In terms of the logical evaluation of the loop, there is of course no difference, so the question is: can you compile
++x into something more efficient than
And yes, indeed you can if you look close enough. In order to perform the increment on the variable, you need to load its value onto the stack (or a register, or wherever - for the sake of simplicity, I'll just keep saying stack), then perform the increment operation. Your stack will then contain the incremented value at the top. That's the same for both ways though, so why is there a difference?
It does make a difference, once you start using these expressions in larger ones. Consider
f(x++). In order to create code that performs the function call, you need to place its argument onto the stack. Now if the argument is
x++, then you place
x on the stack and call the method, which removes its arguments from the stack again. The problem is that after all of this, you need to again load
x onto the stack in order to perform the increment operation.
That being said: while using
++x may give you a few CPU cycles of performance, this is absolutely not the sort of performance difference that you should even have on your radar.
In addition, as ratchet freak pointed out, the
++ operation itself can be overloaded in some languages, resulting in vastly more complex behaviors and even differing results. However, in these cases, I consider it a criminal act to inline these operations (or in case of different results to even define them as such). And once you consider the statement
++x in isolation, there's nothing interesting to be said about performance anymore anyways.