[Python-ideas] Disable all peephole optimizations

[Ned Batchelder]

On 5/21/14 7:41 AM, Nick Coghlan wrote:
>
>
> On 21 May 2014 21:06, "Ned Batchelder" <ned at nedbatchelder.com 
> <mailto:ned at nedbatchelder.com>> wrote:
> > ** Implementation
> >
> > Although it may seem like a big change to be able to disable the 
> optimizer, the heart of it is quite simple.  In compile.c is the only 
> call to PyCode_Optimize.  That function takes a string of bytecode and 
> returns another.  If we skip that call, the peephole optimizer is 
> disabled.
> >
> > ** User Interface
> >
> > Unfortunately, the -O command-line switch does not lend itself to a 
> new value that means, "less optimization than the default."  I propose 
> a new switch -P, to control the peephole optimizer, with a value of 
> -P0 meaning no optimization at all. The PYTHONPEEPHOLE environment 
> variable would also control the option.
>
> Since this is a CPython specific thing, a -X named command line option 
> would be more appropriate.
>
I had overlooked the introduction of -X.  Yes, that seems like the right 
way: -Xpeephole=0
>
> >
> > There are about a dozen places internal to CPython where 
> optimization level is indicated with an integer, for example, in 
> Py_CompileStringObject.  Those uses also don't allow for new values 
> indicating less optimization than the default: 0 and -1 already have 
> meanings.  Unless we want to start using -2 for less that the 
> default.  I'm not sure we need to provide for those values, or if the 
> PYTHONPEEPHOLE environment variable provides enough control.
>
> I assume you want the environment variable so the setting can be 
> inherited by subprocesses?
>
It allows it to be inherited by subprocesses, yes.  I was hoping it 
would mean the setting would be available deeper in the interpreter, but 
now that I think about it, environment variables are interpreted at the 
top of the interpreter, and then the settings passed along internally.  
I'll do a survey to figure out where the setting has to be plumbed 
through the layers to get to compile.c properly.

--Ned.
>
> Cheers,
> Nick.
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/python-ideas/attachments/20140521/31448219/attachment.html>