[neonsunset]

Any sufficiently advanced compiler will rewrite those arbitrarily depending on its heuristics. What authors usually forget is that there is defined behavior and specification which the compiler abides by, but it is otherwise free to produce any codegen that preserves the defined program order. Branch reordering, generating jump tables, optimizing away or coalescing checks into branchless forms are all very common. When someone says "oh I write C because it lets you tell CPU how exactly to execute the code" is simply a sign that a person never actually looked at disassembly and has little to no idea how the tool they use works.

[cogman10]

A complier will definitely try this, but it's important to note that if/else blocks tell the compiler that "you will run these evaluations in order". Now, if the compiler can detect that the evaluations have no side effects (which, in this simple example with just integer checks, is fairly likely) then yeah I can see a jump table getting shoved in as an optimization.

However, the moment you add a side effect or something more complicated like a method call, it becomes really hard for the complier to know if that sort of optimization is safe to do.

The benefit of the switch statement is that it's already well positioned for the compiler to optimize as it does not have the "you must run these evaluations in order" requirement. It forces you to write code that is fairly compiler friendly.

All that said, probably a waste of time debating :D. Ideally you have profiled your code and the profiler has told you "this is the slow block" before you get to the point of worrying about how to make it faster.

[tombert]

I agree with what you said but in this particular case, it actually was a direct integer equality check, there was zero risk of hitting side effects and that was plainly obvious to me, the checker, and compiler.

[cogman10]

And to your original comment, I think the reviewer was wrong to reject the PR over that. Performance has to be measured before you can use it to reject (or create...) a PR. If someone hasn't done that then unless it's something obvious like "You are making a ton of tiny heap allocations in a tight loop" then I think nitpicking these sorts of things is just wrong.