Returning tuple broken when enabling fullAOT+LLVM

[spouliot]

Steps to Reproduce

1. Call the following code from an iOS app

public static async Task<(bool isAnswerCorrect, bool isInternetConnectionAvailable)> Test ()
{
	return (true, true);
}

note: full test case in xamarin/xamarin-macios#5798

2. Run on device without LLVM -> success
3. Run on device with LLVM -> failure (false is returned)

Current Behavior

Broken (regression, it works in XI stable) when enabling LLVM

Expected Behavior

Should work on both mono and LLVM fullAOT backend

On which platforms did you notice this

[x] iOS
[ ] macOS
[ ] Linux
[ ] Windows

Version Used:

2018-08 (d16-0), 2018-10 (xamarin-macios/master) and 2019-02 are all broken

Current XI stable is fine (2018-04)

Stacktrace

none

[spouliot]

c.c. @chamons @vargaz

[marek-safar]

@alexanderkyte @vargaz please investigate the regression

[alexanderkyte]

Here, let me add a sane-sized executable reproduction: https://gist.github.com/alexanderkyte/1974de18f51cb2a984908524809ec87c

[alexanderkyte]

Looks like we don't have any unit tests for this on the mono side, only acceptance/integration tests. This PR caused this breakage: #13312 .

I'll have a fix for this shortly.

We need to add this bug reproduction to the test harness at some point.

[lewurm]

This PR caused this breakage: #13312 .

Mentioned PR was merged 6 days ago, but the bug started to happen with 2018-08. Regression was likely introduced by something else.

[vargaz]

I can reproduce. When was the last time this worked ?

[spouliot]

mentioned above
2018-08 (d16-0), 2018-10 (xamarin-macios/master) and 2019-02 are all broken
Current XI stable is fine (2018-04)

[vargaz]

So 2018-04 was still using the old llvm 3.6.

[spouliot]

ouch :(

[lambdageek]

Doesn't have to be a tuple. This also fails (prints 0. expected to print 1)

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

public struct OneThing<T1> {
	public T1 Item1;
}

public class P {

	[MethodImpl (MethodImplOptions.NoInlining)]
	public static int TestCaller () {
		var t = Task.FromResult<OneThing<int>>(new OneThing<int> {Item1 = 42});
		t.Wait ();
		int a = t.Result.Item1;
		return (a == 42) ? 1 : 0;
	}

	public static int Main () {
		var t = TestCaller ();
		var i = t;
		Console.WriteLine ($"{i}");
		return 0;
	}
}

compile with mono --runtime=mobile --aot=llvmonly example.exe run with mono --runtime=mobile --llvmonly example.exe

example.opt.ll

[lambdageek]

Don't need tasks either. Just a generic method will do.

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

public struct OneThing<T1> {
	public T1 Item1;
}

public class S<T> {
	public T Result;

	public S(T val) {
		Result = val;
	}

}

public class Maker {
	[MethodImpl (MethodImplOptions.NoInlining)]
	public static S<T> FromResult<T> (T result) {
		return new S<T>(result);
	}
}

public class P {

	[MethodImpl (MethodImplOptions.NoInlining)]
	public static int TestCaller () {
		var t = Maker.FromResult<OneThing<int>>(new OneThing<int> {Item1 = 42});
		int a = t.Result.Item1;
		return (a == 42) ? 1 : 0;
	}

	public static int Main () {
		var t = TestCaller ();
		var i = t;
		Console.WriteLine ($"{i}");
		return 0;
	}
}