RFR: 8350488: [leyden] Experimental AOT-only mode

[Vladimir Ivanov]

On Fri, 21 Feb 2025 10:36:19 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

> There are interesting use cases where we want the AOT-only mode. We can emulate this in current Leyden prototype by relying on preload code, and stopping any profiling, which would naturally lead to no JIT compilations. This would also make interpreter code a bit faster in case we need to fall back there. This mode looks also helpful for studying the compiler dynamics.
> 
> Additional testing:
>  - [x] Eyeballing compilation logs with `-XX:+PreloadOnly`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds`
>  - [x] Linux x86_64 server fastdebug, `runtime/cds` with `-XX:+PreloadOnly`

Proposed solution looks to me way too specific and niche. 

Instead, I'd prefer to see a way to combine different JIT-compilation modes (`-XX:TieredStopAtLevel=01234`) with ability to limit usage of AOTed code (e.g., `-XX:DisableAOTCodeLevels=P124`).  `PreloadOnly` is equivalent to `-XX:TieredStopAtLevel=0` and `-XX:DisableAOTCodeLevels=124`.

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PR Comment: https://git.openjdk.org/leyden/pull/44#issuecomment-2675809710