[commit: ghc] master: Fix a performance bug in GhcMake.downsweep (1893ba1)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/1893ba12fe1fa2ade35a62c336594afcd569736e/ghc

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

commit 1893ba12fe1fa2ade35a62c336594afcd569736e
Author: Simon Marlow <marlowsd at gmail.com>
Date:   Wed May 10 05:05:38 2017 -0700

    Fix a performance bug in GhcMake.downsweep
    
    Every time we encountered a non-home module during the downsweep, we
    were removing it from the finder cache.  That meant we were searching
    the filesystem for every import, rather than once per downsweep.  The
    fix is just to flush the finder cache before the downsweep, and
    repopulate it for home modules that haven't changed.
    
    Speeds up downsweep by about 25% on a large example I have.
    
    Test Plan: Harbourmaster
    
    Reviewers: bgamari, niteria, austin, erikd
    
    Reviewed By: bgamari, niteria
    
    Subscribers: rwbarton, thomie
    
    Differential Revision: https://phabricator.haskell.org/D3554


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

1893ba12fe1fa2ade35a62c336594afcd569736e
 compiler/main/GhcMake.hs | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/compiler/main/GhcMake.hs b/compiler/main/GhcMake.hs
index 4d06b6e..176c086 100644
--- a/compiler/main/GhcMake.hs
+++ b/compiler/main/GhcMake.hs
@@ -130,6 +130,12 @@ depanal excluded_mods allow_dup_roots = do
               text "Chasing modules from: ",
               hcat (punctuate comma (map pprTarget targets))])
 
+    -- Home package modules may have been moved or deleted, and new
+    -- source files may have appeared in the home package that shadow
+    -- external package modules, so we have to discard the existing
+    -- cached finder data.
+    liftIO $ flushFinderCaches hsc_env
+
     mod_graphE <- liftIO $ downsweep hsc_env old_graph
                                      excluded_mods allow_dup_roots
     mod_graph <- reportImportErrors mod_graphE
@@ -1915,6 +1921,12 @@ summariseFile hsc_env old_summaries file mb_phase obj_allowed maybe_buf
                         then liftIO $ getObjTimestamp location NotBoot
                         else return Nothing
                   hi_timestamp <- maybeGetIfaceDate dflags location
+
+                  -- We have to repopulate the Finder's cache because it
+                  -- was flushed before the downsweep.
+                  _ <- liftIO $ addHomeModuleToFinder hsc_env
+                    (moduleName (ms_mod old_summary)) (ms_location old_summary)
+
                   return old_summary{ ms_obj_date = obj_timestamp
                                     , ms_iface_date = hi_timestamp }
            else
@@ -2034,11 +2046,6 @@ summariseModule hsc_env old_summary_map is_boot (L loc wanted_mod)
                 new_summary location (ms_mod old_summary) src_fn src_timestamp
 
     find_it = do
-        -- Don't use the Finder's cache this time.  If the module was
-        -- previously a package module, it may have now appeared on the
-        -- search path, so we want to consider it to be a home module.  If
-        -- the module was previously a home module, it may have moved.
-        uncacheModule hsc_env wanted_mod
         found <- findImportedModule hsc_env wanted_mod Nothing
         case found of
              Found location mod