error: Undefined Behavior: write access through <TAG> is forbidden because it is a child of <TAG> which is Frozen.
  --> $DIR/alternate-read-write.rs:LL:CC
   |
LL |     *y += 1; // Failure
   |     ^^^^^^^ write access through <TAG> is forbidden because it is a child of <TAG> which is Frozen.
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
   = note: BACKTRACE:
   = note: inside `main` at $DIR/alternate-read-write.rs:LL:CC

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

error: aborting due to previous error