RFR: 8349457: [leyden] Workaround Leyden problems with -XX:-TieredCompilation [v4]

[Aleksey Shipilev]

On Mon, 10 Feb 2025 16:38:09 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Currently, supplying `-XX:-TieredCompilation` would break with Leyden workflows, because the archive-backed code cache heap would only be created if `SegmentedCodeCache` is enabled. With default compilation policy, this happens normally when tiered compilation is enabled, but not without it.
>> 
>> There are other minor peculiarities that we need to handle, which are exposed with `runtime/cds` + `-XX:-TieredCompilation` runs.
>> 
>> This prevents us from testing C2-only Leyden configs and studying compilation dynamics without tiered policy getting in the way.
>> 
>> Additional testing:
>>  - [x] Ad-hoc Leyden experiments now work with `-XX:-TieredCompilation`: the C2-only code is being stored and loaded successfully from the CDS archive
>>  - [x] `runtime/cds` now passes with `-XX:-TieredCompilation`
>>  - [x] `runtime/cds` still passes by default (i.e. with tiered compilation)
>
> Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains five additional commits since the last revision:
> 
>  - Merge branch 'premain' into JDK-8349457-enable-c2
>  - Revert Precompiler additions
>  - Merge branch 'premain' into JDK-8349457-enable-c2
>  - More fixes
>  - Fix

Thanks!

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PR Comment: https://git.openjdk.org/leyden/pull/32#issuecomment-2649979376