Built-in SVE types are POD in much the same that scalars and
fixed-length vectors are.
Can you rearrange this so isSizelessBuiltinType() is at the bottom? It should be rare. (Assuming it doesn't need to be before the isIncompleteType() check.)
I should have mentioned that, but yeah: the call is placed here so that it continues to work when/if IsCompleteType returns true for these types. (I have a patch for that, similar to D76221, but I don't know whether it will be acceptable.)
Okay, then LGTM