Cgraph alias reorg 8/14 (ipa-cp and ipa-prop update)

[Jan Hubicka]

> Hi,
> 
> On Fri, Jun 10, 2011 at 04:55:43PM +0200, Jan Hubicka wrote:
> > Hi,
> 
> > this patch updated ipa-cp and ipa-prop for aliases.  It is basically
> > easy - we don't analyze nodes represneting aliases and when
> > propagating we skip them, like everywhere else.
> > 
> > There are two problems I noticed.  First we should not propagate
> > through calls that are overwritable.  When non-overwritable function
> > A has overwritable alias B, we should propagate through calls to A,
> > but not throug calls to B.  As discussed on IRC it is probably best
> > to zap the jump functions in question at IPA stage (because at
> > analysis stage it is not clear at all if the alias will end up
> > overwritable with LTO).
> > 
> 
> OK.  Nevertheless, I'd prefer to do this in context of the new
> IPA-CP.  

Yep, lets see how much work will be to get new ipa-cp in.  I will try
to look into it more this week.
> 
> > Similar problem already exists with code in
> > ipa_compute_jump_functions that looks into a callee that might
> > change with LTO.
> 
> I either don't understand or fail to see how this is different from
> the first problem.  We even compute jump functions of indirect edges
> precisely because we hope they will be changed later on...

Well, it is sort of similar. What is new that same function can be now
called in overwritable and non-overwritable way.  The old problem is that
what used to be overwritable at analysis time is not neccesarily so at WPA
time.
> 
> 
> > Index: ipa-cp.c
> > ===================================================================
> > --- ipa-cp.c	(revision 174905)
> > +++ ipa-cp.c	(working copy)
> > @@ -818,7 +828,7 @@ ipcp_iterate_stage (void)
> >      /* Some lattices have changed from IPA_TOP to IPA_BOTTOM.
> >         This change should be propagated.  */
> >      {
> > -      gcc_assert (n_cloning_candidates);
> > +      /*gcc_assert (n_cloning_candidates);*/
> >        ipcp_propagate_stage ();
> >      }
> >    if (dump_file)
> 
> 
> I know this assert can be horribly irritating but so far it has been
> very useful at spotting all kinds of errors at various places.  (In
> fact, you added it :-)
> 
> But as I want to get the whole IPA-CP replaced, I don't care all that
> much.

I am pretty sure I didn't meant to remove it and had the whole thing tested with the assert.
The issue was that once aliases are skipped by propagate stage, the lattices stay top.
But I already fixed it elsewhere, so I will regtest reverting that hunk.  Thanks for
pointing this out!

Honza
> 
> Martin