J9 verification permits non-interfaces on operand stack of invokeinterface

[tajila]

With the following example:

Interface val = new Concrete[elements];
val.ifaceMethod(); //throws IncompatibleClassChangeError on J9 whereas RI throws a verification failure much earlier

Test files:
TestFiles.zip

Run with:
java TestInterface

We need to align the behaviour with RI for the following reasons

1. It forces the JIT to be conservative and treat every interface type as a potential array
2. Better aligns J9 behaviour with the RI

[theresa-m]

There's not currently a way to distinguish the array of a reference/object from an object. See the 5 bits that are reserved for types https://github.com/eclipse-openj9/openj9/blob/master/runtime/oti/bytecodewalk.h#L100-L104
I think BCV_TAG_BASE_ARRAY_OR_NULL can be redefined to mean a reference or a base array so that:

• 0x10 tag means a reference array
• 0x11 means a base array

Does that make sense @tajila ?

[tajila]

There's not currently a way to distinguish the array of a reference/object from an object.

I thought it was classIndex | (arity << BCV_ARITY_SHIFT) with the BCV_JAVA_LANG_OBJECT_INDEX bit set (its not actually set but implied) ?

[theresa-m]

Oh right that makes sense. I'll try that, thanks.