While the basic access control aspect of JEP-181 (being implemented under JDK-8010319) has no compiler specific parts, part of the change involves the use of invokeinterface, rather than invokespecial, for invoking private interface methods. This requires changes to the interpreter and compilers (C1 and C2 are already handled). In addition this use of invokeinterface requires extensions of the receiver typecheck logic that was put in place by JDK-8174962.
Graal will need to be updated to reflect these changes.