hg: jdk7/hotspot-gc/hotspot: 6948537: CMS: BOT walkers observe out-of-thin-air zeros on sun4v sparc/CMT

[y.s.ramakrishna at oracle.com]

Changeset: 3bfae429e2cf
Author:    ysr
Date:      2010-05-03 10:24 -0700
URL:       http://hg.openjdk.java.net/jdk7/hotspot-gc/hotspot/rev/3bfae429e2cf

6948537: CMS: BOT walkers observe out-of-thin-air zeros on sun4v sparc/CMT
Summary: On sun4v/CMT avoid use of memset() in BOT updates so as to prevent concurrent BOT readers from seeing the phantom zeros arising from memset()'s use of BIS.
Reviewed-by: jmasa, johnc, minqi, poonam, tonyp

! src/cpu/sparc/vm/vm_version_sparc.cpp
! src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp
! src/share/vm/memory/blockOffsetTable.hpp
! src/share/vm/runtime/globals.hpp