Cleanup String/FastString conversions

Remove unused mkPtrString and isUnderscoreFS.
We no longer use mkPtrString since 1d03d8bef96.

Remove unnecessary conversions between FastString and String and back.

17 files changed, 67 insertions, 99 deletions

diff --git a/compiler/GHC/Core/Opt/Stats.hs b/compiler/GHC/Core/Opt/Stats.hs
index 79dfffbcfb..7f2043dfc7 100644
--- a/compiler/GHC/Core/Opt/Stats.hs
+++ b/compiler/GHC/Core/Opt/Stats.hs
@@ -213,7 +213,7 @@ pprTickCounts counts
 
 pprTickGroup :: NonEmpty (Tick, Int) -> SDoc
 pprTickGroup group@((tick1,_) :| _)
-  = hang (int (sum (fmap snd group)) <+> text (tickString tick1))
+  = hang (int (sum (fmap snd group)) <+> pprTickType tick1)
        2 (vcat [ int n <+> pprTickCts tick
                                     -- flip as we want largest first
                | (tick,n) <- sortOn (Down . snd) (NE.toList group)])
@@ -242,7 +242,7 @@ data Tick  -- See Note [Which transformations are innocuous]
   | SimplifierDone              -- Ticked at each iteration of the simplifier
 
 instance Outputable Tick where
-  ppr tick = text (tickString tick) <+> pprTickCts tick
+  ppr tick = pprTickType tick <+> pprTickCts tick
 
 instance Eq Tick where
   a == b = case a `cmpTick` b of
@@ -270,23 +270,23 @@ tickToTag (FillInCaseDefault _)         = 13
 tickToTag SimplifierDone                = 16
 tickToTag (AltMerge _)                  = 17
 
-tickString :: Tick -> String
-tickString (PreInlineUnconditionally _) = "PreInlineUnconditionally"
-tickString (PostInlineUnconditionally _)= "PostInlineUnconditionally"
-tickString (UnfoldingDone _)            = "UnfoldingDone"
-tickString (RuleFired _)                = "RuleFired"
-tickString LetFloatFromLet              = "LetFloatFromLet"
-tickString (EtaExpansion _)             = "EtaExpansion"
-tickString (EtaReduction _)             = "EtaReduction"
-tickString (BetaReduction _)            = "BetaReduction"
-tickString (CaseOfCase _)               = "CaseOfCase"
-tickString (KnownBranch _)              = "KnownBranch"
-tickString (CaseMerge _)                = "CaseMerge"
-tickString (AltMerge _)                 = "AltMerge"
-tickString (CaseElim _)                 = "CaseElim"
-tickString (CaseIdentity _)             = "CaseIdentity"
-tickString (FillInCaseDefault _)        = "FillInCaseDefault"
-tickString SimplifierDone               = "SimplifierDone"
+pprTickType :: Tick -> SDoc
+pprTickType (PreInlineUnconditionally _) = text "PreInlineUnconditionally"
+pprTickType (PostInlineUnconditionally _)= text "PostInlineUnconditionally"
+pprTickType (UnfoldingDone _)            = text "UnfoldingDone"
+pprTickType (RuleFired _)                = text "RuleFired"
+pprTickType LetFloatFromLet              = text "LetFloatFromLet"
+pprTickType (EtaExpansion _)             = text "EtaExpansion"
+pprTickType (EtaReduction _)             = text "EtaReduction"
+pprTickType (BetaReduction _)            = text "BetaReduction"
+pprTickType (CaseOfCase _)               = text "CaseOfCase"
+pprTickType (KnownBranch _)              = text "KnownBranch"
+pprTickType (CaseMerge _)                = text "CaseMerge"
+pprTickType (AltMerge _)                 = text "AltMerge"
+pprTickType (CaseElim _)                 = text "CaseElim"
+pprTickType (CaseIdentity _)             = text "CaseIdentity"
+pprTickType (FillInCaseDefault _)        = text "FillInCaseDefault"
+pprTickType SimplifierDone               = text "SimplifierDone"
 
 pprTickCts :: Tick -> SDoc
 pprTickCts (PreInlineUnconditionally v) = ppr v
diff --git a/compiler/GHC/Data/FastString.hs b/compiler/GHC/Data/FastString.hs
index 483d40cca1..98814fa6b3 100644
--- a/compiler/GHC/Data/FastString.hs
+++ b/compiler/GHC/Data/FastString.hs
@@ -30,8 +30,8 @@
 --   * Pointer and size of a Latin-1 encoded string.
 --   * Practically no operations.
 --   * Outputting them is fast.
---   * Generated by 'mkPtrString'.
---   * Length of string literals (mkPtrString "abc") is computed statically
+--   * Generated by 'mkPtrString#'.
+--   * Length of string literals (mkPtrString# "abc"#) is computed statically
 --   * Turn into 'GHC.Utils.Outputable.SDoc' with 'GHC.Utils.Outputable.ptext'
 --   * Requires manual memory management.
 --     Improper use may lead to memory leaks or dangling pointers.
@@ -85,7 +85,6 @@ module GHC.Data.FastString
         concatFS,
         consFS,
         nilFS,
-        isUnderscoreFS,
         lexicalCompareFS,
         uniqCompareFS,
 
@@ -101,7 +100,6 @@ module GHC.Data.FastString
 
         -- ** Construction
         mkPtrString#,
-        mkPtrString,
 
         -- ** Deconstruction
         unpackPtrString,
@@ -134,7 +132,6 @@ import Foreign.C
 import System.IO
 import Data.Data
 import Data.IORef
-import Data.Char
 import Data.Semigroup as Semi
 
 import Foreign
@@ -623,9 +620,6 @@ uniqueOfFS fs = uniq fs
 nilFS :: FastString
 nilFS = mkFastString ""
 
-isUnderscoreFS :: FastString -> Bool
-isUnderscoreFS fs = fs == fsLit "_"
-
 -- -----------------------------------------------------------------------------
 -- Stats
 
@@ -667,30 +661,6 @@ mkPtrString# :: Addr# -> PtrString
 {-# INLINE mkPtrString# #-}
 mkPtrString# a# = PtrString (Ptr a#) (ptrStrLength (Ptr a#))
 
--- | Encode a 'String' into a newly allocated 'PtrString' using Latin-1
--- encoding.  The original string must not contain non-Latin-1 characters
--- (above codepoint @0xff@).
-{-# NOINLINE[0] mkPtrString #-} -- see rules below
-mkPtrString :: String -> PtrString
-mkPtrString s =
- -- we don't use `unsafeDupablePerformIO` here to avoid potential memory leaks
- -- and because someone might be using `eqAddr#` to check for string equality.
- unsafePerformIO (do
-   let len = length s
-   p <- mallocBytes len
-   let
-     loop :: Int -> String -> IO ()
-     loop !_ []    = return ()
-     loop n (c:cs) = do
-        pokeByteOff p n (fromIntegral (ord c) :: Word8)
-        loop (1+n) cs
-   loop 0 s
-   return (PtrString p len)
- )
-
-{-# RULES "mkPtrString"
-    forall x . mkPtrString (unpackCString# x) = mkPtrString#  x #-}
-
 -- | Decode a 'PtrString' back into a 'String' using Latin-1 encoding.
 -- This does not free the memory associated with 'PtrString'.
 unpackPtrString :: PtrString -> String
diff --git a/compiler/GHC/Hs/Dump.hs b/compiler/GHC/Hs/Dump.hs
index 77d2036425..942ece7f37 100644
--- a/compiler/GHC/Hs/Dump.hs
+++ b/compiler/GHC/Hs/Dump.hs
@@ -158,7 +158,7 @@ showAstData bs ba a0 = blankLine $$ showAstData' a0
 
             occName n  =  braces $
                           text "OccName:"
-                      <+> text (occNameString n)
+                      <+> ftext (occNameFS n)
 
             moduleName :: ModuleName -> SDoc
             moduleName m = braces $ text "ModuleName:" <+> ppr m
diff --git a/compiler/GHC/HsToCore/Foreign/C.hs b/compiler/GHC/HsToCore/Foreign/C.hs
index 13ba3123f4..ed9137f99d 100644
--- a/compiler/GHC/HsToCore/Foreign/C.hs
+++ b/compiler/GHC/HsToCore/Foreign/C.hs
@@ -423,7 +423,7 @@ mkFExportCBits dflags c_nm maybe_target arg_htys res_hty is_IO_res_ty cc
   arg_cname n stg_ty
         | libffi    = char '*' <> parens (stg_ty <> char '*') <>
                       text "args" <> brackets (int (n-1))
-        | otherwise = text ('a':show n)
+        | otherwise = char 'a' <> int n
 
   -- generate a libffi-style stub if this is a "wrapper" and libffi is enabled
   libffi = platformMisc_libFFI (platformMisc dflags) && isNothing maybe_target
@@ -552,16 +552,16 @@ mkFExportCBits dflags c_nm maybe_target arg_htys res_hty is_IO_res_ty cc
      ]
 
 mkHObj :: Type -> SDoc
-mkHObj t = text "rts_mk" <> text (showFFIType t)
+mkHObj t = text "rts_mk" <> showFFIType t
 
 unpackHObj :: Type -> SDoc
-unpackHObj t = text "rts_get" <> text (showFFIType t)
+unpackHObj t = text "rts_get" <> showFFIType t
 
 showStgType :: Type -> SDoc
-showStgType t = text "Hs" <> text (showFFIType t)
+showStgType t = text "Hs" <> showFFIType t
 
-showFFIType :: Type -> String
-showFFIType t = getOccString (getName (typeTyCon t))
+showFFIType :: Type -> SDoc
+showFFIType t = ftext (occNameFS (getOccName (typeTyCon t)))
 
 typeTyCon :: Type -> TyCon
 typeTyCon ty
diff --git a/compiler/GHC/HsToCore/Pmc/Solver/Types.hs b/compiler/GHC/HsToCore/Pmc/Solver/Types.hs
index fa22807358..e9c8c66033 100644
--- a/compiler/GHC/HsToCore/Pmc/Solver/Types.hs
+++ b/compiler/GHC/HsToCore/Pmc/Solver/Types.hs
@@ -766,7 +766,7 @@ it's already overloaded.
 
 instance Outputable PmLitValue where
   ppr (PmLitInt i)        = ppr i
-  ppr (PmLitRat r)        = ppr (double (fromRat r)) -- good enough
+  ppr (PmLitRat r)        = double (fromRat r) -- good enough
   ppr (PmLitChar c)       = pprHsChar c
   ppr (PmLitString s)     = pprHsString s
   ppr (PmLitOverInt n i)  = minuses n (ppr i)
diff --git a/compiler/GHC/HsToCore/Quote.hs b/compiler/GHC/HsToCore/Quote.hs
index c707a29368..18126d3a4f 100644
--- a/compiler/GHC/HsToCore/Quote.hs
+++ b/compiler/GHC/HsToCore/Quote.hs
@@ -744,7 +744,7 @@ repForD (L loc (ForeignImport { fd_name = name, fd_sig_ty = typ
       MkC cc' <- repCCallConv cc
       MkC s' <- repSafety s
       cis' <- conv_cimportspec cis
-      MkC str <- coreStringLit (static ++ chStr ++ cis')
+      MkC str <- coreStringLit (mkFastString (static ++ chStr ++ cis'))
       dec <- rep2 forImpDName [cc', s', str, name', typ']
       return (locA loc, dec)
  where
@@ -818,7 +818,7 @@ repRuleD (L loc (HsRule { rd_name = n
                          ; tm_bndrs' <- repListM ruleBndrTyConName
                                                 repRuleBndr
                                                 tm_bndrs
-                         ; n'   <- coreStringLit $ unpackFS $ unLoc n
+                         ; n'   <- coreStringLit $ unLoc n
                          ; act' <- repPhases act
                          ; lhs' <- repLE lhs
                          ; rhs' <- repLE rhs
@@ -1861,7 +1861,7 @@ rep_implicit_param_bind (L loc (IPBind _ (L _ n) (L _ rhs)))
       ; return (locA loc, ipb) }
 
 rep_implicit_param_name :: HsIPName -> MetaM (Core String)
-rep_implicit_param_name (HsIPName name) = coreStringLit (unpackFS name)
+rep_implicit_param_name (HsIPName name) = coreStringLit name
 
 rep_val_binds :: HsValBinds GhcRn -> MetaM [(SrcSpan, Core (M TH.Dec))]
 -- Assumes: all the binders of the binding are already in the meta-env
@@ -2195,8 +2195,8 @@ globalVar name
         ; rep2_nwDsM mkNameLName [occ,uni] }
   where
       mod = assert (isExternalName name) nameModule name
-      name_mod = moduleNameString (moduleName mod)
-      name_pkg = unitString (moduleUnit mod)
+      name_mod = moduleNameFS (moduleName mod)
+      name_pkg = unitFS (moduleUnit mod)
       name_occ = nameOccName name
       mk_varg | isDataOcc name_occ = mkNameG_dName
               | isVarOcc  name_occ = mkNameG_vName
@@ -2235,10 +2235,10 @@ wrapGenSyms binds body@(MkC b)
                       gensym_app (MkC (Lam id body')) }
 
 nameLit :: Name -> DsM (Core String)
-nameLit n = coreStringLit (occNameString (nameOccName n))
+nameLit n = coreStringLit (occNameFS (nameOccName n))
 
 occNameLit :: OccName -> MetaM (Core String)
-occNameLit name = coreStringLit (occNameString name)
+occNameLit name = coreStringLit (occNameFS name)
 
 
 -- %*********************************************************************
@@ -2416,7 +2416,7 @@ repDoBlock doName maybeModName (MkC ss) = do
     coreModNameM :: MetaM (Core (Maybe TH.ModName))
     coreModNameM = case maybeModName of
       Just m -> do
-        MkC s <- coreStringLit (moduleNameString m)
+        MkC s <- coreStringLit (moduleNameFS m)
         mName <- rep2_nw mkModNameName [s]
         coreJust modNameTyConName mName
       _ -> coreNothing modNameTyConName
@@ -2950,17 +2950,17 @@ repUnboundVar (MkC name) = rep2 unboundVarEName [name]
 
 repOverLabel :: FastString -> MetaM (Core (M TH.Exp))
 repOverLabel fs = do
-                    (MkC s) <- coreStringLit $ unpackFS fs
+                    MkC s <- coreStringLit fs
                     rep2 labelEName [s]
 
 repGetField :: Core (M TH.Exp) -> FastString -> MetaM (Core (M TH.Exp))
 repGetField (MkC exp) fs = do
-  MkC s <- coreStringLit $ unpackFS fs
+  MkC s <- coreStringLit fs
   rep2 getFieldEName [exp,s]
 
 repProjection :: NonEmpty FastString -> MetaM (Core (M TH.Exp))
 repProjection fs = do
-  MkC xs <- coreListNonEmpty stringTy <$> mapM (coreStringLit . unpackFS) fs
+  MkC xs <- coreListNonEmpty stringTy <$> mapM coreStringLit fs
   rep2 projectionEName [xs]
 
 ------------ Lists -------------------
@@ -3004,8 +3004,8 @@ nonEmptyCoreList xs@(MkC x:_) = MkC (mkListExpr (exprType x) (map unC xs))
 nonEmptyCoreList' :: NonEmpty (Core a) -> Core [a]
 nonEmptyCoreList' xs@(MkC x:|_) = MkC (mkListExpr (exprType x) (toList $ fmap unC xs))
 
-coreStringLit :: MonadThings m => String -> m (Core String)
-coreStringLit s = do { z <- mkStringExpr s; return(MkC z) }
+coreStringLit :: MonadThings m => FastString -> m (Core String)
+coreStringLit s = do { z <- mkStringExprFS s; return (MkC z) }
 
 ------------------- Maybe ------------------
 
diff --git a/compiler/GHC/Parser.y b/compiler/GHC/Parser.y
index 2a4f66f057..7b7ab4f4c8 100644
--- a/compiler/GHC/Parser.y
+++ b/compiler/GHC/Parser.y
@@ -67,7 +67,7 @@ import GHC.Prelude
 import qualified GHC.Data.Strict as Strict
 
 import GHC.Types.Name.Reader
-import GHC.Types.Name.Occurrence ( varName, dataName, tcClsName, tvName, occNameFS, mkVarOcc, occNameString)
+import GHC.Types.Name.Occurrence ( varName, dataName, tcClsName, tvName, occNameFS, mkVarOccFS, occNameString)
 import GHC.Types.SrcLoc
 import GHC.Types.Basic
 import GHC.Types.Error ( GhcHint(..) )
@@ -3447,7 +3447,7 @@ fbind   :: { forall b. DisambECP b => PV (Fbind b) }
                                 final = last fields
                                 l = comb2 (reLoc $1) $3
                                 isPun = True
-                            var <- mkHsVarPV (L (noAnnSrcSpan $ getLocA final) (mkRdrUnqual . mkVarOcc . unpackFS . field_label . unLoc . dfoLabel . unLoc $ final))
+                            var <- mkHsVarPV (L (noAnnSrcSpan $ getLocA final) (mkRdrUnqual . mkVarOccFS . field_label . unLoc . dfoLabel . unLoc $ final))
                             fmap Right $ mkHsProjUpdatePV l (L l fields) var isPun []
                         }
 
@@ -3830,7 +3830,7 @@ special_id
 
 special_sym :: { Located FastString }
 special_sym : '.'       { sL1 $1 (fsLit ".") }
-            | '*'       { sL1 $1 (fsLit (starSym (isUnicode $1))) }
+            | '*'       { sL1 $1 (starSym (isUnicode $1)) }
 
 -----------------------------------------------------------------------------
 -- Data constructors
diff --git a/compiler/GHC/Parser/HaddockLex.x b/compiler/GHC/Parser/HaddockLex.x
index e215769f9e..682ede39a4 100644
--- a/compiler/GHC/Parser/HaddockLex.x
+++ b/compiler/GHC/Parser/HaddockLex.x
@@ -148,7 +148,7 @@ lexStringLiteral identParser (L l sl@(StringLiteral _ fs _))
       RealSrcSpan span _ -> [(RealSrcSpan span' Strict.Nothing, tok) | (span', tok) <- alexScanTokens (realSrcSpanStart span) bs]
       UnhelpfulSpan reason -> [(UnhelpfulSpan reason, tok) | (_, tok) <- alexScanTokens fakeLoc bs]
 
-    fakeLoc = mkRealSrcLoc (mkFastString "") 0 0
+    fakeLoc = mkRealSrcLoc nilFS 0 0
 
 -- | Lex identifiers from a docstring.
 lexHsDoc :: P (LocatedN RdrName)      -- ^ A precise identifier parser
@@ -169,7 +169,7 @@ lexHsDoc identParser doc =
     plausibleIdents (L (UnhelpfulSpan reason) (HsDocStringChunk s))
       = [(UnhelpfulSpan reason, tok) | (_, tok) <- alexScanTokens fakeLoc s] -- preserve the original reason
 
-    fakeLoc = mkRealSrcLoc (mkFastString "") 0 0
+    fakeLoc = mkRealSrcLoc nilFS 0 0
 
 validateIdentWith :: P (LocatedN RdrName) -> SrcSpan -> ByteString -> Maybe (Located RdrName)
 validateIdentWith identParser mloc str0 =
@@ -191,7 +191,7 @@ validateIdentWith identParser mloc str0 =
       buffer = stringBufferFromByteString str0
       realSrcLc = case mloc of
         RealSrcSpan loc _ -> realSrcSpanStart loc
-        UnhelpfulSpan _ -> mkRealSrcLoc (mkFastString "") 0 0
+        UnhelpfulSpan _ -> mkRealSrcLoc nilFS 0 0
       pstate = initParserState pflags buffer realSrcLc
   in case unP identParser pstate of
     POk _ name -> Just $ case mloc of
diff --git a/compiler/GHC/Parser/PostProcess.hs b/compiler/GHC/Parser/PostProcess.hs
index 02a4723f6f..8e08a8c874 100644
--- a/compiler/GHC/Parser/PostProcess.hs
+++ b/compiler/GHC/Parser/PostProcess.hs
@@ -965,8 +965,7 @@ mkRuleTyVarBndrs = fmap cvt_one
 checkRuleTyVarBndrNames :: [LHsTyVarBndr flag GhcPs] -> P ()
 checkRuleTyVarBndrNames = mapM_ (check . fmap hsTyVarName)
   where check (L loc (Unqual occ)) =
-          -- TODO: don't use string here, OccName has a Unique/FastString
-          when ((occNameString occ ==) `any` ["forall","family","role"])
+          when (occNameFS occ `elem` [fsLit "forall",fsLit "family",fsLit "role"])
             (addFatalError $ mkPlainErrorMsgEnvelope (locA loc) $
                (PsErrParseErrorOnInput occ))
         check _ = panic "checkRuleTyVarBndrNames"
@@ -1009,7 +1008,7 @@ checkTyClHdr is_cls ty
     -- workaround to define '*' despite StarIsType
     go _ (HsParTy an (L l (HsStarTy _ isUni))) acc ops' cps' fix
       = do { addPsMessage (locA l) PsWarnStarBinder
-           ; let name = mkOccName tcClsName (starSym isUni)
+           ; let name = mkOccNameFS tcClsName (starSym isUni)
            ; let a' = newAnns l an
            ; return (L a' (Unqual name), acc, fix
                     , (reverse ops') ++ cps') }
@@ -2776,7 +2775,7 @@ mkExport (L lc cconv) (L le (StringLiteral esrc entity _), v, ty)
 -- want z-encoding (e.g. names with z's in them shouldn't be doubled)
 --
 mkExtName :: RdrName -> CLabelString
-mkExtName rdrNm = mkFastString (occNameString (rdrNameOcc rdrNm))
+mkExtName rdrNm = occNameFS (rdrNameOcc rdrNm)
 
 --------------------------------------------------------------------------------
 -- Help with module system imports/exports
@@ -3142,9 +3141,9 @@ token_location_widenR (TokenLoc (EpaDelta _ _)) _ =
 -----------------------------------------------------------------------------
 -- Token symbols
 
-starSym :: Bool -> String
-starSym True = "★"
-starSym False = "*"
+starSym :: Bool -> FastString
+starSym True = fsLit "★"
+starSym False = fsLit "*"
 
 -----------------------------------------
 -- Bits and pieces for RecordDotSyntax.
diff --git a/compiler/GHC/Tc/Errors/Ppr.hs b/compiler/GHC/Tc/Errors/Ppr.hs
index 84338000b9..bb4b0718cc 100644
--- a/compiler/GHC/Tc/Errors/Ppr.hs
+++ b/compiler/GHC/Tc/Errors/Ppr.hs
@@ -3781,13 +3781,13 @@ pprConversionFailReason = \case
     text "Illegal" <+> pprNameSpace ctxt_ns
     <+> text "name:" <+> quotes (text occ)
   SumAltArityExceeded alt arity ->
-    text "Sum alternative" <+> text (show alt)
-    <+> text "exceeds its arity," <+> text (show arity)
+    text "Sum alternative" <+> int alt
+    <+> text "exceeds its arity," <+> int arity
   IllegalSumAlt alt ->
-    vcat [ text "Illegal sum alternative:" <+> text (show alt)
+    vcat [ text "Illegal sum alternative:" <+> int alt
          , nest 2 $ text "Sum alternatives must start from 1" ]
   IllegalSumArity arity ->
-    vcat [ text "Illegal sum arity:" <+> text (show arity)
+    vcat [ text "Illegal sum arity:" <+> int arity
          , nest 2 $ text "Sums must have an arity of at least 2" ]
   MalformedType typeOrKind ty ->
     text "Malformed " <> text ty_str <+> text (show ty)
diff --git a/compiler/GHC/Types/CostCentre.hs b/compiler/GHC/Types/CostCentre.hs
index 092b727d8d..cbfe4637a3 100644
--- a/compiler/GHC/Types/CostCentre.hs
+++ b/compiler/GHC/Types/CostCentre.hs
@@ -259,7 +259,7 @@ instance Outputable CostCentre where
   ppr cc = getPprStyle $ \ sty ->
            if codeStyle sty
            then ppCostCentreLbl cc
-           else text (costCentreUserName cc)
+           else ftext (costCentreUserNameFS cc)
 
 -- Printing in Core
 pprCostCentreCore :: CostCentre -> SDoc
diff --git a/compiler/GHC/Types/FieldLabel.hs b/compiler/GHC/Types/FieldLabel.hs
index d1da25ca08..2c654926ae 100644
--- a/compiler/GHC/Types/FieldLabel.hs
+++ b/compiler/GHC/Types/FieldLabel.hs
@@ -188,7 +188,7 @@ fieldSelectorOccName lbl dc dup_fields_ok has_sel
   | otherwise     = mkVarOccFS fl
   where
     fl      = field_label lbl
-    str     = ":" ++ unpackFS fl ++ ":" ++ occNameString dc
+    str     = concatFS [fsLit ":", fl, fsLit ":", occNameFS dc]
 
 -- | Undo the name mangling described in Note [FieldLabel] to produce a Name
 -- that has the user-visible OccName (but the selector's unique).  This should
diff --git a/compiler/GHC/Types/Literal.hs b/compiler/GHC/Types/Literal.hs
index 9997859afc..4ece6800ec 100644
--- a/compiler/GHC/Types/Literal.hs
+++ b/compiler/GHC/Types/Literal.hs
@@ -904,7 +904,7 @@ pprLiteral add_par (LitLabel l mb fod) =
     add_par (text "__label" <+> b <+> ppr fod)
     where b = case mb of
               Nothing -> pprHsString l
-              Just x  -> doubleQuotes (text (unpackFS l ++ '@':show x))
+              Just x  -> doubleQuotes (ftext l <> text ('@':show x))
 pprLiteral _       (LitRubbish rep)
   = text "RUBBISH" <> parens (ppr rep)
 
diff --git a/compiler/GHC/Types/Name/Occurrence.hs b/compiler/GHC/Types/Name/Occurrence.hs
index 947982b53d..38eefebc59 100644
--- a/compiler/GHC/Types/Name/Occurrence.hs
+++ b/compiler/GHC/Types/Name/Occurrence.hs
@@ -646,8 +646,8 @@ mkGenR   = mk_simple_deriv tcName "Rep_"
 mkGen1R  = mk_simple_deriv tcName "Rep1_"
 
 -- Overloaded record field selectors
-mkRecFldSelOcc :: String -> OccName
-mkRecFldSelOcc s = mk_deriv varName "$sel" [fsLit s]
+mkRecFldSelOcc :: FastString -> OccName
+mkRecFldSelOcc s = mk_deriv varName "$sel" [s]
 
 mk_simple_deriv :: NameSpace -> FastString -> OccName -> OccName
 mk_simple_deriv sp px occ = mk_deriv sp px [occNameFS occ]
diff --git a/compiler/GHC/Types/Name/Occurrence.hs-boot b/compiler/GHC/Types/Name/Occurrence.hs-boot
index 1c27d943a7..92661cb42b 100644
--- a/compiler/GHC/Types/Name/Occurrence.hs-boot
+++ b/compiler/GHC/Types/Name/Occurrence.hs-boot
@@ -1,6 +1,5 @@
 module GHC.Types.Name.Occurrence where
 
-import GHC.Prelude (String)
 import GHC.Data.FastString
 
 data OccName
@@ -8,6 +7,6 @@ data OccName
 class HasOccName name where
   occName :: name -> OccName
 
-occNameString :: OccName -> String
-mkRecFldSelOcc :: String -> OccName
+occNameFS :: OccName -> FastString
+mkRecFldSelOcc :: FastString -> OccName
 mkVarOccFS :: FastString -> OccName
diff --git a/compiler/GHC/Unit/State.hs b/compiler/GHC/Unit/State.hs
index 403216954f..ca361d69d2 100644
--- a/compiler/GHC/Unit/State.hs
+++ b/compiler/GHC/Unit/State.hs
@@ -2036,7 +2036,7 @@ mayThrowUnitErr = \case
 instance Outputable UnitErr where
     ppr = \case
         CloseUnitErr p mb_parent
-            -> (ftext (fsLit "unknown unit:") <+> ppr p)
+            -> (text "unknown unit:" <+> ppr p)
                <> case mb_parent of
                      Nothing     -> Outputable.empty
                      Just parent -> space <> parens (text "dependency of"
diff --git a/ghc/GHCi/UI.hs b/ghc/GHCi/UI.hs
index 4efb35f35e..519049cad7 100644
--- a/ghc/GHCi/UI.hs
+++ b/ghc/GHCi/UI.hs
@@ -3423,7 +3423,7 @@ pprStopped res =
   text "Stopped in"
     <+> ((case mb_mod_name of
            Nothing -> empty
-           Just mod_name -> text (moduleNameString mod_name) <> char '.')
+           Just mod_name -> ftext (moduleNameFS mod_name) <> char '.')
          <> text (GHC.resumeDecl res))
     <> char ',' <+> ppr (GHC.resumeSpan res)
  where