gistfile1.txt

def cg_add(leftindex, rightindex):
   global tempcount

   ### check for and free temporary variables
   if symbol[leftindex].startswith('.t'):
      tempcount -= 1
   if symbol[rightindex].startswith('.t'):
      tempcount -= 1

   ### check for constants
   constonleft = False
   constonright = False

   if symbol[leftindex].startswith('.i'):
      constonleft = True
   if symbol[rightindex].startswith('.i'):
      constonright = True

   ## check for registers, if so get index
   regonleft = False
   regonright = False

   if loc[leftindex] == None:
      regonleft = False
   else:
      regonleft = True
      leftreg = loc[leftindex]
   if loc[rightindex] == None:
      regonright = False
   else:
      regonright = True
      rightreg = loc[rightindex]

   ## case: ( constant + constant )
   if constonleft and constonright:
      # constant folding
      result = int(value[leftindex]) + int(value[rightindex])
      if result >= 0:
         return enter('.i' + str(result), str(result), False)
      else:
         return enter('.i_' + str(-result), str(result), False)

   ## case: ( register + register )
   elif regonleft and regonright:
      ## get index of next temp variable
      tempindex = cg_gettemp()
      tempreg = loc[tempindex]

      outfile.write('       add ' + tempreg + ', ' + leftreg + ', ' + rightreg + '\n')
      return tempindex

   ## case: ( register + constant/variable )
   elif regonleft:
      outfile.write('       ldr r1, ' + symbol[rightindex] + '\n')
      outfile.write('       add ' + leftreg + ', ' + leftreg + ', r1\n')
      needword[rightindex] = True
      return leftindex

   ## case: ( constant/variable + register )
   if regonright:
      outfile.write('       ldr r0, ' + symbol[leftindex] + '\n')
      outfile.write('       add ' + rightreg + ', ' + rightreg + ', r1\n')
      needword[leftindex] = True
      return rightindex

   ## case: ( constant/variable + constant/variable )
   else:
      ## get index of next temp variable
      tempindex = cg_gettemp()
      tempreg = loc[tempindex]

      outfile.write('       ldr r0, ' + symbol[leftindex] + '\n')
      outfile.write('       ldr r1, ' + symbol[rightindex] + '\n')
      needword[leftindex] = True
      needword[rightindex] = True

      # store sum in temp variable
      outfile.write('       add ' + tempreg + ', r0, r1\n')
      return tempindex