RFC/RFR: Get rid of second bitmap

[Aleksey Shipilev]

On 10/10/2017 11:20 AM, Roman Kennke wrote:
> http://cr.openjdk.java.net/~rkennke/onebitmap/webrev.04/

 *) No, we don't now (happens twice in the patch):

 1371     log_warning(gc)("Hold my beer, we are about to crash this VM.");

 *) So, previous version of ShenandoahHeap::safe_object_iterate used to fix up the fields in
reported objects. This new version does not seem to do that, and I think that is a deal-breaker: we
cannot really report from-space oops in the fields, because users would not expect the need to
perform RBs on them?

 *) I think the JVMTI test should construct the object graph, and verify that the same number of
objects is returned, regardless of the GC phase we are currently in. Actually touching the oop
fields would be the plus, to verify that thing from above.

Thanks,
-Aleksey