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To: Dmitry Stogov <dmitrystogov@gmail.com>,
 Nikita Popov <nikita.ppv@gmail.com>
Cc: Dmitry Stogov <DStogov@perforce.com>,
 PHP internals <internals@lists.php.net>
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Date: Thu, 11 Nov 2021 18:20:21 +1100
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Subject: Re: [PHP-DEV] VM kinds
From: tstarling@wikimedia.org (Tim Starling)

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OK, thanks for the answer.

My PR is up now, with a fixme comment for the GOTO and SWITCH VMs. I'm
still not sure how to make them work.

https://github.com/php/php-src/pull/7642

-- Tim Starling

On 10/11/21 8:10 pm, Dmitry Stogov wrote:
> I prefer to keep GOTO and SWITCH VMs. It's easy to drop something,
> but it's going to be much more complex to reimplement it again.
>
> Note that HYBRID VM (based on CALL and GOTO VMs) was introduced only
> in PHP-7.2, because GOTO was already implemented a long time ago. In
> the future, it's possible to extend HYBRID VM, to make it work with
> GCC-incompatible compilers through SWITCH. We might also like to
> move from direct-threaded to indirect-threaded dispatch.
>
> Thanks. Dmitry.
>
> On Wed, Nov 10, 2021 at 11:35 AM Nikita Popov <nikita.ppv@gmail.com
> <mailto:nikita.ppv@gmail.com>> wrote:
>
>     On Wed, Nov 10, 2021 at 8:13 AM Tim Starling
>     <tstarling@wikimedia.org <mailto:tstarling@wikimedia.org>>
>     wrote:
>
>     > What are VM kinds for? Are they just a prototyping tool to allow
>     > different implementation strategies to be benchmarked? Or are they
>     > permanent? Does anyone use them?
>     >
>     > I ask because I'm working on a VM bug, and non-default VM
>     kinds make
>     > already complex code even more complex and harder to edit.
>     >
>     > -- Tim Starling
>     >
>
>     I don't think anyone uses them, and the GOTO/SWITCH VMs receive
>     little
>     testing in practice (we don't use them in CI), and I believe
>     they're not
>     supported by the JIT either. Personally, I would be fine with simply
>     dropping them, as they do add additional maintenance burden
>     without any
>     apparent benefit. Maybe Dmitry has some thoughts on this.
>
>     Regards,
>     Nikita
>


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