RFR: 8365047: Remove exception handler stub code in C2 [v9]

[Ruben]

On Tue, 28 Oct 2025 23:18:48 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code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.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 refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains three new commits since the last revision:
> 
>  - Address review comments and fix a mistype
>  - Check for NOP and MOVK separately in NativePostCallNop
>  - Test for deoptimization in virtual threads
>    
>    Change-Id: I9ef51b426d34e9b44a3891f6a45307232f900e5a

Hi everyone,
The PR has been updated to address the discovered issues and is ready for review.
Part of the update is the new test on deoptimization in virtual threads - as, in my experience, the existing tests didn't reliably trigger the new assertion added in `fetch_unroll_info_helper` while `far_jump` was incorrectly used instead of `far_call` on AArch64.

@theRealAph, would it be possible to confirm if the update is suitable from your perspective?

@TheRealMDoerr, @RealFYang, @offamitkumar, @bulasevich, would it be possible to run tests on your platforms for this latest version please?

-------------

PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3461691035