February 2018 - ghc-tickets

Re: [GHC] #6087: Join points need strictness analysis
by GHC 21 Feb '18

21 Feb '18

#6087: Join points need strictness analysis -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: infoneeded Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Correct. Another example might be {{{ f :: Int -> [Int] f 0 = [] f n = n : f (n-1) }}} It's strict all right, but we need the boxed 'n' for the result. "Boxity" analysis might try to figure out when the boxed version is needed, and pass that too. At one stage I had that but it seemed unprincipled. Bottom line so far: late demand analysis can be a win, but only rarely so; and it can be a loss. It's a pity -- I'd like to make it part of -O2. But we probably have higher priorities for now. ''Can you add the nofib numbers in a comment, please, for posterity?'' -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6087#comment:32> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7206: Implement cheap build
by GHC 21 Feb '18

21 Feb '18

#7206: Implement cheap build -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 7.4.2 Resolution: | Keywords: FloatOut Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #8763, #13422 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by osa1): * Attachment "cheap_build_nofib" added. nofib reuslts with `wip/cheap-build-osa1` branch. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7206> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #7206: Implement cheap build
by GHC 21 Feb '18

21 Feb '18

#7206: Implement cheap build -------------------------------------+------------------------------------- Reporter: simonpj | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 7.4.2 Resolution: | Keywords: FloatOut Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #8763, #13422 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by osa1): I pushed my branch to `wip/cheap-build-osa1` in GHC's git repo as well. Also attached the nofib output. As to why `nums` is not inlined in comment:24, I see this in `-ddump- inlinings` output: {{{ Considering inlining: nums_aSY arg infos [] interesting continuation RuleArgCtxt some_benefit False is exp: False is work-free: False guidance ALWAYS_IF(arity=0,unsat_ok=False,boring_ok=False) ANSWER = NO }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7206#comment:26> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #6087: Join points need strictness analysis
by GHC 21 Feb '18

21 Feb '18

#6087: Join points need strictness analysis -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: infoneeded Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by osa1): We decided to put this on hold at the meeting. Just a small update: the case in comment:27 seems to be a limitation with the current demand analyser. It sometimes introduces reboxing that can't be eliminated by the simplifier. Example: {{{ {-# NOINLINE check #-} check :: Int -> Bool check !n = True f_ :: Int -> Int f_ n = if check n then n else n * f_ (n - 1) }}} even after simplifications we rebox the argument: {{{ Rec { -- RHS size: {terms: 17, types: 3, coercions: 0, joins: 0/0} $wf_ $wf_ = \ ww_s28U -> case check (I# ww_s28U) of { False -> case $wf_ (-# ww_s28U 1#) of ww1_s28Y { __DEFAULT -> *# ww_s28U ww1_s28Y }; True -> ww_s28U } end Rec } }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6087#comment:31> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #6087: Join points need strictness analysis
by GHC 21 Feb '18

21 Feb '18

#6087: Join points need strictness analysis -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: infoneeded Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 7.4.1 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ömer Sinan Ağacan <omeragacan@…>): In [changeset:"a032ff77210736df45cf49820c882f40dc10230e/ghc" a032ff7/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="a032ff77210736df45cf49820c882f40dc10230e" Add references to #6087 [skip ci] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6087#comment:30> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14536: Ghc panics while building stage2 with -dstg-lint
by GHC 21 Feb '18

21 Feb '18

#14536: Ghc panics while building stage2 with -dstg-lint -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 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: -------------------------------------+------------------------------------- Building ghc at 54fda257d4a7bfddaa0c1fa0be698d1a849c4124 with the following mk/build.mk: {{{ BuildFlavour = validate ifneq "$(BuildFlavour)" "" include mk/flavours/$(BuildFlavour).mk endif GhcStage2HcOpts += -dcore-lint -dstg-lint -dcmm-lint }}} building with: {{{ make compiler/stage2/build/Exception.o }}} panics with: {{{ ghc-stage1: panic! (the 'impossible' happened) (GHC version 8.3.20171127 for x86_64-unknown-linux): ASSERT failed! dataConInstArgTys Unit# [k0_10, a_11] ['TupleRep '[], 'IntRep, State# RealWorld, Int#] Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1208:22 in ghc:Outputable assertPprPanic, called at compiler/basicTypes/DataCon.hs:1256:76 in ghc:DataCon Call stack: CallStack (from HasCallStack): callStackDoc, called at compiler/utils/Outputable.hs:1150:37 in ghc:Outputable pprPanic, called at compiler/utils/Outputable.hs:1206:5 in ghc:Outputable assertPprPanic, called at compiler/basicTypes/DataCon.hs:1256:76 in ghc:DataCon Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug }}} Once this is resolved, is there any reason that -dstg-ling and -dcmm-lint are not set on validate (at least with SLOW)? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14536> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14541: Stg lint failure while building ghc-stage2: compiler/stage2/build/Hoopl/Block.o
by GHC 21 Feb '18

21 Feb '18

#14541: Stg lint failure while building ghc-stage2: compiler/stage2/build/Hoopl/Block.o -------------------------------------+------------------------------------- Reporter: duog | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 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: -------------------------------------+------------------------------------- With the tree at: https://github.com/duog/ghc/tree/trac-14536 Which fixes ticket:14536 With build.mk: {{{ BuildFlavour = validate ifneq "$(BuildFlavour)" "" include mk/flavours/$(BuildFlavour).mk endif GhcStage2HcOpts += -dcore-lint -dstg-lint -dcmm-lint }}} building with: {{{ make compiler/stage2/build/Hoopl/Blocks.o }}} I get the following Stg lint error (extracts, full dump attached): {{{ <no location info>: warning: [in body of lambda with binders ds_s4dH :: a_a3as -> b_a3at, ds1_s4dI :: MaybeO ex_a3ao a_a3as] In some algebraic case alternative, number of arguments doesn't match constructor: JustO (arity 2) [a1_s4dK] }}} ... {{{ $fFunctorMaybeO_$cfmap :: forall ex a b. (a -> b) -> MaybeO ex a -> MaybeO ex b [GblId, Arity=2, Caf=NoCafRefs, Str=<L,1*C1(U)><S,1*U>, Unf=OtherCon []] = [] \r [ds_s4dH ds1_s4dI] case ds1_s4dI of { JustO a1_s4dK [Occ=Once] -> let { sat_s4dL [Occ=Once] :: b_a3at [LclId] = [ds_s4dH a1_s4dK] \u [] ds_s4dH a1_s4dK; } in JustO [sat_s4dL]; NothingO -> $WNothingO; }; }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14541> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14829: Linking error with ANN pragma
by GHC 20 Feb '18

20 Feb '18

#14829: Linking error with ANN pragma -------------------------------------+------------------------------------- Reporter: ehubinette | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | Operating System: Linux Architecture: | Type of failure: Compile-time Unknown/Multiple | crash or panic Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- There seems to be an issue with the ANN pragma, with fatal compilation errors. To reproduce, setup two modules as such: {{{#!hs module Test where import Weights (Weight(..)) {-# ANN mainTest (Weight 2) #-} mainTest :: IO () mainTest = return () }}} {{{#!hs {-# LANGUAGE DeriveDataTypeable #-} module Weights (Weight(..)) where import Data.Data (Data(..)) newtype Weight = Weight Integer deriving Data }}} Compiling with GHC version `8.2.2` yields: {{{ λ ghc Test.hs [2 of 2] Compiling Test ( Test.hs, Test.o ) Test.hs:5:1: fatal: cannot find object file ‘./Weights.dyn_o’ while linking an interpreted expression }}} The issue persists with `-dynamic-too`: {{{ λ ghc -dynamic-too Test.hs [2 of 2] Compiling Test ( Test.hs, Test.o ) Test.hs:5:1: fatal: cannot find object file ‘./Weights.dyn_o’ while linking an interpreted expression }}} ...but disappears with `-dynamic`: {{{ λ ghc -dynamic Test.hs [1 of 2] Compiling Weights ( Weights.hs, Weights.o ) [2 of 2] Compiling Test ( Test.hs, Test.o ) }}} Sidenote: with GHC version `8.5.20180219`, the issue disappears with `-dynamic-too` ''or'' `-dynamic`: {{{ λ ../../ghc/inplace/bin/ghc-stage2 -dynamic-too Test.hs [1 of 2] Compiling Weights ( Weights.hs, Weights.o ) [2 of 2] Compiling Test ( Test.hs, Test.o ) }}} Remove the ANN pragma, and the compiler behaves just fine with both GHC versions. Please tell me if I can provide more information. Cheers. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14829> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14001: Inlining does not work between modules
by GHC 20 Feb '18

20 Feb '18

#14001: Inlining does not work between modules -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: (none) Type: bug | Status: new Priority: high | 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: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Hi! I discovered today something that looks like a terrifying bug. I was discussing it on IRC and so far there is no explanation why it happens. Let's grab a test code from here: https://github.com/luna/dependent- state/tree/irc-testing (branch irc-testing). If you download it and execute `stack --stack-yaml stack-develop.yaml bench dependent-state:layered-state-benchmark` benchmarks from `test/bench/Main.hs` will be executed. Everything is compiled with `-O2` etc (see stack-develop.yaml for details). And now (everything regarding file `Control/Monad/State/Layered.hs`): 1. If you change lines `94-111` to use pointfree instead of normal arg, you get 40x slowdown 2. If you then uncomment lines `80-81`, everything is fast again. The problem is that lines `80-81` are: {{{ (.) :: (b -> c) -> (a -> b) -> a -> c (.) f g = \x -> f (g x) ; {-# INLINE (.) #-} }}} It seems that this function is inlined ONLY if is defined in this module. If we use the one from base OR if we move this function to separate module, we can observe the slowdown. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14001> 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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