[GHC] #12545: Compilation time/space regression in GHC 8.0/8.1 (search in type-level lists and -O)

#12545: Compilation time/space regression in GHC 8.0/8.1 (search in type-level lists and -O) -------------------------------------+------------------------------------- Reporter: | Owner: mikhail.vorozhtsov | Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Keywords: | Operating System: Unknown/Multiple Architecture: | Type of failure: Compile-time Unknown/Multiple | performance bug Test Case: | Blocked By: Blocking: | Related Tickets: Differential Rev(s): | Wiki Page: -------------------------------------+------------------------------------- After upgrading to GHC 8.0.1 I've noticed that compilation time of one of my libraries got unacceptably long. Please find the attached test case. Here are some numbers from my machine: {{{ $ time ~/Prefixes/ghc-7.10.3/bin/ghc -O -c -Rghc-timing TypeList.hs Regression.hs <> real 0m20.160s user 0m19.937s sys 0m0.197s $ time ~/Prefixes/ghc-8.0.1/bin/ghc -O -c -Rghc-timing TypeList.hs Regression.hs <> real 2m10.195s user 2m9.773s sys 0m0.400s }}} Both versions are the official Debian 8 x86_64 binaries from haskell.org. I also compiled the git master and unfortunately it is affected as well. It is worth mentioning that turning off optimization makes the problem disappear: {{{ $ time ~/Prefixes/ghc-8.0.1/bin/ghc -O0 -c -Rghc-timing TypeList.hs Regression.hs <> real 0m3.593s user 0m3.507s sys 0m0.073s }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12545 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler