Update associated_item_def_ids

src/librustc/query/mod.rs

@@ -262,7 +262,7 @@ rustc_queries! {
 
     Other {
         /// Maps from an impl/trait `DefId to a list of the `DefId`s 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 {}

src/librustc/ty/mod.rs

@@ -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 {

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

@@ -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;
@@ -108,10 +109,10 @@ 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) }