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[GHC] #13429: Optimizer produces Core with an infinite <<loop>>
by GHC 15 Jun '17

15 Jun '17

#13429: Optimizer produces Core with an infinite <<loop>> -------------------------------------+------------------------------------- Reporter: lehins | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- While using vector package to implement convolution and supplying `-O1` or `-02` to ghc compilation results in core with an infinite loop. In order to trigger this behavior at least two modules is required. Attached is the minimal setup that I could come up with, that demonstrates the issue. Here is the stack trace: {{{ $ stack --install-ghc --resolver lts-8.3 exec -- ghc -O1 -prof -fprof-auto main.hs && ./main +RTS -xc [1 of 2] Compiling Loop ( Loop.hs, Loop.o ) [2 of 2] Compiling Main ( main.hs, main.o ) Linking main ... *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: Main.CAF --> evaluated by: Main.main, called from Main.CAF --> evaluated by: Loop.toKernel.\, called from Data.Vector.Fusion.Util.>>=, called from Loop.toKernel, called from Main.main, called from Main.CAF --> evaluated by: Data.Vector.Fusion.Util.>>=, called from Loop.toKernel, called from Main.main, called from Main.CAF *** Exception (reporting due to +RTS -xc): (THUNK_STATIC), stack trace: Main.CAF main: <<loop>> }}} At first I though that it might be a bug in a vector package, which is still a possibility, but since I was not able to observe that issue with ghc-7.8.4, I decided to open an ticket here. I tested attached code with all of subsequent released ghc versions (7.10.1 - 8.0.2), which resulted in the infinite loop. Worth noting that sometimes, when recompilation of only the `main.hs` file is enforced, program starts to work as expected. Here is an example: {{{ $ stack --resolver ghc-7.10.3 exec --package vector-0.11.0.0 --package primitive-0.6.1.0 -- ghc -O1 main.hs && ./main [1 of 2] Compiling Loop ( Loop.hs, Loop.o ) [2 of 2] Compiling Main ( main.hs, main.o ) Linking main ... main: <<loop>> $ touch main.hs $ stack --resolver ghc-7.10.3 exec --package vector-0.11.0.0 --package primitive-0.6.1.0 -- ghc -O1 main.hs && ./main [2 of 2] Compiling Main ( main.hs, main.o ) Linking main ... <Image 1x1> }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13429> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13756: Typo in user guide suggests that there's an -O* option
by GHC 15 Jun '17

15 Jun '17

#13756: Typo in user guide suggests that there's an -O* option -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 Component: Documentation | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In https://downloads.haskell.org/~ghc/7.10.3/docs/html/users_guide /options-optimise.html it still correctly said: {{{ No -O*-type option specified: This is taken to mean: “Please compile quickly ... }}} But in https://downloads.haskell.org/~ghc/latest/docs/html/users_guide /using-optimisation.html#ghc-flag--O* it says: {{{ -O* This is taken to mean: “Please compile quickly ... }}} The `No -O*-type option specified:` bit must have been accidentally dropped in the conversion to the new user guide format. (I dared put this into 8.2.1 because it's probably trivial to fix if one understands the syntax language that the user guide is written in.) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13756> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13829: ghc --make should not relink when we know the binary doesn't change
by GHC 15 Jun '17

15 Jun '17

#13829: ghc --make should not relink when we know the binary doesn't change -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #13828 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- I would expect GHC not to relink after touching a file, since no actual program code was changed. But it does: {{{ $ echo "main = return ()" > Main.hs $ ghc --make Main.hs [1 of 1] Compiling Main ( Main.hs, Main.o ) Linking Main ... $ touch Main.hs $ ghc --make Main.hs [1 of 1] Compiling Main ( Main.hs, Main.o ) Linking Main ... }}} I would expect that the recompilation avoidance makes GHC stop continuing as soon as it has noticed that the same object code (`.o` file) was generated as in the first build. Perhaps even earlier (e.g. after parsing). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13829> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13828: Re-linking is not avoided when -dynamic is used
by GHC 15 Jun '17

15 Jun '17

#13828: Re-linking is not avoided when -dynamic is used -------------------------------------+------------------------------------- Reporter: nh2 | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 (Linking) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- In normal builds, GHC will no re-link executables when that's not necesary (e.g. when no code has changed). But when `-dynamic` is used, it re-links every time. Minimal example for reproduction: https://github.com/nh2/cabal-relink-test -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13828> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13826: :t Predicate (length :: [] -> Int)
by GHC 14 Jun '17

14 Jun '17

#13826: :t Predicate (length :: [] -> Int) --------------------------------+------------------------------------- Reporter: dpsrt | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.2 Keywords: | Operating System: Unknown/Multiple Architecture: Other | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: --------------------------------+------------------------------------- {{{ Prelude> :t Predicate (length :: [] -> Int) ghc: panic! (the 'impossible' happened) (GHC version 8.0.2 for x86_64-unknown-mingw32): initTc: unsolved constraints WC {wc_insol = [W] Predicate_a64B :: t_a64A[tau:3] (CHoleCan: Predicate)} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13826> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13820: GHC goes out of memory while compiling nothing
by GHC 13 Jun '17

13 Jun '17

#13820: GHC goes out of memory while compiling nothing -------------------------------------+------------------------------------- Reporter: seunje | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Compiling this results in GHC using all memory and eventually segfaulting {{{#!haskell f = id id id id id id id id id id id id id id id id id id id id id id id id id id id main = print 1 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13820> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #2600: Bind type variables in RULES
by GHC 13 Jun '17

13 Jun '17

#2600: Bind type variables in RULES -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: feature request | Status: new Priority: lowest | Milestone: Component: Compiler | Version: 6.8.3 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #2110 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): Ideas to fix this are in [https://github.com/ghc-proposals/ghc- proposals/pull/55 this recent proposal]. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/2600#comment:23> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12056: Too aggressive `-w` option
by GHC 13 Jun '17

13 Jun '17

#12056: Too aggressive `-w` option -------------------------------------+------------------------------------- Reporter: asr | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect Unknown/Multiple | warning at compile-time Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- By running {{{ ghc -w -Wunrecognised-warning-flags -Wfoo Main.hs }}} I would expect the warning {{{ on the commandline: warning: unrecognised warning flag: -Wfoo }}} however this warning isn't reported. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12056> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13781: (a :: (k :: Type)) is too exotic for Template Haskell
by GHC 13 Jun '17

13 Jun '17

#13781: (a :: (k :: Type)) is too exotic for Template Haskell -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Template | Version: 8.0.1 Haskell | Keywords: TypeInType | Operating System: Unknown/Multiple Architecture: | Type of failure: GHC rejects Unknown/Multiple | valid program Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- On GHC 8.0.1 or later, GHC will choke on this code: {{{#!hs {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE TypeInType #-} module Bug where import Data.Kind import Data.Proxy $([d| f :: Proxy (a :: (k :: Type)) f = Proxy |]) }}} {{{ GHCi, version 8.2.0.20170522: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Bug.hs:8:3: error: Exotic form of kind not (yet) handled by Template Haskell (k :: Type) | 8 | $([d| f :: Proxy (a :: (k :: Type)) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^... }}} I don't think this would be too hard to support, though. I'll take a shot at fixing this. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13781> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12545: Compilation time/space regression in GHC 8.0/8.1 (search in type-level lists and -O)
by GHC 13 Jun '17

13 Jun '17

#12545: Compilation time/space regression in GHC 8.0/8.1 (search in type-level lists and -O) -------------------------------------+------------------------------------- Reporter: | Owner: mikhail.vorozhtsov | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- After upgrading to GHC 8.0.1 I've noticed that compilation time of one of my libraries got unacceptably long. Please find the attached test case. Here are some numbers from my machine: {{{ $ time ~/Prefixes/ghc-7.10.3/bin/ghc -O -c -Rghc-timing TypeList.hs Regression.hs <<ghc: 19103924976 bytes, 1441 GCs, 73048470/256579104 avg/max bytes residency (18 samples), 542M in use, 0.000 INIT (0.002 elapsed), 14.163 MUT (14.257 elapsed), 5.707 GC (5.830 elapsed) :ghc>> real 0m20.160s user 0m19.937s sys 0m0.197s $ time ~/Prefixes/ghc-8.0.1/bin/ghc -O -c -Rghc-timing TypeList.hs Regression.hs <<ghc: 147662211104 bytes, 9635 GCs, 190336418/433097448 avg/max bytes residency (38 samples), 1210M in use, 0.000 INIT (0.001 elapsed), 101.707 MUT (101.840 elapsed), 27.907 GC (28.259 elapsed) :ghc>> real 2m10.195s user 2m9.773s sys 0m0.400s }}} Both versions are the official Debian 8 x86_64 binaries from haskell.org. I also compiled the git master and unfortunately it is affected as well. It is worth mentioning that turning off optimization makes the problem disappear: {{{ $ time ~/Prefixes/ghc-8.0.1/bin/ghc -O0 -c -Rghc-timing TypeList.hs Regression.hs <<ghc: 3779057184 bytes, 225 GCs, 17923355/81566792 avg/max bytes residency (8 samples), 164M in use, 0.000 INIT (0.001 elapsed), 2.847 MUT (2.941 elapsed), 0.553 GC (0.572 elapsed) :ghc>> real 0m3.593s user 0m3.507s sys 0m0.073s }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12545> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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