RFR: 8339939: [JVMCI] Don't compress abstract and interface Klasses

[Gilles Duboscq]

On Wed, 11 Sep 2024 13:09:07 GMT, Yudi Zheng <yzheng at openjdk.org> wrote:

> https://github.com/openjdk/jdk/pull/19157 disallows storing abstract and interface Klasses in class metaspace. JVMCI has to respect this and avoids compressing abstract and interface Klasses

src/jdk.internal.vm.ci/share/classes/jdk/vm/ci/hotspot/HotSpotConstant.java line 40:

> 38:      * Determines if this constant is compressible.
> 39:      */
> 40:     boolean isCompressible();

It might be worth adding a note about the fact that even if this returns true, `compress()` might still throw `IllegalArgumentException` if `isCompressed()` is also true.

Or is might be a bit more intuitive to ask for the invariant that `isCompressible()` should return `false` if `isCompressed()` is true, an reword the javadoc below.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20949#discussion_r1754773712