code: boolean inSameSubroutine(final Label block) {
          for (int i = 0; i < srcAndRefPositions.length; ++i) {
              if ((srcAndRefPositions[i] & block.srcAndRefPositions[i]) != 0) {
                  return true;
              }
          }
          return false;
      }
docs: Returns true if this basic block and the given one belong to a common
  subroutine.
  
  @param block another basic block.
  @return true if this basic block and the given one belong to a common
  subroutine.