#14880: GHC panic: updateRole -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: goldfire Type: bug | Status: new Priority: normal | Milestone: 8.8.1 Component: Compiler (Type | Version: 8.2.2 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple crash or panic | Test Case: Blocked By: | Blocking: Related Tickets: #15076 | Differential Rev(s): Phab:D4769 Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): OK. So `NDFV` behaves roughly identically to `FV` -- faster than just a bare `VarSet`. But ''why''? Let's look at the difference between `NDFV` and `VarSet`. 1. The former has an `InterestingVarFun`. But I don't believe that's used in your tests. 2. The former maintains a set of elements to be removed, while the latter just algorithmically removes elements when necessary. 3. The former uses an accumulator to build sets, while the latter does not. Which of these factors contributes to the performance change? To learn this, we can test each in isolation, by removing the difference and then measuring. I suspect (2). If this is the case, perhaps we'll discover an optimization that can apply well beyond GHC! -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14880#comment:83 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler