From 25b34de8c9b3cbda6f6de0d62f369ef3bb1d883c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Tue, 8 Sep 2026 16:32:22 +0200
Subject: [PATCH 1/2] Reuse `reachable_inlined_items`

---
 compiler/rustc_monomorphize/src/partitioning.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/compiler/rustc_monomorphize/src/partitioning.rs b/compiler/rustc_monomorphize/src/partitioning.rs
index 29b624afd0614..24fac7db1f773 100644
--- a/compiler/rustc_monomorphize/src/partitioning.rs
+++ b/compiler/rustc_monomorphize/src/partitioning.rs
@@ -216,6 +216,7 @@ where
 
     let cgu_name_builder = &mut CodegenUnitNameBuilder::new(cx.tcx);
     let cgu_name_cache = &mut UnordMap::default();
+    let mut reachable_inlined_items = FxIndexSet::default();
 
     for mono_item in mono_items {
         // Handle only root (GloballyShared) items directly here. Inlined (LocalCopy) items
@@ -264,15 +265,15 @@ where
         // going via another root item. This includes drop-glue, functions from
         // external crates, and local functions the definition of which is
         // marked with `#[inline]`.
-        let mut reachable_inlined_items = FxIndexSet::default();
+        reachable_inlined_items.clear();
         get_reachable_inlined_items(cx.tcx, mono_item, cx.usage_map, &mut reachable_inlined_items);
 
         // Add those inlined items. It's possible an inlined item is reachable
         // from multiple root items within a CGU, which is fine, it just means
         // the `insert` will be a no-op.
-        for inlined_item in reachable_inlined_items {
+        for inlined_item in &reachable_inlined_items {
             // This is a CGU-private copy.
-            cgu.items_mut().entry(inlined_item).or_insert_with(|| MonoItemData {
+            cgu.items_mut().entry(*inlined_item).or_insert_with(|| MonoItemData {
                 inlined: true,
                 linkage: Linkage::Internal,
                 visibility: Visibility::Default,

From 430c6f4c4464a9f76b3e0098b3eca1156ea18a02 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Tue, 8 Sep 2026 15:03:10 +0200
Subject: [PATCH 2/2] Reserve capacity for used and mentioned items

---
 compiler/rustc_monomorphize/src/collector.rs | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/compiler/rustc_monomorphize/src/collector.rs b/compiler/rustc_monomorphize/src/collector.rs
index 4ee1abe4a1ff4..70b6bda25be5e 100644
--- a/compiler/rustc_monomorphize/src/collector.rs
+++ b/compiler/rustc_monomorphize/src/collector.rs
@@ -326,6 +326,10 @@ impl<'tcx> MonoItems<'tcx> {
         self.items.entry(item.node).or_insert(item.span);
     }
 
+    fn reserve(&mut self, additional: usize) {
+        self.items.reserve(additional);
+    }
+
     fn items(&self) -> impl Iterator<Item = MonoItem<'tcx>> {
         self.items.keys().cloned()
     }
@@ -487,7 +491,9 @@ fn collect_items_rec<'tcx>(
                     def_path_str,
                 });
             };
+            used_items.reserve(used.len());
             used_items.extend(used.into_iter().copied());
+            mentioned_items.reserve(mentioned.len());
             mentioned_items.extend(mentioned.into_iter().copied());
         }
         MonoItem::GlobalAsm(item_id) => {