Details of Function Call

1. For each argument, use genarith to compute the argument. If needed, move the result from the register returned by genarith to %xmm0 and mark the genarith register unused.

2. Return the function result register ( %xmm0, %eax or %rax) as the result of genarith.

If the rhs of an operation involves a function call, as in

   y := exp(-x)*sin(c*x)

1. If the lhs register is in use, save it on the stack.

2. Call the function

3. Get a new register, restore the lhs value to it from the stack, and set the lhs register to that register.