RFR: 8365047: Remove exception handler stub code in C2 [v4]

[Martin Doerr]

On Fri, 12 Sep 2025 16:36:56 GMT, Ruben <duke at openjdk.org> wrote:

>> The C2 exception handler stub code is only a trampoline to the generated exception handler blob. This change removes the extra step on the way to the generated blob.
>> 
>> According to some comments in the source code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.
>
> Ruben has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - Offset the deoptimization handler entry point
>    
>    Change-Id: I596317ec6a364b341e4642636fa5cf08f87ed722
>  - Revert "Ensure stub code is not adjacent to a call"

I guess that the previous version also works on s390 like on ppc64 (with the old deopt handlers).

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PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3322930604