This is a follow-on issue to JDK-8140630. When devkit was updated to version 4.9.2 on Linux-x86_64, the JDK test java/nio/Buffer/Basic.java crashed with a SIG_SEGV in Mach5 testing. This is a tier 1 failure.
It was found that compiling src/java.base/share/native/libjava/Bits.c using normal (-O2) optimization instead of high (-O3) resolved the immediate problem. The concern however is that there is an underlying pattern in the optimized compiled code which might manifest itself elsewhere. It would be better to examine the problem in detail in order to find the root cause and hopefully a better solution.