I think you are thinking about the memory that 'in' and 'out' point to aliasing each other. That's handled with the "restricted" keyword, as you say. I'm talki

I think you are thinking about the memory that 'in' and 'out' point to aliasing each other. That's handled with the "restricted" keyword, as you say. I'm talking about something else, the issue of 'in' and 'out' pointing into the stack, so writing to them changing the value of the local variables. That is basically treated as UB by every C compiler, and no compiler I am aware of provides any switches which would make it easier to handle, it's just horrible and your code behaves in different ways depending on the compiler and optimisation level.