#10215: Optimizer has bugs regarding handling of -0.0 -------------------------------------+------------------------------------- Reporter: lerkok | Owner: Type: bug | Status: new Priority: high | Milestone: Component: Compiler | Version: 7.8.3 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: #9238 Differential Revisions: | -------------------------------------+------------------------------------- This is most likely related to https://ghc.haskell.org/trac/ghc/ticket/9238 Perhaps it can be merged into that if it is indeed the case, though it'd be good for an expert to take a look and make sure first that the culprit is indeed the same. In any case, the program in this ticket can at least serve as a test-case. I observed this on 7.8.3; though I suspect the same holds in the just released 7.10.1 as well. For the following program: {{{#!hs testF :: Float -> Bool testF x = x == 0 && not (isNegativeZero x) testD :: Double -> Bool testD x = x == 0 && not (isNegativeZero x) main :: IO () main = do print $ testF (-0.0) print $ testD (-0.0) }}} If I compile with no optimizations, then I get the correct answers: {{{ $ /bin/rm -f a.hi a.o a; ghc -O0 a; ./a [1 of 1] Compiling Main ( a.hs, a.o ) Linking a ... False False }}} But if I turn optimizations on, then I get: {{{ $ /bin/rm -f a.hi a.o a; ghc -O2 a; ./a [1 of 1] Compiling Main ( a.hs, a.o ) Linking a ... True True }}} which is just plain wrong. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10215 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler