RFR: 8357619: [JVMCI] Revisit phantom_ref parameter in JVMCINMethodData::get_nmethod_mirror [v2]

[Doug Simon]

On Fri, 30 May 2025 16:05:23 GMT, Tom Rodriguez <never at openjdk.org> wrote:

>> Doug Simon has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   still rely on get_nmethod_mirror in invalidate_nmethod_mirror
>
> src/hotspot/share/jvmci/jvmciRuntime.cpp line 801:
> 
>> 799: 
>> 800: void JVMCINMethodData::invalidate_nmethod_mirror(nmethod* nm) {
>> 801:   if (_nmethod_mirror_index == -1) {
> 
> This part is actually wrong as that's the first part of `get_nmethod_mirror` and we must always check that `get_nmethod_mirror` doesn't return nullptr.  I'd assumed that the mirror was always non-null if `_nmethod_mirror_index != -1` but that's not true.  The slot is reserved for all non-default nmethods and must stay around so that `translate` can work.

Fixed: https://github.com/openjdk/jdk/pull/25488/commits/7456988a6fcab00bf13e602553f9e5a295d75b0f

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PR Review Comment: https://git.openjdk.org/jdk/pull/25488#discussion_r2121658848