RFR (XS): Fix DerivedPointerTable handling when scanning roots twice in init-evac phase

[Aleksey Shipilev]

On 03/07/2017 11:47 AM, Roman Kennke wrote:
> With my last fix, we're potentially scanning the roots twice: once for
> the initial-evacuation+update-refs, and if we run into OOM, another time
> to update remaining refs. This 2nd scan can cause problems in
> DerivedPointerTable: it asserts that every root is only visited once.
> This patch fixes it by enclosing each pass into DerivedPointerTable
> separately.
> 
> http://cr.openjdk.java.net/~rkennke/fixdpt/webrev.00/

I don't get why do you need to duplicate update_pointers() call. Isn't it enough
to clear the table when concgc was cancelled, and then let the rest run its course?

if (cancelled_concgc()) {
  COMPILER2_PRESENT(DerivedPointerTable::clear());
  ...
}

COMPILER2_PRESENT(DerivedPointerTable::update_pointers());

Thanks,
-Aleksey