#13369: Float-out is not idempotent -------------------------------------+------------------------------------- Reporter: simonpj | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: None/Unknown Unknown/Multiple | Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- Consider {{{ f x = BIG }}} where BIG is bottoming. In HEAD, the float-out pass decides to float BIG to the top level, producing {{{ lvl x = BIG f x = lvl x }}} which is obviously stupid. There's a whole Note to explain this problem and how we avoid it: {{{ Note [Floating from a RHS] ~~~~~~~~~~~~~~~~~~~~~~~~~~ When float the RHS of a let-binding, we don't always want to apply lvlMFE to the body of a lambda, as we usually do, because the entire binding body is already going to the right place (dest_lvl). A particular example is the top level. Consider concat = /\ a -> foldr ..a.. (++) [] We don't want to float the body of the lambda to get lvl = /\ a -> foldr ..a.. (++) [] concat = /\ a -> lvl a That would be stupid. }}} But I forgot to take account of the possibility that `abs_vars` might abstract over Ids. Easily fixed. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13369 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler