public IntList labelToPredecessors(int label) {
    if (exitPredecessors == null) {
      calcPredecessors();
    }

    IntList result = predecessors[label];

    if (result == null) {
      throw new RuntimeException("no such block: " + Hex.u2(label));
    }

    return result;
  }
Gets the predecessors associated with the given block. This throws an exception if there is no
block with the given label.

@param label {@code >= 0;} the label of the block in question
@return {@code non-null;} the predecessors of that block
android/android_framework/dex-maker/src/main/java/com/android/dx/rop/code/RopMethod.java