Optimization .NET. App break

Question

In one of the applications, I encountered an error related to code optimization.

I tried to repeat this behavior in a test application. The app is available on GitHub: https://github.com/altk/NullableError

The error occurs only when compiling using .NET Native, but not everywhere. The error is reproduced on several PCs.

The application code is very simple. It should print on the console:

-------------- ELSE --------------
-------------- SUCCESS ------ --------

But due to optimization, it prints:

-------------- ELSE --------------
-------------- FAIL ------ --------

All application code:

#define DEBUG
using System;
using System.Collections.Generic;
using System.Diagnostics;

namespace NullableError
{
    sealed partial class App
    {
        private readonly Dictionary<String, String> _dictionary = new Dictionary<String, String>();

        public App()
        {
            InitializeComponent();

            Execute();
            Exit();
        }

        private Int64? NullableInt64
        {
            get
            {
                var resultString = this[nameof(NullableInt64)];
                return String.IsNullOrEmpty(resultString) ? default(Int64?) : Int64.Parse(resultString);
            }
            //-----FIX VARIANT------
            //UNCOMMENT NEXT LINE TO FIX 
            //[System.Runtime.CompilerServices.MethodImpl(System.Runtime.CompilerServices.MethodImplOptions.NoOptimization)]
            set
            {
                //-----FIX VARIANT------
                //REPLACE WITH 
                //this[nameof(NullableInt64)] = value != null ? value.Value.ToString() : null;
                this[nameof(NullableInt64)] = value?.ToString();
            }
        }

        private Int64? AnotherNullableInt64
        {
            get
            {
                var resultString = this[nameof(AnotherNullableInt64)];
                return String.IsNullOrEmpty(resultString) ? default(Int64?) : Int64.Parse(resultString);
            }
            set { this[nameof(AnotherNullableInt64)] = value?.ToString(); }
        }

        private void Execute()
        {
            //-----FIX VARIANT------
            //REPLACE WITH IF-ELSE WITH
            //NullableInt64 = (DateTimeOffset.Now - DateTimeOffset.MinValue).TotalMilliseconds < 0 ? (Int64?) 125 : null;
            if ((DateTimeOffset.Now - DateTimeOffset.MinValue).TotalMilliseconds < 0)
            {
                Debug.WriteLine("-------------- IF --------------");
                NullableInt64 = 125;
            }
            else
            {
                Debug.WriteLine("-------------- ELSE --------------");
                NullableInt64 = null;
            }

            //-----FIX VARIANT------
            //REPLACE WITH 
            //AnotherNullableInt64 = 0;
            AnotherNullableInt64 = null;

            Debug.WriteLine(String.Format("-------------- {0} --------------", this[nameof(NullableInt64)] == "0" ? "FAIL" : "SUCCESS"));
        }

        private String this[String key]
        {
            get
            {
                String result;
                return _dictionary.TryGetValue(key, out result) ? result : null;
            }
            set { _dictionary[key] = value; }
        }
    }
}

Answer 1

Microsoft . https://connect.microsoft.com/VisualStudio/feedback/details/2164313/net-native-optimization-breaks-an-application#

VS 2015 Update 2