evas - Clip mark performance improvement

evas - Clip mark performance improvement

stable release - cherry-pick me!

We propose a patch that reduces graph traversal work in
evas_object_child_map_across_mark(). It fixes a few particular
slowdowns around Tizen applications, including 0.6 seconds slowdown.

evas_object_child_map_across_mark() does not seem to need to
recursively call itself on the same object many times. Yet we have
noticed that in some scenarios it repeatedly traverses the same
subtrees of objects over and over again, whenever there is more than
one way of reaching these subtrees. In the production issue mentioned
above, certain elm_object_part_content_set() call results in millions
of recursive calls of evas_object_child_map_across_mark(), taking
~0.6sec total.

We propose to allocate a hash table during top-level call to store all
objects visited, and return from sub-calls instantly whenever we are
called over an object we already visited.