crates/vm/src/gc_state.rs (1)

465-473: Reduce avoidable cloning in the GC hot path.

At Line 473 and Lines 501-504, referent vectors are cloned multiple times. This adds extra allocations during collection and can be trimmed without changing behavior.

♻️ Proposed refactor (same behavior, fewer allocations)

-        let mut referents_map: std::collections::HashMap<GcPtr, Vec<NonNull<PyObject>>> =
+        let mut referents_map: std::collections::HashMap<GcPtr, Vec<NonNull<PyObject>>> =
             std::collections::HashMap::new();
         for &ptr in &collecting {
             let obj = unsafe { ptr.0.as_ref() };
             if obj.strong_count() == 0 {
                 continue;
             }
             let referent_ptrs = unsafe { obj.gc_get_referent_ptrs() };
-            referents_map.insert(ptr, referent_ptrs.clone());
-            for child_ptr in referent_ptrs {
+            for &child_ptr in &referent_ptrs {
                 let gc_ptr = GcPtr(child_ptr);
                 if collecting.contains(&gc_ptr)
                     && let Some(refs) = gc_refs.get_mut(&gc_ptr)
                 {
                     *refs = refs.saturating_sub(1);
                 }
             }
+            referents_map.insert(ptr, referent_ptrs);
         }
@@
-                let referent_ptrs = referents_map
-                    .get(&ptr)
-                    .cloned()
-                    .unwrap_or_else(|| unsafe { obj.gc_get_referent_ptrs() });
-                for child_ptr in referent_ptrs {
+                let referent_ptrs = referents_map
+                    .get(&ptr)
+                    .map(|v| std::borrow::Cow::Borrowed(v.as_slice()))
+                    .unwrap_or_else(|| {
+                        std::borrow::Cow::Owned(unsafe { obj.gc_get_referent_ptrs() })
+                    });
+                for &child_ptr in referent_ptrs.iter() {
                     let gc_ptr = GcPtr(child_ptr);
                     if collecting.contains(&gc_ptr) && reachable.insert(gc_ptr) {
                         worklist.push(gc_ptr);
                     }
                 }

Also applies to: 501-505

🤖 Prompt for AI Agents

Verify each finding against the current code and only fix it if needed.

In `@crates/vm/src/gc_state.rs` around lines 465 - 473, The GC hot path currently
clones referent vectors unnecessarily: when iterating over collecting you call
obj.gc_get_referent_ptrs() and insert referents_map.insert(ptr,
referent_ptrs.clone()), then later clone again (lines ~501-505). Change this to
move the original Vec<NonNull<PyObject>> into the map (avoid .clone()) and, when
later iterating, borrow or drain the stored Vec as needed instead of cloning it
(update uses around where referents_map.get/entry is accessed). Specifically
modify the code around referents_map, the loop over collecting, and usages of
gc_get_referent_ptrs()/referents_map so that the Vec returned by
gc_get_referent_ptrs() is inserted by value and reused rather than cloned.