RFR: 8280283: Dead compiler code found during the JDK-8272058 code review

[Anton Seoane Ampudia]

On Tue, 2 Dec 2025 14:59:50 GMT, Boris Ulasevich <bulasevich at openjdk.org> wrote:

>> This PR removes some dead code that was found during review for [JDK-8272058](https://bugs.openjdk.org/browse/JDK-8272058).
>> 
>> `target_addr_for_insn_or_null` is never run with a `ldrw` to `zr` (i.e. a safepoint poll). This is just a remnant from global safepointing, before we moved to using thread-local handshakes. No safepoint polling code reaches this function. More information can be read in the [original code review](https://github.com/openjdk/jdk18/pull/51#discussion_r774922087). Additionally, I have run tiers 1-6 to make sure this path did not exercise.
>> 
>> This changeset also cleans up the unused `is_nop` function, following the comments in the issue. Other dead code mentioned there has since been long disappered.
>> 
>> **Testing:** passes tiers 1-4
>
> Nice cleanup. Cleaning up dead code always helps reduce technical debt.
> Are you sure there isn’t more to clean up? Have you tried building with GCC’s -Wunused options to catch additional unused symbols?

Thanks @bulasevich! I built the relevant files with `-Wunused` and a few more dead lines came up. I've addressed them with my last commit.

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PR Comment: https://git.openjdk.org/jdk/pull/28473#issuecomment-3616158434