From c7f5916ef6458c764b77810419f5788cfebcae4e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Aleksey=20Kliger=20=28=CE=BBgeek=29?= <alklig@microsoft.com>
Date: Thu, 18 Jul 2019 16:46:55 -0400
Subject: [PATCH] [mini] Runtime check if boxing is needed for DIM constrained
 calls (mono/mono#15729)

This is to handle the following example.  The issue is that in Check() we have
a constrained call where the called method is IAdder`1<!!U>::PlusPlus() which
is a default interface method, and we need to determine at runtime whether to
box the this argument.

```
using System;

public interface IAdder<T> {
	int Add (int x);

	int PlusPlus () {
		return Add (1);
	}
}

interface IGen3<T> { }

struct Adder<T> : IAdder<IGen3<T>> {
	int _field;
	public int Add (int x) {
		_field = x + _field;
		return _field;
	}
}

public class P {
	public static int Check<T, U>(T t) where T : IAdder<U> {
		return t.PlusPlus () + t.PlusPlus ();
	}

	public static void Main () {
		var x = new Adder<object> ();
		int y = Check<Adder<object>, IGen3<object>> (x);
		Console.WriteLine ("expect 2, got {0}", y);
	}
}
```

Commit migrated from https://github.com/mono/mono/commit/3f55bfb5cc305c1c416edf84fff5440843784deb
---
 src/mono/mono/mini/method-to-ir.c | 4 +++-
 src/mono/mono/tests/Makefile.am   | 1 -
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/mono/mono/mini/method-to-ir.c b/src/mono/mono/mini/method-to-ir.c
index ff048d3991672d..0fc5164756bf38 100644
--- a/src/mono/mono/mini/method-to-ir.c
+++ b/src/mono/mono/mini/method-to-ir.c
@@ -5636,10 +5636,12 @@ handle_constrained_call (MonoCompile *cfg, MonoMethod *cmethod, MonoMethodSignat
 		 * A simple solution would be to box always and make a normal virtual call, but that would
 		 * be bad performance wise.
 		 */
-		if (mono_class_is_interface (cmethod->klass) && mono_class_is_ginst (cmethod->klass)) {
+		if (mono_class_is_interface (cmethod->klass) && mono_class_is_ginst (cmethod->klass) &&
+		    (cmethod->flags & METHOD_ATTRIBUTE_ABSTRACT)) {
 			/*
 			 * The parent classes implement no generic interfaces, so the called method will be a vtype method, so no boxing neccessary.
 			 */
+			/* If the method is not abstract, it's a default interface method, and we need to box */
 			need_box = FALSE;
 		}
 
diff --git a/src/mono/mono/tests/Makefile.am b/src/mono/mono/tests/Makefile.am
index 567c2f7572fc89..c7929aa3983e51 100755
--- a/src/mono/mono/tests/Makefile.am
+++ b/src/mono/mono/tests/Makefile.am
@@ -1736,7 +1736,6 @@ KNOWN_FAILING_TESTS = \
 	appdomain-marshalbyref-assemblyload.exe	\
 	abort-try-holes.exe \
 	threads-init.exe \
-	dim-constrainedcall.exe \
 	gptail1.exe \
 	itaili1.exe \
 	sirtail1.exe \