error: Undefined Behavior: not granting access to tag <TAG> because that would remove [SharedReadOnly for <TAG>] which is protected because it is an argument of call ID
  --> $DIR/aliasing_mut4.rs:LL:CC
   |
LL | pub fn safe(_x: &i32, _y: &mut Cell<i32>) {}
   |                       ^^ not granting access to tag <TAG> because that would remove [SharedReadOnly for <TAG>] which is protected because it is an argument of call ID
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
help: <TAG> was created by a Unique retag at offsets [0x0..0x4]
  --> $DIR/aliasing_mut4.rs:LL:CC
   |
LL |     let xref = &mut x;
   |                ^^^^^^
help: <TAG> is this argument
  --> $DIR/aliasing_mut4.rs:LL:CC
   |
LL | pub fn safe(_x: &i32, _y: &mut Cell<i32>) {}
   |             ^^
   = note: BACKTRACE:
   = note: inside `safe` at $DIR/aliasing_mut4.rs:LL:CC
note: inside `main` at $DIR/aliasing_mut4.rs:LL:CC
  --> $DIR/aliasing_mut4.rs:LL:CC
   |
LL |     safe_raw(xshr, xraw as *mut _);
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

note: some details are omitted, run with `MIRIFLAGS=-Zmiri-backtrace=full` for a verbose backtrace

error: aborting due to previous error