[dzaima]

Strict aliasing in particular is very dependent on coding style; I too just turn it off with essentially no harm, but certain styles of code that don't involve carefully manually CSEing everything might benefit a good bit (though with it being purely type-based imo it's not that useful).

Outside of freestanding/kernel scenarios, null treatment shouldn't affect anything, and again can similarly benefit probably a decent amount of code by removing what is unquestionably just dead code. There's the question of pointer addition resulting in/having an argument of null being UB, which is rather bad for offsetof shenanigans or misusing pointers as arbitrary data, but that's a question of provenance, not anything about null.

Global integer overflow UB is probably the most questionable thing in that list, and I'd quite prefer having separate wrap-on-overflow and UB-on-overflow types (allowing having unsigned UB-on-overflow too). That said, even having had multiple cases of code that could hit integer overflow and thus UB, I don't recall any of them actually resulting in the compiler breaking things (granted, I know not to write a+1<a & similar for signed ints), whereas I have had a case where the compiler "fixed" the code, turning a `a-b < 0` into the more correct (at least in the scenario in question) `a<b`!

I do think that it would make sense to have an easy uniform way to choose some specific behavior for most kinds of UB.