September 2015 - ghc-tickets

[GHC] #10723: Make declarations in signatures "weakly bound" until they are used
by GHC 17 Dec '16

17 Dec '16

#10723: Make declarations in signatures "weakly bound" until they are used -------------------------------------+------------------------------------- Reporter: ezyang | Owner: ezyang Type: feature | Status: new request | Priority: normal | Milestone: Component: Package | Version: 7.11 system | Keywords: backpack | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Suppose you are the author of a library in a Backpack world, and you publish a signature package which defines the entire public facing interface of your library. The library `foo` which uses of your library decides to `include` the signature package for convenience, but actually only uses a small portion of the API. Later, you make a BC-breaking change in one part of the library and release a new signature package. The library `bar` which uses your library includes this NEW signature package, using a different portion of the API which was unaffected by the by the BC change. Now, a hapless user tries to use `foo` and `bar`, but Backpack complains that the requirements are not compatible. What's the problem here? The practice of writing reusable signature packages for people to use caused the requirements of `foo` and `bar` to become too large, since they included a lot of junk that these libraries didn't actually use. It would be far better if you could `include` a signature package, but only "require" the bits of it that you actually used! How can we achieve this? 1. We augment the `ModIface` of signature merges (#10690) to record whether or not a declaration was (transitively) used or not by some module. Used declarations must be filled, but unused ones are treated more flexibly: if they are merged with a different, incompatible but used requirement, they disappear, and we don't check if an implementing module actually implemented the declaration. (If two unused incompatible requirements are merged, we just erase the name.) 2. How do we compute the usage info? I think it will have to be done during shaping (which runs the renamer). We only need to annotate each declaration a signature with the transitive set of names from other signatures that it has used--this can be incrementally computed. (It's not necessary to annotate declarations in modules, since they are always assumed to use holes). Then whenever a declaration from a signature is used in a module, we mark its transitive set as used. This information can then be used later when constructing the merged `ModIface` which represents the "public requirement" of the package. So, for example, a package containing only signatures would contain all unused declarations (however, they may start being used by a package which includes them). Any unused declaration which isn't mixed with another incompatible declaration can be imported (causing it to be used), but we will complain if you try to use a name and we can't tell which declaration to use. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10723> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9601: Make the rewrite rule system more powerful
by GHC 16 Dec '16

16 Dec '16

#9601: Make the rewrite rule system more powerful -------------------------------------+------------------------------------- Reporter: spacekitteh | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more | Type of failure: than a week) | None/Unknown Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- It would be amazing if the current RULES system could be upgraded to include various predicates, or even into a full-on strategic programming system. This would allow far far more optimisations to be possible, rather than the current conservative system where you have to make sure that the optimisations ALWAYS apply. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9601> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8299: Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size)
by GHC 16 Dec '16

16 Dec '16

#8299: Add richer data model address arithmetic: AddrDiff and AddrInt (ie d Int_ptr_diff and Int_ptr_size) ----------------------------------------------+---------------------------- Reporter: carter | Owner: Type: feature request | Status: new Priority: high | Milestone: 7.10.1 Component: Compiler | Version: 7.6.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Project (more than a week) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: 8287 ----------------------------------------------+---------------------------- currently GHC's internals and code gen don't provide a strong distinction between Ints as data, and Ints for pointer / address arithmetic. This also comes up as being problematical in a number of ways. 1. We wind up having many portability issues around Int and pointer / address sizes. 2. adds some inessential complexity / problems to adding new architectures to ghc. eg x32 ABI which has 32bit pointers and 64bit ints somewhat breaks current assumptions in the GHC primops (because arrays are indexed by a byte offset, and the valid range for those is determined by the ABI pointer size!) 3. this Ints and Ptrs confusion we currently have, also means we can't leverage the Integer support in SIMD registers that is in most modern CPUs! If we could have those two separated better, theres a lot of low leve optimizations we could do for Int/Word data that we currently cant do! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8299> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10301: Plugins/dynamic loading subtly broken (it seems)
by GHC 15 Dec '16

15 Dec '16

#10301: Plugins/dynamic loading subtly broken (it seems) -------------------------------------+------------------------------------- Reporter: | Owner: thoughtpolice | Status: new Type: bug | Milestone: 7.10.2 Priority: normal | Version: 7.8.2 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: Compile-time Architecture: | crash Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #8276 Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Imported from #8276, which was originally about a Haddock bug (that was different in nature but appeared similarly): > I still experience this panic on GHC 7.8.2 with Windows x86_64: > > {{{ > $ ghci > GHCi, version 7.8.2: http://www.haskell.org/ghc/ :? for help > Loading package ghc-prim ... linking ... done. > Loading package integer-gmp ... linking ... done. > Loading package base ... linking ... done. > λ> import StaticFlags > λ> import Data.IORef > λ> readIORef v_opt_C_ready > Loading package array-0.5.0.0 ... linking ... done. > Loading package deepseq-1.3.0.2 ... linking ... done. > Loading package bytestring-0.10.4.0 ... linking ... done. > Loading package containers-0.5.5.1 ... linking ... done. > Loading package Win32-2.3.0.2 ... linking ... done. > Loading package filepath-1.3.0.2 ... linking ... done. > Loading package old-locale-1.0.0.6 ... linking ... done. > Loading package time-1.4.2 ... linking ... done. > Loading package directory-1.2.1.0 ... linking ... done. > Loading package pretty-1.1.1.1 ... linking ... done. > Loading package process-1.2.0.0 ... linking ... done. > Loading package Cabal-1.18.1.3 ... linking ... done. > Loading package binary-0.7.1.0 ... linking ... done. > Loading package bin-package-db-0.0.0.0 ... linking ... done. > Loading package hoopl-3.10.0.1 ... linking ... done. > Loading package hpc-0.6.0.1 ... linking ... done. > Loading package template-haskell ... linking ... done. > Loading package transformers-0.3.0.0 ... linking ... done. > Loading package ghc-7.8.2 ... linking ... done. > False > λ> staticFlags > ghc.exe: panic! (the 'impossible' happened) > (GHC version 7.8.2 for x86_64-unknown-mingw32): > Static flags have not been initialised! > Please call GHC.parseStaticFlags early enough. > > Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug > }}} > > But not with GHC 7.8.2 on Linux x86_64: > > {{{ > $ ghci > GHCi, version 7.8.2: http://www.haskell.org/ghc/ :? for help > Loading package ghc-prim ... linking ... done. > Loading package integer-gmp ... linking ... done. > Loading package base ... linking ... done. > λ> import StaticFlags > λ> import Data.IORef > λ> readIORef v_opt_C_ready > Loading package array-0.5.0.0 ... linking ... done. > Loading package deepseq-1.3.0.2 ... linking ... done. > Loading package bytestring-0.10.4.0 ... linking ... done. > Loading package containers-0.5.5.1 ... linking ... done. > Loading package filepath-1.3.0.2 ... linking ... done. > Loading package old-locale-1.0.0.6 ... linking ... done. > Loading package time-1.4.2 ... linking ... done. > Loading package directory-1.2.1.0 ... linking ... done. > Loading package pretty-1.1.1.1 ... linking ... done. > Loading package process-1.2.0.0 ... linking ... done. > Loading package Cabal-1.18.1.3 ... linking ... done. > Loading package binary-0.7.1.0 ... linking ... done. > Loading package bin-package-db-0.0.0.0 ... linking ... done. > Loading package hoopl-3.10.0.1 ... linking ... done. > Loading package hpc-0.6.0.1 ... linking ... done. > Loading package template-haskell ... linking ... done. > Loading package transformers-0.3.0.0 ... linking ... done. > Loading package ghc-7.8.2 ... linking ... done. > True > λ> staticFlags > [] > }}} > > This has caused problems for me when running programs such as [https://github.com/ku-fpg/hermit/ HERMIT] on Windows, since at some point, {{{parseStaticFlagsFull}}} seems to be called during program execution. A workaround is to call {{{initStaticOpts}}} manually somewhere in the program, but I feel like that shouldn't be necessary. The one above was on Windows. Also reported: > Hello, > > A similar panic also happens when running Liquid Haskell [http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/about/] on a file that uses the Units of Measure plugin [https://github.com/adamgundry/uom- plugin] > > > {{{ > liquid: liquid: panic! (the 'impossible' happened) > (GHC version 7.10.1 for x86_64-unknown-linux): > Static flags have not been initialised! > Please call GHC.parseStaticFlags early enough. > }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10301> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10294: Missing instances if compiling with -fplugin
by GHC 15 Dec '16

15 Dec '16

#10294: Missing instances if compiling with -fplugin -------------------------------------+------------------------------------- Reporter: jscholl | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 (Type checker) | Operating System: Linux Keywords: | Type of failure: GHC rejects Architecture: x86_64 | valid program (amd64) | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Using the example from "9.3.3.2. Using Annotations" of the GHC user manual does not work correctly with GHC 7.10. The following fails: $ ghc -c Bug1.hs -fplugin=SayAnnNames.Plugin {{{ Bug1.hs:5:1: No instance for (Data SomeAnn) arising from an annotation In the annotation: {-# ANN foo SomeAnn #-} }}} It does not seem to matter why the type class is required: $ ghc -c Bug2.hs -fplugin=SayAnnNames.Plugin {{{ Bug2.hs:10:7: No instance for (Data SomeAnn) arising from a use of ‘bar’ In the expression: bar SomeAnn In an equation for ‘baz’: baz = bar SomeAnn }}} Compiling without -fplugin works fine, though. If SomeAnn is defined in a different module than SayAnnNames.Plugin and reexported from it, the instances are in scope, too. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10294> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9890: RTS -qa option is helpful but under-documented
by GHC 15 Dec '16

15 Dec '16

#9890: RTS -qa option is helpful but under-documented -------------------------------------+------------------------------------- Reporter: adamgundry | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Runtime System | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | Documentation bug Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The entire documentation for the RTS `-qa` option is Use the OS's affinity facilities to try to pin OS threads to CPU cores. This is an experimental feature, and may or may not be useful. Please let us know whether it helps for you! It does help for us: enabling it on a multithreaded, moderately GC-heavy web server led to a sizeable improvement (~20%) in throughput benchmarks. However, it would be nice if the GHC documentation was a little more descriptive about what exactly this option does and how experimental it is now considered! (Relatedly, perhaps it would be worth adding a single index of RTS options in the user's guide, much like the flag reference for GHC itself.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9890> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10614: Show constraints in ``Found hole...''
by GHC 15 Dec '16

15 Dec '16

#10614: Show constraints in ``Found hole...'' -------------------------------------+------------------------------------- Reporter: bjmprice | Owner: Type: feature | Status: new request | Milestone: Priority: normal | Version: 7.10.1 Component: Compiler | Operating System: Unknown/Multiple Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Currently it is not clear when types are known equal. Consider writing castWith: {{{#!hs {-# LANGUAGE GADTs , TypeOperators #-} import Data.Type.Equality hiding (castWith) castWith :: a :~: b -> a -> b castWith Refl x = _ }}} which results in {{{ TypeEq.hs:5:19: error: Found hole: _ :: b Where: ‘b’ is a rigid type variable bound by the type signature for: castWith :: a :~: b -> a -> b at TypeEq.hs:4:13 Relevant bindings include x :: a (bound at TypeEq.hs:5:15) castWith :: a :~: b -> a -> b (bound at TypeEq.hs:5:1) In the expression: _ In an equation for ‘castWith’: castWith Refl x = _ }}} Filling the hole with x is correct, but it is not clear from the message that GHC knows this. It would be useful to have a section "Constraints include" e.g. {{{ TypeEq.hs:5:19: error: Found hole: _ :: b Where: ‘b’ is a rigid type variable bound by the type signature for: castWith :: a :~: b -> a -> b at TypeEq.hs:4:13 Relevant bindings include x :: a (bound at TypeEq.hs:5:15) castWith :: a :~: b -> a -> b (bound at TypeEq.hs:5:1) Constraints include <------ NEW LINE a ~ b (from Refl :: a :~: a at TypeEq.hs:5:10) <------ NEW LINE In the expression: _ In an equation for ‘castWith’: castWith Refl x = _ }}} And show class constraints (Show a etc.) similarly -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10614> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9696: readRawBufferPtr and writeRawBufferPtr allocate memory
by GHC 13 Dec '16

13 Dec '16

#9696: readRawBufferPtr and writeRawBufferPtr allocate memory -------------------------------------+------------------------------------- Reporter: mergeconflict | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: x86_64 (amd64) | Unknown/Multiple Difficulty: Unknown | Type of failure: Runtime Blocked By: | performance bug Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- I initially filed this as a [http://stackoverflow.com/questions/26333815 /why-do-hgetbuf-hputbuf-etc-allocate-memory question on StackOverflow], assuming that the behavior I'm seeing was intentional, or that I was misinterpreting the profiler results... but Kazu Yamamoto [https://twitter.com/kazu_yamamoto/status/522583112249663488 suggested] I should file this as an issue here. It's my first GHC ticket, so here goes: {{{#!hs main :: IO () main = do buf <- mallocArray 1 echo buf echo :: Ptr Word8 -> IO () echo buf = forever $ do len <- readRawBufferPtr "read" stdin buf 0 1 writeRawBufferPtr "write" stdout buf 0 (fromIntegral len) }}} I expect the only heap allocation here should be my explicit `mallocArray`, but profiling with `+RTS -P` indicates this isn't the case: both the read and write operations do appear to allocate some short-lived heap objects. In contrast: {{{#!hs echo :: Ptr Word8 -> IO () echo buf = forever $ do threadWaitRead $ Fd 0 len <- c_read 0 buf 1 c_write 1 buf (fromIntegral len) yield }}} does not appear to allocate. I did a bit of digging (copying bits of source code from `base` into my own project, to get cost center annotations) and it seems like the allocation might be happening in `throwErrnoIfRetryMayBlock`. See [https://gist.github.com/anonymous/3ba3cfa118e1d05870d4 this gist] for more detail, including core output from `-ddump-simpl`. In all honesty, I don't know whether this is a bug. I was just surprised by it, when I first encountered it using `hGetBuf` / `hPutBuf`, so I'm trying to understand whether this is expected behavior and why. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9696> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8248: GHCi should not warn if group writable
by GHC 13 Dec '16

13 Dec '16

#8248: GHCi should not warn if group writable ----------------------------+---------------------------------------------- Reporter: afcowie | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 7.6.3 Keywords: | Operating System: Linux Architecture: | Type of failure: GHC rejects valid program Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ----------------------------+---------------------------------------------- Any number of Linux distros support the idea of user groups, whereby when a new user is created there is also simultaneously a group created with the same name; ie, instead of {{{ -rw-r--r--. 1 andrew users 19 Sep 5 08:29 ghci.conf }}} as us old traditionalists would have it, you get {{{ -rw-rw-r--. 1 andrew andrew 19 Sep 5 08:29 ghci.conf }}} because the umask in such cases is 0002 instead of 0022. There is entirely nothing unusual or incorrect about this approach, and it is followed, for example, in the Fedora family of distros. GHC, however, is being a bit silly in emitting the following: {{{ $ ghci GHCi, version 7.6.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. *** WARNING: /home/andrew/.ghc/ghci.conf is writable by someone else, IGNORING! Prelude> }}} Foremost the fact that the file is group writable is not a problem and the user's choice, //particularly// in this case because it's group writable in the user's group! Regardless of that, GHCi should not be ignoring files with other than 0644 permissions; this isn't `.ssh/`. Can this check and attendant behaviour be removed? AfC -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8248> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9308: nofib fannkuch-redux runs perpetually with -fllvm
by GHC 10 Dec '16

10 Dec '16

#9308: nofib fannkuch-redux runs perpetually with -fllvm ------------------------------------+------------------------------------- Reporter: jrp | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Running the nofib benchmarks with make -k EXTRA_HC_OPTS=-fllvm on a HEAD build of ghc configured with perf-llvm (3.4.2) results in fannkuch-redux running in an infinite loop. The benchmark runs in about 3.5s without the -fllvm {{{ HC = /Users/xx/Projects/ghc/inplace/bin/ghc-stage2 HC_OPTS = -O2 -Rghc-timing -H32m -hisuf hi -fllvm -rtsopts -XBangPatterns -O2 RUNTEST_OPTS = -ghc-timing ==nofib== fannkuch-redux: time to compile Main follows... /Users/jrp/Projects/ghc/inplace/bin/ghc-stage2 -O2 -Rghc-timing -H32m -hisuf hi -fllvm -rtsopts -XBangPatterns -O2 -c Main.hs -o Main.o <<ghc: 358716248 bytes, 313 GCs, 10827462/27497216 avg/max bytes residency (6 samples), 57M in use, 0.00 INIT (0.00 elapsed), 0.20 MUT (0.53 elapsed), 0.21 GC (0.23 elapsed) :ghc>> ==nofib== fannkuch-redux: size of Main.o follows... __TEXT __DATA __OBJC others dec hex 10333 497 0 0 10830 2a4e ==nofib== fannkuch-redux: time to link fannkuch-redux follows... <<ghc: 19914544 bytes, 16 GCs, 1005021/2239600 avg/max bytes residency (3 samples), 25M in use, 0.00 INIT (0.00 elapsed), 0.01 MUT (0.53 elapsed), 0.02 GC (0.02 elapsed) :ghc>> ==nofib== fannkuch-redux: size of fannkuch-redux follows... __TEXT __DATA __OBJC others dec hex 4075520 446464 0 4295945496 4300467480 10053ed18 ==nofib== fannkuch-redux: time to run fannkuch-redux follows... ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; ../../runstdtest/runstdtest ./fannkuch-redux -o1 fannkuch-redux.stdout -o1 fannkuch-redux.stdout -ghc-timing 11; }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9308> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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