[08:49:35] <ori>	 https://gerrit.wikimedia.org/r/c/mediawiki/extensions/Scribunto/+/1232313 2x speed-up for many/most calls to mw.ustring.gsub(), which is 0.5% of index.php wall time and a lot more than that on edits and parser cache misses.
[09:03:36] <ori>	 I did a fair bit of this kind of work when I joined Google in 2016. It was a lot of fun, but within a few years all the low-hanging opportunities in hot code paths were picked clean, and I had to wean myself off. But looking at Wikimedia flame graphs made me fall into bad habits again.