{compiledMethod, codeCache, javaClasses, systemDictionary}.hpp are unnecessarily included in some popular headers. This introduces unnecessary dependencies and slows down compile time:

http://hg.openjdk.java.net/jdk/jdk/file/431d17e9235f/src/hotspot/share/runtime/vmOperations.hpp
http://hg.openjdk.java.net/jdk/jdk/file/431d17e9235f/src/hotspot/share/runtime/thread.hpp
http://hg.openjdk.java.net/jdk/jdk/file/431d17e9235f/src/hotspot/share/prims/methodHandles.hpp
http://hg.openjdk.java.net/jdk/jdk/file/431d17e9235f/src/hotspot/share/ci/ciEnv.hpp