-0 rational?

[Moritz Angermann]

Hi *,

I just ran into the following case:

> fromRat (-0 :: Rational) :: Double
0.0

> -0 :: Rational
0 % 1

How do I encode negative zero as a rational? The question come
up as `CmmFloat` is defined as `CmmFloat  Rational Width` in 
compiler/cmm/CmmExpr.hs. And my code generator thus turned
(Int, Rational) into a floating point expression, and when trying
to turn it into a `double` value, I ended up getting bad negative
zeros.

This makes me believe I can’t actually encode `-0` as a Rational,
and such `CmmFloat` will never contain `-0`?

Cheers,
 Moritz