Created attachment 162690 [details]
EnumSet.of.png

It appears that there is huge performance difference between EnumSet.of() with EnumSet.noneOf().add() - the first one is roughly 3-4 times slower (because of inner call to Class.getSuperClass()) and in the amount of iterations for UsagesData.addUsage() this is rather significant difference in overall time. Attached is the 'proof-link' for another similar case in another module.

Required change is rather minor

    void addUsage(
            @NonNull final T className,
            @NonNull final ClassIndexImpl.UsageType type) {
        Set<ClassIndexImpl.UsageType> usageType = usages.get (className);
        if (usageType == null) {
            usageType = EnumSet.of(type);
            usages.put (className, usageType);
        } else {
            usageType.add (type);
        }
    }

-->

    void addUsage(
            @NonNull final T className,
            @NonNull final ClassIndexImpl.UsageType type) {
        Set<ClassIndexImpl.UsageType> usageType = usages.get (className);
        if (usageType == null) {
            usageType = EnumSet.noneOf(ClassIndexImpl.UsageType.class);
            usages.put (className, usageType);
        }
        usageType.add (type);
    }