Fix and enable object unloading in GHCi

Fixes #16525 by tracking dependencies between object file symbols and
marking symbol liveness during garbage collection

See Note [Object unloading] in CheckUnload.c for details.

1 files changed, 4 insertions, 5 deletions

diff --git a/compiler/GHC/Linker/Loader.hs b/compiler/GHC/Linker/Loader.hs
index 28e74aa2d9..a23a1f735d 100644
--- a/compiler/GHC/Linker/Loader.hs
+++ b/compiler/GHC/Linker/Loader.hs
@@ -1150,15 +1150,15 @@ unload_wkr hsc_env keep_linkables pls@LoaderState{..}  = do
   where
     unloadObjs :: Linkable -> IO ()
     unloadObjs lnk
+        -- The RTS's PEi386 linker currently doesn't support unloading.
+      | isWindowsHost = return ()
+
       | hostIsDynamic = return ()
         -- We don't do any cleanup when linking objects with the
         -- dynamic linker.  Doing so introduces extra complexity for
         -- not much benefit.
 
-      -- Code unloading currently disabled due to instability.
-      -- See #16841.
-      -- id False, so that the pattern-match checker doesn't complain
-      | id False -- otherwise
+      | otherwise
       = mapM_ (unloadObj hsc_env) [f | DotO f <- linkableUnlinked lnk]
                 -- The components of a BCO linkable may contain
                 -- dot-o files.  Which is very confusing.
@@ -1166,7 +1166,6 @@ unload_wkr hsc_env keep_linkables pls@LoaderState{..}  = do
                 -- But the BCO parts can be unlinked just by
                 -- letting go of them (plus of course depopulating
                 -- the symbol table which is done in the main body)
-      | otherwise = return () -- see #16841
 
 {- **********************************************************************