When I read that it's const I can in my mind "drop it". It's there, I know where the value was set and don't have to skim any longer for updates. It isn't for the compiler, its for me, the next guy who has to read your code.
Same thing with doing two separate things in the loop. Not only can it stop the the compiler from optimisations from time to time (the c++ compiler is very clever... but many times it gives up), I've had speed increases in breaking it up into several loops, but I also have to search and in my mind break things up. Very easy to do when I'm writing the code (and I'd probably do the same because of laziness), but quite annoying when I read someone else's code that does it.
Same thing with doing two separate things in the loop. Not only can it stop the the compiler from optimisations from time to time (the c++ compiler is very clever... but many times it gives up), I've had speed increases in breaking it up into several loops, but I also have to search and in my mind break things up. Very easy to do when I'm writing the code (and I'd probably do the same because of laziness), but quite annoying when I read someone else's code that does it.