Hello, I've found small performance problem in standard library, https://youtrack.jetbrains.com/issue/KT-22042, but I don't know whether I should try to contribute fix for it. What's the current policy about stdlib performance? Is it okay to sacrifice a bit of local code readability/reusing for the sake of minor (~10-20%) improvements?

Yes, it's ok to improve the performance at a price of increased verbosity.