Avoid code generation for ThinVec<Diagnostic>'s destructor in the query system

Author: Zoxc

compiler/rustc_query_impl/src/on_disk_cache.rs

@@ -380,8 +380,6 @@ impl<'sess> OnDiskCache<'sess> {
     /// Stores a `QuerySideEffects` emitted during the current compilation session.
     /// Anything stored like this will be available via `load_side_effects` in
     /// the next compilation session.
-    #[inline(never)]
-    #[cold]
     pub fn store_side_effects(&self, dep_node_index: DepNodeIndex, side_effects: QuerySideEffects) {
         let mut current_side_effects = self.current_side_effects.borrow_mut();
         let prev = current_side_effects.insert(dep_node_index, side_effects);
@@ -405,8 +403,6 @@ impl<'sess> OnDiskCache<'sess> {
     /// Since many anonymous queries can share the same `DepNode`, we aggregate
     /// them -- as opposed to regular queries where we assume that there is a
     /// 1:1 relationship between query-key and `DepNode`.
-    #[inline(never)]
-    #[cold]
     pub fn store_side_effects_for_anon_node(
         &self,
         dep_node_index: DepNodeIndex,

compiler/rustc_query_impl/src/plumbing.rs

@@ -79,12 +79,16 @@ impl QueryContext for QueryCtxt<'_> {
             .unwrap_or_default()
     }
 
+    #[inline(never)]
+    #[cold]
     fn store_side_effects(self, dep_node_index: DepNodeIndex, side_effects: QuerySideEffects) {
         if let Some(c) = self.queries.on_disk_cache.as_ref() {
             c.store_side_effects(dep_node_index, side_effects)
         }
     }
 
+    #[inline(never)]
+    #[cold]
     fn store_side_effects_for_anon_node(
         self,
         dep_node_index: DepNodeIndex,

compiler/rustc_query_system/src/query/plumbing.rs

@@ -464,15 +464,18 @@ where
 
     prof_timer.finish_with_query_invocation_id(dep_node_index.into());
 
-    let diagnostics = diagnostics.into_inner();
-    let side_effects = QuerySideEffects { diagnostics };
+    let side_effects = QuerySideEffects { diagnostics: diagnostics.into_inner() };
 
     if std::intrinsics::unlikely(!side_effects.is_empty()) {
         if Q::ANON {
             qcx.store_side_effects_for_anon_node(dep_node_index, side_effects);
         } else {
             qcx.store_side_effects(dep_node_index, side_effects);
         }
+    } else {
+        // Avoid generating code for the destructor here. This does not leak memory since
+        // `QuerySideEffects` only owns memory if it's non-empty.
+        mem::forget(side_effects);
     }
 
     (result, dep_node_index)