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From "Geir Magnusson Jr." <ge...@apache.org>
Subject Re: [arch] Interpreter vs. JIT for Harmony VM
Date Thu, 22 Sep 2005 10:34:44 GMT

On Sep 21, 2005, at 11:11 AM, Tom Tromey wrote:

>>>>>> "Geir" == Geir Magnusson <geirm@apache.org> writes:
>>> On the other hand, a fast code-generating JIT can call runtime
>>> helpers and native methods without additional glue code whereas an
>>> interpreter has to have special glue code to make it work in a JIT
>>> environment.
> Geir> I believe you, but I don't understand this.  Can you explain  
> in more
> Geir> detail?
> It is about handling calling conventions.



>>> Our experience is that a fast, zero optimizing JIT can yield low-
>>> enough response time. So, I think at least Harmony has the option
>>> of having a decent system without an interpreter. Thoughts?
> Geir> Basic thought is yes, I always figured we'd have this  
> pluggable, with
> Geir> an interpreter for ease of porting, and then platform- 
> specific JIT.
> It seems to me that there's a design question here.  For instance, if
> you want to eventually take interpreted code and compile it (when it
> is "hot"), for full pluggability your JIT(s) and your interpreter need
> to agree on some set of bookkeeping details in order to make this
> possible.  OTOH, you could make other decisions that make this problem
> go away, for instance having a single choice of execution engine up
> front; so the "fast JIT" and the "optimizing JIT" are just part of the
> same code base and only need to talk to each other, and can be built
> in an ad hoc way.
> Personally I'd be just as happy if we only had a JIT.  There are
> already plenty of interpreters out there.

But I would think that we'd want both, right?   An interpreter that  
builds on anything to ensure wide platform portability, with the the  
ability to augment with a JIT for those platforms for which people  
are interested in creating a JIT...


> Tom

Geir Magnusson Jr                                  +1-203-665-6437

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