Auto merge of #49645 - birkenfeld:unsized_rcs, r=<try>

Use Rc<str> and Rc<[T]> instead of Rc<String> and Rc<Vec<T>>

to save a bit of memory and pointer chasing.

For the `Vec<T>` case, there is one instance each of `get_mut` and `make_mut` that preclude the use of the slice type:

* the `get_mut` one does `push`, so I left it as is
* the `make_mut` one does a `reverse`, which would be fine but `Lrc<[T]>` does not impl `Clone` (should it?) - however, the reverse seems to be unnecessary - please if the solution makes sense

Had some unrelated-looking local test failures, let's see if if CI gets them too.

Author: bors

src/librustc/middle/cstore.rs

@@ -399,10 +399,9 @@ pub fn used_crates(tcx: TyCtxt, prefer: LinkagePreference)
             Some((cnum, path))
         })
         .collect::<Vec<_>>();
-    let mut ordering = tcx.postorder_cnums(LOCAL_CRATE);
-    Lrc::make_mut(&mut ordering).reverse();
+    let ordering = tcx.postorder_cnums(LOCAL_CRATE);
     libs.sort_by_key(|&(a, _)| {
-        ordering.iter().position(|x| *x == a)
+        ordering.iter().rev().position(|x| *x == a)
     });
     libs
 }

src/librustc/middle/resolve_lifetime.rs

@@ -217,7 +217,7 @@ pub struct ResolveLifetimes {
     defs: FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Region>>>,
     late_bound: FxHashMap<LocalDefId, Lrc<FxHashSet<ItemLocalId>>>,
     object_lifetime_defaults:
-        FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
+        FxHashMap<LocalDefId, Lrc<FxHashMap<ItemLocalId, Lrc<[ObjectLifetimeDefault]>>>>,
 }
 
 impl_stable_hash_for!(struct ::middle::resolve_lifetime::ResolveLifetimes {
@@ -406,7 +406,7 @@ fn resolve_lifetimes<'tcx>(
             .or_insert_with(|| Lrc::new(FxHashMap()));
         Lrc::get_mut(map)
             .unwrap()
-            .insert(hir_id.local_id, Lrc::new(v));
+            .insert(hir_id.local_id, Lrc::from(v));
     }
 
     Lrc::new(ResolveLifetimes {

src/librustc/traits/mod.rs

@@ -803,11 +803,11 @@ fn substitute_normalize_and_test_predicates<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx
 fn vtable_methods<'a, 'tcx>(
     tcx: TyCtxt<'a, 'tcx, 'tcx>,
     trait_ref: ty::PolyTraitRef<'tcx>)
-    -> Lrc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>
+    -> Lrc<[Option<(DefId, &'tcx Substs<'tcx>)>]>
 {
     debug!("vtable_methods({:?})", trait_ref);
 
-    Lrc::new(
+    Lrc::from(
         supertraits(tcx, trait_ref).flat_map(move |trait_ref| {
             let trait_methods = tcx.associated_items(trait_ref.def_id())
                 .filter(|item| item.kind == ty::AssociatedKind::Method);
@@ -850,7 +850,7 @@ fn vtable_methods<'a, 'tcx>(
 
                 Some((def_id, substs))
             })
-        }).collect()
+        }).collect::<Vec<_>>()
     )
 }
 

src/librustc/ty/context.rs

@@ -846,7 +846,7 @@ pub struct GlobalCtxt<'tcx> {
                                        Lrc<StableVec<TraitCandidate>>>>>,
 
     /// Export map produced by name resolution.
-    export_map: FxHashMap<DefId, Lrc<Vec<Export>>>,
+    export_map: FxHashMap<DefId, Lrc<[Export]>>,
 
     pub hir: hir_map::Map<'tcx>,
 
@@ -859,7 +859,7 @@ pub struct GlobalCtxt<'tcx> {
     // Records the free variables refrenced by every closure
     // expression. Do not track deps for this, just recompute it from
     // scratch every time.
-    freevars: FxHashMap<DefId, Lrc<Vec<hir::Freevar>>>,
+    freevars: FxHashMap<DefId, Lrc<[hir::Freevar]>>,
 
     maybe_unused_trait_imports: FxHashSet<DefId>,
 
@@ -1254,10 +1254,10 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
             types: common_types,
             trait_map,
             export_map: resolutions.export_map.into_iter().map(|(k, v)| {
-                (k, Lrc::new(v))
+                (k, Lrc::from(v))
             }).collect(),
             freevars: resolutions.freevars.into_iter().map(|(k, v)| {
-                (hir.local_def_id(k), Lrc::new(v))
+                (hir.local_def_id(k), Lrc::from(v))
             }).collect(),
             maybe_unused_trait_imports:
                 resolutions.maybe_unused_trait_imports
@@ -1335,7 +1335,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
         self.stability_index(LOCAL_CRATE)
     }
 
-    pub fn crates(self) -> Lrc<Vec<CrateNum>> {
+    pub fn crates(self) -> Lrc<[CrateNum]> {
         self.all_crate_nums(LOCAL_CRATE)
     }
 
@@ -2450,7 +2450,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     }
 
     pub fn object_lifetime_defaults(self, id: HirId)
-        -> Option<Lrc<Vec<ObjectLifetimeDefault>>>
+        -> Option<Lrc<[ObjectLifetimeDefault]>>
     {
         self.object_lifetime_defaults_map(id.owner)
             .and_then(|map| map.get(&id.local_id).cloned())
@@ -2529,7 +2529,7 @@ pub fn provide(providers: &mut ty::maps::Providers) {
     };
     providers.maybe_unused_extern_crates = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Lrc::new(tcx.maybe_unused_extern_crates.clone())
+        Lrc::from(tcx.maybe_unused_extern_crates.clone())
     };
 
     providers.stability_index = |tcx, cnum| {
@@ -2552,11 +2552,11 @@ pub fn provide(providers: &mut ty::maps::Providers) {
     };
     providers.all_crate_nums = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Lrc::new(tcx.cstore.crates_untracked())
+        Lrc::from(tcx.cstore.crates_untracked())
     };
     providers.postorder_cnums = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);
-        Lrc::new(tcx.cstore.postorder_cnums_untracked())
+        Lrc::from(tcx.cstore.postorder_cnums_untracked())
     };
     providers.output_filenames = |tcx, cnum| {
         assert_eq!(cnum, LOCAL_CRATE);

src/librustc/ty/maps/mod.rs

@@ -132,13 +132,13 @@ define_maps! { <'tcx>
 
     /// Maps from def-id of a type or region parameter to its
     /// (inferred) variance.
-    [] fn variances_of: ItemVariances(DefId) -> Lrc<Vec<ty::Variance>>,
+    [] fn variances_of: ItemVariances(DefId) -> Lrc<[ty::Variance]>,
 
     /// Maps from def-id of a type to its (inferred) outlives.
     [] fn inferred_outlives_of: InferredOutlivesOf(DefId) -> Vec<ty::Predicate<'tcx>>,
 
     /// Maps from an impl/trait def-id to a list of the def-ids of its items
-    [] fn associated_item_def_ids: AssociatedItemDefIds(DefId) -> Lrc<Vec<DefId>>,
+    [] fn associated_item_def_ids: AssociatedItemDefIds(DefId) -> Lrc<[DefId]>,
 
     /// Maps from a trait item to the trait item "descriptor"
     [] fn associated_item: AssociatedItems(DefId) -> ty::AssociatedItem,
@@ -252,7 +252,7 @@ define_maps! { <'tcx>
     [] fn rvalue_promotable_map: RvaluePromotableMap(DefId) -> Lrc<ItemLocalSet>,
     [] fn is_mir_available: IsMirAvailable(DefId) -> bool,
     [] fn vtable_methods: vtable_methods_node(ty::PolyTraitRef<'tcx>)
-                          -> Lrc<Vec<Option<(DefId, &'tcx Substs<'tcx>)>>>,
+                          -> Lrc<[Option<(DefId, &'tcx Substs<'tcx>)>]>,
 
     [] fn trans_fulfill_obligation: fulfill_obligation_dep_node(
         (ty::ParamEnv<'tcx>, ty::PolyTraitRef<'tcx>)) -> Vtable<'tcx, ()>,
@@ -279,7 +279,7 @@ define_maps! { <'tcx>
                                             ty::layout::LayoutError<'tcx>>,
 
     [] fn dylib_dependency_formats: DylibDepFormats(CrateNum)
-                                    -> Lrc<Vec<(CrateNum, LinkagePreference)>>,
+                                    -> Lrc<[(CrateNum, LinkagePreference)]>,
 
     [fatal_cycle] fn is_panic_runtime: IsPanicRuntime(CrateNum) -> bool,
     [fatal_cycle] fn is_compiler_builtins: IsCompilerBuiltins(CrateNum) -> bool,
@@ -294,7 +294,7 @@ define_maps! { <'tcx>
     [] fn specializes: specializes_node((DefId, DefId)) -> bool,
     [] fn in_scope_traits_map: InScopeTraits(DefIndex)
         -> Option<Lrc<FxHashMap<ItemLocalId, Lrc<StableVec<TraitCandidate>>>>>,
-    [] fn module_exports: ModuleExports(DefId) -> Option<Lrc<Vec<Export>>>,
+    [] fn module_exports: ModuleExports(DefId) -> Option<Lrc<[Export]>>,
     [] fn lint_levels: lint_levels_node(CrateNum) -> Lrc<lint::LintLevelMap>,
 
     [] fn impl_defaultness: ImplDefaultness(DefId) -> hir::Defaultness,
@@ -319,9 +319,9 @@ define_maps! { <'tcx>
     [] fn is_reachable_non_generic: IsReachableNonGeneric(DefId) -> bool,
 
 
-    [] fn native_libraries: NativeLibraries(CrateNum) -> Lrc<Vec<NativeLibrary>>,
+    [] fn native_libraries: NativeLibraries(CrateNum) -> Lrc<[NativeLibrary]>,
 
-    [] fn foreign_modules: ForeignModules(CrateNum) -> Lrc<Vec<ForeignModule>>,
+    [] fn foreign_modules: ForeignModules(CrateNum) -> Lrc<[ForeignModule]>,
 
     [] fn plugin_registrar_fn: PluginRegistrarFn(CrateNum) -> Option<DefId>,
     [] fn derive_registrar_fn: DeriveRegistrarFn(CrateNum) -> Option<DefId>,
@@ -330,17 +330,17 @@ define_maps! { <'tcx>
     [] fn original_crate_name: OriginalCrateName(CrateNum) -> Symbol,
 
     [] fn implementations_of_trait: implementations_of_trait_node((CrateNum, DefId))
-        -> Lrc<Vec<DefId>>,
+        -> Lrc<[DefId]>,
     [] fn all_trait_implementations: AllTraitImplementations(CrateNum)
-        -> Lrc<Vec<DefId>>,
+        -> Lrc<[DefId]>,
 
     [] fn dllimport_foreign_items: DllimportForeignItems(CrateNum)
         -> Lrc<FxHashSet<DefId>>,
     [] fn is_dllimport_foreign_item: IsDllimportForeignItem(DefId) -> bool,
     [] fn is_statically_included_foreign_item: IsStaticallyIncludedForeignItem(DefId) -> bool,
     [] fn native_library_kind: NativeLibraryKind(DefId)
         -> Option<NativeLibraryKind>,
-    [] fn link_args: link_args_node(CrateNum) -> Lrc<Vec<String>>,
+    [] fn link_args: link_args_node(CrateNum) -> Lrc<[String]>,
 
     // Lifetime resolution. See `middle::resolve_lifetimes`.
     [] fn resolve_lifetimes: ResolveLifetimes(CrateNum) -> Lrc<ResolveLifetimes>,
@@ -349,31 +349,31 @@ define_maps! { <'tcx>
     [] fn is_late_bound_map: IsLateBound(DefIndex) ->
         Option<Lrc<FxHashSet<ItemLocalId>>>,
     [] fn object_lifetime_defaults_map: ObjectLifetimeDefaults(DefIndex)
-        -> Option<Lrc<FxHashMap<ItemLocalId, Lrc<Vec<ObjectLifetimeDefault>>>>>,
+        -> Option<Lrc<FxHashMap<ItemLocalId, Lrc<[ObjectLifetimeDefault]>>>>,
 
     [] fn visibility: Visibility(DefId) -> ty::Visibility,
     [] fn dep_kind: DepKind(CrateNum) -> DepKind,
     [] fn crate_name: CrateName(CrateNum) -> Symbol,
-    [] fn item_children: ItemChildren(DefId) -> Lrc<Vec<Export>>,
+    [] fn item_children: ItemChildren(DefId) -> Lrc<[Export]>,
     [] fn extern_mod_stmt_cnum: ExternModStmtCnum(DefId) -> Option<CrateNum>,
 
     [] fn get_lang_items: get_lang_items_node(CrateNum) -> Lrc<LanguageItems>,
-    [] fn defined_lang_items: DefinedLangItems(CrateNum) -> Lrc<Vec<(DefId, usize)>>,
-    [] fn missing_lang_items: MissingLangItems(CrateNum) -> Lrc<Vec<LangItem>>,
+    [] fn defined_lang_items: DefinedLangItems(CrateNum) -> Lrc<[(DefId, usize)]>,
+    [] fn missing_lang_items: MissingLangItems(CrateNum) -> Lrc<[LangItem]>,
     [] fn extern_const_body: ExternConstBody(DefId) -> ExternConstBody<'tcx>,
     [] fn visible_parent_map: visible_parent_map_node(CrateNum)
         -> Lrc<DefIdMap<DefId>>,
     [] fn missing_extern_crate_item: MissingExternCrateItem(CrateNum) -> bool,
     [] fn used_crate_source: UsedCrateSource(CrateNum) -> Lrc<CrateSource>,
-    [] fn postorder_cnums: postorder_cnums_node(CrateNum) -> Lrc<Vec<CrateNum>>,
+    [] fn postorder_cnums: postorder_cnums_node(CrateNum) -> Lrc<[CrateNum]>,
 
-    [] fn freevars: Freevars(DefId) -> Option<Lrc<Vec<hir::Freevar>>>,
+    [] fn freevars: Freevars(DefId) -> Option<Lrc<[hir::Freevar]>>,
     [] fn maybe_unused_trait_import: MaybeUnusedTraitImport(DefId) -> bool,
     [] fn maybe_unused_extern_crates: maybe_unused_extern_crates_node(CrateNum)
-        -> Lrc<Vec<(DefId, Span)>>,
+        -> Lrc<[(DefId, Span)]>,
 
     [] fn stability_index: stability_index_node(CrateNum) -> Lrc<stability::Index<'tcx>>,
-    [] fn all_crate_nums: all_crate_nums_node(CrateNum) -> Lrc<Vec<CrateNum>>,
+    [] fn all_crate_nums: all_crate_nums_node(CrateNum) -> Lrc<[CrateNum]>,
 
     [] fn exported_symbols: ExportedSymbols(CrateNum)
         -> Arc<Vec<(ExportedSymbol, SymbolExportLevel)>>,
@@ -425,9 +425,9 @@ define_maps! { <'tcx>
 
     [] fn features_query: features_node(CrateNum) -> Lrc<feature_gate::Features>,
 
-    [] fn program_clauses_for: ProgramClausesFor(DefId) -> Lrc<Vec<Clause<'tcx>>>,
+    [] fn program_clauses_for: ProgramClausesFor(DefId) -> Lrc<[Clause<'tcx>]>,
 
-    [] fn wasm_custom_sections: WasmCustomSections(CrateNum) -> Lrc<Vec<DefId>>,
+    [] fn wasm_custom_sections: WasmCustomSections(CrateNum) -> Lrc<[DefId]>,
     [] fn wasm_import_module_map: WasmImportModuleMap(CrateNum)
         -> Lrc<FxHashMap<DefId, String>>,
 }

src/librustc/ty/mod.rs

@@ -337,10 +337,10 @@ pub struct CrateVariancesMap {
     /// 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>>>,
+    pub variances: FxHashMap<DefId, Lrc<[ty::Variance]>>,
 
     /// An empty vector, useful for cloning.
-    pub empty_variance: Lrc<Vec<ty::Variance>>,
+    pub empty_variance: Lrc<[ty::Variance]>,
 }
 
 impl Variance {
@@ -2641,7 +2641,7 @@ 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>> {
+                                     -> Lrc<[DefId]> {
     let id = tcx.hir.as_local_node_id(def_id).unwrap();
     let item = tcx.hir.expect_item(id);
     let vec: Vec<_> = match item.node {
@@ -2660,7 +2660,7 @@ fn associated_item_def_ids<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         hir::ItemTraitAlias(..) => vec![],
         _ => span_bug!(item.span, "associated_item_def_ids: not impl or trait")
     };
-    Lrc::new(vec)
+    Lrc::from(vec)
 }
 
 fn def_span<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) -> Span {
@@ -2772,6 +2772,7 @@ pub fn provide(providers: &mut ty::maps::Providers) {
 /// (constructing this map requires touching the entire crate).
 #[derive(Clone, Debug)]
 pub struct CrateInherentImpls {
+    // Note: needs to be a Lrc<Vec<DefId>> since get_mut().push() is used
     pub inherent_impls: DefIdMap<Lrc<Vec<DefId>>>,
 }
 

src/librustc/ty/relate.rs

@@ -131,7 +131,7 @@ 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: &'tcx Substs<'tcx>,
                                         b_subst: &'tcx Substs<'tcx>)
                                         -> RelateResult<'tcx, &'tcx Substs<'tcx>>