error: Undefined Behavior: not granting access to tag <TAG> because incompatible item is protected: [Unique for <TAG>] (call ID)
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL |     unsafe { *y = 2 };
   |              ^^^^^^ not granting access to tag <TAG> because incompatible item is protected: [Unique for <TAG>] (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 retag at offsets [0x0..0x4]
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL |     let p = x as *mut u32;
   |             ^
help: <TAG> was protected due to <TAG> which was created here
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL |     foo(x, p);
   |         ^
help: this protector is live for this call
  --> $DIR/illegal_write6.rs:LL:CC
   |
LL | / fn foo(a: &mut u32, y: *mut u32) -> u32 {
LL | |     *a = 1;
LL | |     let _b = &*a;
LL | |     unsafe { *y = 2 };
LL | |     return *a;
LL | | }
   | |_^
   = 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