February 2018 - ghc-tickets

Re: [GHC] #855: Improvements to SpecConstr
by GHC 22 Feb '18

22 Feb '18

#855: Improvements to SpecConstr -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: task | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.4.2 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: N/A Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by sgraf): * cc: sgraf (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/855#comment:10> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #3831: SpecConstr should exploit cases where there is exactly one call pattern
by GHC 22 Feb '18

22 Feb '18

#3831: SpecConstr should exploit cases where there is exactly one call pattern -------------------------------------+------------------------------------- Reporter: igloo | Owner: simonpj Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 6.13 Resolution: | Keywords: SpecConstr Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Compile-time | Test Case: performance bug | simplCore/should_compile/T3831 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by sgraf): I'm trying to reproduce what the missed opportunity was here. I ran T3831 and realized that the test is ineffective for detecting a regression of this ticket: The compiler invocation misses a `-O2`. Re: missed tantalising opportunity: I think you are referring to `setAttributes`, specifically to this nesting of join points: {{{ join { $j1 $j1 x1 m1 = case m1 of { Nothing -> (# x1, Nothing #); Just x1 -> case ... x1 of { (# y1, n1 #) -> join { $j2 $j2 x2 m2 = ... -- many more join { $j12 x12 m12 = case m12 of { Nothing -> (# x12, Nothing #); Just f -> (# x12, Just (\a -> ...) #) } } in ... case m2 of { Nothing -> jump $j12 x2 Nothing; Just f -> case ... x2 of { (# x12', m12' #) -> case m12' of { Nothing -> jump $j12 x12' (Just (x6 lvl7)); Just _ -> jump $j12 x12' (Just ...) } } } } in case n1 of { Nothing -> jump $j2 y1 Nothing; Just _ -> jump $j2 y1 (Just ...) } } in }}} I probably have made some errors while simplifying, but the idea is that these join points aren't specialised at all. 1. These are all non-recursive. I was under the impression that we have the inliner for non-recursive bindings to decide if inlining is worthwhile. 2. I don't see how there's only one call-pattern for each join point. There are 3: one Nothing, two Justs. Specialising (branching factor 2) or even inlining (3) these would mean exponential blow-up in code size. So either I'm referring to the wrong fragment of the code (I found no other join points, let alone recursive ones) or things have changed since then. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/3831#comment:17> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #1409: Allow recursively dependent modules transparently (without .hs-boot or anything)
by GHC 21 Feb '18

21 Feb '18

#1409: Allow recursively dependent modules transparently (without .hs-boot or anything) -------------------------------------+------------------------------------- Reporter: Isaac Dupree | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: ⊥ Component: Compiler | Version: 6.10.2 Resolution: | Keywords: backpack Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #9256 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by atravers): Replying to [comment:73 simonpj]: > I'm not sure which comment you are replying to; Darn - I assumed the "comment: 72 in reply to: 49" annotation was enough; the comment I was replying to was: > Lots of people would like this fixed; but no one has proposed a precise, worked-out, *design*. The way lies open! Now for the next assumption: > and I fear I don't understand what "something like this" is. Okay, so I was assuming that the machinery for the "--make" option for GHC had some resemblance to computeInOuts in the paper... > The big trouble with recursive modules is that: either you need a programmer written signature file (i.e. `.hs-boot`) or you have to compile all the modules in the SCC at once. I don't see any other path. In 2016, I rebuilt a HBC-based **bubble-gum-and-baling-wire sharp-edges- everywhere** implementation which copes with import-recursion (at least for what sources I've tested it on so far). The biggest catch? == **IT IS SLOW.** ...way too slow for practical use (if it only working with Haskell B. wasn't - in 2018 - impractical enough), hence no download links here or elsewhere. I had been working to improve its performance, with little success. But if you don't mind "going retro" for a while, I should be able to get it working again and send you the sources - just contact me on my GHC-Trac email address. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/1409#comment:75> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14837: Semigroup and Monoid instances for ST
by GHC 21 Feb '18

21 Feb '18

#14837: Semigroup and Monoid instances for ST -------------------------------------+------------------------------------- Reporter: andrewthad | Owner: (none) Type: feature | Status: new request | Priority: low | Milestone: Component: Compiler | Version: 8.2.2 Keywords: base | 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 `base-4.9`, a `Monoid` instance for `IO` was introduced. I would like to propose adding a similar instance for `ST`. This should be even less controversial since there is only one meaningful `Monoid` instance for `ST` (it lacks the exception-catching facilities of `IO`). The behavior of the `Semigroup` and `Monoid` instances would need to match this: {{{ instance Monoid a => Monoid (ST s a) where mappend = liftA2 mappend mempty = pure mempty }}} This would let me use `fold` and `foldMap` over `ST` computations, which would occasionally be useful. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14837> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14836: GHC fails to infer implied superclass constraint
by GHC 21 Feb '18

21 Feb '18

#14836: GHC fails to infer implied superclass constraint -------------------------------------+------------------------------------- Reporter: crockeea | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | 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: -------------------------------------+------------------------------------- The following code should compile, but does not. {{{ {-# LANGUAGE FlexibleInstances, UndecidableInstances #-} module Bug where class (Monad m) => RequiresMonad m where class (Monad m) => ImpliesMonad m where instance (ImpliesMonad m) => RequiresMonad m where }}} The basic idea is that I put the constraint `ImpliesMonad m` on the `RequiresMonad` instance, which does in fact imply `Monad m`. However, GHC complains: {{{ • Could not deduce (Monad m) arising from the superclasses of an instance declaration from the context: ImpliesMonad m bound by the instance declaration at Bug.hs:9:10-44 Possible fix: add (Monad m) to the context of the instance declaration • In the instance declaration for ‘RequiresMonad m’ }}} Of course, GHC is perfectly happy if I replace the instance constraint `ImpliesMonad m` with `Monad m`. Possibly related to #10338 or #11948. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14836> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14328: ld.gold -r brokenness breaks SplitSections=YES builds
by GHC 21 Feb '18

21 Feb '18

#14328: ld.gold -r brokenness breaks SplitSections=YES builds -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: 14291 | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- See https://sourceware.org/bugzilla/show_bug.cgi?id=22266. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14328> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #14564: CAF isn't floated
by GHC 21 Feb '18

21 Feb '18

#14564: CAF isn't floated -------------------------------------+------------------------------------- Reporter: neil.mayhew | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.2 Keywords: | 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: -------------------------------------+------------------------------------- In the following code, `pattern` isn't floated, and the execution time is 20x slower than it should be: {{{#!hs import Text.Regex.TDFA (Regex, makeRegex, match) main :: IO () main = do entries <- map parseFilename . lines <$> getContents let check (Right (_, t)) = last t == 'Z' check _ = False print $ all check entries parseFilename :: String -> Either String (String, String) parseFilename fn = case (pattern `match` fn :: [[String]]) of [[_, full, _, time]] -> Right $ (full, time) _ -> Left fn where pattern :: Regex pattern = makeRegex "^\\./duplicity-(full|inc|new)(-signatures)?\\.\ \([0-9][0-9][0-9][0-9][0-9][0-9][0-9][0-9]T[0-9][0-9][0-9][0-9][0-9][0-9]Z)\\." }}} Curiously, it is floated when profiling is enabled, so the profiled program ends up being 7x faster than the unprofiled one. I can float the code manually (by taking out `where` and unindenting) and the program then runs at an acceptable speed. I get the same behaviour with 8.0.2, 8.2.1 and 8.2.2 but 7.10.3 is OK. I don't think the OS and architecture makes a difference, but for the record I'm on various flavours of 64-bit Linux. Test input data is [https://gist.github.com/neilmayhew/247a30738c0e294902e7c2830ca2c6f5 here] -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14564> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5927: A type-level "implies" constraint on Constraints
by GHC 21 Feb '18

21 Feb '18

#5927: A type-level "implies" constraint on Constraints -------------------------------------+------------------------------------- Reporter: illissius | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.4.1 checker) | Keywords: Resolution: | QuantifiedConstraints Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by kcsongor): * cc: kcsongor (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5927#comment:29> 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): (the text below is also attached as file "analyse") {{{ NoFib Results -------------------------------------------------------------------------------- Program Size Allocs Runtime Elapsed TotalMem -------------------------------------------------------------------------------- CS 0.0% 0.0% 0.156 0.156 0.0% CSD 0.0% 0.0% -19.8% -19.8% 0.0% FS 0.0% 0.0% -7.0% -7.0% 0.0% S 0.0% 0.0% -11.6% -11.6% 0.0% VS 0.0% 0.0% -5.5% -5.6% 0.0% VSD 0.0% 0.0% 0.009 0.009 0.0% VSM 0.0% 0.0% -14.3% -14.3% 0.0% anna +0.2% +0.0% 0.056 0.056 0.0% ansi 0.0% 0.0% 0.000 0.000 0.0% atom +0.0% 0.0% 0.136 0.136 0.0% awards +0.0% 0.0% 0.000 0.000 0.0% banner +0.0% 0.0% 0.000 0.000 0.0% bernouilli -0.0% 0.0% 0.095 0.095 0.0% binary-trees +0.0% 0.0% -8.5% -8.5% 0.0% boyer +0.0% -0.0% 0.024 0.024 0.0% boyer2 0.0% -2.1% 0.006 0.006 0.0% bspt +0.1% +0.2% 0.006 0.006 +50.0% cacheprof +0.2% -0.0% 0.191 0.191 -1.8% calendar +0.1% +0.0% 0.001 0.001 0.0% cichelli -0.0% 0.0% 0.042 0.042 -2.7% circsim +0.1% +0.2% -2.6% -2.6% -2.8% clausify +0.1% +0.0% 0.020 0.021 0.0% comp_lab_zift -0.0% -0.3% 0.097 0.097 -11.1% compress 0.0% 0.0% 0.076 0.076 0.0% compress2 +0.1% -0.0% 0.078 0.078 0.0% constraints +0.1% +0.6% +0.4% +0.3% -0.8% cryptarithm1 0.0% 0.0% -0.9% -0.7% 0.0% cryptarithm2 +0.0% 0.0% 0.005 0.005 0.0% cse +0.0% +0.2% 0.001 0.001 0.0% digits-of-e1 0.0% 0.0% +2.0% +2.0% 0.0% digits-of-e2 -0.1% +0.0% -3.2% -3.2% 0.0% eliza +0.0% -0.0% 0.001 0.001 0.0% event +0.1% +0.0% 0.075 0.075 0.0% exact-reals +0.2% 0.0% +1.2% +1.2% 0.0% exp3_8 0.0% 0.0% 0.125 0.125 0.0% expert +0.1% +0.1% 0.000 0.001 0.0% fannkuch-redux 0.0% 0.0% -6.1% -6.1% 0.0% fasta +0.0% 0.0% +54.1% +53.9% 0.0% fem +0.0% -0.0% 0.015 0.015 0.0% fft +0.0% +0.0% 0.024 0.024 0.0% fft2 +0.0% 0.0% 0.045 0.045 0.0% fibheaps +0.0% 0.0% 0.016 0.016 0.0% fish 0.0% 0.0% 0.006 0.006 0.0% fluid +0.2% +0.3% 0.005 0.005 0.0% fulsom +0.1% 0.0% 0.136 0.136 0.0% gamteb -0.1% -0.1% 0.022 0.022 0.0% gcd 0.0% 0.0% 0.025 0.025 0.0% gen_regexps -0.0% 0.0% 0.000 0.000 0.0% genfft -0.0% -0.2% 0.019 0.019 0.0% gg +0.1% +0.0% 0.008 0.008 0.0% grep +0.0% 0.0% 0.000 0.000 0.0% hidden -0.0% -0.2% 0.193 0.193 0.0% hpg +0.0% 0.0% 0.068 0.068 0.0% ida +0.1% +0.4% 0.048 0.048 0.0% infer +0.0% 0.0% 0.033 0.033 0.0% integer 0.0% 0.0% -1.0% -1.0% 0.0% integrate 0.0% 0.0% 0.060 0.060 0.0% k-nucleotide -0.0% 0.0% -10.6% -10.8% 0.0% kahan 0.0% 0.0% 0.172 0.172 0.0% knights 0.0% 0.0% 0.004 0.004 0.0% lambda 0.0% 0.0% -1.4% -1.4% 0.0% last-piece -0.1% -1.2% -3.5% -3.6% 0.0% lcss +0.0% 0.0% +0.3% +0.4% 0.0% life -0.0% 0.0% 0.124 0.124 0.0% lift +0.0% 0.0% 0.001 0.001 0.0% linear +0.1% 0.0% +7.2% +7.2% 0.0% listcompr +0.0% -0.0% 0.051 0.051 0.0% listcopy +0.0% -0.0% 0.052 0.052 0.0% maillist +0.1% +0.0% 0.034 0.034 +2.7% mandel 0.0% 0.0% 0.033 0.033 0.0% mandel2 +0.0% -11.3% 0.004 0.004 0.0% mate -0.2% +5.0% -17.9% -17.9% 0.0% minimax 0.0% 0.0% 0.002 0.002 0.0% mkhprog 0.0% 0.0% 0.001 0.001 0.0% multiplier +0.0% -0.0% 0.052 0.052 0.0% n-body -0.0% -0.1% -1.9% -1.9% 0.0% nucleic2 -0.3% +1.5% 0.035 0.035 0.0% para +0.2% +1.3% 0.148 0.148 0.0% paraffins +0.0% 0.0% 0.065 0.065 0.0% parser +0.0% 0.0% 0.017 0.017 0.0% parstof +0.2% 0.0% 0.004 0.004 0.0% pic -0.0% -1.0% 0.005 0.005 0.0% pidigits +0.0% 0.0% -3.2% -3.2% 0.0% power +0.3% 0.0% 0.190 0.191 0.0% pretty 0.0% 0.0% 0.000 0.000 0.0% primes +0.0% 0.0% 0.041 0.041 0.0% primetest -0.0% -0.2% 0.061 0.061 0.0% prolog +0.0% -0.0% 0.001 0.001 0.0% puzzle +0.2% 0.0% 0.068 0.068 0.0% queens 0.0% 0.0% 0.012 0.012 0.0% reptile +0.1% +0.0% 0.007 0.007 0.0% reverse-complem 0.0% 0.0% 0.078 0.078 0.0% rewrite +0.1% -0.0% 0.011 0.011 0.0% rfib 0.0% 0.0% 0.009 0.009 0.0% rsa +0.0% -0.0% 0.017 0.017 0.0% scc 0.0% 0.0% 0.000 0.000 0.0% sched +0.1% -0.0% 0.013 0.013 0.0% scs -0.3% +0.0% -1.5% -1.5% 0.0% simple -0.1% -0.7% 0.109 0.109 0.0% solid +0.1% -0.1% 0.063 0.063 0.0% sorting +0.0% 0.0% 0.002 0.002 0.0% spectral-norm 0.0% 0.0% -0.1% -0.1% 0.0% sphere +0.0% 0.0% 0.026 0.026 0.0% symalg +0.0% 0.0% 0.007 0.007 0.0% tak 0.0% 0.0% 0.006 0.006 0.0% transform -0.0% -0.8% 0.165 0.165 0.0% treejoin 0.0% 0.0% 0.077 0.077 0.0% typecheck +0.1% -0.0% 0.131 0.131 0.0% veritas +0.0% 0.0% 0.001 0.001 0.0% wang +0.1% -0.0% 0.053 0.053 0.0% wave4main +0.0% 0.0% 0.125 0.125 0.0% wheel-sieve1 0.0% 0.0% -0.2% -0.2% 0.0% wheel-sieve2 +0.0% 0.0% 0.116 0.116 0.0% x2n1 +0.0% 0.0% 0.003 0.003 0.0% -------------------------------------------------------------------------------- Min -0.3% -11.3% -19.8% -19.8% -11.1% Max +0.3% +5.0% +54.1% +53.9% +50.0% Geometric Mean +0.0% -0.1% -2.8% -2.8% +0.2% }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/6087#comment:33> 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 simonpj): Bottom line seems to be: * Nofib results are no better, but no worse * Some examples/tickets (which specifically?) really do improve. Conclusion: let's do it. Ensuring that a Note gives a clear explanation, and points to this ticket. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7206#comment:27> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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