#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): I guess some function getting inlined too early is preventing list fusion. The combination of `-fexpose-all-unfoldings` and `-fspecialise- aggressively` is not "exactly" equivalent to putting everything in the same module. O1 with everything in the same module finishes in 8ms while with the combination of these two finishes in 4ms. So they do something more. I guess the added effect is that they make everything INLINEABLE. When everything is in the same module and `toList` marked NOINLINE then it takes 14ms (i.e. the worst case) irrespective of the monoid functions being marked INLINE or not. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14208#comment:17 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler