error: Undefined Behavior: trying to retag from <TAG> for SharedReadWrite permission at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
  --> $DIR/interior_mut2.rs:LL:CC
   |
LL |         let _val = *inner_shr.get();
   |                     ^^^^^^^^^^^^^^^
   |                     |
   |                     trying to retag from <TAG> for SharedReadWrite permission at ALLOC[0x0], but that tag does not exist in the borrow stack for this location
   |                     this error occurs as part of 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 SharedReadWrite retag at offsets [0x0..0x4]
  --> $DIR/interior_mut2.rs:LL:CC
   |
LL |         let inner_shr = &*inner_uniq;
   |                         ^^^^^^^^^^^^
help: <TAG> was later invalidated at offsets [0x0..0x4] by a write access
  --> $DIR/interior_mut2.rs:LL:CC
   |
LL |         *c.get() = UnsafeCell::new(0); // now inner_shr gets invalidated
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: BACKTRACE:
   = note: inside `main` at $DIR/interior_mut2.rs:LL:CC

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

error: aborting due to previous error