#8326: Place heap checks common in case alternatives before the case -------------------------------------+------------------------------------- Reporter: jstolarek | Owner: Type: task | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.7 Resolution: | Keywords: Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: #1498 Test Case: | Blocking: 8317 | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:7 jstolarek]:
Replying to [comment:3 dfeuer]:
If I hand it `12#`, it will dutifully tell me `False`. What exactly have I learned from that? That the argument you passed is not a valid tag for `True`.
This ticket is not really about `isTrue#` or `isFalse#` - which are just tools a programmer might want or not want to use - but about fixing the heap checks and thus fixing #8317. If you feel that `isTrue#` and `isFalse#` don't offer you any benefit you can still use `tagToEnum#`.
I'm not sure where the appropriate place is for this line of discussion, but it seems that in the wild (all over the library source), `isTrue#` is typically used as a function for converting from `Int#`, produced by a comparison operator, to `Bool`, rather than as a validity test for `True`. I have yet to see any explanation of why that is appropriate. Certainly, optimizing heap checks is an entirely different matter, and presumably a good idea regardless. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8326#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler