Some header files introduced in loom has unnecessary #includes. For example:

https://github.com/openjdk/jdk/blob/2bf5c9a6877b51377a535c6021a9e38549c89029/src/hotspot/share/oops/instanceStackChunkKlass.inline.hpp#L30

These aren't necessary

#include "code/codeBlob.inline.hpp"
#include "code/codeCache.inline.hpp"
#include "code/nativeInst.hpp"
#include "compiler/oopMap.hpp"
#include "gc/shared/barrierSetNMethod.hpp"
#include "gc/shared/collectedHeap.hpp"
#include "gc/shared/gc_globals.hpp"
#include "logging/log.hpp"
#include "oops/instanceKlass.inline.hpp"
#include "oops/klass.hpp"

Also, some hpp files have complex inline functions that should be moved to either inline.hpp or cpp files.