error[E0308]: mismatched types
  --> $DIR/issue-12997-2.rs:16:1
   |
LL | fn bar(x: isize) { }
   | ^^^^^^^^^^^^^^^^^^^^ expected isize, found mutable reference
   |
   = note: expected type `isize`
              found type `&mut test::Bencher`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.