[GHC] #13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures

[GHC]

#13043: GHC 7.10->8.0 regression: GHC code-generates duplicate _closures
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        Reporter:  hvr               |                Owner:
            Type:  bug               |               Status:  new
        Priority:  normal            |            Milestone:  8.0.2
       Component:  Compiler          |              Version:  8.0.2-rc2
      Resolution:                    |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
 Type of failure:  Compile-time      |  Unknown/Multiple
  crash or panic                     |            Test Case:
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |
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Comment (by RyanGlScott):

 Here's a minimized version with no dependencies:

 {{{#!hs
 {-# LANGUAGE BangPatterns #-}
 module Bug (foo, bar) where

 import Data.IORef (IORef, newIORef, readIORef, writeIORef)
 import System.IO.Unsafe (unsafePerformIO)

 {-# NOINLINE scServerState #-}
 scServerState :: SCServerState
 scServerState = unsafePerformIO (return undefined)

 data SCServerState = SCServerState
      { scServer_socket :: IORef (Maybe Int)
      }

 foo :: IO Int
 foo = do
    let !_ = scServerState
    readIORef (scServer_socket scServerState) >>= \xs -> case xs of
       Nothing -> do
          s <- undefined
          writeIORef (scServer_socket scServerState) (Just s)
          return s
       Just s -> return s

 bar :: IO ()
 bar = do
    let !_ = scServerState
    return ()
 }}}

 You can get this error message with GHC 8.0.1, 8.0.2, or HEAD:

 {{{
 $ /opt/ghc/8.0.1/bin/ghc -fforce-recomp -O1 Bug.hs
 [1 of 1] Compiling Bug              ( Bug.hs, Bug.o )
 /tmp/ghc654_0/ghc_2.s: Assembler messages:

 /tmp/ghc654_0/ghc_2.s:562:0: error:
      Error: symbol `Bug_scServerState_closure' is already defined
 `gcc' failed in phase `Assembler'. (Exit code: 1)
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/13043#comment:1>
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