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Date: Tue, 10 Nov 2015 11:42:15 +0100
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To: Dmitry Stogov <dmitry@zend.com>
Cc: Xinchen Hui <xinchen.h@zend.com>, Bob Weinand <bobwei9@hotmail.com>, 
	PHP Internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary=047d7beba1daf803da05242d5c43
Subject: Re: Safe Temporary Cleanup on Exception (Variable Liveness)
From: nikita.ppv@gmail.com (Nikita Popov)

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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.

Nikita

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