[Python-Dev] Wordcode v2

[Cesare Di Mauro]

2016-02-15 8:14 GMT+01:00 Andrew Barnert via Python-Dev <
python-dev at python.org>:

> Despite the name (and inspiration), my fork has very little to do with
> WPython. I'm just focused on simpler (hopefully = faster) fetch code; he
> started with that, but ended up going the exact opposite direction,
> accepting more complicated (and much slower) fetch code as a reasonable
> cost for drastically reducing the number of instructions. (If you double
> the 30% fetch-and-parse overhead per instruction, but cut the number of
> instructions to 40%, the net is a huge win.)


I don't know why you consider slower the WPython's code that fetches the
more complicated instructions. On the contrary, I've structured such
"superinstructions" in order to simplify their decoding. Arguments are
decoded as they are needed in a specific moment, in order to reduce or
completely avoid the usage of temporary variables to keep such values.

Can you provide some example about your claim?

Regarding the WPython goal, it wasn't only about introducing simpler
instructions. As I've written also in my presentation, it's an hybrid VM:
stack and register-based. I've introduced a new instruction format for the
existing CPython's instructions, which are now easier to fetch, decode,
execute, and provide a better density too (for the most common case:
arguments with a maximum of 255 as value/index).
However I've also added superinstructions to better pack more "useful
work", which provides more code density and they are the primary
responsible for improving the execution speed.

Regards,
Cesare
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