diff --git a/Cargo.lock b/Cargo.lock
index db9f0069ced0c..7a7d8eecd71d9 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2877,6 +2877,7 @@ dependencies = [
  "rustc_errors 0.0.0",
  "rustc_target 0.0.0",
  "serialize 0.0.0",
+ "smallvec 0.6.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "stable_deref_trait 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntax 0.0.0",
  "syntax_ext 0.0.0",
diff --git a/src/libarena/lib.rs b/src/libarena/lib.rs
index ce5e5f23a94b8..d6bec816e4ee6 100644
--- a/src/libarena/lib.rs
+++ b/src/libarena/lib.rs
@@ -486,9 +486,31 @@ impl DroplessArena {
         }
     }
 
+    #[inline]
+    unsafe fn write_from_iter<T, I: Iterator<Item = T>>(
+        &self,
+        mut iter: I,
+        len: usize,
+        mem: *mut T,
+    ) -> &mut [T] {
+        let mut i = 0;
+        // Use a manual loop since LLVM manages to optimize it better for
+        // slice iterators
+        loop {
+            let value = iter.next();
+            if i >= len || value.is_none() {
+                // We only return as many items as the iterator gave us, even
+                // though it was supposed to give us `len`
+                return slice::from_raw_parts_mut(mem, i);
+            }
+            ptr::write(mem.offset(i as isize), value.unwrap());
+            i += 1;
+        }
+    }
+
     #[inline]
     pub fn alloc_from_iter<T, I: IntoIterator<Item = T>>(&self, iter: I) -> &mut [T] {
-        let mut iter = iter.into_iter();
+        let iter = iter.into_iter();
         assert!(mem::size_of::<T>() != 0);
         assert!(!mem::needs_drop::<T>());
 
@@ -505,10 +527,7 @@ impl DroplessArena {
                 let size = len.checked_mul(mem::size_of::<T>()).unwrap();
                 let mem = self.alloc_raw(size, mem::align_of::<T>()) as *mut _ as *mut T;
                 unsafe {
-                    for i in 0..len {
-                        ptr::write(mem.offset(i as isize), iter.next().unwrap())
-                    }
-                    slice::from_raw_parts_mut(mem, len)
+                    self.write_from_iter(iter, len, mem)
                 }
             }
             (_, _) => {
diff --git a/src/librustc/arena.rs b/src/librustc/arena.rs
index b48d81f2ef8f4..d2797e652407b 100644
--- a/src/librustc/arena.rs
+++ b/src/librustc/arena.rs
@@ -6,6 +6,15 @@ use std::cell::RefCell;
 use std::marker::PhantomData;
 use smallvec::SmallVec;
 
+/// This declares a list of types which can be allocated by `Arena`.
+///
+/// The `few` modifier will cause allocation to use the shared arena and recording the destructor.
+/// This is faster and more memory efficient if there's only a few allocations of the type.
+/// Leaving `few` out will cause the type to get its own dedicated `TypedArena` which is
+/// faster and more memory efficient if there is lots of allocations.
+///
+/// Specifying the `decode` modifier will add decode impls for &T and &[T] where T is the type
+/// listed. These impls will appear in the implement_ty_decoder! macro.
 #[macro_export]
 macro_rules! arena_types {
     ($macro:path, $args:tt, $tcx:lifetime) => (
@@ -14,7 +23,7 @@ macro_rules! arena_types {
                 rustc::hir::def_id::DefId,
                 rustc::ty::subst::SubstsRef<$tcx>
             )>,
-            [few] mir_keys: rustc::util::nodemap::DefIdSet,
+            [few, decode] mir_keys: rustc::util::nodemap::DefIdSet,
             [decode] specialization_graph: rustc::traits::specialization_graph::Graph,
             [] region_scope_tree: rustc::middle::region::ScopeTree,
             [] item_local_set: rustc::util::nodemap::ItemLocalSet,
@@ -58,6 +67,17 @@ macro_rules! arena_types {
                 rustc::infer::canonical::Canonical<'tcx,
                     rustc::infer::canonical::QueryResponse<'tcx, rustc::ty::Ty<'tcx>>
                 >,
+            [few] crate_inherent_impls: rustc::ty::CrateInherentImpls,
+            [decode] borrowck: rustc::middle::borrowck::BorrowCheckResult,
+            [few] upstream_monomorphizations:
+                rustc::util::nodemap::DefIdMap<
+                    rustc_data_structures::fx::FxHashMap<
+                        rustc::ty::subst::SubstsRef<'tcx>,
+                        rustc::hir::def_id::CrateNum
+                    >
+                >,
+            [few] resolve_lifetimes: rustc::middle::resolve_lifetime::ResolveLifetimes,
+            [decode] generic_predicates: rustc::ty::GenericPredicates<'tcx>,
         ], $tcx);
     )
 }
@@ -119,7 +139,7 @@ pub trait ArenaAllocatable {}
 
 impl<T: Copy> ArenaAllocatable for T {}
 
-pub unsafe trait ArenaField<'tcx>: Sized {
+unsafe trait ArenaField<'tcx>: Sized {
     /// Returns a specific arena to allocate from.
     /// If None is returned, the DropArena will be used.
     fn arena<'a>(arena: &'a Arena<'tcx>) -> Option<&'a TypedArena<Self>>;
diff --git a/src/librustc/middle/resolve_lifetime.rs b/src/librustc/middle/resolve_lifetime.rs
index 2402d0eefde48..7d645e3880caf 100644
--- a/src/librustc/middle/resolve_lifetime.rs
+++ b/src/librustc/middle/resolve_lifetime.rs
@@ -15,7 +15,6 @@ use crate::rustc::lint;
 use crate::session::Session;
 use crate::util::nodemap::{DefIdMap, FxHashMap, FxHashSet, HirIdMap, HirIdSet};
 use errors::{Applicability, DiagnosticBuilder};
-use rustc_data_structures::sync::Lrc;
 use rustc_macros::HashStable;
 use std::borrow::Cow;
 use std::cell::Cell;
@@ -211,10 +210,10 @@ struct NamedRegionMap {
 /// See [`NamedRegionMap`].
 #[derive(Default)]
 pub struct ResolveLifetimes {
-    defs: FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Region>>>,
-    late_bound: FxHashMap<LocalDefId, Lrc<FxHashSet<ItemLocalId>>>,
+    defs: FxHashMap<LocalDefId, FxHashMap<ItemLocalId, Region>>,
+    late_bound: FxHashMap<LocalDefId, FxHashSet<ItemLocalId>>,
     object_lifetime_defaults:
-        FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
+        FxHashMap<LocalDefId, FxHashMap<ItemLocalId, Vec<ObjectLifetimeDefault>>>,
 }
 
 impl_stable_hash_for!(struct crate::middle::resolve_lifetime::ResolveLifetimes {
@@ -347,7 +346,7 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
 
         named_region_map: |tcx, id| {
             let id = LocalDefId::from_def_id(DefId::local(id)); // (*)
-            tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id).cloned()
+            tcx.resolve_lifetimes(LOCAL_CRATE).defs.get(&id)
         },
 
         is_late_bound_map: |tcx, id| {
@@ -355,7 +354,6 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
             tcx.resolve_lifetimes(LOCAL_CRATE)
                 .late_bound
                 .get(&id)
-                .cloned()
         },
 
         object_lifetime_defaults_map: |tcx, id| {
@@ -363,7 +361,6 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
             tcx.resolve_lifetimes(LOCAL_CRATE)
                 .object_lifetime_defaults
                 .get(&id)
-                .cloned()
         },
 
         ..*providers
@@ -379,7 +376,7 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
 fn resolve_lifetimes<'tcx>(
     tcx: TyCtxt<'_, 'tcx, 'tcx>,
     for_krate: CrateNum,
-) -> Lrc<ResolveLifetimes> {
+) -> &'tcx ResolveLifetimes {
     assert_eq!(for_krate, LOCAL_CRATE);
 
     let named_region_map = krate(tcx);
@@ -388,24 +385,22 @@ fn resolve_lifetimes<'tcx>(
 
     for (hir_id, v) in named_region_map.defs {
         let map = rl.defs.entry(hir_id.owner_local_def_id()).or_default();
-        Lrc::get_mut(map).unwrap().insert(hir_id.local_id, v);
+        map.insert(hir_id.local_id, v);
     }
     for hir_id in named_region_map.late_bound {
         let map = rl.late_bound
             .entry(hir_id.owner_local_def_id())
             .or_default();
-        Lrc::get_mut(map).unwrap().insert(hir_id.local_id);
+        map.insert(hir_id.local_id);
     }
     for (hir_id, v) in named_region_map.object_lifetime_defaults {
         let map = rl.object_lifetime_defaults
             .entry(hir_id.owner_local_def_id())
             .or_default();
-        Lrc::get_mut(map)
-            .unwrap()
-            .insert(hir_id.local_id, Lrc::new(v));
+        map.insert(hir_id.local_id, v);
     }
 
-    Lrc::new(rl)
+    tcx.arena.alloc(rl)
 }
 
 fn krate<'tcx>(tcx: TyCtxt<'_, 'tcx, 'tcx>) -> NamedRegionMap {
diff --git a/src/librustc/query/mod.rs b/src/librustc/query/mod.rs
index 2fff4c3f109b1..64b20105da601 100644
--- a/src/librustc/query/mod.rs
+++ b/src/librustc/query/mod.rs
@@ -61,7 +61,7 @@ rustc_queries! {
         /// predicate gets in the way of some checks, which are intended
         /// to operate over only the actual where-clauses written by the
         /// user.)
-        query predicates_of(_: DefId) -> Lrc<ty::GenericPredicates<'tcx>> {}
+        query predicates_of(_: DefId) -> &'tcx ty::GenericPredicates<'tcx> {}
 
         query native_libraries(_: CrateNum) -> Lrc<Vec<NativeLibrary>> {
             desc { "looking up the native libraries of a linked crate" }
@@ -166,11 +166,11 @@ rustc_queries! {
         /// equal to the `explicit_predicates_of` predicates plus the
         /// `inferred_outlives_of` predicates.
         query predicates_defined_on(_: DefId)
-            -> Lrc<ty::GenericPredicates<'tcx>> {}
+            -> &'tcx ty::GenericPredicates<'tcx> {}
 
         /// Returns the predicates written explicit by the user.
         query explicit_predicates_of(_: DefId)
-            -> Lrc<ty::GenericPredicates<'tcx>> {}
+            -> &'tcx ty::GenericPredicates<'tcx> {}
 
         /// Returns the inferred outlives predicates (e.g., for `struct
         /// Foo<'a, T> { x: &'a T }`, this would return `T: 'a`).
@@ -182,14 +182,14 @@ rustc_queries! {
         /// evaluate them even during type conversion, often before the
         /// full predicates are available (note that supertraits have
         /// additional acyclicity requirements).
-        query super_predicates_of(key: DefId) -> Lrc<ty::GenericPredicates<'tcx>> {
+        query super_predicates_of(key: DefId) -> &'tcx ty::GenericPredicates<'tcx> {
             desc { |tcx| "computing the supertraits of `{}`", tcx.def_path_str(key) }
         }
 
         /// To avoid cycles within the predicates of a single item we compute
         /// per-type-parameter predicates for resolving `T::AssocTy`.
         query type_param_predicates(key: (DefId, DefId))
-            -> Lrc<ty::GenericPredicates<'tcx>> {
+            -> &'tcx ty::GenericPredicates<'tcx> {
             no_force
             desc { |tcx| "computing the bounds for type parameter `{}`", {
                 let id = tcx.hir().as_local_hir_id(key.1).unwrap();
@@ -264,7 +264,7 @@ rustc_queries! {
 
     Other {
         /// Maps from an impl/trait def-id to a list of the def-ids of its items
-        query associated_item_def_ids(_: DefId) -> Lrc<Vec<DefId>> {}
+        query associated_item_def_ids(_: DefId) -> &'tcx [DefId] {}
 
         /// Maps from a trait item to the trait item "descriptor"
         query associated_item(_: DefId) -> ty::AssociatedItem {}
@@ -279,7 +279,7 @@ rustc_queries! {
         /// Maps a DefId of a type to a list of its inherent impls.
         /// Contains implementations of methods that are inherent to a type.
         /// Methods in these implementations don't need to be exported.
-        query inherent_impls(_: DefId) -> Lrc<Vec<DefId>> {
+        query inherent_impls(_: DefId) -> &'tcx [DefId] {
             eval_always
         }
     }
@@ -361,7 +361,7 @@ rustc_queries! {
     }
 
     Other {
-        query used_trait_imports(_: DefId) -> Lrc<DefIdSet> {}
+        query used_trait_imports(_: DefId) -> &'tcx DefIdSet {}
     }
 
     TypeChecking {
@@ -373,7 +373,7 @@ rustc_queries! {
     }
 
     BorrowChecking {
-        query borrowck(_: DefId) -> Lrc<BorrowCheckResult> {}
+        query borrowck(_: DefId) -> &'tcx BorrowCheckResult {}
 
         /// Borrow checks the function body. If this is a closure, returns
         /// additional requirements that the closure's creator must verify.
@@ -385,7 +385,7 @@ rustc_queries! {
         /// Not meant to be used directly outside of coherence.
         /// (Defined only for `LOCAL_CRATE`.)
         query crate_inherent_impls(k: CrateNum)
-            -> Lrc<CrateInherentImpls> {
+            -> &'tcx CrateInherentImpls {
             eval_always
             desc { "all inherent impls defined in crate `{:?}`", k }
         }
@@ -683,11 +683,11 @@ rustc_queries! {
     Codegen {
         query upstream_monomorphizations(
             k: CrateNum
-        ) -> Lrc<DefIdMap<Lrc<FxHashMap<SubstsRef<'tcx>, CrateNum>>>> {
+        ) -> &'tcx DefIdMap<FxHashMap<SubstsRef<'tcx>, CrateNum>> {
             desc { "collecting available upstream monomorphizations `{:?}`", k }
         }
         query upstream_monomorphizations_for(_: DefId)
-            -> Option<Lrc<FxHashMap<SubstsRef<'tcx>, CrateNum>>> {}
+            -> Option<&'tcx FxHashMap<SubstsRef<'tcx>, CrateNum>> {}
     }
 
     Other {
@@ -726,12 +726,12 @@ rustc_queries! {
 
     TypeChecking {
         query implementations_of_trait(_: (CrateNum, DefId))
-            -> Lrc<Vec<DefId>> {
+            -> &'tcx [DefId] {
             no_force
             desc { "looking up implementations of a trait in a crate" }
         }
         query all_trait_implementations(_: CrateNum)
-            -> Lrc<Vec<DefId>> {
+            -> &'tcx [DefId] {
             desc { "looking up all (?) trait implementations" }
         }
     }
@@ -756,19 +756,19 @@ rustc_queries! {
 
     BorrowChecking {
         // Lifetime resolution. See `middle::resolve_lifetimes`.
-        query resolve_lifetimes(_: CrateNum) -> Lrc<ResolveLifetimes> {
+        query resolve_lifetimes(_: CrateNum) -> &'tcx ResolveLifetimes {
             desc { "resolving lifetimes" }
         }
         query named_region_map(_: DefIndex) ->
-            Option<Lrc<FxHashMap<ItemLocalId, Region>>> {
+            Option<&'tcx FxHashMap<ItemLocalId, Region>> {
             desc { "looking up a named region" }
         }
         query is_late_bound_map(_: DefIndex) ->
-            Option<Lrc<FxHashSet<ItemLocalId>>> {
+            Option<&'tcx FxHashSet<ItemLocalId>> {
             desc { "testing if a region is late bound" }
         }
         query object_lifetime_defaults_map(_: DefIndex)
-            -> Option<Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>> {
+            -> Option<&'tcx FxHashMap<ItemLocalId, Vec<ObjectLifetimeDefault>>> {
             desc { "looking up lifetime defaults for a region" }
         }
     }
@@ -786,7 +786,7 @@ rustc_queries! {
             eval_always
             desc { "fetching what a crate is named" }
         }
-        query item_children(_: DefId) -> Lrc<Vec<Export<hir::HirId>>> {}
+        query item_children(_: DefId) -> &'tcx [Export<hir::HirId>] {}
         query extern_mod_stmt_cnum(_: DefId) -> Option<CrateNum> {}
 
         query get_lib_features(_: CrateNum) -> Lrc<LibFeatures> {
diff --git a/src/librustc/ty/context.rs b/src/librustc/ty/context.rs
index c9fee02f66bbd..cccdfd13197c4 100644
--- a/src/librustc/ty/context.rs
+++ b/src/librustc/ty/context.rs
@@ -201,6 +201,10 @@ impl<'gcx: 'tcx, 'tcx> CtxtInterners<'tcx> {
     }
 }
 
+pub struct Common<'tcx> {
+    pub empty_predicates: ty::GenericPredicates<'tcx>,
+}
+
 pub struct CommonTypes<'tcx> {
     pub unit: Ty<'tcx>,
     pub bool: Ty<'tcx>,
@@ -1045,6 +1049,9 @@ pub struct GlobalCtxt<'tcx> {
 
     pub dep_graph: DepGraph,
 
+    /// Common objects.
+    pub common: Common<'tcx>,
+
     /// Common types, pre-interned for your convenience.
     pub types: CommonTypes<'tcx>,
 
@@ -1252,6 +1259,12 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             s.fatal(&err);
         });
         let interners = CtxtInterners::new(&arenas.interner);
+        let common = Common {
+            empty_predicates: ty::GenericPredicates {
+                parent: None,
+                predicates: vec![],
+            },
+        };
         let common_types = CommonTypes::new(&interners);
         let common_lifetimes = CommonLifetimes::new(&interners);
         let common_consts = CommonConsts::new(&interners, &common_types);
@@ -1308,6 +1321,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             global_arenas: &arenas.global,
             global_interners: interners,
             dep_graph,
+            common,
             types: common_types,
             lifetimes: common_lifetimes,
             consts: common_consts,
@@ -2982,10 +2996,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn object_lifetime_defaults(self, id: HirId)
-        -> Option<Lrc<Vec<ObjectLifetimeDefault>>>
+        -> Option<&'gcx [ObjectLifetimeDefault]>
     {
         self.object_lifetime_defaults_map(id.owner)
-            .and_then(|map| map.get(&id.local_id).cloned())
+            .and_then(|map| map.get(&id.local_id).map(|v| &**v))
     }
 }
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index 2f71861d4dc0d..0d22b8e0f4d5f 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -2298,7 +2298,7 @@ impl<'a, 'gcx, 'tcx> AdtDef {
     }
 
     #[inline]
-    pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> Lrc<GenericPredicates<'gcx>> {
+    pub fn predicates(&self, tcx: TyCtxt<'a, 'gcx, 'tcx>) -> &'tcx GenericPredicates<'gcx> {
         tcx.predicates_of(self.did)
     }
 
@@ -3106,7 +3106,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
 
 pub struct AssociatedItemsIterator<'a, 'gcx: 'tcx, 'tcx: 'a> {
     tcx: TyCtxt<'a, 'gcx, 'tcx>,
-    def_ids: Lrc<Vec<DefId>>,
+    def_ids: &'gcx [DefId],
     next_index: usize,
 }
 
@@ -3183,26 +3183,27 @@ fn adt_sized_constraint<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn associated_item_def_ids<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                      def_id: DefId)
-                                     -> Lrc<Vec<DefId>> {
+                                     -> &'tcx [DefId] {
     let id = tcx.hir().as_local_hir_id(def_id).unwrap();
     let item = tcx.hir().expect_item_by_hir_id(id);
-    let vec: Vec<_> = match item.node {
+    match item.node {
         hir::ItemKind::Trait(.., ref trait_item_refs) => {
-            trait_item_refs.iter()
-                           .map(|trait_item_ref| trait_item_ref.id)
-                           .map(|id| tcx.hir().local_def_id_from_hir_id(id.hir_id))
-                           .collect()
+            tcx.arena.alloc_from_iter(
+                trait_item_refs.iter()
+                               .map(|trait_item_ref| trait_item_ref.id)
+                               .map(|id| tcx.hir().local_def_id_from_hir_id(id.hir_id))
+            )
         }
         hir::ItemKind::Impl(.., ref impl_item_refs) => {
-            impl_item_refs.iter()
-                          .map(|impl_item_ref| impl_item_ref.id)
-                          .map(|id| tcx.hir().local_def_id_from_hir_id(id.hir_id))
-                          .collect()
+            tcx.arena.alloc_from_iter(
+                impl_item_refs.iter()
+                              .map(|impl_item_ref| impl_item_ref.id)
+                              .map(|id| tcx.hir().local_def_id_from_hir_id(id.hir_id))
+            )
         }
-        hir::ItemKind::TraitAlias(..) => vec![],
+        hir::ItemKind::TraitAlias(..) => &[],
         _ => span_bug!(item.span, "associated_item_def_ids: not impl or trait")
-    };
-    Lrc::new(vec)
+    }
 }
 
 fn def_span<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Span {
@@ -3388,7 +3389,7 @@ pub fn provide(providers: &mut ty::query::Providers<'_>) {
 /// (constructing this map requires touching the entire crate).
 #[derive(Clone, Debug, Default, HashStable)]
 pub struct CrateInherentImpls {
-    pub inherent_impls: DefIdMap<Lrc<Vec<DefId>>>,
+    pub inherent_impls: DefIdMap<Vec<DefId>>,
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, RustcEncodable, RustcDecodable)]
diff --git a/src/librustc/ty/query/values.rs b/src/librustc/ty/query/values.rs
index a4b8d365a12ef..8834bc9f0f70b 100644
--- a/src/librustc/ty/query/values.rs
+++ b/src/librustc/ty/query/values.rs
@@ -14,12 +14,6 @@ impl<'tcx, T> Value<'tcx> for T {
     }
 }
 
-impl<'tcx, T: Default> Value<'tcx> for T {
-    default fn from_cycle_error<'a>(_: TyCtxt<'a, 'tcx, 'tcx>) -> T {
-        T::default()
-    }
-}
-
 impl<'tcx> Value<'tcx> for Ty<'tcx> {
     fn from_cycle_error<'a>(tcx: TyCtxt<'a, 'tcx, 'tcx>) -> Ty<'tcx> {
         tcx.types.err
diff --git a/src/librustc_borrowck/borrowck/mod.rs b/src/librustc_borrowck/borrowck/mod.rs
index 65a550b1b8914..7dca47485bb92 100644
--- a/src/librustc_borrowck/borrowck/mod.rs
+++ b/src/librustc_borrowck/borrowck/mod.rs
@@ -32,7 +32,6 @@ use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
 use std::fmt;
 use std::rc::Rc;
-use rustc_data_structures::sync::Lrc;
 use std::hash::{Hash, Hasher};
 use syntax::source_map::CompilerDesugaringKind;
 use syntax_pos::{MultiSpan, Span};
@@ -75,7 +74,7 @@ pub struct AnalysisData<'a, 'tcx: 'a> {
 }
 
 fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
-    -> Lrc<BorrowCheckResult>
+    -> &'tcx BorrowCheckResult
 {
     assert!(tcx.use_ast_borrowck() || tcx.migrate_borrowck());
 
@@ -89,7 +88,7 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
             // those things (notably the synthesized constructors from
             // tuple structs/variants) do not have an associated body
             // and do not need borrowchecking.
-            return Lrc::new(BorrowCheckResult {
+            return tcx.arena.alloc(BorrowCheckResult {
                 used_mut_nodes: Default::default(),
                 signalled_any_error: SignalledError::NoErrorsSeen,
             })
@@ -136,7 +135,7 @@ fn borrowck<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, owner_def_id: DefId)
         check_loans::check_loans(&mut bccx, &loan_dfcx, &flowed_moves, &all_loans, body);
     }
 
-    Lrc::new(BorrowCheckResult {
+    tcx.arena.alloc(BorrowCheckResult {
         used_mut_nodes: bccx.used_mut_nodes.into_inner(),
         signalled_any_error: bccx.signalled_any_error.into_inner(),
     })
diff --git a/src/librustc_codegen_ssa/back/symbol_export.rs b/src/librustc_codegen_ssa/back/symbol_export.rs
index a55f783df43a3..616049ea112a4 100644
--- a/src/librustc_codegen_ssa/back/symbol_export.rs
+++ b/src/librustc_codegen_ssa/back/symbol_export.rs
@@ -282,7 +282,7 @@ fn exported_symbols_provider_local<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 fn upstream_monomorphizations_provider<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     cnum: CrateNum)
-    -> Lrc<DefIdMap<Lrc<FxHashMap<SubstsRef<'tcx>, CrateNum>>>>
+    -> &'tcx DefIdMap<FxHashMap<SubstsRef<'tcx>, CrateNum>>
 {
     debug_assert!(cnum == LOCAL_CRATE);
 
@@ -326,20 +326,16 @@ fn upstream_monomorphizations_provider<'a, 'tcx>(
         }
     }
 
-    Lrc::new(instances.into_iter()
-                      .map(|(key, value)| (key, Lrc::new(value)))
-                      .collect())
+    tcx.arena.alloc(instances)
 }
 
 fn upstream_monomorphizations_for_provider<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId)
-    -> Option<Lrc<FxHashMap<SubstsRef<'tcx>, CrateNum>>>
+    -> Option<&'tcx FxHashMap<SubstsRef<'tcx>, CrateNum>>
 {
     debug_assert!(!def_id.is_local());
-    tcx.upstream_monomorphizations(LOCAL_CRATE)
-       .get(&def_id)
-       .cloned()
+    tcx.upstream_monomorphizations(LOCAL_CRATE).get(&def_id)
 }
 
 fn is_unreachable_local_definition_provider(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) -> bool {
diff --git a/src/librustc_metadata/Cargo.toml b/src/librustc_metadata/Cargo.toml
index e234f4f880703..76aba33b6a404 100644
--- a/src/librustc_metadata/Cargo.toml
+++ b/src/librustc_metadata/Cargo.toml
@@ -13,6 +13,7 @@ crate-type = ["dylib"]
 flate2 = "1.0"
 log = "0.4"
 memmap = "0.6"
+smallvec = { version = "0.6.7", features = ["union", "may_dangle"] }
 rustc = { path = "../librustc" }
 rustc_data_structures = { path = "../librustc_data_structures" }
 errors = { path = "../librustc_errors", package = "rustc_errors" }
diff --git a/src/librustc_metadata/cstore_impl.rs b/src/librustc_metadata/cstore_impl.rs
index 087256a971056..19db99a1e185d 100644
--- a/src/librustc_metadata/cstore_impl.rs
+++ b/src/librustc_metadata/cstore_impl.rs
@@ -21,6 +21,7 @@ use rustc::hir::map::definitions::DefPathTable;
 use rustc::util::nodemap::DefIdMap;
 use rustc_data_structures::svh::Svh;
 
+use smallvec::SmallVec;
 use std::any::Any;
 use rustc_data_structures::sync::Lrc;
 use std::sync::Arc;
@@ -95,9 +96,11 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     generics_of => {
         tcx.alloc_generics(cdata.get_generics(def_id.index, tcx.sess))
     }
-    predicates_of => { Lrc::new(cdata.get_predicates(def_id.index, tcx)) }
-    predicates_defined_on => { Lrc::new(cdata.get_predicates_defined_on(def_id.index, tcx)) }
-    super_predicates_of => { Lrc::new(cdata.get_super_predicates(def_id.index, tcx)) }
+    predicates_of => { tcx.arena.alloc(cdata.get_predicates(def_id.index, tcx)) }
+    predicates_defined_on => {
+        tcx.arena.alloc(cdata.get_predicates_defined_on(def_id.index, tcx))
+    }
+    super_predicates_of => { tcx.arena.alloc(cdata.get_super_predicates(def_id.index, tcx)) }
     trait_def => {
         tcx.alloc_trait_def(cdata.get_trait_def(def_id.index, tcx.sess))
     }
@@ -108,10 +111,10 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     }
     variances_of => { tcx.arena.alloc_from_iter(cdata.get_item_variances(def_id.index)) }
     associated_item_def_ids => {
-        let mut result = vec![];
+        let mut result = SmallVec::<[_; 8]>::new();
         cdata.each_child_of_item(def_id.index,
           |child| result.push(child.res.def_id()), tcx.sess);
-        Lrc::new(result)
+        tcx.arena.alloc_slice(&result)
     }
     associated_item => { cdata.get_associated_item(def_id.index) }
     impl_trait_ref => { cdata.get_impl_trait(def_id.index, tcx) }
@@ -134,7 +137,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         (cdata.mir_const_qualif(def_id.index), tcx.arena.alloc(BitSet::new_empty(0)))
     }
     fn_sig => { cdata.fn_sig(def_id.index, tcx) }
-    inherent_impls => { Lrc::new(cdata.get_inherent_implementations_for_type(def_id.index)) }
+    inherent_impls => { cdata.get_inherent_implementations_for_type(tcx, def_id.index) }
     is_const_fn_raw => { cdata.is_const_fn_raw(def_id.index) }
     is_foreign_item => { cdata.is_foreign_item(def_id.index) }
     static_mutability => { cdata.static_mutability(def_id.index) }
@@ -207,18 +210,12 @@ provide! { <'tcx> tcx, def_id, other, cdata,
 
     extra_filename => { cdata.root.extra_filename.clone() }
 
-
     implementations_of_trait => {
-        let mut result = vec![];
-        let filter = Some(other);
-        cdata.get_implementations_for_trait(filter, &mut result);
-        Lrc::new(result)
+        cdata.get_implementations_for_trait(tcx, Some(other))
     }
 
     all_trait_implementations => {
-        let mut result = vec![];
-        cdata.get_implementations_for_trait(None, &mut result);
-        Lrc::new(result)
+        cdata.get_implementations_for_trait(tcx, None)
     }
 
     visibility => { cdata.get_visibility(def_id.index) }
@@ -228,9 +225,9 @@ provide! { <'tcx> tcx, def_id, other, cdata,
     }
     crate_name => { cdata.name }
     item_children => {
-        let mut result = vec![];
+        let mut result = SmallVec::<[_; 8]>::new();
         cdata.each_child_of_item(def_id.index, |child| result.push(child), tcx.sess);
-        Lrc::new(result)
+        tcx.arena.alloc_slice(&result)
     }
     defined_lib_features => { Lrc::new(cdata.get_lib_features()) }
     defined_lang_items => { Lrc::new(cdata.get_lang_items()) }
diff --git a/src/librustc_metadata/decoder.rs b/src/librustc_metadata/decoder.rs
index d882fe6f27ecc..31d0b56e48eda 100644
--- a/src/librustc_metadata/decoder.rs
+++ b/src/librustc_metadata/decoder.rs
@@ -1012,39 +1012,45 @@ impl<'a, 'tcx> CrateMetadata {
         None
     }
 
-    pub fn get_inherent_implementations_for_type(&self, id: DefIndex) -> Vec<DefId> {
-        self.entry(id)
-            .inherent_impls
-            .decode(self)
-            .map(|index| self.local_def_id(index))
-            .collect()
+    pub fn get_inherent_implementations_for_type(
+        &self,
+        tcx: TyCtxt<'_, 'tcx, '_>,
+        id: DefIndex
+    ) -> &'tcx [DefId] {
+        tcx.arena.alloc_from_iter(self.entry(id)
+                                      .inherent_impls
+                                      .decode(self)
+                                      .map(|index| self.local_def_id(index)))
     }
 
-    pub fn get_implementations_for_trait(&self,
-                                         filter: Option<DefId>,
-                                         result: &mut Vec<DefId>) {
+    pub fn get_implementations_for_trait(
+        &self,
+        tcx: TyCtxt<'_, 'tcx, '_>,
+        filter: Option<DefId>,
+    ) -> &'tcx [DefId] {
         if self.proc_macros.is_some() {
             // proc-macro crates export no trait impls.
-            return
+            return &[]
         }
 
         // Do a reverse lookup beforehand to avoid touching the crate_num
         // hash map in the loop below.
         let filter = match filter.map(|def_id| self.reverse_translate_def_id(def_id)) {
             Some(Some(def_id)) => Some((def_id.krate.as_u32(), def_id.index)),
-            Some(None) => return,
+            Some(None) => return &[],
             None => None,
         };
 
         if let Some(filter) = filter {
-            if let Some(impls) = self.trait_impls
-                                     .get(&filter) {
-                result.extend(impls.decode(self).map(|idx| self.local_def_id(idx)));
+            if let Some(impls) = self.trait_impls.get(&filter) {
+                tcx.arena.alloc_from_iter(impls.decode(self).map(|idx| self.local_def_id(idx)))
+            } else {
+                &[]
             }
         } else {
-            for impls in self.trait_impls.values() {
-                result.extend(impls.decode(self).map(|idx| self.local_def_id(idx)));
-            }
+            tcx.arena.alloc_from_iter(self.trait_impls.values().flat_map(|impls| {
+                impls.decode(self).map(|idx| self.local_def_id(idx))
+            }))
         }
     }
 
diff --git a/src/librustc_privacy/lib.rs b/src/librustc_privacy/lib.rs
index cd21713cddf97..cfeff4d193a09 100644
--- a/src/librustc_privacy/lib.rs
+++ b/src/librustc_privacy/lib.rs
@@ -67,7 +67,7 @@ trait DefIdVisitor<'a, 'tcx: 'a> {
     fn visit_trait(&mut self, trait_ref: TraitRef<'tcx>) -> bool {
         self.skeleton().visit_trait(trait_ref)
     }
-    fn visit_predicates(&mut self, predicates: Lrc<ty::GenericPredicates<'tcx>>) -> bool {
+    fn visit_predicates(&mut self, predicates: &ty::GenericPredicates<'tcx>) -> bool {
         self.skeleton().visit_predicates(predicates)
     }
 }
@@ -89,8 +89,8 @@ impl<'a, 'tcx, V> DefIdVisitorSkeleton<'_, 'a, 'tcx, V>
         (!self.def_id_visitor.shallow() && substs.visit_with(self))
     }
 
-    fn visit_predicates(&mut self, predicates: Lrc<ty::GenericPredicates<'tcx>>) -> bool {
-        let ty::GenericPredicates { parent: _, predicates } = &*predicates;
+    fn visit_predicates(&mut self, predicates: &ty::GenericPredicates<'tcx>) -> bool {
+        let ty::GenericPredicates { parent: _, predicates } = predicates;
         for (predicate, _span) in predicates {
             match predicate {
                 ty::Predicate::Trait(poly_predicate) => {
diff --git a/src/librustc_typeck/astconv.rs b/src/librustc_typeck/astconv.rs
index 4b052aec5fc2f..8032a95ea1ca1 100644
--- a/src/librustc_typeck/astconv.rs
+++ b/src/librustc_typeck/astconv.rs
@@ -17,7 +17,6 @@ use rustc::ty::{GenericParamDef, GenericParamDefKind};
 use rustc::ty::subst::{Kind, Subst, InternalSubsts, SubstsRef};
 use rustc::ty::wf::object_region_bounds;
 use rustc::mir::interpret::ConstValue;
-use rustc_data_structures::sync::Lrc;
 use rustc_target::spec::abi;
 use crate::require_c_abi_if_c_variadic;
 use smallvec::SmallVec;
@@ -46,7 +45,7 @@ pub trait AstConv<'gcx, 'tcx> {
     /// Returns the set of bounds in scope for the type parameter with
     /// the given id.
     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
-                                 -> Lrc<ty::GenericPredicates<'tcx>>;
+                                 -> &'tcx ty::GenericPredicates<'tcx>;
 
     /// What lifetime should we use when a lifetime is omitted (and not elided)?
     fn re_infer(&self, span: Span, _def: Option<&ty::GenericParamDef>)
diff --git a/src/librustc_typeck/check/mod.rs b/src/librustc_typeck/check/mod.rs
index 362b6f0504d99..1abea8a78678d 100644
--- a/src/librustc_typeck/check/mod.rs
+++ b/src/librustc_typeck/check/mod.rs
@@ -97,7 +97,6 @@ use crate::namespace::Namespace;
 use rustc::infer::{self, InferCtxt, InferOk, InferResult};
 use rustc::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
 use rustc_data_structures::indexed_vec::Idx;
-use rustc_data_structures::sync::Lrc;
 use rustc_target::spec::abi::Abi;
 use rustc::infer::opaque_types::OpaqueTypeDecl;
 use rustc::infer::type_variable::{TypeVariableOrigin};
@@ -808,8 +807,8 @@ fn has_typeck_tables<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
 fn used_trait_imports<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 def_id: DefId)
-                                -> Lrc<DefIdSet> {
-    tcx.typeck_tables_of(def_id).used_trait_imports.clone()
+                                -> &'tcx DefIdSet {
+    &*tcx.typeck_tables_of(def_id).used_trait_imports
 }
 
 fn typeck_tables_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
@@ -1907,7 +1906,7 @@ impl<'a, 'gcx, 'tcx> AstConv<'gcx, 'tcx> for FnCtxt<'a, 'gcx, 'tcx> {
     fn tcx<'b>(&'b self) -> TyCtxt<'b, 'gcx, 'tcx> { self.tcx }
 
     fn get_type_parameter_bounds(&self, _: Span, def_id: DefId)
-                                 -> Lrc<ty::GenericPredicates<'tcx>>
+                                 -> &'tcx ty::GenericPredicates<'tcx>
     {
         let tcx = self.tcx;
         let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
@@ -1915,7 +1914,7 @@ impl<'a, 'gcx, 'tcx> AstConv<'gcx, 'tcx> for FnCtxt<'a, 'gcx, 'tcx> {
         let item_def_id = tcx.hir().local_def_id_from_hir_id(item_id);
         let generics = tcx.generics_of(item_def_id);
         let index = generics.param_def_id_to_index[&def_id];
-        Lrc::new(ty::GenericPredicates {
+        tcx.arena.alloc(ty::GenericPredicates {
             parent: None,
             predicates: self.param_env.caller_bounds.iter().filter_map(|&predicate| {
                 match predicate {
diff --git a/src/librustc_typeck/coherence/inherent_impls.rs b/src/librustc_typeck/coherence/inherent_impls.rs
index d167c7fcafbe4..644d95963e652 100644
--- a/src/librustc_typeck/coherence/inherent_impls.rs
+++ b/src/librustc_typeck/coherence/inherent_impls.rs
@@ -13,14 +13,13 @@ use rustc::hir;
 use rustc::hir::itemlikevisit::ItemLikeVisitor;
 use rustc::ty::{self, CrateInherentImpls, TyCtxt};
 
-use rustc_data_structures::sync::Lrc;
 use syntax::ast;
 use syntax_pos::Span;
 
 /// On-demand query: yields a map containing all types mapped to their inherent impls.
 pub fn crate_inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                       crate_num: CrateNum)
-                                      -> Lrc<CrateInherentImpls> {
+                                      -> &'tcx CrateInherentImpls {
     assert_eq!(crate_num, LOCAL_CRATE);
 
     let krate = tcx.hir().krate();
@@ -29,13 +28,13 @@ pub fn crate_inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         impls_map: Default::default(),
     };
     krate.visit_all_item_likes(&mut collect);
-    Lrc::new(collect.impls_map)
+    tcx.arena.alloc(collect.impls_map)
 }
 
 /// On-demand query: yields a vector of the inherent impls for a specific type.
 pub fn inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                 ty_def_id: DefId)
-                                -> Lrc<Vec<DefId>> {
+                                -> &'tcx [DefId] {
     assert!(ty_def_id.is_local());
 
     // NB. Until we adopt the red-green dep-tracking algorithm (see
@@ -53,15 +52,11 @@ pub fn inherent_impls<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     //
     // [the plan]: https://github.com/rust-lang/rust-roadmap/issues/4
 
-    thread_local! {
-        static EMPTY_DEF_ID_VEC: Lrc<Vec<DefId>> = Lrc::new(vec![])
-    }
-
     let result = tcx.dep_graph.with_ignore(|| {
         let crate_map = tcx.crate_inherent_impls(ty_def_id.krate);
         match crate_map.inherent_impls.get(&ty_def_id) {
-            Some(v) => v.clone(),
-            None => EMPTY_DEF_ID_VEC.with(|v| v.clone())
+            Some(v) => &v[..],
+            None => &[],
         }
     });
 
@@ -289,13 +284,8 @@ impl<'a, 'tcx> InherentCollect<'a, 'tcx> {
             // type def ID, if there is a base type for this implementation and
             // the implementation does not have any associated traits.
             let impl_def_id = self.tcx.hir().local_def_id_from_hir_id(item.hir_id);
-            let mut rc_vec = self.impls_map.inherent_impls
-                                           .entry(def_id)
-                                           .or_default();
-
-            // At this point, there should not be any clones of the
-            // `Lrc`, so we can still safely push into it in place:
-            Lrc::get_mut(&mut rc_vec).unwrap().push(impl_def_id);
+            let vec = self.impls_map.inherent_impls.entry(def_id).or_default();
+            vec.push(impl_def_id);
         } else {
             struct_span_err!(self.tcx.sess,
                              item.span,
diff --git a/src/librustc_typeck/collect.rs b/src/librustc_typeck/collect.rs
index 6527e8655b5ef..498d7e561274c 100644
--- a/src/librustc_typeck/collect.rs
+++ b/src/librustc_typeck/collect.rs
@@ -31,7 +31,6 @@ use rustc::ty::{self, AdtKind, ToPolyTraitRef, Ty, TyCtxt};
 use rustc::ty::{ReprOptions, ToPredicate};
 use rustc::util::captures::Captures;
 use rustc::util::nodemap::FxHashMap;
-use rustc_data_structures::sync::Lrc;
 use rustc_target::spec::abi;
 
 use syntax::ast;
@@ -178,7 +177,7 @@ impl<'a, 'tcx> AstConv<'tcx, 'tcx> for ItemCtxt<'a, 'tcx> {
     }
 
     fn get_type_parameter_bounds(&self, span: Span, def_id: DefId)
-                                 -> Lrc<ty::GenericPredicates<'tcx>> {
+                                 -> &'tcx ty::GenericPredicates<'tcx> {
         self.tcx
             .at(span)
             .type_param_predicates((self.item_def_id, def_id))
@@ -243,7 +242,7 @@ impl<'a, 'tcx> AstConv<'tcx, 'tcx> for ItemCtxt<'a, 'tcx> {
 fn type_param_predicates<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     (item_def_id, def_id): (DefId, DefId),
-) -> Lrc<ty::GenericPredicates<'tcx>> {
+) -> &'tcx ty::GenericPredicates<'tcx> {
     use rustc::hir::*;
 
     // In the AST, bounds can derive from two places. Either
@@ -264,16 +263,11 @@ fn type_param_predicates<'a, 'tcx>(
         tcx.generics_of(item_def_id).parent
     };
 
-    let mut result = parent.map_or_else(
-        || Lrc::new(ty::GenericPredicates {
-            parent: None,
-            predicates: vec![],
-        }),
-        |parent| {
-            let icx = ItemCtxt::new(tcx, parent);
-            icx.get_type_parameter_bounds(DUMMY_SP, def_id)
-        },
-    );
+    let result = parent.map_or(&tcx.common.empty_predicates, |parent| {
+        let icx = ItemCtxt::new(tcx, parent);
+        icx.get_type_parameter_bounds(DUMMY_SP, def_id)
+    });
+    let mut extend = None;
 
     let item_hir_id = tcx.hir().as_local_hir_id(item_def_id).unwrap();
     let ast_generics = match tcx.hir().get_by_hir_id(item_hir_id) {
@@ -298,9 +292,7 @@ fn type_param_predicates<'a, 'tcx>(
                     // Implied `Self: Trait` and supertrait bounds.
                     if param_id == item_hir_id {
                         let identity_trait_ref = ty::TraitRef::identity(tcx, item_def_id);
-                        Lrc::make_mut(&mut result)
-                            .predicates
-                            .push((identity_trait_ref.to_predicate(), item.span));
+                        extend = Some((identity_trait_ref.to_predicate(), item.span));
                     }
                     generics
                 }
@@ -317,11 +309,12 @@ fn type_param_predicates<'a, 'tcx>(
     };
 
     let icx = ItemCtxt::new(tcx, item_def_id);
-    Lrc::make_mut(&mut result)
-        .predicates
-        .extend(icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty,
-            OnlySelfBounds(true)));
-    result
+    let mut result = (*result).clone();
+    result.predicates.extend(extend.into_iter());
+    result.predicates
+          .extend(icx.type_parameter_bounds_in_generics(ast_generics, param_id, ty,
+                  OnlySelfBounds(true)));
+    tcx.arena.alloc(result)
 }
 
 impl<'a, 'tcx> ItemCtxt<'a, 'tcx> {
@@ -690,7 +683,7 @@ fn adt_def<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> &'tcx ty::Ad
 fn super_predicates_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     trait_def_id: DefId,
-) -> Lrc<ty::GenericPredicates<'tcx>> {
+) -> &'tcx ty::GenericPredicates<'tcx> {
     debug!("super_predicates(trait_def_id={:?})", trait_def_id);
     let trait_hir_id = tcx.hir().as_local_hir_id(trait_def_id).unwrap();
 
@@ -734,7 +727,7 @@ fn super_predicates_of<'a, 'tcx>(
         }
     }
 
-    Lrc::new(ty::GenericPredicates {
+    tcx.arena.alloc(ty::GenericPredicates {
         parent: None,
         predicates: superbounds,
     })
@@ -1842,7 +1835,7 @@ fn early_bound_lifetimes_from_generics<'a, 'tcx>(
 fn predicates_defined_on<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId,
-) -> Lrc<ty::GenericPredicates<'tcx>> {
+) -> &'tcx ty::GenericPredicates<'tcx> {
     debug!("predicates_defined_on({:?})", def_id);
     let mut result = tcx.explicit_predicates_of(def_id);
     debug!(
@@ -1858,9 +1851,9 @@ fn predicates_defined_on<'a, 'tcx>(
             def_id,
             inferred_outlives,
         );
-        Lrc::make_mut(&mut result)
-            .predicates
-            .extend(inferred_outlives.iter().map(|&p| (p, span)));
+        let mut predicates = (*result).clone();
+        predicates.predicates.extend(inferred_outlives.iter().map(|&p| (p, span)));
+        result = tcx.arena.alloc(predicates);
     }
     debug!("predicates_defined_on({:?}) = {:?}", def_id, result);
     result
@@ -1872,7 +1865,7 @@ fn predicates_defined_on<'a, 'tcx>(
 fn predicates_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId,
-) -> Lrc<ty::GenericPredicates<'tcx>> {
+) -> &'tcx ty::GenericPredicates<'tcx> {
     let mut result = tcx.predicates_defined_on(def_id);
 
     if tcx.is_trait(def_id) {
@@ -1889,9 +1882,9 @@ fn predicates_of<'a, 'tcx>(
         // used, and adding the predicate into this list ensures
         // that this is done.
         let span = tcx.def_span(def_id);
-        Lrc::make_mut(&mut result)
-            .predicates
-            .push((ty::TraitRef::identity(tcx, def_id).to_predicate(), span));
+        let mut predicates = (*result).clone();
+        predicates.predicates.push((ty::TraitRef::identity(tcx, def_id).to_predicate(), span));
+        result = tcx.arena.alloc(predicates);
     }
     debug!("predicates_of(def_id={:?}) = {:?}", def_id, result);
     result
@@ -1902,7 +1895,7 @@ fn predicates_of<'a, 'tcx>(
 fn explicit_predicates_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     def_id: DefId,
-) -> Lrc<ty::GenericPredicates<'tcx>> {
+) -> &'tcx ty::GenericPredicates<'tcx> {
     use rustc::hir::*;
     use rustc_data_structures::fx::FxHashSet;
 
@@ -2017,7 +2010,7 @@ fn explicit_predicates_of<'a, 'tcx>(
 
                     if impl_trait_fn.is_some() {
                         // impl Trait
-                        return Lrc::new(ty::GenericPredicates {
+                        return tcx.arena.alloc(ty::GenericPredicates {
                             parent: None,
                             predicates: bounds.predicates(tcx, opaque_ty),
                         });
@@ -2228,7 +2221,7 @@ fn explicit_predicates_of<'a, 'tcx>(
         );
     }
 
-    let result = Lrc::new(ty::GenericPredicates {
+    let result = tcx.arena.alloc(ty::GenericPredicates {
         parent: generics.parent,
         predicates,
     });
diff --git a/src/librustdoc/clean/auto_trait.rs b/src/librustdoc/clean/auto_trait.rs
index 11e8192521d79..8e2460a14b87a 100644
--- a/src/librustdoc/clean/auto_trait.rs
+++ b/src/librustdoc/clean/auto_trait.rs
@@ -104,8 +104,10 @@ impl<'a, 'tcx> AutoTraitFinder<'a, 'tcx> {
                     // Instead, we generate `impl !Send for Foo<T>`, which better
                     // expresses the fact that `Foo<T>` never implements `Send`,
                     // regardless of the choice of `T`.
-                    let params = (self.cx.tcx.generics_of(param_env_def_id), &Default::default())
-                        .clean(self.cx).params;
+                    let params = (
+                        self.cx.tcx.generics_of(param_env_def_id),
+                        &&self.cx.tcx.common.empty_predicates,
+                    ).clean(self.cx).params;
 
                     Generics {
                         params,
diff --git a/src/librustdoc/clean/mod.rs b/src/librustdoc/clean/mod.rs
index f91cb469e4629..296ce53ceb6db 100644
--- a/src/librustdoc/clean/mod.rs
+++ b/src/librustdoc/clean/mod.rs
@@ -10,7 +10,6 @@ mod auto_trait;
 mod blanket_impl;
 
 use rustc_data_structures::indexed_vec::{IndexVec, Idx};
-use rustc_data_structures::sync::Lrc;
 use rustc_target::spec::abi::Abi;
 use rustc_typeck::hir_ty_to_ty;
 use rustc::infer::region_constraints::{RegionConstraintData, Constraint};
@@ -1690,7 +1689,7 @@ impl Clean<Generics> for hir::Generics {
 }
 
 impl<'a, 'tcx> Clean<Generics> for (&'a ty::Generics,
-                                    &'a Lrc<ty::GenericPredicates<'tcx>>) {
+                                    &'a &'tcx ty::GenericPredicates<'tcx>) {
     fn clean(&self, cx: &DocContext<'_>) -> Generics {
         use self::WherePredicate as WP;
 
@@ -4430,7 +4429,7 @@ pub fn path_to_def(tcx: TyCtxt<'_, '_, '_>, path: &[Symbol]) -> Option<DefId> {
         loop {
             let segment = path_it.next()?;
 
-            for item in mem::replace(&mut items, Lrc::new(vec![])).iter() {
+            for item in mem::replace(&mut items, &[]).iter() {
                 if item.ident.name == *segment {
                     if path_it.peek().is_none() {
                         return match item.res {
diff --git a/src/test/incremental/cyclic-trait-hierarchy.rs b/src/test/incremental/cyclic-trait-hierarchy.rs
index 4102eb32580f0..27287d06d54b1 100644
--- a/src/test/incremental/cyclic-trait-hierarchy.rs
+++ b/src/test/incremental/cyclic-trait-hierarchy.rs
@@ -7,7 +7,6 @@ pub trait T2 { }
 #[cfg(cfail2)]
 pub trait T2: T1 { }
 //[cfail2]~^ ERROR cycle detected when computing the supertraits of `T2`
-//[cfail2]~| ERROR cycle detected when computing the supertraits of `T2`
 
 pub trait T1: T2 { }
 
diff --git a/src/test/ui/cycle-projection-based-on-where-clause.rs b/src/test/ui/cycle-projection-based-on-where-clause.rs
index 336b67852cd01..d3609acfdff63 100644
--- a/src/test/ui/cycle-projection-based-on-where-clause.rs
+++ b/src/test/ui/cycle-projection-based-on-where-clause.rs
@@ -16,7 +16,6 @@ struct A<T>
     where T : Trait,
           T : Add<T::Item>
     //~^ ERROR cycle detected
-    //~| ERROR associated type `Item` not found for `T`
 {
     data: T
 }
diff --git a/src/test/ui/cycle-projection-based-on-where-clause.stderr b/src/test/ui/cycle-projection-based-on-where-clause.stderr
index e5a5e2897cd0a..59815138e2e36 100644
--- a/src/test/ui/cycle-projection-based-on-where-clause.stderr
+++ b/src/test/ui/cycle-projection-based-on-where-clause.stderr
@@ -11,13 +11,6 @@ note: cycle used when processing `A`
 LL |           T : Add<T::Item>
    |                   ^^^^^^^
 
-error[E0220]: associated type `Item` not found for `T`
-  --> $DIR/cycle-projection-based-on-where-clause.rs:17:19
-   |
-LL |           T : Add<T::Item>
-   |                   ^^^^^^^ associated type `Item` not found
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0220, E0391.
-For more information about an error, try `rustc --explain E0220`.
+For more information about this error, try `rustc --explain E0391`.
diff --git a/src/test/ui/issues/issue-20772.rs b/src/test/ui/issues/issue-20772.rs
index 36551e7014f10..1500bc831528a 100644
--- a/src/test/ui/issues/issue-20772.rs
+++ b/src/test/ui/issues/issue-20772.rs
@@ -1,6 +1,5 @@
 trait T : Iterator<Item=Self::Item>
 //~^ ERROR cycle detected
-//~| ERROR associated type `Item` not found for `Self`
 {}
 
 fn main() {}
diff --git a/src/test/ui/issues/issue-20772.stderr b/src/test/ui/issues/issue-20772.stderr
index 3b5dd975ce9e9..d64636310a368 100644
--- a/src/test/ui/issues/issue-20772.stderr
+++ b/src/test/ui/issues/issue-20772.stderr
@@ -3,7 +3,6 @@ error[E0391]: cycle detected when computing the supertraits of `T`
    |
 LL | / trait T : Iterator<Item=Self::Item>
 LL | |
-LL | |
 LL | | {}
    | |__^
    |
@@ -13,17 +12,9 @@ note: cycle used when collecting item types in top-level module
    |
 LL | / trait T : Iterator<Item=Self::Item>
 LL | |
-LL | |
 LL | | {}
    | |__^
 
-error[E0220]: associated type `Item` not found for `Self`
-  --> $DIR/issue-20772.rs:1:25
-   |
-LL | trait T : Iterator<Item=Self::Item>
-   |                         ^^^^^^^^^^ associated type `Item` not found
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0220, E0391.
-For more information about an error, try `rustc --explain E0220`.
+For more information about this error, try `rustc --explain E0391`.
diff --git a/src/test/ui/issues/issue-21177.rs b/src/test/ui/issues/issue-21177.rs
index 9d153696b885e..258e362d1317c 100644
--- a/src/test/ui/issues/issue-21177.rs
+++ b/src/test/ui/issues/issue-21177.rs
@@ -5,6 +5,5 @@ trait Trait {
 
 fn foo<T: Trait<A = T::B>>() { }
 //~^ ERROR cycle detected
-//~| ERROR associated type `B` not found for `T`
 
 fn main() { }
diff --git a/src/test/ui/issues/issue-21177.stderr b/src/test/ui/issues/issue-21177.stderr
index 6841fe85dd792..00d9a3c46a723 100644
--- a/src/test/ui/issues/issue-21177.stderr
+++ b/src/test/ui/issues/issue-21177.stderr
@@ -11,13 +11,6 @@ note: cycle used when processing `foo`
 LL | fn foo<T: Trait<A = T::B>>() { }
    |                     ^^^^
 
-error[E0220]: associated type `B` not found for `T`
-  --> $DIR/issue-21177.rs:6:21
-   |
-LL | fn foo<T: Trait<A = T::B>>() { }
-   |                     ^^^^ associated type `B` not found
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0220, E0391.
-For more information about an error, try `rustc --explain E0220`.
+For more information about this error, try `rustc --explain E0391`.
diff --git a/src/test/ui/issues/issue-23302-3.rs b/src/test/ui/issues/issue-23302-3.rs
index e17c5eea2a445..da75f33079886 100644
--- a/src/test/ui/issues/issue-23302-3.rs
+++ b/src/test/ui/issues/issue-23302-3.rs
@@ -1,5 +1,4 @@
 const A: i32 = B; //~ ERROR cycle detected
-//~^ ERROR cycle detected
 
 const B: i32 = A;
 
diff --git a/src/test/ui/issues/issue-23302-3.stderr b/src/test/ui/issues/issue-23302-3.stderr
index 94624640809b7..a7d643987f710 100644
--- a/src/test/ui/issues/issue-23302-3.stderr
+++ b/src/test/ui/issues/issue-23302-3.stderr
@@ -10,36 +10,18 @@ note: ...which requires checking which parts of `A` are promotable to static...
 LL | const A: i32 = B;
    |                ^
 note: ...which requires const checking if rvalue is promotable to static `B`...
-  --> $DIR/issue-23302-3.rs:4:1
+  --> $DIR/issue-23302-3.rs:3:1
    |
 LL | const B: i32 = A;
    | ^^^^^^^^^^^^^^^^^
 note: ...which requires checking which parts of `B` are promotable to static...
-  --> $DIR/issue-23302-3.rs:4:16
+  --> $DIR/issue-23302-3.rs:3:16
    |
 LL | const B: i32 = A;
    |                ^
    = note: ...which again requires const checking if rvalue is promotable to static `A`, completing the cycle
    = note: cycle used when running analysis passes on this crate
 
-error[E0391]: cycle detected when processing `A`
-  --> $DIR/issue-23302-3.rs:1:16
-   |
-LL | const A: i32 = B;
-   |                ^
-   |
-note: ...which requires processing `B`...
-  --> $DIR/issue-23302-3.rs:4:16
-   |
-LL | const B: i32 = A;
-   |                ^
-   = note: ...which again requires processing `A`, completing the cycle
-note: cycle used when processing `A`
-  --> $DIR/issue-23302-3.rs:1:1
-   |
-LL | const A: i32 = B;
-   | ^^^^^^^^^^^^^^^^^
-
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
 For more information about this error, try `rustc --explain E0391`.