GCNDownwardRPTracker RPTracker.reset() skips debug instructions for NextMI so RPTracker.getNext() will never give the beginning of a sched region if it is a debug value. In this case we will never set the live-ins for that block.
Add check to see if getNext also equals the MI after skipping debug instructions.
could you just apply skipDebuInstructionsForward to MBB->begin instead of adding a second check