This is part of what David Horner wants. However,
it does not give him the fault-on-first
with zero length complete mechanism. It
could, if there were something else in the system that
guaranteed forward progress
My take is that requiring that element 0 either complete
or trap is already a solid mechanism for guaranteeing
forward progress, and cleanly matches the while-loop
Yep, it's sufficient for the needs of while loop Vectorization.
It is suboptimal for "SIMT on vector". For that you need a
completion mask. and it is far too late to add that to the
RISC-V vector spec.