There are a number of occurrences of '#ifdef DEBUG' in the source, mostly in GC files. They give a false sense of security since DEBUG is not defined in fastdebug builds, so the code is eliminated, and most testing uses fastdebug builds.

src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp:6659: #ifdef DEBUG
src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp:6816: #ifdef DEBUG
src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp:6843: #ifdef DEBUG
src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp:8074: #ifdef DEBUG
src/share/vm/gc_implementation/g1/g1CollectorPolicy.cpp:1069:#ifdef DEBUG
src/share/vm/gc_implementation/g1/heapRegion.cpp:453:#ifdef DEBUG
src/share/vm/gc_implementation/g1/heapRegion.hpp:797:#ifdef DEBUG
src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.cpp:521:#ifdef DEBUG
src/share/vm/gc_implementation/parallelScavenge/psPromotionManager.cpp:615:#ifdef DEBUG
src/share/vm/memory/dump.cpp:274:#ifdef DEBUG
src/share/vm/memory/dump.cpp:1090:#ifdef DEBUG
src/share/vm/runtime/vmThread.cpp:106:#ifdef DEBUG