Performance Gains with Visual Studio Whole Program Optimization

Question

Our product is a library which we deliver as a dll or static library. I've noticed that using Whole Program Optimization in Visual Studio improves the performance around 30%. This is good but referring to http://blogs.msdn.com/b/vcblog/archive/2009/02/24/quick-tips-on-using-whole-program-optimization.aspx I see that it is not suggested to use whole program optimization for libraries that are delivered to customers.

The same article mentions around 3-4% improvement in performance. Now that we see 10 times of the expected performance gain, I am thinking whether we are doing something wrong.

Not sure how to formulate this but I'll give it a try: Apparently our code base has a "problem" that WPO can solve very well. Whatever this "problem" (or problems?) is , it is less important in other software hence WPO has relatively small impact. Now my question is what might be this problem? We would like to optimize our code manually since turning on WPO is not an option.

Answer 1

Probably, you have some functions called many times, which can't be inlined without WPO due to being defined in source files. You can use a profiler to identify these, then move them into headers and mark them inline .