[9] RFR (S): 8162101: C2: Handle "wide" aliases for unsafe accesses

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8162101/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8162101

Improve detection of unique alias categories for unsafe accesses.

Mixed (can_access_non_heap == true) and on-heap mismatched accesses have 
wide aliases and, hence, need memory barriers around them.

TypeInstPtr::KLASS & TypeAryPtr::RANGE are not covered since 
GraphKit::make_load() doesn't produce correct LoadNode flavors for them 
(LoadKlassNode/LoadRangeNode).

Testing: JPRT, RBT (hs-tier0-comp).

Thanks!

Best regards,
Vladimir Ivanov