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Date: Thu, 31 Mar 2016 23:39:07 +0100
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Subject: Re: [PHP-DEV] Copy On Write and Assign By Reference perform different
 on PHP5 and PHP7
From: rowan.collins@gmail.com (Rowan Collins)

On 31/03/2016 18:23, Rowan Collins wrote:
> Maybe in PHP 5 the opcodes are the same, but $2 and $3 somehow end up 
> as references to !0, rather than new zvals

So, it turns out, this is exactly what happens. Specifically, there is a 
call to SEPARATE_ZVAL_IF_NOT_REF(var_ptr); in the definition of the 
ZEND_PRE_INC opcode 
[http://lxr.php.net/xref/PHP_5_6/Zend/zend_vm_def.h#814] If the zval 
*is* a reference, the code just ends up incrementing its reference 
count, returning a reference to it rather than the calculated value.

In PHP 7, references are very different, and integers aren't refcounted, 
so it's all a different story.

I got a bit curious and did some deep investigation, which I've written 
up on StackOverflow: http://stackoverflow.com/a/36344524/157957 I've 
about reached my limit now, though, so I'll leave it to others to 
correct or fill in any further info. :)

Regards,

-- 
Rowan Collins
[IMSoP]