June 2018 - ghc-devs - Haskell.org

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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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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accuracy of asinh and atanh
by Matt Peddie 03 Aug '18

03 Aug '18

Hi devs, I tried to use asinh :: Double -> Double and discovered that it's inaccurate compared to my system library (GNU libm), even returning -Infinity in place of finite values in the neighborhood of -22 for large negative arguments. `atanh` is also inaccurate compared to the system library. I wrote up a more detailed description of the problem including plots in the README file at https://github.com/peddie/ghc-inverse-hyperbolic -- this repository is package that can help you examine the error for yourself or generate the plots, and it also contains accurate pure-Haskell translations of the system library's implementation for these functions. What's the next step to fixing this in GHC? Cheers Matt Peddie

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Steps to propose a new primop in GHC
by Mitsutoshi Aoe 25 Jul '18

25 Jul '18

Hi devs, I'm thinking to add a primop in GHC but not sure how I should proceed. The primop I have in mind is something like: traceEventBinary# :: Addr# -> Int# -> State# s -> State# s This function is similar to the existing traceEvent# but it takes a chunk of bytes rather than a null-terminated string. It is useful to trace custom user events (e.g. network packet arrival timestamps in an network application) in eventlogs. At library level, it is supposed to be used like the tracing functions in Debug.Trace but with ByteString argument: traceEventBinary :: ByteString -> a -> a traceEventBinaryIO :: ByteString -> IO () Note that this can't live in base because of the dependency on bytestring. So how should I proceed from here? Am I supposed to submit a GHC proposal or should I ask on the libraries list? This is not a prominently visible change in GHC. It rather affects only ghc-prim and no effects in base. Thanks, Mitsutoshi

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Is it possible to enhance the vector STG registers(Xmm, Ymm, Zmm) with more information?
by Abhiroop Sarkar 16 Jul '18

16 Jul '18

Hello all, I am currently working on adding support for SIMD operations to the native code generator. One of the roadblocks I faced recently was the definition of the `globalRegType` function in "compiler/cmm/CmmExpr.hs". The `globalRegType` function maps the STG registers to the respective `CmmType` datatype. For Xmm, Ymm, Zmm registers the function defines globalRegType like this: https://github.com/ghc/ghc/blob/master/compiler/cmm/CmmExpr.hs#L585-L587 Consider the case for an Xmm register, the above definition limits an Xmm register to hold only vectors of size 4. However we can store 2 64-bit Doubles or 16 Int8s or 8 Int16s and so on The function `globalRegType` is internally called by the function `cmmRegType` ( https://github.com/ghc/ghc/blob/838b69032566ce6ab3918d70e8d5e098d0bcee02/co…) which is itself used in a number of places in the x86 code generator. In fact depending on the result of the `cmmRegType` function is another important function `cmmTypeFormat` defined in Format.hs whose result is used to print the actual assembly instruction. I have extended all the other Format types to include VectorFormats, however this definition of the `globalRegType` seems incorrect to me. Looking at the signature of the function itself: `globalRegType :: DynFlags -> GlobalReg -> CmmType` its actually difficult to predict the CmmType by just looking at the GlobalReg in case of Xmm, Ymm, Zmm. So thats why my original question how do I go about solving this. Should I modify the GlobalReg type to contain more information like Width and Length(for Xmm, Ymm, Zmm) or do I somehow pass the length and width information to the globalRegType function? Thanks Abhiroop Sakar

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[ANNOUNCE] GHC 8.6.1-alpha1 available
by Ben Gamari 10 Jul '18

10 Jul '18

The GHC development team is pleased to announce the first alpha release leading up to GHC 8.6.1. The usual release artifacts are available from https://downloads.haskell.org/~ghc/8.6.1-alpha1 This is the first release (partially) generated using our new CI infrastructure. One known issue is that the haddock documentation is currently unavailable. This will be fixed in the next alpha release. Do let us know if you spot anything else amiss. As always, do let us know if you encounter any trouble in the course of testing. Thanks for your help! Cheers, - Ben

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Loading GHC into GHCi (and ghcid)
by Matthew Pickering 04 Jul '18

04 Jul '18

Hi all, Csongor has informed me that he has worked out how to load GHC into GHCi which can then be used with ghcid for a more interactive development experience. 1. Put this .ghci file in compiler/ https://gist.github.com/mpickering/73749e7783f40cc762fec171b879704c 2. Run "../inplace/bin/ghc-stage2 --interactive -odir tmp -hidir tmp" from inside compiler/ It may take a while and require a little bit of memory but in the end all 500 or so modules will be loaded. It can also be used with ghcid. ghcid -c "../inplace/bin/ghc-stage2 --interactive -odir tmp -hidir tmp" Hopefully someone who has more RAM than I. Can anyone suggest the suitable place on the wiki for this information? Cheers, Matt

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req_interp tests
by Ömer Sinan Ağacan 02 Jul '18

02 Jul '18

Hi, I have a few problems with req_interp tests. First, req_interp doesn't actually skip the test, it runs it but expects it to fail. This causes problems when testing stage 1 compiler because 629 req_interp tests are run for no reason. Ideally I think req_interp would skip the test, and for the error messages ("not build for interactive use" etc.) we'd have a few stage 1 tests (maybe we alrady have this). This would make the testsuite much faster for testing stage 1. Second, combination of req_interp and compile_fail currently doesn't work, because req_interp makes a failing test pass, but compile_fail expects the test to fail. See T3953 as an example. Making req_interp skip the test fixes this problem as well. So I'd like to make req_interp skip the test instead of expecting it to fail. Any objections to this? Ömer

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Booting ghc with system-wide installed Cabal?
by Ömer Sinan Ağacan 02 Jul '18

02 Jul '18

Currently we have to build Cabal from scratch after every make clean. Ideally I should be able to skip this step by installing the correct versions of Cabal and cabal-install system-wide, but as far as I can see we currently doesn't support this. Any ideas on how to make this work? Thanks, Ömer

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