error: Undefined Behavior: trying to retag from <TAG> for SharedReadOnly permission at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
  --> $DIR/aliasing_mut3.rs:LL:CC
   |
LL | pub fn safe(_x: &mut i32, _y: &i32) {}
   |                           ^^
   |                           |
   |                           trying to retag from <TAG> for SharedReadOnly permission at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
   |                           this error occurs as part of FnEntry retag at ALLOC[0x0..0x4]
   |
   = 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 SharedReadOnly retag at offsets [0x0..0x4]
  --> $DIR/aliasing_mut3.rs:LL:CC
   |
LL |     safe_raw(xraw, xshr);
   |                    ^^^^
help: <TAG> was later invalidated at offsets [0x0..0x4] by a Unique FnEntry retag inside this call
  --> $DIR/aliasing_mut3.rs:LL:CC
   |
LL |     safe_raw(xraw, xshr);
   |     ^^^^^^^^^^^^^^^^^^^^
   = note: BACKTRACE:
   = note: inside `safe` at $DIR/aliasing_mut3.rs:LL:CC
note: inside `main`
  --> $DIR/aliasing_mut3.rs:LL:CC
   |
LL |     safe_raw(xraw, xshr);
   |     ^^^^^^^^^^^^^^^^^^^^

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

error: aborting due to previous error