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[Bug c++/13776] [tree-ssa] Many C++ compile-time regression in 3.5-tree-ssa 040120
- From: "dberlin at dberlin dot org" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 13 Mar 2004 15:57:49 -0000
- Subject: [Bug c++/13776] [tree-ssa] Many C++ compile-time regression in 3.5-tree-ssa 040120
- References: <20040120183908.13776.kgardas@objectsecurity.com>
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
------- Additional Comments From dberlin at dberlin dot org 2004-03-13 15:57 -------
Subject: Re: [tree-ssa] Many C++ compile-time regression in 3.5-tree-ssa 040120
On Mar 13, 2004, at 6:46 AM, rguenth at tat dot physik dot
uni-tuebingen dot de wrote:
>>>
>>
>> Could we add thresholds to back away from overly complicated
>> functions?
>
> Or just "split" them up using sort of windowing? It looks clearly
> wrong
> to not limit a O(n^2) or O(n^3) algorithm.
>
It's only collecting expressions that is O(n^2). The other parts of the
algorithm just has a large constant.
Also, it *is* splitting up the function. It performs PRE one expression
at a time.
We can't perform it one basic block at a time or anything with the
current algorithm (and it wouldn't make sense to, because you can't
find the optimal insertion points).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=13776