RFR: 8338526: Don't store abstract and interface Klasses in class metaspace

[Thomas Stuefe]

On Thu, 9 May 2024 13:51:09 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

> This change stores InstanceKlass for interface and abstract classes in the non-class metaspace, since class metaspace will have limits on number of classes that can be represented when Lilliput changes go in.  Classes that have no instances created for them don't require compressed class pointers.  The generated LambdaForm classes are also AllStatic, and changing them to abstract moves them to non-class metaspace too.  It's not technically great to make them abstract and not final but you can't have both.  Java classfile access flags have no way of specifying something like AllStatic.
> 
> Tested with tier1-8.

I am surprised that this patch is so small. I would have assumed a lot of code exists that unconditionally assumes we always can encode decode Klass*<->narrowKlass.

I looked through the typical cases (eg Klass validation) and all of them seem to be okay. I will keep looking.

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PR Comment: https://git.openjdk.org/jdk/pull/19157#issuecomment-2304169936