[GHC] #12757: Compiled program segfaults at -O1

[GHC]

#12757: Compiled program segfaults at -O1
-------------------------------------+-------------------------------------
           Reporter:  hvr            |             Owner:
               Type:  bug            |            Status:  new
           Priority:  highest        |         Milestone:  8.0.2
          Component:  Compiler       |           Version:  8.1
           Keywords:                 |  Operating System:  Unknown/Multiple
       Architecture:                 |   Type of failure:  Runtime crash
  Unknown/Multiple                   |
          Test Case:                 |        Blocked By:
           Blocking:                 |   Related Tickets:
Differential Rev(s):                 |         Wiki Page:
-------------------------------------+-------------------------------------
 This affects GHC 8.0.2dev (d84a824cebe94711528727bcb587bfc369ec36a2) as
 well as GHC HEAD (c23dc6164d54eacc654516b885104dc8b7678f16)

 The following program results in a segfault when compiled at -O1 or more:

 {{{#!hs
 {-# LANGUAGE OverloadedStrings #-}

 module Main (main) where

 import           Data.ByteString        (ByteString)
 import qualified Data.ByteString        as B

 answers :: [ByteString]
 answers = map (B.filter (/= 0x20))
     [ "e3b0c442 98fc1c14 9afbf4c8 996fb924 27ae41e4 649b934c a495991b
 7852b855"
     , "d7a8fbb3 07d78094 69ca9abc b0082e4f 8d5651e4 6d3cdb76 2d02d0bf
 37c9e592"
     , "e4c4d8f3 bf76b692 de791a17 3e053211 50f7a345 b46484fe 427f6acc
 7ecc81be"
     , "ba7816bf 8f01cfea 414140de 5dae2223 b00361a3 96177a9c b410ff61
 f20015ad"
     , "248d6a61 d20638b8 e5c02693 0c3e6039 a33ce459 64ff2167 f6ecedd4
 19db06c1"
     , "cf5b16a7 78af8380 036ce59e 7b049237 0b249b11 e8f07a51 afac4503
 7afee9d1"
     , "cdc76e5c 9914fb92 81a1c7e2 84d73e67 f1809a48 a497200e 046d39cc
 c7112cd0"
     ]

 x, y :: ByteString
 x = "e3b0c442 98fc1c14 9afbf4c8 996fb924 27ae41e4 649b934c a495991b
 7852b855"
 y = B.filter (/= 0x20) x

 main :: IO ()
 main = do
     print (seq x ())
     print (seq y ())
     print (length answers)
     print (seq (head answers) ()) -- segfault!
 }}}


 {{{
 $ ghc-8.0.2 -fforce-recomp --make -O1 bug.hs && ./bug
 [1 of 1] Compiling Main             ( bug.hs, bug.o )
 Linking bug ...
 ()
 ()
 7
 Segmentation fault
 }}}

 {{{
 $ ghc-8.0.2 -fforce-recomp --make -O0 bug.hs && ./bug
 [1 of 1] Compiling Main             ( bug.hs, bug.o )
 Linking bug ...
 ()
 ()
 7
 ()
 }}}

 I haven't yet investigated why this happens.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/12757>
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