Đây có phải là lỗi của GHC không?

Question

Tôi có chương trình sau và chương trình sẽ không biên dịch; nó chỉ bị kẹt khi biên dịch chính. Tôi không chắc chắn lý do tại sao nó bị đóng băng vì nó là một lỗi hoặc tôi đang thiếu một cái gì đó?

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

Vâng, tôi nghĩ rằng đây là lỗi: https://ghc.haskell.org/trac/ghc/ticket/5550

Sử dụng -v, bạn có thể thấy rằng GHC treo khi thực hiện SpecConstr tối ưu hóa:

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 

Bạn cũng có thể kiểm tra rằng việc sử dụng -fno-spec-constr hoặc -fno-enable-rewrite-rules làm cho các lỗi biến mất. Nó đã thử nghiệm nó với GHC mới nhất (7.8.2), và vấn đề dường như được cố định ở đó.