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.
#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
* 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:
+ 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.
* 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.andr...@gmx.at
<mailto:klebinger.andr...@gmx.at>or look for AndreasK in #ghc
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