CoreCLR TieredCompilation JIT bug

output.txt

> .\repro.cmd
C:\tmp\TieredJit\TierJit\TierJit>set COMPlus_TieredCompilation=0

C:\tmp\TieredJit\TierJit\TierJit>dotnet run -c Release
Correct value: True

C:\tmp\TieredJit\TierJit\TierJit>set COMPlus_TieredCompilation=1

C:\tmp\TieredJit\TierJit\TierJit>dotnet run -c Release
Correct value: False

Program.cs

using System;

namespace TierJit
{
    class Program
    {
        static void Main(string[] args)
        {
            var array = new byte[] {0x00, 0x01};
            var reader = new BinaryTokenStreamReader(array);

            var val = reader.ReadByte();

            // Prints true if tiered jit is disabled
            // and false if tiered jit is enabled.
            Console.WriteLine("Correct value: " + (val == 0x01));
        }
    }

    public class BinaryTokenStreamReader
    {
        private readonly byte[] currentBuffer;

        public BinaryTokenStreamReader(byte[] input)
        {
            this.currentBuffer = input;
        }

        byte[] CheckLength(out int offset)
        {
            // In the original code, this logic is more complicated.
            // It's simplified here to demonstrate the bug.
            offset = 1;
            return currentBuffer;
        }

        public byte ReadByte()
        {
            int offset;
            var buff = CheckLength(out offset);
            return buff[offset];
        }
    }
}

repro.cmd

set COMPlus_TieredCompilation=0
dotnet run -c Release

set COMPlus_TieredCompilation=1
dotnet run -c Release

TierJit.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.1</TargetFramework>
  </PropertyGroup>

</Project>