RFR: 8365047: Remove exception handler stub code in C2

[Dean Long]

On Thu, 7 Aug 2025 15:49:20 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code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.

Re: CodeOffsets::DeoptMH, what I meant is that it is just an exact copy of the CodeOffsets::Deopt stub code.  Apparently at some point in the JSR 292 evolution, we needed to distinguish between the two, but it looks to me that we no longer need to do that.  So we should be able to get rid of DeoptMH and related code, like nmethod::is_deopt_mh_entry().

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PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3176849923