#14965: GHC 8.4.1 bug: -O + separate compilation + three list fields + concatenation; core-lint fails -------------------------------------+------------------------------------- Reporter: blynn | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.4.1 Keywords: | Operating System: Linux Architecture: | Type of failure: Incorrect result Unknown/Multiple | at runtime Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- A simple program that works in 8.2.1 fails in 8.4.1 when compiled with -O. (Sorry, haven't tested 8.2.2.) GHC with -dcore-lint reports an error. See attached files. In one file I declared: {{{#!hs module Sep where data Sep = Sep { bugVanishesWithoutThis :: [()] , middle :: [String] , orThis :: [()] } catSep :: Sep -> Sep -> Sep catSep (Sep a b c) (Sep x y z) = Sep (a ++ x) (b ++ y) (c ++ z) cc :: Sep -> Bool cc boost = elem "foo" $ middle boost }}} and in a second file, simple code fails when compiled with -O: {{{#!hs module Main (main) where import Sep main :: IO () main = print $ cc bb bb :: Sep bb = catSep b1 b2 b1 :: Sep b1 = Sep [] ["foo"] [] b2 :: Sep b2 = Sep [] ["bar"] [] }}} This should print "True", and does so for GHC 8.2.1, and GHC 8.4.1 without -O, but prints "False" for GHC 8.4.1 with -O. I was unable to reproduce the bug with a single file. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14965 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler