> how do you know which cases to separate the code into?
It takes practice. For this you really just have to read the assembly, and profile the code. Then try separating it one way and see if it helps, and if not then another. In my experience, it takes many tries to update your perf knowledge, and optimizations sometimes don’t work even when your knowledge is current. All this is why the article noted people should be “Giving the compiler an opportunity to do something is useful, but measure carefully before forcing it.”
It takes practice. For this you really just have to read the assembly, and profile the code. Then try separating it one way and see if it helps, and if not then another. In my experience, it takes many tries to update your perf knowledge, and optimizations sometimes don’t work even when your knowledge is current. All this is why the article noted people should be “Giving the compiler an opportunity to do something is useful, but measure carefully before forcing it.”