What happens under the hood when using array initialization syntax to initialize a Dictionary instance on C#?

Question

Does anyone know what C# compiler does under the hood with the following code?

dict = new Dictionary<int, string>()
{
    { 1, "value1" },
    { 2, "value2" }
}

It is not clear to if it creates the KeyValuePair instances and call the Add method, or do something more optimized. Does anyone of you know it?