Fibonacci Recursivo ASM

.data
    f0: .word   0
    f1:     .word   1
    n:  .word   4
    res:    .word   0
.text
    main:   lw $4, n($0)
        jal fib
        sw $2, res($0)
        li $2, 10
        syscall

    fib:    bgt $4, 1, else     #if n<1 then
        add $2, $0, $4      #return n
        jr $31
    else:   subi $29, $29, 12   #else
        sw $4, 0($29)       #guardamos n en la pila
        sw $31, 8($29)
        subi $4, $4, 1      #n = n-1
        jal fib         #call fib(n-1)
        sw $2, 4($29)       #guardamos fib(n-1) en la pila
        lw $4, 0($29)       #cargamos n
        subi $4, $4, 2      #n = n-2
        jal fib         #call fib(n-2)
        lw $8, 4($29)       #$8 <- fin(n-1)
        lw $31, 8($29)
        addi $29, $29, 12   #restauramos la pila
        add $2, $8, $2      #$2 <- $8 + fib(n-2)
        jr $31