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Do you need to use std::move to store a parameter passed by value?

If you have a class which needs to store a construction parameter internally, and you want to take advantage of move semantics, I understand that the parameter should be passed by value:

    class Foo {
        std::string _string;
    public:
        Foo(std::string s): _string(s) {}
    };
    ...
    Foo foo(std::string("Temporary value")); // rvalue is moved in

However I'm a little unclear on the code required inside the constructor. Do you need to use `std::move` to preserve the rvalue reference, e.g.

        Foo(std::string s): _string(std::move(s)) {}

or does the compiler treat the parameter `s` as a moveable value by default (since it's going to be destroyed at the end of the function body), rendering the `std::move` unnecessary:

        Foo(std::string s): _string(s) {}