Well, you can write whatever rule you like! The rule can test for NaNs, but behave as before for non-NaNs. That might be best, no? Simon | -----Original Message----- | From: Jan Stolarek [mailto:jan.stolarek@p.lodz.pl] | Sent: 22 April 2013 15:51 | To: Simon Peyton-Jones | Cc: ghc-devs@haskell.org | Subject: Re: Handling of NaN | | > Same happens in HEAD, so nothing to do with your changes. | I didn't notice that, I was comparing against 7.6.2 :/ | | > Better define mkFloatingRelOpRule instead, which doesn't have the | equal-args thing. | That's what I did initially, but I wasn't sure if that's acceptable | because some optimisations will be gone, e.g. ==# 3.0 3.0 will not | rewrite to #1 (perhaps this isn't that bad, because comparing floating | point numbers for equality isn't a good idea anyway). | | Janek | | > | > Simon | > | > | -----Original Message----- | > | From: ghc-devs-bounces@haskell.org | > | [mailto:ghc-devs-bounces@haskell.org] | > | On Behalf Of Jan Stolarek | > | Sent: 22 April 2013 13:48 | > | To: ghc-devs@haskell.org | > | Subject: Handling of NaN | > | | > | 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 | > | | > | _______________________________________________ | > | ghc-devs mailing list | > | ghc-devs@haskell.org | > | http://www.haskell.org/mailman/listinfo/ghc-devs |