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Date: Fri, 27 Feb 2015 13:55:27 -0500
Message-ID: <CAAyV7nHpf8JT0nAF-M9d-65JQHDbYnK7F+c9CUtoyLkkfRiROg@mail.gmail.com>
To: Zeev Suraski <zeev@zend.com>
Cc: Dmitry Stogov <dmitry@zend.com>, Jordi Boggiano <j.boggiano@seld.be>, 
	PHP Internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] Re: Zend JIT Open Sourced
From: ircmaxell@gmail.com (Anthony Ferrara)

Zeev,

>> Right now it compiles script (php file) at once.
>> So yes, our JIT uses some kind of AOT approach, but completely
>> transparently for the rest of PHP.
>
> Just to slightly further clarify - we don't compile the whole codebase at
> once, but we keep the existing semantics that every file is independent, may
> change independently of other files, and include() may end up load one file
> in one flow and another one in another flow.  There's isn't any cross-file
> optimization.
>
>> We also tried few different approaches to collect formation about hot
>> functions and generate code only for them.
>> Unfortunately, this didn't change the picture.
>
> (again, the picture being no performance gains in common Web apps).

Well, I just want to make one clarification here to your point:
there's no performance gains to this AOT approach for common web apps.

It's not really fair to judge a true JIT implementation based on this
because it lacks crucial runtime information that a real JIT compiler
would have (such as input types, values, etc). So it would be left
generating generic native code instead of specific code. I just want
to point out that the results here aren't really applicable to a JIT
approach. And that should be made clear when discussing it.

That's not to say there's anything wrong with this approach, nor that
there isn't a ton we can learn from it. I think it's a fantastic
research effort and plan on digging through it myself. Thank you for
open sourcing it.

Anthony