An Intrinsic can take IntrinsicProperty, which are applied during CodeGen. Some of these IntrinsicProperties have their is_default bit set to true (e.g. IntrNoCallback, IntrNoSync, IntrNoFree, and IntrWillReturn).
Using DefaultAttrsIntrinsic sets disable_default_attributes to false, so that all IntrinsicProperties, including those with is_default = true, will be applied, whereas just using Intrinsic defaults disable_default_attributes set to true and will ignore the default properties.
What then, is the purpose of having IntrinsicProperties with is_default = true applied to Intrinsic definitions where disable_default_attributes is true (e.g. int_memmove_element_unordered_atomic)?