Value Types Bytecodes - "Level 0" prototype

[David Simms]

Recently pushed some basic "value type" prototype code to Valhalla 
repository.

Usual caveats apply *this is a prototype*, things will change, the 
format of the bytecodes or whether we go ahead with said bytecodes at 
all. From bytecodes.hpp (mostly correspond to aref bytecodes):

     // value-type bytecodes
     _vload                = 203, // 0xcb
     _vstore               = 204, // 0xcc
     _vaload               = 205, // 0xcd
     _vastore              = 206, // 0xce
     _vnew                 = 207, // 0xcf
     _vnewarray            = 208, // 0xd0
     _multivnewarray       = 209, // 0xd1
     _vreturn              = 210, // 0xd2
     _vgetfield            = 211, // 0xd3
     _typed                = 212, // 0xd4
     _invokedirect         = 213, // 0xd5


"Level 0" Prototype: Currently value types are simply modelled with oops 
and heap allocated for simplicity (class derives from instanceKlass). 
The semantics of value types are mostly there, but there is currently no 
stack or thread local allocation, work for the future. There is initial 
support for flattened compositions of values and array elements.

The prototype "value types" have no JIT or verifier support, so code 
that wants to play with value types:

  * x86_64, Linux and Mac only.
  * "-noverify -Xint", no verify or JIT support
  * GC should be fine, not that we have extensively tested all GC
    configurations
  * invokedirect can execute values methods, that's about it
      o the type system isn't anywhere near being completely defined
        (e.g. should value types implement interfaces, and if so, how)

Folks that don't use value types shouldn't notice any restrictions using 
the JIT etc.

Cheers
/David Simms