review for 7032963: StoreCM shouldn't participate in store elimination

[Tom Rodriguez]

I could push this to hotspot-gc so it gets more CMS testing .

http://cr.openjdk.java.net/~never/7032963

7032963: StoreCM shouldn't participate in store elimination
Reviewed-by:

StoreCM shouldn't participate in redundant store elimination since
that could violate the requirement that a StoreCM must be strictly
after a field update.  This results in a large number of redundant
StoreCMs being emitted for blocks of fields updates, so I added an
optimization to fold them up safely.  Previously the extra dependence
was converted into a precedence edge just before register allocation
but I moved this logic into final_graph_reshape.  I then added logic
to search through chains of StoreCMs to eliminate earlier redundant
ones and transfer their precedence edges to the one that is kept.
This ensures that they are scheduled properly.  This actually
eliminates duplicates that were previously missed so the code quality
is slightly better.  Tested by inspecting code generation with script
to identify duplicates.  Also ran CTW with -XX:+UseCondCardMark and
-XX:+UseG1GC.