AFAIK, these functions have no overheard when they're called with a \. That's because they're resolved at compile time. Would you mind verifying please?

Verified here also, measurable perf gain confirmed (<10%).
Actually, we wondered about this change before and concluded we cannot do it because of PHP5.5 support: call_user_func($a) accepts more callables than $a() in PHP5.5. see https://3v4l.org/NGGth
Then, merging this into master is technically possible, but would open for years of merge conflicts we'll have to deal with weekly. I'd better not.

What we could do is wonder case by case when such a change is safe doing for 5.5 (ie no foo::bar style can possibly be used) and merge them on 3.4.

How do you solve these conflicts? Intellij knows how to resolve such simple conflicts automatically.

I don't think there are much cases when we can safely assume foo::bar is not used

Whatever the tool, not having to resolve anything is always going to be faster :)

You can even configure it to do this automatically every time without asking ;)

Closing as explained, thanks for submitting.

What makes you think this will cause conflicts on weekly basis? Those lines are rarely changed. I really don't see how are changes like #29245 preferable over this one. Performance gain is very similar but lot of places benefit from it instead of one, it has 0 complexity penalty nor change of behavior and very easy to solve conflicts. Lastly, if you are so worried about merge conflicts that are solvable automatically, you should fix your merge tool.

I tend to agree with @ostrolucky here. I'm not sure it will be such a pain, and if the gains are substantial, it might be worth reconsidering

Then let's merge this in 4.1? 55 files modified, that's a lot of potential future conflicts I fear.

Should I rebase? I didn't base it on older branch because I wanted to convert as much calls as possible, there are some new places in 4.2 that are missing in 4.1. Will you apply it to rest of the places during merge?

Yes please rebase. We'll handle the 4.2-only sites either while merging or in another PR (eg you can keep this one for reference)

rebased, only fabpot failures not cause by my changes

Thank you @ostrolucky.