rustup; add an interesting alias test case

rust-version

@@ -1 +1 @@
-15d1f811963649c2f18a88c8e0b39958ec02fd70
+158f8d034b15e65ba8dc0d066358dd0632bfcd6e

tests/compile-fail/box-cell-alias.rs

@@ -0,0 +1,18 @@
+// compile-flags: -Zmiri-track-raw-pointers
+
+// Taken from <https://github.com/rust-lang/unsafe-code-guidelines/issues/194#issuecomment-520934222>.
+
+use std::cell::Cell;
+
+fn helper(val: Box<Cell<u8>>, ptr: *const Cell<u8>) -> u8 {
+    val.set(10);
+    unsafe { (*ptr).set(20); } //~ ERROR does not have an appropriate item in the borrow stack
+    val.get()
+}
+
+fn main() {
+    let val: Box<Cell<u8>> = Box::new(Cell::new(25));
+    let ptr: *const Cell<u8> = &*val;
+    let res = helper(val, ptr);
+    assert_eq!(res, 20);
+}