[pypy-dev] Virtualizables in RPython

[Armin Rigo]

Hi Anton,

On 24 April 2014 12:38, Anton Gulenko
<anton.gulenko at student.hpi.uni-potsdam.de> wrote:
> appreciate your input. I want to collect details about the underlying
> concept, and also about the specific implementation in the RPython JIT. For
> example, was this concept first introduced in Pypy, or is it an older idea?
> How exactly does the optimizer decide which objects can be virtualized, and
> which can not?

We first need to clarify some details.  Are you talking about
"virtualizables", or "virtuals"?  These are two very different
concepts.  The latter is a very strong form of escape analysis, and
probably the single most efficient concept we have in the RPython JIT.
 The former, on the other hand, is more of a hack that was added at
some point in time, and that we're trying to remove --- unsuccessfully
so far, because it gives slighty better results than virtuals only,
for the specific use case where it works.

I'm unsure which one you're talking about: only the frame object is a
"virtualizable", and it's not the job of the optimizer to decide that;
it's explicitly marked in the jitdriver.  See
https://pypy.readthedocs.org/en/latest/jit/virtualizable.html .  On
the other hand, if you're talking about "virtuals", then indeed we
have code in the optimizer to handle them.  It's some kind of escape
analysis leading to allocation removal.


A bientôt,

Armin.