Does the compiler optimize the function parameters passed by value?

Question

Lets say I have a function where the parameter is passed by value instead of const-reference. Further, lets assume that only the value is used inside the function i.e. the f

Answer 1

If you pass a variable instead of a temporary, the compiler is not allowed to optimize away the copy if the copy constructor of it does anything you would notice when running the program ("observable behavior": inputs/outputs, or changing volatile variables).

Apart from that, the compiler is free to do everything it wants (it only needs to resemble the observable behavior as-if it wouldn't have optimized at all).

Only when the argument is an rvalue (most temporary), the compiler is allowed to optimize the copy to the by-value parameter even if the copy constructor has observable side effects.