[GHC] #10521: Wrong results in strict Word8 storage on x64

[GHC]

#10521: Wrong results in strict Word8 storage on x64
-------------------------------------+-------------------------------------
        Reporter:  VincentBerthoux2  |                   Owner:
            Type:  bug               |                  Status:  new
        Priority:  highest           |               Milestone:  7.10.2
       Component:  Compiler          |                 Version:  7.10.1
      Resolution:                    |                Keywords:
Operating System:  Unknown/Multiple  |            Architecture:  x86_64
 Type of failure:  Incorrect result  |  (amd64)
  at runtime                         |               Test Case:
      Blocked By:                    |                Blocking:
 Related Tickets:                    |  Differential Revisions:
-------------------------------------+-------------------------------------

Comment (by rwbarton):

 The commit that merged F1 and D1 was
 e2f6bbd3a27685bc667655fdb093734cb565b4cf which is in 7.8 but not 7.6. Here
 is a reproducer for 7.8 too:
 {{{
 {-# LANGUAGE MagicHash #-}

 import GHC.Exts

 f :: Float# -> Float#
 f x = x
 {-# NOINLINE f #-}

 g :: Double# -> Double#
 g x = x
 {-# NOINLINE g #-}

 h :: Float -> Float
 h (F# x) = let a = F# (f x)
                b = D# (g (2.0##))
            in a `seq` (b `seq` a)

 main = print (h 1.0)   -- with ghc -O, prints 0.0
 }}}

 Not sure yet whether it is better to revert (parts of) that commit or to
 try to account for STG global registers overlapping in the cmmSink pass
 and wherever else it might be necessary.

--
Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/10521#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler