Performance regression on typechecking type families?

[Richard Eisenberg]

I'm certainly unaware of any reason this should be expected. I would report as a bug, and, personally, would label it "High" priority. I think there is plenty of room for GHC to be more efficient around type families.

Thanks for putting together a test!

Richard

On Nov 29, 2014, at 5:17 AM, "Dr. ERDI Gergo" <gergo at erdi.hu> wrote:

> Hi,
> 
> Prompted by this question: http://stackoverflow.com/questions/26538595/more-efficient-type-level-computations-using-type-families
> I wrote some code today using closed type families and datakinds. Also, as a baseline, I typechecked the code using open type families from the original question.
> 
> The two files are here:
> 
> https://gist.github.com/gergoerdi/727f028e4c1ed158ac9a
> https://gist.github.com/gergoerdi/f96d1a9a58f5e3dccc18
> 
> On GHC 7.8.3, typechecking took about 45 seconds for each. However, on a 'perf' build of GHC 7.9 d8c437b3, with ghc-stage2, the first one took 1m3s and the second one 1m12s. A 40% and 60% increase in typechecking time, respectively!
> 
> Is this some known regression, something surprising, or is 'perf' simply not the right build flavour for this kind of comparison?
> 
> Bye,
> 	Gergo
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