diff --git a/compiler/rustc_arena/src/lib.rs b/compiler/rustc_arena/src/lib.rs
index a4248a82bce73..3e318b84b77f2 100644
--- a/compiler/rustc_arena/src/lib.rs
+++ b/compiler/rustc_arena/src/lib.rs
@@ -612,7 +612,11 @@ impl DroplessArena {
 ///   arguments. The `TypedArena` will be used for them.
 ///
 #[rustc_macro_transparency = "semiopaque"]
-pub macro declare_arena([$($a:tt $name:ident: $ty:ty,)*]) {
+pub macro declare_arena(
+    $(
+        [] $name:ident: $ty:ty,
+    )*
+) {
     #[derive(Default)]
     pub struct Arena<'tcx> {
         pub dropless: $crate::DroplessArena,
diff --git a/compiler/rustc_hir/src/arena.rs b/compiler/rustc_hir/src/arena.rs
index 827538f58f980..aa3ddcbfb59e8 100644
--- a/compiler/rustc_hir/src/arena.rs
+++ b/compiler/rustc_hir/src/arena.rs
@@ -1,15 +1,11 @@
-/// This higher-order macro declares a list of types which can be allocated by `Arena`.
-/// Note that all `Copy` types can be allocated by default and need not be specified here.
-#[macro_export]
-macro_rules! arena_types {
-    ($macro:path) => (
-        $macro!([
-            // HIR types
-            [] asm_template: rustc_ast::InlineAsmTemplatePiece,
-            [] attribute: rustc_hir::Attribute,
-            [] owner_info: rustc_hir::OwnerInfo<'tcx>,
-            [] macro_def: rustc_ast::MacroDef,
-            [] delegation_info: rustc_hir::DelegationInfo,
-        ]);
-    )
+//! Declares an arena that can allocate values of any `Copy` type, and of
+//! any needs-drop type listed below.
+
+rustc_arena::declare_arena! {
+    // HIR types
+    [] asm_template: rustc_ast::InlineAsmTemplatePiece,
+    [] attribute: rustc_hir::Attribute,
+    [] owner_info: rustc_hir::OwnerInfo<'tcx>,
+    [] macro_def: rustc_ast::MacroDef,
+    [] delegation_info: rustc_hir::DelegationInfo,
 }
diff --git a/compiler/rustc_hir/src/lib.rs b/compiler/rustc_hir/src/lib.rs
index 9b976d21d5365..008ad52e0339f 100644
--- a/compiler/rustc_hir/src/lib.rs
+++ b/compiler/rustc_hir/src/lib.rs
@@ -47,4 +47,4 @@ pub use rustc_ast::attr::version::*;
 pub use stability::*;
 pub use target::{MethodKind, Target};
 
-arena_types!(rustc_arena::declare_arena);
+pub use crate::arena::Arena;
diff --git a/compiler/rustc_middle/src/arena.rs b/compiler/rustc_middle/src/arena.rs
index 87e19fafc0e22..10c39ee1257bb 100644
--- a/compiler/rustc_middle/src/arena.rs
+++ b/compiler/rustc_middle/src/arena.rs
@@ -1,135 +1,202 @@
-/// This higher-order macro declares a list of types which can be allocated by `Arena`.
-///
-/// Specifying the `decode` modifier will add decode impls for `&T` and `&[T]` where `T` is the type
-/// listed. See the `impl_arena_allocatable_decoder!` macro for more.
-#[macro_export]
-macro_rules! arena_types {
-    ($macro:path) => (
-        $macro!([
-            [] layout: rustc_abi::LayoutData<rustc_abi::FieldIdx, rustc_abi::VariantIdx>,
-            [] proxy_coroutine_layout: rustc_middle::mir::CoroutineLayout<'tcx>,
-            [] fn_abi: rustc_target::callconv::FnAbi<'tcx, rustc_middle::ty::Ty<'tcx>>,
-            [] adt_def: rustc_middle::ty::AdtDefData,
-            [] steal_thir: rustc_data_structures::steal::Steal<rustc_middle::thir::Thir<'tcx>>,
-            [] steal_mir: rustc_data_structures::steal::Steal<rustc_middle::mir::Body<'tcx>>,
-            [decode] mir: rustc_middle::mir::Body<'tcx>,
-            [] steal_promoted:
-                rustc_data_structures::steal::Steal<
-                    rustc_index::IndexVec<
-                        rustc_middle::mir::Promoted,
-                        rustc_middle::mir::Body<'tcx>
-                    >
-                >,
-            [decode] promoted:
-                rustc_index::IndexVec<
-                    rustc_middle::mir::Promoted,
-                    rustc_middle::mir::Body<'tcx>
-                >,
-            [decode] typeck_results: rustc_middle::ty::TypeckResults<'tcx>,
-            [] borrowck_result: rustc_data_structures::fx::FxIndexMap<
-                rustc_hir::def_id::LocalDefId,
-                rustc_middle::ty::DefinitionSiteHiddenType<'tcx>,
-            >,
-            [] resolver: rustc_data_structures::steal::Steal<rustc_middle::ty::ResolverAstLowering<'tcx>>,
-            [] index_ast: rustc_index::IndexVec<
-                rustc_span::def_id::LocalDefId,
-                rustc_data_structures::steal::Steal<(
-                    std::sync::Arc<rustc_middle::ty::ResolverAstLowering<'tcx>>,
-                    rustc_ast::AstOwner
-                )>
-            >,
-            [] crate_alone: rustc_data_structures::steal::Steal<rustc_ast::Crate>,
-            [] crate_for_resolver: rustc_data_structures::steal::Steal<(rustc_ast::Crate, rustc_ast::AttrVec)>,
-            [] resolutions: rustc_middle::ty::ResolverGlobalCtxt,
-            [] const_allocs: rustc_middle::mir::interpret::Allocation,
-            [] region_scope_tree: rustc_middle::middle::region::ScopeTree,
-            // Required for the incremental on-disk cache
-            [] mir_keys: rustc_hir::def_id::DefIdSet,
-            [] dropck_outlives:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx,
-                        rustc_middle::traits::query::DropckOutlivesResult<'tcx>
-                    >
-                >,
-            [] normalize_canonicalized_projection:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx,
-                        rustc_middle::traits::query::NormalizationResult<'tcx>
-                    >
-                >,
-            [] implied_outlives_bounds:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx,
-                        Vec<rustc_middle::traits::query::OutlivesBound<'tcx>>
-                    >
-                >,
-            [] dtorck_constraint: rustc_middle::traits::query::DropckConstraint<'tcx>,
-            [] candidate_step: rustc_middle::traits::query::CandidateStep<'tcx>,
-            [] autoderef_bad_ty: rustc_middle::traits::query::MethodAutoderefBadTy<'tcx>,
-            [] query_region_constraints: rustc_middle::infer::canonical::QueryRegionConstraints<'tcx>,
-            [] type_op_subtype:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx, ()>
-                >,
-            [] type_op_normalize_poly_fn_sig:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::PolyFnSig<'tcx>>
-                >,
-            [] type_op_normalize_fn_sig:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::FnSig<'tcx>>
-                >,
-            [] type_op_normalize_clause:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::Clause<'tcx>>
-                >,
-            [] type_op_normalize_ty:
-                rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::Ty<'tcx>>
-                >,
-            [] inspect_probe: rustc_middle::traits::solve::inspect::Probe<rustc_middle::ty::TyCtxt<'tcx>>,
-            [] effective_visibilities: rustc_middle::middle::privacy::EffectiveVisibilities,
-            [] upvars_mentioned: rustc_data_structures::fx::FxIndexMap<rustc_hir::HirId, rustc_hir::Upvar>,
-            [] dyn_compatibility_violations: rustc_middle::traits::DynCompatibilityViolation,
-            [] codegen_unit: rustc_middle::mono::CodegenUnit<'tcx>,
-            [decode] attribute: rustc_hir::Attribute,
-            [] name_set: rustc_data_structures::unord::UnordSet<rustc_span::Symbol>,
-            [] autodiff_item: rustc_hir::attrs::AutoDiffItem,
-            [] ordered_name_set: rustc_data_structures::fx::FxIndexSet<rustc_span::Symbol>,
-            [] stable_order_of_exportable_impls:
-                rustc_data_structures::fx::FxIndexMap<rustc_hir::def_id::DefId, usize>,
+//! Declares [`rustc_middle::arena::Arena`], which can allocate values of any
+//! `Copy` type, and any needs-drop type explicitly listed below.
 
-            // Note that this deliberately duplicates items in the `rustc_hir::arena`,
-            // since we need to allocate this type on both the `rustc_hir` arena
-            // (during lowering) and the `rustc_middle` arena (for decoding MIR)
-            [decode] asm_template: rustc_ast::InlineAsmTemplatePiece,
-            [decode] used_trait_imports: rustc_data_structures::unord::UnordSet<rustc_hir::def_id::LocalDefId>,
-            [] is_late_bound_map: rustc_data_structures::fx::FxIndexSet<rustc_hir::ItemLocalId>,
-            [decode] impl_source: rustc_middle::traits::ImplSource<'tcx, ()>,
+use rustc_serialize::Decodable;
 
-            [] dep_kind_vtable: rustc_middle::dep_graph::DepKindVTable<'tcx>,
+use crate::ty::codec::{RefDecodable, TyDecoder};
+use crate::ty::{Ty, TyCtxt};
 
-            [decode] trait_impl_trait_tys:
-                rustc_data_structures::unord::UnordMap<
-                    rustc_hir::def_id::DefId,
-                    rustc_middle::ty::EarlyBinder<'tcx, rustc_middle::ty::Ty<'tcx>>
-                >,
-            [] external_constraints: rustc_middle::traits::solve::ExternalConstraintsData<rustc_middle::ty::TyCtxt<'tcx>>,
-            [] doc_link_resolutions: rustc_hir::def::DocLinkResMap,
-            [] stripped_cfg_items: rustc_hir::attrs::StrippedCfgItem,
-            [] mod_child: rustc_middle::metadata::ModChild,
-            [] features: rustc_feature::Features,
-            [decode] specialization_graph: rustc_middle::traits::specialization_graph::Graph,
-            [] crate_inherent_impls: rustc_middle::ty::CrateInherentImpls,
-            [] hir_owner_nodes: rustc_hir::OwnerNodes<'tcx>,
-            [decode] token_stream: rustc_ast::tokenstream::TokenStream,
-            [] maybe_owner: rustc_middle::hir::ProjectedMaybeOwner<'tcx>,
-            [] owner_info: rustc_middle::hir::ProjectedOwnerInfo<'tcx>,
-            [] parenting: rustc_hir::def_id::LocalDefIdMap<rustc_hir::ItemLocalId>,
-            [] trait_candidates: rustc_hir::ItemLocalMap<&'tcx [rustc_hir::TraitCandidate<'tcx>]>,
-            [] delayed_lints: rustc_data_structures::steal::Steal<rustc_hir::lints::DelayedLints>,
-        ]);
-    )
+rustc_arena::declare_arena! {
+    [] layout: rustc_abi::LayoutData<rustc_abi::FieldIdx, rustc_abi::VariantIdx>,
+    [] proxy_coroutine_layout: rustc_middle::mir::CoroutineLayout<'tcx>,
+    [] fn_abi: rustc_target::callconv::FnAbi<'tcx, Ty<'tcx>>,
+    [] adt_def: rustc_middle::ty::AdtDefData,
+    [] steal_thir: rustc_data_structures::steal::Steal<rustc_middle::thir::Thir<'tcx>>,
+    [] steal_mir: rustc_data_structures::steal::Steal<rustc_middle::mir::Body<'tcx>>,
+    [] mir: rustc_middle::mir::Body<'tcx>,
+    [] steal_promoted:
+        rustc_data_structures::steal::Steal<
+            rustc_index::IndexVec<
+                rustc_middle::mir::Promoted,
+                rustc_middle::mir::Body<'tcx>
+            >
+        >,
+    [] promoted:
+        rustc_index::IndexVec<
+            rustc_middle::mir::Promoted,
+            rustc_middle::mir::Body<'tcx>
+        >,
+    [] typeck_results: rustc_middle::ty::TypeckResults<'tcx>,
+    [] borrowck_result:
+        rustc_data_structures::fx::FxIndexMap<
+            rustc_hir::def_id::LocalDefId,
+            rustc_middle::ty::DefinitionSiteHiddenType<'tcx>,
+        >,
+    [] resolver: rustc_data_structures::steal::Steal<rustc_middle::ty::ResolverAstLowering<'tcx>>,
+    [] index_ast:
+        rustc_index::IndexVec<
+            rustc_span::def_id::LocalDefId,
+            rustc_data_structures::steal::Steal<(
+                std::sync::Arc<rustc_middle::ty::ResolverAstLowering<'tcx>>,
+                rustc_ast::AstOwner
+            )>
+        >,
+    [] crate_alone: rustc_data_structures::steal::Steal<rustc_ast::Crate>,
+    [] crate_for_resolver: rustc_data_structures::steal::Steal<(rustc_ast::Crate, rustc_ast::AttrVec)>,
+    [] resolutions: rustc_middle::ty::ResolverGlobalCtxt,
+    [] const_allocs: rustc_middle::mir::interpret::Allocation,
+    [] region_scope_tree: rustc_middle::middle::region::ScopeTree,
+    // Required for the incremental on-disk cache
+    [] mir_keys: rustc_hir::def_id::DefIdSet,
+    [] dropck_outlives:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx,
+                rustc_middle::traits::query::DropckOutlivesResult<'tcx>
+            >
+        >,
+    [] normalize_canonicalized_projection:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx,
+                rustc_middle::traits::query::NormalizationResult<'tcx>
+            >
+        >,
+    [] implied_outlives_bounds:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx,
+                Vec<rustc_middle::traits::query::OutlivesBound<'tcx>>
+            >
+        >,
+    [] dtorck_constraint: rustc_middle::traits::query::DropckConstraint<'tcx>,
+    [] candidate_step: rustc_middle::traits::query::CandidateStep<'tcx>,
+    [] autoderef_bad_ty: rustc_middle::traits::query::MethodAutoderefBadTy<'tcx>,
+    [] query_region_constraints: rustc_middle::infer::canonical::QueryRegionConstraints<'tcx>,
+    [] type_op_subtype:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx, ()>
+        >,
+    [] type_op_normalize_poly_fn_sig:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::PolyFnSig<'tcx>>
+        >,
+    [] type_op_normalize_fn_sig:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::FnSig<'tcx>>
+        >,
+    [] type_op_normalize_clause:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::Clause<'tcx>>
+        >,
+    [] type_op_normalize_ty:
+        rustc_middle::infer::canonical::Canonical<'tcx,
+            rustc_middle::infer::canonical::QueryResponse<'tcx, Ty<'tcx>>
+        >,
+    [] inspect_probe: rustc_middle::traits::solve::inspect::Probe<TyCtxt<'tcx>>,
+    [] effective_visibilities: rustc_middle::middle::privacy::EffectiveVisibilities,
+    [] upvars_mentioned: rustc_data_structures::fx::FxIndexMap<rustc_hir::HirId, rustc_hir::Upvar>,
+    [] dyn_compatibility_violations: rustc_middle::traits::DynCompatibilityViolation,
+    [] codegen_unit: rustc_middle::mono::CodegenUnit<'tcx>,
+    [] attribute: rustc_hir::Attribute,
+    [] name_set: rustc_data_structures::unord::UnordSet<rustc_span::Symbol>,
+    [] autodiff_item: rustc_hir::attrs::AutoDiffItem,
+    [] ordered_name_set: rustc_data_structures::fx::FxIndexSet<rustc_span::Symbol>,
+    [] stable_order_of_exportable_impls:
+        rustc_data_structures::fx::FxIndexMap<rustc_hir::def_id::DefId, usize>,
+
+    // Note that this deliberately duplicates items in the `rustc_hir::arena`,
+    // since we need to allocate this type on both the `rustc_hir` arena
+    // (during lowering) and the `rustc_middle` arena (for decoding MIR)
+    [] asm_template: rustc_ast::InlineAsmTemplatePiece,
+    [] used_trait_imports: rustc_data_structures::unord::UnordSet<rustc_hir::def_id::LocalDefId>,
+    [] is_late_bound_map: rustc_data_structures::fx::FxIndexSet<rustc_hir::ItemLocalId>,
+    [] impl_source: rustc_middle::traits::ImplSource<'tcx, ()>,
+
+    [] dep_kind_vtable: rustc_middle::dep_graph::DepKindVTable<'tcx>,
+
+    [] trait_impl_trait_tys:
+        rustc_data_structures::unord::UnordMap<
+            rustc_hir::def_id::DefId,
+            rustc_middle::ty::EarlyBinder<'tcx, Ty<'tcx>>
+        >,
+    [] external_constraints: rustc_middle::traits::solve::ExternalConstraintsData<TyCtxt<'tcx>>,
+    [] doc_link_resolutions: rustc_hir::def::DocLinkResMap,
+    [] stripped_cfg_items: rustc_hir::attrs::StrippedCfgItem,
+    [] mod_child: rustc_middle::metadata::ModChild,
+    [] features: rustc_feature::Features,
+    [] specialization_graph: rustc_middle::traits::specialization_graph::Graph,
+    [] crate_inherent_impls: rustc_middle::ty::CrateInherentImpls,
+    [] hir_owner_nodes: rustc_hir::OwnerNodes<'tcx>,
+    [] token_stream: rustc_ast::tokenstream::TokenStream,
+    [] maybe_owner: rustc_middle::hir::ProjectedMaybeOwner<'tcx>,
+    [] owner_info: rustc_middle::hir::ProjectedOwnerInfo<'tcx>,
+    [] parenting: rustc_hir::def_id::LocalDefIdMap<rustc_hir::ItemLocalId>,
+    [] trait_candidates: rustc_hir::ItemLocalMap<&'tcx [rustc_hir::TraitCandidate<'tcx>]>,
+    [] delayed_lints: rustc_data_structures::steal::Steal<rustc_hir::lints::DelayedLints>,
 }
 
-arena_types!(rustc_arena::declare_arena);
+#[inline]
+fn decode_arena_allocable<'tcx, D, C, T>(decoder: &mut D) -> &'tcx T
+where
+    D: TyDecoder<'tcx>,
+    T: ArenaAllocatable<'tcx, C> + Decodable<D>,
+{
+    let value: T = Decodable::decode(decoder);
+    decoder.interner().arena.alloc(value)
+}
+
+#[inline]
+fn decode_arena_allocable_slice<'tcx, D, C, T>(decoder: &mut D) -> &'tcx [T]
+where
+    D: TyDecoder<'tcx>,
+    T: ArenaAllocatable<'tcx, C> + Decodable<D>,
+{
+    let values: Vec<T> = Decodable::decode(decoder);
+    decoder.interner().arena.alloc_from_iter(values)
+}
+
+/// Implements [`RefDecodable`] for `T` (and `[T]`), by decoding to `T` and
+/// then moving the value or values into an arena allocation.
+macro_rules! impl_ref_decodable_into_arena {
+    (
+        $(
+            $ty:ty,
+        )*
+    ) => {
+        $(
+            impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for $ty {
+                #[inline]
+                fn decode(decoder: &mut D) -> &'tcx Self {
+                    decode_arena_allocable(decoder)
+                }
+            }
+
+            impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [$ty] {
+                #[inline]
+                fn decode(decoder: &mut D) -> &'tcx Self {
+                    decode_arena_allocable_slice(decoder)
+                }
+            }
+        )*
+    }
+}
+
+impl_ref_decodable_into_arena! {
+    // tidy-alphabetical-start
+    (rustc_middle::middle::exported_symbols::ExportedSymbol<'tcx>, rustc_middle::middle::exported_symbols::SymbolExportInfo),
+    rustc_ast::InlineAsmTemplatePiece,
+    rustc_ast::tokenstream::TokenStream,
+    rustc_data_structures::unord::UnordMap<rustc_span::def_id::DefId, rustc_middle::ty::EarlyBinder<'tcx, Ty<'tcx>>>,
+    rustc_data_structures::unord::UnordSet<rustc_span::def_id::LocalDefId>,
+    rustc_hir::Attribute,
+    rustc_index::IndexVec<rustc_middle::mir::Promoted, rustc_middle::mir::Body<'tcx>>,
+    rustc_middle::middle::deduced_param_attrs::DeducedParamAttrs,
+    rustc_middle::mir::Body<'tcx>,
+    rustc_middle::traits::ImplSource<'tcx, ()>,
+    rustc_middle::traits::specialization_graph::Graph,
+    rustc_middle::ty::TypeckResults<'tcx>,
+    rustc_middle::ty::Variance,
+    rustc_span::Ident,
+    rustc_span::Span,
+    rustc_span::def_id::DefId,
+    rustc_span::def_id::LocalDefId,
+    // tidy-alphabetical-end
+}
diff --git a/compiler/rustc_middle/src/ty/codec.rs b/compiler/rustc_middle/src/ty/codec.rs
index 5f76467ed7db2..0b2a1c55cfcf5 100644
--- a/compiler/rustc_middle/src/ty/codec.rs
+++ b/compiler/rustc_middle/src/ty/codec.rs
@@ -17,7 +17,6 @@ use rustc_middle::ty::Const;
 use rustc_serialize::{Decodable, Encodable};
 use rustc_span::{Span, SpanDecoder, SpanEncoder, Spanned};
 
-use crate::arena::ArenaAllocatable;
 use crate::infer::canonical::{CanonicalVarKind, CanonicalVarKinds};
 use crate::mir::interpret::{AllocId, ConstAllocation, CtfeProvenance};
 use crate::mono::MonoItem;
@@ -206,24 +205,6 @@ impl<'tcx, E: TyEncoder<'tcx>> Encodable<E> for ty::ParamEnv<'tcx> {
     }
 }
 
-#[inline]
-fn decode_arena_allocable<'tcx, D: TyDecoder<'tcx>, T: ArenaAllocatable<'tcx> + Decodable<D>>(
-    decoder: &mut D,
-) -> &'tcx T {
-    decoder.interner().arena.alloc(Decodable::decode(decoder))
-}
-
-#[inline]
-fn decode_arena_allocable_slice<
-    'tcx,
-    D: TyDecoder<'tcx>,
-    T: ArenaAllocatable<'tcx> + Decodable<D>,
->(
-    decoder: &mut D,
-) -> &'tcx [T] {
-    decoder.interner().arena.alloc_from_iter(<Vec<T> as Decodable<D>>::decode(decoder))
-}
-
 impl<'tcx, D: TyDecoder<'tcx>> Decodable<D> for Ty<'tcx> {
     #[allow(rustc::usage_of_ty_tykind)]
     fn decode(decoder: &mut D) -> Ty<'tcx> {
@@ -500,64 +481,6 @@ macro_rules! __impl_decoder_methods {
     }
 }
 
-macro_rules! impl_arena_allocatable_decoder {
-    ([]       $name:ident: $ty:ty) => {};
-    ([decode] $name:ident: $ty:ty) => {
-        impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for $ty {
-            #[inline]
-            fn decode(decoder: &mut D) -> &'tcx Self {
-                decode_arena_allocable(decoder)
-            }
-        }
-
-        impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [$ty] {
-            #[inline]
-            fn decode(decoder: &mut D) -> &'tcx Self {
-                decode_arena_allocable_slice(decoder)
-            }
-        }
-    };
-}
-
-macro_rules! impl_arena_allocatable_decoders {
-    ([$($a:tt $name:ident: $ty:ty,)*]) => {
-        $(
-            impl_arena_allocatable_decoder!($a $name: $ty);
-        )*
-    }
-}
-
-rustc_hir::arena_types!(impl_arena_allocatable_decoders);
-arena_types!(impl_arena_allocatable_decoders);
-
-macro_rules! impl_arena_copy_decoder {
-    (<$tcx:tt> $($ty:ty,)*) => {
-        $(impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for $ty {
-            #[inline]
-            fn decode(decoder: &mut D) -> &'tcx Self {
-                decoder.interner().arena.alloc(Decodable::decode(decoder))
-            }
-        }
-
-        impl<'tcx, D: TyDecoder<'tcx>> RefDecodable<'tcx, D> for [$ty] {
-            #[inline]
-            fn decode(decoder: &mut D) -> &'tcx Self {
-                decoder.interner().arena.alloc_from_iter(<Vec<_> as Decodable<D>>::decode(decoder))
-            }
-        })*
-    };
-}
-
-impl_arena_copy_decoder! {<'tcx>
-    Span,
-    rustc_span::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),
-    rustc_middle::middle::deduced_param_attrs::DeducedParamAttrs,
-}
-
 #[macro_export]
 macro_rules! implement_ty_decoder {
     ($DecoderName:ident <$($typaram:tt),*>) => {