C# IL code optimization: conditional operator (?:) and re-assignment of same variable

Question

I was reading C# 7.0 changelog and ran into an example that shows new tuples syntax.

private static (int Max, int Min) Range(IEnumerable<int> numbers)
{
    int min = int.MaxValue;
    int max = int.MinValue;
    foreach(var n in numbers)
    {
        min = (n < min) ? n : min;
        max = (n > max) ? n : max;
    }
    return (max, min);
}

And I got curious if the compiler optimizes lines like min = (n < min) ? n : min; cause min = min operation seems a bit useless. I compiled the code (in release mode) and opened it in ILDASM and saw that min = min assignment was still there.

Is it a tough question for the compiler to skip the assignment? Or maybe it's because of some multi-threading issue?

Answer 1

The way that the conditional operator works is that you always get a value assigned, since the compiler will always expect a value after the '='. Of course the compiler could be written to check whether the left and right hand side is the same, rewriting the variable (right to left) is faster most of the times than using a check to compare the two variables, when taking into account that in most cases a min = min scenario is unlikely and this would only result in an extra check and slow down execution 99.9% of the time.

It's the job of the programmer to determine when to use a conditional operator or a simple if

int min = int.MaxValue;
int max = int.MinValue;
foreach(var n in numbers)
{

    if(n < min) min = n;
    if(n > max) max = n;
}

This way the min = min assignment can be avoided for such circumstances.