RFR: 8299327: Allow super late barrier expansion of store barriers in C2 [v2]

[Martin Doerr]

On Tue, 10 Jan 2023 09:04:03 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> src/hotspot/cpu/aarch64/aarch64.ad line 7976:
>> 
>>> 7974: %{
>>> 7975:   match(Set mem (StoreP mem src));
>>> 7976:   predicate(n->as_Store()->barrier_data() == 0);
>> 
>> Why does the instruction below (`storeimmP0_volatile`) not require a similar predicate? Just checking - I guess the omission is intentional since it follows from the ZGC repo.
>
> No, you are right - it does need a similar predicate. The storeimmP0_volatile rule seems to be quite recent, and I wrote this code before it existed and then we must have merged without noticing. Nice catch!

Yeah, nice catch! This would have been a bad bug. SATB could have missed Oops which were overwritten by Store0.

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PR: https://git.openjdk.org/jdk/pull/11779