apply_filters() performance

[ryan]

Pushing and popping to the wp_current_filter array is not necessary if there is not a function hooked to the filter.

On my test setup, that patch eliminates 2886 calls to array_pop() as well as the corresponding assignments and reduces time spent in apply_filters() by almost 50%. Most filters, like the often called gettext one, have nothing hooked to them so the pushing and popping is a waste of time. For cases where there is hook on the filter, the patch adds one isset check.

Nice catch.

Could this be applied to do_action() as well?

Above my head to do it myself, but since apply_filters_ref_array() is almost identical, could this patch be used in that function as well (but slightly modified if needed)?

Extend to apply_filters* and do_action*

On a front page load with 5 posts and default theme, that reduces the number of array_pop() calls from 3272 to 250.

With a scratch install having just the default post, benchmarks suggest a 2.4% performance improvement. With more posts (and more filters without attached functions being called) the improvement becomes more notable. With 10 simple posts I see a 3% improvement.

(In [17638]) Avoid array push/pops for empty filters and actions. fixes #17110