Espasa discusses this around 6:45 of https://www.youtube.com/watch?v=WzID6kk8RNs.
Agree agnostic would help, but the machine also has to handle SW asking for mask/tail unchanged, right?
Yes, but it should rarely do so.
The problem is that because of the vl=0 case you always have a dependency on avl. I think the motivavtion for the vl=0 case was that any serious ooo implementation will need to predict vl/vtype anyways, so there might as well be this nice to have feature.
IMO they should've only supported ta,mu. I think the only usecase for ma, is when you need to avoid exceptions. And while tu is usefull, e.g. summing am array, it could be handled differently. E.g. once vl<vlmax you write the summ to a difgerent vector and do two reductions (or rather two diffetent vectors given the avl to vl rules).
If hardware will be predicting vl, I'd imagine that would break down anyway. Potentially catastrophically so if hardware always chooses to predict vl=0 doesn't happen.
The agnosticness flags can be forwarded at decode-time (at the cost of the non-immediate-vtype vsetvl being very slow), so for most purposes it could be as fast as if it were a bit inside the vector instruction itself. Doesn't help vl=0 though.