Re: GHC 8.10 backports?

Yes, only changing the rule did indeed cause regressions. Whichwhen not including the string changes. I don't think it's worth having one without the other. But it seems you already backported this? See https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5263 Cheers Andreas Am 22/03/2021 um 07:02 schrieb Moritz Angermann:

The commit message from https://gitlab.haskell.org/ghc/ghc/-/commit/f10d11fa49fa9a7a506c4fdbdf86521c... https://gitlab.haskell.org/ghc/ghc/-/commit/f10d11fa49fa9a7a506c4fdbdf86521c...,

makes the changes to string seem required. Applying the commit on its own doesn't apply cleanly and pulls in quite a bit of extra dependent commits. Just applying the elem rules appears rather risky. Thus will I agree that having that would be a nice fix to have, the amount of necessary code changes makes me rather uncomfortable for a minor release :-/

On Mon, Mar 22, 2021 at 1:58 PM Gergő Érdi mailto:gergo@erdi.hu> wrote:

Thanks, that makes it less appealing. In the original thread, I got no further replies after my email announcing my "discovery" of that commit, so I thought that was the whole story.

On Mon, Mar 22, 2021, 13:53 Viktor Dukhovni mailto:ietf-dane@dukhovni.org> wrote:

On Mon, Mar 22, 2021 at 12:39:28PM +0800, Gergő Érdi wrote:

> I'd love to have this in a GHC 8.10 release: > https://mail.haskell.org/pipermail/ghc-devs/2021-March/019629.html https://mail.haskell.org/pipermail/ghc-devs/2021-March/019629.html

This is already in 9.0, 9.2 and master, but it is a rather non-trivial change, given all the new work that went into the String case.  So I am not sure it is small/simple enough to make for a compelling backport.

There's a lot of recent activity in this space.  See also <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5259 https://gitlab.haskell.org/ghc/ghc/-/merge_requests/5259>, which is not yet merged into master, and might still be eta-reduced one more step).

I don't know whether such optimisation tweaks (not a bugfix) are in scope for backporting, we certainly need to be confident they'll not cause any new problems.  FWIW, 5259 is dramatically simpler...

Of course we also have <https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4890 https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4890> in much the same territory, but there we're still blocked on someone figuring out what's going on with the 20% compile-time hit with T13056, and whether that's acceptable or not...

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