Standard way to supply hints to branches

[Rob T]

On Saturday, 24 August 2024 at 02:34:04 UTC, Walter Bright wrote:
> I recently learned a syntactical trick on how to do this.
>
> ```
> if (x) return;
> if (y) return;
> if (z) return;
> hotPath();
> ```
>
> Rewrite as:
>
> ```
> do
> {
>     if (x) break;
>     if (y) break;
>     if (z) break;
>     hotPath();
> } while (0);
> ```
>
> Of course, this will also work:
>
> ```
> if (x) goto Lreturn;
> if (y) goto Lreturn;
> if (z) goto Lreturn;
> hotPath();
> Lreturn:
> ```

I almost always do a similar thing as a general coding principle, 
ie, get all the conditional checks out of the way first, before 
moving on to the main code path. In most cases, the "hot path" 
will be the main code path to take, but the main reason I do it 
in this way (as a general rule), is to make the code easier to 
understand and manage.

As for the branch predicting, my understanding is that it will 
depend on the combination of the choice of compiler, and the 
processor the code is executed on. Some processors, will attempt 
to execute more than one path simultaneously until the correct 
path is determined. As for optimizing your code, in my 
experience, is that in general, there will always be much more 
effective methods to prioritize than trying to optimize branch 
predictions, but I suppose it depends entirely on the fine 
details of what is being attempted.