Tool for minimizing examples
Devs: as I'm sure you know, the hardest part of reporting a GHC bug is finding a minimal example that triggers the bug. When I initially trigger a bug in my large code base, my workflow is something like: 1. write a driver that triggers the bug 2. do manual dead code elimination by removing unused files and functions 3. "human required" step to figure out what can be trimmed to further minimize 4. go to step 2 until example is simple enouogh Since I work on a large library (>60 modules) and also report a fair number of bugs, I spend a nontrivial amount of time on step 2, which is completely mechanical. It would be nice to have a tool that can help out. Specifically, something that takes a "driver" file, and produces a copy of the code contents to a new directory sans unimported files, and unused functions from imported files. Ideally, this tool would make a "closed universe" assumption so that exported functions can also be eliminated as dead, if they are never used elsewhere. A bonus feature would be to remove unused imports, and even unused build-depends from the cabal file. Are there any tools out there that can do any portion of this process for me? Perhaps it is possible to output contents after the compiler does a DCE pass? Regards, Eric Crockett
I asked about this on Twitter a while back https://twitter.com/johnregehr/status/768693836616912898 and John Regehr suggested that we give C-reduce a try. I have not yet but if you try it out I'm quite curious to see what happens. Edward Excerpts from Eric Crockett's message of 2016-10-26 00:27:11 -0400:
Devs: as I'm sure you know, the hardest part of reporting a GHC bug is finding a minimal example that triggers the bug. When I initially trigger a bug in my large code base, my workflow is something like:
1. write a driver that triggers the bug 2. do manual dead code elimination by removing unused files and functions 3. "human required" step to figure out what can be trimmed to further minimize 4. go to step 2 until example is simple enouogh
Since I work on a large library (>60 modules) and also report a fair number of bugs, I spend a nontrivial amount of time on step 2, which is completely mechanical. It would be nice to have a tool that can help out. Specifically, something that takes a "driver" file, and produces a copy of the code contents to a new directory sans unimported files, and unused functions from imported files.
Ideally, this tool would make a "closed universe" assumption so that exported functions can also be eliminated as dead, if they are never used elsewhere. A bonus feature would be to remove unused imports, and even unused build-depends from the cabal file.
Are there any tools out there that can do any portion of this process for me? Perhaps it is possible to output contents after the compiler does a DCE pass?
Regards, Eric Crockett
Great question.
And just to add: I _really_ appreciate the fact that you make small examples. Thank you.
Simon
From: ghc-devs [mailto:ghc-devs-bounces@haskell.org] On Behalf Of Eric Crockett
Sent: 26 October 2016 05:27
To: ghc-devs
Eric Crockett
Are there any tools out there that can do any portion of this process for me?
This is a good question. Unfortunately I don't know of any; I do my minimizations by hand.
Perhaps it is possible to output contents after the compiler does a DCE pass?
Unfortunately I don't believe this would be helpful as DCE isn't done on the Haskell syntax tree representation and we have no external representation of Core. That being said, you might be able to write something without too much difficulty using the GHC API. I have a small toy project that I once used to explore the API; you might find that it's a useful place to start [1]. Sorry for the not-so-helpful response! Cheers, - Ben [1] https://github.com/bgamari/play-type-search
participants (4)
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Ben Gamari -
Edward Z. Yang -
Eric Crockett -
Simon Peyton Jones