==== increment weirdness: ++$m + $m++ ==========
   m = 20 at 0x80ab23c 
   p = ++m + m++ 
     *** inc  0x80ab23c : 20 --> 21 
          m is 21 at 0x80ab23c 
     *** copy 0x80ab23c --> 0x804c120 
          m is 21 at 0x80ab23c 
     *** inc  0x804c120 : 21 --> 22 
          m is 22 at 0x804c120 
     *** add : 22 at 0x804c120 + 21 at 0x80ab23c = 43 at 0x80ab11c 
          m is 22 at 0x804c120 
   p = 43 at 0x80ab11c