No C doesn't have RVO in the C++ sense. Sure C can optimize the copies implied by "returning values" in the same way they can optimize other copies or anything

No C doesn't have RVO in the C++ sense. Sure C can optimize the copies implied by "returning values" in the same way they can optimize other copies or anything at all, if the observable behavior is the same, due to "as if" - but that's not RVO (as it is discussed in C++). It doesn't even need a special name: it's just plain old optimization. RVO is a very specific optimization that has its own language in the standard (which is notable since the standard is pretty much silent on the vast majority of optimizations) and it is special precisely because it allows the optimization to occur even if it changes observable behavior. C does not have it, and compilers must compile the some code more conservatively because of it: e.g., if the address of return values escape in the caller and/or callee, a C compiler must ensure that the program always observes distinct addresses for distinct objects in the source, but in C++ one is free to observe that two apparently different objects are the same. Now, sure, at least 90% of actual RVO is about eliminating constructors and destructors with side effects - which C doesn't have and so RVO simply doesn't apply most of the time: but one shouldn't conclude that "C has RVO", rather "C mostly doesn't need RVO, and in the cases were it could use it, it is not allowed and must be more conservative than C++".