Buffered means a later divide may be executed out-of-order while a
prior divide is sitting (buffered) in a reservation station.

You can tell it's not pipelined, because operations that use it
reserve it for more than one cycle:

def : WriteRes<WriteIDiv, [HWPort0, HWDivider]> {
  let Latency = 25;
  let ResourceCycles = [1, 10];
}

We don't currently distinguish between an unpipeline operation and one
that is split into multiple micro-ops requiring the same unit. Except
that the later may have NumMicroOps > 1 if they also consume
issue/dispatch resources.

llvm-svn: 178519