HotSpotJVMCIMetaAccessContext.createClass is a synchronized wrapper around a WeakHashMap with WeakReference values.  During bytecode parsing this can be a heavy contention point between between multiple threads.  Additionally the use of WeakReferences for the keys and values is expensive.  A ClassValue<WeakReference<ResolvedJavaType>>  would avoid the contention around the synchronized method and would eliminate one of the two required WeakReferences.