code: def delete_from(self, basic_block):
          
          if basic_block is None:
              return
  
          if self.lock:
              return
  
          self.lock = True
  
          if self.prev is basic_block:
              if self.prev.next is self:
                  self.prev.next = None
              self.prev = None
  
          for i in range(len(self.comes_from)):
              if self.comes_from[i] is basic_block:
                  self.comes_from.pop(i)
                  break
  
          self.lock = False
docs: Removes the basic_block ptr from the list for "comes_from"
          if it exists. It also sets self.prev to None if it is basic_block.