RFR: 8373392: Replace CDS object subgraphs with @AOTSafeClassInitializer

[Chen Liang]

On Wed, 10 Dec 2025 09:31:37 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> In legacy CDS, Java objects used by certain classes are computed ahead of time using "object subgraphs"
> 
> https://github.com/openjdk/jdk/blob/1bbbce75c5e68429c2a32519eb3c36d964dcdf57/src/hotspot/share/cds/heapShared.cpp#L168-L171
> 
> Examples of subgraphs:
> 
> - `java.lang.Integer$IntegerCache::cache`
> - `jdk.internal.module.ArchivedBootLayer::bootLayer`
> 
> The implementation requires special code (in both Java and C++) to be executed when a CDS archive is created or loaded. As a result, we have an execution model that's difficult to implement/extend and the behavior is hard to understand.
> 
> To move towards the AOT Cache Snapshot Model ([JDK-8365645](https://bugs.openjdk.org/browse/JDK-8365645)) we should replace the subgraphs with the use of `@AOTSafeClassInitializer`, and if necessary, `@AOTRuntimeSetup`. This will simplify the current implementation, and make it possible to extend AOT-initializations to more core classes.
> 
> Note, the use of `@AOTSafeClassInitializer` requires `-XX:+AOTClassLinking`. For the time being, we retain the old CDS object subgraph code to cover the `-XX:-AOTClassLinking` cases. Such code will be marked with comments like `/* Legacy CDS archive support (to be deprecated) */`. All future AOT creation of Java objects will be done with  `@AOTSafeClassInitializer`.

The Java code changes look reasonable.

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28736#pullrequestreview-3563746741