In order to better test the concurrency support in JVM, we introduced StressLCM/StressGCM flags that randomize C2's instruction scheduling:

  develop(bool, StressLCM, false, \
          "Randomize instruction scheduling in LCM") \
                                                                            \
  develop(bool, StressGCM, false, \
          "Randomize instruction scheduling in GCM") \
                                                                            \

This, however, requires fastdebug build, which is not really fast for concurrency testing, as it does lots of asserts in VM codepaths (notably, GC). We would be better off turning these flags to diagnostic, to pop out in product builds.