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Date: Thu, 31 Jan 2019 18:29:28 -0600
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Subject: Re: [PHP-DEV] [RFC] JIT
From: larry@garfieldtech.com (Larry Garfield)

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On Thursday, January 31, 2019 12:30:52 PM CST Chase Peeler wrote:
> On Thu, Jan 31, 2019 at 12:04 PM Zeev Suraski <zeev@php.net> wrote:
> > On Thu, Jan 31, 2019 at 6:47 PM Kalle Sommer Nielsen <kalle@php.net>
> > 
> > wrote:
> > > Without my usual Windows bias, I do believe it is a considerable fact
> > > like Nikita pointed out as Windows is a first class citizen in terms
> > > of operating systems we support. While PHP on Windows may not have the
> > > speed that the Unix counterpart have, it is still a very important
> > > development platform. Many developers develop on Windows and deploy on
> > > a Unix based system, being unable to test such an important feature in
> > > a development environment is also a large question mark.
> > 
> > As long as we can agree that very few actually *deploy *on Windows, I
> > think
> > we're on solid grounds.
> > As the JIT implementation is likely to have at least *some* significant
> > differences compared to Linux, I'm not sure what testing it on Windows
> > would give you.  JIT is supposed to be entirely transparent, and the
> > performance characteristics - as well as the bug patterns - are likely to
> > be quite different on Linux vs. Windows, at least in many cases.
> > Is it really that important to have?
> > 
> > I'm honestly a bit perplexed by how many people here viewing Windows
> > support as a must have, while at the same time I think we all agree PHP is
> > very scarcely found on production Windows servers, and JIT is a
> > predominantly production feature.
> > 
> > I'm personally interested in taking a look at it (and I'm certain
> > 
> > > Anatol does too), but simply dismissing is a no-go for me.
> > 
> > It'd be interesting to evaluate the cost associated with supporting
> > Windows.  Bare in mind, we're proposing to vote on this as a production
> > feature for PHP 8 - which realistically means almost two years from now
> > *at
> > the earliest*.  I'm sure we'd have Windows support a lot sooner than that
> > if we decide that it's a must have.  I agree with Nikita that the key
> > question is in fact, do we or do we not want to introduce JIT in - with
> > the
> > main question being the maintenance cost.  Let's tackle this question
> > first, otherwise - why send Dmitry (and maybe others) for doing more work
> > (Windows support) if we are likely to flush it all down the toilet?
> > 
> Maybe we're the only ones, but we run production PHP on Windows. I have no
> issues with the idea of not initially having support for Windows. I can
> probably even live with never having support for Windows - provided that we
> don't find ourselves in a situation like Nikita mentioned where features
> start getting developed in PHP instead of C and require JIT in order to
> function.

Question from a non-compiler-engineer: Could we end up in a situation where 
future language features (in 8.3 or something) are only performant on JIT-
enabled platforms?  I know there were some RFCs rejected in the past on the 
grounds that they involved too many runtime checks (and thus a performance 
hit); if it were possible for a JIT to optimize some of those away, it might 
make the cost acceptable.  However, if a JIT only works on some systems that 
might widen the gap between have- and have-not platforms.

Is that a concern, or am I making things up?  Or, is it a concern but we're 
legit OK with that happening (which is also an entirely valid decision to 
make)?

--Larry Garfield
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