c++c++17nrvoearly-return

Does early return of the same variable prevent NRVO?

Here is the code:

std::vector<int> foo(bool cond) {
    std::vector<int> result;
    if (cond) {
        return result;      // (1)
    }
    result.push_back(42);
    return result;          // (2)
}

The same variable result is being returned from two places. Is that still considered as a condition for NRVO?

P.S. I realize that this code can be refactored to return this value from a single point, so my question is theoretical.

Update: Ok, NRVO is optional even in C++17. Is there any reason why multiple returns would prevent the compiler to use NRVO but the optimization would be used for a single return?

Solution

  • Does early return of the same variable prevent NRVO?

    No, NRVO is still possible and most implementations will indeed use it in this situation.