Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:116313
MIME-Version: 1.0
References: <e06cea29-f796-019f-cc23-b20abc1b2941@wikimedia.org> <CAF+90c_G_EDXF7vU1poPfOZ-n8NRq-oFFq-Q4g8Dnpptnz0g4g@mail.gmail.com>
In-Reply-To: <CAF+90c_G_EDXF7vU1poPfOZ-n8NRq-oFFq-Q4g8Dnpptnz0g4g@mail.gmail.com>
Date: Wed, 10 Nov 2021 12:10:34 +0300
Message-ID: <CAPVMwwvvjagFBL47RgZhpgdB8pbQpzn7kjcQR8i3thkNiVbUTA@mail.gmail.com>
To: Nikita Popov <nikita.ppv@gmail.com>
Cc: Tim Starling <tstarling@wikimedia.org>, Dmitry Stogov <DStogov@perforce.com>, 
	PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000f0f3df05d06b9922"
Subject: Re: [PHP-DEV] VM kinds
From: dmitrystogov@gmail.com (Dmitry Stogov)

--000000000000f0f3df05d06b9922
Content-Type: text/plain; charset="UTF-8"

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> wrote:

> On Wed, Nov 10, 2021 at 8:13 AM Tim Starling <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
>

--000000000000f0f3df05d06b9922--