So it should never do function inlining, or replace multiplication by two with a bit shift? Because both of them quite fit "invisibly modifying non-dead code during translation".

> or it could do what you fracking told it to, consequences be damned

Yes, that's precisely what happens. The point is agreeing on what you "told it". The agreement stipulated in the standard is that in some cases (when you hit UB) you're effectively not agreeing on anything, i.e., the compiler can do what it want.

If that's not what you like, please let me know what should be mandated in the case of the fragment I wrote above, and how a compiler could offer that guarantee in an efficient and effective manner.