avoid mixing accesses of ptrs derived from a mutable ref and parent ptrs

Author: RalfJung

Diff for: library/core/tests/ptr.rs

@@ -25,7 +25,7 @@ fn test() {
             snd: isize,
         }
         let mut p = Pair { fst: 10, snd: 20 };
-        let pptr: *mut Pair = &mut p;
+        let pptr: *mut Pair = addr_of_mut!(p);
         let iptr: *mut isize = pptr as *mut isize;
         assert_eq!(*iptr, 10);
         *iptr = 30;
@@ -1070,8 +1070,8 @@ fn swap_copy_untyped() {
     let mut x = 5u8;
     let mut y = 6u8;
 
-    let ptr1 = &mut x as *mut u8 as *mut bool;
-    let ptr2 = &mut y as *mut u8 as *mut bool;
+    let ptr1 = addr_of_mut!(x).cast::<bool>();
+    let ptr2 = addr_of_mut!(y).cast::<bool>();
 
     unsafe {
         ptr::swap(ptr1, ptr2);