It's absolutely essential to be able to change vsetvli in the middle of a kernel. It is expected that in a future expanded Vector instruction set with 48 bit o

It's absolutely essential to be able to change vsetvli in the middle of a kernel. It is expected that in a future expanded Vector instruction set with 48 bit or 64 bit opcodes the vtype will be explicitly encoded in every instruction and can change every instruction. Right now the vsetvli is setting (slightly) persistent state that affects following instructions. You're allowed to put one before every vector instruction if you want, without significant execution penalty -- there will be a little, from extra instruction fetch and decode -- but similar to doing, say, an integer add between each vector instruction. The natural implementation even now is to have each vector instruction pick up the current vtype when it is decoded and carry it along with it through the pipeline as a few extra bits of opcode. You certainly don't want to have any stalls or pipeline flushes just because the vtype changes.