[Python-Dev] Python 3.5 on VC14 - update

["Martin v. Löwis"]

Am 10.06.14 18:30, schrieb Steve Dower:
> I ran a quick test with profile-guided optimization (PGO, pronounced
> "pogo"), which has supposedly been improved since VC9, and saw a very
> unscientific 20% speed improvement on pybench.py and 10% size
> reduction in python35.dll. I'm not sure what we used to get from VC9,
> but it certainly seems worth enabling provided it doesn't break
> anything. (Interestingly, PGO decided that only 1% of functions
> needed to be compiled for speed. Not sure if I can find out which
> ones those are but if anyone's interested I can give it a shot?)

You probably ran too little Python code. See PCbuild/build_pgo.bat
for what used to be part of the release process. It takes quite some
time, but it rebuilt more than 1% (IIRC).

FWIW, I stopped using PGO for the official releases when it was
demonstrated to generate bad code. In my experience, a compiler
that generates bad code has lost trust "forever", so it will be
hard to justify re-enabling PGO (like "but it really works this
time"). I wasn't sad when I found a justification to skip the
profiling, since it significantly held up the release process.

Regards,
Martin