Re: Assuming optimization? What is best of these code alternatives?

[Adam Beneschan <adambeneschan@gmail.com>]

On Thursday, September 11, 2014 6:34:44 AM UTC-7, J-P. Rosen wrote:

> > begin
> >     (Read i1, i2 and n - do not change after)
> >     loop
> >       for i in i1 + i2 .. n loop -- will recalculate "i1 + i2" ?
> >           Do something...
> >       end loop;
> >     end loop;

> Response 1: don't bother with such micro-optimization
> Response 2: the language requires that the bounds be evaluated only
> once, not on each loop. Therefore, it won't make any difference.

I think you missed the outer loop.  The for loop is an inner loop, and i1+i2 does need to be recalculated for every iteration of the outer loop.  However, the OP has stated that i1 and i2 will not change, and his proposed initialization takes place outside the outer loop.

The question is, if i1 and i2 won't change, will the compiler optimize so that it doesn't have to re-perform the addition in each iteration of the outer loop.  The only answer is to try it with your compiler and see.

                                  -- Adam