different asm code

hi:)

  I have compiled a .S file ,using command gcc -c x.S -o x.
  Then I use objdump to look up its asm code, even find that some code is not the
  same as that .S file , more important is , some code in origin  .S file has disappear .
  
  what is about the reason ? If it is due to version , why some code chould get lost after compile?


thanks!