using System.Runtime.CompilerServices;
using System.Threading;

public interface IClass {}
public class ClassA : IClass {}
public class ClassB : ClassA {}


public class Program
{
    [MethodImpl(MethodImplOptions.NoInlining)]
    static ClassA CastToClassA(object o) => (ClassA)o; // currently we always emit a fast path for ClassA here
                                                       // but in my case o is always ClassB (PGO helps)

    [MethodImpl(MethodImplOptions.NoInlining)]
    static bool IsClassA(object o) => o is ClassA;     // we don't expand it without PGO

    [MethodImpl(MethodImplOptions.NoInlining)]
    static IClass CastToIClass(object o) => (IClass)o; // we don't expand it without PGO

    [MethodImpl(MethodImplOptions.NoInlining)]
    static bool IsIClass(object o) => o is IClass;     // we don't expand it without PGO


    public static void Main()
    {
        // promote methods to tier1
        var b = new ClassB();
        for (int i = 0; i < 100; i++)
        {
            CastToClassA(b);
            IsClassA(b);
            CastToIClass(b);
            IsIClass(b);
            Thread.Sleep(16);
        }
    }
}