Build the schedule DAG with register pressure tracking enabled.
Declared in <llvm/CodeGen/MachineScheduler.h>
void
buildDAGWithRegPressure();
Calls ScheduleDAGInstrs::buildSchedGraph with pressure tracking. This sets up three trackers. RPTracker covers the entire DAG region; TopTracker and BottomTracker are initialized to the top and bottom of the DAG region without covering any unscheduled instruction.