RFR 8223345 [lworld] Implement ValueTypeReturnedAsFields for C1

[Tobias Hartmann]

Hi Ioi,

On 04.05.19 02:13, Ioi Lam wrote:
> https://bugs.openjdk.java.net/browse/JDK-8223345
> http://cr.openjdk.java.net/~iklam/valhalla/8223345-c1_return_vt_as_fields.v01/
> 
> The implementation is pretty straight-forward as most of the work of packing/unpacking is done
> inside runtime functions, the same as the interpreter.
> 
> I refactored MacroAssembler::store_value_type_fields_to_buf so that it can be reused between the
> interpreter and C1.

Looks good to me.

> One problem with the current way of using the runtime functions is that it's neither fast, nor small
> :-(
> 
> + For better performance, it might be better to do the packing/unpacking in-line.
>   I'll leave that for future optimization.

Right, let's leave that for later.

> + On the other hand, if we want smaller code, I think the inline-allocation code can
>   be moved into ValueKlass::pack_handler(). I might do that as a separate RFE.

The pack_handler is also used by C2 and there we might want the allocation to happen in compiled
code to allow optimizations. But we can investigate this as part of a separate RFE.

Thanks,
Tobias

> I've added FIXME comments in the code for the above.
> 
> Thanks
> - Ioi