Re: [patch] Avoid ssa update in cfg cleanup

[Daniel Berlin <dberlin at dberlin dot org>]

On Sat, 2006-02-04 at 22:28 +0100, Zdenek Dvorak wrote:
> Hello,
> 
> > > The key observation is that no new vops should ever appear in this way,
> > > only the old ones may disappear.  If new vops appear, it means that we
> > > either had incorrect alias information before (very bad), or that by
> > > making the copy propagation, we are losing information (not good,
> > > either).  
> > 
> > While not good, it happens right now.  DOM, for example, will propagate
> > things that will lose alias information in some cases.
> > 
> > Sadly, i believe doing this in your patch will have some negative
> > generated code performance impact, but maybe i am wrong.
> 
> as the testing shows, none of the DOM (or other) testcases we have in
> testsuite seems to be affected by the change.  I will run SPEC's
> overnight to get some idea whether there are performance loses or not.

Thanks.

I can construct testcases for you where DOM will do propagate things
that will cause us to lose NMT information, if you want them, but i'm
only concerned whether it actually matters in practice.