RFR(M): 8212243: More gc interface tweaks for arraycopy and some other smaller changes in preparation for Shenandoah

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/8212243/webrev.00/

This change adds 2 more entry point for arraycopy to the gc interface:

- one, when an arraycopy is turned into loads/stores and the field or
  element being copied is a reference. In that case, barriers may have
  to be applied.

- another, when a clone is expanded into a stub call. In that case a
  postbarrier may be required. That one is only required when a
  reference field or element may be encountered. That's where the
  ciInstanceKlass changes come in.

The other complicated change is in loopPredicate.cpp. We have:

Predicate 1
..
Predicate n

profile predicate 1
..
profile predicate n

loop head

Shenandoah write barriers produce memory, can be hoisted out of loop but
can also depend on some predicate so may end up with:

Predicate 1
..
Predicate n

profile predicate 1
..
write barrier
...
profile predicate n

loop head


In that case, all predicates branch to a region that dominates the
uncommon trap call. Same is true for profile predicates. Because of the
write barrier, the region for profile predicates has a memory phi to
merge memory state before the barrier and after the barrier. Now when
clone_loop_predicates() is called:

Predicate 1
..
Predicate n

profile predicate 1
..
write barrier
...
profile predicate n

cloned predicate

cloned profile predicate

loop head


the cloned predicate branches to the region shared by all
predicates. Same goes for the cloned profile predicate and the profile
predicates. The memory state for the cloned predicate should be the one
following the barrier but after cloning it's the one from the predicate
n, before the barrier. That memory state needs to be adjusted.

Other changes tweak the gc interface and make sure that when nodes are
disconnected, nodes that need special treatment are processed.

Roland.