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Date: Wed, 28 Jan 2015 11:22:38 +0800
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To: Dmitry Stogov <dmitry@zend.com>
Cc: Benjamin Coutu <ben.coutu@zeyos.com>, Nikita Popov <nikita.ppv@gmail.com>, 
	"internals@lists.php.net" <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] Improvements to for-each implementation
From: xinchen.h@zend.com (Xinchen Hui)

Hey:

On Wed, Jan 28, 2015 at 12:55 AM, Dmitry Stogov <dmitry@zend.com> wrote:
> Hi,
>
> I'm working on a PoC, implementing the proposed behavior -
> https://gist.github.com/dstogov/a311e8b0b2cabee4dab4
>
> Only few PHPT tests had to be changed to confirm new behavior and actually
> they started to behave as HHVM.
> 2 tests are still unfixed XFAILed. Foreach by reference is still need to be
> improved to support different array modifications.
>
> The patch makes ~1% improvement on Wordpress-3.6 (saving duplication and
> destruction of 200 arrays on each request)

I just have got an idea:

Droping use of ZEND_OP_DATA make it possible to generate better
foreach loop opcodes

previously FE_RESET and FE_FETCH  share one same OP_DATA based on offset.

0 FE_RESET
1 FE_FETCH fail-> 5
2 OP_DATA
3  ..... statements
4 JMP 1
5....

without depending on that OP_DATA, we can change this to

0 FE_RESET
1 JMP 3
2 ....statements
3 FE_FETCH success->2
4 ....

that will reduce on JMP in every foreach loop

could you please also try this?

thanks

>
> Thanks. Dmitry.
>
>
>
> On Thu, Jan 22, 2015 at 1:38 PM, Benjamin Coutu <ben.coutu@zeyos.com> wrote:
>>
>> Hi Nikita,
>>
>> I would suggest using the proposal for the by-value case and sticking with
>> the current behavior for the by-reference case as you suggested. Granted, we
>> then cannot remove the internal pointer all together, but we would just use
>> it for the less common by-reference case as well as for the legacy
>> reset/next functions, of course. This would still improve most for-each
>> traversals. At least we then wouldn't have to find a replacement solution
>> for rest/prev/next/end. Moreover we can then move the internal position
>> pointer out of the hashtable structure into zend_array because it is only
>> used for userland arrays, not other hash tables (such as object properties
>> or internal structures that build upon the hashtable struct).
>>
>> Thanks,
>>
>> Ben
>>
>> ========== Original ==========
>> From: Nikita Popov <nikita.ppv@gmail.com>
>> To: Benjamin Coutu <ben.coutu@zeyos.com>
>> Date: Thu, 22 Jan 2015 10:53:19 +0100
>> Subject: Re: [PHP-DEV] Improvements to for-each implementation
>>
>> Doing this was the idea I had in mind as well, i.e. change the semantics
>> of
>> foreach to say that it will always work on a copy for by-value iteration
>> (which ironically avoids having to actually copy it). Note that this will
>> differ from the current behavior in a number of ways. In particular it
>> means that changes to arrays that were references prior to iteration will
>> not influence the iteration.
>>
>> The real question is what we should do in the by-reference case. Given
>> that
>> we need to acquire references to elements of the original array we can't
>> reasonably work with copy-semantics (at least I don't see how). So would
>> we
>> just stick with the previous behavior (using the hash position hack) for
>> that?
>>
>> Nikita
>>
>>
>> --
>> PHP Internals - PHP Runtime Development Mailing List
>> To unsubscribe, visit: http://www.php.net/unsub.php
>>
>



-- 
Xinchen Hui
@Laruence
http://www.laruence.com/