rustc_metadata: use a table for impl_trait_ref.

src/librustc_metadata/decoder.rs

@@ -711,7 +711,7 @@ impl<'a, 'tcx> CrateMetadata {
         }
     }
 
-    fn get_impl_data(&self, id: DefIndex) -> ImplData<'tcx> {
+    fn get_impl_data(&self, id: DefIndex) -> ImplData {
         match self.kind(id) {
             EntryKind::Impl(data) => data.decode(self),
             _ => bug!(),
@@ -738,7 +738,7 @@ impl<'a, 'tcx> CrateMetadata {
     }
 
     crate fn get_impl_trait(&self, id: DefIndex, tcx: TyCtxt<'tcx>) -> Option<ty::TraitRef<'tcx>> {
-        self.get_impl_data(id).trait_ref.map(|tr| tr.decode((self, tcx)))
+        self.root.per_def.impl_trait_ref.get(self, id).map(|tr| tr.decode((self, tcx)))
     }
 
     /// Iterates over all the stability attributes in the given crate.

src/librustc_metadata/encoder.rs

@@ -72,6 +72,7 @@ struct PerDefTables<'tcx> {
 
     ty: PerDefTable<Lazy<Ty<'tcx>>>,
     fn_sig: PerDefTable<Lazy<ty::PolyFnSig<'tcx>>>,
+    impl_trait_ref: PerDefTable<Lazy<ty::TraitRef<'tcx>>>,
     inherent_impls: PerDefTable<Lazy<[DefIndex]>>,
     variances: PerDefTable<Lazy<[ty::Variance]>>,
     generics: PerDefTable<Lazy<ty::Generics>>,
@@ -511,6 +512,7 @@ impl<'tcx> EncodeContext<'tcx> {
 
             ty: self.per_def.ty.encode(&mut self.opaque),
             fn_sig: self.per_def.fn_sig.encode(&mut self.opaque),
+            impl_trait_ref: self.per_def.impl_trait_ref.encode(&mut self.opaque),
             inherent_impls: self.per_def.inherent_impls.encode(&mut self.opaque),
             variances: self.per_def.variances.encode(&mut self.opaque),
             generics: self.per_def.generics.encode(&mut self.opaque),
@@ -1152,7 +1154,6 @@ impl EncodeContext<'tcx> {
                     defaultness,
                     parent_impl: parent,
                     coerce_unsized_info,
-                    trait_ref: trait_ref.map(|trait_ref| self.lazy(trait_ref)),
                 };
 
                 EntryKind::Impl(self.lazy(data))
@@ -1226,6 +1227,11 @@ impl EncodeContext<'tcx> {
         if let hir::ItemKind::Fn(..) = item.kind {
             record!(self.per_def.fn_sig[def_id] <- tcx.fn_sig(def_id));
         }
+        if let hir::ItemKind::Impl(..) = item.kind {
+            if let Some(trait_ref) = self.tcx.impl_trait_ref(def_id) {
+                record!(self.per_def.impl_trait_ref[def_id] <- trait_ref);
+            }
+        }
         self.encode_inherent_implementations(def_id);
         match item.kind {
             hir::ItemKind::Enum(..) |

src/librustc_metadata/schema.rs

@@ -239,6 +239,7 @@ crate struct LazyPerDefTables<'tcx> {
 
     pub ty: Lazy!(PerDefTable<Lazy!(Ty<'tcx>)>),
     pub fn_sig: Lazy!(PerDefTable<Lazy!(ty::PolyFnSig<'tcx>)>),
+    pub impl_trait_ref: Lazy!(PerDefTable<Lazy!(ty::TraitRef<'tcx>)>),
     pub inherent_impls: Lazy!(PerDefTable<Lazy<[DefIndex]>>),
     pub variances: Lazy!(PerDefTable<Lazy<[ty::Variance]>>),
     pub generics: Lazy!(PerDefTable<Lazy<ty::Generics>>),
@@ -276,7 +277,7 @@ crate enum EntryKind<'tcx> {
     Closure,
     Generator(Lazy!(GeneratorData<'tcx>)),
     Trait(Lazy<TraitData>),
-    Impl(Lazy!(ImplData<'tcx>)),
+    Impl(Lazy<ImplData>),
     Method(Lazy<MethodData>),
     AssocType(AssocContainer),
     AssocOpaqueTy(AssocContainer),
@@ -330,14 +331,14 @@ crate struct TraitData {
 }
 
 #[derive(RustcEncodable, RustcDecodable)]
-crate struct ImplData<'tcx> {
+crate struct ImplData {
     pub polarity: ty::ImplPolarity,
     pub defaultness: hir::Defaultness,
     pub parent_impl: Option<DefId>,
 
     /// This is `Some` only for impls of `CoerceUnsized`.
+    // FIXME(eddyb) perhaps compute this on the fly if cheap enough?
     pub coerce_unsized_info: Option<ty::adjustment::CoerceUnsizedInfo>,
-    pub trait_ref: Option<Lazy!(ty::TraitRef<'tcx>)>,
 }