#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: Operating System: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by nomeata): * cc: nomeata (added) Comment: The polymorphic `go` in comment:3 is a separate problem from the one that I described further up (but it might well be the OP’s problem). It could be fixed by static argument transformation. On my TODO list, after #14068, is SAT for join points, but it would not help here, because only after SAT it is a join point. Exitification unfortunately also does not help to turn this into a joint point. Maybe worth opening a separate ticket. Your example in comment:4 is precisely what I described, thanks for working it out. The fix here probably requires some significant thought about the join point typing. Maybe it is enough to relax the rule “The return type must not depend on any arguments” to “The return type must be representatoinally equal for all arguments” and that might allow us to {{{e `cast` co}}} to be a tail-call position. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14610#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler