compiler: Use compact representation for UsageFile (#22744)

Use FastString to store filepaths in interface files, as this data is
highly redundant so we want to share all instances of filepaths in the
compiler session.

4 files changed, 9 insertions, 6 deletions

diff --git a/compiler/GHC/HsToCore/Usage.hs b/compiler/GHC/HsToCore/Usage.hs
index e2ac533ba8..59a8c01073 100644
--- a/compiler/GHC/HsToCore/Usage.hs
+++ b/compiler/GHC/HsToCore/Usage.hs
@@ -35,6 +35,7 @@ import GHC.Unit.Module.ModIface
 import GHC.Unit.Module.Deps
 
 import GHC.Data.Maybe
+import GHC.Data.FastString
 
 import Data.IORef
 import Data.List (sortBy)
@@ -86,7 +87,7 @@ mkUsageInfo uc plugins fc unit_env this_mod dir_imp_mods used_names dependent_fi
     let all_home_ids = ue_all_home_unit_ids unit_env
     mod_usages <- mk_mod_usage_info uc hu all_home_ids this_mod
                                        dir_imp_mods used_names
-    let usages = mod_usages ++ [ UsageFile { usg_file_path = f
+    let usages = mod_usages ++ [ UsageFile { usg_file_path = mkFastString f
                                            , usg_file_hash = hash
                                            , usg_file_label = Nothing }
                                | (f, hash) <- zip dependent_files hashes ]
@@ -174,7 +175,7 @@ mkObjectUsage pit plugins fc hug th_links_needed th_pkgs_needed = do
 
     msg m = moduleNameString (moduleName m) ++ "[TH] changed"
 
-    fing mmsg fn = UsageFile fn <$> lookupFileCache fc fn <*> pure mmsg
+    fing mmsg fn = UsageFile (mkFastString fn) <$> lookupFileCache fc fn <*> pure mmsg
 
     unlinkedToUsage m ul =
       case nameOfObject_maybe ul of
diff --git a/compiler/GHC/Iface/Load.hs b/compiler/GHC/Iface/Load.hs
index 16f4b900b5..f5628e8fb6 100644
--- a/compiler/GHC/Iface/Load.hs
+++ b/compiler/GHC/Iface/Load.hs
@@ -1175,7 +1175,7 @@ pprUsage usage@UsageHomeModule{}
         )
 pprUsage usage@UsageFile{}
   = hsep [text "addDependentFile",
-          doubleQuotes (text (usg_file_path usage)),
+          doubleQuotes (ftext (usg_file_path usage)),
           ppr (usg_file_hash usage)]
 pprUsage usage@UsageMergedRequirement{}
   = hsep [text "merged", ppr (usg_mod usage), ppr (usg_mod_hash usage)]
diff --git a/compiler/GHC/Iface/Recomp.hs b/compiler/GHC/Iface/Recomp.hs
index b0e668f0e6..298e876595 100644
--- a/compiler/GHC/Iface/Recomp.hs
+++ b/compiler/GHC/Iface/Recomp.hs
@@ -771,12 +771,12 @@ checkModUsage fc UsageFile{ usg_file_path = file,
                             usg_file_label = mlabel } =
   liftIO $
     handleIO handler $ do
-      new_hash <- lookupFileCache fc file
+      new_hash <- lookupFileCache fc $ unpackFS file
       if (old_hash /= new_hash)
          then return recomp
          else return UpToDate
  where
-   reason = FileChanged file
+   reason = FileChanged $ unpackFS file
    recomp  = needsRecompileBecause $ fromMaybe reason $ fmap CustomReason mlabel
    handler = if debugIsOn
       then \e -> pprTrace "UsageFile" (text (show e)) $ return recomp
diff --git a/compiler/GHC/Unit/Module/Deps.hs b/compiler/GHC/Unit/Module/Deps.hs
index 583b7fdaaa..75063e901f 100644
--- a/compiler/GHC/Unit/Module/Deps.hs
+++ b/compiler/GHC/Unit/Module/Deps.hs
@@ -21,6 +21,8 @@ where
 
 import GHC.Prelude
 
+import GHC.Data.FastString
+
 import GHC.Types.SafeHaskell
 import GHC.Types.Name
 
@@ -275,7 +277,7 @@ data Usage
   -- | A file upon which the module depends, e.g. a CPP #include, or using TH's
   -- 'addDependentFile'
   | UsageFile {
-        usg_file_path  :: FilePath,
+        usg_file_path  :: FastString,
         -- ^ External file dependency. From a CPP #include or TH
         -- addDependentFile. Should be absolute.
         usg_file_hash  :: Fingerprint,