SUGGESTED FIX

Set control edge for EncodeP and DecodeN nodes using MemNode::Ideal_DU_PostCCP().

Also fix next problems:
- replace Type::is_narrow() with more precise Type::is_ptr_to_narrowoop()
  defined during TypeOopPtr construction,
- use subclass check instead of alias types check in CallNode::may_modify(), 
- call PhiNode::split_out_instance() also for Phi nodes with
  non-instance OopPtr type which matches the instance type,
- stop compilation instead of VM exit when there is no space 
  for scratch buffer in CodeCache,
- don't flatten instance type in alias types,
- skip the split through phi in LoadNode::Ideal() if the Region node
  dominates load's address,
- an allocation is not scalar replaceable if the resuilt is stored
  into unknown array's element,
- try both Region's input paths in Node::dominates(),
- add missing checks for ConN node.

Added the test case. Also added the test case for 6689060.
                                     

EVALUATION

The problem is EncodeP node's type nullness.

After CastPP is removed by PhaseCCP EncodeP was moved above the null check
(EncodeP and DecodeN don't have control edge) so the NotNULL type
is not valid any more.