Re: Any plan for rewriting loop.c using cfgloop.c

[Jan Hubicka <jh at suse dot cz>]

>     Rest of loop optimizer is going to be more dificult as many of
>     transformations are better done on higher level IL than RTL is 
> 
> I will take this opportunity to state again that I *strongly* disagree
> with that statement.  Many of the transformation can't be done until
> the RTL level because knowing what to do requires detailed knowlege
> of the available instructions.

Yes, this is understood problem.  In particular expample, of strength
reduction, to do it strength reduction effectivly, one should know what
are the costs and addressing modes not available at tree-ssa level.  To
do it correctly one should know about overflow semantics of input
language not available at RTL level.

It is however not very well understood how to best deal with it.  It is
probably best to experiment with both implmentations and
we will likely end up with loop optimizer split into multiple parts some
running at tree-ssa and some running at RTL level.  THat is why I do
believe that Zdenek's work on RTL loop optimizer is important even after
merging tree-ssa.

Honza