Cache more queries on disk.

15 files changed, 104 insertions, 83 deletions

diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 4d4d4a28499..c52fbaf0061 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -2129,7 +2129,7 @@ pub struct FnSig<'hir> {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub struct TraitItemId {
     pub def_id: LocalDefId,
 }
@@ -2192,7 +2192,7 @@ pub enum TraitItemKind<'hir> {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub struct ImplItemId {
     pub def_id: LocalDefId,
 }
@@ -2787,7 +2787,7 @@ impl<'hir> VariantData<'hir> {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, Hash, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, Hash, HashStable_Generic)]
 pub struct ItemId {
     pub def_id: LocalDefId,
 }
@@ -3034,7 +3034,7 @@ pub enum AssocItemKind {
 // The bodies for items are stored "out of line", in a separate
 // hashmap in the `Crate`. Here we just record the hir-id of the item
 // so it can fetched later.
-#[derive(Copy, Clone, PartialEq, Eq, Encodable, Debug, HashStable_Generic)]
+#[derive(Copy, Clone, PartialEq, Eq, Encodable, Decodable, Debug, HashStable_Generic)]
 pub struct ForeignItemId {
     pub def_id: LocalDefId,
 }
diff --git a/compiler/rustc_index/src/vec.rs b/compiler/rustc_index/src/vec.rs
index 4656994ac08..a8c611e18ff 100644
--- a/compiler/rustc_index/src/vec.rs
+++ b/compiler/rustc_index/src/vec.rs
@@ -65,12 +65,6 @@ impl<S: Encoder, I: Idx, T: Encodable<S>> Encodable<S> for IndexVec<I, T> {
     }
 }
 
-impl<S: Encoder, I: Idx, T: Encodable<S>> Encodable<S> for &IndexVec<I, T> {
-    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
-        Encodable::encode(&self.raw, s)
-    }
-}
-
 impl<D: Decoder, I: Idx, T: Decodable<D>> Decodable<D> for IndexVec<I, T> {
     fn decode(d: &mut D) -> Self {
         IndexVec { raw: Decodable::decode(d), _marker: PhantomData }
diff --git a/compiler/rustc_metadata/src/rmeta/encoder.rs b/compiler/rustc_metadata/src/rmeta/encoder.rs
index 81388a0bf58..7a017e2b77a 100644
--- a/compiler/rustc_metadata/src/rmeta/encoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/encoder.rs
@@ -25,7 +25,6 @@ use rustc_middle::middle::exported_symbols::{
     metadata_symbol_name, ExportedSymbol, SymbolExportInfo,
 };
 use rustc_middle::mir::interpret;
-use rustc_middle::thir;
 use rustc_middle::traits::specialization_graph;
 use rustc_middle::ty::codec::TyEncoder;
 use rustc_middle::ty::fast_reject::{self, SimplifiedType, TreatParams};
@@ -351,18 +350,6 @@ impl<'a, 'tcx> TyEncoder<'tcx> for EncodeContext<'a, 'tcx> {
     }
 }
 
-impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for &'tcx [thir::abstract_const::Node<'tcx>] {
-    fn encode(&self, s: &mut EncodeContext<'a, 'tcx>) -> opaque::EncodeResult {
-        (**self).encode(s)
-    }
-}
-
-impl<'a, 'tcx> Encodable<EncodeContext<'a, 'tcx>> for &'tcx [(ty::Predicate<'tcx>, Span)] {
-    fn encode(&self, s: &mut EncodeContext<'a, 'tcx>) -> opaque::EncodeResult {
-        (**self).encode(s)
-    }
-}
-
 /// Helper trait to allow overloading `EncodeContext::lazy` for iterators.
 trait EncodeContentsForLazy<'a, 'tcx, T: ?Sized + LazyMeta> {
     fn encode_contents_for_lazy(self, ecx: &mut EncodeContext<'a, 'tcx>) -> T::Meta;
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 7c90cbb9092..def061aaea0 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -82,7 +82,7 @@ macro_rules! arena_types {
             [] upvars_mentioned: rustc_data_structures::fx::FxIndexMap<rustc_hir::HirId, rustc_hir::Upvar>,
             [] object_safety_violations: rustc_middle::traits::ObjectSafetyViolation,
             [] codegen_unit: rustc_middle::mir::mono::CodegenUnit<'tcx>,
-            [] attribute: rustc_ast::Attribute,
+            [decode] attribute: rustc_ast::Attribute,
             [] name_set: rustc_data_structures::fx::FxHashSet<rustc_span::symbol::Symbol>,
             [] hir_id_set: rustc_hir::HirIdSet,
 
@@ -95,9 +95,6 @@ macro_rules! arena_types {
             // since we need to allocate this type on both the `rustc_hir` arena
             // (during lowering) and the `librustc_middle` arena (for decoding MIR)
             [decode] asm_template: rustc_ast::InlineAsmTemplatePiece,
-
-            // This is used to decode the &'tcx [Span] for InlineAsm's line_spans.
-            [decode] span: rustc_span::Span,
             [decode] used_trait_imports: rustc_data_structures::fx::FxHashSet<rustc_hir::def_id::LocalDefId>,
             [decode] impl_source: rustc_middle::traits::ImplSource<'tcx, ()>,
 
diff --git a/compiler/rustc_middle/src/hir/mod.rs b/compiler/rustc_middle/src/hir/mod.rs
index f18067145dd..b50f121eff2 100644
--- a/compiler/rustc_middle/src/hir/mod.rs
+++ b/compiler/rustc_middle/src/hir/mod.rs
@@ -36,7 +36,7 @@ impl<'a, 'tcx> HashStable<StableHashingContext<'a>> for Owner<'tcx> {
 
 /// Gather the LocalDefId for each item-like within a module, including items contained within
 /// bodies.  The Ids are in visitor order.  This is used to partition a pass between modules.
-#[derive(Debug, HashStable)]
+#[derive(Debug, HashStable, Encodable, Decodable)]
 pub struct ModuleItems {
     submodules: Box<[LocalDefId]>,
     items: Box<[ItemId]>,
diff --git a/compiler/rustc_middle/src/middle/stability.rs b/compiler/rustc_middle/src/middle/stability.rs
index 6918046390e..8b11e35a7c3 100644
--- a/compiler/rustc_middle/src/middle/stability.rs
+++ b/compiler/rustc_middle/src/middle/stability.rs
@@ -29,7 +29,7 @@ pub enum StabilityLevel {
 }
 
 /// An entry in the `depr_map`.
-#[derive(Copy, Clone, HashStable, Debug)]
+#[derive(Copy, Clone, HashStable, Debug, Encodable, Decodable)]
 pub struct DeprecationEntry {
     /// The metadata of the attribute associated with this entry.
     pub attr: Deprecation,
diff --git a/compiler/rustc_middle/src/query/mod.rs b/compiler/rustc_middle/src/query/mod.rs
index 0ef694a3c85..c6916697905 100644
--- a/compiler/rustc_middle/src/query/mod.rs
+++ b/compiler/rustc_middle/src/query/mod.rs
@@ -59,6 +59,7 @@ rustc_queries! {
     query hir_module_items(key: LocalDefId) -> rustc_middle::hir::ModuleItems {
         storage(ArenaCacheSelector<'tcx>)
         desc { |tcx| "HIR module items in `{}`", tcx.def_path_str(key.to_def_id()) }
+        cache_on_disk_if { true }
     }
 
     /// Gives access to the HIR node for the HIR owner `key`.
@@ -128,6 +129,7 @@ rustc_queries! {
     /// parameter. e.g. `fn example<const N: usize=3>` called on `N` would return `3`.
     query const_param_default(param: DefId) -> ty::Const<'tcx> {
         desc { |tcx| "compute const default for a given parameter `{}`", tcx.def_path_str(param)  }
+        cache_on_disk_if { param.is_local() }
         separate_provide_extern
     }
 
@@ -223,6 +225,7 @@ rustc_queries! {
     /// Bounds from the parent (e.g. with nested impl trait) are not included.
     query explicit_item_bounds(key: DefId) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
         desc { |tcx| "finding item bounds for `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -508,6 +511,7 @@ rustc_queries! {
     /// Returns the predicates written explicitly by the user.
     query explicit_predicates_of(key: DefId) -> ty::GenericPredicates<'tcx> {
         desc { |tcx| "computing explicit predicates of `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -515,6 +519,7 @@ rustc_queries! {
     /// Foo<'a, T> { x: &'a T }`, this would return `T: 'a`).
     query inferred_outlives_of(key: DefId) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
         desc { |tcx| "computing inferred outlives predicates of `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -526,6 +531,7 @@ rustc_queries! {
     /// additional acyclicity requirements).
     query super_predicates_of(key: DefId) -> ty::GenericPredicates<'tcx> {
         desc { |tcx| "computing the super predicates of `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -549,6 +555,7 @@ rustc_queries! {
     query trait_def(key: DefId) -> ty::TraitDef {
         desc { |tcx| "computing trait definition for `{}`", tcx.def_path_str(key) }
         storage(ArenaCacheSelector<'tcx>)
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
     query adt_def(key: DefId) -> ty::AdtDef<'tcx> {
@@ -558,6 +565,7 @@ rustc_queries! {
     }
     query adt_destructor(key: DefId) -> Option<ty::Destructor> {
         desc { |tcx| "computing `Drop` impl for `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -587,11 +595,13 @@ rustc_queries! {
     /// `is_const_fn` function.
     query impl_constness(key: DefId) -> hir::Constness {
         desc { |tcx| "checking if item is const fn: `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
     query asyncness(key: DefId) -> hir::IsAsync {
         desc { |tcx| "checking if the function is async: `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -609,12 +619,14 @@ rustc_queries! {
     /// Returns `true` if this is a foreign item (i.e., linked via `extern { ... }`).
     query is_foreign_item(key: DefId) -> bool {
         desc { |tcx| "checking if `{}` is a foreign item", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
     /// Returns `Some(generator_kind)` if the node pointed to by `def_id` is a generator.
     query generator_kind(def_id: DefId) -> Option<hir::GeneratorKind> {
         desc { |tcx| "looking up generator kind of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -627,6 +639,7 @@ rustc_queries! {
     /// Maps from the `DefId` of a type or region parameter to its (inferred) variance.
     query variances_of(def_id: DefId) -> &'tcx [ty::Variance] {
         desc { |tcx| "computing the variances of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -639,6 +652,7 @@ rustc_queries! {
     /// Maps from an impl/trait `DefId` to a list of the `DefId`s of its items.
     query associated_item_def_ids(key: DefId) -> &'tcx [DefId] {
         desc { |tcx| "collecting associated items of `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -646,6 +660,7 @@ rustc_queries! {
     query associated_item(key: DefId) -> ty::AssocItem {
         desc { |tcx| "computing associated item data for `{}`", tcx.def_path_str(key) }
         storage(ArenaCacheSelector<'tcx>)
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -685,10 +700,12 @@ rustc_queries! {
     /// Return `None` if this is an inherent impl.
     query impl_trait_ref(impl_id: DefId) -> Option<ty::TraitRef<'tcx>> {
         desc { |tcx| "computing trait implemented by `{}`", tcx.def_path_str(impl_id) }
+        cache_on_disk_if { impl_id.is_local() }
         separate_provide_extern
     }
     query impl_polarity(impl_id: DefId) -> ty::ImplPolarity {
         desc { |tcx| "computing implementation polarity of `{}`", tcx.def_path_str(impl_id) }
+        cache_on_disk_if { impl_id.is_local() }
         separate_provide_extern
     }
 
@@ -701,6 +718,7 @@ rustc_queries! {
     /// Methods in these implementations don't need to be exported.
     query inherent_impls(key: DefId) -> &'tcx [DefId] {
         desc { |tcx| "collecting inherent impls for `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -745,6 +763,7 @@ rustc_queries! {
     /// Computes the signature of the function.
     query fn_sig(key: DefId) -> ty::PolyFnSig<'tcx> {
         desc { |tcx| "computing function signature of `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -820,6 +839,7 @@ rustc_queries! {
     /// Caches `CoerceUnsized` kinds for impls on custom types.
     query coerce_unsized_info(key: DefId) -> ty::adjustment::CoerceUnsizedInfo {
         desc { |tcx| "computing CoerceUnsized info for `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -1033,28 +1053,33 @@ rustc_queries! {
 
     query opt_def_kind(def_id: DefId) -> Option<DefKind> {
         desc { |tcx| "looking up definition kind of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
     /// Gets the span for the definition.
     query def_span(def_id: DefId) -> Span {
         desc { |tcx| "looking up span for `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
     /// Gets the span for the identifier of the definition.
     query def_ident_span(def_id: DefId) -> Option<Span> {
         desc { |tcx| "looking up span for `{}`'s identifier", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
     query lookup_stability(def_id: DefId) -> Option<attr::Stability> {
         desc { |tcx| "looking up stability of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
     query lookup_const_stability(def_id: DefId) -> Option<attr::ConstStability> {
         desc { |tcx| "looking up const stability of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -1064,6 +1089,7 @@ rustc_queries! {
 
     query lookup_deprecation_entry(def_id: DefId) -> Option<DeprecationEntry> {
         desc { |tcx| "checking whether `{}` is deprecated", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -1074,6 +1100,7 @@ rustc_queries! {
 
     query item_attrs(def_id: DefId) -> &'tcx [ast::Attribute] {
         desc { |tcx| "collecting attributes of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -1090,6 +1117,7 @@ rustc_queries! {
 
     query fn_arg_names(def_id: DefId) -> &'tcx [rustc_span::symbol::Ident] {
         desc { |tcx| "looking up function parameter names for `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
     /// Gets the rendered value of the specified constant or associated constant.
@@ -1097,10 +1125,12 @@ rustc_queries! {
     query rendered_const(def_id: DefId) -> String {
         storage(ArenaCacheSelector<'tcx>)
         desc { |tcx| "rendering constant intializer of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
     query impl_parent(def_id: DefId) -> Option<DefId> {
         desc { |tcx| "computing specialization parent impl of `{}`", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -1108,15 +1138,18 @@ rustc_queries! {
     /// Return `None` if the `DefId` is not an associated item.
     query trait_of_item(associated_item: DefId) -> Option<DefId> {
         desc { |tcx| "finding trait defining `{}`", tcx.def_path_str(associated_item) }
+        cache_on_disk_if { associated_item.is_local() }
         separate_provide_extern
     }
 
     query is_ctfe_mir_available(key: DefId) -> bool {
         desc { |tcx| "checking if item has ctfe mir available: `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
     query is_mir_available(key: DefId) -> bool {
         desc { |tcx| "checking if item has mir available: `{}`", tcx.def_path_str(key) }
+        cache_on_disk_if { key.is_local() }
         separate_provide_extern
     }
 
@@ -1358,6 +1391,7 @@ rustc_queries! {
 
     query impl_defaultness(def_id: DefId) -> hir::Defaultness {
         desc { |tcx| "looking up whether `{}` is a default impl", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
 
@@ -1391,6 +1425,7 @@ rustc_queries! {
     }
     query is_reachable_non_generic(def_id: DefId) -> bool {
         desc { |tcx| "checking whether `{}` is an exported symbol", tcx.def_path_str(def_id) }
+        cache_on_disk_if { def_id.is_local() }
         separate_provide_extern
     }
     query is_unreachable_local_definition(def_id: LocalDefId) -> bool {
@@ -1705,9 +1740,9 @@ rustc_queries! {
     /// - All names contained in `exported_symbols(cnum)` are guaranteed to
     ///   correspond to a publicly visible symbol in `cnum` machine code.
     /// - The `exported_symbols` sets of different crates do not intersect.
-    query exported_symbols(_: CrateNum)
-        -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
+    query exported_symbols(cnum: CrateNum) -> &'tcx [(ExportedSymbol<'tcx>, SymbolExportInfo)] {
         desc { "exported_symbols" }
+        cache_on_disk_if { *cnum == LOCAL_CRATE }
         separate_provide_extern
     }
 
diff --git a/compiler/rustc_middle/src/ty/assoc.rs b/compiler/rustc_middle/src/ty/assoc.rs
index 49f846562a3..2c93af50667 100644
--- a/compiler/rustc_middle/src/ty/assoc.rs
+++ b/compiler/rustc_middle/src/ty/assoc.rs
@@ -9,7 +9,7 @@ use rustc_span::symbol::{Ident, Symbol};
 
 use super::{TyCtxt, Visibility};
 
-#[derive(Clone, Copy, PartialEq, Eq, Debug, HashStable, Hash)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, HashStable, Hash, Encodable, Decodable)]
 pub enum AssocItemContainer {
     TraitContainer(DefId),
     ImplContainer(DefId),
@@ -41,7 +41,7 @@ impl AssocItemContainer {
 }
 
 /// Information about an associated item
-#[derive(Copy, Clone, Debug, PartialEq, HashStable, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, HashStable, Eq, Hash, Encodable, Decodable)]
 pub struct AssocItem {
     pub def_id: DefId,
     pub name: Symbol,
@@ -81,7 +81,7 @@ impl AssocItem {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Debug, HashStable, Eq, Hash)]
+#[derive(Copy, Clone, PartialEq, Debug, HashStable, Eq, Hash, Encodable, Decodable)]
 pub enum AssocKind {
     Const,
     Fn,
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 23c377651cc..2a5191008a9 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -168,25 +168,6 @@ impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for AllocId {
     }
 }
 
-macro_rules! encodable_via_deref {
-    ($($t:ty),+) => {
-        $(impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for $t {
-            fn encode(&self, e: &mut E) -> Result<(), E::Error> {
-                (**self).encode(e)
-            }
-        })*
-    }
-}
-
-encodable_via_deref! {
-    &'tcx ty::TypeckResults<'tcx>,
-    &'tcx traits::ImplSource<'tcx, ()>,
-    &'tcx mir::Body<'tcx>,
-    &'tcx mir::UnsafetyCheckResult,
-    &'tcx mir::BorrowCheckResult<'tcx>,
-    &'tcx mir::coverage::CodeRegion
-}
-
 pub trait TyDecoder<'tcx>: Decoder {
     const CLEAR_CROSS_CRATE: bool;
 
@@ -466,6 +447,33 @@ macro_rules! impl_arena_allocatable_decoders {
 rustc_hir::arena_types!(impl_arena_allocatable_decoders);
 arena_types!(impl_arena_allocatable_decoders);
 
+macro_rules! impl_arena_copy_decoder {
+    (<$tcx:tt> $($ty:ty,)*) => {
+        $(impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for $ty {
+            #[inline]
+            fn decode(decoder: &mut D) -> &'tcx Self {
+                decoder.tcx().arena.alloc(Decodable::decode(decoder))
+            }
+        }
+
+        impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [$ty] {
+            #[inline]
+            fn decode(decoder: &mut D) -> &'tcx Self {
+                decoder.tcx().arena.alloc_from_iter(<Vec<_> as Decodable<D>>::decode(decoder))
+            }
+        })*
+    };
+}
+
+impl_arena_copy_decoder! {<'tcx>
+    Span,
+    rustc_span::symbol::Ident,
+    ty::Variance,
+    rustc_span::def_id::DefId,
+    rustc_span::def_id::LocalDefId,
+    (rustc_middle::middle::exported_symbols::ExportedSymbol<'tcx>, rustc_middle::middle::exported_symbols::SymbolExportInfo),
+}
+
 #[macro_export]
 macro_rules! implement_ty_decoder {
     ($DecoderName:ident <$($typaram:tt),*>) => {
diff --git a/compiler/rustc_middle/src/ty/list.rs b/compiler/rustc_middle/src/ty/list.rs
index 197dc9205b4..3c9e96df59a 100644
--- a/compiler/rustc_middle/src/ty/list.rs
+++ b/compiler/rustc_middle/src/ty/list.rs
@@ -122,13 +122,6 @@ impl<S: Encoder, T: Encodable<S>> Encodable<S> for List<T> {
     }
 }
 
-impl<S: Encoder, T: Encodable<S>> Encodable<S> for &List<T> {
-    #[inline]
-    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
-        (**self).encode(s)
-    }
-}
-
 impl<T: PartialEq> PartialEq for List<T> {
     #[inline]
     fn eq(&self, other: &List<T>) -> bool {
diff --git a/compiler/rustc_middle/src/ty/mod.rs b/compiler/rustc_middle/src/ty/mod.rs
index d847068b5bf..e21cdcb7303 100644
--- a/compiler/rustc_middle/src/ty/mod.rs
+++ b/compiler/rustc_middle/src/ty/mod.rs
@@ -228,7 +228,7 @@ impl fmt::Display for ImplPolarity {
     }
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, Copy, Hash, TyEncodable, TyDecodable, HashStable)]
+#[derive(Clone, Debug, PartialEq, Eq, Copy, Hash, Encodable, Decodable, HashStable)]
 pub enum Visibility {
     /// Visible everywhere (including in other crates).
     Public,
@@ -1629,7 +1629,7 @@ where
     }
 }
 
-#[derive(Copy, Clone, Debug, HashStable)]
+#[derive(Copy, Clone, Debug, HashStable, Encodable, Decodable)]
 pub struct Destructor {
     /// The `DefId` of the destructor method
     pub did: DefId,
diff --git a/compiler/rustc_query_impl/src/lib.rs b/compiler/rustc_query_impl/src/lib.rs
index 6ebff5388f4..2fa030f9b3f 100644
--- a/compiler/rustc_query_impl/src/lib.rs
+++ b/compiler/rustc_query_impl/src/lib.rs
@@ -21,7 +21,7 @@ use rustc_middle::dep_graph::{self, DepKindStruct, SerializedDepNodeIndex};
 use rustc_middle::ty::query::{query_keys, query_storage, query_stored, query_values};
 use rustc_middle::ty::query::{ExternProviders, Providers, QueryEngine};
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_span::def_id::LocalDefId;
+use rustc_span::def_id::{LocalDefId, LOCAL_CRATE};
 use rustc_span::Span;
 
 #[macro_use]
diff --git a/compiler/rustc_query_impl/src/on_disk_cache.rs b/compiler/rustc_query_impl/src/on_disk_cache.rs
index f2f895367ff..c4920408527 100644
--- a/compiler/rustc_query_impl/src/on_disk_cache.rs
+++ b/compiler/rustc_query_impl/src/on_disk_cache.rs
@@ -788,10 +788,24 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [rustc_ast::InlineAsm
     }
 }
 
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [Span] {
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {
-        RefDecodable::decode(d)
-    }
+macro_rules! impl_ref_decoder {
+    (<$tcx:tt> $($ty:ty,)*) => {
+        $(impl<'a, $tcx> Decodable<CacheDecoder<'a, $tcx>> for &$tcx [$ty] {
+            fn decode(d: &mut CacheDecoder<'a, $tcx>) -> Self {
+                RefDecodable::decode(d)
+            }
+        })*
+    };
+}
+
+impl_ref_decoder! {<'tcx>
+    Span,
+    rustc_ast::Attribute,
+    rustc_span::symbol::Ident,
+    ty::Variance,
+    rustc_span::def_id::DefId,
+    rustc_span::def_id::LocalDefId,
+    (rustc_middle::middle::exported_symbols::ExportedSymbol<'tcx>, rustc_middle::middle::exported_symbols::SymbolExportInfo),
 }
 
 //- ENCODING -------------------------------------------------------------------
diff --git a/compiler/rustc_serialize/src/collection_impls.rs b/compiler/rustc_serialize/src/collection_impls.rs
index dee6dc010fe..761e988360a 100644
--- a/compiler/rustc_serialize/src/collection_impls.rs
+++ b/compiler/rustc_serialize/src/collection_impls.rs
@@ -171,16 +171,6 @@ where
     }
 }
 
-impl<E: Encoder, T, S> Encodable<E> for &HashSet<T, S>
-where
-    T: Encodable<E> + Eq,
-    S: BuildHasher,
-{
-    fn encode(&self, s: &mut E) -> Result<(), E::Error> {
-        (**self).encode(s)
-    }
-}
-
 impl<D: Decoder, T, S> Decodable<D> for HashSet<T, S>
 where
     T: Decodable<D> + Hash + Eq,
diff --git a/compiler/rustc_serialize/src/serialize.rs b/compiler/rustc_serialize/src/serialize.rs
index 7d6b8c760ff..36e575b2427 100644
--- a/compiler/rustc_serialize/src/serialize.rs
+++ b/compiler/rustc_serialize/src/serialize.rs
@@ -268,6 +268,15 @@ direct_serialize_impls! {
     char emit_char read_char
 }
 
+impl<S: Encoder, T: ?Sized> Encodable<S> for &T
+where
+    T: Encodable<S>,
+{
+    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
+        (**self).encode(s)
+    }
+}
+
 impl<S: Encoder> Encodable<S> for ! {
     fn encode(&self, _s: &mut S) -> Result<(), S::Error> {
         unreachable!()
@@ -298,12 +307,6 @@ impl<S: Encoder> Encodable<S> for str {
     }
 }
 
-impl<S: Encoder> Encodable<S> for &str {
-    fn encode(&self, s: &mut S) -> Result<(), S::Error> {
-        s.emit_str(self)
-    }
-}
-
 impl<S: Encoder> Encodable<S> for String {
     fn encode(&self, s: &mut S) -> Result<(), S::Error> {
         s.emit_str(&self[..])