Re: [GHC] #15164: Slowdown in ghc compile times from GHC 8.0.2 to GHC 8.2.1 when doing Called arity analysis

#15164: Slowdown in ghc compile times from GHC 8.0.2 to GHC 8.2.1 when doing Called arity analysis -------------------------------------+------------------------------------- Reporter: flip101 | Owner: (none) Type: bug | Status: new Priority: highest | Milestone: 8.6.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: Operating System: Linux | Architecture: x86_64 | (amd64) Type of failure: Compile-time | Test Case: performance bug | perf/compiler/T15164 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Joachim Breitner ): In [changeset:"db6085b84139f4454cebf34f887cb5560a4fbc7b/ghc" db6085b8/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="db6085b84139f4454cebf34f887cb5560a4fbc7b" Improve performance of CallArity the hot path contained a call to v `elemUnVarSet` (neighbors g v) and creating the set of neighbors just to check if `v` is inside accounted for half the allocations of the test case of #15164. By introducing a non-allocating function `hasLoopAt` for this we shave off half the allocations. This brings the total cost of Call Arity down to 20% of time and 23% of allocations, according to a profiled run. Not amazing, but still much better. Differential Revision: https://phabricator.haskell.org/D4718 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15164#comment:23 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler