib.rs b/src/librustc_resolve/lib.rs
index cca9eabe7bcf8..66e5612b627b4 100644
--- a/src/librustc_resolve/lib.rs
+++ b/src/librustc_resolve/lib.rs
@@ -38,7 +38,7 @@ use rustc_hir::def::{self, CtorOf, DefKind, NonMacroAttrKind, PartialRes};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, CRATE_DEF_INDEX};
 use rustc_hir::definitions::{DefKey, Definitions};
 use rustc_hir::PrimTy::{self, Bool, Char, Float, Int, Str, Uint};
-use rustc_hir::TraitMap;
+use rustc_hir::TraitCandidate;
 use rustc_metadata::creader::{CStore, CrateLoader};
 use rustc_middle::hir::exports::ExportMap;
 use rustc_middle::middle::cstore::{CrateStore, MetadataLoaderDyn};
@@ -881,7 +881,7 @@ pub struct Resolver<'a> {
     /// `CrateNum` resolutions of `extern crate` items.
     extern_crate_map: FxHashMap<LocalDefId, CrateNum>,
     export_map: ExportMap<LocalDefId>,
-    trait_map: TraitMap<NodeId>,
+    trait_map: NodeMap<Vec<TraitCandidate>>,
 
     /// A map from nodes to anonymous modules.
     /// Anonymous modules are pseudo-modules that are implicitly created around items
@@ -1287,14 +1287,7 @@ impl<'a> Resolver<'a> {
         let trait_map = self
             .trait_map
             .into_iter()
-            .map(|(k, v)| {
-                (
-                    definitions.node_id_to_hir_id(k),
-                    v.into_iter()
-                        .map(|tc| tc.map_import_ids(|id| definitions.node_id_to_hir_id(id)))
-                        .collect(),
-                )
-            })
+            .map(|(k, v)| (definitions.node_id_to_hir_id(k), v))
             .collect();
         let maybe_unused_trait_imports = self.maybe_unused_trait_imports;
         let maybe_unused_extern_crates = self.maybe_unused_extern_crates;
@@ -1325,17 +1318,7 @@ impl<'a> Resolver<'a> {
             trait_map: self
                 .trait_map
                 .iter()
-                .map(|(&k, v)| {
-                    (
-                        self.definitions.node_id_to_hir_id(k),
-                        v.iter()
-                            .cloned()
-                            .map(|tc| {
-                                tc.map_import_ids(|id| self.definitions.node_id_to_hir_id(id))
-                            })
-                            .collect(),
-                    )
-                })
+                .map(|(&k, v)| (self.definitions.node_id_to_hir_id(k), v.clone()))
                 .collect(),
             glob_map: self.glob_map.clone(),
             maybe_unused_trait_imports: self.maybe_unused_trait_imports.clone(),
diff --git a/src/librustc_typeck/check/method/mod.rs b/src/librustc_typeck/check/method/mod.rs
index ac3fa15417e9c..259c4a8664f1b 100644
--- a/src/librustc_typeck/check/method/mod.rs
+++ b/src/librustc_typeck/check/method/mod.rs
@@ -194,11 +194,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             self.lookup_probe(span, segment.ident, self_ty, call_expr, ProbeScope::TraitsInScope)?;
 
         for import_id in &pick.import_ids {
-            let import_def_id = self.tcx.hir().local_def_id(*import_id);
-            debug!("used_trait_import: {:?}", import_def_id);
+            debug!("used_trait_import: {:?}", import_id);
             Lrc::get_mut(&mut self.tables.borrow_mut().used_trait_imports)
                 .unwrap()
-                .insert(import_def_id.to_def_id());
+                .insert(*import_id);
         }
 
         self.tcx.check_stability(pick.item.def_id, Some(call_expr.hir_id), span);
@@ -461,9 +460,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let mut tables = self.tables.borrow_mut();
             let used_trait_imports = Lrc::get_mut(&mut tables.used_trait_imports).unwrap();
             for import_id in pick.import_ids {
-                let import_def_id = tcx.hir().local_def_id(import_id);
-                debug!("resolve_ufcs: used_trait_import: {:?}", import_def_id);
-                used_trait_imports.insert(import_def_id.to_def_id());
+                debug!("resolve_ufcs: used_trait_import: {:?}", import_id);
+                used_trait_imports.insert(import_id);
             }
         }
 
diff --git a/src/librustc_typeck/check/method/probe.rs b/src/librustc_typeck/check/method/probe.rs
index 93bcd5cf29149..eb8f76687174e 100644
--- a/src/librustc_typeck/check/method/probe.rs
+++ b/src/librustc_typeck/check/method/probe.rs
@@ -28,6 +28,7 @@ use rustc_middle::ty::{
 };
 use rustc_session::config::nightly_options;
 use rustc_session::lint;
+use rustc_span::def_id::LocalDefId;
 use rustc_span::{symbol::Ident, Span, Symbol, DUMMY_SP};
 use rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_trait_selection::traits::query::method_autoderef::MethodAutoderefBadTy;
@@ -129,7 +130,7 @@ struct Candidate<'tcx> {
     xform_ret_ty: Option<Ty<'tcx>>,
     item: ty::AssocItem,
     kind: CandidateKind<'tcx>,
-    import_ids: SmallVec<[hir::HirId; 1]>,
+    import_ids: SmallVec<[LocalDefId; 1]>,
 }
 
 #[derive(Debug)]
@@ -158,7 +159,7 @@ enum ProbeResult {
 pub struct Pick<'tcx> {
     pub item: ty::AssocItem,
     pub kind: PickKind<'tcx>,
-    pub import_ids: SmallVec<[hir::HirId; 1]>,
+    pub import_ids: SmallVec<[LocalDefId; 1]>,
 
     // Indicates that the source expression should be autoderef'd N times
     //
@@ -930,7 +931,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
 
     fn assemble_extension_candidates_for_trait(
         &mut self,
-        import_ids: &SmallVec<[hir::HirId; 1]>,
+        import_ids: &SmallVec<[LocalDefId; 1]>,
         trait_def_id: DefId,
     ) -> Result<(), MethodError<'tcx>> {
         debug!("assemble_extension_candidates_for_trait(trait_def_id={:?})", trait_def_id);
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index b60b06567d6fa..3281c216a1573 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -96,7 +96,7 @@ use rustc_errors::ErrorReported;
 use rustc_errors::{pluralize, struct_span_err, Applicability, DiagnosticBuilder, DiagnosticId};
 use rustc_hir as hir;
 use rustc_hir::def::{CtorOf, DefKind, Res};
-use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, DefIdSet, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LOCAL_CRATE};
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::lang_items::{
@@ -840,7 +840,7 @@ fn has_typeck_tables(tcx: TyCtxt<'_>, def_id: DefId) -> bool {
     }
 }
 
-fn used_trait_imports(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &DefIdSet {
+fn used_trait_imports(tcx: TyCtxt<'_>, def_id: LocalDefId) -> &FxHashSet<LocalDefId> {
     &*tcx.typeck_tables_of(def_id).used_trait_imports
 }
 
diff --git a/src/librustc_typeck/check/writeback.rs b/src/librustc_typeck/check/writeback.rs
index ba806430f17fd..4704d8fc7666f 100644
--- a/src/librustc_typeck/check/writeback.rs
+++ b/src/librustc_typeck/check/writeback.rs
@@ -4,10 +4,8 @@
 
 use crate::check::FnCtxt;
 
-use rustc_data_structures::sync::Lrc;
 use rustc_errors::ErrorReported;
 use rustc_hir as hir;
-use rustc_hir::def_id::DefIdSet;
 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
 use rustc_infer::infer::InferCtxt;
@@ -67,10 +65,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         wbcx.visit_user_provided_sigs();
         wbcx.visit_generator_interior_types();
 
-        let used_trait_imports = mem::replace(
-            &mut self.tables.borrow_mut().used_trait_imports,
-            Lrc::new(DefIdSet::default()),
-        );
+        let used_trait_imports = mem::take(&mut self.tables.borrow_mut().used_trait_imports);
         debug!("used_trait_imports({:?}) = {:?}", item_def_id, used_trait_imports);
         wbcx.tables.used_trait_imports = used_trait_imports;
 
diff --git a/src/librustc_typeck/check_unused.rs b/src/librustc_typeck/check_unused.rs
index eaaff70472bfb..81daf064bb368 100644
--- a/src/librustc_typeck/check_unused.rs
+++ b/src/librustc_typeck/check_unused.rs
@@ -1,14 +1,14 @@
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_errors::Applicability;
 use rustc_hir as hir;
-use rustc_hir::def_id::{DefId, DefIdSet, LocalDefId, LOCAL_CRATE};
+use rustc_hir::def_id::{DefId, LocalDefId, LOCAL_CRATE};
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::lint;
 use rustc_span::{Span, Symbol};
 
 pub fn check_crate(tcx: TyCtxt<'_>) {
-    let mut used_trait_imports = DefIdSet::default();
+    let mut used_trait_imports = FxHashSet::default();
     for &body_id in tcx.hir().krate().bodies.keys() {
         let item_def_id = tcx.hir().body_owner_def_id(body_id);
         let imports = tcx.used_trait_imports(item_def_id);
@@ -39,7 +39,7 @@ impl ItemLikeVisitor<'v> for CheckVisitor<'tcx> {
 
 struct CheckVisitor<'tcx> {
     tcx: TyCtxt<'tcx>,
-    used_trait_imports: DefIdSet,
+    used_trait_imports: FxHashSet<LocalDefId>,
 }
 
 impl CheckVisitor<'tcx> {
@@ -49,7 +49,7 @@ impl CheckVisitor<'tcx> {
             return;
         }
 
-        if self.used_trait_imports.contains(&def_id.to_def_id()) {
+        if self.used_trait_imports.contains(&def_id) {
             return;
         }