[Bug tree-optimization/18792] ICE with -O1 -ftree-loop-linear on small test case

["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  2004-12-07 23:04 -------
Subject: Re:  ICE with -O1 -ftree-loop-linear on small test case

> >> There are basically two ways how to fix this:  either make the code
> >> that changes the order of loops in the nests to also renumber the loops
> >> (which would in turn invalidate all scev caches, that would need to be
> >> flushed).  Or fix the code that assumes the ordering of the loops.
> >
> > Sorry for a bit missleading formulation -- the later solution does not
> > avoid need for flushing the scev caches when the "linear" pass changes
> > order of loops; the data are invalidated anyway.
> >
> You've missed the actual bug here.
> The bug doesn't occur *after* linear loops, it occurs *before* it.
> When computing data dependence, we expect that all loop indexes in a given 
> loop nest are sequential.
> In this case, they are not.
> The question is whether this is correct or not.

Ahh... then this is something different than what I thought.
Assuming that the numbers of loops inside the nests are sequential
is wrong (at least we do not try to preserve this property anywhere, and
it does not seem to be something terribly useful to me).


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18792