oop.hpp is included by 860 out of 1000 HotSpot .o files. It includes access.hpp for this member function declaration only:

  template <DecoratorSet decorator>
  oop obj_field_access(int offset) const;

Instead of access.hpp, oop.hpp should include accessDecorators.hpp. This avoids including lots of header files from the Access API.

HotSpot build time is reduced by about 0.5% for this single-line change.