#15226: GHC doesn't know that seq# produces something in WHNF -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.4.3 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): Phab:D4796 Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:7 simonpj]:
We should (I believe) rewrite
Yes -- this is a variant of the case binder-swap in `OccurAnal`. See `Note [Binder swap]` in `OccurAnal`. This is the place to do it.
I eventually found that, but I'm not at all sure how to deal with coercions in that context. We could, for example, have something like {{{#!hs case seq# x a `cast` ... of (# s', x' #) -> ... }}} in which case we have to work out how to rejigger all the coercions. I don't know enough about that machinery yet. In the current `OccurAnal` code, the coercion in the scrutinee is always on a variable, but here it's on a pair containing the variable, so I'm not going to be able to code monkey it. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15226#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler