error: Undefined Behavior: not granting access to tag <TAG> because that would remove [Unique for <TAG>] which is strongly protected because it is an argument of call ID
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL |     unsafe { *y = 2 };
   |              ^^^^^^ not granting access to tag <TAG> because that would remove [Unique for <TAG>] which is strongly 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 SharedReadWrite retag at offsets [0x0..0x4]
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL |     let p = x as *mut u32;
   |             ^
help: <TAG> is this argument
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL | fn foo(a: &mut u32, y: *mut u32) -> u32 {
   |        ^
   = note: BACKTRACE:
   = note: inside `foo` at $DIR/illegal_write6.rs:LL:CC
note: inside `main` at $DIR/illegal_write6.rs:LL:CC
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL |     foo(x, p);
   |     ^^^^^^^^^

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

error: aborting due to previous error