> I think this is not really true. Or rather, it depends on the UB you are talking about.

I mean, if you're going to argue that a compiler can do anything with any UB, then by all means make that argument.

Otherwise, then no, I don't think it's reasonable for a compiler to cause an infinite loop inside a function simply because that function itself doesn't return a value.

When you say "cause", do you mean insert on purpose, or do you mean cause by accident? I could see the latter happening, for example because the compiler doesn't generate a ret if the non-void function doesn't return anything, so control flow falls through to whatever code happens to be next in memory. I'm not aware of any compiler that does that, but it's something I could see happening, and the developers would have no reason to "fix" it, because it's perfectly up to spec.