1 files changed, 11 insertions, 5 deletions
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 5d099a49854..acbc325a514 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -319,7 +319,7 @@ pub struct Weak<
     // but it is not necessarily a valid pointer.
     // `Weak::new` sets this to `usize::MAX` so that it doesn’t need
     // to allocate space on the heap. That's not a value a real pointer
-    // will ever have because RcBox has alignment at least 2.
+    // will ever have because RcInner has alignment at least 2.
     // This is only possible when `T: Sized`; unsized `T` never dangle.
     ptr: NonNull<ArcInner<T>>,
     alloc: A,
@@ -1581,7 +1581,7 @@ impl<T: ?Sized, A: Allocator> Arc<T, A> {
     pub fn as_ptr(this: &Self) -> *const T {
         let ptr: *mut ArcInner<T> = NonNull::as_ptr(this.ptr);
 
-        // SAFETY: This cannot go through Deref::deref or RcBoxPtr::inner because
+        // SAFETY: This cannot go through Deref::deref or RcInnerPtr::inner because
         // this is required to retain raw/mut provenance such that e.g. `get_mut` can
         // write through the pointer after the Rc is recovered through `from_raw`.
         unsafe { &raw mut (*ptr).data }
@@ -2936,7 +2936,7 @@ impl<T: ?Sized, A: Allocator> Weak<T, A> {
             // Otherwise, we're guaranteed the pointer came from a nondangling Weak.
             // SAFETY: data_offset is safe to call, as ptr references a real (potentially dropped) T.
             let offset = unsafe { data_offset(ptr) };
-            // Thus, we reverse the offset to get the whole RcBox.
+            // Thus, we reverse the offset to get the whole RcInner.
             // SAFETY: the pointer originated from a Weak, so this offset is safe.
             unsafe { ptr.byte_sub(offset) as *mut ArcInner<T> }
         };
@@ -3447,7 +3447,13 @@ impl<T: Default> Default for Arc<T> {
     /// assert_eq!(*x, 0);
     /// ```
     fn default() -> Arc<T> {
-        Arc::new(Default::default())
+        let x = Box::into_raw(Box::write(Box::new_uninit(), ArcInner {
+            strong: atomic::AtomicUsize::new(1),
+            weak: atomic::AtomicUsize::new(1),
+            data: T::default(),
+        }));
+        // SAFETY: `Box::into_raw` consumes the `Box` and never returns null
+        unsafe { Self::from_inner(NonNull::new_unchecked(x)) }
     }
 }
 
@@ -3861,7 +3867,7 @@ impl<T: ?Sized, A: Allocator> Unpin for Arc<T, A> {}
 /// valid instance of T, but the T is allowed to be dropped.
 unsafe fn data_offset<T: ?Sized>(ptr: *const T) -> usize {
     // Align the unsized value to the end of the ArcInner.
-    // Because RcBox is repr(C), it will always be the last field in memory.
+    // Because RcInner is repr(C), it will always be the last field in memory.
     // SAFETY: since the only unsized types possible are slices, trait objects,
     // and extern types, the input safety requirement is currently enough to
     // satisfy the requirements of align_of_val_raw; this is an implementation