RE: Loop Optimizer Deficiency revisited

["Nitin Gupta" <ngupta at GlobespanVirata dot com>]

> >>>>>> Zack Weinberg writes:
> >
> > 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.

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