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The program

main = print $ if negativeZero == 0.0 then 1 / negativeZero else 0.0
  where
    negativeZero = negate 0.0

outputs -Infinity when compiled with GHC 7.6.3 and Infinity when compiled with GHC 7.8.3 and the optimization level -O2. The relevant pieces of Core:

-- GHC 7.6.3
Main.main2 =
  case GHC.Prim.==## (GHC.Prim.negateDouble# 0.0) 0.0 of _ {
    GHC.Types.False -> Main.main3 (GHC.Types.[] @ GHC.Types.Char);
    GHC.Types.True ->
      case GHC.Prim./## 1.0 (GHC.Prim.negateDouble# 0.0)
      of wild2_aK6 { __DEFAULT ->
      GHC.Float.$w$sshowSignedFloat
        GHC.Float.$fShowDouble_$sshowFloat
        GHC.Show.shows26
        wild2_aK6
        (GHC.Types.[] @ GHC.Types.Char)
      }
  }

-- GHC 7.8.3
Main.main2 =
  case GHC.Prim.negateDouble# 0.0 of _ [Occ=Dead] {
    __DEFAULT -> Main.main3 (GHC.Types.[] @ GHC.Types.Char);
    0.0 ->
      case GHC.Prim./## 1.0 0.0 of wild2_a1NU { __DEFAULT ->
      GHC.Float.$w$sshowSignedFloat
        GHC.Float.$fShowDouble_$sshowFloat
        GHC.Show.shows27
        wild2_a1NU
        (GHC.Types.[] @ GHC.Types.Char)
      }
  }

I don't think this problem is operating system/architecture dependent, but for the sake of completeness I'm on a 32-bit Linux, and this issue was first discovered on 64-bit Windows running in a virtual machine.

Trac metadata

Trac field	Value
Version	7.8.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system
Architecture