Well... I'm in embedded systems. In embedded systems, you almost never change compilers. You usually don't even upgrade the compiler. Whatever the compiler is for a project, that's what it will be for that project forever. And in your case, it sounds like you only compiled that code with one compiler.

But as far as UB goes, that's cheating. We're playing on "easy mode". We know what that compiler is going to do, and that's all we need.

"Hard mode" for UB is when you have to worry about what a different, unknown, perhaps not-yet-written compiler is going to do with your code. What is the absolute worst that a compiler could do, within the rules, to your code? You and I don't worry about this, and it doesn't bite us. People writing library code do have to worry about it far more than we do.

So I agree that the concern is overblown. But I think that maybe we miss that it's a real concern, because it doesn't hit us.