How to write code that is good for compiler optimization

To emulate the behavior of prefix ++ for primitive types, operator++() can modify the object and return a reference to the modified object. What about emulating the behavior of postfix ++ for primitive types? Remember? "The result of the postfix ++ operator is the value of the operand. After the result is obtained, the value of the operand is incremented." Just like the non-linear code above, the implementer of operator++(int) must copy the original object, modify the original object, and return the copy by value. Because of the copy operation, operator++(int) has a higher overhead than operator++().

For primitive types, the optimizer can often eliminate unnecessary copies if the result of i++ is ignored, but the optimizer cannot transform a call to one overloaded operator into another. If you write i++ instead of ++i out of habit, you are calling the more expensive increment operator.

Although we have been advocating against postincrement, we have to admit that postincrement is useful in some cases. If you really want to postincrement a variable, then go ahead. If the postincrement operation is consistent with what you expect, use it. But be careful not to use postincrement just to avoid writing an extra line of code to increment a variable.

Every time you add an unnecessary post-increment to a loop condition, an if condition, a switch expression, a ?:- expression, or a function call parameter, you force the compiler to generate larger, slower code. Is this list too long to remember? Start developing good habits today! Before using a post-increment, ask yourself if you can use the increment as the next statement.

Conclusion

Of course, software development does not only require developers to "make do" with compilers. The mutual cooperation between them and the compiler is one of the foundations for completing programming work quickly and efficiently. In addition, from the perspective of the development process of compilers, they must not only iterate and innovate with the evolution of technology and language, but also refer to more development habits. Compilers with a longer history and wider use can bring higher efficiency to developers.

Therefore, after understanding how to write code that is optimized by an excellent compiler, users can work more efficiently with less effort. The principles and tips mentioned in this article are also the best practices summarized by companies such as IAR Systems over a long period of time, and can be verified and explored in the company's Embedded Workbench. In its tool interface, you can view the execution time and code size of the code to find the best solution.

In addition to general code compilation optimization, good tools also support highly flexible custom optimization settings. For example, IAR Embedded Workbench includes different optimization levels for operating efficiency and code size. For different application requirements, you can also set the optimization level from the entire project to each source code file, and even each function, to help engineers adapt the best optimization solution for their applications. I hope this article will help developers to have a deeper understanding of program optimization.