#12706: Collecting type info is slow -------------------------------------+------------------------------------- Reporter: vshabanov | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: GHCi | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by vshabanov): I tried profiled compiler. Unfortunately I don't know GHC internals well enough to fix it but, anyway, here are my findings. Most time is spent in source:ghc/ghc/GHCi/UI/Info.hs Half time is spent in `typecheckModule` call and another half in `everythingAllSpans`. First problem here is a bad `cacheInvalid` function. It checks file time of object file, but there are no object files in GHCi. So types are always collected for all modules instead of new/modified ones. I don't know how to correctly check what files were recompiled but it's the first thing to do to shorten "Collecting type info" phase. Clearing cache on `:l` in GHCi is also necessary to free memory. I'm also not sure about call to `typecheckModule`. Aren't modules already type checked? Maybe it's possible to get type check results that were already calculated. Harder thing to do is to optimize `everythingAllSpans`. It uses SYB approach to extract `LHsBind`, `LHsExpr` and `LPat` from `TypecheckedSource = Bag (Located HsBindLR)`. It could be rewritten using direct recursion over `HsBindLR` without `cast` and `gmapQ`. But it looks like quite a big task. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12706#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler