[GHC] #921: Floating point with -O and -fasm is broken

[GHC]

#921: Floating point with -O  and -fasm is broken
-------------------------------+--------------------------------------------
    Reporter:  guest           |        Owner:         
        Type:  bug             |       Status:  new    
    Priority:  normal          |    Milestone:         
   Component:  Compiler (NCG)  |      Version:  6.4.1  
    Severity:  normal          |     Keywords:         
          Os:  Linux           |   Difficulty:  Unknown
Architecture:  x86_64 (amd64)  |  
-------------------------------+--------------------------------------------
I have some simple floating-point code that fails badly when you compile
 it with -O and -fasm on x86_64. Here is the program:

 log2 x = ceiling log_x
   where log_x :: Double
         log_x = logBase 2 (fromIntegral (max 1 x))

 vals = [1, 2, 17, 259, 1000, 10000,
         2^30 + 9000, 2^31 - 1, 2^31, 2^31 + 1,
         2^32 - 1, 2^32, 2^32 + 1]

 main :: IO ()
 main = putStrLn (show (map log2 vals))

 The result should be: [0,1,5,9,10,14,31,31,32,32,32,32,33]

 With -O and -fasm on x86_64 the last five values are corrupted (four very
 large numbers I'm not going to paste here, followed by 0).

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/921>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler