This chapter has discussed a large number of optimizations, most of which are found on the control flow graph. The reader may be wondering what the improvements really are. Is it worth the time and effort at compile time -- not to mention at compiler creation time -- to perform such aggressive optimizations?
The answer is -- it depends. Statistics have shown that there is a 5-25% improvement in running time for the loop optimizations:
There is a 1-5% improvement for:
Interestingly, the topic of the next chapter, register allocation, has been shown to improve code more than the optimizations above. Because good register alloction does improve code, it is often discussed in chapters on optimization.
The optimizations performed after code generation, peephole optimization, also have a high payoff. We discuss these in Chapter 11.