Consider the following subroutine in Fortran 77: subroutine shift(a, b, c) integer a, b, c a=b b=c end Suppose we want to call shift(x, y, 0) but we don’t want to change the value of y. Knowing that...

Consider the following subroutine in Fortran 77:

subroutine shift(a, b, c)

integer a, b, c

a=b

b=c

end

Suppose we want to call shift(x, y, 0) but we don’t want to change the

value of y. Knowing that built-up expressions are passed as temporaries,

we decide to call shift(x, y+0, 0). Our code works fine at first, but then

(with some compilers) fails when we enable optimization. What is going

on? What might we do instead?