this involves treating each CR as providing one bit of predicate. If
there is limited space in SVPrefix it will be a fixed bit (bit 0)
-otherwise it may be selected (bit 0 to 3 of the CR)
+otherwise it may be selected (bit 0 to 3 of the CR) through a firld in the opcode.
the crucial advantage of this proposal is that the Function Units can
have one more register (a CR) added as their Read Dependency Hazards