[detrino]

Returning a stack allocated value is a move in C++11/14. It is also true that in many circumstances a compiler may optimize that move away using RVO/NRVO.

Consider this example: http://ideone.com/T872Oj

In F1 the compiler can NRVO away the move.

In F2 it cannot.

Both will fail to compile if you delete the move constructor.

[poizan42]

Does that mean that side effects in a move constructor is undefined behavior since you can't know whether it's going to be called?

Edit: I see that StephanTLavavej clarified that below.