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

[Dean Long]

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code, the exception handler stub code used to be patched upon deoptimization, however presumably these comments are outdated as the patching upon deoptimization happens for post-call NOPs only.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

Re: SafeFetch, it is probably OK to make NativePostCallNop_at slightly slower for uses like make_deoptimized(), but the oopmap optimizations like CodeCache::find_blob_and_oopmap() were highly optimized to make loom/VirtualThread performance reasonable.  Adding a SafeFetch here might cause a regression.

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PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3470251792