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[Bug tree-optimization/18595] [4.0 Regression] IV-OPTS is O(N^3)
- From: "sebastian dot pop at cri dot ensmp dot fr" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 25 Jan 2005 16:27:04 -0000
- Subject: [Bug tree-optimization/18595] [4.0 Regression] IV-OPTS is O(N^3)
- References: <20041121145949.18595.pinskia@gcc.gnu.org>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From sebastian dot pop at cri dot ensmp dot fr 2005-01-25 16:26 -------
Subject: Re: [4.0 Regression] IV-OPTS is O(N^3)
> > If you decide to reconstruct the tree expression, there is no reason
> > to stop on a phi node that has a single argument. Why would you like
> > to get this answer as the reconstructed tree?
>
> because this answer preserves loop closed ssa form -- the answer x_1 + 1
> copy propagates the value outsied of the loop. In some applications
> this choice could make sense.
>
Okay, if it makes sense, you could modify the analyzer such that it
stops reconstructing the tree once it is on the phi following a loop.
This won't change the information provided after the instantiation.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18595