This chapter has used the results of the last two chapters to improve programs so that the ultimate code executes faster. In some cases, this also performs a space improvement; in some cases the improvement in time produces code which consumes more space.
We divide these improvements into three catagories: local, loop and global. The divisions are somewhat arbitrary in that loop optimizations may be classified as either local or global. Loop optimizations, in general, improve code more that other optimizations.
There are two more improvements, often categorized as optimizations because they improve program performance greatly: good register allocation and peephole optimization (see Chapter 10).