November 2016 - ghc-tickets

[GHC] #12706: Collecting type info is slow
by GHC 02 Mar '18

02 Mar '18

#12706: Collecting type info is slow -------------------------------------+------------------------------------- Reporter: vshabanov | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | 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: -------------------------------------+------------------------------------- With `:set +c` option in GHCi, I'm waiting for 10-15 seconds for {{{ Collecting type info for 34 module(s) ... }}} after both first load and subsequent reloads, even if only top-level module was modified. And GHCi uses about 1.5-2x more memory than it uses without `:set +c`. My app has about 30k lines of code. Is it expected behavior and some performance improvements are planned or it's a bug? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12706> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12790: GHC 8.0.1 uses copious amounts of RAM and time when trying to compile lambdabot-haskell-plugins
by GHC 02 Mar '18

02 Mar '18

#12790: GHC 8.0.1 uses copious amounts of RAM and time when trying to compile lambdabot-haskell-plugins -------------------------------------+------------------------------------- Reporter: clint | Owner: 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: -------------------------------------+------------------------------------- When building lambdabot-haskell-plugins, Lambdabot.Plugin.Haskell.Pl.Parser compiles without incident on the non- profiling run, but cripples the build machine on the profiling run. An excerpt of -v3 output is below to show the number of terms skyrocketing. *** Common sub-expression [Lambdabot.Plugin.Haskell.Pl.Parser]: Result size of Common sub-expression = {terms: 39,049, types: 30,851, coercions: 990} !!! Common sub-expression [Lambdabot.Plugin.Haskell.Pl.Parser]: finished in 72.00 milliseconds, allocated 44.536 megabytes *** Float inwards [Lambdabot.Plugin.Haskell.Pl.Parser]: Result size of Float inwards = {terms: 39,049, types: 30,851, coercions: 990} !!! Float inwards [Lambdabot.Plugin.Haskell.Pl.Parser]: finished in 68.00 milliseconds, allocated 60.337 megabytes *** Simplifier [Lambdabot.Plugin.Haskell.Pl.Parser]: Result size of Simplifier iteration=1 = {terms: 977,045, types: 299,334, coercions: 1,058} Result size of Simplifier iteration=2 = {terms: 926,036, types: 263,306, coercions: 932} Result size of Simplifier = {terms: 922,724, types: 262,202, coercions: 932} !!! Simplifier [Lambdabot.Plugin.Haskell.Pl.Parser]: finished in 15480.00 milliseconds, allocated 9384.823 megabytes *** CoreTidy [Lambdabot.Plugin.Haskell.Pl.Parser]: Result size of Tidy Core = {terms: 922,623, types: 261,789, coercions: 865} !!! CoreTidy [Lambdabot.Plugin.Haskell.Pl.Parser]: finished in 2060.00 milliseconds, allocated 613.585 megabytes writeBinIface: 95 Names writeBinIface: 259 dict entries *** CorePrep [Lambdabot.Plugin.Haskell.Pl.Parser]: Result size of CorePrep = {terms: 1,128,145, types: 347,063, coercions: 865} !!! CorePrep [Lambdabot.Plugin.Haskell.Pl.Parser]: finished in 3468.00 milliseconds, allocated 1718.453 megabytes *** Stg2Stg: *** CodeGen [Lambdabot.Plugin.Haskell.Pl.Parser]: -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12790> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11107: Can't use type wildcard infix
by GHC 25 Feb '18

25 Feb '18

#11107: Can't use type wildcard infix -------------------------------------+------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.11 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: -------------------------------------+------------------------------------- This fails: {{{ foo :: Int `_a` Bool foo = Right True }}} But moving `_a` to be prefix works. I observe the same behavior with an unnamed type wildcard. This was discovered while poking around in the renamer, not in real code! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11107> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11777: RTS source code issues
by GHC 25 Feb '18

25 Feb '18

#11777: RTS source code issues -------------------------------------+------------------------------------- Reporter: simonpj | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- Tiago Silva <tiagosilva(a)hush.com> writes: Last night I started looking at the C files used in GHC and noticed these issues: {{{ /driver/utils/cwrapper.c : int main(int, char **); }}} `void *p` is apparently unused, even if the compiler optimizes it away.. you should check if something went missing. {{{ /rts/RetainerProfile.c : static nat sanityCheckHeapClosure(StgClosure *) }}} `StgInfoTable *info` has the same issue as above {{{ /rts/RetainerSet.c #elif defined(RETAINER_SCHEME_CC) // Retainer scheme 3: retainer = cost centre void printRetainerSetShort(FILE *f, RetainerSet *rs, nat max_length) { char tmp[max_length + 1]; int size; nat j; } }}} Unlike the other functions around it, this function does nothing. Its variables are also not unused? {{{ /rts/sm/MarkWeak.c : void markWeakPtrList (void); if (w->header.info == &stg_DEAD_WEAK_info) { last_w = &(w->link); } else { last_w = &(w->link); } }}} Not sure what's going on here. Regardless of the test the two branches do the same thing. {{{ /rts/win32/IOManager.c : AddIORequest, AddDelayRequest, AddProcRequest functions }}} If `(!ioMan || !wItem)` the functions either return 0 or FALSE, but they don't free `wItem` before. Is this optimized by the compiler? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11777> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8597: Git Hook script to prevent large binary blobs being checked in
by GHC 23 Feb '18

23 Feb '18

#8597: Git Hook script to prevent large binary blobs being checked in ------------------------------------+------------------------------------- Reporter: hvr | Owner: hvr Type: task | Status: new Priority: normal | Milestone: Component: Trac & Git | Version: Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- It has already occurred in the past in `testsuite.git` repo, that executables were checked in by accident, and caused the Git history to get bloated. In order to avoid such accidents in the future a Git hook script in the style of [http://stackoverflow.com/questions/20226132/is-there-a-git-hook- which-can-prevent-binary-check-ins this] might be useful, but taking also into account the size, and/or possibly with a magic safeword to be put in the commit message, to override the check for a single commit, if the author really knows what (s)he's doing. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8597> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11826: unsafe causes bug, news @ 11
by GHC 23 Feb '18

23 Feb '18

#11826: unsafe causes bug, news @ 11 -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- I know there has been plenty of levity here lately but here goes :) I didn't expect ‘isUndefined’ to be safe but this may be interesting to the devs (I am obedient and report it thusly and hereby-ly per GHC's request) {{{#!haskell % ghci -ignore-dot-ghci GHCi, version 8.1.20160117: http://www.haskell.org/ghc/ :? for help Prelude> import Control.Exception Prelude Control.Exception> import System.IO.Unsafe Prelude Control.Exception System.IO.Unsafe> import Unsafe.Coerce Prelude Control.Exception System.IO.Unsafe Unsafe.Coerce> isUndefined x = unsafePerformIO $ catch ((unsafeCoerce x :: IO ()) >> return False) (const $ return True :: SomeException -> IO Bool) Prelude Control.Exception System.IO.Unsafe Unsafe.Coerce> isUndefined (succ True) True Prelude Control.Exception System.IO.Unsafe Unsafe.Coerce> isUndefined (succ False) <interactive>: internal error: stg_ap_v_ret (GHC version 8.1.20160117 for x86_64_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted (core dumped) % }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11826> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12524: RFC: Allow prefixing result evaluated at GHCi prompt
by GHC 23 Feb '18

23 Feb '18

#12524: RFC: Allow prefixing result evaluated at GHCi prompt -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: feature | Status: new request | Priority: lowest | Milestone: Component: GHCi | 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: -------------------------------------+------------------------------------- Similar to `prompt`, `prompt-cont` (previously `prompt2`): allowing users to supply a prefix to evaluation results with `result` has two use cases I can think of {{{ :set prompt " ghci> " :set prompt-cont " ghci| " :set result " " }}} the desired outcome would be `↓` as indented code for IRC, also reddit code format: {{{ ghci> 1 + 2 + 3 6 ghci> reverse "hello" "olleh" }}} ---- The other case came from [https://twitter.com/rightfold/status/767301255140179968 this tweet] {{{ :set prompt "" :set result "-- " }}} {{{ 1 + 2 + 3 -- 6 reverse "hello" -- "olleh" }}} This can be copied/pasted back to a separate GHCi session where the result is ignored. ---- I haven't seen this feature in any other repl, I'm not sure if this would see much use. This wouldn't work with IO actions without some magic. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12524> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11285: Static linking is really slow sometimes
by GHC 20 Feb '18

20 Feb '18

#11285: Static linking is really slow sometimes -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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: -------------------------------------+------------------------------------- I'm testing on Cabal `Setup.hs`, which links against Cabal. On a beefy machine with many cores and lots of RAM, I see a x2 regression in linking time from GHC 7.10.2 to GHC 8.0 (a recent HEAD) using GNU ld (not gold): {{{ [ezyang@hs01 ezyang]$ rm A; time ghc --make A.hs -fforce-recomp [1 of 1] Compiling Main ( A.hs, A.o ) Linking A ... real 0m1.273s user 0m0.990s sys 0m0.210s [ezyang@hs01 ezyang]$ rm A; time ghc-8.0/usr/bin/ghc --make A.hs -fforce- recomp [1 of 1] Compiling Main ( A.hs, A.o ) Linking A ... real 0m3.270s user 0m2.727s sys 0m0.523s }}} On a puny eight year-old laptop, I see a x2 regression from 7.6 to 7.10 (with not much change with 8.0) {{{ ezyang@sabre:~$ rm A; time ghc --make -O0 A.hs -fforce-recomp rm: cannot remove ‘A’: No such file or directory [1 of 1] Compiling Main ( A.hs, A.o ) Linking A ... real 0m3.058s user 0m1.860s sys 0m1.164s ezyang@sabre:~$ rm A; time ghc-7.10 --make -O0 A.hs -fforce-recomp [1 of 1] Compiling Main ( A.hs, A.o ) Linking A ... real 0m7.139s user 0m4.616s sys 0m2.488s }}} There must be something which is causing the linker to run slowly in one case, and quickly in the other. It would be really good to figure out what this is. Slow linking is NOT NICE. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11285> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11427: TypeSynonyms not deduced
by GHC 20 Feb '18

20 Feb '18

#11427: TypeSynonyms not deduced -------------------------------------+------------------------------------- Reporter: phadej | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1-rc1 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: -------------------------------------+------------------------------------- {{{ class (AllF f xs, SListI xs) => All (f :: k -> Constraint) (xs :: [k]) instance #if __GLASGOW_HASKELL__ >= 710 {-# OVERLAPPING #-} #endif All SListI xss => SingI (xss :: [[k]]) where sing = sList }}} fails with {{{ • Could not deduce (SListI xss) arising from the superclasses of an instance declaration from the context: All SListI xss bound by the instance declaration at src/Generics/SOP/Constraint.hs:141:3-40 • In the instance declaration for ‘SingI xss’ }}} See https://travis-ci.org/well-typed/generics-sop/jobs/102388817 and https://github.com/phadej/generics-sop/tree/ghc-8.0.1 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11427> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11791: Remove the `isInlinePragma prag` test
by GHC 19 Feb '18

19 Feb '18

#11791: Remove the `isInlinePragma prag` test -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: #11781, #5928 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- This is a spin off of tickjet:11781#comment:9, where simonpjs writes: > What is more mysterious to me is why the unfolding for `$fApplicativeIO_$c*>` doesn't have `bindIO`, and then `bindIO` inlined into it, which would allow a cascade of further improvements, which would, I think, produce essentially the same code as `thenIO`. > > The offending corner is this > {{{ > active_unfolding_gentle id > = isInlinePragma prag -- WHY?? > && isEarlyActive (inlinePragmaActivation prag) > }}} > So I tried removing the `isInlinePragma prag` test, and indeed the code becomes identical. > > Conclusion: > * I'd love to make the above change to `active_unfolding_gentle` and see if any other performance numbers budge. I doubt that anything will change a lot -- it really only affects whether optimisation happens before or after inlining -- but it should improve compiler performance a bit for that very reason. This could be a separate ticket > > Incidentally, see #5928 which is somewhat related. This ticket tracks that idea. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11791> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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