Is returning by rvalue reference more efficient?

Question

for example:

Beta_ab&&
Beta::toAB() const {
    return move(Beta_ab(1, 1));
}

Answer 1

It can be more efficient, for example, in a bit different context:

template 
T&& min_(T&& a, T &&b) {
    return std::move(a < b? a: b);
}

int main() {
   const std::string s = min_(std::string("A"), std::string("B"));
   fprintf(stderr, "min: %s\n", s.c_str());
   return 0;
}

As an interesting observation, on my machine clang++ -O3 generates 54 instructions for code above versus 62 instructions for regular std::min. However, with -O0 it generates 518 instructions for code above versus 481 for regular std::min.