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Date: Mon, 23 Feb 2015 08:52:31 -0500
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To: Robert Stoll <php@tutteli.ch>
Cc: PHP internals <internals@lists.php.net>
Content-Type: text/plain; charset=UTF-8
Subject: Re: [PHP-DEV] JIT (was RE: [PHP-DEV] Coercive Scalar Type Hints RFC)
From: ircmaxell@gmail.com (Anthony Ferrara)

Robert,

On Mon, Feb 23, 2015 at 3:27 AM, Robert Stoll <php@tutteli.ch> wrote:
> Hey all,
>
> tl;dr
>
> Just one point which JIT/AOT people should consider when dealing with PHP. PHP is highly dynamic and there are enough use cases which makes it impossible for a static analyser to infer types accurately without using a top type like mixed.
> How would you deal with variable function calls, variable variables, reflection, dynamic includes etc.
>
> Your inferred types would simply be wrong without using mixed. Consider the following
>
> function foo(int $a){}
> $a = 1;  //can be int for sure right?
> $b = "a";
> $$b = "h"; //oh no, your generated code would crash
> foo($a);
>
> Maybe I am wrong and there is a possibility, if so, please let me know, would be interesting to know.

This very specific example is easy to type. The reason is that we can
use constant propagation to know that $$b is really $a at compile
time. Hence we can reduce it to:

$a = "h";
foo($a);

And hence know **at compile time** that's an error.

This isn't the general case, but we can error in that case (from a
static analysis perspective at least) and say "this code is too
dynamic". In strict mode at least.

Anthony