Assertion failed 'retExpr->gtOper == GT_RETURN' caused by SuppressGCTransition

[jkotas]

Starting:    System.Runtime.Extensions.Tests (parallel test collections = on, max threads = 2)

Assert failure(PID 29805 [0x0000746d], Thread: 29824 [0x7480]): Assertion failed 'retExpr->gtOper == GT_RETURN' in 'System.Diagnostics.Tests.StopwatchTests:GetTimestamp()' (IL size 26)

    File: /__w/2/s/src/jit/morph.cpp Line: 18653
    Image: /home/helixbot/work/409fcbf4-4e6f-4b59-a1b8-38c6da3609f0/Payload/dotnet

[jkotas]

@AaronRobinsonMSFT We should hold off adding SuppressGCTransition in any more places until this is fixed. (I expect that the problem is affecting all platforms. We just got lucky to not hit it anywhere else yet.)

[AaronRobinsonMSFT]

@jkotas Agreed.

[AaronRobinsonMSFT]

Issue doesn't repro on Windows x64. I am using the following code and setting COMPlus_TieredCompilation=0 to try and reproduce the issue. The generated code gen on Windows is unusual, but the JIT doesn't assert. I will try on a Linux x64 or macOS and if I still don't see issue fallback to the CoreFX test itself.

Managed

using System;
using System.Threading;
using System.Runtime.InteropServices;

namespace System.Runtime.InteropServices
{
    public class SuppressGCTransitionAttribute : Attribute
    {
        public SuppressGCTransitionAttribute() { }
    }
}

partial class SW
{
    public static long GetTimestamp()
    {
        return QueryPerformanceCounter();
    }
}

partial class SW
{
    private static long QueryPerformanceCounter()
    {
        return (long)NativeLib.GetTimestamp();
    }

    static class NativeLib
    {
        public const string Path = @"NativeLib.dll";

        [DllImport(Path, EntryPoint = "SystemNative_GetTimestamp", ExactSpelling = true)]
        [SuppressGCTransition]
        internal static extern ulong GetTimestamp();

    }
}

namespace PInvokeTesting
{
    public unsafe class Program
    {
        private static readonly ManualResetEvent s_sleepEvent = new ManualResetEvent(false);

        static void Main(string[] args)
        {
            long ts1 = SW.GetTimestamp();
            Sleep();
            long ts2 = SW.GetTimestamp();
            Assert.NotEqual(ts1, ts2);
        }

        private static void Sleep(int milliseconds = 1)
        {
            s_sleepEvent.WaitOne(milliseconds);
        }
    }

    public static class Assert
    {
        static public void NotEqual(long a, long b)
        {
            if (a == b)
            {
                throw new Exception("Bad");
            }
        }
    }
}

Native

#include <cstdint>

#define EXPORT extern "C" __declspec(dllexport)
#define CALLCONV __stdcall

namespace
{
    std::atomic<uint64_t> _n{ 0 };
}

EXPORT
uint64_t CALLCONV SystemNative_GetTimestamp()
{
    return (++_n);
}

[AaronRobinsonMSFT]

Also unable to reproduce this on macOS using the above source. I am going to try Linux, but getting less optimistic the code above represents the issue or this is a targeted issue on the Linux platform.

[AaronRobinsonMSFT]

Failing CoreFX test: https://github.com/dotnet/corefx/blob/cf28b7896a762f71c990a5896a160a4138d833c9/src/System.Runtime.Extensions/tests/System/Diagnostics/Stopwatch.cs#L16-L22

[jkotas]

You may need to disable tiered compilation to reproduce this.

[AaronRobinsonMSFT]

@jkotas I have been passing COMPlus_TieredCompilation=0 in all scenarios and verifying it via JIT dump. Is there another way to accomplish/verify this?