Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:89147
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain zend.com designates 209.85.213.177 as permitted sender)
MIME-Version: 1.0
In-Reply-To: <CAF+90c9bJMq3B=j=rcoLNmFD4L7JhwuP-FQ+0HihcG0PhwHYBA@mail.gmail.com>
References: <CA+9eiLvDmAMeYuiEvD=huG7Pt_2k59804oz3Wez0FyB7BJYYVQ@mail.gmail.com>
	<CAF+90c9bJMq3B=j=rcoLNmFD4L7JhwuP-FQ+0HihcG0PhwHYBA@mail.gmail.com>
Date: Tue, 10 Nov 2015 14:29:57 +0300
Message-ID: <CA+9eiLsgDUUXgrtTbTF3XKreZCeC9knch=AjSxSedB5EKjaf=g@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: Xinchen Hui <xinchen.h@zend.com>, Bob Weinand <bobwei9@hotmail.com>, 
	PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=047d7b3a9c76944d0605242e0787
Subject: Re: Safe Temporary Cleanup on Exception (Variable Liveness)
From: dmitry@zend.com (Dmitry Stogov)

--047d7b3a9c76944d0605242e0787
Content-Type: text/plain; charset=UTF-8

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.

Thanks. Dmitry,



>
> Nikita
>
>

--047d7b3a9c76944d0605242e0787--