#8814: 7.8 optimizes attoparsec improperly --------------------------------------------+------------------------------ Reporter: joelteon | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.1-rc1 Resolution: | Keywords: Operating System: MacOS X | Architecture: x86_64 Type of failure: Runtime performance bug | (amd64) Test Case: | Difficulty: Unknown Blocking: | Blocked By: | Related Tickets: #8763 --------------------------------------------+------------------------------ Comment (by simonpj): We're a bit stalled here. There is something mysterious going on, which a single INLINE pragma (Bryan's patch) fixes. But why? My guess is that it's something to do with the interaction between inlning and attoparsec's RULES. For example if a rule optimises `(f (g x))`, and `g` gets inlined, the rule won't fire. Or, if {{{ h x = f x + 1 }}} then the expression `h (g x)` won't fire the rule unless `h` is first inlined. The "phase" annotations on INLINE pragmas and RULES let you control this stuff. So the bug might not be in GHC; it might just be a missing phase annotation. Or there might be a bug in GHC. We won't know until someone digs further. Apart from lack of time, the difficulty is that I have no clue how attoparsec's RULES are supposed to work. So I think we are stalled unless/until someone feels able to do some digging to isolate what is going on. Thanks! Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8814#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler