error[E0282]: type annotations needed
  --> $DIR/regression-issue-81317.rs:44:9
   |
LL |     let iv = S ^ index.into();
   |         ^^
LL |
LL |     &iv.to_bytes_be();
   |         ----------- type must be known at this point
   |
help: consider giving `iv` an explicit type
   |
LL |     let iv: /* Type */ = S ^ index.into();
   |           ++++++++++++

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0282`.