RFR: 8365047: Remove exception handler stub code in C2 [v7]

[Andrew Dinn]

On Thu, 23 Oct 2025 08:48:54 GMT, Ruben <duke at openjdk.org> wrote:

> I meant to refer to this check implementation, which reads 8 bytes from where LR points to and checks whether they contain the NOP+MOVK sequence.

Ah, my apologies for misunderstanding you and also and what was going on in this code. It is indeed reading two instructions at once and checking them both in one go.

I agree with you that this is best split up into two separate reads+checks to deal with the case where we don't have a NOP and might drop off the end of the current buffer. I think this will still be less work than using SafeFetch but @theRealAph may want to override me here.

> It might be beneficial to add an assertion in the `fetch_unroll_info_helper` that ensures, for case `exec_mode` is `Unpack_deopt` (and potentially, for `Unpack_exception` too) that the `LR` is indeed pointing to the deoptimization handler stub code.

That sounds like a good idea.

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PR Comment: https://git.openjdk.org/jdk/pull/26678#issuecomment-3436002622