Value Types Bytecodes - "Level 0" prototype

David Simms david.simms at oracle.com
Tue Jun 28 15:56:53 UTC 2016


Correct, there is still a fair amount of work to be done on what it 
means to be boxed


On 28/06/2016 5:27 p.m., Paul Benedict wrote:
> Do the value byte codes work only on the "flat" representation of the 
> type? I don't think Valhalla has gotten to the point of boxing the 
> type (has it?), but I am curious if these also operate on the boxed 
> representation?
>
> Cheers,
> Paul
>
> On Tue, Jun 28, 2016 at 6:57 AM, David Simms <david.simms at oracle.com 
> <mailto:david.simms at oracle.com>> wrote:
>
>
>     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
>
>



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