RFR: 8252889: C2 crashes when disabling InsertMemBarAfterArraycopy

[David Holmes]

Hi Aleksey,

On 8/09/2020 8:23 pm, Aleksey Shipilev wrote:
> 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?

Product flags can be directly obsoleted without being deprecated first 
if they are basically non-functional, as this one seems to be.

Cheers,
David
-----

> 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?
> 
> -------------
> 
> Changes requested by shade (Reviewer).
> 
> PR: https://git.openjdk.java.net/jdk/pull/69
>