methods on objects should always be called via invokevirtual() and not invokeinterface()

idea/src/org/jetbrains/jet/codegen/JetTypeMapper.java

@@ -165,7 +165,7 @@ public class JetTypeMapper {
 
     public boolean isInterface(ClassDescriptor jetClass, OwnerKind kind) {
         PsiElement declaration = bindingContext.getDeclarationPsiElement(jetClass);
-        if (declaration instanceof JetObjectDeclaration && ((JetObjectDeclaration) declaration).isObjectLiteral()) {
+        if (declaration instanceof JetObjectDeclaration) {
             return false;
         }
         return kind == OwnerKind.INTERFACE;

idea/testData/codegen/objects/methodOnObject.jet

@@ -0,0 +1,5 @@
+object A {
+  fun result() = "OK"
+}
+
+fun box(): String = A.result()

idea/tests/org/jetbrains/jet/codegen/ObjectGenTest.java

@@ -11,4 +11,8 @@ public class ObjectGenTest extends CodegenTestCase {
     public void testObjectLiteral() throws Exception {
         blackBoxFile("objects/objectLiteral.jet");
     }
+
+    public void testMethodOnObject() throws Exception {
+        blackBoxFile("objects/methodOnObject.jet");
+    }
 }