RFR/RFC: C2: limited support for vbox/vunbox

[Zoltán Majó]

Hi,


this patch adds basic C2 support for the vbox/vunbox bytecodes.

http://cr.openjdk.java.net/~zmajo/valhalla/02.vbox-vunbox.webrev.00/

The suggested change is in a prototype phase, thus it works for only a 
limited set of use cases (covered by tests 37--40). In more detail, the 
patch
- does not enable C2 to generate checks currently performed by the 
interpreter to verify that the bytecodes handle a value-capable class 
and it's corresponding derived value type;
- relies on the assumption that the memory layout of the derived value 
type is the same as the memory layout of the value-capable class.

The patch also contains a minor refactoring of method names in 
ValueTypeNode so that the names better match with the HotSpot Style Guide.

I tested with ValueTypeTestBench.java and with the Octane+Nashorn 
benchmarks.

Thank you!

Best regards,


Zoltan