Simplify.hs depends on typechecker

[Simon Peyton Jones]

I agree.

Both of these code paths go through initTcForLookup which is massive overkill, as the comment with `TcEnv.lookupGlobal` says.  There's clearly a ToDo here to strip off the redundant stuff and do a minimal lookup.

Would you like to make a ticket?

Simon


|  -----Original Message-----
|  From: ghc-devs [mailto:ghc-devs-bounces at haskell.org] On Behalf Of
|  Joachim Breitner
|  Sent: 24 October 2017 16:40
|  To: ghc-devs at haskell.org
|  Subject: Simplify.hs depends on typechecker
|  
|  Hi,
|  
|  while rebuilding Simplify.o only I noticed that all of the type
|  checker, and HsSyn stuff, and renamer stuff, and so needed to be
|  rebuilt, which I found strange.
|  
|  After a little investigation, it seems that the simplifier depends on
|  CoreMonad, and that pulls some very few type-checker related things:
|  
|  1.
|      import TcRnMonad        ( initTcForLookup )
|      import {-# SOURCE #-} TcSplice ( lookupThName_maybe )
|  
|  for
|  
|      thNameToGhcName :: TH.Name -> CoreM (Maybe Name)
|      thNameToGhcName th_name = do
|          hsc_env <- getHscEnv
|          liftIO $ initTcForLookup hsc_env (lookupThName_maybe th_name)
|  
|  which is not even used in GHC, but only in GHC Plugins, so this could
|  probably be moved to a separate module pulled in by GhcPlugins.hs
|  
|  2.
|  
|      import TcEnv            ( lookupGlobal )
|  
|  for
|  
|      instance MonadThings CoreM where
|          lookupThing name = do { hsc_env <- getHscEnv
|                                ; liftIO $ lookupGlobal hsc_env name }
|  
|  This might be a bit harder to disentangle. But if successful, it would
|  probably make building GHC in parallel quite a bit faster. And it just
|  seems strange to me that the Core-to-Core code should depend on the
|  type checker…
|  
|  
|  I’m sending this out there in case someone has dug in that direction
|  before and has insights to share.
|  
|  
|  Greetings,
|  Joachim
|  
|  (Attached is a transitively reduced dependency graph of Simplify.hs,
|  created using Iavor’s
|  https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub
|  .com%2Fyav%2Fgraphmod%2Fwiki&data=02%7C01%7Csimonpj%40microsoft.com%7Cb
|  16c817556de4d55d74c08d51af5a8cd%7C72f988bf86f141af91ab2d7cd011db47%7C1%
|  7C0%7C636444565247573129&sdata=oHpA%2F%2BHGyc0mHv%2FWj3nzGBiJCM2ufriryF
|  oZYNHSjqk%3D&reserved=0).
|  
|  
|  --
|  Joachim “nomeata” Breitner
|    mail at joachim-breitner.de
|  
|  https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.jo
|  achim-
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|  erved=0