Compilers optimizing code
The optimizing compiler is critically important for achieving high performance. Just try running a program compiled with no optimization at all to appreciate the role of the compiler: it is not uncommon for an unoptimized program (optimization level zero) to run an order of magnitude slower than the program compiled with all optimizations enabled.
Very often, however, it is the case that the optimizer can use some help from the programmer. This help can take the form of very subtle and often counter-intuitive changes. Before we look at some specific techniques to improve the optimization of your code, it helps to understand how the compiler sees your program.
Basics of compiler optimizations
The most important thing you must understand about optimization is that any code that is correct must remain correct. Correct here has nothing to do with your view of what is correct: the program may have bugs and give an answer you consider wrong, but the compiler...
