Register Allocation

When generating intermediate code in Chap. 6, we have freely used as many variables as we found convenient. In Chap. 7, we have simply translated variables in the intermediate language one-to-one into registers in the machine language. Processors, however, do not have an unlimited number of registers, so we need register allocation to handle this conflict. The purpose of register allocation is to map a large number of variables into a small(ish) number of registers. This can often be done by letting several variables share a single register, but sometimes there are simply not enough registers in the processor. In this case, some of the variables must be temporarily stored in memory. This is called spilling.