RFR: 8356595: Convert -Xlog:cds to -Xlog:aot [v3]

[Ioi Lam]

On Tue, 13 May 2025 08:52:17 GMT, David Holmes <dholmes at openjdk.org> wrote:

> Some drive-by comments, not a full review as I find this all rather confusing because I don't understand why we used "cds" in AOT specific code in the first place. It makes perfect sense to me that AOT specific code logs to "aot".
> 
> It makes far less sense to me why you ever introduced logging that required "cds" and "aot" in the first place, so getting rid of that is a good thing.
> 
> For code shared between cds and aot it is less clear to me how to proceed. If the intent is that CDS will be no more and everything is AOT, then a transition path is needed for the logging. I guess this is where your macros come in, though I'm a bit unclear as to why it can be controlled by a user-defined command-line flag rather than only by the CDS/AOT selection arguments operating directly on an internal CDS/AOT configuration setting. ???

Since [JEP 483](https://openjdk.org/jeps/483), all ahead-of-time optimizations in HotSpot fall under the "AOT" umbrella. We have several JEPs for new optimizations that use the AOT terminology. E.g., [JEP 515 - Ahead-of-Time Method Profiling](https://openjdk.org/jeps/515).

The traditional CDS functionality is part of (a strict subset of) AOT -- ahead-of-time processing of class metadata. Classical CDS VM flags such as `-Xshare` can be seen as special interfaces to a subset of the AOT functionality. We are providing these flags for backwards compatibility, as there are equivalent ways to access the same features (and more) with the new `-XX:AOTXXX` flags introduced in JEP 483. Eventually, I think we will deprecate and remove the classical CDS flags.

Given this background, moving `-Xlog:cds` to `-Xlog:aot` is part of the transition plan. These logs will probably be the first legacy CDS interfaces to be removed from the JDK.

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PR Comment: https://git.openjdk.org/jdk/pull/25136#issuecomment-2878368790