public void addLiveIn(int regV) {
    if (liveIn == null) {
      liveIn = SetFactory.makeLivenessSet(parent.getRegCount());
    }

    liveIn.add(regV);
  }
Adds {@code regV} to the live-in list for this block. This is called by the liveness analyzer.

@param regV register that is live-in for this block.
android/android_framework/dex-maker/src/main/java/com/android/dx/ssa/SsaBasicBlock.java