I need some help with my work on ticket #6135. Consider this program:
{-# LANGUAGE BangPatterns, MagicHash #-}
module Main where
import GHC.Exts
main = print $ nan## ==## nan##
where !(D# nan##) = 0.0 / 0.0
This prints False, which is a correct implementation of IEEE754 standard.
However when I compile
this with my modified compiler that uses new comparison primops (they return
Int# instead of
Bool) I get True, whcih obviously is incorrect. I belive that the problem lies
in this piece of
code from prelude/PrelRules.hs:
mkRelOpRule :: Name -> (forall a . Ord a => a -> a -> Bool)
-> [RuleM CoreExpr] -> Maybe CoreRule
mkRelOpRule nm cmp extra
= mkPrimOpRule nm 2 $ rules ++ extra
where
rules = [ binaryLit (\_ -> cmpOp cmp)
, equalArgs >>
-- x `cmp` x does not depend on x, so
-- compute it for the arbitrary value 'True'
-- and use that result
return (if cmp True True
then trueVal
else falseVal) ]
It looks that equalArgs suddenly started to return True, whereas it previously
returned False. On
the other hand in GHCi I get correct result (False). Can anyone give me a hint
why is this
happening?
Janek
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