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Date: Fri, 16 Jan 2015 21:09:37 +0400
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To: Xinchen Hui <xinchen.h@zend.com>, Nikita Popov <nikic@php.net>
Cc: Benjamin Coutu <ben.coutu@zeyos.com>, PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Generating more efficient code for while-loop
From: dmitry@zend.com (Dmitry Stogov)

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See the patch for "while" and "for" loops

https://gist.github.com/dstogov/9cc5767a14f3b88e1275

All tests passed.
The patch leads to 2% improvement in number of CPU instructions retired on
bench.php.
Unfortunately, It doesn't make any visible speed difference.

Anyway, I'm going to commit it on Monday.
Xinchen, Nikita, please verify me.

Thanks. Dmitry.

On Fri, Jan 16, 2015 at 7:58 PM, Xinchen Hui <xinchen.h@zend.com> wrote:

> Hey:
>
> On Sat, Jan 17, 2015 at 12:12 AM, Dmitry Stogov <dmitry@zend.com> wrote:
> > Hi Benjamin,
> >
> > Thanks for idea.
> > With PHP7 AST compiler, it's quite easy to implement this (it took us 15
> > minutes to try :)
> yeah... by handy :)
>
> > However, it doesn't make big improvement on our benchmarks.
> in reallife app, IR has no significant difference while running
> wordpress homepage
>
> thanks
> > We will take a look into possibilities to apply your idea to other
> patterns
> > (e.g. for and foreach loops).
> >
> > Anyway, it makes full sense to include this optimization into PHP7.
> > I just like to try other opportunities first.
> >
> > Thanks. Dmitry.
> >
> > On Fri, Jan 16, 2015 at 10:56 AM, Benjamin Coutu <ben.coutu@zeyos.com>
> > wrote:
> >>
> >> Hello,
> >>
> >> Please consider the following PHP code:
> >>
> >> while ( <CONDITION> ) {
> >>   <STATEMENT>
> >> }
> >>
> >> It currently compiles to something like this for the Zend Engine:
> >>
> >> 0: <CONDITION>
> >> 1: JMPZ -> 4
> >> 2: <STATEMENT>
> >> 3: JMP -> 0
> >> 4: ...
> >>
> >> This can easily be rewritten in an equivalent but much more efficient
> >> form:
> >>
> >> 0: JMP -> 2
> >> 1: <STATEMENT>
> >> 2: <CONDITION>
> >> 3: JMPNZ -> 1
> >>
> >> The trick is to jump to the conditional expression before the first
> >> iteration and then only having to continue with just on conditional
> jump on
> >> every subsequent cycle.
> >>
> >> This would result in only 1 jump per loop iteration compared to
> >> effectively 2 jumps needed per iteration with the current
> implementation.
> >>
> >> It would also make the loop tighter as upon entering the loop (after
> first
> >> conditional evaluation), one less opcode remains relevant to the loop.
> >>
> >> An analogous approach can be taken for the for-loop.
> >>
> >> Thanks,
> >>
> >> Ben
> >>
> >> PS: This is my first post on a PHP mailinglist - I am very excited! :)
> >>
> >> --
> >>
> >> Benjamin Coutu
> >> Zeyon Technologies Inc.
> >> http://www.zeyos.com
> >>
> >>
> >> --
> >> PHP Internals - PHP Runtime Development Mailing List
> >> To unsubscribe, visit: http://www.php.net/unsub.php
> >>
> >
>
>
>
> --
> Xinchen Hui
> @Laruence
> http://www.laruence.com/
>

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