I switched two of the int-based enums in javac to use Java enums, and I noted a
roughly 40% performance penalty. A bit of investigation showed that the problem
is entirely due to the type-checking code in java.lang.Enum.compareTo(). It
turns out that the method Class.getSuperclass() is not cheap enough.

This will be a serious problem for anyone switching to language enums. In fact
there is no need for the type checking code. Please remove it.