When making java calls (or inlined functions), if both args and param are primitive, no widening conversion is used to locate the proper overloaded method/constructor.
In the above, a call is made via reflection to Numbers.shiftLeft(Object, Object) and its associated auto-boxing, instead of directly to the perfectly adequate Numbers.shiftLeft(long, int).
Explicitly casting to the formal type.
Ancillary benefits of fixing:
It would also reduce the amount of method overloading, e.g., RT.intCast(char), intCast(byte), intCast(short), could all be removed, since such calls would pass to RT.intCast(int).