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Date: Sat, 26 Oct 2019 10:35:30 +0200
Message-ID: <CAG9XoMQxFY8t76e1Epp7FCX=sxn3-Y=eWg=w0NTFGHNG=ePDgg@mail.gmail.com>
To: Rowan Tommins <rowan.collins@gmail.com>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000ea41a90595cc26ff"
Subject: Re: [PHP-DEV] Re: [RFC] Union Types v2
From: benjamin.morel@gmail.com (Benjamin Morel)

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>
> I think this performance impact is a real concern; PHP is the only langua=
ge
> I know of which implements type checks entirely at run-time in production
> code, and we should ask ourselves if that's definitely the right approach=
.


Would it be possible, at least in principle, to build a static analysis
> tool which could prove that certain type checks would never fail, and pri=
me
> OpCache with code that leaves them out? As I understand it, this is how
> Dart works: the compiler only emits run-time checks for assertions it can=
't
> prove true by static analysis.



I was wondering the same thing, especially in the light of preloading,
where a lot of class/function definitions are known on startup.

For example, doing:

  function x(): int {}
  function y(int $foo) {}
  y(x());

Should definitely not redundantly check the type of the y() parameter, if
possible.

Also, in the case of JIT, shouldn't type hints actually *improve*
performance?

=E2=80=94 Benjamin


On Thu, 24 Oct 2019 at 14:47, Rowan Tommins <rowan.collins@gmail.com> wrote=
:

> Hi Dmitry,
>
> On Wed, 23 Oct 2019 at 16:43, Dmitry Stogov <dmitry@zend.com> wrote:
>
> > Actually, I think PHP already took wrong direction implementing "typed
> > references" and "type variance".
> > Introducing more "typing", we suggest using it, but this "typing" comes
> > with a huge cost of run-time checks.
> > From 10% (scalar type hint of argument) to 3 times (typed reference
> > assignment) performance degradation.
> > Anyone may rerun my benchmarks
> > https://gist.github.com/dstogov/fb32023e8dd55e58312ae0e5029556a9
> >
>
>
> I think this performance impact is a real concern; PHP is the only langua=
ge
> I know of which implements type checks entirely at run-time in production
> code, and we should ask ourselves if that's definitely the right approach=
.
>
> Would it be possible, at least in principle, to build a static analysis
> tool which could prove that certain type checks would never fail, and pri=
me
> OpCache with code that leaves them out? As I understand it, this is how
> Dart works: the compiler only emits run-time checks for assertions it can=
't
> prove true by static analysis.
>
> The simpler idea I had in this area was caching what type checks a value
> had passed, either on each zval or perhaps just at the class level, so th=
at
> checking the same type again would be much faster, even if it was a compl=
ex
> union with multiple interfaces.
>
> Regards,
> --
> Rowan Tommins
> [IMSoP]
>

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