RFR: 8349814: [leyden] Avoid uncommon traps in preload code [v2]

[Aleksey Shipilev]

On Tue, 11 Feb 2025 16:39:39 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Preload code is the C2 code we load very early, before it gets substituted by more advanced C2 code. We are seeing lots of uncommon traps from the preloaded code, though, which invalidates it too early. We can do precompile code without uncommon traps to alleviate this. 
>> 
>> Additional testing:
>>  - [x] Ad-hoc perf tests (see comment below)
>>  - [x] Linux x86_64 server fastdebug, `runtime/cds`
>
> 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 three additional commits since the last revision:
> 
>  - Merge branch 'premain' into JDK-8349814-preload-avoid-uncommon-traps
>  - Comment
>  - Fix

In addition to Vladimir's comments above, I also found this greatly expands the size of generated code for preloading, which leads to expanded code buffers, which makes more methods ineligible for SCC. So the net effect can be negative. This PR is on hold until I figure out a way out of this.

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PR Comment: https://git.openjdk.org/leyden/pull/38#issuecomment-2656570866