Performance penalty for using 'unnecessary' local variable in C#?

Question

Is there a performance penalty when using an extra local variable to store a method's result?

public string void ToFunkyDutchDate(DateTime this theDate) {
    var result = string.Format("{0:dd-MM-yyyy}", theDate);
    return result;
}

In similar trivial cases I could even tend to return the formatted string immediately. But this is just a simple example, because in a little more complex functions I often use this 'trick' of assigning the result to a temporary local variable first.

My main reason for this is that this allows easier debugging. I can just put a breakpoint on the return result; line, run and inspect if the result my function came up with is correct.

But the extra temporary result variable still feels a bit like unperformant then the alternative without:"

public static string ToFunkyDutchDate(DateTime this theDate) {
    return string.Format("{0:dd-MM-yyyy}", theDate);
}

I have eased this nagging feeling in three ways:

• Any performance decrease would be negligable
• Having a variable like result makes the code a bit more legible then return very long multi-line expression, which is worse any performance decrease
• If C-sharp's compiler was anywhere decent - which I think it is - then it SHOULD compile the extra variable away. E.g. make the resultant bytecode the exact same as if the function just returned the calculated result immediately without using a temporary variable. Either immediately (when not running in debug mode) - or perhaps when doing an optimized/production build (/optimize+).

Any compiler wizards here that know? :)

Answer 1

Normally no speed difference. See for example here and here.

Both versions of the code produce the same IL code in Release mode.

In Debug mode the IL code is a little longer (because the store to a local variable is made explicit): Example