Allow Closures to reuse their run_time_cache when opcache is enabled

[arnaud-lb]

Possible alternative fix for GH-10782

This implements the approach described in #10782 (comment):

may be storing "scope" in the first slot of the closure's run_time_cache

Unfortunately this results in a small regression on the Symfony benchmark (0.20% wall time, 0.03% icount).

[bwoebi]

Not only is it a CPU time regression, but it also leaks memory on the arena (it's just not reported as a leak, because arena).
Every time the scope changes (e.g. an inherited function called on different extending objects), a new run time cache is allocated.

If you want to meaningfully do this, you'll have to store the closures run_time_cache in e.g. class_mutable_data of the scope they belong to.

Otherwise, I think Dmitrys suggestion was to do this just once. I.e. store the scope for the first time the runtime cache is allocated (i.e. when ZEND_MAP_PTR_GET() is NULL) and otherwise heap allocate.
This would still cause repeated observer initializations, but make it consistent between opcache and non-opcache.

[arnaud-lb]

Yeah, I planned to analyze the regression and check for mistakes, because I didn't expected that.

My goal was only to have a similar reuse rate with opcache than without, but indeed there may be ways to improve that even more.

it also leaks memory on the arena [...]. Every time the scope changes (e.g. an inherited function called on different extending objects), a new run time cache is allocated.

I'm not sure what you mean here. Do you have an example where the scope of a closure changes? (without binding it explicitly). All I can think of is traits, but even in that case I allocate on the arena only once.

With the current changes, I never allocate on the arena more than once per Closure.

Otherwise, I think Dmitrys suggestion was to do this just once. I.e. store the scope for the first time the runtime cache is allocated (i.e. when ZEND_MAP_PTR_GET() is NULL) and otherwise heap allocate.

That's what I was targeting, but it's possible I've made mistakes that prevent this.

[bwoebi]

			} else if (!ptr
			 && func->common.fn_flags & ZEND_ACC_CLOSURE) {

I see what I missed - the !ptr and the closure check are on two different lines and missed that they belong to the same condition.