Pushing S Registers

The subroutine now looks like:

## maxExp -- compute the maximum of three expressions
##
## Input:
## $a0 -- a signed integer, x
## $a1 -- a signed integer, y
##           
## Returns: 
## $v0 -- the maximum of x*x,  x*y, or 5*y
##
## Registers:
## $s0 --  x*x
## $s1 --  x*y
## $s2 --  5*y

         .text
         .globl maxExp

maxExp:
         # prolog
         sub     $sp,$sp,4        # push the return address
         sw      $ra,($sp)
         
         sub     $sp,$sp,4        # push $s0
         sw      $s0,($sp)
         
         sub     $sp,$sp,4        # push $s1
         sw      $s1,($sp)
         
         sub     $sp,$sp,4        # push $s2
         sw      $s2,($sp)
         
         # body

         # subroutine maxInt call
         # subroutine maxInt return

         # subroutine maxInt call
         # subroutine maxInt return

         # epilog