Re: [PATCH] Make alias_sets_conflict_p less conservative

[Michael Matz <matz at suse dot de>]

Hi,

On Wed, 5 Mar 2008, Richard Kenner wrote:

> > alias_sets_conflict_p() is used to determine if an addressable variable 
> > and a type conflict also from the tree-ssa alias machinery (in effect to 
> > determine which virtual variables need to be clobbered).  It just isn't 
> > feed COMPONENT_REFs, that's what you found very wrong, and I explained the 
> > reasons for not doing so.  If we were to do that (and hence become more 
> > precise) we would have to increase memory use as just explained.  You were 
> > asking how feeding COMPONENT_REFs would be connected with memory use, and 
> > I explained it.
> 
> Why can't you keep the vops as they are now, but when you call
> alias_sets_conflict_p, pass the actual reference from the op, not the vop?

Because as explained already, making use of whatever alias_sets_conflict_p 
would tell us when given COMPONENT_REFs would require blowing up our 
explicit dependency representation.  It's not the case that we inherently 
can't call alias_sets_conflict_p() with the COMPONENT_REF if we have one.  
We could.  But we have no way to express the resulting dependencies 
without needing much more memory.


Ciao,
Michael.