Hello

I upgraded from 3.2 to 3.4 today. When I opened digikam afterwards, the GUI was extremely sluggish, moving the mouse over anything took very long and CPU load was always 100% on one core.

I managed to narrow it down to the tags tree. If it is not visible, then browsing works fast as usual, albeit still generally a bit slow-ish. If I open the tag filter sidebar, then digikam hangs for a while and then returns to normal. It will also hang if I move the mouse over the tag tree. If I open the tag editing sidebar, then browsing images becomes very slow, too, because the tree needs to be updated for every image.

Also, instead of the usual icons, I have question mark icons in front of all tags.

So it seems something is very wrong with loading tag information. For profiling, I loaded digikam into valgrind and opened the tag filter sidebar. I waited for it to open and settle down in terms of CPU load. Then I enabled callgrind through SSH (so I don't have to switch programs which would fudge the measurement) and only moved the mose a bit over the tag tree. Once the CPU load had settled again, I switched callgrind off. See attached KCacheGrind’s output for the measurement.

It seems that loading icons for the tags is the problem...
99.7% of the time that the CPU spends heating my room is in KIconLoader::loadIcon.
The database used has 199 tags, 13002 images and 16696 imagetags.

I rebuild digikam with debug symbols enabled. So if you want me to debug more specifically, please let me know.

Reproducible: Always