RFR: C1 xchg handling is broken: no item available after WB

[Roman Kennke]

Am 06.06.2018 um 17:51 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/c1-fix-atomic/webrev.01/
> 
> SwingSet2 is the clear reproducer for the problem:
> 
> # A fatal error has been detected by the Java Runtime Environment:
> #
> #  Internal Error
> (/home/shade/trunks/shenandoah-jdk/src/hotspot/share/gc/shared/c1/barrierSetC1.hpp:49), pid=69797,
> tid=69906
> #  assert(_item != __null) failed: sanity
> #
> 
> This happens because of the simple overlook: we should use _resolved, like any other post-WB user
> does. I have checked SBSC1::atomic_xchg_at is the only broken place like that.
> 
> Testing: tier3_gc_shenandoah, SwingSet2
> 
> Thanks,
> -Aleksey
> 

Yes, please. Thanks for fixing this!!

Roman