#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 tdammers): Replying to [comment:71 simonpj]:
I was suspicious about comment:64 so I took a look. Sure enough
* The list `[1..n]` wasn't being fused away because it was shared between `insert` and `union`, while `balanced` worked differently and generated no intermediate list.
Ah yes. Lesson learned once again: benchmarking is hard and subtle.
* More significantly, the integers were in ascending order which is fantastically good for balanced union: the tree that implements the set is always balanced and never needs to be transformed.
Right. I probably had the wrong intuition about set performance characteristics here. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14880#comment:72 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler