Please review 6687581: Make CMS work with compressed oops

[Coleen Phillimore - Sun Microsystems]

Please email your comments to me regarding this bug fix, described below:

Fixed 6687581: Make CMS work with compressed oops

Make FreeChunk read markword instead of LSB in _klass pointer to 
indicate that it's a FreeChunk for compressed oops.  Moved the size 
field first so that it is used consistently for 64 bits w/out compressed 
oops, and 32 bits to reduce ifdefs.

Also needed to change set_klass to not zero the gap since CMS uses this 
to copy objects.  Decoupled set_klass and set_klass_gap in the case of 
compressed oops.

Changed FreeChunk and associated code in SA.

Performance results looked very good(not provided). Thanks to jmasa and 
ramki for their analysis, discussion of the change and prereview.

Webrev:  http://webrev.invokedynamic.info/coleenp/6687581/
Fix verified: y
Testing:  nsk stress, sajdi and my sanity testlists with CMS+compressedoops.
          runthese
          refworkload/GCOld
Reviewed-by: <your name here>