// live_in[5] = use[5]   U (live_out[5] - def[5])
//            = {%3}     U ({∅} - {∅})            = {%3}
// live_in[4] = use[4]   U (live_out[4] - def[4])
//            = {%1, %2} U ({%3} - {%3})          = {%1, %2}
// live_in[3] = use[3]   U (live_out[3] - def[3])
//            = {%0, %1} U ({%1, %2} - {%2})      = {%0, %1}
// live_in[2] = use[2]   U (live_out[2] - def[2])

	//	varkill: killed variables (set in block)
	uevar   bitvec.BitVec
	varkill bitvec.BitVec

	// Computed during Liveness.solve using control flow information:
	//
	//	livein: variables live at block entry
	//	liveout: variables live at block exit
	livein  bitvec.BitVec
	liveout bitvec.BitVec
}

// A collection of global state used by liveness analysis.
type liveness struct {
	fn         *ir.Func
	f          *ssa.Func