RFR (XXL): 8223347: Integration of Vector API (Incubator): General HotSpot changes

[Vladimir Ivanov]

>> So the VM supports is enabled either because there is an explicit 
>> --add-modules or because the module is transitively reachable from the 
>> root modules.
>> It means that it doesn't work if the module jdk.incubator.vector is 
>> loaded using a ModuleLayer. Users has to use XX:+EnableVectorSupport 
>> in that case.
>>
> Is jdk.incubator.vector is mapped to the boot loader? If so then it 
> can't be loaded into a child layer.

Yes, jdk.incubator.vector is a boot module. The reason to put it there 
is to be able to trust final instance fields by the JVM.

Since the module extensively uses VM annotations, it should be either 
boot or platform module in order to have access to them, but in case of 
platform module existing logic for trusting final instance fields 
doesn't work and all such fields should be marked as @Stable instead.

Best regards,
Vladimir Ivanov