gistfile1.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace Benchmarks
{
    class Program
    {
        static void Main(string[] args)
            => BenchmarkRunner.Run<BenchmarkClass>();
    }

    public class BenchmarkClass
    {
        [Benchmark]
        public int BenchmarkValue() => runMethod1(1000);

        [Benchmark]
        public int BenchmarkIsInst() => runMethod2(1000);

        private int runMethod1(int? parameter)
        {
            // Using isinst to cause branching but not cause additional overheads due to method invocation
            // We only care about the .Value invocations below
            // NB: Each invocation of this method has _two_ .Value invocations
            if (parameter is { } value)
            {
                int result = 0;

                for (int i = 0; i < parameter.Value; i++)
                    result += parameter.Value;

                return result;
            }

            return 0;
        }

        private int runMethod2(int? parameter)
        {
            if (parameter is { } value)
            {
                int result = 0;

                for (int i = 0; i < value; i++)
                    result += value;

                return result;
            }

            return 0;
        }
    }
}