Why is Console.WriteLine(i + "") faster than Console.WriteLine(i) in C#?

Question

I tested the speed of i.ToString(), i + "", Console.WriteLine(i+"") and Console.WriteLine(i). (i was an int) The results were the following:

i.ToString() (149 ms) was faster than i + "" (202 ms).

But when I used Console.WriteLine Console.WriteLine(i + "") (743 ms) was a lot faster than Console.WriteLine(i) (927 ms, according to TextWriter source Console.WriteLine calls ToString() internally).

Now my question is: Why is i + "" faster in combination with Console.WriteLine()?

Notes:

1. I used 1,000,000 iterations for the non-console stuff and 1,000 for my console tests.
2. I use .NET Framework 4.7.1
3. The code was compiled with Debug configuration in Visual Studio 2017 (version 15.9.4). Release gives similar results.
4. The project type is console application.
5. Code is available as a GitHub Gist

Answer 1

When I looked at source code, I saw this:

i + "" = String.Concat(object) which call obj.ToString() There is one more String.Concat(object). So it is slower.

1st way) With Console.WriteLine it is simple:

    public static void WriteLine(String value)
    {
        Out.WriteLine(value);
    }

https://referencesource.microsoft.com/#mscorlib/system/console.cs,5ac7c4fda643413b

Internaly it creates 1 buffer with value + '\r\n' and call .Write(char[], int, int) only once.

2nd way) When you call it with int, it is different.

    public virtual void WriteLine(int value) {
        Write(value);
        WriteLine();
    }

https://referencesource.microsoft.com/#mscorlib/system/console.cs,82d5745bf4a5ecc6

That way it calls Write(char[], int, int) twice. And it can be that slowdown but I can't tell for sure. It is only the hint, where the problem can be.

EDIT:

Additionaly the 2nd way, it calls int.ToString(IFormatProvider) to get string representation of number where is another overhead that can slow it down a little because it can get the instance of that provider every time. https://referencesource.microsoft.com/#mscorlib/system/globalization/numberformatinfo.cs,9c4284b5db21c23a