Simple Register Allocation

Note that there may be several classes of registers, e.g., integer data registers, index registers, floating point registers.

A very simple register allocation algorithm is:

1. At the beginning of a statement, mark all registers as not used.

2. When a register is requested,
   1. If there is an unused register, mark it used and return the register number.

   2. Otherwise, punt.[E.g., print a message saying that the expression is too complex and needs to be simplified.]

On a machine with 8 or more registers, this algorithm will almost always work. However, we need to handle the case of running out of registers.