RFR: ShenandoahRootProcessor corrupts none Shenandoah VM_Operations

[Aleksey Shipilev]

On 06/20/2018 04:06 AM, Zhengyu Gu wrote:
> There are actually two bugs:
> 
> 1. We did not clear bitmap before marking
> 2. We blindly cast VM_Operation to VM_ShenandoahOperation and set field, corrupts none Shenandoah
> VM_Operations, such as HeapDump and ThreadDump.
> 
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/vm_op_corruption/webrev.00/

Looks good. Note that ShenandoahRootProcessor constructor also have accesses to
VM_ShenandoahOperation fields, and should also be protected with is_at_shenandoah_safepoint.

-Aleksey