zBarrier.inline.hpp is a popular header file (it's included by about 430 out of 1000 hotspot .o files). It includes javaClasses.hpp only for the inline function verify_on_weak(), which is used only for assert purposes in debug builds.

javaClasses.hpp is large and in turn pulls in other large header files. If we move verify_on_weak() into zBarrier.cpp and stop including javaClasses.hpp in zBarrier.inline.hpp, building hotspot is about 0.5% faster. The number of .o files that include javaClasses.hpp is reduced from 459 to 175.