This allows stuff like:

int mycompare(int i, int j) { j - i } 
...
list.sort(this::mycompare)

It is like a manual transmission lambda. The main idea here is allowing pointers to functions in our own class (whether user explicitly wrote them or we wrote them on their behalf).

So a few cleanups were needed:

1. allow creating FunctionRef to these (lots of refactoring here)
2. allow dynamic code (Def) to access these. We need a runtime whitelist, and we'd like to keep all methods private, avoid reflection/security issues/etc. We add a whitelist to the class itself, a pointer to each function like this:

private static final MethodHandle handle$mycompare$2;

These are initialized in <clinit> with ldc (they are simply constants).
We can lookup from this by name and arity exactly, and we have what we need.
3. general cleanup of functions in our ASM code (thanks @uschindler).