[Vm-dev] Re: [squeak-dev] uncompacting classes

Stefan Marr squeak at stefan-marr.de
Wed Nov 30 09:47:54 UTC 2011


On 30 Nov 2011, at 10:19, Mariano Martinez Peck wrote:

> I would like to have one extra free bit in the object header. I can hack my own VM which uses 4 bits for CompactClasses rather than 5, but do you think we can do this for the official Cog VM as well? this would allow "researched" a much nice infrastructure out of the box.

If you really need more flexibility, consider adding a compile-time option to add an extra preheader to each object.
We have that in the RoarVM.
Of course, there is a performance impact. But in return you get what you have dreamed of in your wildest dreams... And it is easy to add just another word, or another one...

We had a bug recently, that required me to clean up the code, I could point you at the fix. That should give an indication where you would need to adapt the VM.
And this approach should work at least for the classic interpreter. Not sure what that would entail for the stackVM, but for Cog you would probably need to adapt the code generation.

Best regards

Stefan Marr
Software Languages Lab
Vrije Universiteit Brussel
Pleinlaan 2 / B-1050 Brussels / Belgium
Phone: +32 2 629 2974
Fax:   +32 2 629 3525

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