[pypy-dev] How do I get better jit_libffi traces?

I'm trying to optimize the FFI functionality in Pixie, and I'm not sure how to proceed. From what I understand, the JIT generator is able to optimize away calls to jit_libffi and simply replace them with bare calls to the c functions. However, not matter how I hint or mark things as immutable, I seem to always have a call to "jit_ffi_call_int". What exactly triggers the JIT to remove that call? The part of the trace involved in the jit call looks like this: https://gist.github.com/halgari/31b188e8e4757ccb3218 Any ideas? Thanks, Timothy