May 2017 - ghc-tickets

[GHC] #13344: Core string literal patch regresses compiler performance considerably
by GHC 15 Aug '17

15 Aug '17

#13344: Core string literal patch regresses compiler performance considerably -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 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: -------------------------------------+------------------------------------- The Core string literals patch regresses compiler performance by nearly 5%. https://perf.haskell.org/ghc/#revision/d49b2bb21691892ca6ac8f2403e31f2a5e53… We should really understand why this is; this is a huge regression for something that really shouldn't be costly. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13344> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13390: Strict literal float-out during desugaring regresses T1969 at -O0
by GHC 15 Aug '17

15 Aug '17

#13390: Strict literal float-out during desugaring regresses T1969 at -O0 -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.2.1 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: -------------------------------------+------------------------------------- Phab:D1259, which teaches the compiler to aggressively float-out string literals during desugaring, regresses compiler allocations on `T1969` by 15% or so at -O0`. = The problem = In the case of `T1969` (compiled with `-O0`) the difference is quite stark: with floating the non-optimizing simplifier pass produces `{terms: 16,893, types: 7,552, coercions: 0, joins: 0/0}`, without it produces `{terms: 12,693, types: 4,552, coercions: 0, joins: 0/0}`. The (minimized) test looks like, {{{#!hs module T1969 where class C a where c :: a -> String d :: a -> String d x = c x e :: a -> String e x = c x data A1 = A1 instance C A1 where c A1 = "A1" }}} == Post-desugar == The reason for the regression is in part due to the fact that we float out the `unpackCString# "An"` expression. That is, after desugaring without floating we get (looking at just the `A1` bindings), {{{#!hs T1969.$dme :: forall a. C a => a -> String T1969.$dme = \ (@ a_aM1) ($dC_a1h9 :: C a_aM1) (x_aM3 :: a_aM1) -> c @ a_aM1 $dC_a1h9 x_aM3 -- same as $dme T1969.$dmd :: forall a. C a => a -> String T1969.$dmd = \ (@ a_aM1) ($dC_a1h9 :: C a_aM1) (x_aM2 :: a_aM1) -> c @ a_aM1 $dC_a1h9 x_aM2 $cc_a1i7 :: A1 -> String $cc_a1i7= \ (ds_d1jJ :: A1) -> case ds_d1jJ of { A1 -> GHC.CString.unpackCString# "A1"# } Rec { T1969.$fCA3 :: C A3 T1969.$fCA3 = T1969.C:C @ A3 $cc_a1hl $cd_a1hp $ce_a1hy $ce_a1hy :: A3 -> String $ce_a1hy = T1969.$dme @ A3 T1969.$fCA3 $cd_a1hp :: A3 -> String $cd_a1hp = T1969.$dmd @ A3 T1969.$fCA3 end Rec } }}} Whereas with floating we get, {{{#!hs -- same as above T1969.$dme :: forall a. C a => a -> String T1969.$dmd :: forall a. C a => a -> String ds_d1k4 :: [Char] ds_d1k4 = GHC.CString.unpackCString# "A1"# $cc_a1i7 :: A1 -> String $cc_a1i7 = \ (ds_d1k3 :: A1) -> case ds_d1k3 of { A1 -> ds_d1k4 } Rec { T1969.$fCA1 :: C A1 T1969.$fCA1 = T1969.C:C @ A1 $cc_a1i7 $cd_a1ib $ce_a1ik $ce_a1ik :: A1 -> String $ce_a1ik = T1969.$dme @ A1 T1969.$fCA1 $cd_a1ib :: A1 -> String $cd_a1ib = T1969.$dmd @ A1 T1969.$fCA1 end Rec } }}} So far things aren't so bad: the only interesting difference is the floated `[Char]`, which we would expect. However, let's then see what happens during simplification. == Post-simplification == Without floating we see, {{{#!hs T1969.$fCA1 :: C A1 T1969.$fCA1 = T1969.C:C @ A1 $cc_a1i7 $cc_a1i7 $cc_a1i7 $cc_a1i7 :: A1 -> String $cc_a1i7 = \ (ds_d1jJ :: A1) -> case ds_d1jJ of { A1 -> GHC.CString.unpackCString# "A1"# } }}} Whereas with floating we have, {{{#!hs ds_d1k4 :: [Char] ds_d1k4 = GHC.CString.unpackCString# "A1"# $cc_a1i7 :: A1 -> String $cc_a1i7 = \ (ds_d1k3 :: A1) -> case ds_d1k3 of { A1 -> ds_d1k4 } $cd_a1ib :: A1 -> String $cd_a1ib = \ (x_aM2 :: A1) -> case x_aM2 of { A1 -> ds_d1k4 } $ce_a1ik :: A1 -> String $ce_a1ik = \ (x_aM3 :: A1) -> case x_aM3 of { A1 -> ds_d1k4 } T1969.$fCA1 :: C A1 T1969.$fCA1 = T1969.C:C @ A1 $cc_a1i7 $cd_a1ib $ce_a1ik }}} This is quite interesting: without floating we are somehow able to collapse each of the `A1 -> String` bindings into a single binding (despite CSE being disabled due to `-O0`!). -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13390> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10809: Add prefetch{Small}{Mutable}Array[0..3]#
by GHC 15 Aug '17

15 Aug '17

#10809: Add prefetch{Small}{Mutable}Array[0..3]# -------------------------------------+------------------------------------- Reporter: ekmett | Owner: simonmar Type: feature | Status: new request | Priority: normal | Milestone: Component: Runtime | Version: 7.10.2 System | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- We now have a number of prefetch operations: {{{ prefetchAddr0# prefetchMutableByteArray0# prefetchAddr1# prefetchMutableByteArray1# prefetchAddr2# prefetchMutableByteArray2# prefetchAddr3# prefetchMutableByteArray3# prefetchByteArray0# prefetchValue0# prefetchByteArray1# prefetchValue1# prefetchByteArray2# prefetchValue2# prefetchByteArray3# prefetchValue3# }}} but we are missing variants for fetching slots of a `{Small}{Mutable}Array#`. This differs from fetching the item pointed to by the entry at that address, so `prefetchValueX` does us no good there. Basically this just needs to compute the offset of the appropriate slot and prefetch the memory for that portion of the array as an address like we do indexing into a byte array. I have some code that could benefit a fair bit from being able to prefetch a binary search on array elements this way, when storing those elements either in a traditional sorted order or Eytzinger layout. I've verified this experimentally by unsafeCoercing existing bytearray primitives to make them work on other array types. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10809> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12553: Reference kind in a type instance declaration defined in another instance declaration
by GHC 15 Aug '17

15 Aug '17

#12553: Reference kind in a type instance declaration defined in another instance declaration -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: 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: -------------------------------------+------------------------------------- Old code: {{{#!hs data Full :: Type -> Type data AST :: (Type -> Type) -> (Type -> Type) -- ASTF :: (Type -> Type) -> (Type -> Type) type ASTF dom a = AST dom (Full a) class Syntactic a where type Domain a :: Type -> Type type Internal a :: Type desugar :: a -> ASTF (Domain a) (Internal a) sugar :: ASTF (Domain a) (Internal a) -> a }}} ---- New code with richer kinds {{{#!hs data Sig a = Full a | a :-> Sig a data AST :: (Sig a -> Type) -> (Sig a -> Type) data Sig a = Full a | a :-> Sig a -- ASTF :: (Sig a -> Type) -> (a -> Type) type ASTF dom a = AST dom (Full a) class Syntactic a where type Domain a :: Sig Type -> Type type Internal a :: Type desugar :: a -> ASTF (Domain a) (Internal a) sugar :: ASTF (Domain a) (Internal a) -> a }}} As the type of `ASTF` hints at it could accept arguments of kind `Sig a -> Type` and `a`. I would like to reference the variable `a` from the kind of `Domain` in the kind of `Internal`, but this fails: {{{#!hs -- • Kind variable ‘u’ is implicitly bound in datatype -- ‘Internal’, but does not appear as the kind of any -- of its type variables. Perhaps you meant -- to bind it (with TypeInType) explicitly somewhere? -- Type variables with inferred kinds: a -- • In the class declaration for ‘Syntactic’ class Syntactic a where type Domain a :: Sig u -> Type type Internal a :: u desugar :: a -> ASTF (Domain a) (Internal a) sugar :: ASTF (Domain a) (Internal a) -> a }}} ---- Should the `u` in the kind of `Domain a` be quantified over (which makes this compile)? {{{#!hs type Domain a :: forall k. Sig k -> Type }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12553> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13364: Remove checkValidTelescope
by GHC 15 Aug '17

15 Aug '17

#13364: Remove checkValidTelescope -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: task | 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: -------------------------------------+------------------------------------- All of this new `TypeInType` nonsense has provided a number of ways that we can arrive at ill-scoped kinds. Let's assume we have {{{ data SameKind :: k -> k -> Type }}} and then here are three subtly ill-scoped kinds: {{{ forall a (b :: a) (c :: Proxy d). SameKind b d forall a. forall (b :: a). forall (c :: Proxy d). SameKind b d forall d. forall a (b :: a). SameKind b d }}} Despite the close similarity between these cases, they are all handled separately. See `Note [Bad telescopes]` in !TcValidity for an overview, but these are spread between `tcImplicitTKBndrsX`, `tcExplicitTKBndrsX`, and those functions' calls to `checkValidTelescope`, `checkZonkValidTelescope`, and `checkValidInferredKinds`. While I am unaware of a concrete bug this all causes, it's a mess. Better would be to use the existing machinery to prevent skolem-escape: `TcLevel`s and implication constraints. Specifically, it's quite plausible that all this can be avoided by a simple rule: bump the `TcLevel` (and create an implication constraint) for ''every'' new type variable brought into scope (including implicitly). (Actually, implicit variables have an implicit ordering that GHC is free to decide, so all implicitly bound variables should be brought into scope at once, with just one bump in the `TcLevel`.) It might all just work! And then we can delete gobs of hairy code. Hooray! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13364> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #12931: tc_infer_args does not set in-scope set correctly
by GHC 15 Aug '17

15 Aug '17

#12931: tc_infer_args does not set in-scope set correctly -------------------------------------+------------------------------------- Reporter: johnleo | Owner: goldfire 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: #12549 #11371 | #12785 Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- As noted in https://ghc.haskell.org/trac/ghc/ticket/12785#comment:6, `TcHsType.tc_infer_args` does not set its in-scope set correctly, which means the call to `TcMType.new_meta_tv_x` will fail if `substTyUnchecked` is replaced by `substTy` in the line {{{ kind = substTyUnchecked subst (tyVarKind tv) }}} This is the only known caller of `new_meta_tv_x` to not set the in-scope set, now that #12549 has been fixed. Once this bug is fixed, change `substTyUnchecked` back to `substTy` in the line noted above. Note that other calls to `substTyUnchecked` that need to be converted to `substTy` are covered in the general ticket #11371. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12931> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13711: uname: illegal option -- o when running make clean in nofib
by GHC 15 Aug '17

15 Aug '17

#13711: uname: illegal option -- o when running make clean in nofib -------------------------------------+------------------------------------- Reporter: mpickering | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: NoFib | Version: 8.0.1 benchmark suite | 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: -------------------------------------+------------------------------------- When running `make clean` in nofib, there are lots of warnings/errors like the following. I don't know if this is serious or not. I am on OS X. {{{ uname: illegal option -- o usage: uname [-amnprsv] rm -f Main.o *.CKP *.ln *.BAK *.bak .*.bak *.o core a.out errs ,* *.a .emacs_* tags TAGS *.ind *.ilg *.idx *.idx-prev *.aux *.aux-prev *.dvi *.log *.toc *.lot *.lof *.blg *.cb *_stub.c *_stub.h *.raw_s *.a.list a.out ./*.hi Main.hc reverse-complement Finished making clean in reverse-complement: 0 ------------------------------------------------------------------------ == /Applications/Xcode.app/Contents/Developer/usr/bin/make clean - --no- print-directory; in /Users/matt/Documents/haskell/ghc/nofib/shootout/spectral-norm ------------------------------------------------------------------------ uname: illegal option -- o usage: uname [-amnprsv] }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13711> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13615: Wrong results from what supposed to be pure function with presense of parallel evaluation
by GHC 09 Aug '17

09 Aug '17

#13615: Wrong results from what supposed to be pure function with presense of parallel evaluation -------------------------------------+------------------------------------- Reporter: pacak | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1-rc2 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: -------------------------------------+------------------------------------- Mostly self contained sample - only depends on base, deepseq and locally provided hashable and unordered-containers. No unsafePtrEq involved, but unsafeThaw/Freese is - affected function uses `foldl'` to insert stuff into hashmap - I don't think there's a way to obtain multiple references to the same map. Making arguments strict or rnf'ing them doesn't help. Issue is reproduceable with HEAD with -O0 but not with O2. in ghc 8.0.2 and 7.10.1 it's reproduceable with -O2 as well. {{{ sum (map snd xs) = map snd (toList $ fromListWith (+) xs) }}} ^ this statement fails to hold when xs contains stuff with memocombinators and parallel evaluation from evaluation strategies I found which inplace update needs to be replaced with copy and update to make things work - bug is fixed after changing unsafeInsertWith, BitmapIndexed branch: {{{ - A.unsafeUpdateM ary i st' - return t + let ary' = A.update ary i st' + return $ BitmapIndexed b ary' }}} Steps: clone this: {{{ https://github.com/pacak/cuddly-bassoon }}} {{{ stack build }}} {{{ ./.stack-work/install/x86_64-linux/ghc-8.0.2/8.0.2/bin/gamebooksolver- solvebook02 }}} Last command will either finish successfully printing `"solving\n0.0"` or will die with `error` in `src/Solver.hs` `regroup` function. To reproduce the problem computer must have at least 3 CPUs, running with +RTS -N1 or -N2 "fixes" the problem. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13615> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8147: Exponential behavior in instance resolution on fixpoint-of-sum
by GHC 07 Aug '17

07 Aug '17

#8147: Exponential behavior in instance resolution on fixpoint-of-sum -------------------------+------------------------------------------------- Reporter: | Owner: jkoppel | Status: new Type: bug | Milestone: Priority: | Version: 7.6.3 normal | Operating System: Unknown/Multiple Component: | Type of failure: Compile-time performance bug Compiler | Test Case: Keywords: | Blocking: performance, | Architecture: | Unknown/Multiple | Difficulty: | Unknown | Blocked By: | Related Tickets: | -------------------------+------------------------------------------------- Doing instance resolution on a fixpoint-of-sum type takes a very long time. This is possibly the same issue as issue #5642. These are the numbers I see for various n: {{{ 10 : 0.329s 20 : 0.479s 40 : 0.935s 80 : 2.821s 160 : 11.694s 320 : 1m30.39s 640: Ran for over 1 hour without terminating }}} This uses a couple of attached support files. Apologies for not being able to reduce further. {{{ -- Test.hs {-# LANGUAGE MultiParamTypeClasses, FlexibleInstances, UndecidableInstances, OverlappingInstances, TypeOperators, DeriveFunctor, TemplateHaskell #-} module Test where import Control.Monad import Lib import TH {- With n=3, produces data X1 e = X1 e deriving (Functor) data X2 e = X2 e deriving (Functor) data X3 e = X3 e deriving (Functor) type X = X1 :+: X2 :+: X3 -} $(let n = 320 in liftM concat $ sequence [liftM concat $ mapM mkDec $ map (('X':).show) [1..n] , makeSumType "X" (map (('X':).show) [1..n])]) data Y0 e = Y0 e deriving ( Functor ) type X' = Y0 :+: X class Lift f g where lift' :: f (Fix g) -> Fix g instance (Lift f g, Lift f' g) => Lift (f :+: f') g where lift' x = case x of L e -> lift' e R e -> lift' e instance (Functor f, f :<: g) => Lift f g where lift' = In . inj cata :: (Functor f) => (f a -> a) -> Fix f -> a cata f = f . fmap (cata f) . out lift :: Fix X -> Fix X' lift = cata lift' }}} Virtually all the time is spent in compiling lift. For example, with n=640, commenting out lift makes it compile in around 2 seconds. Interestingly, when I add the following code, compilation times only increase by 10-20%. In the original code where I encountered this issue, doing so doubles compilation time. {{{ instance Lift Y0 X where lift' = undefined lower :: Fix X' -> Fix X lower = cata lift' }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8147> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #13190: Add a flag to dump compiler output as JSON
by GHC 07 Aug '17

07 Aug '17

#13190: Add a flag to dump compiler output as JSON -------------------------------------+------------------------------------- Reporter: mpickering | Owner: mpickering Type: feature | Status: new request | Priority: normal | Milestone: 8.2.1 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): Phab:D3010 | Wiki Page: -------------------------------------+------------------------------------- This ticket is to track the `-ddump-json` flag which is implemented by Phab:D3010. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13190> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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