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Date: Tue, 12 May 2009 10:25:47 +0400
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To: Paul Biggar <paul.biggar@gmail.com>
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Subject: Re: [PHP-DEV] Method call improvements
From: dmitry@zend.com (Dmitry Stogov)

Hi Paul,

Paul Biggar wrote:
> On Mon, May 11, 2009 at 7:47 PM, Guilherme Blanco
> <guilhermeblanco@gmail.com> wrote:
>> What's the status on this one?!
> 
> I think it died from neglect. But it was a really good idea.
> 
> 
> One question that was raised was:
> 
>> On Thu, Jan 22, 2009 at 10:20 AM, Dmitry Stogov <dmitry@zend.com> wrote:
>>> However we can introduce some indirect table associated with op_array, which
>>> can be used to implement inline caches without direct opcode modification
>>> (in the same way as IS_CV variables work). There are a lot of papers about
>>> polymorphic inline caches (e.g.
>>> http://research.sun.com/self/papers/pics.html) which we probably should use
>>> to not to invite bicycle.
> 
> You can't actually use PICs or even ICs with the Zend engine, because
> you can't insert code into the callee method's header (you would need
> a JIT). You also wouldn't want to, since PHP can't use the
> recompilation techniques that Self had. You can use lookup caches,
> which is exactly what the original patch was.

I know PHP limitations, and I meant additional lookup caches for one or 
few results connected directly to ZEND_INIT_METHOD_CALL (and family) 
opcodes.

> FWIW, since PHP has a static inheritence chain, the best approach
> seems to be to build a virtual dispatch table, instead of a hashtable
> for functions. However, there might be some esoteric extensions which
> make this difficult.

The real things is even worse as during compilation of a class it's 
parent class doesn't have to be known. So construction of VMTs becomes a 
bit problematic. BTW we could think in this way...

Thanks. Dmitry.

> 
> 
> Paul
>