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

[dberlin at dberlin dot org]

------- Additional Comments From dberlin at dberlin dot org  2004-12-07 22:56 -------
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.



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