gcc should be passed the -fwrapv flag

I get a floating point exception building HEAD with 6.6. I tracked it down to getCommonNodeUFMData in UniqFM:

getCommonNodeUFMData :: NodeUFMData -> NodeUFMData -> NodeUFMData

getCommonNodeUFMData (NodeUFMData i p) (NodeUFMData i2 p2)
  | p ==# p2	= getCommonNodeUFMData_ p j j2
  | p <# p2	= getCommonNodeUFMData_ p2 (j `quotFastInt` (p2 `quotFastInt` p)) j2
  | otherwise	= getCommonNodeUFMData_ p j (j2 `quotFastInt` (p `quotFastInt` p2))
  where
    l  = (_ILIT(1) :: FastInt)
    j  = i  `quotFastInt` (p  `shiftL_` l)
    j2 = i2 `quotFastInt` (p2 `shiftL_` l)

    getCommonNodeUFMData_ :: FastInt -> FastInt -> FastInt -> NodeUFMData

    getCommonNodeUFMData_ p j j_
      | j ==# j_
      = NodeUFMData (((j `shiftL_` l) +# l) *# p) p
      | otherwise
      = getCommonNodeUFMData_ (p `shiftL_`  l) (j `shiftR_` l) (j_ `shiftR_` l)

The division j2 is a divide-by-zero; p2 is zero.

Compiling UniqFM with DEBUG makes it go away. Compiling with -fasm has no effect, so it isn't dependent on the back-end.

This may be architecture-specific; I've only seen it on x86_64 so far.

Trac metadata

Trac field	Value
Version	6.6
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
Test case
Differential revisions
BlockedBy
Related
Blocking
CC
Operating system	Linux
Architecture	x86_64 (amd64)