[Python-Dev] Python optmizations

[Gustavo Niemeyer]

Hello Skip!

I've been reading some books and papers about stack virtual machines
optimization, and playing around with Python's bytecode and inner loop
organization. As always, I found some interesting results and some
frustrating ones.

Recently, I have found your paper about peephole optimization, and other
tries you've made in the same job. Well, basically I discovered that I'm
not original, and repeated most of your ideas and mistakes. :-) But
that's ok. It gave me a good idea of paths to follow if I want to keep
playing with this.

One thing I thought and also found a reference in your paper is about
some instructions that should be turned into a single opcode. To
understand how this would affect the code, I have disassembled the
whole Python standard library, and the whole Zope library. After that
I've run a script to detect opcode repeatings (excluding SET_LINENO).

Here are the top repeatings:

23632   LOAD_FAST, LOAD_ATTR
15382   LOAD_CONST, LOAD_CONST
12842   JUMP_IF_FALSE, POP_TOP
12397   CALL_FUNCTION, POP_TOP
12121   LOAD_FAST, LOAD_FAST

Not by casuality, I found in your paper references to a LOAD_FAST_ATTR
opcode. Since you probably have mentioned this to others, I wouldn't
like to bother everyone again asking why it was not implemented. Could
you please explain me the reasons that left this behind?

If you have the time, I'd also like to understand what's the trouble
involved in getting a peephole optimizer in the python compiler itself.
Is it just about compiling performance?  I don't remember to have read
about this in your paper, but you probably thought about that as well.

Thank you!

-- 
Gustavo Niemeyer

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