RFR: Update roots should always handle derived pointers

[Roman Kennke]

Am 30.05.2017 um 12:12 schrieb Aleksey Shipilev:
> Hi,
>
> Follow my logic here.
>
> It looks to me that every root modification needs to be wrapped with DPT::clear
> and DPT::update_pointers to capture the rare stack-alloced beasts. However, we
> are missing this pair for Final Update Refs. Therefore, this is the valid
> fix/cleanup:
>   http://cr.openjdk.java.net/~shade/shenandoah/update-roots-dpt/webrev.01/
>
> (Also checked all usages of ShenandoahRootEvacuator)
>
> Testing: hotspot_gc_shenandoah

Ugh. Lucky that it hasn't crashed on us yet.

Good to go!

Roman