November 2015 - ghc-tickets

[GHC] #10678: integer-gmp's runS seems unnecessarily expensive
by GHC 13 Nov '15

13 Nov '15

#10678: integer-gmp's runS seems unnecessarily expensive -------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1 (CodeGen) | Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Runtime Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- integer-gmp uses an unsafePerformIO-like operation to work with mutable BigNats (unsafePerformIO and even the IO type are not yet available, since integer-gmp is a dependency of base): {{{ type S s a = State# s -> (# State# s, a #) -- NB: equivalent of GHC.IO.unsafeDupablePerformIO, see notes there runS :: S RealWorld a -> a runS m = lazy (case m realWorld# of (# _, r #) -> r) {-# NOINLINE runS #-} }}} It's tempting to think of such an operation as "free" like an unsafeCoerce, but it is actually somewhat expensive. Consider `plusBigNat` for instance. (Most BigNat operations have a similar structure.) {{{ plusBigNat :: BigNat -> BigNat -> BigNat plusBigNat x y | isTrue# (eqBigNatWord# x 0##) = y | isTrue# (eqBigNatWord# y 0##) = x | isTrue# (nx# >=# ny#) = go x nx# y ny# | True = go y ny# x nx# where go (BN# a#) na# (BN# b#) nb# = runS $ do mbn@(MBN# mba#) <- newBigNat# na# (W# c#) <- liftIO (c_mpn_add mba# a# na# b# nb#) case c# of 0## -> unsafeFreezeBigNat# mbn _ -> unsafeSnocFreezeBigNat# mbn c# nx# = sizeofBigNat# x ny# = sizeofBigNat# y }}} The assembly for `go` begins {{{ 00000000000001d0 <integerzmgmp_GHCziIntegerziType_zdwgo_info>: 1d0: 49 83 c4 28 add $0x28,%r12 1d4: 4d 3b a5 58 03 00 00 cmp 0x358(%r13),%r12 1db: 77 26 ja 203 <integerzmgmp_GHCziIntegerziType_zdwgo_info+0x33> 1dd: 49 c7 44 24 e0 00 00 movq $0x0,-0x20(%r12) 1e4: 00 00 1e2: R_X86_64_32S .text+0x38 1e6: 4d 89 74 24 e8 mov %r14,-0x18(%r12) 1eb: 49 89 7c 24 f0 mov %rdi,-0x10(%r12) 1f0: 49 89 74 24 f8 mov %rsi,-0x8(%r12) 1f5: 4d 89 04 24 mov %r8,(%r12) 1f9: 4d 8d 74 24 e1 lea -0x1f(%r12),%r14 1fe: e9 00 00 00 00 jmpq 203 <integerzmgmp_GHCziIntegerziType_zdwgo_info+0x33> 1ff: R_X86_64_PC32 integerzmgmp_GHCziIntegerziType_runS_info-0x4 203: ... ; heap overflow }}} This allocates a 5-word closure (containing `a#`, `na#`, `b#`, `nb#`) whose code is at `.text+0x38` and passes it to `runS`, which does some `stg_ap`-y things to call back into the closure, which reads its free variables back from the heap and finally does all the real work. Altogether it's around two dozen instructions compared to if we could call directly from `go` to the argument of `runS`. The old integer-gmp somehow avoided this particular overhead by instead using the implicit "unsafePerformIO" of a foreign import prim which performed both the allocation and the addition. Is this overhead a necessary consequence of doing the work in multiple steps in Haskell? I understand that we cannot allow everything to be inlined and, for example, the `newBigNat#` to be shared between a `plusBigNat` and `minusBigNat` with the same arguments. But once `runS` has done its job of keeping the `newBigNat#/c_mpn_add/unsafeFreeze*` together, it would be nice to eliminate it completely in the backend when compiling `go`, or any inlined version of `go`. I'm not sure whether this should be fixed in the code generator or in integer-gmp itself. I'm also aware that this is a tricky subject but haven't really done my homework on the related tickets, so I might be missing something important! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10678> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10061: Remove fun_infix from Funbind, as it is now in Match
by GHC 13 Nov '15

13 Nov '15

#10061: Remove fun_infix from Funbind, as it is now in Match -------------------------------------+------------------------------------- Reporter: alanz | Owner: Type: task | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.10.1-rc2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: #9988 Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- One of the changes Phab:D538 introduced is to add m_fun_id_infix to Match {{{#!hs data Match id body = Match { m_fun_id_infix :: (Maybe (Located id,Bool)), -- fun_id and fun_infix for functions with multiple equations -- only present for a RdrName. See note [fun_id in Match] m_pats :: [LPat id], -- The patterns m_type :: (Maybe (LHsType id)), -- A type signature for the result of the match -- Nothing after typechecking m_grhss :: (GRHSs id body) } deriving (Typeable) }}} This was done to track the individual locations and fixity of the fun_id for each of the defining equations for a function when there are more than one. For example, the function (&&&) is defined with some prefix and some infix equations below. {{{#!hs (&&& ) [] [] = [] xs &&& [] = xs ( &&& ) [] ys = ys }}} This means that the fun_infix is now superfluous in the FunBind. This has not been removed as a potentially risky change just before 7.10 RC2, and so must be done after. This ticket captures that task, which includes processing these fields through the renamer and beyond. Ticket #9988 introduced these fields into Match through renaming, this ticket it to continue through type checking and then remove it from FunBind completely. The split happened so that #9988 could land in 7.10 -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10061> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10942: CPP pragma ignored if top comments and Opt_KeepRawTokenStream
by GHC 13 Nov '15

13 Nov '15

#10942: CPP pragma ignored if top comments and Opt_KeepRawTokenStream -------------------------------------+------------------------------------- Reporter: alanz | Owner: alanz Type: bug | Status: new Priority: normal | Milestone: 8.0.1 Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | -------------------------------------+------------------------------------- HaRe sets `Opt_KeepRawTokenStream` to be able to round trip the source code. If we have a module starting {{{#!hs {- A normal comment, to check if we can still pick up the CPP directive after it. -} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE CPP #-} -- Check that we can parse a file which requires CPP module BCpp where bob :: Int -> Int -> Int #if __GLASGOW_HASKELL__ > 704 bob x y = x + y #else bob x y = x + y * 2 #endif }}} then the call to `loadTargets` via the GHC API fails with `SourceError (lexical error at character 'i'` which is the normal error when `#if` is hit and CPP is not enabled. If `Opt_KeepRawTokenStream` is not set it loads without problems. Also, files using CPP but not having a top comment load properly too. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10942> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10172: Cross-platform sed
by GHC 12 Nov '15

12 Nov '15

#10172: Cross-platform sed -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Build | Version: 7.11 System | Operating System: Solaris Keywords: | Type of failure: None/Unknown Architecture: | Blocked By: Unknown/Multiple | Related Tickets: Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- It's quite easy to accidentally use GNU extensions in sed expressions, which means Solaris builds start failing. See https://phabricator.haskell.org/D740 for an example. What should we do? Here are a few possibilities: * Force use of POSIX sed with `--posix` flag. I haven't tested, but maybe this won't work if Solaris sed chokes on the `--posix`. Alternately, use `$(SED)` and add `--posix` only if it's supported * Detect GNU sed in autoconfigure and use `$(SED)` in all Makefile scripts * Stop using sed in the scripts for something else I don't know if this admonition applies to other random POSIX tools we use. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10172> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5467: Template Haskell: support for Haddock comments
by GHC 11 Nov '15

11 Nov '15

#5467: Template Haskell: support for Haddock comments -------------------------------------+------------------------------------- Reporter: reinerp | Owner: Type: feature request | Status: new Priority: normal | Milestone: 8.0.1 Component: Template Haskell | Version: 7.2.1 Resolution: | Keywords: 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 ekmett): * cc: ekmett (added) -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5467#comment:17> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Re: [GHC] #5467: Template Haskell: support for Haddock comments
by GHC 11 Nov '15

11 Nov '15

#5467: Template Haskell: support for Haddock comments -------------------------------------+------------------------------------- Reporter: reinerp | Owner: Type: feature request | Status: new Priority: normal | Milestone: 8.0.1 Component: Template Haskell | Version: 7.2.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by ekmett): This has been the cause of a standing issue for `lens` for some time. https://github.com/ekmett/lens/issues/614 is the latest incarnation of it. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/5467#comment:16> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #11079: Add ability to access and generate haddock-style comments through template haskell
by GHC 11 Nov '15

11 Nov '15

#11079: Add ability to access and generate haddock-style comments through template haskell -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: feature | Status: new request | Priority: normal | Milestone: Component: Template | Version: 7.10.2 Haskell | 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: -------------------------------------+------------------------------------- We've had a number of suggestions throughout the last few years that we either by default or by option permit the copying of comments from the original field to the lenses we generates via `template-haskell`. There isn't a way to do this currently. Ideally we'd be able to access the haddocks associated with a name and generate comments as a form of declaration suitable for the top level or in a class definition. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/11079> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10870: PPC.Ppr: Shift by 32 bits is not allowed.
by GHC 11 Nov '15

11 Nov '15

#10870: PPC.Ppr: Shift by 32 bits is not allowed. -------------------------------------+------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 (CodeGen) | Keywords: | Operating System: Unknown/Multiple Architecture: powerpc | Type of failure: None/Unknown Test Case: | Blocked By: Blocking: | Related Tickets: Differential Revisions: | -------------------------------------+------------------------------------- Hi, when compiling `vector-algorithms` on powerpc, I get {{{ [ 7 of 10] Compiling Data.Vector.Algorithms.Tim ( src/Data/Vector/Algorithms/Tim.hs, dist- ghc/build/Data/Vector/Algorithms/Tim.o ) ghc: panic! (the 'impossible' happened) (GHC version 7.10.2 for powerpc-unknown-linux): PPC.Ppr: Shift by 32 bits is not allowed. }}} I do not get this error on other 32bit architectures. The offending code seems to be {{{ minrun :: Int -> Int minrun n0 = (n0 `unsafeShiftR` extra) + if (lowMask .&. n0) > 0 then 1 else 0 where -- smear the bits down from the most significant bit !n1 = n0 .|. unsafeShiftR n0 1 !n2 = n1 .|. unsafeShiftR n1 2 !n3 = n2 .|. unsafeShiftR n2 4 !n4 = n3 .|. unsafeShiftR n3 8 !n5 = n4 .|. unsafeShiftR n4 16 !n6 = n5 .|. unsafeShiftR n5 32 }}} The call to panic was introduced by Erik in the fix for #5900. Is the code at fault, or the compiler? -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10870> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #10974: Fix SysTools.readElfSection on platforms where "readelf" have different name
by GHC 11 Nov '15

11 Nov '15

#10974: Fix SysTools.readElfSection on platforms where "readelf" have different name -------------------------------------+------------------------------------- Reporter: ony | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.2 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Other Unknown/Multiple | Test Case: | Blocked By: driver/recomp011 | Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Some linux systems may use target-prefixed names for `binutils`. For example on my Exherbo Linux readelf is named as `x86_64-pc-linux-gnu- readelf`. This leads to errors like: > readelf: createProcess: runInteractiveProcess: exec: does not exist (No such file or directory) To fix this GHC needs to give ability to configure name of this tool (like `SysTools.runSplit` and `SysTools.runCc`) or use `libelf`-like library. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10974> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9988: Remove fun_id, is_infix from FunBind, as they are now in Match
by GHC 11 Nov '15

11 Nov '15

#9988: Remove fun_id, is_infix from FunBind, as they are now in Match -------------------------------------+------------------------------------- Reporter: alanz | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.1-rc1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Blocked By: Test Case: | Related Tickets: Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- One of the changes Phab:D538 introduced is to add m_fun_id_infix to Match {{{#!hs data Match id body = Match { m_fun_id_infix :: (Maybe (Located id,Bool)), -- fun_id and fun_infix for functions with multiple equations -- only present for a RdrName. See note [fun_id in Match] m_pats :: [LPat id], -- The patterns m_type :: (Maybe (LHsType id)), -- A type signature for the result of the match -- Nothing after typechecking m_grhss :: (GRHSs id body) } deriving (Typeable) }}} This was done to track the individual locations and fixity of the fun_id for each of the defining equations for a function when there are more than one. For example, the function (&&&) is defined with some prefix and some infix equations below. {{{#!hs (&&& ) [] [] = [] xs &&& [] = xs ( &&& ) [] ys = ys }}} This means that the fun_id / is_infix is now superfluous in the FunBind. This has not been removed as a potentially risky change just before 7.10 RC2, and so must be done after. This ticket captures that task. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9988> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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