#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: Unknown/Multiple | Architecture: Type of failure: Runtime | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: 8317 Related Tickets: #1498 | Differential Revisions: Phab:D343 -------------------------------------+------------------------------------- Comment (by simonpj): Good point. Trying that is an excellent idea. Note that in a tree of (primop) conditionals, if even one branch allocates, then we'll do a heap check in all cases. It might be interesting to gather the following statistic in ticky-ticky profiling * Total number of heap checks * Total number of times that `Hp` is wound back to zero. This winding back is done by `adjustHpBackwards`. You can tell if you are winding back to zero because `vHp` is zero. If we wind back to zero, that means that we allocated nothing, so the original heap check was wasted. Then we can see what proportion of heap checks are wasted. I guess the worry is that this might happen a lot in some hot inner loop, but let's see. Thanks for doing this. If it looks reasonable it'd be a much simpler cleaner solution. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8326#comment:28 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler