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Date: Wed, 11 Nov 2015 11:11:02 +0800
Message-ID: <CABBJUpe8emf-3CDz02NSXCSyfMsX_+7sQYb7LtrLei31X-NYUw@mail.gmail.com>
To: Dmitry Stogov <dmitry@zend.com>
Cc: Nikita Popov <nikita.ppv@gmail.com>, Bob Weinand <bobwei9@hotmail.com>, 
	PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=94eb2c0bd7b44dcf7805243b2e5e
Subject: Re: Safe Temporary Cleanup on Exception (Variable Liveness)
From: xinchen.h@zend.com (Xinchen Hui)

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On Wed, Nov 11, 2015 at 11:10 AM, Xinchen Hui <xinchen.h@zend.com> wrote:

> Hey:
>
> On Tue, Nov 10, 2015 at 7:29 PM, Dmitry Stogov <dmitry@zend.com> wrote:
>
>>
>>
>> On Tue, Nov 10, 2015 at 1:42 PM, Nikita Popov <nikita.ppv@gmail.com>
>> wrote:
>>
>>> On Tue, Nov 10, 2015 at 10:53 AM, Dmitry Stogov <dmitry@zend.com> wrote:
>>>
>>>> Hi,
>>>>
>>>> Please take a look into
>>>> https://gist.github.com/dstogov/43eaa3f3b68583877322
>>>>
>>>> This is variation on Bob's idea about variable liveness.
>>>> The patch is incomplete. Liveness construction is still naive. However,
>>>> all tests are passed.
>>>>
>>>> Ranges are represented by start/end/variable cartages. (I suppose this
>>>> representation is more compact, than in the original proposal).
>>>> In general, it's possible to use few ranges for the same variable, if
>>>> its whole live range is not linear. (this is not implemented yet).
>>>>
>>>> Related ideas and tests are welcome.
>>>>
>>>> Thanks. Dmitry.
>>>>
>>>
>>> One leak this does not cover yet is a discarded delayed return value:
>>>
>>> function test() {
>>>     try {
>>>         $a = [1, 2, 3];
>>>         return $a + [];
>>>     } finally {
>>>         throw new Exception;
>>>     }
>>> }
>>>
>>> try {
>>>     test();
>>> } catch (Exception $e) {}
>>>
>>> This case is a bit tricky because it violates the usual invariant that
>>> all temporaries have well-defined liveness ranges (either alive or not, no
>>> maybe). We'd have to change that first.
>>>
>>
>> I see the problem. We can't statically define live-ranges for finally
>> code, because we don't know where it's going to be called from.
>> May be we may reconstruct this at run-time.
>>
> Or maybe we could separate ZEND_RETURN(_BY_REF) into two parts
>
> the first part, set the return value to EX(return_value),  the second part
> do the really leave(leave_helper).
>
> thus, we can keep the liveness of the variable won't be intrruptted?
>
> like:  previously we emit:   ZEND_ADD, ZEND_FAST_CALL, ZEND_RETURN.
>
>         now we emit: ZEND_ADD,  ZEND_RETURN, ZEND_FAST_CALL, ZEND_RETURN
>
s #ZEND_RETURN$#ZEND_LEAVE#

thanks

>
>         then in HANDLE_EXCEPTION we can dtor EX(return_value) if it is
> already set?
>
> this could also fixed double return memory leak
> like Zend/tests/try/bug70228.phpt
>
> thanks
>
>>
>> Thanks. Dmitry,
>>
>>
>>
>>>
>>> Nikita
>>>
>>>
>>
>
>
> --
> Xinchen Hui
> @Laruence
> http://www.laruence.com/
>



-- 
Xinchen Hui
@Laruence
http://www.laruence.com/

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