Looking for GSoC Mentor

Andreas Klebinger klebinger.andreas at gmx.at
Wed Feb 14 19:51:18 UTC 2018

Hello Everyone,
I'm looking for a mentor for a GSoC Project/Proposal.

The whole idea revolves around:
* Getting hot path information from static analysis and user annotations.
* Making sure it's not destroyed by optimization passes.
* Using it to generate better code where applicable.

See also:
#14672: Make likelihood of branches/conditions available throughout the 

Towards these goals I would like for GSoC:
* Land https://phabricator.haskell.org/D4327(Branchweights in STG and Cmm)
   + It might be ready before then. But it's a prerequisite so worth 
listing here.
* Design and implement a way for users to:
   + Mark hot paths in Haskell code.
   + Push the information through the passes (up to STG) on a best 
effort basis. STG and beyond is part of the diff above.
   + The current backend already uses this information in some places, 
so this alone should lead to small but consistent gains.
   + I don't plan to add additional optimizations unless there is time 
left at the end.

Where I think I will need help/experience from a mentor is:
* Frontend questions:
   I haven't looked at GHC's parser/renamer yet so while
   this is surmountable I expect some questions to arise there.

* Design questions/feedback:
   Things like:
   + How should the user be able to give this information.
   + What should be flag controlled? What always on?
   + Things like compile time/executable speed tradeoffs.

* Potentially the simplifier:
   I've looked into it briefly as originally D4327 was aimed at the
   core stage instead of stg.
   There doesn't seem to be a lot that could
   mess with hot path information/branchweights. But I haven't worked on
   the simplifier before and it seems like a good place for unexpected
   issues to arise.

* If this involves the proposal process then also guidance there.

For myself:
* I'm studying at TU Vienna (Software & Information Engineering)
   and am close to finishing my undergrad. Located in Austria (UTC+1)
* I have contributed a few small changes to GHC throughout last year.
   See AndreasK on Phab/Trac.
* If you want to know more contact me!

If you are interested in mentoring me or looking for more details feel free
to contact me at klebinger.andreas at gmx.at 
<mailto:klebinger.andreas at gmx.at>or look for AndreasK in #ghc

Best Regards
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