[Bug middle-end/38729] long time needed in tree canonical iv

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

------- Comment #3 from rguenth at gcc dot gnu dot org  2009-06-20 16:43 -------
My guess is that this is the number-of-iteration code which tries to use
predicate information (that is obviously available a lot with -fbounds-check).
At -O1 we do not do value-range propagation, so practically all of the
-fbounds-check tests remain.

Which leads to my recommendation to _not_ enable -fbounds-check without also
enabling value-range propagation.

What we could do is limit the walking of the predicates a lot more at -O1.

Another candidate is find_loop_niter_by_eval as loops with bound checks have
a lot of exits.  We could limit that to flag_expensive_optimizations.

Or we can simply enable VRP at -O1, possibly without tracking symbolic
ranges and equivalences (which is the most expensive parts here).


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2009-06-20 16:43:34
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38729