[commit: ghc] master: Avoid linear lookup in unload_wkr in the Linker (c1d9690)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/c1d9690619ea38bad3b9aa529d72d10c6206f2e9/ghc

>---------------------------------------------------------------

commit c1d9690619ea38bad3b9aa529d72d10c6206f2e9
Author: Bartosz Nitka <bnitka at fb.com>
Date:   Fri Jul 21 11:41:41 2017 -0700

    Avoid linear lookup in unload_wkr in the Linker
    
    I've encountered an issue with following
    reproduction steps:
    * `:load` a large number of modules (~2000)
    * compile a BCO that depends on many other BCOs from many other modules
    * `:reload`
    * try to compile anything, even `1` works
    
    Before this patch the last step takes ~5s.
    It takes 80ms after.
    
    Test Plan: harbormaster
    
    Reviewers: simonmar, austin, hvr, bgamari
    
    Subscribers: rwbarton, thomie
    
    Differential Revision: https://phabricator.haskell.org/D3770


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c1d9690619ea38bad3b9aa529d72d10c6206f2e9
 compiler/ghci/Linker.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/compiler/ghci/Linker.hs b/compiler/ghci/Linker.hs
index f326590..aee7684 100644
--- a/compiler/ghci/Linker.hs
+++ b/compiler/ghci/Linker.hs
@@ -1091,13 +1091,13 @@ unload_wkr hsc_env keep_linkables pls = do
                    filter (not . null . linkableObjs) bcos_to_unload))) $
     purgeLookupSymbolCache hsc_env
 
-  let bcos_retained = map linkableModule remaining_bcos_loaded
+  let bcos_retained = mkModuleSet $ map linkableModule remaining_bcos_loaded
 
       -- Note that we want to remove all *local*
       -- (i.e. non-isExternal) names too (these are the
       -- temporary bindings from the command line).
       keep_name (n,_) = isExternalName n &&
-                        nameModule n `elem` bcos_retained
+                        nameModule n `elemModuleSet` bcos_retained
 
       itbl_env'     = filterNameEnv keep_name (itbl_env pls)
       closure_env'  = filterNameEnv keep_name (closure_env pls)