#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 Resolution: | Keywords: Inlining 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: | -------------------------------------+------------------------------------- Comment (by simonpj): Several points here * We don't yet know why 8.0 is worse than 7.10. That would e helpful. * The coercions record a proof of all the list manipulations involved. It's not surprising that they can get big. What is surprising is why they are bigger with 8.0 * GHC includes a "coercion optimiser" `OptCoercion.hs`, which tries to shrink a big coercion to a smaller but equivalent coercion. It's possible that 8.0 is somehow missing a crucial optimisation that fires in 7.10. * We also have a plan, recorded in Trac #8095, to discard coercions altogether. But neither Richard or I have found time to execute on that plan. See also #11598 Bottom line: more insight into what is going on would be really helpful. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12545#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler