Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:44198
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain uk.ibm.com designates 195.212.29.139 as permitted sender)
In-Reply-To: <af54caaf0906061828i651d4a5ax3e9242c25e5cb240@mail.gmail.com>
References: <af54caaf0906041620o1de77e2br10d1d80ef0130192@mail.gmail.com> 	<DEA757D29DE3314393C26D2EA705A7E73605C1B34B@SC-MBXC1.TheFacebook.com> 
	<E6C35D22F6874DCD96473EEF91D0BABD@PC3EE1F19287> <af54caaf0906061828i651d4a5ax3e9242c25e5cb240@mail.gmail.com>
To: Paul Biggar <paul.biggar@gmail.com>
Cc: Graham Kelly <grahamk@facebook.com>,
        PHP Internals <internals@lists.php.net>, Nuno Lopes <nlopess@php.net>,
        Brian Shire <shire@facebook.com>
MIME-Version: 1.0
Message-ID: <OF9F6B7696.A53B60EE-ON802575CE.003840A6-802575CE.0041799A@uk.ibm.com>
Date: Sun, 7 Jun 2009 12:55:08 +0100
Content-Type: multipart/alternative; boundary="=_alternative 003B1E7A802575CE_="
Subject: Re: [PHP-DEV] RE: Optimizer discussion
From: rob_nicholson@uk.ibm.com (Rob Nicholson)

--=_alternative 003B1E7A802575CE_=
Content-Type: text/plain; charset="US-ASCII"

Graham, Paul,

Paul Biggar <paul.biggar@gmail.com> wrote on 07/06/2009 02:28:48:
> 
> On Fri, Jun 5, 2009 at 11:23 PM, Nuno Lopes<nlopess@php.net> wrote:
> 
> > About runkit & friends, I wouldn't worr
>  much about them. If you're running
> > them problably you also don't care about optimizations. If you want to 
be
> > able to optimize something, you need to remove as many freedom degrees 
as
> > you can..
> 
> This is probably true of runkit. However, I would be careful what you
> remove for extra freedom. There is very likely PHP code out there that
> relies (possibly by accident) on some edge cases.
> 

Firsly its great to see more and more folks experimenting with the 
implementation
of PHP. I think this will be good for the wider PHP community as the 
design 
of PHP and the possible optimisations become better understood.

I think you'll find that there are a lot of "edge cases" as Paul mentions 
in PHP that PHP code relies on. I work on IBM's project zero and we have 
hit
quite a lot of them.  Just one example to illustrate. 
We found that the evaluation order within assignments is not at all what 
you
might predict and that existing PHP applications actually rely on the 
evaluation 
order. Consider the following where foo() bar() and baz() have some 
coupling.
$a[foo()]=$b[bar()][baz()];

Even though the test coverage of the Zend Engine as measured by line 
coverage is 
fairly complete we found that there were missing testcases to verify this 
behaviour. We've been following a policy of writing new tests for any such 
behaviour 
that we find so I would suggest that you ensure that you can run and
pass all the PHPT tescases under /tests/lang and under /Zend. 

For example the tests for the behaviour I mention above are 
tests/lang/engine_assignExecutionOrder_XXX.phpt

Then if you find any more PHP code that does not run the same optimised as 
it
does unoptimised it would be great if you could contribute testcases for 
them. 

Actually for full disclosure I should say that although most of the tests 
we have
written are now in cvs, we are still a little behind with contributing all 
the 
engine tests we have written. Hopefully they'll all be there before you 
need them.


Rob Nicholson





Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number 
741598. 
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU






--=_alternative 003B1E7A802575CE_=--