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Date: Tue, 5 Apr 2016 15:14:08 +0300
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Subject: Re: [PHP-DEV] RETURN micro optimization
From: dmitry@zend.com (Dmitry Stogov)



On 04/05/2016 12:04 PM, Derick Rethans wrote:
> On Tue, 5 Apr 2016, Dmitry Stogov wrote:
>
>> I propose a micro optimization for RETURN statement.
>>
>> Currently "return $x" increments reference counter of $x, then in
>> zend_leave_helper() we perform zval_ptr_dtor() on the same $x.
>>
>> The patch sets the original value of $x to null in first place, so
>> zval_ptr_dtor() is not going to be called.
>>
>> https://gist.github.com/dstogov/36f68b206242a39691ac539c2fc85d40
>>
>> the performance impact is invisible (0.1% less instruction retired on
>> Wordpress).
>>
>> It breaks sapi/phpdbg/tests/breakpoints_005.phpt, but this is probably
>> not a big deal.
>>
>> BTW: this change may affect debuggers in some other way.
> I'd like to know why this breaks before saying something. It'd be a PITA
> if this micro optimisation wouldn't actually do a lot performance wise,
> but makes some debugging not possible.
Actually, the patch has a bug.
It doesn't take into account that "return $x;" might be used in global 
scope.
Setting $x to NULL in this case isn't right, of course.

Introducing another check would probably negate the effect of 
micro-optimization.

So, ignore this for now, and sorry for noise.

Thanks. Dmitry.


>
> cheers,
> Derick