Optimzed vs. readable code

[Howard Hinnant]

On Nov 29, 2005, at 8:48 AM, Pierre THIERRY wrote:

> Hi,
>
> I just noted that the convention for the algorithms I have read in the
> GNU STL, when using a starting and ending iterator between which one
> want to move, seems to be to increment the first iterator.
>
> We have things like this:
>
> 	++first;
>
> And tests like this:
>
> 	*first == something
>
> Semantically, that doesn't seem very nice. One can eventually get  
> used to
> it, when one knows, but wouldn't it be more judicious for the code to
> become more readable, by adding:
>
> 	current = first;
>
> Thus, we get:
>
> 	++current;
>
> 	*current == something
>
> I suppose using the (rather ugly) 'first' as moving iterator has a  
> goal
> of optimization, but any decent compiler is now able to optimize  
> this (a
> variable initialized with another who is never accessed anymore,  
> locally
> to a function), so that this change in the code indeed makes no
> difference the the compiled result.
>
> So would a patch with this kind of change be accepted?

You are the victim of unfortunate timing. :-)  I just posted in  
another thread:

> That philosophy is basically:  Keep things as simple as possible.   
> Don't gratuitously add code just to see if the compiler can  
> optimize it back out.

(sorry :-) )

I think what you suggest is a valuable refactoring in some contexts.   
Very readable code is a real asset.  That being said, libstdc++ is  
(or should be) an industrial strength, highly optimized library  
targeted for use in a great many applications world wide.  I think in  
this context, readability is very important, but must take a back  
seat to performance (be it size of speed).  And while you are  
probably correct that an optimizer will result in identical object  
code for changes like this, such a change is adding to the complexity  
of the overall product (library + compiler).  More parts must work  
right in order to deliver the end-product: a small/fast algorithm.

I have been known to make decisions regarding readability in favor of  
better readability sometimes.  But in this case I feel that the  
benefits do not outweigh the risks.

Just my .02 of course.  I am not in a position to accept or reject  
your change.

-Howard