Auto merge of #132053 - matthiaskrgr:rollup-u5ds6i3, r=matthiaskrgr

Rollup of 5 pull requests

Successful merges:

 - #131707 (Run most `core::num` tests in const context too)
 - #132002 (abi/compatibility: also test Option-like types)
 - #132026 (analyse: remove unused uncanonicalized field)
 - #132031 (Optimize `Rc<T>::default`)
 - #132040 (relnotes: fix stabilizations of `assume_init`)

r? `@ghost`
`@rustbot` modify labels: rollup

2 files changed, 20 insertions, 8 deletions

diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index e98ae7c31ad..582d850e14b 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -2312,7 +2312,16 @@ impl<T: Default> Default for Rc<T> {
     /// ```
     #[inline]
     fn default() -> Rc<T> {
-        Rc::new(Default::default())
+        unsafe {
+            Self::from_inner(
+                Box::leak(Box::write(Box::new_uninit(), RcInner {
+                    strong: Cell::new(1),
+                    weak: Cell::new(1),
+                    value: T::default(),
+                }))
+                .into(),
+            )
+        }
     }
 }
 
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index acbc325a514..13677245e98 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -3447,13 +3447,16 @@ impl<T: Default> Default for Arc<T> {
     /// assert_eq!(*x, 0);
     /// ```
     fn default() -> Arc<T> {
-        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)) }
+        unsafe {
+            Self::from_inner(
+                Box::leak(Box::write(Box::new_uninit(), ArcInner {
+                    strong: atomic::AtomicUsize::new(1),
+                    weak: atomic::AtomicUsize::new(1),
+                    data: T::default(),
+                }))
+                .into(),
+            )
+        }
     }
 }