Papers that inspire Exupery

Hi Bryce,

I would like to know if you can provide us a list a papers on Jit.
Anything that inspire/explain what your doing in Exupery.

And also what do you think of stack base VM vs. register base VM?
I am asking because in smalltalk I am wondering if it worth register base VM.

Thanks

        Mth





       

       
               
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On Mon, 2010-07-05 at 21:15 +0200, Mathieu Suen wrote:
> Hi Bryce,
>
> I would like to know if you can provide us a list a papers on Jit.
> Anything that inspire/explain what your doing in Exupery.

http://wiki.squeak.org/squeak/5792

The short answer is it's an attempt build on the insights from Holzle's
work on Self compilation and allow type feedback to be used with solid
optimization.

Good inlining and type information through type feedback opens the door
to serious optimization but standard type feedback VMs rely on very fast
compilers which don't have time to optimize well.

> And also what do you think of stack base VM vs. register base VM?
> I am asking because in smalltalk I am wondering if it worth register base VM.

My view is the bytecode should be stack based but the JIT register
based. It's easy to do very good register allocation across trees (i.e.
stack based).

Trees are a convenient structure to work with and a stack based bytecode
is just a linear representation of a tree.

If you're optimizing heavily it doesn't matter too much what
representation you choose as you'll transform it through several
representations during compilation. If you're optimizing quickly and
simply trees are convenient.

Bryce

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On Jul 5, 2010, at 11:35 PM, Bryce Kampjes wrote:

> On Mon, 2010-07-05 at 21:15 +0200, Mathieu Suen wrote:
>> Hi Bryce,
>>
>> I would like to know if you can provide us a list a papers on Jit.
>> Anything that inspire/explain what your doing in Exupery.
>
> http://wiki.squeak.org/squeak/5792

Link of your papers seems broken.


Thanks for your answer I agree that for the point of view of Jit there is no big deal.
But if you stay on the bytecode level then having some #sendArgTemp0: can avoid dispatching the #pushTemp:0  bytecode.

Also have you an idea on what is faster:
 - Make a small optimization but work throw the tree many time.
 - Make a big optimization and avoiding tree walk

I guess you have some optimization that can't be done in several tree walk?

>
> Bryce
>
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-- Mathieu


       

       
               
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On Tue, 2010-07-06 at 19:02 +0200, Mathieu Suen wrote:
Hmm, it is. I'll need to investigate.

Bytecode dispatch performance changes depending on what CPU you're
using. The Pentium 4's were the worst given how fast they were and how
badly they suffered from branch misspredicts. Later CPUs optimize for
branch prediction much more and so will suffer from the dispatch
overhead less.

Also stack bytecode is likely to be more compact with a decent encoding
which will reduce the amount of time spent fetching bytecode into the
CPU's caches.

I've noticed that the difference in performance of Exupery compared with
the bytecode interpreter changes wildly depending on the CPU. Exupery is
fasted compared with the bytecode interpreter on the P4 but it's never
been tuned for that CPU because I never owned a machine that used it.

> Also have you an idea on what is faster:
>  - Make a small optimization but work throw the tree many time.
>  - Make a big optimization and avoiding tree walk
>
> I guess you have some optimization that can't be done in several tree walk?

If you can perform an optimization as a simple tree walk then that's
very fast. Exupery does many optimizations that way.

Exupery also does some analysis that's more sophisticated than simple
tree walks.

Bryce

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