Text and changing number primops in GHC 9.2
David Feuer
david.feuer at gmail.com
Wed Feb 17 17:38:21 UTC 2021
I still don't understand why GHC is making this change in such a breaky way
without even going through the proposal process.
On Wed, Feb 17, 2021, 12:35 PM John Ericson <john.ericson at obsidian.systems>
wrote:
> Hi all,
>
> First, background. I have a PR
> https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4492 that is one of
> the moving pieces for https://gitlab.haskell.org/ghc/ghc/-/issues/19026,
> which is slated for 9.2 according to Ben's email
> https://mail.haskell.org/pipermail/ghc-devs/2021-February/019478.html. (I
> just added the milestone to the issue to reflect this.)
>
> Despite this being a breaking change (to unstable interfaces) containers,
> bytestring, and binary could all updated in a way that didn't used CPP.
> (See the linked PRs in the GHC !4492's description). Text is a different
> case, because the unboxed computation there is more pervasive. The current
> PR is https://github.com/haskell/text/pull/305, and uses CPP for 9.2. We
> have a few different options:
>
> - Keep as is. There will surely be no perf regressions this way on any
> of the supported compilers. This does however mean adding CPP for 9.2
> before the associated GHC change lands in master. I think that's
> fine---inevitable even based on the current policy for how GHC submodules
> are bumped---but it's given many library maintainers the heebie jeebies.
> - Try the same tricks in the other PRs of using hyper-local unboxing
> that is easy to unbox away. This will be a bit ugly however than the other
> cases, and I am not sure whether it won't be a regression for the oldest
> supported GHCs.
> - Do the above, but bump the base version to the point where there are
> no perf regressions with the oldest supported GHCs (because those compilers
> are no longer supported). If we bump the version more aggressively, perhaps
> we can get rid of much of the unboxing altogether / otherwise get rid of
> the ugliness.
>
> We'll need to reach some sort of decision here to move forward.
>
> I'll also add that while Oleg Grenrus has helped merge a preparatory PR,
> Oleg expressed a *dis*interest in being de facto text maintainer, so I am
> emailing the list in part so this does not fall upon Oleg alone any longer.
>
> John
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