[cv5005]

You dont need UB for that.

A simple model for both compilers and programmers to understand:

"A variable whose address has not been taken need not be reachable via a random pointer".

I mean that's how an assembly programmer would think - if I put something in r0 I don't expect a store instruction to clobber it.

[UncleMeat]

What you describe there is UB. If you define this in the standard, you are defining a kind of runtime behavior that can never happen in a well formed program and the compiler does not have to make a program that encounters this behavior do anything in particular.