RFR (S): JDK-6991197 G1: specialize deal_with_reference() for narrowOop*

[Thomas Schatzl]

Hi all,

  can I have your opinion and optionally a review for the following
small change? Like the bug title reads, the change manually specializes
G1ParScanThreadState::deal_with_reference() for the narrowOop*, allowing
some additional specialization.

Measurements indicate a small improvement (~1%) on object copy time for
specjbb, however not significant.

As I have the change on hand (I had to do it anyway for measurements) I
would like to ask your opinion whether to keep it or not. If so, ask for
review.

I am actually undecided - personally I tend to like it (as it trims fat)
and it seems small enough to keep it and does not distract too much, but
it does not really show up on measurements.

Testing:
jprt, specjbb2005/13, specjvm98/2008, CRM Fuse

Bug entry:
https://bugs.openjdk.java.net/browse/JDK-6991197

Webrev:
http://cr.openjdk.java.net/~tschatzl/6991197/webrev/

Thanks,
Thomas