With project Valhalla, if the type of a field is an inline type, the JVM can decide to flatten this field, which means the field doesn't contain a reference to an instance of this inline type, but the individual values of the different fields of this inline type.

MetadataField.getValue(Address addr) is a method that is supposed to return the metadata for a field at a given address. The current method to return the metadata is to follow the reference, and use the klass pointer from the header of the instance pointed by the field.

This method cannot work with flattened fields because they have no indirection and no header. For flattened fields, the metadata must be retrieved from the field's holder metadata.