The bits in MemberName.flags is running out, that in mainline it only has 2 free bits. However, in project valhalla, we need to represent the layout of a inlined/flat field in a MemberName to avoid repeated queries to the backing InstanceKlass. We currently have about 5 layouts, which requires 3 bits.

As a result, we should expand the flags field to be 64-bit instead of just 32-bit, so we have more freedom to encode more information. This is assigned to hotspot runtime due to the flags being extensively used in platform-specific assembly and hotspot, which is out of reach for core library developers.