[Python-Dev] Register-based VM [Was: Possible performance regression]

[Victor Stinner]

No, I wasn't aware of this project. My starting point was:

http://static.usenix.org/events/vee05/full_papers/p153-yunhe.pdf
Yunhe Shi, David Gregg, Andrew Beatty, M. Anton Ertl, 2005

See also my email to python-dev that I sent in 2012:
https://mail.python.org/pipermail/python-dev/2012-November/122777.html

Ah, my main issue was my implementation is that I started without
taking care of clearing registers when the stack-based bytecode
implicitly cleared a reference (decref), like "POP_TOP" operation.

I added "CLEAR_REG" late in the development and it caused me troubles,
and the "correct" register-based bytecode was less efficient than
bytecode without CLEAR_REG. But my optimizer was very limited, too
limited.

Another implementation issue that I had was to understand some
"implicit usage" of the stack like try/except which do black magic,
whereas I wanted to make everything explicit for registers. I'm
talking about things like "POP_BLOCK" and "SETUP_EXCEPT". In my
implementation, I kept support for stack-based bytecode, and so I had
some inefficient code and some corner cases.

My approach was to convert stack-based bytecode to register-based
bytecode on the fly. Having both in the same code allowed to me run
some benchmarks. Maybe it wasn't the best approach, but I didn't feel
able to write a real compiler (AST => bytecode).

Victor

Le mar. 26 févr. 2019 à 21:58, Neil Schemenauer <nas-python at python.ca> a écrit :
>
> On 2019-02-26, Victor Stinner wrote:
> > I made an attempt once and it was faster:
> > https://faster-cpython.readthedocs.io/registervm.html
>
> Interesting.  I don't think I have seen that before.  Were you aware
> of "Rattlesnake" before you started on that?  It seems your approach
> is similar.  Probably not because I don't think it is easy to find.
> I uploaded a tarfile I had on my PC to my web site:
>
>     http://python.ca/nas/python/rattlesnake20010813/
>
> It seems his name doesn't appear in the readme or source but I think
> Rattlesnake was Skip Montanaro's project.  I suppose my idea of
> unifying the local variables and the registers could have came from
> Rattlesnake.  Very little new in the world. ;-P
>
> Cheers,
>
>   Neil



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Night gathers, and now my watch begins. It shall not end until my death.