RFR: 8252889: Obsolete -XX:+InsertMemBarAfterArraycopy

[Tobias Hartmann]

On Tue, 8 Sep 2020 10:19:17 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> The InsertMemBarAfterArraycopy product flag (enabled by default) is broken. I propose to simply remove it.
>> The corresponding CSR (JDK-8252890) is still waiting for approval.
>> 
>> Thanks,
>> Tobias
>
> src/hotspot/share/opto/macroArrayCopy.cpp line 1106:
> 
>> 1104:     RegionNode* slow_region = new RegionNode(1);
>> 1105:     transform_later(slow_region);
>> 1106:
> 
> This cleanup does not seem related?

Yes but it does not seem justified to create a separate PR for removing dead code in the same file.

> src/hotspot/share/runtime/arguments.cpp line 556:
> 
>> 554:   { "UseSemaphoreGCThreadsSynchronization", JDK_Version::undefined(), JDK_Version::jdk(16), JDK_Version::jdk(17) },
>> 555:   { "ForceNUMA",                     JDK_Version::jdk(15), JDK_Version::jdk(16), JDK_Version::jdk(17) },
>> 556:   { "InsertMemBarAfterArraycopy",    JDK_Version::undefined(), JDK_Version::jdk(16), JDK_Version::jdk(17) },
> 
> This seems like a product flag, so needs to follow `ForceNUMA` example? E.g. 16 -> 17 -> 18? And a provisional CSR?

Since the flag is broken, I think immediate obsoletion, rather than deprecation makes more sense. See also discussion
in JDK-8252889. A CSR has been created (JDK-8252890).

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PR: https://git.openjdk.java.net/jdk/pull/69