Do I need to use std::move(...) when returning string result from std::stringstream?

For my implementation of the std-lib the str() implementation for std::stringstream has a str() && version, making it possible to move the string out of the stream without copying it.

My question is, when returning from a function, do you need to specify std::move(...) or is it assumed automatically and can be left out?

Toy example:

#include <sstream>
#include <iostream>

std::string f() {
    auto ss = std::ostringstream{};

    ss << std::string(10000000, '*');
    
    // 开发者_JAVA百科return std::move(ss.str()); // Is move() required here?
    // return ss.str() // or does this use the str() && implementation?
    return std::move(ss).str(); // Syntax suggested by ALX23z
}

int main() {
    auto x = f();
    std::cout << x << "\n";
}

Edit: Updated to show that my question does not have to do with SSO.

Edit: The answers marked as duplicates does not answer the question I am asking with member functions, and if you were to use the answers given in the "duplicate" questions you would get worse performance. (it's now reopened)