Save a few processing cycles in `WP_Hook`

[bor0]

I found two low-hanging fruits that could improve the performance of hooks:

1. Use count only when really needed (sometimes it may not be needed)
2. is_object is redundant in is_object( $x ) && $x instance of X

[davidbaumwald]

Thanks @bor0! I am adding the performance keyword so that this gets picked up during one of their scrubs.

[bor0]

Thanks @davidbaumwald.

Some more context for the second change, as the first change (count) seems straightforward.

In case we pass an object, the performance will be better as the call to is_object will be redundant. In the other case where we pass a non-object, the instanceof operator (a variant of is_a()) will first ​check if it is an object before doing any further processing. Therefore, no additional cycles should be wasted in both cases.

[johnbillion]

Thanks for the patch @bor0. Removing the is_object() call makes sense.

The change to the count( $args ) call could actually increase the number of times it gets counted. Currently the count happens exactly once for every call to apply_filters(). With this change in place the number of times the count happens is equal to the number of callbacks attached to the filter where accepted_args is greater than or equal to the number of arguments passed to the filter. Worth some more thought.

[johnbillion]

Correction: With this change in place the count actually happens once for every callback where accepted_args is not set to 0. Seems like therefore this will most often increase the number of counts that happen.

[bor0]

@johnbillion, great catch! What an oversight. I totally missed that the processing is happening within a loop for all callbacks.

[SergeyBiryukov]

In 55748:

Plugins: Remove is_object() check in WP_Hook:build_preinitialized_hooks().

This is a minor performance enhancement:

• If an object is passed, the call to is_object() will be redundant.
• If a non-object is passed, the instanceof operator (a variant of is_a()) will first ​check if it is an object before doing any further processing.

Therefore, no additional processing cycles should be wasted in both cases.

Follow-up to [38571].

Props bor0, johnbillion, davidbaumwald.
Fixes #58290.