[Python-ideas] More compact bytecode

[Serhiy Storchaka]

On 04.02.16 23:43, Andrew Barnert via Python-ideas wrote:
> I just tried it out to see what's hard. And it seems like it's all easy. I was able to get it working (not passing all tests, of course--you'd have to fix dis, pdb, etc. for that) on my lunch hour.
>
>
> I didn't try to be smart anywhere: every opcode gets 8 bits for an arg, and uses up to three EXTENDED_ARG ops if it needs more. I didn't do any simplification, nor did I cast the bytecode to unsigned short *.
> The hardest changes are in ceval (plus frameobject--I didn't realize lasti has to start lasti at -2 instead of -1 until I tried to run it and immediately got errors about unknown opcodes at odd offsets).
>
> Compile is pretty easy by comparison.
>
> Nothing at all has to be done for bootstrap, freeze, marshal, etc. (unless you want to add backward-compat code to load non-word-based .pyc files).
>
> You'd also need to fix at least peephole (I just disabled it), dis, and pdb, but none of them look too hard.
>
> The bootstrap bytecode and stdlib .pyc files ends up about 5% smaller (and that's with the peephole optimizer disabled, so presumably it would be better in real life).
>
>
> If anyone wants to look at or play with the code, I'm in the process of regenerating my github fork, but it'll be branch wpy on https://github.com/abarnert/cpython once that's done (maybe 20 minutes? I forget how long cloning takes).

Looks good. Right now I'm implementing the first option (the hard part 
is peephole optimizer). We could compare both approaches later.