#14619: Output value of program changes upon compiling with -O optimizations -------------------------------------+------------------------------------- Reporter: sheaf | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.4.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: Operating System: Windows | Architecture: x86_64 Type of failure: Incorrect result | (amd64) at runtime | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Phyx-): I'm starting to think this isn't a GHC bug. I've attached two dumps created with the current `HEAD` and `8.2.2`. Because the representation of `show` for `Float` seems to have changed I'm avoiding using it. My repro is {{{ module Main where import Prelude hiding((*>), (<*)) type V3 = (Double, Double, Double) infixl 6 <+> infixl 7 <.> infix 8 *> (<+>) :: V3 -> V3 -> V3 (<+>) (x, y, z) (x', y', z') = (x+x', y+y', z+z') (*>) :: Double -> V3 -> V3 (*>) a (x', y', z') = (a*x', a*y', a*z') (<.>) :: V3 -> V3 -> Double (<.>) (x, y, z) (x', y', z') = x*x'+y*y'+z*z' sphereIntersection :: V3 -> V3 -> V3 -> Maybe (V3, Double) sphereIntersection orig dir@(_, _, dirz) c | b < 0 = Nothing | t1 > 0 = Just (t1 *> dir, dirz) | t2 > 0 = Just (t2 *> orig, dirz) | otherwise = Nothing where oc = c <+> orig b = oc <.> dir sqrtDisc = sqrt b t1 = b - sqrtDisc t2 = b + sqrtDisc result = sphereIntersection (0, 0, 0) (0, 0, 1) (0, 0, 200) main :: IO (Maybe (V3, Double)) main = return result }}} Both are compiled with `-fforce-recomp -O2 -ddump-cmm -ddump-to-file` and there is no meaningful difference in code gen. only label names. The only remaining difference is in toolchain. 8.4.1 has an upgraded toolchain (and so head) vs 8.2.2. So this is looking like an upstream issue. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14619#comment:19 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler