This will technically only work on pipelined architectures of which all major CPU architectures are one. You will be able to see a significant boost to performance given the following are all true:
* You have no inter dependancy of information across the lines
* All your data is in the cache
* You don't have instructions generated between the two lines that will require some sort of operand forwarding
Basically, if you already have the stuff in the cache, the calculation is invarent to the last calculation, and you have a processor capable of it you'll see a large speed improvement.
There is a great talk about this [0] (for the exact moment go to [1]). If you're interested further I'd very much recommend finding some sort of GOOD computer architecture class. Luckily now we have a fantastic resource to locate these such courses [2]. This seems like dark magic and many programmers refuse to come to terms with it's existence. Check out `dreta`'s comment to see an example.
Now I do agree with dreta, this is VERY much architecture dependant but most architectures would benifit from this sort of optimization. Pretty much all modern Intel and AMD CPU's caches are large enough, they support a big enough cache, and they also all have pipelines under the hood. Intel started this in the pentium series with a 5-stage-pipeline (which I find very funny due to the GHz wars that came from that time period desipte the pipeline being probably the pargest performance boon in most cases that you would want to brag about).
[0] - https://www.youtube.com/watch?v=e08kOj2kISU
[1] - https://youtu.be/e08kOj2kISU?t=26m50s
[2] - https://github.com/Developer-Y/cs-video-courses#computer-org...