[GHC] #6156: Optimiser bug on linux-powerpc

[GHC]

#6156: Optimiser bug on linux-powerpc
------------------------------------------+---------------------------------
  Reporter:  erikd                        |          Owner:  igloo  
      Type:  bug                          |         Status:  new    
  Priority:  normal                       |      Milestone:  7.6.1  
 Component:  Compiler                     |        Version:  7.4.1  
Resolution:                               |       Keywords:         
        Os:  Linux                        |   Architecture:  powerpc
   Failure:  Incorrect result at runtime  |     Difficulty:  Unknown
  Testcase:                               |      Blockedby:         
  Blocking:                               |        Related:         
------------------------------------------+---------------------------------

Comment(by erikd):

 Digging deeper:

 {{{
 {-# LANGUAGE MagicHash #-}
 import GHC.Int
 import GHC.Word
 import GHC.IntWord64
 import Numeric (showHex)

 main :: IO ()
 main = putStrLn (showHex (wordToInt64 input) "")

 input :: Word64
 input = 0x1a2a3a4a5a6a7a8a

 wordToInt64 :: Word64 -> Int64
 wordToInt64 (W64# x) = I64# (word64ToInt64# x)
 }}}

 also gives an incorrect result when optimisation is on. The
 `word64ToInt64#` is foreign imported as:

 {{{
 foreign import ccall unsafe "hs_word64ToInt64" word64ToInt64# :: Word64#
 -> Int64#
 }}}

 and `hs_word64ToInt64` is defined in C as :

 {{{
 HsInt64  hs_word64ToInt64 (HsWord64 w) {return (HsInt64)  w;}
 }}}

 and testing that function in isolation in a small C program shows no
 problem.

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6156#comment:35>
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