RFR: -XX:+ValueTypePassFieldsAsArgs is broken with value type fields < 4 byte

[Tobias Hartmann]

Hi,

please review the following fix:
http://cr.openjdk.java.net/~thartmann/valhalla/vt_prototype/webrev.11/

When passing value type fields as arguments, the IC2 and C2I adapters need to read/write the value type fields from/to the (heap) buffer. Right now, we always read/write >= 4 bytes. I fixed this by reading/writing the appropriate field size and also refactored the code.

Thanks,
Tobias