#7866: floor (0/0) :: Int is different with -O0 and -O1 ------------------------------------------------+-------------------------- Reporter: alang9 | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.6.2 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 Type of failure: Incorrect result at runtime | (amd64) Test Case: | Difficulty: Blocking: | Unknown | Blocked By: | Related Tickets: ------------------------------------------------+-------------------------- Changes (by bgamari): * difficulty: => Unknown Comment: This appears to be due to the (lack of) handling of NaN in `compiler/nativeGen/X86/CodeGen.hs:coerceFP2Int` which in the SSE case lowers to a plain `CVTTSD2TIQ` instruction. In the event that the source is NaN, this places the indeterminate integer value (which appears to be 0x80000000) in the destination register. Oddly enough, your test produces instead a value of -0x8000000000000000. Regardless, assuming the produce is NaN handling, it's not entirely clear how this should be handled without performance loss. If the goal were perfect "correctness" (whatever this means in the fact of NaN values being cast to integers), we'd want to ensure we check for an indeterminate result and return the "appropriate" value (which judging from the -O0 results is apparently 0). This seems like an excessive measure, however, punishing all users for what is likely a rare occurrence and one that should be handled explicitly anyways. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/7866#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler