Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:73026
Mailing-List: contact internals-help@lists.php.net; run by ezmlm
Received-SPF: pass (pb1.pair.com: domain bof.de designates 80.242.145.70 as permitted sender)
MIME-Version: 1.0
In-Reply-To: <531BFEF1.5000305@sugarcrm.com>
References: <CAMauByU4oBTu7UYnZU15n7C6mhA1HCZLvC1UVD066ei+XRsDkw@mail.gmail.com>
	<531BFEF1.5000305@sugarcrm.com>
Date: Sun, 9 Mar 2014 09:35:38 +0100
Message-ID: <CAJ26g5TmZ8Was6YHtdMKo8vaqSAqYfn4GQH5d9u1WFw9tox2Hg@mail.gmail.com>
To: Stas Malyshev <smalyshev@sugarcrm.com>
Cc: internals <internals@lists.php.net>, Marco Schuster <marco@m-s-d.eu>
Content-Type: multipart/alternative; boundary=001a11c1e05422920b04f4285f92
Subject: Re: [PHP-DEV] Idea: ifdef-like feature to ease userland BC
From: bof@bof.de (Patrick Schaaf)

--001a11c1e05422920b04f4285f92
Content-Type: text/plain; charset=ISO-8859-1

Am 09.03.2014 06:41 schrieb "Stas Malyshev" <smalyshev@sugarcrm.com>:

> How is it supposed to be implemented? PHP has no separate "compile-time"
> than can produce significant improvement in performance, like C-like
> languages do, and given opcode caching, such conditions should either be
> resolved statically - which means limited usability, as you'd have to
> drive them off something that you can use no code to define, or use some
> logic to resolve them dynamically, which logic would probably take
> nearly as much time and space as regular if() would.

Such compile-time optimization, especially regarding opcaches leaving out
entire blocks of code completely for the rest of their livetime, can be
sanely driven, as far as I can see, exactly for the set of constants that
have already been defined at the end of MINIT. A single bit giving that
meta information on the constant, would suffice to signal that possibility.

That would basically be all constants defined by PHP core and loaded
extensions, Which might already be, in my eye, a useful thing to support,
providing dead block elimination for PHP version constant compares, tests
that certain socket flags are present, and so on.

To me (and others when they would use it), it would be even more useful
when a "configurable constants" extension like PHP-Defcon (see github) is
used. We use that to define diverse server-type constants on different
servers all using the same PHP code base.

Now, all that does not need new syntax - "just" a compile time evaluation
of any branchy constant expression regarding "does it use only literals and
constants already defined at the end of MINIT".

Maybe I'm stupid to not know that APC and/or opcache already does that?
Couldn't see it immediately so I thought I'd write the issue down.

best regards
  Patrick

--001a11c1e05422920b04f4285f92--