From 0b1ab91d6604cf3277ef562eabd04f107015de58 Mon Sep 17 00:00:00 2001
From: Matthew Jasper <mjjasper1@gmail.com>
Date: Thu, 18 Nov 2021 20:59:12 +0000
Subject: [PATCH] Deserialization less in associated_item_def_ids

---
 compiler/rustc_metadata/src/rmeta/decoder.rs           | 10 ++++++++++
 .../rustc_metadata/src/rmeta/decoder/cstore_impl.rs    |  7 +------
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/compiler/rustc_metadata/src/rmeta/decoder.rs b/compiler/rustc_metadata/src/rmeta/decoder.rs
index bb9a58a0b62aa..5dbd26694c520 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder.rs
@@ -1258,6 +1258,16 @@ impl<'a, 'tcx> CrateMetadataRef<'a> {
         }
     }
 
+    fn get_associated_item_def_ids(&self, tcx: TyCtxt<'tcx>, id: DefIndex) -> &'tcx [DefId] {
+        if let Some(children) = self.root.tables.children.get(self, id) {
+            tcx.arena.alloc_from_iter(
+                children.decode((self, tcx.sess)).map(|child_index| self.local_def_id(child_index)),
+            )
+        } else {
+            &[]
+        }
+    }
+
     fn get_associated_item(&self, id: DefIndex, sess: &Session) -> ty::AssocItem {
         let def_key = self.def_key(id);
         let parent = self.local_def_id(def_key.parent.unwrap());
diff --git a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
index aac0aa61ea65e..804f277e26e12 100644
--- a/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
+++ b/compiler/rustc_metadata/src/rmeta/decoder/cstore_impl.rs
@@ -103,12 +103,7 @@ provide! { <'tcx> tcx, def_id, other, cdata,
         tcx.calculate_dtor(def_id, |_,_| Ok(()))
     }
     variances_of => { tcx.arena.alloc_from_iter(cdata.get_item_variances(def_id.index)) }
-    associated_item_def_ids => {
-        let mut result = SmallVec::<[_; 8]>::new();
-        cdata.each_child_of_item(def_id.index,
-          |child| result.push(child.res.def_id()), tcx.sess);
-        tcx.arena.alloc_slice(&result)
-    }
+    associated_item_def_ids => { cdata.get_associated_item_def_ids(tcx, def_id.index) }
     associated_item => { cdata.get_associated_item(def_id.index, tcx.sess) }
     impl_trait_ref => { cdata.get_impl_trait(def_id.index, tcx) }
     impl_polarity => { cdata.get_impl_polarity(def_id.index) }