code: @Override
      public Fact getFactAtLocation(Location location) throws DataflowAnalysisException {
          Fact start = getStartFact(location.getBasicBlock());
          Fact result = createFact();
          makeFactTop(result);
          transfer(location.getBasicBlock(), location.getHandle(), start, result);
          return result;
      }
docs: Get the dataflow fact representing the point just before given Location.
  Note "before" is meant in the logical sense, so for backward analyses,
  before means after the location in the control flow sense.
  
  @param location
  the location
  @return the fact at the point just before the location