#7450: Regression in optimisation time of functions with many patterns (6.12 to 7.4)? -------------------------------------+------------------------------------- Reporter: iustin | Owner: bgamari Type: bug | Status: patch Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: 7.6.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: Compile-time | Unknown/Multiple performance bug | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Revisions: Phab:D1012 -------------------------------------+------------------------------------- Comment (by Ben Gamari <ben@…>): In [changeset:"4681f55970cabc6e33591d7e698621580818f9a2/ghc"]: {{{ #!CommitTicketReference repository="ghc" revision="4681f55970cabc6e33591d7e698621580818f9a2" Specialise: Avoid unnecessary recomputation of free variable information When examining compile times for code with large ADTs (particularly those with many record constructors), I found that the specialiser contributed disproportionately to the compiler runtime. Some profiling suggested that the a great deal of time was being spent in `pair_fvs` being called from `consDictBind`. @simonpj pointed out that `flattenDictBinds` as called by `specBind` was unnecessarily discarding cached free variable information, which then needed to be recomputed by `pair_fvs`. Here I refactor the specializer to retain the free variable cache whenever possible. **Open Qustions** * I used `fst` in a couple of places to extract the bindings from a `DictBind`. Perhaps this is a sign that `DictBind` has outgrown its type synonym status? Test Plan: validate Reviewers: austin, simonpj Reviewed By: simonpj Subscribers: thomie, bgamari, simonpj Differential Revision: https://phabricator.haskell.org/D1012 GHC Trac Issues: #7450 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/7450#comment:21> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler