Fix analysis of interface methods on generic types

Fixes an issue observed in #92881. The dependency analysis within the compiler was incorrectly considering `Equals(object x, object y)` to be the implementation of `IEqualityComparer<T>.Equals(T, T)`. When we generate the interface dispatch table, we'd use the correct algorithm (that looks at uninstantiated types) and fail the compilation. The fix is to use the same algorithm during dependency analysis.

Looks like this has been broken ever since interface support was added to CoreRT: dotnet/corert#626.

Author: MichalStrehovsky

src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/EETypeNode.cs

@@ -437,10 +437,14 @@ public sealed override IEnumerable<CombinedDependencyListEntry> GetConditionalSt
                 // Add conditional dependencies for interface methods the type implements. For example, if the type T implements
                 // interface IFoo which has a method M1, add a dependency on T.M1 dependent on IFoo.M1 being called, since it's
                 // possible for any IFoo object to actually be an instance of T.
+                DefType defTypeDefinition = (DefType)defType.GetTypeDefinition();
                 DefType[] defTypeRuntimeInterfaces = defType.RuntimeInterfaces;
+                DefType[] defTypeDefinitionRuntimeInterfaces = defTypeDefinition.RuntimeInterfaces;
+                Debug.Assert(defTypeDefinitionRuntimeInterfaces.Length == defTypeRuntimeInterfaces.Length);
                 for (int interfaceIndex = 0; interfaceIndex < defTypeRuntimeInterfaces.Length; interfaceIndex++)
                 {
                     DefType interfaceType = defTypeRuntimeInterfaces[interfaceIndex];
+                    DefType interfaceDefinitionType = defTypeDefinitionRuntimeInterfaces[interfaceIndex];
 
                     Debug.Assert(interfaceType.IsInterface);
 
@@ -457,11 +461,22 @@ public sealed override IEnumerable<CombinedDependencyListEntry> GetConditionalSt
                         if (!isStaticInterfaceMethod && !needsDependenciesForInstanceInterfaceMethodImpls)
                             continue;
 
+                        MethodDesc interfaceMethodDefinition = interfaceMethod;
+                        if (interfaceType != interfaceDefinitionType)
+                            interfaceMethodDefinition = factory.TypeSystemContext.GetMethodForInstantiatedType(interfaceMethodDefinition.GetTypicalMethodDefinition(), (InstantiatedType)interfaceDefinitionType);
+
                         MethodDesc implMethod = isStaticInterfaceMethod ?
-                            defType.ResolveInterfaceMethodToStaticVirtualMethodOnType(interfaceMethod) :
-                            defType.ResolveInterfaceMethodToVirtualMethodOnType(interfaceMethod);
+                            defTypeDefinition.ResolveInterfaceMethodToStaticVirtualMethodOnType(interfaceMethodDefinition) :
+                            defTypeDefinition.ResolveInterfaceMethodToVirtualMethodOnType(interfaceMethodDefinition);
                         if (implMethod != null)
                         {
+                            TypeDesc implType = defType;
+                            while (!implType.HasSameTypeDefinition(implMethod.OwningType))
+                                implType = implType.BaseType;
+
+                            if (!implType.IsTypeDefinition)
+                                implMethod = factory.TypeSystemContext.GetMethodForInstantiatedType(implMethod.GetTypicalMethodDefinition(), (InstantiatedType)implType);
+
                             if (isStaticInterfaceMethod)
                             {
                                 Debug.Assert(!implMethod.IsVirtual);
@@ -500,12 +515,7 @@ public sealed override IEnumerable<CombinedDependencyListEntry> GetConditionalSt
                             // Is the implementation provided by a default interface method?
                             // If so, add a dependency on the entrypoint directly since nobody else is going to do that
                             // (interface types have an empty vtable, modulo their generic dictionary).
-                            TypeDesc interfaceOnDefinition = defType.GetTypeDefinition().RuntimeInterfaces[interfaceIndex];
-                            MethodDesc interfaceMethodDefinition = interfaceMethod;
-                            if (!interfaceType.IsTypeDefinition)
-                                interfaceMethodDefinition = factory.TypeSystemContext.GetMethodForInstantiatedType(interfaceMethod.GetTypicalMethodDefinition(), (InstantiatedType)interfaceOnDefinition);
-
-                            var resolution = defType.GetTypeDefinition().ResolveInterfaceMethodToDefaultImplementationOnType(interfaceMethodDefinition, out implMethod);
+                            var resolution = defTypeDefinition.ResolveInterfaceMethodToDefaultImplementationOnType(interfaceMethodDefinition, out implMethod);
                             if (resolution == DefaultInterfaceMethodResolution.DefaultImplementation)
                             {
                                 DefType providingInterfaceDefinitionType = (DefType)implMethod.OwningType;

src/tests/nativeaot/SmokeTests/UnitTests/Interfaces.cs

@@ -40,6 +40,7 @@ public static int Run()
         TestDefaultInterfaceVariance.Run();
         TestVariantInterfaceOptimizations.Run();
         TestSharedInterfaceMethods.Run();
+        TestGenericAnalysis.Run();
         TestCovariantReturns.Run();
         TestDynamicInterfaceCastable.Run();
         TestStaticInterfaceMethodsAnalysis.Run();
@@ -653,6 +654,54 @@ public static void Run()
         }
     }
 
+    class TestGenericAnalysis
+    {
+        interface IInterface
+        {
+            string Method(object p);
+        }
+
+        interface IInterface<T>
+        {
+            string Method(T p);
+        }
+
+        class C1<T> : IInterface, IInterface<T>
+        {
+            public string Method(object p) => "Method(object)";
+            public string Method(T p) => "Method(T)";
+        }
+
+        class C2<T> : IInterface, IInterface<T>
+        {
+            public string Method(object p) => "Method(object)";
+            public string Method(T p) => "Method(T)";
+        }
+
+        class C3<T> : IInterface, IInterface<T>
+        {
+            public string Method(object p) => "Method(object)";
+            public string Method(T p) => "Method(T)";
+        }
+
+        static IInterface s_c1 = new C1<object>();
+        static IInterface<object> s_c2 = new C2<object>();
+        static IInterface<object> s_c3a = new C3<object>();
+        static IInterface s_c3b = new C3<object>();
+
+        public static void Run()
+        {
+            if (s_c1.Method(null) != "Method(object)")
+                throw new Exception();
+            if (s_c2.Method(null) != "Method(T)")
+                throw new Exception();
+            if (s_c3a.Method(null) != "Method(T)")
+                throw new Exception();
+            if (s_c3b.Method(null) != "Method(object)")
+                throw new Exception();
+        }
+    }
+
     class TestCovariantReturns
     {
         interface IFoo