RFR: 8280283: Dead compiler code found during the JDK-8272058 code review [v2]

[Boris Ulasevich]

On Fri, 5 Dec 2025 10:08:33 GMT, Anton Seoane Ampudia <aseoane 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
>
> Anton Seoane Ampudia has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Delete more unused code

Marked as reviewed by bulasevich (Committer).

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PR Review: https://git.openjdk.org/jdk/pull/28473#pullrequestreview-3553913872