ClosureInfo.lhs 31.3 KB
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% (c) The University of Glasgow 2006
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% (c) The Univserity of Glasgow 1992-2004
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	Data structures which describe closures, and
	operations over those data structures

		Nothing monadic in here
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Much of the rationale for these things is in the ``details'' part of
the STG paper.

\begin{code}
module ClosureInfo (
	ClosureInfo, LambdaFormInfo, SMRep, 	-- all abstract
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	StandardFormInfo, 
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	ArgDescr(..), Liveness(..), 
	C_SRT(..), needsSRT,
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	mkLFThunk, mkLFReEntrant, mkConLFInfo, mkSelectorLFInfo,
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	mkApLFInfo, mkLFImported, mkLFArgument, mkLFLetNoEscape,
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	mkClosureInfo, mkConInfo,

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	closureSize, closureNonHdrSize,
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	closureGoodStuffSize, closurePtrsSize,
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	slopSize, 
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	closureName, infoTableLabelFromCI,
	closureLabelFromCI, closureSRT,
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	closureLFInfo, isLFThunk,closureSMRep, closureUpdReqd, 
	closureNeedsUpdSpace, closureIsThunk,
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	closureSingleEntry, closureReEntrant, isConstrClosure_maybe,
	closureFunInfo,	isStandardFormThunk, isKnownFun,
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	enterIdLabel, enterLocalIdLabel, enterReturnPtLabel,
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	nodeMustPointToIt, 
	CallMethod(..), getCallMethod,
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	blackHoleOnEntry,
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	staticClosureRequired,
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	getClosureType,
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	isToplevClosure,
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	closureValDescr, closureTypeDescr,	-- profiling
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	isStaticClosure,
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	cafBlackHoleClosureInfo, seCafBlackHoleClosureInfo,
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	staticClosureNeedsLink,
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    ) where

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#include "../includes/MachDeps.h"
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#include "HsVersions.h"
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import StgSyn
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import SMRep
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import CLabel
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import Packages
import PackageConfig
import StaticFlags
import Id
import DataCon
import Name
import OccName
import Type
import TypeRep
import TcType
import TyCon
import BasicTypes
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import FastString
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import Outputable
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import Constants
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\end{code}

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%************************************************************************
%*									*
\subsection[ClosureInfo-datatypes]{Data types for closure information}
%*									*
%************************************************************************

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Information about a closure, from the code generator's point of view.

A ClosureInfo decribes the info pointer of a closure.  It has
enough information 
  a) to construct the info table itself
  b) to allocate a closure containing that info pointer (i.e.
	it knows the info table label)

We make a ClosureInfo for
	- each let binding (both top level and not)
	- each data constructor (for its shared static and
		dynamic info tables)
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\begin{code}
data ClosureInfo
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  = ClosureInfo {
	closureName   :: !Name,		  -- The thing bound to this closure
	closureLFInfo :: !LambdaFormInfo, -- NOTE: not an LFCon (see below)
	closureSMRep  :: !SMRep,	  -- representation used by storage mgr
	closureSRT    :: !C_SRT,	  -- What SRT applies to this closure
	closureType   :: !Type,		  -- Type of closure (ToDo: remove)
	closureDescr  :: !String	  -- closure description (for profiling)
    }

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  -- Constructor closures don't have a unique info table label (they use
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  -- the constructor's info table), and they don't have an SRT.
  | ConInfo {
	closureCon       :: !DataCon,
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	closureSMRep     :: !SMRep,
	closureDllCon	 :: !Bool	-- is in a separate DLL
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    }
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-- C_SRT is what StgSyn.SRT gets translated to... 
-- we add a label for the table, and expect only the 'offset/length' form

data C_SRT = NoC_SRT
	   | C_SRT !CLabel !WordOff !StgHalfWord {-bitmap or escape-}

needsSRT :: C_SRT -> Bool
needsSRT NoC_SRT       = False
needsSRT (C_SRT _ _ _) = True
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\end{code}

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%************************************************************************
%*									*
\subsubsection[LambdaFormInfo-datatype]{@LambdaFormInfo@: source-derivable info}
%*									*
%************************************************************************

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Information about an identifier, from the code generator's point of
view.  Every identifier is bound to a LambdaFormInfo in the
environment, which gives the code generator enough info to be able to
tail call or return that identifier.

Note that a closure is usually bound to an identifier, so a
ClosureInfo contains a LambdaFormInfo.

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\begin{code}
data LambdaFormInfo
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  = LFReEntrant		-- Reentrant closure (a function)
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	TopLevelFlag	-- True if top level
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	!Int		-- Arity. Invariant: always > 0
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	!Bool		-- True <=> no fvs
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	ArgDescr	-- Argument descriptor (should reall be in ClosureInfo)
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  | LFCon		-- A saturated constructor application
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	DataCon		-- The constructor
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  | LFThunk		-- Thunk (zero arity)
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	TopLevelFlag
	!Bool		-- True <=> no free vars
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	!Bool		-- True <=> updatable (i.e., *not* single-entry)
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	StandardFormInfo
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	!Bool		-- True <=> *might* be a function type
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  | LFUnknown		-- Used for function arguments and imported things.
			--  We know nothing about  this closure.  Treat like
			-- updatable "LFThunk"...
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			-- Imported things which we do know something about use
			-- one of the other LF constructors (eg LFReEntrant for
			-- known functions)
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	!Bool		-- True <=> *might* be a function type
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  | LFLetNoEscape	-- See LetNoEscape module for precise description of
			-- these "lets".
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	!Int		-- arity;
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  | LFBlackHole		-- Used for the closures allocated to hold the result
			-- of a CAF.  We want the target of the update frame to
			-- be in the heap, so we make a black hole to hold it.
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        CLabel          -- Flavour (info label, eg CAF_BLACKHOLE_info).
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-------------------------
-- An ArgDsecr describes the argument pattern of a function
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data ArgDescr
  = ArgSpec		-- Fits one of the standard patterns
	!Int		-- RTS type identifier ARG_P, ARG_N, ...
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  | ArgGen	 	-- General case
	Liveness	-- Details about the arguments
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-------------------------
-- We represent liveness bitmaps as a Bitmap (whose internal
-- representation really is a bitmap).  These are pinned onto case return
-- vectors to indicate the state of the stack for the garbage collector.
-- 
-- In the compiled program, liveness bitmaps that fit inside a single
-- word (StgWord) are stored as a single word, while larger bitmaps are
-- stored as a pointer to an array of words. 
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data Liveness
  = SmallLiveness	-- Liveness info that fits in one word
	StgWord		-- Here's the bitmap

  | BigLiveness		-- Liveness info witha a multi-word bitmap
	CLabel		-- Label for the bitmap
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-------------------------
-- StandardFormInfo tells whether this thunk has one of 
-- a small number of standard forms
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data StandardFormInfo
  = NonStandardThunk
	-- Not of of the standard forms
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  | SelectorThunk
	-- A SelectorThunk is of form
	--      case x of
	--	       con a1,..,an -> ak
	-- and the constructor is from a single-constr type.
       WordOff             	-- 0-origin offset of ak within the "goods" of 
			-- constructor (Recall that the a1,...,an may be laid
			-- out in the heap in a non-obvious order.)
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  | ApThunk 
	-- An ApThunk is of form
	--	x1 ... xn
	-- The code for the thunk just pushes x2..xn on the stack and enters x1.
	-- There are a few of these (for 1 <= n <= MAX_SPEC_AP_SIZE) pre-compiled
	-- in the RTS to save space.
	Int		-- Arity, n
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\end{code}

%************************************************************************
%*									*
\subsection[ClosureInfo-construction]{Functions which build LFInfos}
%*									*
%************************************************************************

\begin{code}
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mkLFReEntrant :: TopLevelFlag	-- True of top level
	      -> [Id]		-- Free vars
	      -> [Id] 		-- Args
	      -> ArgDescr	-- Argument descriptor
	      -> LambdaFormInfo

mkLFReEntrant top fvs args arg_descr 
  = LFReEntrant top (length args) (null fvs) arg_descr

mkLFThunk thunk_ty top fvs upd_flag
  = ASSERT( not (isUpdatable upd_flag) || not (isUnLiftedType thunk_ty) )
    LFThunk top (null fvs) 
	    (isUpdatable upd_flag)
	    NonStandardThunk 
	    (might_be_a_function thunk_ty)
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might_be_a_function :: Type -> Bool
might_be_a_function ty
  | Just (tc,_) <- splitTyConApp_maybe (repType ty), 
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    not (isFunTyCon tc)  && not (isAbstractTyCon tc) = False
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	-- don't forget to check for abstract types, which might
	-- be functions too.
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  | otherwise = True
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\end{code}

@mkConLFInfo@ is similar, for constructors.

\begin{code}
mkConLFInfo :: DataCon -> LambdaFormInfo
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mkConLFInfo con = LFCon con
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mkSelectorLFInfo id offset updatable
  = LFThunk NotTopLevel False updatable (SelectorThunk offset) 
	(might_be_a_function (idType id))
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mkApLFInfo id upd_flag arity
  = LFThunk NotTopLevel (arity == 0) (isUpdatable upd_flag) (ApThunk arity)
	(might_be_a_function (idType id))
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\end{code}

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Miscellaneous LF-infos.

\begin{code}
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mkLFArgument id = LFUnknown (might_be_a_function (idType id))

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mkLFLetNoEscape = LFLetNoEscape

mkLFImported :: Id -> LambdaFormInfo
mkLFImported id
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  = case idArity id of
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      n | n > 0 -> LFReEntrant TopLevel n True (panic "arg_descr")  -- n > 0
      other -> mkLFArgument id -- Not sure of exact arity
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\end{code}
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\begin{code}
isLFThunk :: LambdaFormInfo -> Bool
isLFThunk (LFThunk _ _ _ _ _)  = True
isLFThunk (LFBlackHole _)      = True
	-- return True for a blackhole: this function is used to determine
	-- whether to use the thunk header in SMP mode, and a blackhole
	-- must have one.
isLFThunk _ = False
\end{code}

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%************************************************************************
%*									*
	Building ClosureInfos
%*									*
%************************************************************************

\begin{code}
mkClosureInfo :: Bool		-- Is static
	      -> Id
	      -> LambdaFormInfo 
	      -> Int -> Int	-- Total and pointer words
	      -> C_SRT
	      -> String		-- String descriptor
	      -> ClosureInfo
mkClosureInfo is_static id lf_info tot_wds ptr_wds srt_info descr
  = ClosureInfo { closureName = name, 
		  closureLFInfo = lf_info,
		  closureSMRep = sm_rep, 
		  closureSRT = srt_info,
		  closureType = idType id,
		  closureDescr = descr }
  where
    name   = idName id
    sm_rep = chooseSMRep is_static lf_info tot_wds ptr_wds

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mkConInfo :: PackageId
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	  -> Bool	-- Is static
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	  -> DataCon	
	  -> Int -> Int	-- Total and pointer words
	  -> ClosureInfo
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mkConInfo this_pkg is_static data_con tot_wds ptr_wds
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   = ConInfo {	closureSMRep = sm_rep,
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		closureCon = data_con,
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		closureDllCon = isDllName this_pkg (dataConName data_con) }
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  where
    sm_rep = chooseSMRep is_static (mkConLFInfo data_con) tot_wds ptr_wds
\end{code}

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%************************************************************************
%*									*
\subsection[ClosureInfo-sizes]{Functions about closure {\em sizes}}
%*									*
%************************************************************************

\begin{code}
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closureSize :: ClosureInfo -> WordOff
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closureSize cl_info = hdr_size + closureNonHdrSize cl_info
  where hdr_size  | closureIsThunk cl_info = thunkHdrSize
  		  | otherwise      	   = fixedHdrSize
	-- All thunks use thunkHdrSize, even if they are non-updatable.
	-- this is because we don't have separate closure types for
	-- updatable vs. non-updatable thunks, so the GC can't tell the
	-- difference.  If we ever have significant numbers of non-
	-- updatable thunks, it might be worth fixing this.
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closureNonHdrSize :: ClosureInfo -> WordOff
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closureNonHdrSize cl_info
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  = tot_wds + computeSlopSize tot_wds cl_info
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  where
    tot_wds = closureGoodStuffSize cl_info

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closureGoodStuffSize :: ClosureInfo -> WordOff
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closureGoodStuffSize cl_info
  = let (ptrs, nonptrs) = sizes_from_SMRep (closureSMRep cl_info)
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    in	ptrs + nonptrs

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closurePtrsSize :: ClosureInfo -> WordOff
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closurePtrsSize cl_info
  = let (ptrs, _) = sizes_from_SMRep (closureSMRep cl_info)
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    in	ptrs

-- not exported:
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sizes_from_SMRep :: SMRep -> (WordOff,WordOff)
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sizes_from_SMRep (GenericRep _ ptrs nonptrs _)   = (ptrs, nonptrs)
sizes_from_SMRep BlackHoleRep			 = (0, 0)
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\end{code}

Computing slop size.  WARNING: this looks dodgy --- it has deep
knowledge of what the storage manager does with the various
representations...

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Slop Requirements: every thunk gets an extra padding word in the
header, which takes the the updated value.
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\begin{code}
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slopSize cl_info = computeSlopSize payload_size cl_info
  where payload_size = closureGoodStuffSize cl_info
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computeSlopSize :: WordOff -> ClosureInfo -> WordOff
computeSlopSize payload_size cl_info
  = max 0 (minPayloadSize smrep updatable - payload_size)
  where
	smrep        = closureSMRep cl_info
	updatable    = closureNeedsUpdSpace cl_info
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-- we leave space for an update if either (a) the closure is updatable
-- or (b) it is a static thunk.  This is because a static thunk needs
-- a static link field in a predictable place (after the slop), regardless
-- of whether it is updatable or not.
closureNeedsUpdSpace (ClosureInfo { closureLFInfo = 
					LFThunk TopLevel _ _ _ _ }) = True
closureNeedsUpdSpace cl_info = closureUpdReqd cl_info
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minPayloadSize :: SMRep -> Bool -> WordOff
minPayloadSize smrep updatable
  = case smrep of
	BlackHoleRep		 		-> min_upd_size
	GenericRep _ _ _ _      | updatable     -> min_upd_size
	GenericRep True _ _ _                   -> 0 -- static
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	GenericRep False _ _ _                  -> mIN_PAYLOAD_SIZE
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          --       ^^^^^___ dynamic
  where
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   min_upd_size =
	ASSERT(mIN_PAYLOAD_SIZE <= sIZEOF_StgSMPThunkHeader)
	0 	-- check that we already have enough
		-- room for mIN_SIZE_NonUpdHeapObject,
		-- due to the extra header word in SMP
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\end{code}

%************************************************************************
%*									*
\subsection[SMreps]{Choosing SM reps}
%*									*
%************************************************************************

\begin{code}
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chooseSMRep
	:: Bool			-- True <=> static closure
	-> LambdaFormInfo
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	-> WordOff -> WordOff	-- Tot wds, ptr wds
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	-> SMRep

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chooseSMRep is_static lf_info tot_wds ptr_wds
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  = let
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	 nonptr_wds   = tot_wds - ptr_wds
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	 closure_type = getClosureType is_static ptr_wds lf_info
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    in
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    GenericRep is_static ptr_wds nonptr_wds closure_type	
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-- We *do* get non-updatable top-level thunks sometimes.  eg. f = g
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-- 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.
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getClosureType :: Bool -> WordOff -> LambdaFormInfo -> ClosureType
getClosureType is_static ptr_wds lf_info
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  = case lf_info of
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	LFCon con | is_static && ptr_wds == 0	-> ConstrNoCaf
		  | otherwise			-> Constr
  	LFReEntrant _ _ _ _ 			-> Fun
	LFThunk _ _ _ (SelectorThunk _) _ 	-> ThunkSelector
	LFThunk _ _ _ _ _ 			-> Thunk
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	_ -> panic "getClosureType"
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\end{code}

%************************************************************************
%*									*
\subsection[ClosureInfo-4-questions]{Four major questions about @ClosureInfo@}
%*									*
%************************************************************************

Be sure to see the stg-details notes about these...

\begin{code}
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nodeMustPointToIt :: LambdaFormInfo -> Bool
nodeMustPointToIt (LFReEntrant top _ no_fvs _)
  = not no_fvs ||   -- Certainly if it has fvs we need to point to it
    isNotTopLevel top
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		    -- If it is not top level we will point to it
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		    --   We can have a \r closure with no_fvs which
		    --   is not top level as special case cgRhsClosure
		    --   has been dissabled in favour of let floating

		-- For lex_profiling we also access the cost centre for a
		-- non-inherited function i.e. not top level
		-- the  not top  case above ensures this is ok.

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nodeMustPointToIt (LFCon _) = True
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	-- 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.

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nodeMustPointToIt (LFThunk _ no_fvs updatable NonStandardThunk _)
  = updatable || not no_fvs || opt_SccProfilingOn
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	  -- 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)

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nodeMustPointToIt (LFThunk _ no_fvs updatable some_standard_form_thunk _)
  = True  -- Node must point to any standard-form thunk
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nodeMustPointToIt (LFUnknown _)     = True
nodeMustPointToIt (LFBlackHole _)   = True    -- BH entry may require Node to point
nodeMustPointToIt (LFLetNoEscape _) = False 
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\end{code}

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.

\begin{tabular}{lllll}
Closure Characteristics & Parallel & Node Req'd & Argument Passing & Enter Via \\
Unknown 			& no & yes & stack	& node \\
Known fun ($\ge$ 1 arg), no fvs 	& no & no  & registers 	& fast entry (enough args) \\
\ & \ & \ & \ 						& slow entry (otherwise) \\
Known fun ($\ge$ 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@ 		& no & yes & n/a 	& direct entry \\
0 arg, fvs @\u@ 		& no & yes & n/a 	& node \\

Unknown 			& yes & yes & stack	& node \\
Known fun ($\ge$ 1 arg), no fvs 	& yes & no  & registers & fast entry (enough args) \\
\ & \ & \ & \ 						& slow entry (otherwise) \\
Known fun ($\ge$ 1 arg), fvs	& yes & yes & registers & 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\\
\end{tabular}

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When black-holing, single-entry closures could also be entered via node
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(rather than directly) to catch double-entry.

\begin{code}
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data CallMethod
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  = EnterIt				-- no args, not a function
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  | JumpToIt CLabel			-- no args, not a function, but we
					-- know what its entry code is

  | ReturnIt				-- it's a function, but we have
					-- zero args to apply to it, so just
					-- return it.

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  | ReturnCon DataCon			-- It's a data constructor, just return it

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  | SlowCall				-- Unknown fun, or known fun with
					-- too few args.
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  | DirectEntry 			-- Jump directly, with args in regs
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	CLabel 				--   The code label
	Int 				--   Its arity
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getCallMethod :: PackageId
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	      -> Name		-- Function being applied
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	      -> LambdaFormInfo	-- Its info
	      -> Int		-- Number of available arguments
	      -> CallMethod

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getCallMethod this_pkg name lf_info n_args
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  | nodeMustPointToIt lf_info && opt_Parallel
  =	-- If we're parallel, then we must always enter via node.  
	-- The reason is that the closure may have been 	
	-- fetched since we allocated it.
    EnterIt

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getCallMethod this_pkg name (LFReEntrant _ arity _ _) n_args
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  | n_args == 0    = ASSERT( arity /= 0 )
		     ReturnIt	-- No args at all
  | n_args < arity = SlowCall	-- Not enough args
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  | otherwise      = DirectEntry (enterIdLabel this_pkg name) arity
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getCallMethod this_pkg name (LFCon con) n_args
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  = ASSERT( n_args == 0 )
    ReturnCon con

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getCallMethod this_pkg name (LFThunk _ _ updatable std_form_info is_fun) n_args
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  | is_fun 	-- *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
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		-- is the fast-entry code]

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  -- Since is_fun is False, we are *definitely* looking at a data value
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  | updatable || opt_DoTickyProfiling  -- to catch double entry
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      {- 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
	-}
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  = ASSERT2( n_args == 0, ppr name ) EnterIt
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  | otherwise	-- Jump direct to code for single-entry thunks
  = ASSERT( n_args == 0 )
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    JumpToIt (thunkEntryLabel this_pkg name std_form_info updatable)
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getCallMethod this_pkg name (LFUnknown True) n_args
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  = SlowCall -- might be a function

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getCallMethod this_pkg name (LFUnknown False) n_args
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  = ASSERT2 ( n_args == 0, ppr name <+> ppr n_args ) 
    EnterIt -- Not a function
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getCallMethod this_pkg name (LFBlackHole _) n_args
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  = SlowCall	-- Presumably the black hole has by now
		-- been updated, but we don't know with
		-- what, so we slow call it

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getCallMethod this_pkg name (LFLetNoEscape 0) n_args
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  = JumpToIt (enterReturnPtLabel (nameUnique name))

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getCallMethod this_pkg name (LFLetNoEscape arity) n_args
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  | n_args == arity = DirectEntry (enterReturnPtLabel (nameUnique name)) arity
  | otherwise = pprPanic "let-no-escape: " (ppr name <+> ppr arity)

blackHoleOnEntry :: ClosureInfo -> Bool
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-- Static closures are never themselves black-holed.
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-- Updatable ones will be overwritten with a CAFList cell, which points to a 
-- black hole;
-- Single-entry ones have no fvs to plug, and we trust they don't form part 
-- of a loop.
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blackHoleOnEntry ConInfo{} = False
blackHoleOnEntry (ClosureInfo { closureLFInfo = lf_info, closureSMRep = rep })
  | isStaticRep rep
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  = False	-- Never black-hole a static closure
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  | otherwise
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  = case lf_info of
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	LFReEntrant _ _ _ _	  -> False
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	LFLetNoEscape _		  -> False
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	LFThunk _ no_fvs updatable _ _
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	  -> if updatable
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	     then not opt_OmitBlackHoling
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	     else opt_DoTickyProfiling || not no_fvs
                  -- the former to catch double entry,
                  -- and the latter to plug space-leaks.  KSW/SDM 1999-04.

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	other -> panic "blackHoleOnEntry"	-- Should never happen
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isStandardFormThunk :: LambdaFormInfo -> Bool
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isStandardFormThunk (LFThunk _ _ _ (SelectorThunk _) _) = True
isStandardFormThunk (LFThunk _ _ _ (ApThunk _) _)	= True
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isStandardFormThunk other_lf_info 			= False
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isKnownFun :: LambdaFormInfo -> Bool
isKnownFun (LFReEntrant _ _ _ _) = True
isKnownFun (LFLetNoEscape _) = True
isKnownFun _ = False
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\end{code}

-----------------------------------------------------------------------------
SRT-related stuff
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\begin{code}
staticClosureNeedsLink :: ClosureInfo -> Bool
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-- 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
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--	b) it's a constructor with one or more pointer fields
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-- In case (b), the constructor's fields themselves play the role
-- of the SRT.
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staticClosureNeedsLink (ClosureInfo { closureSRT = srt })
  = needsSRT srt
staticClosureNeedsLink (ConInfo { closureSMRep = sm_rep, closureCon = con })
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  = not (isNullaryRepDataCon con) && not_nocaf_constr
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  where
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    not_nocaf_constr = 
	case sm_rep of 
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	   GenericRep _ _ _ ConstrNoCaf -> False
	   _other			-> True
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\end{code}

Avoiding generating entries and info tables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
At present, for every function we generate all of the following,
just in case.  But they aren't always all needed, as noted below:

[NB1: all of this applies only to *functions*.  Thunks always
have closure, info table, and entry code.]

[NB2: All are needed if the function is *exported*, just to play safe.]


* Fast-entry code  ALWAYS NEEDED

* Slow-entry code
	Needed iff (a) we have any un-saturated calls to the function
	OR	   (b) the function is passed as an arg
	OR	   (c) we're in the parallel world and the function has free vars
			[Reason: in parallel world, we always enter functions
			with free vars via the closure.]

* The function closure
	Needed iff (a) we have any un-saturated calls to the function
	OR	   (b) the function is passed as an arg
	OR	   (c) if the function has free vars (ie not top level)

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  Why case (a) here?  Because if the arg-satis check fails,
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  UpdatePAP stuffs a pointer to the function closure in the PAP.
  [Could be changed; UpdatePAP could stuff in a code ptr instead,
   but doesn't seem worth it.]

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  [NB: these conditions imply that we might need the closure
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  without the slow-entry code.  Here's how.

	f x y = let g w = ...x..y..w...
		in
		...(g t)...

  Here we need a closure for g which contains x and y,
  but since the calls are all saturated we just jump to the
  fast entry point for g, with R1 pointing to the closure for g.]


* Standard info table
	Needed iff (a) we have any un-saturated calls to the function
	OR	   (b) the function is passed as an arg
	OR 	   (c) the function has free vars (ie not top level)
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	NB.  In the sequential world, (c) is only required so that the function closure has
	an info table to point to, to keep the storage manager happy.
	If (c) alone is true we could fake up an info table by choosing
	one of a standard family of info tables, whose entry code just
	bombs out.

	[NB In the parallel world (c) is needed regardless because
	we enter functions with free vars via the closure.]

	If (c) is retained, then we'll sometimes generate an info table
	(for storage mgr purposes) without slow-entry code.  Then we need
	to use an error label in the info table to substitute for the absent
	slow entry code.

\begin{code}
staticClosureRequired
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	:: Name
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	-> StgBinderInfo
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	-> LambdaFormInfo
	-> Bool
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staticClosureRequired binder bndr_info
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		      (LFReEntrant top_level _ _ _)	-- It's a function
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  = ASSERT( isTopLevel top_level )
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	-- Assumption: it's a top-level, no-free-var binding
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	not (satCallsOnly bndr_info)
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staticClosureRequired binder other_binder_info other_lf_info = True
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\end{code}

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%************************************************************************
%*									*
\subsection[ClosureInfo-misc-funs]{Misc functions about @ClosureInfo@, etc.}
%*									*
%************************************************************************

\begin{code}

isStaticClosure :: ClosureInfo -> Bool
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isStaticClosure cl_info = isStaticRep (closureSMRep cl_info)
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closureUpdReqd :: ClosureInfo -> Bool
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closureUpdReqd ClosureInfo{ closureLFInfo = lf_info } = lfUpdatable lf_info
closureUpdReqd ConInfo{} = False

lfUpdatable :: LambdaFormInfo -> Bool
lfUpdatable (LFThunk _ _ upd _ _)  = upd
lfUpdatable (LFBlackHole _)	   = True
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	-- Black-hole closures are allocated to receive the results of an
	-- alg case with a named default... so they need to be updated.
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lfUpdatable _ = False

closureIsThunk :: ClosureInfo -> Bool
closureIsThunk ClosureInfo{ closureLFInfo = lf_info } = isLFThunk lf_info
closureIsThunk ConInfo{} = False
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closureSingleEntry :: ClosureInfo -> Bool
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closureSingleEntry (ClosureInfo { closureLFInfo = LFThunk _ _ upd _ _}) = not upd
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closureSingleEntry other_closure = False
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closureReEntrant :: ClosureInfo -> Bool
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closureReEntrant (ClosureInfo { closureLFInfo = LFReEntrant _ _ _ _ }) = True
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closureReEntrant other_closure = False
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isConstrClosure_maybe :: ClosureInfo -> Maybe DataCon
isConstrClosure_maybe (ConInfo { closureCon = data_con }) = Just data_con
isConstrClosure_maybe _ 				  = Nothing
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closureFunInfo :: ClosureInfo -> Maybe (Int, ArgDescr)
closureFunInfo (ClosureInfo { closureLFInfo = LFReEntrant _ arity _ arg_desc})
  = Just (arity, arg_desc)
closureFunInfo _
  = Nothing
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\end{code}

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\begin{code}
isToplevClosure :: ClosureInfo -> Bool
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isToplevClosure (ClosureInfo { closureLFInfo = lf_info })
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  = case lf_info of
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      LFReEntrant TopLevel _ _ _ -> True
      LFThunk TopLevel _ _ _ _   -> True
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      other -> False
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isToplevClosure _ = False
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\end{code}

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Label generation.

\begin{code}
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infoTableLabelFromCI :: ClosureInfo -> CLabel
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infoTableLabelFromCI (ClosureInfo { closureName = name,
				    closureLFInfo = lf_info, 
				    closureSMRep = rep })
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  = case lf_info of
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	LFBlackHole info -> info
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	LFThunk _ _ upd_flag (SelectorThunk offset) _ -> 
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	LFThunk _ _ upd_flag (ApThunk arity) _ -> 
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	LFThunk{}      -> mkLocalInfoTableLabel name
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	LFReEntrant _ _ _ _ -> mkLocalInfoTableLabel name
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	other -> panic "infoTableLabelFromCI"

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infoTableLabelFromCI (ConInfo { closureCon = con, 
				closureSMRep = rep,
				closureDllCon = dll })
  | isStaticRep rep = mkStaticInfoTableLabel  name dll
  | otherwise	    = mkConInfoTableLabel     name dll
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  where
    name = dataConName con
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-- ClosureInfo for a closure (as opposed to a constructor) is always local
closureLabelFromCI (ClosureInfo { closureName = nm }) = mkLocalClosureLabel nm
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closureLabelFromCI _ = panic "closureLabelFromCI"
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-- thunkEntryLabel is a local help function, not exported.  It's used from both
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-- entryLabelFromCI and getCallMethod.
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thunkEntryLabel this_pkg thunk_id (ApThunk arity) is_updatable
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  = enterApLabel is_updatable arity
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thunkEntryLabel this_pkg thunk_id (SelectorThunk offset) upd_flag
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  = enterSelectorLabel upd_flag offset
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thunkEntryLabel this_pkg thunk_id _ is_updatable
  = enterIdLabel this_pkg thunk_id
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enterApLabel is_updatable arity
  | tablesNextToCode = mkApInfoTableLabel is_updatable arity
  | otherwise        = mkApEntryLabel is_updatable arity

enterSelectorLabel upd_flag offset
  | tablesNextToCode = mkSelectorInfoLabel upd_flag offset
  | otherwise        = mkSelectorEntryLabel upd_flag offset

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enterIdLabel this_pkg id
  | tablesNextToCode = mkInfoTableLabel this_pkg id
  | otherwise        = mkEntryLabel this_pkg id
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enterLocalIdLabel id
  | tablesNextToCode = mkLocalInfoTableLabel id
  | otherwise        = mkLocalEntryLabel id
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enterReturnPtLabel name
  | tablesNextToCode = mkReturnInfoLabel name
  | otherwise        = mkReturnPtLabel name
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\end{code}

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We need a black-hole closure info to pass to @allocDynClosure@ when we
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want to allocate the black hole on entry to a CAF.  These are the only
ways to build an LFBlackHole, maintaining the invariant that it really
is a black hole and not something else.
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\begin{code}
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cafBlackHoleClosureInfo (ClosureInfo { closureName = nm,
				       closureType = ty })
  = ClosureInfo { closureName   = nm,
		  closureLFInfo = LFBlackHole mkCAFBlackHoleInfoTableLabel,
		  closureSMRep  = BlackHoleRep,
		  closureSRT    = NoC_SRT,
		  closureType   = ty,
		  closureDescr  = "" }
cafBlackHoleClosureInfo _ = panic "cafBlackHoleClosureInfo"

seCafBlackHoleClosureInfo (ClosureInfo { closureName = nm,
				         closureType = ty })
  = ClosureInfo { closureName   = nm,
		  closureLFInfo = LFBlackHole mkSECAFBlackHoleInfoTableLabel,
		  closureSMRep  = BlackHoleRep,
		  closureSRT    = NoC_SRT,
		  closureType   = ty,
		  closureDescr  = ""  }
seCafBlackHoleClosureInfo _ = panic "seCafBlackHoleClosureInfo"
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\end{code}

%************************************************************************
%*									*
\subsection[ClosureInfo-Profiling-funs]{Misc functions about for profiling info.}
%*									*
%************************************************************************

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Profiling requires two pieces of information to be determined for
each closure's info table --- description and type.
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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@.

\begin{code}
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closureValDescr, closureTypeDescr :: ClosureInfo -> String
closureValDescr (ClosureInfo {closureDescr = descr}) 
  = descr
closureValDescr (ConInfo {closureCon = con})
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  = occNameString (getOccName con)
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closureTypeDescr (ClosureInfo { closureType = ty })
  = getTyDescription ty
closureTypeDescr (ConInfo { closureCon = data_con })
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  = occNameString (getOccName (dataConTyCon data_con))
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getTyDescription :: Type -> String
getTyDescription ty
  = case (tcSplitSigmaTy ty) of { (_, _, tau_ty) ->
    case tau_ty of
      TyVarTy _	       	     -> "*"
      AppTy fun _      	     -> getTyDescription fun
      FunTy _ res      	     -> '-' : '>' : fun_result res
      TyConApp tycon _ 	     -> getOccString tycon
      NoteTy (FTVNote _) ty  -> getTyDescription ty
      PredTy sty	     -> getPredTyDescription sty
      ForAllTy _ ty          -> getTyDescription ty
    }
  where
    fun_result (FunTy _ res) = '>' : fun_result res
    fun_result other	     = getTyDescription other

getPredTyDescription (ClassP cl tys) = getOccString cl
getPredTyDescription (IParam ip ty)  = getOccString (ipNameName ip)
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\end{code}