August 2018 - ghc-devs

GHC's module hierarchy
by Simon Peyton Jones 02 Oct '19

02 Oct '19

Dear ghc-devs hsyl20 proposes a radical overhaul of the module structure of GHC itself. He or she suggested it six months ago in https://ghc.haskell.org/trac/ghc/ticket/13009 and has now offered a monster patch https://phabricator.haskell.org/D3647 It's clearly the result of a lot of work, but I was the only one who responded on the original ticket, and it'll affect all of your lives in a very immediate way. So, would you like to * consider the idea * look at the actual re-mapping of modules hsyl20 proposals * express an opinion about whether to go ahead Probably the ticket, rather than Phab, is the best place to comment on the general idea. I'd like to thank hsyl20. GHC's rather flat module structure has grown incrementally over years. But still, there are pros and cons. Simon

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Any ways to test a GHC build against large set of packages (including test suites)?
by Ömer Sinan Ağacan 25 Jul '19

25 Jul '19

Hi, I'd like to test some GHC builds + some compile and runtime flag combinations against a large set of packages by building them and running test suites. For this I need - A set of packages that are known to work with latest GHC - A way to build them and run their test suites (if I could specify compile and runtime flags that'd be even better) I think stackage can serve as (1) but I don't know how to do (2). Can anyone point me to the right direction? I vaguely remember some nix-based solution for this that was being discussed on the IRC channel, but can't recall any details. Thanks, Ömer

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Default options for -threaded
by lonetiger＠gmail.com 04 Jan '19

04 Jan '19

Hi All, A user on https://ghc.haskell.org/trac/ghc/ticket/11054 has asked why -N -qa isn’t the default for -threaded. I’m afraid I don’t know a good reason why it’s not. Can anyone help shed some light on this? If there is no good reason, Would anyone object to making it the default? Thanks, Tamar

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perf.haskell.org functional again
by Joachim Breitner 30 Nov '18

30 Nov '18

Hi, after a system upgrade to avoid weird linker errors, and after some fixes in the nofib submodule, http://perf.haskell.org/ghc is running again. I am collecting instruction counts instead of runtime, because the latter was just too often varying too wildly. I hope this will yield less false alarms. I am also running nofib with mode=fast. This way, building GHC, running the testsuite and nofib takes a bit over one hour. I hope this can keep up with y'all's commits (when it took 2h it couldn't). Now nothing of the setup requires a quiet dedicated machine, so if there is a need, we could move these builds into the cloud or into some CI infrastructure - but no changes are immediately planned. Enjoy, Joachim

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Goals for GHC 8.8
by Ben Gamari 16 Oct '18

16 Oct '18

Hi everyone, Since GHC 8.6 is almost released it's time to start thinking about our goals for 8.8, which will branch in November. I have added the items that I know are in-flight to the 8.8 status page[1]. If you have a project that you would like to see present in 8.8 then please do add it as well. If you are uncertain of whether you can have a patch up for review by late October then please do speak to me and we can discuss options. Cheers, - Ben [1] https://ghc.haskell.org/trac/ghc/wiki/Status/GHC-8.8.1

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[ANNOUNCE] GHC 8.6.1-beta1 available
by Ben Gamari 11 Sep '18

11 Sep '18

Hello everyone, The GHC development team is very pleased to announce the first beta leading up to GHC 8.6.1 release. The usual release artifacts are available from https://downloads.haskell.org/~ghc/8.6.1-beta1 This beta fixes most of the bugs reported in the first two alphas and brings all of the core libraries up to their final release versions. The 8.6 release fixes over 300 bugs from the 8.4 series and introduces a number of exciting features. These most notably include: * Significantly better handling of macOS linker command size limits, avoiding linker errors while linking large projects * A new deriving mechanism, `deriving via`, providing a convenient way for users to extend Haskell's typeclass deriving mechanism * Quantified constraints, allowing forall quantification in contexts * An early version of the GHCi `:doc` command * The `ghc-heap-view` package, allowing introspection into the structure of GHC's heap * Valid hole fit hints, helping the user to find terms to fill typed holes in their programs * The BlockArguments extension, allowing the `$` operator to be omitted in some unambiguous contexts * The next phase of the MonadFail proposal, enabling -XMonadFailDesugaring by default A full list of the changes in this release can be found in the release notes: https://downloads.haskell.org/~ghc/8.6.1-beta1/docs/html/users_guide/8.6.1-… This will very likely be the last release before the final 8.6.1 so do give it a thorough testing and, as always, report any issues you encounter. Thanks for your help! Cheers, - Ben

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RE: Hadrian
by Andrey Mokhov 04 Sep '18

04 Sep '18

Simon, If you want to see all command lines, you can pass '--verbose' or '-V' flag to Hadrian and it will then print out everything it does. But you can also choose which particular command lines to print in UserSettings, see: https://github.com/snowleopard/hadrian/blob/master/doc/user-settings.md#ver… So, you can do: verboseCommand = input "//GHC/Real.hs" Or, alternatively, verboseCommand = output "//GHC/Real.hi" Both should produce the same result (in theory). In general, we have the following documents on Hadrian: The README: https://github.com/snowleopard/hadrian/blob/master/README.md How to use UserSettings: https://github.com/snowleopard/hadrian/blob/master/doc/user-settings.md An overview of build flavours: https://github.com/snowleopard/hadrian/blob/master/doc/flavours.md I hope the more Hadrian gets used, the more complete the documentation will become. Cheers, Andrey From: Simon Peyton Jones [mailto:simonpj@microsoft.com] Sent: 30 August 2018 12:19 To: Simon Peyton Jones <simonpj(a)microsoft.com>; Alp Mestanogullari <alp(a)well-typed.com>; Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> Cc: ghc-devs <ghc-devs(a)haskell.org> Subject: RE: Hadrian Sigh. As an inconvenient workaround, I tried adding {-# OPTIONS_GHC -dverbose-core2core #-} to GHC.Real, and then doing cabal new-run hadrian -- -c -j4 --flavour=quick --directory=".." in hadrian/ That did recompile GHC.Real - but all the debug output disappeared! I tried adding {-# OPTIONS_GHC -ddebug-output #-} as well, but that didn't work. I'm stuck - any ideas? Simon From: ghc-devs <ghc-devs-bounces(a)haskell.org> On Behalf Of Simon Peyton Jones via ghc-devs Sent: 30 August 2018 12:12 To: Alp Mestanogullari <alp(a)well-typed.com>; Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> Cc: ghc-devs <ghc-devs(a)haskell.org> Subject: Hadrian Alp, Andrey The old build system printed out every command line; and I often copy-paste that info to build single modules. Eg currently, when trying to understand #15570 I see a suspicious GHC.Real.hi. So I want to manually recompile GHC.Real (from base), adding some debug flags. How can I get the right command line to do that from the build log? Where is the "how to use Hadrian" wiki page? I know you've been writing one. Simon

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Compile times: Average vs worst case runtime
by Andreas Klebinger 01 Sep '18

01 Sep '18

Hello Devs, I developed a patch improving on GHC's code layout during GSoC: https://ghc.haskell.org/trac/ghc/ticket/15124 The gains are pretty nice with most library benchmarks showing improvments in the 1-2% range or more. Even compile times went down comparing head vs stage2 built with, and using my patch! Making compilation of nofib overall faster by 0.5-1% depending on the exact setup. Now the bad news: In some cases the algorithm has bad big O performance, in practice this seems to be code with things like cases with 200+ alternatives. Where these cases also represent most of the code compiled. The worst case I saw was doubled compile time in a Module which only consisted of a 500 deep if/else chain only selecting an value. While there are some small optimizations possible to improve on this I don't expect to make these edge cases much faster overall. However it will also be possible to fall back to the old behavior to avoid the large compile times for modules known to trigger this edge case. Which brings me to my main question: When should we use the new code layout. 1. Always since on average both compile and runtime is faster. 2. -O1/O2 since users often use this when performance matters. 3. -O2 since users expect compilation times to blow up with it? 4. Never as users experience compile time slowdowns when they hit these edge cases. I'm would prefer 2. 3. 1. 4. in that order but I wonder what the wider community is thinking. Cheers Andreas

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RE: Hadrian
by Andrey Mokhov 30 Aug '18

30 Aug '18

> How do I "pass --verbose to Hadrian"? Like this: cabal new-run hadrian -- -c -j4 --flavour=quick --directory=".." -V Everything after "--" in this command line are flags passed to Hadrian. Everything before are flags passed to Cabal. (I hope we'll fix the "build.sh" script for you soon, so you don't need to go via Cabal.) I just tried this with {-# OPTIONS_GHC -dverbose-core2core #-} and this did also print out a lot of Core. And a lot more stuff (somehow this seems to cause further recompilation). > https://ghc.haskell.org/trac/ghc/wiki/Building/Hadrian/QuickStart Artem -- thanks! I forgot to mention this wiki page, which indeed looks Cheers, Andrey -----Original Message----- From: Simon Peyton Jones [mailto:simonpj@microsoft.com] Sent: 30 August 2018 13:00 To: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk>; Alp Mestanogullari <alp(a)well-typed.com> Cc: ghc-devs <ghc-devs(a)haskell.org> Subject: RE: Hadrian | If you want to see all command lines, you can pass '--verbose' or '-V' | flag to Hadrian and it will then print out everything it does. But I am not invoking Hadrian. I am saying (on your instructions) cabal new-run hadrian -- -c -j4 --flavour=quick --directory=".." How do I "pass --verbose to Hadrian"? | -----Original Message----- | From: Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> | Sent: 30 August 2018 12:26 | To: Simon Peyton Jones <simonpj(a)microsoft.com>; Alp Mestanogullari | <alp(a)well-typed.com> | Cc: ghc-devs <ghc-devs(a)haskell.org> | Subject: RE: Hadrian | | Simon, | | If you want to see all command lines, you can pass '--verbose' or '-V' | flag to Hadrian and it will then print out everything it does. | | But you can also choose which particular command lines to print in | UserSettings, see: | | https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c | om%2Fsnowleopard%2Fhadrian%2Fblob%2Fmaster%2Fdoc%2Fuser- | settings.md%23verbose-command- | lines&data=02%7C01%7Csimonpj%40microsoft.com%7C0c6118a504f74269efd508 | d60e6b4fe7%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C63671225140342623 | 1&sdata=tMYhmIGMeVbBYjAtxWQTY5%2F4Kyfc4m981N4OTowGkbQ%3D&reserved | =0 | | So, you can do: | | verboseCommand = input "//GHC/Real.hs" | | Or, alternatively, | | verboseCommand = output "//GHC/Real.hi" | | Both should produce the same result (in theory). | | In general, we have the following documents on Hadrian: | | The README: | https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c | om%2Fsnowleopard%2Fhadrian%2Fblob%2Fmaster%2FREADME.md&data=02%7C01%7 | Csimonpj%40microsoft.com%7C0c6118a504f74269efd508d60e6b4fe7%7C72f988bf86f | 141af91ab2d7cd011db47%7C1%7C0%7C636712251403426231&sdata=7WigmQG7lbDd | eyhYCSaKOQEb0eeZcn0iXAbAKdwZ5A4%3D&reserved=0 | How to use UserSettings: | https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c | om%2Fsnowleopard%2Fhadrian%2Fblob%2Fmaster%2Fdoc%2Fuser- | settings.md&data=02%7C01%7Csimonpj%40microsoft.com%7C0c6118a504f74269 | efd508d60e6b4fe7%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C63671225140 | 3426231&sdata=tRu2lO%2F6TNV3ao5tzNKO%2FAHJMWsxKX%2BqExHn78nuCvU%3D&am | p;reserved=0 | An overview of build flavours: | https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.c | om%2Fsnowleopard%2Fhadrian%2Fblob%2Fmaster%2Fdoc%2Fflavours.md&data=0 | 2%7C01%7Csimonpj%40microsoft.com%7C0c6118a504f74269efd508d60e6b4fe7%7C72f | 988bf86f141af91ab2d7cd011db47%7C1%7C0%7C636712251403426231&sdata=Esye | DdAKLV9DC3PUwkqsuQ4zGoOYKcaJeEov1BAH8lU%3D&reserved=0 | | I hope the more Hadrian gets used, the more complete the documentation | will become. | | Cheers, | Andrey | | From: Simon Peyton Jones [mailto:simonpj@microsoft.com] | Sent: 30 August 2018 12:19 | To: Simon Peyton Jones <simonpj(a)microsoft.com>; Alp Mestanogullari | <alp(a)well-typed.com>; Andrey Mokhov <andrey.mokhov(a)newcastle.ac.uk> | Cc: ghc-devs <ghc-devs(a)haskell.org> | Subject: RE: Hadrian | | Sigh. As an inconvenient workaround, I tried adding {-# OPTIONS_GHC - | dverbose-core2core #-} to GHC.Real, and then doing | cabal new-run hadrian -- -c -j4 --flavour=quick --directory=".." | in hadrian/ | That did recompile GHC.Real - but all the debug output disappeared! | I tried adding {-# OPTIONS_GHC -ddebug-output #-} as well, but that | didn't work. | I'm stuck - any ideas? | Simon | | From: ghc-devs <ghc-devs-bounces(a)haskell.org> On Behalf Of Simon Peyton | Jones via ghc-devs | Sent: 30 August 2018 12:12 | To: Alp Mestanogullari <alp(a)well-typed.com>; Andrey Mokhov | <andrey.mokhov(a)newcastle.ac.uk> | Cc: ghc-devs <ghc-devs(a)haskell.org> | Subject: Hadrian | | Alp, Andrey | The old build system printed out every command line; and I often copy- | paste that info to build single modules. | Eg currently, when trying to understand #15570 I see a suspicious | GHC.Real.hi. So I want to manually recompile GHC.Real (from base), | adding some debug flags. How can I get the right command line to do that | from the build log? | Where is the "how to use Hadrian" wiki page? I know you've been writing | one. | Simon

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Hadrian
by Simon Peyton Jones 30 Aug '18

30 Aug '18

Alp, Andrey The old build system printed out every command line; and I often copy-paste that info to build single modules. Eg currently, when trying to understand #15570 I see a suspicious GHC.Real.hi. So I want to manually recompile GHC.Real (from base), adding some debug flags. How can I get the right command line to do that from the build log? Where is the "how to use Hadrian" wiki page? I know you've been writing one. Simon

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