क्या यह एक जीएचसी बग है?

Question

मेरे पास निम्न प्रोग्राम है और यह संकलित नहीं होगा; यह सिर्फ संकलन मुख्य पर फंस गया है। मुझे यकीन नहीं है कि यह क्यों जम जाता है क्योंकि यह या तो एक बग है या मुझे कुछ याद आ रहा है?

import qualified Data.Vector.Unboxed as V 

test :: [Int] 
test = V.foldl' unique [] k 
where 
    n = 10000000 
    k = V.generate n (\i -> i `div` 1000 * 1000) 
    unique [] k = [k] 
    unique acc@(ck:_) k 
     | k == ck = acc 
     | otherwise = k:acc  

main :: IO() 
main = print $ head test 

GHC --make -O3 -Odph -fllvm test.hs

Answer 1

हाँ, मुझे लगता है कि इस बग है: https://ghc.haskell.org/trac/ghc/ticket/5550

-v उपयोग करके, आप देख सकते हैं कि GHC हैंग हो कर SpecConstr अनुकूलन:

ghc-7.6.3 test.hs -O2 -fforce-recomp -v 
Glasgow Haskell Compiler, Version 7.6.3, stage 2 booted by GHC version 7.0.4 
Using binary package database: /nix/store/x5rdp4smhc6q3rxbw4x1akj10z3h0lvg-haskell-env-ghc-7.6.3/lib/ghc-7.6.3/package.conf.d/package.cache 
hiding package Cabal-1.16.0 to avoid conflict with later version Cabal-1.18.1.3 
hiding package QuickCheck-2.6 to avoid conflict with later version QuickCheck-2.7.3 
hiding package binary-0.5.1.1 to avoid conflict with later version binary-0.7.1.0 
wired-in package ghc-prim mapped to ghc-prim-0.3.0.0-d5221a8c8a269b66ab9a07bdc23317dd 
wired-in package integer-gmp mapped to integer-gmp-0.5.0.0-2f15426f5b53fe4c6490832f9b20d8d7 
wired-in package base mapped to base-4.6.0.1-02ac91ff7de681afee6a8fa62f0c87f3 
wired-in package rts mapped to builtin_rts 
wired-in package template-haskell mapped to template-haskell-2.8.0.0-0cee70fbb279a3d93dcc4ec502790a2b 
wired-in package dph-seq not found. 
wired-in package dph-par not found. 
Hsc static flags: -static 
*** Chasing dependencies: 
Chasing modules from: *test.hs 
Stable obj: [] 
Stable BCO: [] 
Ready for upsweep 
    [NONREC 
     ModSummary { 
     ms_hs_date = 2014-04-15 18:43:29 UTC 
     ms_mod = main:Main, 
     ms_textual_imps = [import (implicit) Prelude, 
          import qualified Data.Vector.Unboxed as V] 
     ms_srcimps = [] 
     }] 
*** Deleting temp files: 
Deleting: 
compile: input file test.hs 
Created temporary directory: /tmp/ghc23870_0 
*** Checking old interface for main:Main: 
[1 of 1] Compiling Main    (test.hs, test.o) 
*** Parser: 
*** Renamer/typechecker: 
*** Desugar: 
Result size of Desugar (after optimization) 
    = {terms: 55, types: 44, coercions: 0} 
*** Simplifier: 
Result size of Simplifier iteration=1 
    = {terms: 46, types: 34, coercions: 5} 
Result size of Simplifier iteration=2 
    = {terms: 48, types: 40, coercions: 5} 
Result size of Simplifier = {terms: 48, types: 40, coercions: 5} 
*** Specialise: 
Result size of Specialise = {terms: 48, types: 40, coercions: 5} 
*** Float out(FOS {Lam = Just 0, Consts = True, PAPs = False}): 
Result size of Float out(FOS {Lam = Just 0, 
           Consts = True, 
           PAPs = False}) 
    = {terms: 66, types: 58, coercions: 5} 
*** Float inwards: 
Result size of Float inwards = {terms: 66, types: 58, coercions: 5} 
*** Simplifier: 
Result size of Simplifier iteration=1 
    = {terms: 76, types: 66, coercions: 36} 
Result size of Simplifier iteration=2 
    = {terms: 71, types: 60, coercions: 26} 
Result size of Simplifier = {terms: 71, types: 60, coercions: 26} 
*** Simplifier: 
Result size of Simplifier iteration=1 
    = {terms: 143, types: 113, coercions: 33} 
Result size of Simplifier iteration=2 
    = {terms: 99, types: 79, coercions: 30} 
Result size of Simplifier = {terms: 99, types: 79, coercions: 30} 
*** Simplifier: 
Result size of Simplifier iteration=1 
    = {terms: 120, types: 88, coercions: 26} 
Result size of Simplifier iteration=2 
    = {terms: 90, types: 64, coercions: 16} 
Result size of Simplifier iteration=3 
    = {terms: 88, types: 63, coercions: 16} 
Result size of Simplifier = {terms: 88, types: 63, coercions: 16} 
*** Demand analysis: 
Result size of Demand analysis 
    = {terms: 88, types: 63, coercions: 16} 
*** Worker Wrapper binds: 
Result size of Worker Wrapper binds 
    = {terms: 108, types: 80, coercions: 23} 
*** Simplifier: 
Result size of Simplifier iteration=1 
    = {terms: 100, types: 72, coercions: 13} 
Result size of Simplifier iteration=2 
    = {terms: 91, types: 58, coercions: 9} 
Result size of Simplifier = {terms: 91, types: 58, coercions: 9} 
*** Float out(FOS {Lam = Just 0, Consts = True, PAPs = True}): 
Result size of Float out(FOS {Lam = Just 0, 
           Consts = True, 
           PAPs = True}) 
    = {terms: 93, types: 59, coercions: 9} 
*** Common sub-expression: 
Result size of Common sub-expression 
    = {terms: 93, types: 59, coercions: 9} 
*** Float inwards: 
Result size of Float inwards = {terms: 93, types: 59, coercions: 9} 
*** Liberate case: 
Result size of Liberate case = {terms: 93, types: 59, coercions: 9} 
*** Simplifier: 
Result size of Simplifier iteration=1 
    = {terms: 93, types: 59, coercions: 9} 
Result size of Simplifier = {terms: 93, types: 59, coercions: 9} 
*** SpecConstr: 
Result size of SpecConstr 

तुम भी परीक्षण कर सकते हैं कि -fno-spec-constr या -fno-enable-rewrite-rules का उपयोग कर बनाता है बग गायब हो जाते हैं। इसने इसे नवीनतम जीएचसी (7.8.2) के साथ परीक्षण किया, और यह मुद्दा वहां तय किया गया प्रतीत होता है।