PROBLEM:

The return type of Klass::super() is a Klass*. See
https://github.com/openjdk/jdk/blob/b06459d3a83c13c0fbc7a0a7698435f17265982e/src/hotspot/share/oops/klass.hpp#L218-L221

// Klass::super() cannot be InstanceKlass* -- Java arrays are covariant, and _super is used
// to implement that. NB: the _super of "[Ljava/lang/Integer;" is "[Ljava/lang/Number;"
// If this is not what your code expects, you're probably looking for Klass::java_super().

However, if you already have an InstanceKlass* ik, it's guaranteed that the object returned by ik->super() must be an InstanceKlass* (or nullptr).

In the past, we had unnecessary casts:

    InstanceKlass* s = InstanceKlass::cast(ik->super());

JDK-8366024 changed that to

    InstanceKlass* s = ik->java_super().

However, this style is still confusing, and forces people to know the difference between Klass::super() and Klass::java_super(). Also, java_super() is a virtual method so it's a bit slower.

PROPOSAL

Add the following function to InstanceKlass to shadow the method of the same name in Klass.

class InstanceKlass : public Klass {
public:
  InstanceKlass* super() const {
    return (Klass::super() == nullptr) ? nullptr : InstanceKlass::cast(Klass::super());
  }
};

If you already have a InstanceKlass* ik, the code can simply call:

    InstanceKlass* s = k->java_super().