RFR: 8359064: Expose reason for marking nmethod non-entrant to JVMCI client [v8]

[Tom Rodriguez]

On Tue, 17 Jun 2025 00:39:54 GMT, Cesar Soares Lucas <cslucas at openjdk.org> wrote:

>> We recently introduced a way to set the reason why a nmethod was being marked as `not entrant`, see [here](https://github.com/openjdk/jdk/pull/23980) and [here](https://github.com/openjdk/jdk/pull/25338).
>> 
>> This PR is to expose in the JVMCI interface the reason why the nmethod was flagged as `not entrant`. This will allow JVMCI-based compilers to implement heuristics to handle re-compilations differently based on what happened to earlier versions of a method, for instance, this will likely be used to address this [RFE in Truffle](https://github.com/oracle/graal/issues/11045
>> ). 
>> 
>> Tested on Linux x86_64, ARM with JTREG tier 1-3.
>
> Cesar Soares Lucas has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Remove extra space

src/hotspot/share/code/nmethod.hpp line 500:

> 498:     WHITEBOX_DEOPTIMIZATION,
> 499:     ZOMBIE,
> 500:     LAST_REASON

This isn't really the last reason, since it's not actually a reason.  So either `LAST_REASON = ZOMBIE` with adjustments to the range check or maybe `REASON_COUNT`?  Why do we need `UNKNOWN` since it seems unused?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25706#discussion_r2155117063