#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 nomeata):

Is it expected behavior and some performance improvements are planned or it's a bug?

I would not be surprised to find that this is a rather rarely used feature and may not have gotten the necessary attention. But this might also mean that there is some low-hanging fruit. I would recommend building a profiled compiler and get a profile for this bit, just to see if there are obvious hotspots. vshabanov, are you interested in working on this, or just reporting it for now? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12706#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#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

#12706: Collecting type info is slow -------------------------------------+------------------------------------- Reporter: vshabanov | Owner: (none) 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): D4459 Wiki Page: | -------------------------------------+------------------------------------- Changes (by alexbiehl): * differential: => D4459 -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12706#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler

#12706: Collecting type info is slow -------------------------------------+------------------------------------- Reporter: vshabanov | Owner: (none) 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): Phab:D4459 Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ben Gamari ): In [changeset:"969e747f67f57f7dd57c2e549d6a007505671158/ghc" 969e747/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="969e747f67f57f7dd57c2e549d6a007505671158" GHCi info: Use src file for cache invalidation Prior to this patch GHCi used the modification time of a module's object file to invalidate the info cache. We now look at the modification time of the source file, if present. This addresses part of https://ghc.haskell.org/trac/ghc/ticket/12706#comment:3. Reviewers: bgamari Reviewed By: bgamari Subscribers: lelf, alpmestan, rwbarton, thomie, carter GHC Trac Issues: #12706 Differential Revision: https://phabricator.haskell.org/D4459 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12706#comment:7 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler