review feedback

Author: AndyAyersMS

src/coreclr/vm/jitinterface.cpp

@@ -8613,18 +8613,18 @@ bool CEEInfo::resolveVirtualMethodHelper(CORINFO_DEVIRTUALIZATION_INFO * info)
 
         if (pObjMT->IsArray())
         {
+            if (pBaseMT->IsSharedByGenericInstantiations())
+            {
+                info->detail = CORINFO_DEVIRTUALIZATION_FAILED_CANON;
+                return false;
+            }
+
             // Does the array implicitly implement this interface?
             //
             isArrayImplicitInterface = pBaseMT->HasInstantiation() && IsImplicitInterfaceOfSZArray(pBaseMT);
 
             if (!isArrayImplicitInterface)
             {
-                if (pBaseMT->IsSharedByGenericInstantiations())
-                {
-                    info->detail = CORINFO_DEVIRTUALIZATION_FAILED_CANON;
-                    return false;
-                }
-
                 // Ensure we can cast the array to the interface type
                 //
                 if (!TypeHandle(pObjMT).CanCastTo(TypeHandle(pBaseMT)))
@@ -8653,6 +8653,7 @@ bool CEEInfo::resolveVirtualMethodHelper(CORINFO_DEVIRTUALIZATION_INFO * info)
                 // The instantiation we want is based on the interface element type, not the
                 // array element type.
                 TypeHandle resultElemType = pBaseMT->GetInstantiation()[0];
+                // We should have ruled this out above.
                 _ASSERTE(!resultElemType.IsCanonicalSubtype());
                 pDevirtMD = GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod(pBaseMD, resultElemType);
             }

src/tests/JIT/Regression/JitBlue/Runtime_120270/Runtime_120270.cs

@@ -3,8 +3,12 @@
 
 using System;
 using System.Linq;
+using System.Runtime.CompilerServices;
 using Xunit;
 
+class Base{}
+class Derived : Base {}
+
 public class Runtime_120270
 {
     [Fact]
@@ -32,5 +36,35 @@ public static int TestEntryPoint()
 
         return failed ? -1 : 100;
     }
+
+    [Fact]
+    public static int TestEntryPoint2()
+    {
+        bool failed = false;
+        try
+        {
+            Foo<Base>([new Derived()]);
+        }
+        catch (Exception ex)
+        {
+            Console.WriteLine(ex);
+            failed = true;
+        }
+        return failed ? -1 : 100;
+    }
+
+    [MethodImpl(MethodImplOptions.NoInlining)]
+    static void Foo<T>(object[] x)
+    {
+        int i = 0;
+        while (i < 100_000)
+        {
+            i++;
+            var values = x.Cast<T>();
+            foreach (var value in values)
+            {
+            }
+        }
+    }
 }