C programming tricks

While programming optimization that makes ones' code completely unreadable is often a bad thing, there are places for it, like that one inner loop of your code that takes up 98% of the program's running time.

What are you tricks for improving performance in C, other than the obvious inline assembly or the like?

The answer is: You can't know. Undefined. The C standard says nothing about what the result will be and the only way to know for sure what i will be after that line lies in how the specific compiler that compiles that piece of code handles it.