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

["dberlin at dberlin dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From dberlin at gcc dot gnu dot org  2005-01-25 01:42 -------
Subject: Re:  [4.0 Regression] IV-OPTS is O(N^3)

>>
>>          * tree-data-ref.c (analyze_overlapping_iterations): chrecs that
>>          are equal overlap on every iteration.
>>
>> This stuff is just simple symbolic differencing, and checking of
>> invariantness of symbols,
>> But it is indeed starting to se the symbolic scev info
>
> Ugh... OK, if you think it is a right way...  Anyway, I am seriously
> considering resurrecting the simple iv analysis for purposes of passes
> that are not interested in this fancy stuff.  Overhead of scev is
> probably acceptable if it is only used for this type of analysis,
> but for other purposes it is clearly overkill.

Uh, almost all high level loop optimizations are going to do very badly in 
the depth of the loop nest.

The fact that scev doesn't do so well on a 100 deep loop nest doesn't 
really concern me at all.



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