RFR: 8371200: ZGC: C2 allocation deopt race

[Erik Österlund]

On Thu, 6 Nov 2025 16:45:52 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Passing-by comment to confirm what @fisk is saying. On any return from runtime call back to compiled code there is check for safepoint request and process it: https://github.com/openjdk/jdk/blob/master/src/hotspot/share/runtime/interfaceSupport.inline.hpp#L113C27-L113C63
> 
> 
> 
> During safepoint any generational GC may move objects to old gen AFAIU.

That is very true. Most GCs clobber some cards after the transition if the object gets promoted to the old generation to counteract the cheating with barriers. With ZGC, we deopt the frame instead and rely on not cheating with barriers.

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PR Comment: https://git.openjdk.org/jdk/pull/28176#issuecomment-3498453051