[llvm-dev] GVN pass limitation.

[Philip Reames via llvm-dev]

+1 to what Danny said

On 04/19/2016 06:49 AM, Daniel Berlin via llvm-dev wrote:
> Necessary super-linear behavior in analysis is pretty rare.
> When it does occur, it should mostly be occurring on strange and 
> wonderful CFGs.
>
> IE andersen's is N^3. You are highly unlikely to find *any* real world 
> cases that trigger N^3 behavior out of the andersen's implementation 
> in GCC.
>
> Honestly, at the point where you've added more than 1-2 knobs to 
> something, it's time to reconsider whether that's the best way to do 
> it anymore.
>
>
> On Tue, Apr 19, 2016 at 6:19 AM, Joerg Sonnenberger via llvm-dev 
> <llvm-dev at lists.llvm.org <mailto:llvm-dev at lists.llvm.org>> wrote:
>
>     On Mon, Apr 18, 2016 at 04:37:58PM -0700, Philip Reames wrote:
>     > Cases like this illustrate why we should avoid arbitrary cutoffs
>     in analysis
>     > passes if at all possible.
>
>     I fully agree on that, but it doesn't help if super-linear behavior,
>     both in terms of CPU time and memory use practically happen. It
>     doesn't
>     mean that we couldn't e.g. tune the limits based on the optimisation
>     level, but currently it is kind of all or nothing.
>
>     Joerg
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