code: def should_compile_incrementally(self, vts, ctx):
      
      if not vts.is_incremental:
        return False
      if not self._clear_invalid_analysis:
        return True
      return os.path.exists(ctx.analysis_file)
docs: Check to see if the compile should try to re-use the existing analysis.
  
      Returns true if we should try to compile the target incrementally.