Re: Non-dominating loop bounds in tree-ssa-loop-niter 3/4

[Jan Hubicka <hubicka@ucw.cz>]

> On Wed, Oct 31, 2012 at 01:30:02PM +0100, Richard Biener wrote:
> > On Wed, 31 Oct 2012, Jan Hubicka wrote:
> > > > unroll you mean.  Because unrolling mutates the CFG too much.
> > > > Well - it was just a starting point, populating -Og with as little
> > > > as possible and 100% profitable transforms (in both debug and speed
> > > > metric).  In late opts we only do (early opt queue is shared):
> > > 
> > > Well, and what about early cunrolli?
> > 
> > It's not there (and I would disable it for -Og).
> 
> Generally, most of the loop transforms are undesirable for -Og.

Hmm, do we have some guidelines what is and is not desirable for -Og?
Unrolling/header copying being code duplicating optimization do not really
throw away any info by themself only require debugger to understand that some
code may get duplicated, but it is not different from i.e. inlining. Of course
the subsequent const prop will make it impossible to write into the iv
variable, but do we want to support reliable writting into user vars (i.e.
disable cprop on user vars) at -Og?

Honza
> 
> 	Jakub