GHC/HsToCore/Coverage.hs

    {-# LANGUAGE DeriveFunctor            #-}
    {-# LANGUAGE NondecreasingIndentation #-}
    {-# LANGUAGE TypeFamilies             #-}

    {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}

    {-
    (c) Galois, 2006
    (c) University of Glasgow, 2007
    -}

    module GHC.HsToCore.Coverage (addTicksToBinds, hpcInitCode) where

    import GHC.Prelude as Prelude

    import GHC.Driver.Session
    import GHC.Driver.Backend
    import GHC.Driver.Ppr
    import GHC.Driver.Env

    import qualified GHC.Runtime.Interpreter as GHCi
    import GHCi.RemoteTypes
    import GHC.ByteCode.Types
    import GHC.Stack.CCS
    import GHC.Hs
    import GHC.Unit
    import GHC.Cmm.CLabel

    import GHC.Core.Type
    import GHC.Core.TyCon

    import GHC.Data.Maybe
    import GHC.Data.FastString
    import GHC.Data.Bag

    import GHC.Utils.Misc
    import GHC.Utils.Outputable as Outputable
    import GHC.Utils.Panic
    import GHC.Utils.Monad
    import GHC.Utils.Logger

    import GHC.Types.SrcLoc
    import GHC.Types.Basic
    import GHC.Types.Id
    import GHC.Types.Var.Set
    import GHC.Types.Name.Set hiding (FreeVars)
    import GHC.Types.Name
    import GHC.Types.HpcInfo
    import GHC.Types.CostCentre
    import GHC.Types.CostCentre.State
    import GHC.Types.ForeignStubs
    import GHC.Types.Tickish

    import Control.Monad
    import Data.List (isSuffixOf, intersperse)
    import Data.Array
    import Data.Time
    import System.Directory

    import Trace.Hpc.Mix
    import Trace.Hpc.Util

    import qualified Data.ByteString as BS
    import Data.Set (Set)
    import qualified Data.Set as Set

    {-
    ************************************************************************
    *                                                                      *
    *              The main function: addTicksToBinds
    *                                                                      *
    ************************************************************************
    -}

    addTicksToBinds
            :: HscEnv
            -> Module
            -> ModLocation          -- ... off the current module
            -> NameSet              -- Exported Ids.  When we call addTicksToBinds,
                                    -- isExportedId doesn't work yet (the desugarer
                                    -- hasn't set it), so we have to work from this set.
            -> [TyCon]              -- Type constructor in this module
            -> LHsBinds GhcTc
            -> IO (LHsBinds GhcTc, HpcInfo, Maybe ModBreaks)

    addTicksToBinds hsc_env mod mod_loc exports tyCons binds
      | let dflags = hsc_dflags hsc_env
            passes = coveragePasses dflags
      , not (null passes)
      , Just orig_file <- ml_hs_file mod_loc = do

         let  orig_file2 = guessSourceFile binds orig_file

              tickPass tickish (binds,st) =
                let env = TTE
                          { fileName     = mkFastString orig_file2
                          , declPath     = []
                          , tte_dflags   = dflags
                          , exports      = exports
                          , inlines      = emptyVarSet
                          , inScope      = emptyVarSet
                          , blackList    = Set.fromList $
                                           mapMaybe (\tyCon -> case getSrcSpan (tyConName tyCon) of
                                                                 RealSrcSpan l _ -> Just l
                                                                 UnhelpfulSpan _ -> Nothing)
                                                    tyCons
                          , density      = mkDensity tickish dflags
                          , this_mod     = mod
                          , tickishType  = tickish
                          }
                    (binds',_,st') = unTM (addTickLHsBinds binds) env st
                in (binds', st')

              initState = TT { tickBoxCount = 0
                             , mixEntries   = []
                             , ccIndices    = newCostCentreState
                             }

              (binds1,st) = foldr tickPass (binds, initState) passes

         let tickCount = tickBoxCount st
             entries = reverse $ mixEntries st
         hashNo <- writeMixEntries dflags mod tickCount entries orig_file2
         modBreaks <- mkModBreaks hsc_env mod tickCount entries

         let logger = hsc_logger hsc_env
         dumpIfSet_dyn logger dflags Opt_D_dump_ticked "HPC" FormatHaskell
           (pprLHsBinds binds1)

         return (binds1, HpcInfo tickCount hashNo, modBreaks)

      | otherwise = return (binds, emptyHpcInfo False, Nothing)

    guessSourceFile :: LHsBinds GhcTc -> FilePath -> FilePath
    guessSourceFile binds orig_file =
         -- Try look for a file generated from a .hsc file to a
         -- .hs file, by peeking ahead.
         let top_pos = catMaybes $ foldr (\ (L pos _) rest ->
                                   srcSpanFileName_maybe (locA pos) : rest) [] binds
         in
         case top_pos of
            (file_name:_) | ".hsc" `isSuffixOf` unpackFS file_name
                          -> unpackFS file_name
            _ -> orig_file

    mkModBreaks :: HscEnv -> Module -> Int -> [MixEntry_] -> IO (Maybe ModBreaks)
    mkModBreaks hsc_env mod count entries
      | Just interp <- hsc_interp hsc_env
      , breakpointsEnabled (hsc_dflags hsc_env) = do
        breakArray <- GHCi.newBreakArray interp (length entries)
        ccs <- mkCCSArray hsc_env mod count entries
        let
               locsTicks  = listArray (0,count-1) [ span  | (span,_,_,_)  <- entries ]
               varsTicks  = listArray (0,count-1) [ vars  | (_,_,vars,_)  <- entries ]
               declsTicks = listArray (0,count-1) [ decls | (_,decls,_,_) <- entries ]
        return $ Just $ emptyModBreaks
                           { modBreaks_flags = breakArray
                           , modBreaks_locs  = locsTicks
                           , modBreaks_vars  = varsTicks
                           , modBreaks_decls = declsTicks
                           , modBreaks_ccs   = ccs
                           }
      | otherwise = return Nothing

    mkCCSArray
      :: HscEnv -> Module -> Int -> [MixEntry_]
      -> IO (Array BreakIndex (RemotePtr GHC.Stack.CCS.CostCentre))
    mkCCSArray hsc_env modul count entries =
      case hsc_interp hsc_env of
        Just interp | GHCi.interpreterProfiled interp -> do
          let module_str = moduleNameString (moduleName modul)
          costcentres <- GHCi.mkCostCentres interp module_str (map mk_one entries)
          return (listArray (0,count-1) costcentres)

        _ -> return (listArray (0,-1) [])
     where
        dflags = hsc_dflags hsc_env
        mk_one (srcspan, decl_path, _, _) = (name, src)
          where name = concat (intersperse "." decl_path)
                src = showSDoc dflags (ppr srcspan)

    writeMixEntries
      :: DynFlags -> Module -> Int -> [MixEntry_] -> FilePath -> IO Int
    writeMixEntries dflags mod count entries filename
      | not (gopt Opt_Hpc dflags) = return 0
      | otherwise   = do
            let
                hpc_dir = hpcDir dflags
                mod_name = moduleNameString (moduleName mod)

                hpc_mod_dir
                  | moduleUnit mod == mainUnit  = hpc_dir
                  | otherwise = hpc_dir ++ "/" ++ unitString (moduleUnit mod)

                tabStop = 8 -- <tab> counts as a normal char in GHC's
                            -- location ranges.

            createDirectoryIfMissing True hpc_mod_dir
            modTime <- getModificationUTCTime filename
            let entries' = [ (hpcPos, box)
                           | (span,_,_,box) <- entries, hpcPos <- [mkHpcPos span] ]
            when (entries' `lengthIsNot` count) $
              panic "the number of .mix entries are inconsistent"
            let hashNo = mixHash filename modTime tabStop entries'
            mixCreate hpc_mod_dir mod_name
                           $ Mix filename modTime (toHash hashNo) tabStop entries'
            return hashNo

    -- -----------------------------------------------------------------------------
    -- TickDensity: where to insert ticks

    data TickDensity
      = TickForCoverage       -- for Hpc
      | TickForBreakPoints    -- for GHCi
      | TickAllFunctions      -- for -prof-auto-all
      | TickTopFunctions      -- for -prof-auto-top
      | TickExportedFunctions -- for -prof-auto-exported
      | TickCallSites         -- for stack tracing
      deriving Eq

    mkDensity :: TickishType -> DynFlags -> TickDensity
    mkDensity tickish dflags = case tickish of
      HpcTicks             -> TickForCoverage
      SourceNotes          -> TickForCoverage
      Breakpoints          -> TickForBreakPoints
      ProfNotes ->
        case profAuto dflags of
          ProfAutoAll      -> TickAllFunctions
          ProfAutoTop      -> TickTopFunctions
          ProfAutoExports  -> TickExportedFunctions
          ProfAutoCalls    -> TickCallSites
          _other           -> panic "mkDensity"

    -- | Decide whether to add a tick to a binding or not.
    shouldTickBind  :: TickDensity
                    -> Bool         -- top level?
                    -> Bool         -- exported?
                    -> Bool         -- simple pat bind?
                    -> Bool         -- INLINE pragma?
                    -> Bool

    shouldTickBind density top_lev exported _simple_pat inline
     = case density of
          TickForBreakPoints    -> False
            -- we never add breakpoints to simple pattern bindings
            -- (there's always a tick on the rhs anyway).
          TickAllFunctions      -> not inline
          TickTopFunctions      -> top_lev && not inline
          TickExportedFunctions -> exported && not inline
          TickForCoverage       -> True
          TickCallSites         -> False

    shouldTickPatBind :: TickDensity -> Bool -> Bool
    shouldTickPatBind density top_lev
      = case density of
          TickForBreakPoints    -> False
          TickAllFunctions      -> True
          TickTopFunctions      -> top_lev
          TickExportedFunctions -> False
          TickForCoverage       -> False
          TickCallSites         -> False

    -- -----------------------------------------------------------------------------
    -- Adding ticks to bindings

    addTickLHsBinds :: LHsBinds GhcTc -> TM (LHsBinds GhcTc)
    addTickLHsBinds = mapBagM addTickLHsBind

    addTickLHsBind :: LHsBind GhcTc -> TM (LHsBind GhcTc)
    addTickLHsBind (L pos bind@(AbsBinds { abs_binds   = binds,
                                           abs_exports = abs_exports })) =
      withEnv add_exports $
        withEnv add_inlines $ do
          binds' <- addTickLHsBinds binds
          return $ L pos $ bind { abs_binds = binds' }
      where
       -- in AbsBinds, the Id on each binding is not the actual top-level
       -- Id that we are defining, they are related by the abs_exports
       -- field of AbsBinds.  So if we're doing TickExportedFunctions we need
       -- to add the local Ids to the set of exported Names so that we know to
       -- tick the right bindings.
       add_exports env =
         env{ exports = exports env `extendNameSetList`
                          [ idName mid
                          | ABE{ abe_poly = pid, abe_mono = mid } <- abs_exports
                          , idName pid `elemNameSet` (exports env) ] }

       -- See Note [inline sccs]
       add_inlines env =
         env{ inlines = inlines env `extendVarSetList`
                          [ mid
                          | ABE{ abe_poly = pid, abe_mono = mid } <- abs_exports
                          , isInlinePragma (idInlinePragma pid) ] }

    addTickLHsBind (L pos (funBind@(FunBind { fun_id = L _ id }))) = do
      let name = getOccString id
      decl_path <- getPathEntry
      density <- getDensity

      inline_ids <- liftM inlines getEnv
      -- See Note [inline sccs]
      let inline   = isInlinePragma (idInlinePragma id)
                     || id `elemVarSet` inline_ids

      -- See Note [inline sccs]
      tickish <- tickishType `liftM` getEnv
      if inline && tickish == ProfNotes then return (L pos funBind) else do

      (fvs, mg) <-
            getFreeVars $
            addPathEntry name $
            addTickMatchGroup False (fun_matches funBind)

      blackListed <- isBlackListed (locA pos)
      exported_names <- liftM exports getEnv

      -- We don't want to generate code for blacklisted positions
      -- We don't want redundant ticks on simple pattern bindings
      -- We don't want to tick non-exported bindings in TickExportedFunctions
      let simple = isSimplePatBind funBind
          toplev = null decl_path
          exported = idName id `elemNameSet` exported_names

      tick <- if not blackListed &&
                   shouldTickBind density toplev exported simple inline
                 then
                    bindTick density name (locA pos) fvs
                 else
                    return Nothing

      let mbCons = maybe Prelude.id (:)
      return $ L pos $ funBind { fun_matches = mg
                               , fun_tick = tick `mbCons` fun_tick funBind }

       where
       -- a binding is a simple pattern binding if it is a funbind with
       -- zero patterns
       isSimplePatBind :: HsBind GhcTc -> Bool
       isSimplePatBind funBind = matchGroupArity (fun_matches funBind) == 0

    -- TODO: Revisit this
    addTickLHsBind (L pos (pat@(PatBind { pat_lhs = lhs
                                        , pat_rhs = rhs }))) = do

      let simplePatId = isSimplePat lhs

      -- TODO: better name for rhs's for non-simple patterns?
      let name = maybe "(...)" getOccString simplePatId

      (fvs, rhs') <- getFreeVars $ addPathEntry name $ addTickGRHSs False False rhs
      let pat' = pat { pat_rhs = rhs'}

      -- Should create ticks here?
      density <- getDensity
      decl_path <- getPathEntry
      let top_lev = null decl_path
      if not (shouldTickPatBind density top_lev)
        then return (L pos pat')
        else do

        let mbCons = maybe id (:)

        let (initial_rhs_ticks, initial_patvar_tickss) = pat_ticks pat'

        -- Allocate the ticks

        rhs_tick <- bindTick density name (locA pos) fvs
        let rhs_ticks = rhs_tick `mbCons` initial_rhs_ticks

        patvar_tickss <- case simplePatId of
          Just{} -> return initial_patvar_tickss
          Nothing -> do
            let patvars = map getOccString (collectPatBinders CollNoDictBinders lhs)
            patvar_ticks <- mapM (\v -> bindTick density v (locA pos) fvs) patvars
            return
              (zipWith mbCons patvar_ticks
                              (initial_patvar_tickss ++ repeat []))

        return $ L pos $ pat' { pat_ticks = (rhs_ticks, patvar_tickss) }

    -- Only internal stuff, not from source, uses VarBind, so we ignore it.
    addTickLHsBind var_bind@(L _ (VarBind {})) = return var_bind
    addTickLHsBind patsyn_bind@(L _ (PatSynBind {})) = return patsyn_bind

    bindTick
      :: TickDensity -> String -> SrcSpan -> FreeVars -> TM (Maybe CoreTickish)
    bindTick density name pos fvs = do
      decl_path <- getPathEntry
      let
          toplev        = null decl_path
          count_entries = toplev || density == TickAllFunctions
          top_only      = density /= TickAllFunctions
          box_label     = if toplev then TopLevelBox [name]
                                    else LocalBox (decl_path ++ [name])
      --
      allocATickBox box_label count_entries top_only pos fvs

    -- Note [inline sccs]
    --
    -- The reason not to add ticks to INLINE functions is that this is
    -- sometimes handy for avoiding adding a tick to a particular function
    -- (see #6131)
    --
    -- So for now we do not add any ticks to INLINE functions at all.
    --
    -- We used to use isAnyInlinePragma to figure out whether to avoid adding
    -- ticks for this purpose. However, #12962 indicates that this contradicts
    -- the documentation on profiling (which only mentions INLINE pragmas).
    -- So now we're more careful about what we avoid adding ticks to.

    -- -----------------------------------------------------------------------------
    -- Decorate an LHsExpr with ticks

    -- selectively add ticks to interesting expressions
    addTickLHsExpr :: LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickLHsExpr e@(L pos e0) = do
      d <- getDensity
      case d of
        TickForBreakPoints | isGoodBreakExpr e0 -> tick_it
        TickForCoverage    -> tick_it
        TickCallSites      | isCallSite e0      -> tick_it
        _other             -> dont_tick_it
     where
       tick_it      = allocTickBox (ExpBox False) False False (locA pos)
                      $ addTickHsExpr e0
       dont_tick_it = addTickLHsExprNever e

    -- Add a tick to an expression which is the RHS of an equation or a binding.
    -- We always consider these to be breakpoints, unless the expression is a 'let'
    -- (because the body will definitely have a tick somewhere).  ToDo: perhaps
    -- we should treat 'case' and 'if' the same way?
    addTickLHsExprRHS :: LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickLHsExprRHS e@(L pos e0) = do
      d <- getDensity
      case d of
         TickForBreakPoints | HsLet{} <- e0 -> dont_tick_it
                            | otherwise     -> tick_it
         TickForCoverage -> tick_it
         TickCallSites   | isCallSite e0 -> tick_it
         _other          -> dont_tick_it
     where
       tick_it      = allocTickBox (ExpBox False) False False (locA pos)
                      $ addTickHsExpr e0
       dont_tick_it = addTickLHsExprNever e

    -- The inner expression of an evaluation context:
    --    let binds in [], ( [] )
    -- we never tick these if we're doing HPC, but otherwise
    -- we treat it like an ordinary expression.
    addTickLHsExprEvalInner :: LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickLHsExprEvalInner e = do
       d <- getDensity
       case d of
         TickForCoverage -> addTickLHsExprNever e
         _otherwise      -> addTickLHsExpr e

    -- | A let body is treated differently from addTickLHsExprEvalInner
    -- above with TickForBreakPoints, because for breakpoints we always
    -- want to tick the body, even if it is not a redex.  See test
    -- break012.  This gives the user the opportunity to inspect the
    -- values of the let-bound variables.
    addTickLHsExprLetBody :: LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickLHsExprLetBody e@(L pos e0) = do
      d <- getDensity
      case d of
         TickForBreakPoints | HsLet{} <- e0 -> dont_tick_it
                            | otherwise     -> tick_it
         _other -> addTickLHsExprEvalInner e
     where
       tick_it      = allocTickBox (ExpBox False) False False (locA pos)
                      $ addTickHsExpr e0
       dont_tick_it = addTickLHsExprNever e

    -- version of addTick that does not actually add a tick,
    -- because the scope of this tick is completely subsumed by
    -- another.
    addTickLHsExprNever :: LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickLHsExprNever (L pos e0) = do
        e1 <- addTickHsExpr e0
        return $ L pos e1

    -- General heuristic: expressions which are calls (do not denote
    -- values) are good break points.
    isGoodBreakExpr :: HsExpr GhcTc -> Bool
    isGoodBreakExpr e = isCallSite e

    isCallSite :: HsExpr GhcTc -> Bool
    isCallSite HsApp{}     = True
    isCallSite HsAppType{} = True
    isCallSite (XExpr (ExpansionExpr (HsExpanded _ e)))
                           = isCallSite e
    -- NB: OpApp, SectionL, SectionR are all expanded out
    isCallSite _           = False

    addTickLHsExprOptAlt :: Bool -> LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickLHsExprOptAlt oneOfMany (L pos e0)
      = ifDensity TickForCoverage
            (allocTickBox (ExpBox oneOfMany) False False (locA pos)
              $ addTickHsExpr e0)
            (addTickLHsExpr (L pos e0))

    addBinTickLHsExpr :: (Bool -> BoxLabel) -> LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addBinTickLHsExpr boxLabel (L pos e0)
      = ifDensity TickForCoverage
            (allocBinTickBox boxLabel (locA pos) $ addTickHsExpr e0)
            (addTickLHsExpr (L pos e0))

    -- -----------------------------------------------------------------------------
    -- Decorate the body of an HsExpr with ticks.
    -- (Whether to put a tick around the whole expression was already decided,
    -- in the addTickLHsExpr family of functions.)

    addTickHsExpr :: HsExpr GhcTc -> TM (HsExpr GhcTc)
    addTickHsExpr e@(HsVar _ (L _ id))  = do freeVar id; return e
    addTickHsExpr e@(HsUnboundVar {})   = return e
    addTickHsExpr e@(HsRecFld _ (Ambiguous id _))   = do freeVar id; return e
    addTickHsExpr e@(HsRecFld _ (Unambiguous id _)) = do freeVar id; return e

    addTickHsExpr e@(HsConLikeOut {}) = return e
      -- We used to do a freeVar on a pat-syn builder, but actually
      -- such builders are never in the inScope env, which
      -- doesn't include top level bindings
    addTickHsExpr e@(HsIPVar {})     = return e
    addTickHsExpr e@(HsOverLit {})   = return e
    addTickHsExpr e@(HsOverLabel{})  = return e
    addTickHsExpr e@(HsLit {})       = return e
    addTickHsExpr (HsLam x mg)       = liftM (HsLam x)
                                             (addTickMatchGroup True mg)
    addTickHsExpr (HsLamCase x mgs)  = liftM (HsLamCase x)
                                             (addTickMatchGroup True mgs)
    addTickHsExpr (HsApp x e1 e2)    = liftM2 (HsApp x) (addTickLHsExprNever e1)
                                                        (addTickLHsExpr      e2)
    addTickHsExpr (HsAppType x e ty) = liftM3 HsAppType (return x)
                                                        (addTickLHsExprNever e)
                                                        (return ty)
    addTickHsExpr (OpApp fix e1 e2 e3) =
            liftM4 OpApp
                    (return fix)
                    (addTickLHsExpr e1)
                    (addTickLHsExprNever e2)
                    (addTickLHsExpr e3)
    addTickHsExpr (NegApp x e neg) =
            liftM2 (NegApp x)
                    (addTickLHsExpr e)
                    (addTickSyntaxExpr hpcSrcSpan neg)
    addTickHsExpr (HsPar x e) =
            liftM (HsPar x) (addTickLHsExprEvalInner e)
    addTickHsExpr (SectionL x e1 e2) =
            liftM2 (SectionL x)
                    (addTickLHsExpr e1)
                    (addTickLHsExprNever e2)
    addTickHsExpr (SectionR x e1 e2) =
            liftM2 (SectionR x)
                    (addTickLHsExprNever e1)
                    (addTickLHsExpr e2)
    addTickHsExpr (ExplicitTuple x es boxity) =
            liftM2 (ExplicitTuple x)
                    (mapM addTickTupArg es)
                    (return boxity)
    addTickHsExpr (ExplicitSum ty tag arity e) = do
            e' <- addTickLHsExpr e
            return (ExplicitSum ty tag arity e')
    addTickHsExpr (HsCase x e mgs) =
            liftM2 (HsCase x)
                    (addTickLHsExpr e) -- not an EvalInner; e might not necessarily
                                       -- be evaluated.
                    (addTickMatchGroup False mgs)
    addTickHsExpr (HsIf x e1 e2 e3) =
            liftM3 (HsIf x)
                    (addBinTickLHsExpr (BinBox CondBinBox) e1)
                    (addTickLHsExprOptAlt True e2)
                    (addTickLHsExprOptAlt True e3)
    addTickHsExpr (HsMultiIf ty alts)
      = do { let isOneOfMany = case alts of [_] -> False; _ -> True
           ; alts' <- mapM (liftL $ addTickGRHS isOneOfMany False) alts
           ; return $ HsMultiIf ty alts' }
    addTickHsExpr (HsLet x binds e) =
            bindLocals (collectLocalBinders CollNoDictBinders binds) $
              liftM2 (HsLet x)
                      (addTickHsLocalBinds binds) -- to think about: !patterns.
                      (addTickLHsExprLetBody e)
    addTickHsExpr (HsDo srcloc cxt (L l stmts))
      = do { (stmts', _) <- addTickLStmts' forQual stmts (return ())
           ; return (HsDo srcloc cxt (L l stmts')) }
      where
            forQual = case cxt of
                        ListComp -> Just $ BinBox QualBinBox
                        _        -> Nothing
    addTickHsExpr (ExplicitList ty es)
      = liftM2 ExplicitList (return ty) (mapM (addTickLHsExpr) es)

    addTickHsExpr (HsStatic fvs e) = HsStatic fvs <$> addTickLHsExpr e

    addTickHsExpr expr@(RecordCon { rcon_flds = rec_binds })
      = do { rec_binds' <- addTickHsRecordBinds rec_binds
           ; return (expr { rcon_flds = rec_binds' }) }

    addTickHsExpr expr@(RecordUpd { rupd_expr = e, rupd_flds = Left flds })
      = do { e' <- addTickLHsExpr e
           ; flds' <- mapM addTickHsRecField flds
           ; return (expr { rupd_expr = e', rupd_flds = Left flds' }) }
    addTickHsExpr expr@(RecordUpd { rupd_expr = e, rupd_flds = Right flds })
      = do { e' <- addTickLHsExpr e
           ; flds' <- mapM addTickHsRecField flds
           ; return (expr { rupd_expr = e', rupd_flds = Right flds' }) }

    addTickHsExpr (ExprWithTySig x e ty) =
            liftM3 ExprWithTySig
                    (return x)
                    (addTickLHsExprNever e) -- No need to tick the inner expression
                                            -- for expressions with signatures
                    (return ty)
    addTickHsExpr (ArithSeq ty wit arith_seq) =
            liftM3 ArithSeq
                    (return ty)
                    (addTickWit wit)
                    (addTickArithSeqInfo arith_seq)
                 where addTickWit Nothing = return Nothing
                       addTickWit (Just fl) = do fl' <- addTickSyntaxExpr hpcSrcSpan fl
                                                 return (Just fl')

    -- We might encounter existing ticks (multiple Coverage passes)
    addTickHsExpr (HsTick x t e) =
            liftM (HsTick x t) (addTickLHsExprNever e)
    addTickHsExpr (HsBinTick x t0 t1 e) =
            liftM (HsBinTick x t0 t1) (addTickLHsExprNever e)

    addTickHsExpr (HsPragE x p e) =
            liftM (HsPragE x p) (addTickLHsExpr e)
    addTickHsExpr e@(HsBracket     {})   = return e
    addTickHsExpr e@(HsTcBracketOut  {}) = return e
    addTickHsExpr e@(HsRnBracketOut  {}) = return e
    addTickHsExpr e@(HsSpliceE  {})      = return e
    addTickHsExpr e@(HsGetField {})      = return e
    addTickHsExpr e@(HsProjection {})    = return e
    addTickHsExpr (HsProc x pat cmdtop) =
            liftM2 (HsProc x)
                    (addTickLPat pat)
                    (liftL (addTickHsCmdTop) cmdtop)
    addTickHsExpr (XExpr (WrapExpr (HsWrap w e))) =
            liftM (XExpr . WrapExpr . HsWrap w) $
                  (addTickHsExpr e)        -- Explicitly no tick on inside
    addTickHsExpr (XExpr (ExpansionExpr (HsExpanded a b))) =
            liftM (XExpr . ExpansionExpr . HsExpanded a) $
                  (addTickHsExpr b)

    addTickTupArg :: HsTupArg GhcTc -> TM (HsTupArg GhcTc)
    addTickTupArg (Present x e)  = do { e' <- addTickLHsExpr e
                                      ; return (Present x e') }
    addTickTupArg (Missing ty) = return (Missing ty)

    addTickMatchGroup :: Bool{-is lambda-} -> MatchGroup GhcTc (LHsExpr GhcTc)
                      -> TM (MatchGroup GhcTc (LHsExpr GhcTc))
    addTickMatchGroup is_lam mg@(MG { mg_alts = L l matches }) = do
      let isOneOfMany = matchesOneOfMany matches
      matches' <- mapM (liftL (addTickMatch isOneOfMany is_lam)) matches
      return $ mg { mg_alts = L l matches' }

    addTickMatch :: Bool -> Bool -> Match GhcTc (LHsExpr GhcTc)
                 -> TM (Match GhcTc (LHsExpr GhcTc))
    addTickMatch isOneOfMany isLambda match@(Match { m_pats = pats
                                                   , m_grhss = gRHSs }) =
      bindLocals (collectPatsBinders CollNoDictBinders pats) $ do
        gRHSs' <- addTickGRHSs isOneOfMany isLambda gRHSs
        return $ match { m_grhss = gRHSs' }

    addTickGRHSs :: Bool -> Bool -> GRHSs GhcTc (LHsExpr GhcTc)
                 -> TM (GRHSs GhcTc (LHsExpr GhcTc))
    addTickGRHSs isOneOfMany isLambda (GRHSs x guarded local_binds) =
      bindLocals binders $ do
        local_binds' <- addTickHsLocalBinds local_binds
        guarded' <- mapM (liftL (addTickGRHS isOneOfMany isLambda)) guarded
        return $ GRHSs x guarded' local_binds'
      where
        binders = collectLocalBinders CollNoDictBinders local_binds

    addTickGRHS :: Bool -> Bool -> GRHS GhcTc (LHsExpr GhcTc)
                -> TM (GRHS GhcTc (LHsExpr GhcTc))
    addTickGRHS isOneOfMany isLambda (GRHS x stmts expr) = do
      (stmts',expr') <- addTickLStmts' (Just $ BinBox $ GuardBinBox) stmts
                            (addTickGRHSBody isOneOfMany isLambda expr)
      return $ GRHS x stmts' expr'

    addTickGRHSBody :: Bool -> Bool -> LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTickGRHSBody isOneOfMany isLambda expr@(L pos e0) = do
      d <- getDensity
      case d of
        TickForCoverage  -> addTickLHsExprOptAlt isOneOfMany expr
        TickAllFunctions | isLambda ->
           addPathEntry "\\" $
             allocTickBox (ExpBox False) True{-count-} False{-not top-} (locA pos) $
               addTickHsExpr e0
        _otherwise ->
           addTickLHsExprRHS expr

    addTickLStmts :: (Maybe (Bool -> BoxLabel)) -> [ExprLStmt GhcTc]
                  -> TM [ExprLStmt GhcTc]
    addTickLStmts isGuard stmts = do
      (stmts, _) <- addTickLStmts' isGuard stmts (return ())
      return stmts

    addTickLStmts' :: (Maybe (Bool -> BoxLabel)) -> [ExprLStmt GhcTc] -> TM a
                   -> TM ([ExprLStmt GhcTc], a)
    addTickLStmts' isGuard lstmts res
      = bindLocals (collectLStmtsBinders CollNoDictBinders lstmts) $
        do { lstmts' <- mapM (liftL (addTickStmt isGuard)) lstmts
           ; a <- res
           ; return (lstmts', a) }

    addTickStmt :: (Maybe (Bool -> BoxLabel)) -> Stmt GhcTc (LHsExpr GhcTc)
                -> TM (Stmt GhcTc (LHsExpr GhcTc))
    addTickStmt _isGuard (LastStmt x e noret ret) =
            liftM3 (LastStmt x)
                    (addTickLHsExpr e)
                    (pure noret)
                    (addTickSyntaxExpr hpcSrcSpan ret)
    addTickStmt _isGuard (BindStmt xbs pat e) =
            liftM4 (\b f -> BindStmt $ XBindStmtTc
                        { xbstc_bindOp = b
                        , xbstc_boundResultType = xbstc_boundResultType xbs
                        , xbstc_boundResultMult = xbstc_boundResultMult xbs
                        , xbstc_failOp = f
                        })
                    (addTickSyntaxExpr hpcSrcSpan (xbstc_bindOp xbs))
                    (mapM (addTickSyntaxExpr hpcSrcSpan) (xbstc_failOp xbs))
                    (addTickLPat pat)
                    (addTickLHsExprRHS e)
    addTickStmt isGuard (BodyStmt x e bind' guard') =
            liftM3 (BodyStmt x)
                    (addTick isGuard e)
                    (addTickSyntaxExpr hpcSrcSpan bind')
                    (addTickSyntaxExpr hpcSrcSpan guard')
    addTickStmt _isGuard (LetStmt x binds) =
            liftM (LetStmt x)
                    (addTickHsLocalBinds binds)
    addTickStmt isGuard (ParStmt x pairs mzipExpr bindExpr) =
        liftM3 (ParStmt x)
            (mapM (addTickStmtAndBinders isGuard) pairs)
            (unLoc <$> addTickLHsExpr (L (noAnnSrcSpan hpcSrcSpan) mzipExpr))
            (addTickSyntaxExpr hpcSrcSpan bindExpr)
    addTickStmt isGuard (ApplicativeStmt body_ty args mb_join) = do
        args' <- mapM (addTickApplicativeArg isGuard) args
        return (ApplicativeStmt body_ty args' mb_join)

    addTickStmt isGuard stmt@(TransStmt { trS_stmts = stmts
                                        , trS_by = by, trS_using = using
                                        , trS_ret = returnExpr, trS_bind = bindExpr
                                        , trS_fmap = liftMExpr }) = do
        t_s <- addTickLStmts isGuard stmts
        t_y <- fmapMaybeM  addTickLHsExprRHS by
        t_u <- addTickLHsExprRHS using
        t_f <- addTickSyntaxExpr hpcSrcSpan returnExpr
        t_b <- addTickSyntaxExpr hpcSrcSpan bindExpr
        t_m <- fmap unLoc (addTickLHsExpr (L (noAnnSrcSpan hpcSrcSpan) liftMExpr))
        return $ stmt { trS_stmts = t_s, trS_by = t_y, trS_using = t_u
                      , trS_ret = t_f, trS_bind = t_b, trS_fmap = t_m }

    addTickStmt isGuard stmt@(RecStmt {})
      = do { stmts' <- addTickLStmts isGuard (unLoc $ recS_stmts stmt)
           ; ret'   <- addTickSyntaxExpr hpcSrcSpan (recS_ret_fn stmt)
           ; mfix'  <- addTickSyntaxExpr hpcSrcSpan (recS_mfix_fn stmt)
           ; bind'  <- addTickSyntaxExpr hpcSrcSpan (recS_bind_fn stmt)
           ; return (stmt { recS_stmts = noLocA stmts', recS_ret_fn = ret'
                          , recS_mfix_fn = mfix', recS_bind_fn = bind' }) }

    addTick :: Maybe (Bool -> BoxLabel) -> LHsExpr GhcTc -> TM (LHsExpr GhcTc)
    addTick isGuard e | Just fn <- isGuard = addBinTickLHsExpr fn e
                      | otherwise          = addTickLHsExprRHS e

    addTickApplicativeArg
      :: Maybe (Bool -> BoxLabel) -> (SyntaxExpr GhcTc, ApplicativeArg GhcTc)
      -> TM (SyntaxExpr GhcTc, ApplicativeArg GhcTc)
    addTickApplicativeArg isGuard (op, arg) =
      liftM2 (,) (addTickSyntaxExpr hpcSrcSpan op) (addTickArg arg)
     where
      addTickArg (ApplicativeArgOne m_fail pat expr isBody) =
        ApplicativeArgOne
          <$> mapM (addTickSyntaxExpr hpcSrcSpan) m_fail
          <*> addTickLPat pat
          <*> addTickLHsExpr expr
          <*> pure isBody
      addTickArg (ApplicativeArgMany x stmts ret pat ctxt) =
        (ApplicativeArgMany x)
          <$> addTickLStmts isGuard stmts
          <*> (unLoc <$> addTickLHsExpr (L (noAnnSrcSpan hpcSrcSpan) ret))
          <*> addTickLPat pat
          <*> pure ctxt

    addTickStmtAndBinders :: Maybe (Bool -> BoxLabel) -> ParStmtBlock GhcTc GhcTc
                          -> TM (ParStmtBlock GhcTc GhcTc)
    addTickStmtAndBinders isGuard (ParStmtBlock x stmts ids returnExpr) =
        liftM3 (ParStmtBlock x)
            (addTickLStmts isGuard stmts)
            (return ids)
            (addTickSyntaxExpr hpcSrcSpan returnExpr)

    addTickHsLocalBinds :: HsLocalBinds GhcTc -> TM (HsLocalBinds GhcTc)
    addTickHsLocalBinds (HsValBinds x binds) =
            liftM (HsValBinds x)
                    (addTickHsValBinds binds)
    addTickHsLocalBinds (HsIPBinds x binds)  =
            liftM (HsIPBinds x)
                    (addTickHsIPBinds binds)
    addTickHsLocalBinds (EmptyLocalBinds x)  = return (EmptyLocalBinds x)

    addTickHsValBinds :: HsValBindsLR GhcTc (GhcPass a)
                      -> TM (HsValBindsLR GhcTc (GhcPass b))
    addTickHsValBinds (XValBindsLR (NValBinds binds sigs)) = do
            b <- liftM2 NValBinds
                    (mapM (\ (rec,binds') ->
                                    liftM2 (,)
                                            (return rec)
                                            (addTickLHsBinds binds'))
                            binds)
                    (return sigs)
            return $ XValBindsLR b
    addTickHsValBinds _ = panic "addTickHsValBinds"

    addTickHsIPBinds :: HsIPBinds GhcTc -> TM (HsIPBinds GhcTc)
    addTickHsIPBinds (IPBinds dictbinds ipbinds) =
            liftM2 IPBinds
                    (return dictbinds)
                    (mapM (liftL (addTickIPBind)) ipbinds)

    addTickIPBind :: IPBind GhcTc -> TM (IPBind GhcTc)
    addTickIPBind (IPBind x nm e) =
            liftM2 (IPBind x)
                    (return nm)
                    (addTickLHsExpr e)

    -- There is no location here, so we might need to use a context location??
    addTickSyntaxExpr :: SrcSpan -> SyntaxExpr GhcTc -> TM (SyntaxExpr GhcTc)
    addTickSyntaxExpr pos syn@(SyntaxExprTc { syn_expr = x }) = do
            x' <- fmap unLoc (addTickLHsExpr (L (noAnnSrcSpan pos) x))
            return $ syn { syn_expr = x' }
    addTickSyntaxExpr _ NoSyntaxExprTc = return NoSyntaxExprTc

    -- we do not walk into patterns.
    addTickLPat :: LPat GhcTc -> TM (LPat GhcTc)
    addTickLPat pat = return pat

    addTickHsCmdTop :: HsCmdTop GhcTc -> TM (HsCmdTop GhcTc)
    addTickHsCmdTop (HsCmdTop x cmd) =
            liftM2 HsCmdTop
                    (return x)
                    (addTickLHsCmd cmd)

    addTickLHsCmd ::  LHsCmd GhcTc -> TM (LHsCmd GhcTc)
    addTickLHsCmd (L pos c0) = do
            c1 <- addTickHsCmd c0
            return $ L pos c1

    addTickHsCmd :: HsCmd GhcTc -> TM (HsCmd GhcTc)
    addTickHsCmd (HsCmdLam x matchgroup) =
            liftM (HsCmdLam x) (addTickCmdMatchGroup matchgroup)
    addTickHsCmd (HsCmdApp x c e) =
            liftM2 (HsCmdApp x) (addTickLHsCmd c) (addTickLHsExpr e)
    {-
    addTickHsCmd (OpApp e1 c2 fix c3) =
            liftM4 OpApp
                    (addTickLHsExpr e1)
                    (addTickLHsCmd c2)
                    (return fix)
                    (addTickLHsCmd c3)
    -}
    addTickHsCmd (HsCmdPar x e) = liftM (HsCmdPar x) (addTickLHsCmd e)
    addTickHsCmd (HsCmdCase x e mgs) =
            liftM2 (HsCmdCase x)
                    (addTickLHsExpr e)
                    (addTickCmdMatchGroup mgs)
    addTickHsCmd (HsCmdLamCase x mgs) =
            liftM (HsCmdLamCase x) (addTickCmdMatchGroup mgs)
    addTickHsCmd (HsCmdIf x cnd e1 c2 c3) =
            liftM3 (HsCmdIf x cnd)
                    (addBinTickLHsExpr (BinBox CondBinBox) e1)
                    (addTickLHsCmd c2)
                    (addTickLHsCmd c3)
    addTickHsCmd (HsCmdLet x binds c) =
            bindLocals (collectLocalBinders CollNoDictBinders binds) $
              liftM2 (HsCmdLet x)
                       (addTickHsLocalBinds binds) -- to think about: !patterns.
                       (addTickLHsCmd c)
    addTickHsCmd (HsCmdDo srcloc (L l stmts))
      = do { (stmts', _) <- addTickLCmdStmts' stmts (return ())
           ; return (HsCmdDo srcloc (L l stmts')) }

    addTickHsCmd (HsCmdArrApp  arr_ty e1 e2 ty1 lr) =
            liftM5 HsCmdArrApp
                   (return arr_ty)
                   (addTickLHsExpr e1)
                   (addTickLHsExpr e2)
                   (return ty1)
                   (return lr)
    addTickHsCmd (HsCmdArrForm x e f fix cmdtop) =
            liftM4 (HsCmdArrForm x)
                   (addTickLHsExpr e)
                   (return f)
                   (return fix)
                   (mapM (liftL (addTickHsCmdTop)) cmdtop)

    addTickHsCmd (XCmd (HsWrap w cmd)) =
      liftM XCmd $
      liftM (HsWrap w) (addTickHsCmd cmd)

    -- Others should never happen in a command context.
    --addTickHsCmd e  = pprPanic "addTickHsCmd" (ppr e)

    addTickCmdMatchGroup :: MatchGroup GhcTc (LHsCmd GhcTc)
                         -> TM (MatchGroup GhcTc (LHsCmd GhcTc))
    addTickCmdMatchGroup mg@(MG { mg_alts = (L l matches) }) = do
      matches' <- mapM (liftL addTickCmdMatch) matches
      return $ mg { mg_alts = L l matches' }

    addTickCmdMatch :: Match GhcTc (LHsCmd GhcTc) -> TM (Match GhcTc (LHsCmd GhcTc))
    addTickCmdMatch match@(Match { m_pats = pats, m_grhss = gRHSs }) =
      bindLocals (collectPatsBinders CollNoDictBinders pats) $ do
        gRHSs' <- addTickCmdGRHSs gRHSs
        return $ match { m_grhss = gRHSs' }

    addTickCmdGRHSs :: GRHSs GhcTc (LHsCmd GhcTc) -> TM (GRHSs GhcTc (LHsCmd GhcTc))
    addTickCmdGRHSs (GRHSs x guarded local_binds) =
      bindLocals binders $ do
        local_binds' <- addTickHsLocalBinds local_binds
        guarded' <- mapM (liftL addTickCmdGRHS) guarded
        return $ GRHSs x guarded' local_binds'
      where
        binders = collectLocalBinders CollNoDictBinders local_binds

    addTickCmdGRHS :: GRHS GhcTc (LHsCmd GhcTc) -> TM (GRHS GhcTc (LHsCmd GhcTc))
    -- The *guards* are *not* Cmds, although the body is
    -- C.f. addTickGRHS for the BinBox stuff
    addTickCmdGRHS (GRHS x stmts cmd)
      = do { (stmts',expr') <- addTickLStmts' (Just $ BinBox $ GuardBinBox)
                                       stmts (addTickLHsCmd cmd)
           ; return $ GRHS x stmts' expr' }

    addTickLCmdStmts :: [LStmt GhcTc (LHsCmd GhcTc)]
                     -> TM [LStmt GhcTc (LHsCmd GhcTc)]
    addTickLCmdStmts stmts = do
      (stmts, _) <- addTickLCmdStmts' stmts (return ())
      return stmts

    addTickLCmdStmts' :: [LStmt GhcTc (LHsCmd GhcTc)] -> TM a
                      -> TM ([LStmt GhcTc (LHsCmd GhcTc)], a)
    addTickLCmdStmts' lstmts res
      = bindLocals binders $ do
            lstmts' <- mapM (liftL addTickCmdStmt) lstmts
            a <- res
            return (lstmts', a)
      where
            binders = collectLStmtsBinders CollNoDictBinders lstmts

    addTickCmdStmt :: Stmt GhcTc (LHsCmd GhcTc) -> TM (Stmt GhcTc (LHsCmd GhcTc))
    addTickCmdStmt (BindStmt x pat c) =
            liftM2 (BindStmt x)
                    (addTickLPat pat)
                    (addTickLHsCmd c)
    addTickCmdStmt (LastStmt x c noret ret) =
            liftM3 (LastStmt x)
                    (addTickLHsCmd c)
                    (pure noret)
                    (addTickSyntaxExpr hpcSrcSpan ret)
    addTickCmdStmt (BodyStmt x c bind' guard') =
            liftM3 (BodyStmt x)
                    (addTickLHsCmd c)
                    (addTickSyntaxExpr hpcSrcSpan bind')
                    (addTickSyntaxExpr hpcSrcSpan guard')
    addTickCmdStmt (LetStmt x binds) =
            liftM (LetStmt x)
                    (addTickHsLocalBinds binds)
    addTickCmdStmt stmt@(RecStmt {})
      = do { stmts' <- addTickLCmdStmts (unLoc $ recS_stmts stmt)
           ; ret'   <- addTickSyntaxExpr hpcSrcSpan (recS_ret_fn stmt)
           ; mfix'  <- addTickSyntaxExpr hpcSrcSpan (recS_mfix_fn stmt)
           ; bind'  <- addTickSyntaxExpr hpcSrcSpan (recS_bind_fn stmt)
           ; return (stmt { recS_stmts = noLocA stmts', recS_ret_fn = ret'
                          , recS_mfix_fn = mfix', recS_bind_fn = bind' }) }
    addTickCmdStmt ApplicativeStmt{} =
      panic "ToDo: addTickCmdStmt ApplicativeLastStmt"

    -- Others should never happen in a command context.
    addTickCmdStmt stmt  = pprPanic "addTickHsCmd" (ppr stmt)

    addTickHsRecordBinds :: HsRecordBinds GhcTc -> TM (HsRecordBinds GhcTc)
    addTickHsRecordBinds (HsRecFields fields dd)
      = do  { fields' <- mapM addTickHsRecField fields
            ; return (HsRecFields fields' dd) }

    addTickHsRecField :: LHsRecField' GhcTc id (LHsExpr GhcTc)
                      -> TM (LHsRecField' GhcTc id (LHsExpr GhcTc))
    addTickHsRecField (L l (HsRecField x id expr pun))
            = do { expr' <- addTickLHsExpr expr
                 ; return (L l (HsRecField x id expr' pun)) }

    addTickArithSeqInfo :: ArithSeqInfo GhcTc -> TM (ArithSeqInfo GhcTc)
    addTickArithSeqInfo (From e1) =
            liftM From
                    (addTickLHsExpr e1)
    addTickArithSeqInfo (FromThen e1 e2) =
            liftM2 FromThen
                    (addTickLHsExpr e1)
                    (addTickLHsExpr e2)
    addTickArithSeqInfo (FromTo e1 e2) =
            liftM2 FromTo
                    (addTickLHsExpr e1)
                    (addTickLHsExpr e2)
    addTickArithSeqInfo (FromThenTo e1 e2 e3) =
            liftM3 FromThenTo
                    (addTickLHsExpr e1)
                    (addTickLHsExpr e2)
                    (addTickLHsExpr e3)

    data TickTransState = TT { tickBoxCount:: !Int
                             , mixEntries  :: [MixEntry_]
                             , ccIndices   :: !CostCentreState
                             }

    addMixEntry :: MixEntry_ -> TM Int
    addMixEntry ent = do
      c <- tickBoxCount <$> getState
      setState $ \st ->
        st { tickBoxCount = c + 1
           , mixEntries = ent : mixEntries st
           }
      return c

    data TickTransEnv = TTE { fileName     :: FastString
                            , density      :: TickDensity
                            , tte_dflags   :: DynFlags
                            , exports      :: NameSet
                            , inlines      :: VarSet
                            , declPath     :: [String]
                            , inScope      :: VarSet
                            , blackList    :: Set RealSrcSpan
                            , this_mod     :: Module
                            , tickishType  :: TickishType
                            }

    --      deriving Show

    data TickishType = ProfNotes | HpcTicks | Breakpoints | SourceNotes
                     deriving (Eq)

    sourceNotesEnabled :: DynFlags -> Bool
    sourceNotesEnabled dflags =
      (debugLevel dflags > 0) || (gopt Opt_InfoTableMap dflags)

    coveragePasses :: DynFlags -> [TickishType]
    coveragePasses dflags =
        ifa (breakpointsEnabled dflags)          Breakpoints $
        ifa (gopt Opt_Hpc dflags)                HpcTicks $
        ifa (sccProfilingEnabled dflags &&
             profAuto dflags /= NoProfAuto)      ProfNotes $
        ifa (sourceNotesEnabled dflags)          SourceNotes []
      where ifa f x xs | f         = x:xs
                       | otherwise = xs

    -- | Should we produce 'Breakpoint' ticks?
    breakpointsEnabled :: DynFlags -> Bool
    breakpointsEnabled dflags = backend dflags == Interpreter

    -- | Tickishs that only make sense when their source code location
    -- refers to the current file. This might not always be true due to
    -- LINE pragmas in the code - which would confuse at least HPC.
    tickSameFileOnly :: TickishType -> Bool
    tickSameFileOnly HpcTicks = True
    tickSameFileOnly _other   = False

    type FreeVars = OccEnv Id
    noFVs :: FreeVars
    noFVs = emptyOccEnv

    -- Note [freevars]
    --   For breakpoints we want to collect the free variables of an
    --   expression for pinning on the HsTick.  We don't want to collect
    --   *all* free variables though: in particular there's no point pinning
    --   on free variables that are will otherwise be in scope at the GHCi
    --   prompt, which means all top-level bindings.  Unfortunately detecting
    --   top-level bindings isn't easy (collectHsBindsBinders on the top-level
    --   bindings doesn't do it), so we keep track of a set of "in-scope"
    --   variables in addition to the free variables, and the former is used
    --   to filter additions to the latter.  This gives us complete control
    --   over what free variables we track.

    newtype TM a = TM { unTM :: TickTransEnv -> TickTransState -> (a,FreeVars,TickTransState) }
        deriving (Functor)
            -- a combination of a state monad (TickTransState) and a writer
            -- monad (FreeVars).

    instance Applicative TM where
        pure a = TM $ \ _env st -> (a,noFVs,st)
        (<*>) = ap

    instance Monad TM where
      (TM m) >>= k = TM $ \ env st ->
                                    case m env st of
                                      (r1,fv1,st1) ->
                                         case unTM (k r1) env st1 of
                                           (r2,fv2,st2) ->
                                              (r2, fv1 `plusOccEnv` fv2, st2)

    instance HasDynFlags TM where
      getDynFlags = TM $ \ env st -> (tte_dflags env, noFVs, st)

    -- | Get the next HPC cost centre index for a given centre name
    getCCIndexM :: FastString -> TM CostCentreIndex
    getCCIndexM n = TM $ \_ st -> let (idx, is') = getCCIndex n $
                                                     ccIndices st
                                  in (idx, noFVs, st { ccIndices = is' })

    getState :: TM TickTransState
    getState = TM $ \ _ st -> (st, noFVs, st)

    setState :: (TickTransState -> TickTransState) -> TM ()
    setState f = TM $ \ _ st -> ((), noFVs, f st)

    getEnv :: TM TickTransEnv
    getEnv = TM $ \ env st -> (env, noFVs, st)

    withEnv :: (TickTransEnv -> TickTransEnv) -> TM a -> TM a
    withEnv f (TM m) = TM $ \ env st ->
                                     case m (f env) st of
                                       (a, fvs, st') -> (a, fvs, st')

    getDensity :: TM TickDensity
    getDensity = TM $ \env st -> (density env, noFVs, st)

    ifDensity :: TickDensity -> TM a -> TM a -> TM a
    ifDensity d th el = do d0 <- getDensity; if d == d0 then th else el

    getFreeVars :: TM a -> TM (FreeVars, a)
    getFreeVars (TM m)
      = TM $ \ env st -> case m env st of (a, fv, st') -> ((fv,a), fv, st')

    freeVar :: Id -> TM ()
    freeVar id = TM $ \ env st ->
                    if id `elemVarSet` inScope env
                       then ((), unitOccEnv (nameOccName (idName id)) id, st)
                       else ((), noFVs, st)

    addPathEntry :: String -> TM a -> TM a
    addPathEntry nm = withEnv (\ env -> env { declPath = declPath env ++ [nm] })

    getPathEntry :: TM [String]
    getPathEntry = declPath `liftM` getEnv

    getFileName :: TM FastString
    getFileName = fileName `liftM` getEnv

    isGoodSrcSpan' :: SrcSpan -> Bool
    isGoodSrcSpan' pos@(RealSrcSpan _ _) = srcSpanStart pos /= srcSpanEnd pos
    isGoodSrcSpan' (UnhelpfulSpan _) = False

    isGoodTickSrcSpan :: SrcSpan -> TM Bool
    isGoodTickSrcSpan pos = do
      file_name <- getFileName
      tickish <- tickishType `liftM` getEnv
      let need_same_file = tickSameFileOnly tickish
          same_file      = Just file_name == srcSpanFileName_maybe pos
      return (isGoodSrcSpan' pos && (not need_same_file || same_file))

    ifGoodTickSrcSpan :: SrcSpan -> TM a -> TM a -> TM a
    ifGoodTickSrcSpan pos then_code else_code = do
      good <- isGoodTickSrcSpan pos
      if good then then_code else else_code

    bindLocals :: [Id] -> TM a -> TM a
    bindLocals new_ids (TM m)
      = TM $ \ env st ->
                     case m env{ inScope = inScope env `extendVarSetList` new_ids } st of
                       (r, fv, st') -> (r, fv `delListFromOccEnv` occs, st')
      where occs = [ nameOccName (idName id) | id <- new_ids ]

    isBlackListed :: SrcSpan -> TM Bool
    isBlackListed (RealSrcSpan pos _) = TM $ \ env st -> (Set.member pos (blackList env), noFVs, st)
    isBlackListed (UnhelpfulSpan _) = return False

    -- the tick application inherits the source position of its
    -- expression argument to support nested box allocations
    allocTickBox :: BoxLabel -> Bool -> Bool -> SrcSpan -> TM (HsExpr GhcTc)
                 -> TM (LHsExpr GhcTc)
    allocTickBox boxLabel countEntries topOnly pos m =
      ifGoodTickSrcSpan pos (do
        (fvs, e) <- getFreeVars m
        env <- getEnv
        tickish <- mkTickish boxLabel countEntries topOnly pos fvs (declPath env)
        return (L (noAnnSrcSpan pos) (HsTick noExtField tickish (L (noAnnSrcSpan pos) e)))
      ) (do
        e <- m
        return (L (noAnnSrcSpan pos) e)
      )

    -- the tick application inherits the source position of its
    -- expression argument to support nested box allocations
    allocATickBox :: BoxLabel -> Bool -> Bool -> SrcSpan -> FreeVars
                  -> TM (Maybe CoreTickish)
    allocATickBox boxLabel countEntries topOnly  pos fvs =
      ifGoodTickSrcSpan pos (do
        let
          mydecl_path = case boxLabel of
                          TopLevelBox x -> x
                          LocalBox xs  -> xs
                          _ -> panic "allocATickBox"
        tickish <- mkTickish boxLabel countEntries topOnly pos fvs mydecl_path
        return (Just tickish)
      ) (return Nothing)

    mkTickish :: BoxLabel -> Bool -> Bool -> SrcSpan -> OccEnv Id -> [String]
              -> TM CoreTickish
    mkTickish boxLabel countEntries topOnly pos fvs decl_path = do

      let ids = filter (not . isUnliftedType . idType) $ occEnvElts fvs
              -- unlifted types cause two problems here:
              --   * we can't bind them  at the GHCi prompt
              --     (bindLocalsAtBreakpoint already filters them out),
              --   * the simplifier might try to substitute a literal for
              --     the Id, and we can't handle that.

          me = (pos, decl_path, map (nameOccName.idName) ids, boxLabel)

          cc_name | topOnly   = head decl_path
                  | otherwise = concat (intersperse "." decl_path)

      dflags <- getDynFlags
      env <- getEnv
      case tickishType env of
        HpcTicks -> HpcTick (this_mod env) <$> addMixEntry me

        ProfNotes -> do
          let nm = mkFastString cc_name
          flavour <- HpcCC <$> getCCIndexM nm
          let cc = mkUserCC nm (this_mod env) pos flavour
              count = countEntries && gopt Opt_ProfCountEntries dflags
          return $ ProfNote cc count True{-scopes-}

        Breakpoints -> Breakpoint noExtField <$> addMixEntry me <*> pure ids

        SourceNotes | RealSrcSpan pos' _ <- pos ->
          return $ SourceNote pos' cc_name

        _otherwise -> panic "mkTickish: bad source span!"

    allocBinTickBox :: (Bool -> BoxLabel) -> SrcSpan -> TM (HsExpr GhcTc)
                    -> TM (LHsExpr GhcTc)
    allocBinTickBox boxLabel pos m = do
      env <- getEnv
      case tickishType env of
        HpcTicks -> do e <- liftM (L (noAnnSrcSpan pos)) m
                       ifGoodTickSrcSpan pos
                         (mkBinTickBoxHpc boxLabel pos e)
                         (return e)
        _other   -> allocTickBox (ExpBox False) False False pos m

    mkBinTickBoxHpc :: (Bool -> BoxLabel) -> SrcSpan -> LHsExpr GhcTc
                    -> TM (LHsExpr GhcTc)
    mkBinTickBoxHpc boxLabel pos e = do
      env <- getEnv
      binTick <- HsBinTick noExtField
        <$> addMixEntry (pos,declPath env, [],boxLabel True)
        <*> addMixEntry (pos,declPath env, [],boxLabel False)
        <*> pure e
      tick <- HpcTick (this_mod env)
        <$> addMixEntry (pos,declPath env, [],ExpBox False)
      let pos' = noAnnSrcSpan pos
      return $ L pos' $ HsTick noExtField tick (L pos' binTick)

    mkHpcPos :: SrcSpan -> HpcPos
    mkHpcPos pos@(RealSrcSpan s _)
       | isGoodSrcSpan' pos = toHpcPos (srcSpanStartLine s,
                                        srcSpanStartCol s,
                                        srcSpanEndLine s,
                                        srcSpanEndCol s - 1)
                                  -- the end column of a SrcSpan is one
                                  -- greater than the last column of the
                                  -- span (see SrcLoc), whereas HPC
                                  -- expects to the column range to be
                                  -- inclusive, hence we subtract one above.
    mkHpcPos _ = panic "bad source span; expected such spans to be filtered out"

    hpcSrcSpan :: SrcSpan
    hpcSrcSpan = mkGeneralSrcSpan (fsLit "Haskell Program Coverage internals")

    matchesOneOfMany :: [LMatch GhcTc body] -> Bool
    matchesOneOfMany lmatches = sum (map matchCount lmatches) > 1
      where
            matchCount :: LMatch GhcTc body -> Int
            matchCount (L _ (Match { m_grhss = GRHSs _ grhss _ }))
              = length grhss

    type MixEntry_ = (SrcSpan, [String], [OccName], BoxLabel)

    -- For the hash value, we hash everything: the file name,
    --  the timestamp of the original source file, the tab stop,
    --  and the mix entries. We cheat, and hash the show'd string.
    -- This hash only has to be hashed at Mix creation time,
    -- and is for sanity checking only.

    mixHash :: FilePath -> UTCTime -> Int -> [MixEntry] -> Int
    mixHash file tm tabstop entries = fromIntegral $ hashString
            (show $ Mix file tm 0 tabstop entries)

    {-
    ************************************************************************
    *                                                                      *
    *              initialisation
    *                                                                      *
    ************************************************************************

    Each module compiled with -fhpc declares an initialisation function of
    the form `hpc_init_<module>()`, which is emitted into the _stub.c file
    and annotated with __attribute__((constructor)) so that it gets
    executed at startup time.

    The function's purpose is to call hs_hpc_module to register this
    module with the RTS, and it looks something like this:

    static void hpc_init_Main(void) __attribute__((constructor));
    static void hpc_init_Main(void)
    {extern StgWord64 _hpc_tickboxes_Main_hpc[];
     hs_hpc_module("Main",8,1150288664,_hpc_tickboxes_Main_hpc);}
    -}

    hpcInitCode :: DynFlags -> Module -> HpcInfo -> CStub
    hpcInitCode _ _ (NoHpcInfo {}) = mempty
    hpcInitCode dflags this_mod (HpcInfo tickCount hashNo)
     = CStub $ vcat
        [ text "static void hpc_init_" <> ppr this_mod
             <> text "(void) __attribute__((constructor));"
        , text "static void hpc_init_" <> ppr this_mod <> text "(void)"
        , braces (vcat [
            text "extern StgWord64 " <> tickboxes <>
                   text "[]" <> semi,
            text "hs_hpc_module" <>
              parens (hcat (punctuate comma [
                  doubleQuotes full_name_str,
                  int tickCount, -- really StgWord32
                  int hashNo,    -- really StgWord32
                  tickboxes
                ])) <> semi
           ])
        ]
      where
        platform  = targetPlatform dflags
        tickboxes = pprCLabel platform CStyle (mkHpcTicksLabel $ this_mod)

        module_name  = hcat (map (text.charToC) $ BS.unpack $
                             bytesFS (moduleNameFS (moduleName this_mod)))
        package_name = hcat (map (text.charToC) $ BS.unpack $
                             bytesFS (unitFS  (moduleUnit this_mod)))
        full_name_str
           | moduleUnit this_mod == mainUnit
           = module_name
           | otherwise
           = package_name <> char '/' <> module_name