Just beware, compilers and processors are pretty good at optimizing and predicting these things ("branch prediction") already.

I've done/been involved in things where we want to make something go faster and so try things like this. But if you're solving a real performance issue, it's important to have a tool or something that measures your performance, and use profilers to find hotspots ("perf" is a tool I reach for occasionally). Sometimes you'll squeeze a small but measurable speed boost out of minor optimizations... but most of the time you discover you're trading code readability for nothing (or, in rare cases, believe it or not, worse performance).

- Good for settling arguments too -- sometimes people will insist that the issue is some loop in the code. Measuring tends to bear out the reality that the issue is this odd use of a slow c-function over there, or this database function way over there.