First we need to reduce the UB zoo because the types of UB in the C standard go all over the place (from "no newline at end of file" to "oops, this specific UB combined with this specific code compiled on this specific version of this specific compiler with these specific compile options leaks execution into the next function").

Also AFAIK the point where UB causes 'runtime disruption' is way after the C frontend in the optimizer passes, e.g. much too late for issuing compilation warnings even if the UB situation could be detected (because as far as I understand the problem, the breakage happens mainly because of unexpected 'spooky actions at a distance' between different optimizer passes, e.g. a specific optimizer pass doesn't even notice that it broke the code).

You can get runtime errors for a lot of serious UB problems via UBSAN though of course (at the cost of some performance).