[Hercuros]

How much does this optimization save in terms of executable size on realistic examples (i.e. a full-sized code base)?

I would naively expect that for most functions you know too little about their arguments or the state in which they will be executed to be able to tell that certain branches will definitely not be taken. Especially since any function that has some mildly interesting side-effects (like loading and storing from a pointer or a class/struct field, or even _calling into any function that does that_) would seem to foil the analysis and turn large chunks of code into "unknown reachability".

Rephrasing, I would expect the set of basic blocks that can be removed just by essentially repeated constant propagation of statically-known function arguments to be pretty small. But I would be happy to be proved wrong if that intuition is not right.

Printf is somewhat of an exception, since the format strings are usually known at compile time, meaning that a lot of the control flow can indeed be deduced by compile-time evaluation, but for most functions I would not expect that.