content: 
  {-# LANGUAGE RecordWildCards #-}
  {-# LANGUAGE LambdaCase #-}
  {-# LANGUAGE MultiParamTypeClasses #-}
  {-# LANGUAGE FlexibleInstances #-}
  
  -----------------------------------------------------------------------------
  --
  -- Stg to C-- code generation:
  --
  -- The types   LambdaFormInfo
  --             ClosureInfo
  --
  -- Nothing monadic in here!
  --
  -----------------------------------------------------------------------------
  
  module GHC.StgToCmm.Closure (
          DynTag,  tagForCon, isSmallFamily,
  
          idPrimRep1, idPrimRepU, isGcPtrRep, addIdReps, addArgReps,
  
          NonVoid(..), fromNonVoid, nonVoidIds, nonVoidStgArgs,
          assertNonVoidIds, assertNonVoidStgArgs,
  
          -- * LambdaFormInfo
          LambdaFormInfo,         -- Abstract
          StandardFormInfo,        -- ...ditto...
          mkLFThunk, mkLFReEntrant, mkConLFInfo, mkSelectorLFInfo,
          mkApLFInfo, importedIdLFInfo, mkLFArgument, mkLFLetNoEscape,
          mkLFStringLit,
          lfDynTag,
          isLFThunk, isLFReEntrant, lfUpdatable,
  
          -- * Used by other modules
          CgLoc(..), CallMethod(..),
          nodeMustPointToIt, isKnownFun, funTag, tagForArity,
          getCallMethod,
  
          -- * ClosureInfo
          ClosureInfo,
          mkClosureInfo,
          mkCmmInfo,
  
          -- ** Inspection
          closureLFInfo, closureName,
  
          -- ** Labels
          -- These just need the info table label
          closureInfoLabel, staticClosureLabel,
          closureSlowEntryLabel, closureLocalEntryLabel,
  
          -- ** Predicates
          -- These are really just functions on LambdaFormInfo
          closureUpdReqd,
          closureReEntrant, closureFunInfo,
          isToplevClosure,
  
          blackHoleOnEntry,  -- Needs LambdaFormInfo and SMRep
          isStaticClosure,   -- Needs SMPre
  
          -- * InfoTables
          mkDataConInfoTable,
          cafBlackHoleInfoTable,
          indStaticInfoTable,
          staticClosureNeedsLink,
          mkClosureInfoTableLabel
      ) where
  
  import GHC.Prelude
  import GHC.Platform
  import GHC.Platform.Profile
  
  import GHC.Stg.Syntax
  import GHC.Runtime.Heap.Layout
  import GHC.Cmm
  import GHC.Cmm.Utils
  import GHC.StgToCmm.Types
  import GHC.StgToCmm.Sequel
  
  import GHC.Types.CostCentre
  import GHC.Cmm.BlockId
  import GHC.Cmm.CLabel
  import GHC.Types.Id
  import GHC.Types.Id.Info
  import GHC.Core.DataCon
  import GHC.Types.Name
  import GHC.Core.Type
  import GHC.Core.TyCo.Rep
  import GHC.Tc.Utils.TcType
  import GHC.Core.TyCon
  import GHC.Types.RepType
  import GHC.Types.Basic
  import GHC.Utils.Outputable
  import GHC.Utils.Panic
  import GHC.Data.Maybe (isNothing)
  
  import Data.Coerce (coerce)
  import qualified Data.ByteString.Char8 as BS8
  import GHC.StgToCmm.Config
  import GHC.Stg.EnforceEpt.TagSig (isTaggedSig)
  
  -----------------------------------------------------------------------------
  --                Data types and synonyms
  -----------------------------------------------------------------------------
  
  -- These data types are mostly used by other modules, especially
  -- GHC.StgToCmm.Monad, but we define them here because some functions in this
  -- module need to have access to them as well
  
  data CgLoc
    = CmmLoc CmmExpr      -- A stable CmmExpr; that is, one not mentioning
                          -- Hp, so that it remains valid across calls
  
    | LneLoc BlockId [LocalReg]             -- A join point
          -- A join point (= let-no-escape) should only
          -- be tail-called, and in a saturated way.
          -- To tail-call it, assign to these locals,
          -- and branch to the block id
  
  instance OutputableP Platform CgLoc where
     pdoc = pprCgLoc
  
  pprCgLoc :: Platform -> CgLoc -> SDoc
  pprCgLoc platform = \case
     CmmLoc e    -> text "cmm" <+> pdoc platform e
     LneLoc b rs -> text "lne" <+> ppr b <+> ppr rs
  
  -- used by ticky profiling
  isKnownFun :: LambdaFormInfo -> Bool
  isKnownFun LFReEntrant{} = True
  isKnownFun LFLetNoEscape = True
  isKnownFun _             = False
  
  
  -------------------------------------
  --        Non-void types
  -------------------------------------
  -- We frequently need the invariant that an Id or a an argument
  -- is of a non-void type. This type is a witness to the invariant.
  
  newtype NonVoid a = NonVoid a
    deriving (Eq, Show)
  
  fromNonVoid :: NonVoid a -> a
  fromNonVoid (NonVoid a) = a
  
  instance (Outputable a) => Outputable (NonVoid a) where
    ppr (NonVoid a) = ppr a
  
  nonVoidIds :: [Id] -> [NonVoid Id]
  nonVoidIds ids = [NonVoid id | id <- ids, not (isZeroBitTy (idType id))]
  
  -- | Used in places where some invariant ensures that all these Ids are
  -- non-void; e.g. constructor field binders in case expressions.
  -- See Note [Post-unarisation invariants] in "GHC.Stg.Unarise".
  assertNonVoidIds :: [Id] -> [NonVoid Id]
  assertNonVoidIds ids = assert (not (any (isZeroBitTy . idType) ids)) $
                         coerce ids
  
  nonVoidStgArgs :: [StgArg] -> [NonVoid StgArg]
  nonVoidStgArgs args = [NonVoid arg | arg <- args, not (null (stgArgRep arg))]
  
  -- | Used in places where some invariant ensures that all these arguments are
  -- non-void; e.g. constructor arguments.
  -- See Note [Post-unarisation invariants] in "GHC.Stg.Unarise".
  assertNonVoidStgArgs :: [StgArg] -> [NonVoid StgArg]
  assertNonVoidStgArgs args = assert (not (any (null . stgArgRep) args)) $
                              coerce args
  
  
  -----------------------------------------------------------------------------
  --                Representations
  -----------------------------------------------------------------------------
  
  -- Why are these here?
  
  -- | Assumes that there is at most one 'PrimRep' of the type. This assumption
  -- holds after unarise.
  -- See Note [Post-unarisation invariants] in GHC.Stg.Unarise.
  -- See Note [VoidRep] in GHC.Types.RepType.
  idPrimRep1 :: Id -> PrimOrVoidRep
  idPrimRep1 id = typePrimRep1 (idType id)
  
  idPrimRepU :: Id -> PrimRep
  idPrimRepU id = typePrimRepU (idType id)
  
  -- | Assumes that Ids have one PrimRep, which holds after unarisation.
  -- See Note [Post-unarisation invariants] in GHC.Stg.Unarise.
  addIdReps :: [NonVoid Id] -> [NonVoid (PrimRep, Id)]
  addIdReps = map (\id -> let id' = fromNonVoid id
                           in NonVoid (idPrimRepU id', id'))
  
  -- | Assumes that arguments have one PrimRep, which holds after unarisation.
  -- See Note [Post-unarisation invariants] in GHC.Stg.Unarise.
  addArgReps :: [NonVoid StgArg] -> [NonVoid (PrimRep, StgArg)]
  addArgReps = map (\arg -> let arg' = fromNonVoid arg
                             in NonVoid (stgArgRepU arg', arg'))
  
  ------------------------------------------------------
  --                Building LambdaFormInfo
  ------------------------------------------------------
  
  mkLFArgument :: Id -> LambdaFormInfo
  mkLFArgument id
    | isUnliftedType ty      = LFUnlifted
    | mightBeFunTy ty = LFUnknown True
    | otherwise              = LFUnknown False
    where
      ty = idType id
  
  -------------
  mkLFLetNoEscape :: LambdaFormInfo
  mkLFLetNoEscape = LFLetNoEscape
  
  -------------
  mkLFReEntrant :: TopLevelFlag    -- True of top level
                -> [Id]            -- Free vars
                -> [Id]            -- Args
                -> ArgDescr        -- Argument descriptor
                -> LambdaFormInfo
  
  mkLFReEntrant _ _ [] _
    = pprPanic "mkLFReEntrant" empty
  mkLFReEntrant top fvs args arg_descr
    = LFReEntrant top (length args) (null fvs) arg_descr
  
  -------------
  mkLFThunk :: Type -> TopLevelFlag -> [Id] -> UpdateFlag -> LambdaFormInfo
  mkLFThunk thunk_ty top fvs upd_flag
    = assert (not (isUpdatable upd_flag) || not (isUnliftedType thunk_ty)) $
      LFThunk top (null fvs)
              (isUpdatable upd_flag)
              NonStandardThunk
              (mightBeFunTy thunk_ty)
  
  -------------
  mkConLFInfo :: DataCon -> LambdaFormInfo
  mkConLFInfo con = LFCon con
  
  -------------
  mkSelectorLFInfo :: Id -> Int -> Bool -> LambdaFormInfo
  mkSelectorLFInfo id offset updatable
    = LFThunk NotTopLevel False updatable (SelectorThunk offset)
          (mightBeFunTy (idType id))
  
  -------------
  mkApLFInfo :: Id -> UpdateFlag -> Arity -> LambdaFormInfo
  mkApLFInfo id upd_flag arity
    = LFThunk NotTopLevel (arity == 0) (isUpdatable upd_flag) (ApThunk arity)
          (mightBeFunTy (idType id))
  
  -------------
  -- | The 'LambdaFormInfo' of an imported Id.
  --   See Note [The LFInfo of Imported Ids]
  importedIdLFInfo :: Id -> LambdaFormInfo
  importedIdLFInfo id =
      -- See Note [Conveying CAF-info and LFInfo between modules] in
      -- GHC.StgToCmm.Types
      case idLFInfo_maybe id of
        Just lf_info ->
          -- Use the existing LambdaFormInfo
          lf_info
        Nothing
          -- Doesn't have a LambdaFormInfo, but we know it must be 'LFReEntrant' from its arity
          | arity > 0
          -> LFReEntrant TopLevel arity True ArgUnknown
  
          -- We can't be sure of the LambdaFormInfo of this imported Id,
          -- so make a conservative one from the type.
          | otherwise
          -> assert (isNothing (isDataConId_maybe id)) $ -- See Note [LFInfo of DataCon workers and wrappers] in GHC.Types.Id.Make
             mkLFArgument id -- Not sure of exact arity
    where
      arity = idFunRepArity id
  
  {-
  Note [The LFInfo of Imported Ids]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  As explained in Note [Conveying CAF-info and LFInfo between modules]
  the LambdaFormInfo records the details of a closure representation and is
  often, when optimisations are enabled, serialized to the interface of a module.
  
  In particular, the `lfInfo` field of the `IdInfo` field of an `Id`:
  * For DataCon workers and wrappers is populated as described in
  Note [LFInfo of DataCon workers and wrappers] in GHC.Types.Id.Make
  * For other Ids defined in the module being compiled: is `Nothing`
  * For other imported Ids:
    * is (Just lf_info) if the LFInfo was serialised into the interface file
      (typically, when the exporting module was compiled with -O)
    * is Nothing if it wasn't serialised
  
  The LambdaFormInfo we give an Id is used in determining how to tag its pointer
  (see `litIdInfo` and `lfDynTag`). Therefore, it's crucial we attribute a correct
  LambdaFormInfo to imported Ids, or otherwise risk having pointers incorrectly
  tagged which can lead to performance issues and even segmentation faults (see
  #23231 and Note [Imported unlifted nullary datacon wrappers must have correct LFInfo]).
  
  In particular, saturated data constructor applications *must* be unambiguously
  given `LFCon`, and if the LFInfo says LFCon, then it really is a static data
  constructor, and similar for LFReEntrant.
  
  In `importedIdLFInfo`, we construct a LambdaFormInfo for imported Ids as follows:
  
  (1) If the `lfInfo` field contains an LFInfo, we use that LFInfo which is
  correct by construction (the invariant being that if it exists, it is correct):
    (1.1) Either it was serialised to the interface we're importing the Id from,
    (1.2) Or it's a DataCon worker or wrapper and its LFInfo was constructed
          according to Note [LFInfo of DataCon workers and wrappers]
  (2) When the `lfInfo` field is `Nothing`
    (2.1) If the `idFunRepArity` of the Id is known and is greater than 0, then
    the Id is unambiguously a function and is given `LFReEntrant`, and pointers
    to this Id will be tagged (by `litIdInfo`) with the corresponding arity.
    (2.2) Otherwise, we can make a conservative estimate from the type.
  
  -}
  
  -------------
  mkLFStringLit :: LambdaFormInfo
  mkLFStringLit = LFUnlifted
  
  -----------------------------------------------------
  --                Dynamic pointer tagging
  -----------------------------------------------------
  
  type DynTag = Int       -- The tag on a *pointer*
                          -- (from the dynamic-tagging paper)
  
  -- Note [Data constructor dynamic tags]
  -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  --
  -- The family size of a data type (the number of constructors
  -- or the arity of a function) can be either:
  --    * small, if the family size < 2**tag_bits
  --    * big, otherwise.
  --
  -- Small families can have the constructor tag in the tag bits.
  -- Big families always use the tag values 1..mAX_PTR_TAG to represent
  -- evaluatedness, the last one lumping together all overflowing ones.
  -- We don't have very many tag bits: for example, we have 2 bits on
  -- x86-32 and 3 bits on x86-64.
  --
  -- Also see Note [Tagging big families] in GHC.StgToCmm.Expr
  --
  -- The interpreter also needs to be updated if we change the
  -- tagging strategy; see tagConstr in rts/Interpreter.c.
  
  isSmallFamily :: Platform -> Int -> Bool
  isSmallFamily platform fam_size = fam_size <= mAX_PTR_TAG platform
  
  tagForCon :: Platform -> DataCon -> DynTag
  tagForCon platform con = min (dataConTag con) (mAX_PTR_TAG platform)
  -- NB: 1-indexed
  
  tagForArity :: Platform -> RepArity -> DynTag
  tagForArity platform arity
   | isSmallFamily platform arity = arity
   | otherwise                    = 0
  
  -- | Return the tag in the low order bits of a variable bound
  -- to this LambdaForm
  lfDynTag :: Platform -> LambdaFormInfo -> DynTag
  lfDynTag platform lf = case lf of
     LFCon con               -> tagForCon   platform con
     LFReEntrant _ arity _ _ -> tagForArity platform arity
     _other                  -> 0
  
  
  -----------------------------------------------------------------------------
  --                Observing LambdaFormInfo
  -----------------------------------------------------------------------------
  
  ------------
  isLFThunk :: LambdaFormInfo -> Bool
  isLFThunk (LFThunk {})  = True
  isLFThunk _ = False
  
  isLFReEntrant :: LambdaFormInfo -> Bool
  isLFReEntrant (LFReEntrant {}) = True
  isLFReEntrant _                = False
  
  -----------------------------------------------------------------------------
  --                Choosing SM reps
  -----------------------------------------------------------------------------
  
  lfClosureType :: LambdaFormInfo -> ClosureTypeInfo
  lfClosureType (LFReEntrant _ arity _ argd) = Fun arity argd
  lfClosureType (LFCon con)                  = Constr (dataConTagZ con)
                                                      (dataConIdentity con)
  lfClosureType (LFThunk _ _ _ is_sel _)     = thunkClosureType is_sel
  lfClosureType _                            = panic "lfClosureType"
  
  thunkClosureType :: StandardFormInfo -> ClosureTypeInfo
  thunkClosureType (SelectorThunk off) = ThunkSelector off
  thunkClosureType _                   = Thunk
  
  -- We *do* get non-updatable top-level thunks sometimes.  eg. f = g
  -- gets compiled to a jump to g (if g has non-zero arity), instead of
  -- messing around with update frames and PAPs.  We set the closure type
  -- to FUN_STATIC in this case.
  
  -----------------------------------------------------------------------------
  --                nodeMustPointToIt
  -----------------------------------------------------------------------------
  
  nodeMustPointToIt :: Profile -> LambdaFormInfo -> Bool
  -- If nodeMustPointToIt is true, then the entry convention for
  -- this closure has R1 (the "Node" register) pointing to the
  -- closure itself --- the "self" argument
  
  nodeMustPointToIt _ (LFReEntrant top _ no_fvs _)
    =  not no_fvs          -- Certainly if it has fvs we need to point to it
    || isNotTopLevel top   -- See Note [GC recovery]
          -- For lex_profiling we also access the cost centre for a
          -- non-inherited (i.e. non-top-level) function.
          -- The isNotTopLevel test above ensures this is ok.
  
  nodeMustPointToIt profile (LFThunk top no_fvs updatable NonStandardThunk _)
    =  not no_fvs            -- Self parameter
    || isNotTopLevel top     -- Note [GC recovery]
    || updatable             -- Need to push update frame
    || profileIsProfiling profile
            -- For the non-updatable (single-entry case):
            --
            -- True if has fvs (in which case we need access to them, and we
            --                    should black-hole it)
            -- or profiling (in which case we need to recover the cost centre
            --                 from inside it)  ToDo: do we need this even for
            --                                    top-level thunks? If not,
            --                                    isNotTopLevel subsumes this
  
  nodeMustPointToIt _ (LFThunk {})        -- Node must point to a standard-form thunk
    = True
  
  nodeMustPointToIt _ (LFCon _) = True
  
          -- Strictly speaking, the above two don't need Node to point
          -- to it if the arity = 0.  But this is a *really* unlikely
          -- situation.  If we know it's nil (say) and we are entering
          -- it. Eg: let x = [] in x then we will certainly have inlined
          -- x, since nil is a simple atom.  So we gain little by not
          -- having Node point to known zero-arity things.  On the other
          -- hand, we do lose something; Patrick's code for figuring out
          -- when something has been updated but not entered relies on
          -- having Node point to the result of an update.  SLPJ
          -- 27/11/92.
  
  nodeMustPointToIt _ (LFUnknown _)   = True
  nodeMustPointToIt _ LFUnlifted      = False
  nodeMustPointToIt _ LFLetNoEscape   = False
  
  {- Note [GC recovery]
  ~~~~~~~~~~~~~~~~~~~~~
  If we a have a local let-binding (function or thunk)
     let f = <body> in ...
  AND <body> allocates, then the heap-overflow check needs to know how
  to re-start the evaluation.  It uses the "self" pointer to do this.
  So even if there are no free variables in <body>, we still make
  nodeMustPointToIt be True for non-top-level bindings.
  
  Why do any such bindings exist?  After all, let-floating should have
  floated them out.  Well, a clever optimiser might leave one there to
  avoid a space leak, deliberately recomputing a thunk.  Also (and this
  really does happen occasionally) let-floating may make a function f smaller
  so it can be inlined, so now (f True) may generate a local no-fv closure.
  This actually happened during bootstrapping GHC itself, with f=mkRdrFunBind
  in GHC.Tc.Deriv.Generate.) -}
  
  -----------------------------------------------------------------------------
  --                getCallMethod
  -----------------------------------------------------------------------------
  
  {- The entry conventions depend on the type of closure being entered,
  whether or not it has free variables, and whether we're running
  sequentially or in parallel.
  
  Closure                           Node   Argument   Enter
  Characteristics              Par   Req'd  Passing    Via
  ---------------------------------------------------------------------------
  Unknown                     & no  & yes & stack     & node
  Known fun (>1 arg), no fvs  & no  & no  & registers & fast entry (enough args)
                                                      & slow entry (otherwise)
  Known fun (>1 arg), fvs     & no  & yes & registers & fast entry (enough args)
  0 arg, no fvs \r,\s         & no  & no  & n/a       & direct entry
  0 arg, no fvs \u            & no  & yes & n/a       & node
  0 arg, fvs \r,\s,selector   & no  & yes & n/a       & node
  0 arg, fvs \r,\s            & no  & yes & n/a       & direct entry
  0 arg, fvs \u               & no  & yes & n/a       & node
  Unknown                     & yes & yes & stack     & node
  Known fun (>1 arg), no fvs  & yes & no  & registers & fast entry (enough args)
                                                      & slow entry (otherwise)
  Known fun (>1 arg), fvs     & yes & yes & registers & node
  0 arg, fvs \r,\s,selector   & yes & yes & n/a       & node
  0 arg, no fvs \r,\s         & yes & no  & n/a       & direct entry
  0 arg, no fvs \u            & yes & yes & n/a       & node
  0 arg, fvs \r,\s            & yes & yes & n/a       & node
  0 arg, fvs \u               & yes & yes & n/a       & node
  
  When black-holing, single-entry closures could also be entered via node
  (rather than directly) to catch double-entry. -}
  
  data CallMethod
    = EnterIt             -- ^ No args, not a function
  
    | JumpToIt BlockId [LocalReg] -- A join point or a header of a local loop
  
    | ReturnIt            -- It's a value (function, unboxed value,
                          -- or constructor), so just return it.
  
    | InferedReturnIt     -- A properly tagged value, as determined by tag inference.
                          -- See Note [Evaluated and Properly Tagged]
                          -- and Note [EPT enforcement] in GHC.Stg.EnforceEpt.
                          -- It behaves /precisely/ like `ReturnIt`, except that when debugging is
                          -- enabled we emit an extra assertion to check that the returned value is
                          -- properly tagged.  We can use this as a check that tag inference is working
                          -- correctly.
                          -- TODO: SPJ suggested we could combine this with EnterIt, but for now I decided
                          -- not to do so.
  
    | SlowCall            -- Unknown fun, or known fun with
                          -- too few args.
  
    | DirectEntry         -- Jump directly, with args in regs
          CLabel          --   The code label
          RepArity        --   Its arity
  
  instance Outputable CallMethod where
    ppr (EnterIt) = text "Enter"
    ppr (JumpToIt {}) = text "JumpToIt"
    ppr (ReturnIt ) = text "ReturnIt"
    ppr (InferedReturnIt) = text "InferedReturnIt"
    ppr (SlowCall ) = text "SlowCall"
    ppr (DirectEntry {}) = text "DirectEntry"
  
  getCallMethod :: StgToCmmConfig
                -> Name           -- Function being applied
                -> Id             -- Function Id used to check if it can refer to
                                  -- CAF's and whether the function is tail-calling
                                  -- itself
                -> LambdaFormInfo -- Its info
                -> RepArity       -- Number of available arguments
                                  -- (including void args)
                -> CgLoc          -- Passed in from cgIdApp so that we can
                                  -- handle let-no-escape bindings and self-recursive
                                  -- tail calls using the same data constructor,
                                  -- JumpToIt. This saves us one case branch in
                                  -- cgIdApp
                -> Maybe SelfLoopInfo -- can we perform a self-recursive tail-call
                -> CallMethod
  
  getCallMethod cfg _ id _  n_args _cg_loc (Just self_loop)
    | stgToCmmLoopification cfg
    , MkSelfLoopInfo
      { sli_id = loop_id, sli_arity = arity
      , sli_header_block = blk_id, sli_registers = arg_regs
      } <- self_loop
    , id == loop_id
    , n_args == arity
    -- If these patterns match then we know that:
    --   * loopification optimisation is turned on
    --   * function is performing a self-recursive call in a tail position
    --   * number of parameters matches the function's arity.
    -- See Note [Self-recursive tail calls] in GHC.StgToCmm.Expr for more details
    = JumpToIt blk_id arg_regs
  
  getCallMethod cfg name id (LFReEntrant _ arity _ _) n_args _cg_loc _self_loop_info
    | n_args == 0 -- No args at all
    && not (profileIsProfiling (stgToCmmProfile cfg))
       -- See Note [Evaluating functions with profiling] in rts/Apply.cmm
    = assert (arity /= 0) ReturnIt
    | n_args < arity = SlowCall        -- Not enough args
    | otherwise      = DirectEntry (enterIdLabel (stgToCmmPlatform cfg) name (idCafInfo id)) arity
  
  getCallMethod _ _name _ LFUnlifted n_args _cg_loc _self_loop_info
    = assert (n_args == 0) ReturnIt
  
  getCallMethod _ _name _ (LFCon _) n_args _cg_loc _self_loop_info
    = assert (n_args == 0) ReturnIt
      -- n_args=0 because it'd be ill-typed to apply a saturated
      --          constructor application to anything
  
  getCallMethod cfg name id (LFThunk _ _ updatable std_form_info is_fun)
                n_args _cg_loc _self_loop_info
  
    | Just sig <- idTagSig_maybe id
    , isTaggedSig sig -- Infered to be already evaluated by EPT analysis
    , n_args == 0     -- See Note [EPT enforcement]
    = InferedReturnIt
  
    | is_fun      -- it *might* be a function, so we must "call" it (which is always safe)
    = SlowCall    -- We cannot just enter it [in eval/apply, the entry code
                  -- is the fast-entry code]
  
    -- Since is_fun is False, we are *definitely* looking at a data value
    | updatable || stgToCmmDoTicky cfg -- to catch double entry
        {- OLD: || opt_SMP
           I decided to remove this, because in SMP mode it doesn't matter
           if we enter the same thunk multiple times, so the optimisation
           of jumping directly to the entry code is still valid.  --SDM
          -}
    = EnterIt
  
    -- even a non-updatable selector thunk can be updated by the garbage
    -- collector, so we must enter it. (#8817)
    | SelectorThunk{} <- std_form_info
    = EnterIt
  
      -- We used to have assert (n_args == 0 ), but actually it is
      -- possible for the optimiser to generate
      --   let bot :: Int = error Int "urk"
      --   in (bot `cast` unsafeCoerce Int (Int -> Int)) 3
      -- This happens as a result of the case-of-error transformation
      -- So the right thing to do is just to enter the thing
  
    | otherwise        -- Jump direct to code for single-entry thunks
    = assert (n_args == 0) $
      DirectEntry (thunkEntryLabel (stgToCmmPlatform cfg) name (idCafInfo id) std_form_info
                  updatable) 0
  
  -- Imported(Unknown) Ids
  getCallMethod cfg name id (LFUnknown might_be_a_function) n_args _cg_locs _self_loop_info
    | n_args == 0
    , Just sig <- idTagSig_maybe id
    , isTaggedSig sig -- Infered to be already evaluated by EPT analysis
    -- When profiling we must enter all potential functions to make sure we update the SCC
    -- even if the function itself is already evaluated.
    -- See Note [Evaluating functions with profiling] in rts/Apply.cmm
    , not (profileIsProfiling (stgToCmmProfile cfg) && might_be_a_function)
    = InferedReturnIt -- See Note [EPT enforcement]
  
    | might_be_a_function = SlowCall
  
    | otherwise =
        assertPpr ( n_args == 0) ( ppr name <+> ppr n_args )
        EnterIt   -- Not a function
  
  -- TODO: Redundant with above match?
  -- getCallMethod _ name _ (LFUnknown False) n_args _cg_loc _self_loop_info
  --   = assertPpr (n_args == 0) (ppr name <+> ppr n_args)
  --     EnterIt -- Not a function
  
  getCallMethod _ _name _ LFLetNoEscape _n_args (LneLoc blk_id lne_regs) _self_loop_info
    = JumpToIt blk_id lne_regs
  
  getCallMethod _ _ _ _ _ _ _ = panic "Unknown call method"
  
  -----------------------------------------------------------------------------
  --              Data types for closure information
  -----------------------------------------------------------------------------
  
  
  {- ClosureInfo: information about a binding
  
     We make a ClosureInfo for each let binding (both top level and not),
     but not bindings for data constructors: for those we build a CmmInfoTable
     directly (see mkDataConInfoTable).
  
     To a first approximation:
         ClosureInfo = (LambdaFormInfo, CmmInfoTable)
  
     A ClosureInfo has enough information
       a) to construct the info table itself, and build other things
          related to the binding (e.g. slow entry points for a function)
       b) to allocate a closure containing that info pointer (i.e.
             it knows the info table label)
  -}
  
  data ClosureInfo
    = ClosureInfo {
          closureName :: !Id,           -- The thing bound to this closure
             -- we don't really need this field: it's only used in generating
             -- code for ticky and profiling, and we could pass the information
             -- around separately, but it doesn't do much harm to keep it here.
  
          closureLFInfo :: !LambdaFormInfo, -- NOTE: not an LFCon
            -- this tells us about what the closure contains: it's right-hand-side.
  
            -- the rest is just an unpacked CmmInfoTable.
          closureInfoLabel :: !CLabel,
          closureSMRep     :: !SMRep,          -- representation used by storage mgr
          closureProf      :: !ProfilingInfo
      }
  
  -- | Convert from 'ClosureInfo' to 'CmmInfoTable'.
  mkCmmInfo :: ClosureInfo -> Id -> CostCentreStack -> CmmInfoTable
  mkCmmInfo ClosureInfo {..} id ccs
    = CmmInfoTable { cit_lbl  = closureInfoLabel
                   , cit_rep  = closureSMRep
                   , cit_prof = closureProf
                   , cit_srt  = Nothing
                   , cit_clo  = if isStaticRep closureSMRep
                                  then Just (id,ccs)
                                  else Nothing }
  
  --------------------------------------
  --        Building ClosureInfos
  --------------------------------------
  
  mkClosureInfo :: Profile
                -> Bool                -- Is static
                -> Id
                -> LambdaFormInfo
                -> Int -> Int        -- Total and pointer words
                -> String         -- String descriptor
                -> ClosureInfo
  mkClosureInfo profile is_static id lf_info tot_wds ptr_wds val_descr
    = ClosureInfo { closureName      = id
                  , closureLFInfo    = lf_info
                  , closureInfoLabel = info_lbl   -- These three fields are
                  , closureSMRep     = sm_rep     -- (almost) an info table
                  , closureProf      = prof }     -- (we don't have an SRT yet)
    where
      sm_rep     = mkHeapRep profile is_static ptr_wds nonptr_wds (lfClosureType lf_info)
      prof       = mkProfilingInfo profile id val_descr
      nonptr_wds = tot_wds - ptr_wds
  
      info_lbl = mkClosureInfoTableLabel (profilePlatform profile) id lf_info
  
  --------------------------------------
  --   Other functions over ClosureInfo
  --------------------------------------
  
  -- Eager blackholing is normally disabled, but can be turned on with
  -- -feager-blackholing.  When it is on, we replace the info pointer of
  -- the thunk with stg_EAGER_BLACKHOLE_info on entry.
  
  -- If we wanted to do eager blackholing with slop filling,
  -- we'd need to do it at the *end* of a basic block, otherwise
  -- we overwrite the free variables in the thunk that we still
  -- need.  We have a patch for this from Andy Cheadle, but not
  -- incorporated yet. --SDM [6/2004]
  --
  -- Previously, eager blackholing was enabled when ticky-ticky
  -- was on. But it didn't work, and it wasn't strictly necessary
  -- to bring back minimal ticky-ticky, so now EAGER_BLACKHOLING
  -- is unconditionally disabled. -- krc 1/2007
  --
  -- Static closures are never themselves black-holed.
  
  blackHoleOnEntry :: ClosureInfo -> Bool
  blackHoleOnEntry cl_info
    | isStaticRep (closureSMRep cl_info)
    = False        -- Never black-hole a static closure
  
    | otherwise
    = case closureLFInfo cl_info of
        LFReEntrant {}            -> False
        LFLetNoEscape             -> False
        LFThunk _ _no_fvs upd _ _ -> upd   -- See Note [Black-holing non-updatable thunks]
        _other -> panic "blackHoleOnEntry"
  
  {- Note [Black-holing non-updatable thunks]
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  We must not black-hole non-updatable (single-entry) thunks otherwise
  we run into issues like #10414. Specifically:
  
    * There is no reason to black-hole a non-updatable thunk: it should
      not be competed for by multiple threads
  
    * It could, conceivably, cause a space leak if we don't black-hole
      it, if there was a live but never-followed pointer pointing to it.
      Let's hope that doesn't happen.
  
    * It is dangerous to black-hole a non-updatable thunk because
       - is not updated (of course)
       - hence, if it is black-holed and another thread tries to evaluate
         it, that thread will block forever
      This actually happened in #10414.  So we do not black-hole
      non-updatable thunks.
  
    * How could two threads evaluate the same non-updatable (single-entry)
      thunk?  See Reid Barton's example below.
  
    * Only eager blackholing could possibly black-hole a non-updatable
      thunk, because lazy black-holing only affects thunks with an
      update frame on the stack.
  
  Here is and example due to Reid Barton (#10414):
      x = \u []  concat [[1], []]
  with the following definitions,
  
      concat x = case x of
          []       -> []
          (:) x xs -> (++) x (concat xs)
  
      (++) xs ys = case xs of
          []         -> ys
          (:) x rest -> (:) x ((++) rest ys)
  
  Where we use the syntax @\u []@ to denote an updatable thunk and @\s []@ to
  denote a single-entry (i.e. non-updatable) thunk. After a thread evaluates @x@
  to WHNF and calls @(++)@ the heap will contain the following thunks,
  
      x = 1 : y
      y = \u []  (++) [] z
      z = \s []  concat []
  
  Now that the stage is set, consider the follow evaluations by two racing threads
  A and B,
  
    1. Both threads enter @y@ before either is able to replace it with an
       indirection
  
    2. Thread A does the case analysis in @(++)@ and consequently enters @z@,
       replacing it with a black-hole
  
    3. At some later point thread B does the same case analysis and also attempts
       to enter @z@. However, it finds that it has been replaced with a black-hole
       so it blocks.
  
    4. Thread A eventually finishes evaluating @z@ (to @[]@) and updates @y@
       accordingly. It does *not* update @z@, however, as it is single-entry. This
       leaves Thread B blocked forever on a black-hole which will never be
       updated.
  
  To avoid this sort of condition we never black-hole non-updatable thunks.
  -}
  
  isStaticClosure :: ClosureInfo -> Bool
  isStaticClosure cl_info = isStaticRep (closureSMRep cl_info)
  
  closureUpdReqd :: ClosureInfo -> Bool
  closureUpdReqd ClosureInfo{ closureLFInfo = lf_info } = lfUpdatable lf_info
  
  lfUpdatable :: LambdaFormInfo -> Bool
  lfUpdatable (LFThunk _ _ upd _ _)  = upd
  lfUpdatable _ = False
  
  closureReEntrant :: ClosureInfo -> Bool
  closureReEntrant (ClosureInfo { closureLFInfo = LFReEntrant {} }) = True
  closureReEntrant _ = False
  
  closureFunInfo :: ClosureInfo -> Maybe (RepArity, ArgDescr)
  closureFunInfo (ClosureInfo { closureLFInfo = lf_info }) = lfFunInfo lf_info
  
  lfFunInfo :: LambdaFormInfo ->  Maybe (RepArity, ArgDescr)
  lfFunInfo (LFReEntrant _ arity _ arg_desc)  = Just (arity, arg_desc)
  lfFunInfo _                                 = Nothing
  
  funTag :: Platform -> ClosureInfo -> DynTag
  funTag platform (ClosureInfo { closureLFInfo = lf_info })
      = lfDynTag platform lf_info
  
  isToplevClosure :: ClosureInfo -> Bool
  isToplevClosure (ClosureInfo { closureLFInfo = lf_info })
    = case lf_info of
        LFReEntrant TopLevel _ _ _ -> True
        LFThunk TopLevel _ _ _ _   -> True
        _other                     -> False
  
  --------------------------------------
  --   Label generation
  --------------------------------------
  
  staticClosureLabel :: Platform -> ClosureInfo -> CLabel
  staticClosureLabel platform = toClosureLbl platform .  closureInfoLabel
  
  closureSlowEntryLabel :: Platform -> ClosureInfo -> CLabel
  closureSlowEntryLabel platform = toSlowEntryLbl platform . closureInfoLabel
  
  closureLocalEntryLabel :: Platform -> ClosureInfo -> CLabel
  closureLocalEntryLabel platform
    | platformTablesNextToCode platform = toInfoLbl  platform . closureInfoLabel
    | otherwise                         = toEntryLbl platform . closureInfoLabel
  
  -- | Get the info table label for a *thunk*.
  mkClosureInfoTableLabel :: Platform -> Id -> LambdaFormInfo -> CLabel
  mkClosureInfoTableLabel platform id lf_info
    = case lf_info of
          LFThunk _ _ upd_flag (SelectorThunk offset) _
                        -> mkSelectorInfoLabel platform upd_flag offset
  
          LFThunk _ _ upd_flag (ApThunk arity) _
                        -> mkApInfoTableLabel platform upd_flag arity
  
          LFThunk{}     -> mkInfoTableLabel name cafs
          LFReEntrant{} -> mkInfoTableLabel name cafs
          _other        -> panic "closureInfoTableLabel"
  
    where
      name = idName id
  
      cafs     = idCafInfo id
  
  -- | thunkEntryLabel is a local help function, not exported.  It's used from
  -- getCallMethod.
  thunkEntryLabel :: Platform -> Name -> CafInfo -> StandardFormInfo -> Bool -> CLabel
  thunkEntryLabel platform thunk_id caf_info sfi upd_flag = case sfi of
     ApThunk arity        -> enterApLabel       platform upd_flag arity
     SelectorThunk offset -> enterSelectorLabel platform upd_flag offset
     _                    -> enterIdLabel       platform thunk_id caf_info
  
  enterApLabel :: Platform -> Bool -> Arity -> CLabel
  enterApLabel platform is_updatable arity
    | platformTablesNextToCode platform = mkApInfoTableLabel platform is_updatable arity
    | otherwise                         = mkApEntryLabel     platform is_updatable arity
  
  enterSelectorLabel :: Platform -> Bool -> WordOff -> CLabel
  enterSelectorLabel platform upd_flag offset
    | platformTablesNextToCode platform = mkSelectorInfoLabel  platform upd_flag offset
    | otherwise                         = mkSelectorEntryLabel platform upd_flag offset
  
  enterIdLabel :: Platform -> Name -> CafInfo -> CLabel
  enterIdLabel platform id c
    | platformTablesNextToCode platform = mkInfoTableLabel id c
    | otherwise                         = mkEntryLabel id c
  
  
  --------------------------------------
  --   Profiling
  --------------------------------------
  
  -- Profiling requires two pieces of information to be determined for
  -- each closure's info table --- description and type.
  
  -- The description is stored directly in the @CClosureInfoTable@ when the
  -- info table is built.
  
  -- The type is determined from the type information stored with the @Id@
  -- in the closure info using @closureTypeDescr@.
  
  mkProfilingInfo :: Profile -> Id -> String -> ProfilingInfo
  mkProfilingInfo profile id val_descr
    | not (profileIsProfiling profile) = NoProfilingInfo
    | otherwise                        = ProfilingInfo ty_descr_w8 (BS8.pack val_descr)
    where
      ty_descr_w8  = BS8.pack (getTyDescription (idType id))
  
  getTyDescription :: Type -> String
  getTyDescription ty
    = case (tcSplitSigmaTy ty) of { (_, _, tau_ty) ->
      case tau_ty of
        TyVarTy _              -> "*"
        AppTy fun _            -> getTyDescription fun
        TyConApp tycon _       -> getOccString tycon
        FunTy {}              -> '-' : fun_result tau_ty
        ForAllTy _  ty         -> getTyDescription ty
        LitTy n                -> getTyLitDescription n
        CastTy ty _            -> getTyDescription ty
        CoercionTy co          -> pprPanic "getTyDescription" (ppr co)
      }
    where
      fun_result (FunTy { ft_res = res }) = '>' : fun_result res
      fun_result other                    = getTyDescription other
  
  getTyLitDescription :: TyLit -> String
  getTyLitDescription l =
    case l of
      NumTyLit n -> show n
      StrTyLit n -> show n
      CharTyLit n -> show n
  
  --------------------------------------
  --   CmmInfoTable-related things
  --------------------------------------
  
  mkDataConInfoTable :: Profile -> DataCon -> ConInfoTableLocation -> Bool -> Int -> Int -> CmmInfoTable
  mkDataConInfoTable profile data_con mn is_static ptr_wds nonptr_wds
   = CmmInfoTable { cit_lbl  = info_lbl
                  , cit_rep  = sm_rep
                  , cit_prof = prof
                  , cit_srt  = Nothing
                  , cit_clo  = Nothing }
   where
     name = dataConName data_con
     info_lbl = mkConInfoTableLabel name mn -- NoCAFRefs
     sm_rep = mkHeapRep profile is_static ptr_wds nonptr_wds cl_type
     cl_type = Constr (dataConTagZ data_con) (dataConIdentity data_con)
                    -- We keep the *zero-indexed* tag in the srt_len field
                    -- of the info table of a data constructor.
  
     prof | not (profileIsProfiling profile) = NoProfilingInfo
          | otherwise                        = ProfilingInfo ty_descr val_descr
  
     ty_descr  = BS8.pack $ occNameString $ getOccName $ dataConTyCon data_con
     val_descr = BS8.pack $ occNameString $ getOccName data_con
  
  -- We need a black-hole closure info to pass to @allocDynClosure@ when we
  -- want to allocate the black hole on entry to a CAF.
  
  cafBlackHoleInfoTable :: CmmInfoTable
  cafBlackHoleInfoTable
    = CmmInfoTable { cit_lbl  = mkCAFBlackHoleInfoTableLabel
                   , cit_rep  = blackHoleRep
                   , cit_prof = NoProfilingInfo
                   , cit_srt  = Nothing
                   , cit_clo  = Nothing }
  
  indStaticInfoTable :: CmmInfoTable
  indStaticInfoTable
    = CmmInfoTable { cit_lbl  = mkIndStaticInfoLabel
                   , cit_rep  = indStaticRep
                   , cit_prof = NoProfilingInfo
                   , cit_srt  = Nothing
                   , cit_clo  = Nothing }
  
  staticClosureNeedsLink :: Bool -> CmmInfoTable -> Bool
  -- A static closure needs a link field to aid the GC when traversing
  -- the static closure graph.  But it only needs such a field if either
  --        a) it has an SRT
  --        b) it's a constructor with one or more pointer fields
  -- In case (b), the constructor's fields themselves play the role
  -- of the SRT.
  staticClosureNeedsLink has_srt CmmInfoTable{ cit_rep = smrep }
    | isConRep smrep         = not (isStaticNoCafCon smrep)
    | otherwise              = has_srt
  