#11688: Bytestring break failing rewrite to breakByte and failing to eliminate boxing/unboxing -------------------------------------+------------------------------------- Reporter: alexbiehl | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.10.3 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): Phab:D1980 Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): This comes up regularly; e.g. #10595, #7141 (maybe), #5973 (maybe), #4397 (I bet the fix is delicate), #2271, #1434. And #10418 is similar but for constructors not class ops. In general, I it's dangerous to match on an overloaded class op. After all, did you really mean to match on `(==)` at every type? I doubt it? In this case we mean `==` at type `Char`. So the advice in comment:4 of #10595, is to write {{{ instance Eq Char where (==) = eqChar eqChar :: Char -> Char -> Bool {-# INLINE [0] eqChar #-} -- Delay inlining }}} and then make the rule be {{{ {-# RULES "bsbreak" forall x chunk. ByteString.break (eqChar x) chunk = ... #-} }}} This is simple and robust. But it does mean chaging the base library to use named functions for instance methods. Probably good practice anyway. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11688#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler