Switch select_unpredictable guard to raw pointer

Author: 197g

library/core/src/hint.rs

@@ -788,19 +788,20 @@ pub fn select_unpredictable<T>(condition: bool, true_val: T, false_val: T) -> T
     let mut false_val = MaybeUninit::new(false_val);
 
     struct DropOnPanic<T> {
-        // Invariant: valid pointer and points to an initialized `MaybeUninit`.
-        inner: *mut MaybeUninit<T>,
+        // Invariant: valid pointer and points to an initialized value that is not further used,
+        // i.e. it can be dropped by this guard.
+        inner: *mut T,
     }
 
     impl<T> Drop for DropOnPanic<T> {
         fn drop(&mut self) {
             // SAFETY: Must be guaranteed on construction of local type `DropOnPanic`.
-            unsafe { (*self.inner).assume_init_drop() }
+            unsafe { self.inner.drop_in_place() }
         }
     }
 
-    let true_ptr = (&mut true_val) as *mut _;
-    let false_ptr = (&mut false_val) as *mut _;
+    let true_ptr = true_val.as_mut_ptr();
+    let false_ptr = false_val.as_mut_ptr();
 
     // SAFETY: The value that is not selected is dropped, and the selected one
     // is returned. This is necessary because the intrinsic doesn't drop the
@@ -813,10 +814,12 @@ pub fn select_unpredictable<T>(condition: bool, true_val: T, false_val: T) -> T
         let guard = crate::intrinsics::select_unpredictable(condition, true_ptr, false_ptr);
         let drop = crate::intrinsics::select_unpredictable(condition, false_ptr, true_ptr);
 
-        // SAFETY: both pointers are to valid `MaybeUninit`, in both variants they do not alias but
-        // the two arguments we have selected from did alias each other.
+        // SAFETY: both pointers are well-aligned and point to initialized values inside a
+        // `MaybeUninit` each. In both possible values for `condition` the pointer `guard` and
+        // `drop` do not alias (even though the two argument pairs we have selected from did alias
+        // each other).
         let guard = DropOnPanic { inner: guard };
-        (*drop).assume_init_drop();
+        drop.drop_in_place();
         crate::mem::forget(guard);
 
         // Note that it is important to use the values here. Reading from the pointer we got makes