fix(allocator): revert changes to get_current_chunk_footer_field_offset (#20964)

overlookmotel · overlookmotel · commit fc7f60cdf6e3 · 2026-04-02T15:09:51.000Z
Partial revert of #18168. #18168 made a small change to `get_current_chunk_footer_field_offset` (used by `Allocator::from_raw_parts`). That change was correct in the context of the other changes made to `Bump` in that PR, but now that #20963 has rolled back most of those changes, this change needs to be reverted too as it's a potential perf regression with current version of `Bump`.
diff --git a/crates/oxc_allocator/src/from_raw_parts.rs b/crates/oxc_allocator/src/from_raw_parts.rs
@@ -259,7 +259,7 @@ fn get_current_chunk_footer_field_offset() -> usize {
         assert!(align_of::<Cell<Option<usize>>>() == align_of::<usize>());
     }
 
-    let bump = ManuallyDrop::new(Bump::new());
+    let bump = ManuallyDrop::new(Bump::<1>::with_min_align());
     bump.set_allocation_limit(Some(123));
 
     // SAFETY:
@@ -269,7 +269,7 @@ fn get_current_chunk_footer_field_offset() -> usize {
     // so either field order means 3rd `usize` is fully initialized
     // (it's either `NonNull<ChunkFooter>>` or the `usize` in `Option<usize>`).
     unsafe {
-        let ptr = ptr::from_ref::<ManuallyDrop<Bump>>(&bump).cast::<usize>();
+        let ptr = ptr::from_ref(&bump).cast::<usize>();
         if *ptr.add(2) == 123 {
             // `allocation_limit` is 2nd field. So `current_chunk_footer` is 1st.
             0

Original file line number	Diff line number	Diff line change
`@@ -259,7 +259,7 @@ fn get_current_chunk_footer_field_offset() -> usize {`
`259`	`259`	`assert!(align_of::<Cell<Option<usize>>>() == align_of::<usize>());`
`260`	`260`	`}`
`261`	`261`
`262`		`- let bump = ManuallyDrop::new(Bump::new());`
	`262`	`+ let bump = ManuallyDrop::new(Bump::<1>::with_min_align());`
`263`	`263`	`bump.set_allocation_limit(Some(123));`
`264`	`264`
`265`	`265`	`// SAFETY:`
`@@ -269,7 +269,7 @@ fn get_current_chunk_footer_field_offset() -> usize {`
`269`	`269`	// so either field order means 3rd `usize` is fully initialized
`270`	`270`	// (it's either `NonNull<ChunkFooter>>` or the `usize` in `Option<usize>`).
`271`	`271`	`unsafe {`
`272`		`- let ptr = ptr::from_ref::<ManuallyDrop<Bump>>(&bump).cast::<usize>();`
	`272`	`+ let ptr = ptr::from_ref(&bump).cast::<usize>();`
`273`	`273`	`if *ptr.add(2) == 123 {`
`274`	`274`	// `allocation_limit` is 2nd field. So `current_chunk_footer` is 1st.
`275`	`275`	`0`