error: Undefined Behavior: not granting access to tag <TAG> because incompatible item [SharedReadOnly for <TAG>] is protected by call ID
  --> $DIR/invalidate_against_barrier2.rs:LL:CC
   |
LL |     unsafe { *x = 0 };
   |              ^^^^^^ not granting access to tag <TAG> because incompatible item [SharedReadOnly for <TAG>] is protected by 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/invalidate_against_barrier2.rs:LL:CC
   |
LL |     let xraw = &mut x as *mut _;
   |                ^^^^^^
help: <TAG> was protected due to <TAG> which was created here
  --> $DIR/invalidate_against_barrier2.rs:LL:CC
   |
LL |     inner(xraw, xref);
   |                 ^^^^
help: this protector is live for this call
  --> $DIR/invalidate_against_barrier2.rs:LL:CC
   |
LL | / fn inner(x: *mut i32, _y: &i32) {
LL | |     // If `x` and `y` alias, retagging is fine with this... but we really
LL | |     // shouldn't be allowed to write to `x` at all because `y` was assumed to be
LL | |     // immutable for the duration of this call.
LL | |     unsafe { *x = 0 };
LL | | }
   | |_^
   = note: backtrace:
   = note: inside `inner` at $DIR/invalidate_against_barrier2.rs:LL:CC
note: inside `main` at $DIR/invalidate_against_barrier2.rs:LL:CC
  --> $DIR/invalidate_against_barrier2.rs:LL:CC
   |
LL |     inner(xraw, xref);
   |     ^^^^^^^^^^^^^^^^^

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

error: aborting due to previous error