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Date: Thu, 23 Apr 2020 18:59:07 +0200
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To: PHP Internals List <internals@lists.php.net>
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Subject: Resolve fallback-to-root-namespace in preloaded implementations
From: nicolas.grekas@gmail.com (Nicolas Grekas)

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Hello,

with preloading and Composer, we don't need anymore to consider autoloading
for functions and/or constants. The reason is that basically Composer is
already doing a great job at loading functions: just give it a list of
files and it will ensure they are included all the time. Actually, Composer
is just an example, all similar "require all the time" strategies work.

The drawback of this approach used to be that requiring a bunch of
(potentially unused) files could be costly. But now that we have
preloading, this cost is zero. As such, autoloading functions/constants
would serve no purpose.

Then, we periodically have discussions about the rules for namespace
resolution of functions/constants. The fallback-to-root-namespace has no
measurable performance overhead - the cache is very effective. Yet, Nikita
has stated a few times that knowing the type of the arguments of the
function being called helps the engine a bit. With JIT, this might be
(/become) more important (is that correct, Dmitry and/or Nikita?)

I'm thus wondering: could we resolve the fallback-to-root-namespace rule at
preload time, for all preloaded implementations? For runtime-loaded code,
we would keep the current behavior.

In practice, this means that during development (when preloading is not
used), we would preserve all the hackability that the rule provides (PHP
being a hackable engine is a big PRO, here, this can help e.g. testing a
lot). The fallback-to-root-namespace is a wise pragmatic rule that serves
the language well IMHO. But in prod, in full-perf mode (aka when preloading
is enabled), this proposal would pave the way for better performance with
JIT, if confirmed.

WDYT?

Nicolas

PS: I fear I would be unable to implement anything related to this proposal
so I'm just sharing the idea to see if it could be interesting.

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