error: Undefined Behavior: write access through <TAG> at ALLOC[0x0] is forbidden
  --> tests/fail/tree_borrows/alternate-read-write.rs:LL:CC
   |
LL |     *y += 1; // Failure
   |     ^^^^^^^ Undefined Behavior occurred here
   |
   = help: this indicates a potential bug in the program: it performed an invalid operation, but the Tree Borrows rules it violated are still experimental
   = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/tree-borrows.md for further information
   = help: the accessed tag <TAG> has state Frozen which forbids this child write access
help: the accessed tag <TAG> was created here, in the initial state Reserved
  --> tests/fail/tree_borrows/alternate-read-write.rs:LL:CC
   |
LL |     let y = unsafe { &mut *(x as *mut u8) };
   |                      ^^^^^^^^^^^^^^^^^^^^
help: the accessed tag <TAG> later transitioned to Unique due to a child write access at offsets [0x0..0x1]
  --> tests/fail/tree_borrows/alternate-read-write.rs:LL:CC
   |
LL |     *y += 1; // Success
   |     ^^^^^^^
   = help: this transition corresponds to the first write to a 2-phase borrowed mutable reference
help: the accessed tag <TAG> later transitioned to Frozen due to a foreign read access at offsets [0x0..0x1]
  --> tests/fail/tree_borrows/alternate-read-write.rs:LL:CC
   |
LL |     let _val = *x;
   |                ^^
   = help: this transition corresponds to a loss of write permissions
   = note: BACKTRACE (of the first span):
   = note: inside `main` at tests/fail/tree_borrows/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 1 previous error