RFR: 8366024: Remove unnecessary InstanceKlass::cast() [v2]

[Coleen Phillimore]

On Wed, 27 Aug 2025 18:11:33 GMT, Ioi Lam <iklam at openjdk.org> wrote:

>> We have a lot of `InstanceKlass::cast(k)` calls where `k` is statically known to be an `InstanceKlass`. I fixed many instances of this pattern:
>> 
>> 
>> InstanceKlass* x = ....;
>> Klass* s = x->super(); // should call java_super()
>> InstanceKlass::cast(s)->xyz();
>> 
>> 
>> The `super()` method has a very confusing API. It has the return type of `Klass*` because for for an `ObjArrayKlass` like `[Ljava/lang/String;`:
>> 
>> - `super()` returns `[Ljava/lang/Object;`
>> - `java_super()` returns `Ljava/lang/Object;`
>> 
>> However, for `[Ljava/lang/Object;`, all `TypeArrayKlasses` and all `InstanceKlasses`, `super()` and `java_super()` return an identical value of that always have the actual type of `InstanceKlass*`.
>> 
>> See here about the difference between `super()` and `java_super()`: https://github.com/openjdk/jdk/blob/7b9969dc8f20989497ff617abb45543d182b684d/src/hotspot/share/oops/klass.hpp#L218-L221
>> 
>> Unfortunately, we have a lot of code that incorrectly uses `super()` instead of `java_super()`, which leads to ` InstanceKlass::cast()` calls. I tried to fixed a bunch of easy ones in this PR, although there are a few more to go.
>> 
>> I also fixed some calls to `local_interafaces()->at()` that widens the return type for `InstanceKlass*` to `Klass*`, which may lead to unnecessary  ` InstanceKlass::cast()` calls.
>> 
>> I also removed the `Klass::superklass()` API. This was used only in a few places and all of them can be safely replaced with `Klass::java_super()`.
>> 
>> To avoid confusion, I think we should rename `super()` to something more obvious, but let's do that in a future PR.
>
> Ioi Lam has updated the pull request incrementally with one additional commit since the last revision:
> 
>   @adinn comment - remove InstanceKlass::cast() in edgeUtils.cpp

This looks good.  We've had several passes of narrowing the Klass types to InstanceKlass so thank you for doing this one.  super() is tricky because of array covariance in subtype checking.  I don't see that this affects that code.
Thank @adinn  for finding more.

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Marked as reviewed by coleenp (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/26908#pullrequestreview-3161236083