code: def lookup_defs(self, variable, size_threshold=32):
          
  
          live_def_locs = set()
  
          if isinstance(variable, SimRegisterVariable):
  
              if variable.reg is None:
                  l.warning('lookup_defs: Got a None for a SimRegisterVariable. Consider fixing.')
                  return live_def_locs
  
              size = min(variable.size, size_threshold)
              offset = variable.reg
              while offset < variable.reg + size:
                  if offset in self._register_map:
                      live_def_locs |= self._register_map[offset]
                  offset += 1
  
          elif isinstance(variable, SimMemoryVariable):
              size = min(variable.size, size_threshold)
              offset = variable.addr
              while offset < variable.addr + size:
                  if offset in self._memory_map:
                      live_def_locs |= self._memory_map[offset]
                  offset += 1
  
          else:
              # umm unsupported variable type
              l.error('Unsupported variable type "%s".', type(variable))
  
          return live_def_locs
docs: Find all definitions of the varaible
  
          :param SimVariable variable: The variable to lookup for.
          :param int size_threshold: The maximum bytes to consider for the variable. For example, if the variable is 100
                                     byte long, only the first `size_threshold` bytes are considered.
          :return: A set of code locations where the variable is defined.
          :rtype: set