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

[Martin Doerr]

On Tue, 10 Jan 2023 09:05:38 GMT, Erik Österlund <eosterlund at openjdk.org> wrote:

>> src/hotspot/cpu/ppc/ppc.ad line 6538:
>> 
>>> 6536: 
>>> 6537: // Store Pointer
>>> 6538: instruct storeP(memoryAlg4 dst, iRegPsrc src) %{
>> 
>> The ADLC peephole replacement logic is not barrier data-aware as far as I can see. I wonder if barrier data is propagated correctly by peephole rules like the one in https://github.com/openjdk/jdk/blob/17a3f0e2577f2f9eb3fe62a4b8261e3dbe4c3b28/src/hotspot/cpu/ppc/ppc.ad#L14877-L14881. But I guess this is a question for PPC maintainers.
>
> Indeed. @TheRealMDoerr would you mind having a look at this?

`OptoPeephole` is a `develop_pd` flag which is only enabled on x86. So, we don't support it for PPC64.
Even if somebody switched it on for PPC64, I don't think it would break anything.
The predicates are used during the matching phase. The peephole optimizer runs later at a point of time at which the barrier data is no longer used.

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