Re: [Squeak-VMdev] Versiojn 4 changes

[Ian P. <ian...@in...>]

On 08 Apr 2004, at 21:46, Bryce Kampjes wrote:

> This sequence is possible if we change from integers having tag 1 to
> integers having tag 0 leaving the tag in the lower bits. The Self
> community wrote some nice papers on tagging and high performance
> simple garbage collection.

Teeny reminder (which may be irrelevant): Itanium cannot add -1 into an 
effective address without introducing an additional add instruction and 
stop bit (!) before each ld/st insn.

(Unless I'm missing some neat trick on the Itanium?  If so, someone 
please enlighten me! ;)

> It would probably be more worthwhile looking at at: and at:put:. Could
> Tim's improvements to primitives be used to create simple at:
> primitives that are quick to execute?

To get the same benefits as the existing at-cache you'd need two 
levels.  The first in the method cache (to get you to the right 
accessor implementation, with fixed field size being stored in a // MC 
slot presumably?) then another instance-specific one (to get you to the 
object's indexable size).

Maybe all this is saying is that we might want to rethink how object 
size is encoded in the header to make it trivially easy to extract the 
indexable size, whatever the format of the object.

(What we really want is to generate format-specific accessor primtives 
on-the-fly.  The fixed field size is then implicit in the 
implementation and all that's needed is the primitive implementation 
address slot in the method cache.)

Bye,
Ian