[Bug tree-optimization/18595] [4.0 Regression] IV-OPTS is O(N^3)

["rakdver at atrey dot karlin dot mff dot cuni dot cz" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From rakdver at atrey dot karlin dot mff dot cuni dot cz  2005-01-25 11:16 -------
Subject: Re:  [4.0 Regression] IV-OPTS is O(N^3)

> > How?  If the reference is left in symbolic form, it means that you know
> > nothing about its value, so the only thing you can do with it is to
> > check its equality/inequality, in code like
> > 
> > while (...)
> >   {
> >     i = something_weird ();
> > 
> >     a[i] = ...;  (a)
> >     a[i+1] = ...;  (b)
> >     a[i] = ...;  (c)
> >   }
> > 
> 
> The following is probably a more frequent case:
> 
> i = 0
> x = something_weird () or a function parameter
> loop
>   i = i + 1 
>   a[i] = ...
>   ... = a[i + x]
> endloop
> 
> where you end with a symbolic distance vector.

But here x is a loop invariant.  Nothing would change here if we were
keeping the evolutions fully instantiated.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18595