[Bug other/46847] Missed optimization for variant of Duff's device

["jjk at acm dot org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46847

--- Comment #3 from Jens Kilian <jjk at acm dot org> 2010-12-08 12:10:02 UTC ---
(In reply to comment #2)
> GCC 4.5 doesn't move end computation inside the loop.  What do you expect
> to be "good" code?  I get at -O[23]:

[snip]

The code generated by 4.5 is what I would have expected.
Feel free to close this as "fixed in the latest version".

> Duffs device may be a fun thing from a C language perspective, but it
> is a bad thing in general because you defy most
> loop optimizations as it is a loop with multiple entries (which means
> the loop isn't recognized as a loop by GCC).

I usually wouldn't consider using it, I just noticed the problem while
trying to tune some heavily used parts of our code.

Thanks,
        Jens.