RFR(S): 8155209: Move setting of young index in cset to G1CollectionSet

[Erik Helin]

On 2016-04-27, Mikael Gerdin wrote:
> Hi all,
> 
> Please review this change to how _young_index_in_cset is set in HeapRegions.
> 
> G1 maintains a numbering of all young regions in the collection set in order
> to record the amount of bytes copied from each young region in a convenient
> fashion.
> This done by having a _young_index_in_cset member in each HeapRegion which
> is -1 for non-young and >= 0 for young regions.
> 
> This change moves the responsibility for setting this value to
> G1CollectionSet, where it's easier to verify that the indices are set in the
> correct manner for survivor and eden regions instead of relying on YoungList
> and its state changes to ensure that the indices are correct and unique.
> 
> The new code is in my mind much more straightforward in how the indices are
> set up but still I've added some verification code to ensure that there are
> no collisions in the numbering.
> 
> This change is part of an effort to simplify the YoungList code.
> 
> Testing: JPRT
> Bug: https://bugs.openjdk.java.net/browse/JDK-8155209
> Webrev: http://cr.openjdk.java.net/~mgerdin/8155209/webrev.0/

Looks good, Reviewed.

Thanks,
Erik

> Thanks
> /Mikael