RFR: 8252889: C2 crashes when disabling InsertMemBarAfterArraycopy

[Aleksey Shipilev]

On Tue, 8 Sep 2020 10:04:35 GMT, Tobias Hartmann <thartmann 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

Synopsis might be changed to "Obsolete -XX:+InsertMemBarAfterArraycopy".

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?

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?

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Changes requested by shade (Reviewer).

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