Re: Loop Optimizer Deficiency revisited

[Zdenek Dvorak <rakdver at atrey dot karlin dot mff dot cuni dot cz>]

Hello,

> > > Zack> However, it is likely to be addressed by completing the
> > store-motion
> > > Zack> pass, which has never worked properly.  If you would like
> > to help with
> > > Zack> that, talk to Daniel Berlin (cc:ed).
> > >
> > > 	I believe that Zdenek has a revised store-motion patch which has
> > > been waiting for approval.
> >
> > I don't consider myself competent to review that patch, but perhaps
> > Mr. Gupta could try it on his test case.
> 
> Thanks for the pointers.
> 
> I think you are talking about "[rtlopt] GCSE global variables removal"
> http://gcc.gnu.org/ml/gcc-patches/2002-09/msg01355.html
> submitted by Zdenek. I'll try this with my test case, and communicate
> if there are any improvements.

Nope, that is something different. The right patch is
http://gcc.gnu.org/ml/gcc-patches/2003-03/msg00467.html.

Zdenek

> To improve my understanding I rephrase the problem and my understanding.
> Please correct me, if I'm wrong.
> 
> GCC 3.2 would duplicate the entire loop test in .jump and would
> not merge is anywhere latter. Since the loop size is small, increase
> in size is significant, it duplicates more expressions hence *increases*
> size furthered when compiled with **-Os** [cse2 performs badly with -Os].
> However GCC 2.96 would do the same in .jump but would merge the loop test in
>  .jump2 (irrespective of -Os is given or not). From the archives I could
> make
> out the jump2 was removed by jump over CFG. But it does not seems to cater
> this problem.  The probable solution is that GCC 3.2 should take care of
> this
> while during GCSE phase while doing code hoisting ( when invoked with -Os).
> 
> Would an improved store motion take care of these cse2 and unification
> issues?
> 
> 
> Regards,
> Nitin
>