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Message-ID: <b853e1a8b0e46f3b0115ca3790551575b5119af4.camel@ageofdream.com>
Subject: Re: [PHP-DEV] [Concept] Flip relative function lookup order
 (global, then local)
To: internals@lists.php.net
Date: Fri, 02 Aug 2024 13:19:41 -0400
In-Reply-To: <CAPyj-LCoBY2bPHLmsyONYDbY9aRSraLz5QNskeTiWfpMD0pTSg@mail.gmail.com>
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From: lists@ageofdream.com (Nick Lockheart)

On Fri, 2024-08-02 at 18:51 +0200, Ilija Tovilo wrote:
> Hi everyone
>=20
> As you probably know, a common performance optimization in PHP is to
> prefix global function calls in namespaced code with a `\`. In
> namespaced code, relative function calls (meaning, not prefixed with
> `\`, not imported and not containing multiple namespace components)
> will be looked up in the current namespace before falling back to the
> global namespace. Prefixing the function name with `\` disambiguates
> the called function by always picking the global function.
>=20
> Not knowing exactly which function is called at compile time has a
> couple of downsides to this:
>=20
> * It leads to the aforementioned double-lookup.
> * It prevents compile-time-evaluation of pure internal functions.
> * It prevents compiling to specialized=C2=A0 opcodes for specialized
> internal functions (e.g. strlen()).
> * It requires branching for frameless functions [1].
> * It prevents an optimization that looks up internal functions by
> offset rather than by name [2].
> * It prevents compiling to more specialized argument sending opcodes
> because of unknown by-value/by-reference passing.
>=20
> All of these are enabled by disambiguating the call. Unfortunately,
> prefixing all calls with `\`, or adding a `use function` at the top
> of
> every file is annoying and noisy. We recently got a feature request
> to
> change how functions are looked up [3].=20

I think there should be some way to use globals first at compile time.

I had suggested a per-file directive in a post to this list a while
back. Something like:

namespace foo;
use global functions;

class MyClass {

 // do stuff.

}


Where `use global functions` would be a special token that the compiler
uses to skip the ns lookup and use dedicated opcodes when available.