#14610: newtype wrapping of a monadic stack kills performance -------------------------------------+------------------------------------- Reporter: mrkkrp | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.2.2 Resolution: | Keywords: JoinPoints Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: #14620 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Good example. But it fails the `isValidJoinPointType` test (c.f. #14620), so even if we roped the `markAllNonTailCalled` in the `Cast` case of occurrence- analysis, we would not get `go` as a join point. And indeed that's not unreasonable. Consider {{{ case ( letrec go n m ds m2 = case ds of ) ( FX co -> m2 |> (...co..) ) ( FS ... -> (go ...) |> co2 ) ( in go t1 t2 a b ) of BLAH }}} Operationally we have a join point, but the transformation to move that case inwards would give this {{{ letrec go n m ds m2 = case ds of FX co -> case m2 |> (...co..) of BLAH FS ... -> (go ...) |> co2 in go t1 t2 a b }}} but now the outer case is scrutinising something involving n, m etc, which makes no sense. Operationally the transformation makes sense, but it's not well typed. I have no idea how to fix this. We still have no example of a program that has a cast in the return (and and hence might benefit from dropping the `makrAllNonTailCalled`) but which passes the `isValidJoinPointType` test. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14610#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler