RFR: Verifier "After Mark" should assert matrix consistency

[Roman Kennke]

Am 04.08.2017 um 13:04 schrieb Aleksey Shipilev:
> I think we are missing a crucial bit of matrix verification after concurrent mark:
>   http://cr.openjdk.java.net/~shade/shenandoah/verifier-aftermark-matrix/webrev.01/
>
> It crashes our current tests today, so I would first pinpoint the bug itself.
>
> Thanks,
> -Aleksey
>
As discussed on IRC, we don't bother keeping matrix up-to-date outside
of UR. We currently need UR before partial cycle, and thus rebuild the
matrix during UR.

Any crazy combination of non-partial heuristics (i.e. adaptive) and
manually setting +UseShenandoahMatrix is tricky to verify because it may
run into piggy-backed UR, where we don't keep matrix updated.

Roman