#13104: runRW# ruins join points -------------------------------------+------------------------------------- Reporter: lukemaurer | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: JoinPoints 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: | -------------------------------------+------------------------------------- Comment (by simonpj): Thinking about #13104 and #15127, I am gradually being driven to the conclusion that we should treat `runRW#` specially in the simplifier. And perhaps a few other primops (like `maskAsyncExceptions#` too). I just can't see a better way to deal with it. Here's my brain-dump: * Require that the argument of `runRW#` is always eta-expanded, with a one-shot lambda. Similar to the RHS of a join point. This would be an invariant of Core, and checked by Core Lint. * Make `Simplify` push the continuation into the body of the `runRW`, just as it does with join points. So, for example: {{{ case (runRW# (\s.e)) of blah ==> runRW# (\s. case e of blah) }}} * I think that `FloatIn` will do the right thing automatically, provided the lambda is marked one-shot. * Maybe, instead of doing mysterious inlining things in `CorePrep` (as we do now), we could just make the code generator do the Right Thing directly? Just as join bindings look like let-bindings, and in most ways behave like them, but have additional invariants that are checked by Core Lint, so similarly with `runRW# (\s.e)`. I have not yet thought through which other primops should particpate in this party. Certainly the `maskAsyncExceptions#` and unmask families. Probably not `catch#` becuase we have to be so careful about moving code into our out of the scope of an exception handler. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13104#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler