Fix space leaks

Summary:
All these were detected by -fghci-leak-check when GHC was
compiled *without* optimisation (e.g. using the "quick" build flavour).

Unfortunately I don't know of a good way to keep this working.  I'd like
to just disable the -fghci-leak-check flag when the compiler is built
without optimisation, but it doesn't look like we have an easy way to do
that. And even if we could, it would be fragile anyway,

Test Plan: `cd testsuite/tests/ghci; make`

Reviewers: bgamari, hvr, erikd, tdammers

Subscribers: tdammers, rwbarton, thomie, carter

GHC Trac Issues: #15246

Differential Revision: https://phabricator.haskell.org/D4872

1 files changed, 19 insertions, 14 deletions

diff --git a/compiler/ghci/Linker.hs b/compiler/ghci/Linker.hs
index 8d0338a9dd..2af03ddde8 100644
--- a/compiler/ghci/Linker.hs
+++ b/compiler/ghci/Linker.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE CPP, NondecreasingIndentation, TupleSections, RecordWildCards #-}
+{-# LANGUAGE BangPatterns #-}
 {-# OPTIONS_GHC -fno-cse #-}
 -- -fno-cse is needed for GLOBAL_VAR's to behave properly
 
@@ -169,10 +170,10 @@ extendLoadedPkgs pkgs =
 
 extendLinkEnv :: [(Name,ForeignHValue)] -> IO ()
 extendLinkEnv new_bindings =
-  modifyPLS_ $ \pls -> do
-    let ce = closure_env pls
-    let new_ce = extendClosureEnv ce new_bindings
-    return pls{ closure_env = new_ce }
+  modifyPLS_ $ \pls@PersistentLinkerState{..} -> do
+    let new_ce = extendClosureEnv closure_env new_bindings
+    return $! pls{ closure_env = new_ce }
+    -- strictness is important for not retaining old copies of the pls
 
 deleteFromLinkEnv :: [Name] -> IO ()
 deleteFromLinkEnv to_remove =
@@ -1095,15 +1096,19 @@ unload_wkr :: HscEnv
 -- Does the core unload business
 -- (the wrapper blocks exceptions and deals with the PLS get and put)
 
-unload_wkr hsc_env keep_linkables pls = do
+unload_wkr hsc_env keep_linkables pls@PersistentLinkerState{..}  = do
+  -- NB. careful strictness here to avoid keeping the old PLS when
+  -- we're unloading some code.  -fghci-leak-check with the tests in
+  -- testsuite/ghci can detect space leaks here.
+
   let (objs_to_keep, bcos_to_keep) = partition isObjectLinkable keep_linkables
 
       discard keep l = not (linkableInSet l keep)
 
       (objs_to_unload, remaining_objs_loaded) =
-         partition (discard objs_to_keep) (objs_loaded pls)
+         partition (discard objs_to_keep) objs_loaded
       (bcos_to_unload, remaining_bcos_loaded) =
-         partition (discard bcos_to_keep) (bcos_loaded pls)
+         partition (discard bcos_to_keep) bcos_loaded
 
   mapM_ unloadObjs objs_to_unload
   mapM_ unloadObjs bcos_to_unload
@@ -1114,7 +1119,7 @@ unload_wkr hsc_env keep_linkables pls = do
                    filter (not . null . linkableObjs) bcos_to_unload))) $
     purgeLookupSymbolCache hsc_env
 
-  let bcos_retained = mkModuleSet $ 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
@@ -1122,13 +1127,13 @@ unload_wkr hsc_env keep_linkables pls = do
       keep_name (n,_) = isExternalName n &&
                         nameModule n `elemModuleSet` bcos_retained
 
-      itbl_env'     = filterNameEnv keep_name (itbl_env pls)
-      closure_env'  = filterNameEnv keep_name (closure_env pls)
+      itbl_env'     = filterNameEnv keep_name itbl_env
+      closure_env'  = filterNameEnv keep_name closure_env
 
-      new_pls = pls { itbl_env = itbl_env',
-                      closure_env = closure_env',
-                      bcos_loaded = remaining_bcos_loaded,
-                      objs_loaded = remaining_objs_loaded }
+      !new_pls = pls { itbl_env = itbl_env',
+                       closure_env = closure_env',
+                       bcos_loaded = remaining_bcos_loaded,
+                       objs_loaded = remaining_objs_loaded }
 
   return new_pls
   where