using System;

namespace Miscompile
{
    class Program
    {       
        static void Main()
        {
            int result = F();
            if (result == 0)
            {
                Console.WriteLine("OK");
            }
            else
            {
                Console.WriteLine($"FAILED! result = {result}");
            }
        }

        // When compiled in Release mode, this function returns 1 under .NET 5
        // Expect it to return 0, which is the case under .NET Core 3.1
        private static int F()
        {
            bool x = false;            
            int c = 0;

            try
            {
                while (true)
                {
                    // It appears this assignment is erroneously removed or hoisted out of loop?
                    c = 0;

                    if (!x)
                    {
                        c++;
                        x = true;
                    }
                    else
                    {
                        return c;
                    }

                    // Uncommenting the below fixes issue, even if the assignment
                    // to c at loop start is commented out
                    // c = 0;
                }
            }
            finally
            {
                // finally block appears necessary to 
                // reproduce the error
                // Commenting out the finally block, the if expression,
                // or even just the WriteLine statement fixes the problem
                if (c != 0)
                {
                    Console.WriteLine("c not zero");
                }
            }
        }        
    }
}