#14208: Performance with O0 is much better than the default or with -O2, runghc performs the best -------------------------------------+------------------------------------- Reporter: harendra | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 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: | -------------------------------------+------------------------------------- Comment (by harendra): When I look at `-ddump-rewrite-rules` output the list fusion rules seem to get fired in the `-fno-pre-inlining` case but not in the `-O1` case. Specifically I do not see the "map" rule (and subsequent other rules triggered by it) in the `-O1` output. As long as we understand why it is happening and there is no easy way to fix it, I guess it is fine. But I hope this can be fixed so that we do not spend time wondering about and figuring out such things and manually tweaking options and pragmas to get to the right combination. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14208#comment:14 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler