Fix x86 only ICastable feature bug.

When we call ICastable.IsInstanceOfInterface, we treat RuntimeTypeHandle as a OBJECTREF, which is incorrect as-per x86 calling convention since RuntimeTypehandle is a struct that contains a RuntimeType ref field and needs to be passed in stack. Our VM simple call helpers CALL_MANAGED_METHOD doesn't handle this correctly (it does the simple thing that always assume all the arguments are passed in register first). I'm fixing this by using a static method that takes RuntimeType instead of RuntimeTypeHandle, then convert it to RuntimeTypehandle.
Also switch to use PREPARE_NONVIRTUAL_CALLSITE(METHODID) as per Jan's suggestion.
ICastable test is now enabled in x86 for both JITs.

1 files changed, 4 insertions, 5 deletions

diff --git a/src/vm/jithelpers.cpp b/src/vm/jithelpers.cpp
index 340d61b838..fffc6ceece 100644
--- a/src/vm/jithelpers.cpp
+++ b/src/vm/jithelpers.cpp
@@ -2446,14 +2446,13 @@ BOOL ObjIsInstanceOf(Object *pObject, TypeHandle toTypeHnd, BOOL throwCastExcept
     // to a given type.
     else if (toTypeHnd.IsInterface() && fromTypeHnd.GetMethodTable()->IsICastable())
     {
-        // Make actuall call to obj.IsInstanceOfInterface(interfaceTypeObj, out exception)
+        // Make actuall call to ICastableHelpers.IsInstanceOfInterface(obj, interfaceTypeObj, out exception)
         OBJECTREF exception = NULL;
         GCPROTECT_BEGIN(exception);
-        MethodTable *pFromTypeMT = fromTypeHnd.GetMethodTable();
-        MethodDesc *pIsInstanceOfMD = pFromTypeMT->GetMethodDescForInterfaceMethod(MscorlibBinder::GetMethod(METHOD__ICASTABLE__ISINSTANCEOF)); //GC triggers
-        OBJECTREF managedType = toTypeHnd.GetManagedClassObject(); //GC triggers
+        
+        PREPARE_NONVIRTUAL_CALLSITE(METHOD__ICASTABLEHELPERS__ISINSTANCEOF);
 
-        PREPARE_NONVIRTUAL_CALLSITE_USING_METHODDESC(pIsInstanceOfMD);
+        OBJECTREF managedType = toTypeHnd.GetManagedClassObject(); //GC triggers
 
         DECLARE_ARGHOLDER_ARRAY(args, 3);
         args[ARGNUM_0] = OBJECTREF_TO_ARGHOLDER(obj);