November 2014 - ghc-tickets

[GHC] #9314: Huge space leak of GHC API 7.8.x
by GHC 07 Dec '16

07 Dec '16

#9314: Huge space leak of GHC API 7.8.x ------------------------------------+------------------------------------- Reporter: kazu-yamamoto | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHC API | Version: 7.8.3 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: Other Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- GHC API 7.8.x uses much more memory than GHC API 7.6.x. Attached two files demonstrate this: - A.hs -- Simple program using GHC API (copied from Wiki) - B.hs -- A target file, just hello world You can compile A.hs as follows: {{{ % ghc A.hs -package ghc -package ghc-paths }}} A.hs stays in 10 seconds. So, we can investigate its memory usage with the "top" command.The following is the result: {{{ Mac (64bit) Linux (64bit) GHC 7.6.3: 20MB 4MB GHC 7.8.3: 106MB 13MB }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9314> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8460: Annotation reification with types in TH
by GHC 07 Dec '16

07 Dec '16

#8460: Annotation reification with types in TH -------------------------------------------+------------------------------- Reporter: errge | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.8.1 Component: Compiler | Version: 7.7 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 hour) | Type of failure: Blocked By: | None/Unknown Related Tickets: #8397 | Test Case: | Blocking: -------------------------------------------+------------------------------- The attached patch adds two simple helper functions to support typed reification of annotations. This was not in the original #8397 patch only because the typed branch was not merged at that time. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8460> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9813: Error when reifying type constructor
by GHC 07 Dec '16

07 Dec '16

#9813: Error when reifying type constructor -------------------------------------+------------------------------------- Reporter: owst | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Unknown | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- The following code works under ghc-7.6.3 and template-haskell-2.8.0.0: {{{#!hs {-# LANGUAGE TemplateHaskell #-} data Huh = ThisDefinitely | UsedToWork constructorNames :: String constructorNames = $(do ty <- reify ''Huh let showCon (NormalC n _) = nameBase n strs = case ty of (TyConI (DataD _ _ _ cons _)) -> map showCon cons return . LitE . StringL $ concat strs) main = putStrLn constructorNames }}} Printing the following at compile time: {{{ [1 of 1] Compiling Main ( Main.hs, Main.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.4.0.1 ... linking ... done. Loading package deepseq-1.3.0.1 ... linking ... done. Loading package containers-0.5.0.0 ... linking ... done. Loading package pretty-1.1.1.0 ... linking ... done. Loading package template-haskell ... linking ... done. Linking Main ... }}} and then successfully executing: {{{ $ ./Main ThisDefinitelyUsedToWork }}} However, using ghc 7.8.3/template-haskell-2.9.0.0 I get the following compile error: {{{ [1 of 1] Compiling Main ( Main.hs, Main.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.5.0.0 ... linking ... done. Loading package deepseq-1.3.0.2 ... linking ... done. Loading package containers-0.5.5.1 ... linking ... done. Loading package pretty-1.1.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Main.hs:8:22: ‘Huh’ is not in the type environment at a reify In the splice: $(do { ty <- reify ''Huh; let showCon (NormalC n _) = ... ....; return . LitE . StringL $ concat strs }) }}} Is this expected? I couldn't see anything in the GHC release notes to suggest this should no longer work. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9813> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8224: Excessive system time -- new IO manager problem?
by GHC 06 Dec '16

06 Dec '16

#8224: Excessive system time -- new IO manager problem? -------------------------------------+------------------------------------- Reporter: rrnewton | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.1 Component: Runtime System | Version: 7.7 Keywords: IO Manager, | Operating System: Linux System Time | Type of failure: Runtime Architecture: x86_64 (amd64) | performance bug Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -------------------------------------+------------------------------------- This is an issue that came to light when testing the patches on #910. You can see some of the numbers there. Basically, recent GHC HEAD builds, running a large number of threads blocked on MVars will result in burning a lot of system time. The attached file provides a mediocre reproducer. With it, you can see that building with HEAD as of Aug 31st and running with `-RTS -N32` will result in around 200ms system time, whereas GHC 7.6.3 spends about 30ms in system time. This shows the disparity, but the result is not that egregious. A more noticeable example is on ticket #910, where when running on 31 threads, there is an 8 minutes of system time for 17 minutes of user time, and yet at one thread that system time drops to under two seconds! {{{ 1 thread: real 1m20.028s user 1m17.921s sys 0m1.768s 31 threads: real 1m27.445s user 17m0.314s sys 8m0.175s }}} It needs to be determined whether this system time is a result of the parallel compilation patches on #910, or whether it is a new problem with the runtime system, and in particular with the parallel IO manager. I am inclined to believe that compiling in parallel involves extra IO (repeatedly reading interface files?), but not eight minutes of it!! -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8224> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8848: Warning: Rule too complicated to desugar
by GHC 01 Dec '16

01 Dec '16

#8848: Warning: Rule too complicated to desugar ------------------------------------+------------------------------------- Reporter: carter | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1-rc2 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- I've a very very modest application of Specialize to fixed sized lists in some of my code which seems to trip up the specialization machinery. Is there any flags I can pass GHC to make sure it doesn't give up on these specialize calls? is the only work around to write my own monomorphic versions and add some hand written rewrite rules?! {{{ rc/Numerical/Types/Shape.hs:225:1: Warning: RULE left-hand side too complicated to desugar let { $dFunctor_a3XB :: Functor (Shape ('S 'Z)) [LclId, Str=DmdType] $dFunctor_a3XB = Numerical.Types.Shape.$fFunctorShape @ 'Z $dFunctor_a3Rn } in map2 @ a @ b @ c @ ('S ('S 'Z)) (Numerical.Types.Shape.$fApplicativeShape @ ('S 'Z) (Numerical.Types.Shape.$fFunctorShape @ ('S 'Z) $dFunctor_a3XB) (Numerical.Types.Shape.$fApplicativeShape @ 'Z $dFunctor_a3XB Numerical.Types.Shape.$fApplicativeShape0)) src/Numerical/Types/Shape.hs:226:1: Warning: RULE left-hand side too complicated to desugar let { $dFunctor_a3XG :: Functor (Shape ('S 'Z)) [LclId, Str=DmdType] $dFunctor_a3XG = Numerical.Types.Shape.$fFunctorShape @ 'Z $dFunctor_a3Rn } in let { $dFunctor_a3XF :: Functor (Shape ('S ('S 'Z))) [LclId, Str=DmdType] $dFunctor_a3XF = Numerical.Types.Shape.$fFunctorShape @ ('S 'Z) $dFunctor_a3XG } in map2 @ a @ b @ c @ ('S ('S ('S 'Z))) (Numerical.Types.Shape.$fApplicativeShape @ ('S ('S 'Z)) (Numerical.Types.Shape.$fFunctorShape @ ('S ('S 'Z)) $dFunctor_a3XF) (Numerical.Types.Shape.$fApplicativeShape @ ('S 'Z) $dFunctor_a3XF (Numerical.Types.Shape.$fApplicativeShape @ 'Z $dFunctor_a3XG Numerical.Types.Shape.$fApplicativeShape0))) }}} the associated code (smashed into a single module ) is {{{ {-# LANGUAGE DataKinds, GADTs, TypeFamilies, ScopedTypeVariables #-} {-# LANGUAGE DeriveDataTypeable #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE BangPatterns #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE CPP #-} {-# LANGUAGE DeriveFunctor #-} {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE NoImplicitPrelude #-} module Numerical.Types.Shape where import GHC.Magic import Data.Data import Data.Typeable() import Data.Type.Equality import qualified Data.Monoid as M import qualified Data.Functor as Fun import qualified Data.Foldable as F import qualified Control.Applicative as A import Prelude hiding (foldl,foldr,init,scanl,scanr,scanl1,scanr1) data Nat = S !Nat | Z deriving (Eq,Show,Read,Typeable,Data) #if defined(__GLASGOW_HASKELL_) && (__GLASGOW_HASKELL__ >= 707) deriving instance Typeable 'Z deriving instance Typeable 'S #endif type family n1 + n2 where Z + n2 = n2 (S n1') + n2 = S (n1' + n2) -- singleton for Nat data SNat :: Nat -> * where SZero :: SNat Z SSucc :: SNat n -> SNat (S n) --gcoerce :: (a :~: b) -> ((a ~ b) => r) -> r --gcoerce Refl x = x --gcoerce = gcastWith -- inductive proof of right-identity of + plus_id_r :: SNat n -> ((n + Z) :~: n) plus_id_r SZero = Refl plus_id_r (SSucc n) = gcastWith (plus_id_r n) Refl -- inductive proof of simplification on the rhs of + plus_succ_r :: SNat n1 -> Proxy n2 -> ((n1 + (S n2)) :~: (S (n1 + n2))) plus_succ_r SZero _ = Refl plus_succ_r (SSucc n1) proxy_n2 = gcastWith (plus_succ_r n1 proxy_n2) Refl type N0 = Z type N1= S N0 type N2 = S N1 type N3 = S N2 type N4 = S N3 type N5 = S N4 type N6 = S N5 type N7 = S N6 type N8 = S N7 type N9 = S N8 type N10 = S N9 {- Need to sort out packed+unboxed vs generic approaches see ShapeAlternatives/ for -} infixr 3 :* {- the concern basically boils down to "will it specialize / inline well" -} newtype At a = At a deriving (Eq, Ord, Read, Show, Typeable, Functor) data Shape (rank :: Nat) a where Nil :: Shape Z a (:*) :: !(a) -> !(Shape r a ) -> Shape (S r) a --deriving (Show) #if defined(__GLASGOW_HASKELL_) && (__GLASGOW_HASKELL__ >= 707) deriving instance Typeable Shape #endif instance Eq (Shape Z a) where (==) _ _ = True instance (Eq a,Eq (Shape s a))=> Eq (Shape (S s) a ) where (==) (a:* as) (b:* bs) = (a == b) && (as == bs ) instance Show (Shape Z a) where show _ = "Nil" instance (Show a, Show (Shape s a))=> Show (Shape (S s) a) where show (a:* as) = show a ++ " :* " ++ show as -- at some point also try data model that -- has layout be dynamicly reified, but for now -- keep it phantom typed for sanity / forcing static dispatch. -- NB: may need to make it more general at some future point --data Strided r a lay = Strided { getStrides :: Shape r a } {-# INLINE reverseShape #-} reverseShape :: Shape n a -> Shape n a reverseShape Nil = Nil reverseShape list = go SZero Nil list where go :: SNat n1 -> Shape n1 a-> Shape n2 a -> Shape (n1 + n2) a go snat acc Nil = gcastWith (plus_id_r snat) acc go snat acc (h :* (t :: Shape n3 a)) = gcastWith (plus_succ_r snat (Proxy :: Proxy n3)) (go (SSucc snat) (h :* acc) t) instance Fun.Functor (Shape Z) where fmap = \ _ Nil -> Nil --{-# INLINE fmap #-} instance (Fun.Functor (Shape r)) => Fun.Functor (Shape (S r)) where fmap = \ f (a :* rest) -> f a :* Fun.fmap f rest --{-# INLINE fmap #-} instance A.Applicative (Shape Z) where pure = \ _ -> Nil --{-# INLINE pure #-} (<*>) = \ _ _ -> Nil --{-# INLINE (<*>) #-} instance A.Applicative (Shape r)=> A.Applicative (Shape (S r)) where pure = \ a -> a :* (A.pure a) --{-# INLINE pure #-} (<*>) = \ (f:* fs) (a :* as) -> f a :* (inline (A.<*>)) fs as --{-# INLINE (<*>) #-} instance F.Foldable (Shape Z) where foldMap = \ _ _ -> M.mempty --{-# fold #-} foldl = \ _ init _ -> init foldr = \ _ init _ -> init foldr' = \_ !init _ -> init foldl' = \_ !init _ -> init instance (F.Foldable (Shape r)) => F.Foldable (Shape (S r)) where foldMap = \f (a:* as) -> f a M.<> F.foldMap f as foldl' = \f !init (a :* as) -> let next = f init a in next `seq` F.foldl f next as foldr' = \f !init (a :* as ) -> f a $! F.foldr f init as foldl = \f init (a :* as) -> let next = f init a in F.foldl f next as foldr = \f init (a :* as ) -> f a $ F.foldr f init as -- map2 :: (A.Applicative (Shape r))=> (a->b ->c) -> (Shape r a) -> (Shape r b) -> (Shape r c ) map2 = \f l r -> A.pure f A.<*> l A.<*> r {-# SPECIALIZE map2 :: (a->b->c)-> (Shape Z a )-> Shape Z b -> Shape Z c #-} {-# SPECIALIZE map2 :: (a->b->c)-> (Shape (S Z) a )-> Shape (S Z) b -> Shape (S Z) c #-} {-# SPECIALIZE map2 :: (a->b->c)-> (Shape (S (S Z)) a )-> Shape (S (S Z)) b -> Shape (S (S Z)) c #-} {-# SPECIALIZE map2 :: (a->b->c)-> (Shape (S (S(S Z))) a )-> Shape (S (S (S Z))) b -> Shape (S (S(S Z))) c #-} -- {-# INLINABLE map2 #-} }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8848> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9184: Allow the use of Python 3 when building GHC
by GHC 01 Dec '16

01 Dec '16

#9184: Allow the use of Python 3 when building GHC -------------------------------------------+------------------------------- Reporter: aspidites | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Build System | Version: 7.8.2 Keywords: python | Operating System: Architecture: Unknown/Multiple | Unknown/Multiple Difficulty: Easy (less than 1 hour) | Type of failure: Blocked By: | None/Unknown Related Tickets: | Test Case: | Blocking: -------------------------------------------+------------------------------- According to the [https://ghc.haskell.org/trac/ghc/wiki/Building/Preparation/Windows wiki], it is preferred that a user have Python 2.7 installed before attempting to build GHC. As I'm on Arch Linux the default Python version is 3.4. As such, rather than simply changing the shebang line to explicitly ask for version 2, I made it so that the scripts all use syntax that works properly for versions 2.7 to 3.4. I don't think I've used anything that disallows 2.6, but don't have that version available to check against. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9184> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8974: 64 bit windows executable built with ghc-7.9.20140405+LLVM segfaults
by GHC 29 Nov '16

29 Nov '16

#8974: 64 bit windows executable built with ghc-7.9.20140405+LLVM segfaults -----------------------------------+---------------------------------- Reporter: awson | Owner: Type: bug | Status: new Priority: high | Milestone: 7.8.2 Component: Compiler (LLVM) | Version: 7.9 Keywords: | Operating System: Windows Architecture: x86_64 (amd64) | Type of failure: Runtime crash Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | -----------------------------------+---------------------------------- {{{ -- test.hs import System.Mem (performMajorGC) main = performMajorGC >> putStrLn "Done" }}} built with `ghc -pgmlo opt -pgmlc llc -fllvm --make test.hs` segfaults both for LLVM 3.4 and 3.5svn (taken from http://sourceforge.net/projects/msys2/files/REPOS/MINGW/x86_64) 32-bit ghc-7.9.20140404+llvm produces good executable. Adding `ArchX86_64` `OSMinGW32` case to `moduleLayout` in `compiler/llvmGen/LlvmCodeGen/Ppr.hs` improves things slightly (some code segfaulting without it starts to work) but still does not cure the code above. Also I've found the Cmm produced for LLVM CG differs from that produced for NCG. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8974> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #9007: relocation R_X86_64_32 against `stg_CHARLIKE_closure' can not be used when making a shared object
by GHC 29 Nov '16

29 Nov '16

#9007: relocation R_X86_64_32 against `stg_CHARLIKE_closure' can not be used when making a shared object ----------------------------------+---------------------------------------- Reporter: nomeata | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.9 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Building GHC failed Unknown/Multiple | Test Case: Difficulty: Unknown | Blocking: Blocked By: | Related Tickets: | ----------------------------------+---------------------------------------- Building HEAD on Debian wheezy with the Debian packaging setup fails: {{{ configure: Building in-tree ghc-pwd /usr/bin/ld: utils/ghc-pwd/dist-boot/Main.o: relocation R_X86_64_32 against `stg_CHARLIKE_closure' can not be used when making a shared object; recompile with -fPIC utils/ghc-pwd/dist-boot/Main.o: could not read symbols: Bad value collect2: error: ld returned 1 exit status configure: error: Building ghc-pwd failed }}} http://deb.haskell.org/dailies/2014-04-16/ghc_7.9.20140416-0.daily_amd64.bu… This is possibly related to the Hardening flags added by Debian: {{{ ~ $ dpkg-buildflags --get LDFLAGS -Wl,-z,relro ~ $ dpkg-buildflags --get CFLAGS -g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror =format-security }}} Other related bug might be #3668 and https://bugs.debian.org/712228 I’ll disable the hardening flags and see if it helps. The error first occurred 2014-03-27. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/9007> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8300: split-objs doesn't split on LLVM
by GHC 22 Nov '16

22 Nov '16

#8300: split-objs doesn't split on LLVM ------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (LLVM) | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- `-split-objs` is allowed with `-fllvm`, but it doesn't really do anything. E.g. in my perf-llvm build I have a `libHSbase-4.7.0.0.a` with `Applicative__1.o`, `Arrow__1.o` etc. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8300> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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[GHC] #8321: improve basic block layout on LLVM backend by predicting stack/heap checks
by GHC 17 Nov '16

17 Nov '16

#8321: improve basic block layout on LLVM backend by predicting stack/heap checks ------------------------------------+------------------------------------- Reporter: rwbarton | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.10.1 Component: Compiler (LLVM) | Version: 7.7 Keywords: | Operating System: Unknown/Multiple Architecture: Unknown/Multiple | Type of failure: None/Unknown Difficulty: Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | ------------------------------------+------------------------------------- Currently we don't give the LLVM optimizer any information about which branch of an `if` is likely to be taken. As a result, the optimizer is likely to produce a basic block layout which is not optimal. Improving the layout can improve performance through better instruction cache usage and better branch prediction by the hardware. We can control LLVM's idea of what is likely with the `llvm.expect` intrinsic function. Some obvious branches which we can predict accurately are the stack and heap checks that appear near the entry of many functions. Here's a small example of some Cmm code and the output of the LLVM optimizer/compiler. {{{ block_c2Lc_entry() // [R1, R2] { info_tbl: [(c2Lc, label: block_c2Lc_info rep:StackRep [])] stack_info: arg_space: 0 updfr_space: Nothing } {offset c2Lc: Hp = Hp + 24; if (Hp > HpLim) goto c2Lm; else goto c2Ll; c2Lm: HpAlloc = 24; R2 = R2; R1 = R1; call stg_gc_pp(R2, R1) args: 8, res: 8, upd: 24; c2Ll: I64[Hp - 16] = :_con_info; P64[Hp - 8] = R1; P64[Hp] = R2; R1 = Hp - 14; Sp = Sp + 8; call (P64[Sp])(R1) args: 24, res: 0, upd: 24; } }] }}} {{{ 00000000000002b8 <c2Lc_info>: 2b8: 4c 89 e0 mov %r12,%rax 2bb: 4c 8d 60 18 lea 0x18(%rax),%r12 2bf: 4d 3b a5 18 01 00 00 cmp 0x118(%r13),%r12 2c6: 76 10 jbe 2d8 <c2Lc_info+0x20> 2c8: 49 c7 85 48 01 00 00 movq $0x18,0x148(%r13) 2cf: 18 00 00 00 2d3: e9 00 00 00 00 jmpq 2d8 <c2Lc_info+0x20> 2d4: R_X86_64_PC32 stg_gc_pp+0xfffffffffffffffc 2d8: 48 c7 40 08 00 00 00 movq $0x0,0x8(%rax) 2df: 00 2dc: R_X86_64_32S ghczmprim_GHCziTypes_ZC_con_info 2e0: 48 89 58 10 mov %rbx,0x10(%rax) 2e4: 4c 89 70 18 mov %r14,0x18(%rax) 2e8: 48 8b 45 08 mov 0x8(%rbp),%rax 2ec: 48 83 c5 08 add $0x8,%rbp 2f0: 49 8d 5c 24 f2 lea -0xe(%r12),%rbx 2f5: ff e0 jmpq *%rax 2f7: 90 nop }}} It would likely be better to invert the branch at `2c6` to a `ja`, so that the common case is adjacent to the function entry, and when `llvm.expect` is used on the condition in the branch, the LLVM optimizer does produce this alternate layout. -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/8321> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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