Auto merge of #59540 - Zoxc:the-arena-2, r=<try>

[WIP] Use arenas to avoid Lrc in queries #1

Based on #59536.

Cargo.lock

@@ -2812,6 +2812,7 @@ 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",

src/librustc/arena.rs

@@ -16,6 +16,7 @@ macro_rules! arena_types {
             )>,
             [few] mir_keys: rustc::util::nodemap::DefIdSet,
             [decode] specialization_graph: rustc::traits::specialization_graph::Graph,
+            [few] crate_inherent_impls: rustc::ty::CrateInherentImpls,
         ], $tcx);
     )
 }

src/librustc/query/mod.rs

@@ -174,7 +174,7 @@ rustc_queries! {
 
         /// Returns the inferred outlives predicates (e.g., for `struct
         /// Foo<'a, T> { x: &'a T }`, this would return `T: 'a`).
-        query inferred_outlives_of(_: DefId) -> Lrc<Vec<ty::Predicate<'tcx>>> {}
+        query inferred_outlives_of(_: DefId) -> &'tcx [ty::Predicate<'tcx>] {}
 
         /// Maps from the `DefId` of a trait to the list of
         /// super-predicates. This is a subset of the full list of
@@ -240,13 +240,13 @@ rustc_queries! {
 
         /// Get a map with the variance of every item; use `item_variance`
         /// instead.
-        query crate_variances(_: CrateNum) -> Lrc<ty::CrateVariancesMap> {
+        query crate_variances(_: CrateNum) -> Lrc<ty::CrateVariancesMap<'tcx>> {
             desc { "computing the variances for items in this crate" }
         }
 
         /// Maps from def-id of a type or region parameter to its
         /// (inferred) variance.
-        query variances_of(_: DefId) -> Lrc<Vec<ty::Variance>> {}
+        query variances_of(_: DefId) -> &'tcx [ty::Variance] {}
     }
 
     TypeChecking {
@@ -259,7 +259,7 @@ 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 {}
@@ -274,7 +274,7 @@ 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
         }
     }
@@ -380,7 +380,7 @@ 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 }
         }

src/librustc/ty/mod.rs

@@ -330,15 +330,11 @@ pub enum Variance {
 /// `tcx.variances_of()` to get the variance for a *particular*
 /// item.
 #[derive(HashStable)]
-pub struct CrateVariancesMap {
+pub struct CrateVariancesMap<'tcx> {
     /// For each item with generics, maps to a vector of the variance
     /// of its generics. If an item has no generics, it will have no
     /// entry.
-    pub variances: FxHashMap<DefId, Lrc<Vec<ty::Variance>>>,
-
-    /// An empty vector, useful for cloning.
-    #[stable_hasher(ignore)]
-    pub empty_variance: Lrc<Vec<ty::Variance>>,
+    pub variances: FxHashMap<DefId, &'tcx [ty::Variance]>,
 }
 
 impl Variance {
@@ -1110,11 +1106,7 @@ pub struct CratePredicatesMap<'tcx> {
     /// For each struct with outlive bounds, maps to a vector of the
     /// predicate of its outlive bounds. If an item has no outlives
     /// bounds, it will have no entry.
-    pub predicates: FxHashMap<DefId, Lrc<Vec<ty::Predicate<'tcx>>>>,
-
-    /// An empty vector, useful for cloning.
-    #[stable_hasher(ignore)]
-    pub empty_predicate: Lrc<Vec<ty::Predicate<'tcx>>>,
+    pub predicates: FxHashMap<DefId, &'tcx [ty::Predicate<'tcx>]>,
 }
 
 impl<'tcx> AsRef<Predicate<'tcx>> for Predicate<'tcx> {
@@ -3091,7 +3083,7 @@ 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,
 }
 
@@ -3180,26 +3172,27 @@ 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 {
@@ -3385,7 +3378,7 @@ 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)]

src/librustc/ty/relate.rs

@@ -60,7 +60,7 @@ pub trait TypeRelation<'a, 'gcx: 'a+'tcx, 'tcx: 'a> : Sized {
                b_subst);
 
         let opt_variances = self.tcx().variances_of(item_def_id);
-        relate_substs(self, Some(&opt_variances), a_subst, b_subst)
+        relate_substs(self, Some(opt_variances), a_subst, b_subst)
     }
 
     /// Switch variance for the purpose of relating `a` and `b`.
@@ -122,7 +122,7 @@ impl<'tcx> Relate<'tcx> for ty::TypeAndMut<'tcx> {
 }
 
 pub fn relate_substs<'a, 'gcx, 'tcx, R>(relation: &mut R,
-                                        variances: Option<&Vec<ty::Variance>>,
+                                        variances: Option<&[ty::Variance]>,
                                         a_subst: SubstsRef<'tcx>,
                                         b_subst: SubstsRef<'tcx>)
                                         -> RelateResult<'tcx, SubstsRef<'tcx>>

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" }

src/librustc_metadata/cstore_impl.rs

@@ -20,6 +20,7 @@ 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;
@@ -105,12 +106,12 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         let _ = cdata;
         tcx.calculate_dtor(def_id, &mut |_,_| Ok(()))
     }
-    variances_of => { Lrc::new(cdata.get_item_variances(def_id.index)) }
+    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.def.def_id()), tcx.sess);
-        Lrc::new(result)
+        tcx.arena.alloc_from_iter(result)
     }
     associated_item => { cdata.get_associated_item(def_id.index) }
     impl_trait_ref => { cdata.get_impl_trait(def_id.index, tcx) }
@@ -133,7 +134,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         (cdata.mir_const_qualif(def_id.index), Lrc::new(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) }
     describe_def => { cdata.get_def(def_id.index) }

src/librustc_metadata/decoder.rs

@@ -998,12 +998,15 @@ 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,

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,

src/librustc_typeck/outlives/mod.rs

@@ -23,7 +23,7 @@ pub fn provide(providers: &mut Providers<'_>) {
 fn inferred_outlives_of<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     item_def_id: DefId,
-) -> Lrc<Vec<ty::Predicate<'tcx>>> {
+) -> &'tcx [ty::Predicate<'tcx>] {
     let id = tcx
         .hir()
         .as_local_hir_id(item_def_id)
@@ -37,8 +37,8 @@ fn inferred_outlives_of<'a, 'tcx>(
                 let predicates = crate_map
                     .predicates
                     .get(&item_def_id)
-                    .unwrap_or(&crate_map.empty_predicate)
-                    .clone();
+                    .map(|p| *p)
+                    .unwrap_or(&[]);
 
                 if tcx.has_attr(item_def_id, "rustc_outlives") {
                     let mut pred: Vec<String> = predicates
@@ -63,10 +63,10 @@ fn inferred_outlives_of<'a, 'tcx>(
                 predicates
             }
 
-            _ => Lrc::new(Vec::new()),
+            _ => &[],
         },
 
-        _ => Lrc::new(Vec::new()),
+        _ => &[],
     }
 }
 
@@ -96,7 +96,7 @@ fn inferred_outlives_crate<'tcx>(
     let predicates = global_inferred_outlives
         .iter()
         .map(|(&def_id, set)| {
-            let vec: Vec<ty::Predicate<'tcx>> = set
+            let predicates = tcx.arena.alloc_from_iter(set
                 .iter()
                 .filter_map(
                     |ty::OutlivesPredicate(kind1, region2)| match kind1.unpack() {
@@ -115,14 +115,11 @@ fn inferred_outlives_crate<'tcx>(
                             None
                         }
                     },
-                ).collect();
-            (def_id, Lrc::new(vec))
+                ));
+            (def_id, &*predicates)
         }).collect();
 
-    let empty_predicate = Lrc::new(Vec::new());
-
     Lrc::new(ty::CratePredicatesMap {
         predicates,
-        empty_predicate,
     })
 }

src/librustc_typeck/variance/mod.rs

@@ -36,7 +36,7 @@ pub fn provide(providers: &mut Providers<'_>) {
 }
 
 fn crate_variances<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum)
-                             -> Lrc<CrateVariancesMap> {
+                             -> Lrc<CrateVariancesMap<'tcx>> {
     assert_eq!(crate_num, LOCAL_CRATE);
     let mut arena = arena::TypedArena::default();
     let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena);
@@ -45,7 +45,7 @@ fn crate_variances<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, crate_num: CrateNum)
 }
 
 fn variances_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
-                          -> Lrc<Vec<ty::Variance>> {
+                          -> &'tcx [ty::Variance] {
     let id = tcx.hir().as_local_hir_id(item_def_id).expect("expected local def-id");
     let unsupported = || {
         // Variance not relevant.
@@ -88,6 +88,6 @@ fn variances_of<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item_def_id: DefId)
 
     let crate_map = tcx.crate_variances(LOCAL_CRATE);
     crate_map.variances.get(&item_def_id)
-                       .unwrap_or(&crate_map.empty_variance)
-                       .clone()
+                       .map(|p| *p)
+                       .unwrap_or(&[])
 }