When flattening the alias type for [KlassPtr + Offset], the code in
flatten_alias_type() is incorrect and leads to assertion failures at:

memnode.cpp line 87:
    assert(adr_type() == NULL || adr_type()->empty() || phase->C->must_alias(adr_type(), alias_idx), "adr_type must match alias idx");


compile.cpp line 908, Compile::flatten_alias_type( const TypePtr *tj )
  ...
  // Klass pointers to object array klasses need some flattening
  const TypeKlassPtr *tk = tj->isa_klassptr();
  if( tk ) {
    // if we are referencing a field within a Klass, we need
    // to assume the worst case of an Object
    if (offset == Type::OffsetBot || offset < sizeof(Klass))
      tj = tk = TypeKlassPtr::make( ptr, TypeKlassPtr::OBJECT->klass(), offset );


The problem occurs when a the memory input to an AddP changes from inexact to
exact and the input to TypeKlassPtr::make changes from TypePtr::NotNull to
TypePtr::Constant. This implies that two memory accesses can be incorrectly
scheduled when one starts out being a Constant and the other does not.

Problem has been observed on AMD64/LIN64 when running 200_check, but is in
machine independent code that is run on all platforms.