% % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[StgSyn]{Shared term graph (STG) syntax for spineless-tagless code generation} This data type represents programs just before code generation (conversion to @AbstractC@): basically, what we have is a stylised form of @CoreSyntax@, the style being one that happens to be ideally suited to spineless tagless code generation. \begin{code}

    module StgSyn (
    	GenStgArg(..),
    	GenStgLiveVars,

    	GenStgBinding(..), GenStgExpr(..), GenStgRhs(..),
    	GenStgAlt, AltType(..),

    	UpdateFlag(..), isUpdatable,

    	StgBinderInfo,
    	noBinderInfo, stgSatOcc, stgUnsatOcc, satCallsOnly,
    	combineStgBinderInfo,

    	-- a set of synonyms for the most common (only :-) parameterisation
    	StgArg, StgLiveVars,
    	StgBinding, StgExpr, StgRhs, StgAlt,

    	-- StgOp
    	StgOp(..),

    	-- SRTs
    	SRT(..),

    	-- utils
    	stgBindHasCafRefs, stgArgHasCafRefs, stgRhsArity,
    	isDllConApp, isStgTypeArg,
    	stgArgType,

    	pprStgBinding, pprStgBindings, pprStgBindingsWithSRTs

    #ifdef DEBUG
    	, pprStgLVs
    #endif
        ) where

    #include "HsVersions.h"

    import CostCentre	( CostCentreStack, CostCentre )
    import VarSet		( IdSet, isEmptyVarSet )
    import Id
    import DataCon
    import IdInfo		( mayHaveCafRefs )
    import Literal		( Literal, literalType )
    import ForeignCall	( ForeignCall )
    import CoreSyn		( AltCon )
    import PprCore		( {- instances -} )
    import PrimOp		( PrimOp, PrimCall )
    import Outputable
    import Type             ( Type )
    import TyCon            ( TyCon )
    import UniqSet
    import Unique		( Unique )
    import Bitmap
    import StaticFlags	( opt_SccProfilingOn )
    import Module
    import FastString

    #if mingw32_TARGET_OS
    import Packages		( isDllName )

    #endif

\end{code} %************************************************************************ %* * \subsection{@GenStgBinding@} %* * %************************************************************************ As usual, expressions are interesting; other things are boring. Here are the boring things [except note the @GenStgRhs@], parameterised with respect to binder and occurrence information (just as in @CoreSyn@): There is one SRT for each group of bindings. \begin{code}

    data GenStgBinding bndr occ
      = StgNonRec	bndr (GenStgRhs bndr occ)
      | StgRec	[(bndr, GenStgRhs bndr occ)]

\end{code} %************************************************************************ %* * \subsection{@GenStgArg@} %* * %************************************************************************ \begin{code}

    data GenStgArg occ
      = StgVarArg	occ
      | StgLitArg   Literal
      | StgTypeArg  Type		-- For when we want to preserve all type info

\end{code} \begin{code}

    isStgTypeArg :: StgArg -> Bool
    isStgTypeArg (StgTypeArg _) = True
    isStgTypeArg _              = False

    isDllConApp :: PackageId -> DataCon -> [StgArg] -> Bool
    -- Does this constructor application refer to
    -- anything in a different *Windows* DLL?
    -- If so, we can't allocate it statically
    #if mingw32_TARGET_OS
    isDllConApp this_pkg con args
      = isDllName this_pkg (dataConName con) || any is_dll_arg args
      where
        is_dll_arg ::StgArg -> Bool
        is_dll_arg (StgVarArg v) = isDllName this_pkg (idName v)
        is_dll_arg _             = False
    #else
    isDllConApp _ _ _ = False
    #endif

    stgArgType :: StgArg -> Type
    	-- Very half baked becase we have lost the type arguments
    stgArgType (StgVarArg v)   = idType v
    stgArgType (StgLitArg lit) = literalType lit
    stgArgType (StgTypeArg _)  = panic "stgArgType called on stgTypeArg"

\end{code} %************************************************************************ %* * \subsection{STG expressions} %* * %************************************************************************ The @GenStgExpr@ data type is parameterised on binder and occurrence info, as before. %************************************************************************ %* * \subsubsection{@GenStgExpr@ application} %* * %************************************************************************ An application is of a function to a list of atoms [not expressions]. Operationally, we want to push the arguments on the stack and call the function. (If the arguments were expressions, we would have to build their closures first.) There is no constructor for a lone variable; it would appear as @StgApp var [] _@. \begin{code}

    type GenStgLiveVars occ = UniqSet occ

    data GenStgExpr bndr occ
      = StgApp
    	occ		-- function
    	[GenStgArg occ]	-- arguments; may be empty

\end{code} %************************************************************************ %* * \subsubsection{@StgConApp@ and @StgPrimApp@---saturated applications} %* * %************************************************************************ There are a specialised forms of application, for constructors, primitives, and literals. \begin{code}

      | StgLit	Literal

    	-- StgConApp is vital for returning unboxed tuples
    	-- which can't be let-bound first
      | StgConApp	DataCon
    		[GenStgArg occ]	-- Saturated

      | StgOpApp	StgOp		-- Primitive op or foreign call
    		[GenStgArg occ]	-- Saturated
    		Type		-- Result type
    				-- We need to know this so that we can
    				-- assign result registers

\end{code} %************************************************************************ %* * \subsubsection{@StgLam@} %* * %************************************************************************ StgLam is used *only* during CoreToStg's work. Before CoreToStg has finished it encodes (\x -> e) as (let f = \x -> e in f) \begin{code}

      | StgLam
    	Type		-- Type of whole lambda (useful when making a binder for it)
    	[bndr]
    	StgExpr		-- Body of lambda

\end{code} %************************************************************************ %* * \subsubsection{@GenStgExpr@: case-expressions} %* * %************************************************************************ This has the same boxed/unboxed business as Core case expressions. \begin{code}

      | StgCase
    	(GenStgExpr bndr occ)
    			-- the thing to examine

    	(GenStgLiveVars occ) -- Live vars of whole case expression,
    			-- plus everything that happens after the case
    			-- i.e., those which mustn't be overwritten

    	(GenStgLiveVars occ) -- Live vars of RHSs (plus what happens afterwards)
    			-- i.e., those which must be saved before eval.
    			--
    			-- note that an alt's constructor's
    			-- binder-variables are NOT counted in the
    			-- free vars for the alt's RHS

    	bndr		-- binds the result of evaluating the scrutinee

    	SRT		-- The SRT for the continuation

    	AltType

    	[GenStgAlt bndr occ]	-- The DEFAULT case is always *first*
    				-- if it is there at all

\end{code} %************************************************************************ %* * \subsubsection{@GenStgExpr@: @let(rec)@-expressions} %* * %************************************************************************ The various forms of let(rec)-expression encode most of the interesting things we want to do. \begin{enumerate} \item \begin{verbatim} let-closure x = [free-vars] expr [args] in e \end{verbatim} is equivalent to \begin{verbatim} let x = (\free-vars -> \args -> expr) free-vars \end{verbatim} \tr{args} may be empty (and is for most closures). It isn't under circumstances like this: \begin{verbatim} let x = (\y -> y+z) \end{verbatim} This gets mangled to \begin{verbatim} let-closure x = [z] [y] (y+z) \end{verbatim} The idea is that we compile code for @(y+z)@ in an environment in which @z@ is bound to an offset from \tr{Node}, and @y@ is bound to an offset from the stack pointer. (A let-closure is an @StgLet@ with a @StgRhsClosure@ RHS.) \item \begin{verbatim} let-constructor x = Constructor [args] in e \end{verbatim} (A let-constructor is an @StgLet@ with a @StgRhsCon@ RHS.) \item Letrec-expressions are essentially the same deal as let-closure/let-constructor, so we use a common structure and distinguish between them with an @is_recursive@ boolean flag. \item \begin{verbatim} let-unboxed u = an arbitrary arithmetic expression in unboxed values in e \end{verbatim} All the stuff on the RHS must be fully evaluated. No function calls either! (We've backed away from this toward case-expressions with suitably-magical alts ...) \item ~[Advanced stuff here! Not to start with, but makes pattern matching generate more efficient code.] \begin{verbatim} let-escapes-not fail = expr in e' \end{verbatim} Here the idea is that @e'@ guarantees not to put @fail@ in a data structure, or pass it to another function. All @e'@ will ever do is tail-call @fail@. Rather than build a closure for @fail@, all we need do is to record the stack level at the moment of the @let-escapes-not@; then entering @fail@ is just a matter of adjusting the stack pointer back down to that point and entering the code for it. Another example: \begin{verbatim} f x y = let z = huge-expression in if y==1 then z else if y==2 then z else 1 \end{verbatim} (A let-escapes-not is an @StgLetNoEscape@.) \item We may eventually want: \begin{verbatim} let-literal x = Literal in e \end{verbatim} (ToDo: is this obsolete?) \end{enumerate} And so the code for let(rec)-things: \begin{code}

      | StgLet
    	(GenStgBinding bndr occ)	-- right hand sides (see below)
    	(GenStgExpr bndr occ)		-- body

      | StgLetNoEscape			-- remember: ``advanced stuff''
    	(GenStgLiveVars occ)		-- Live in the whole let-expression
    					-- Mustn't overwrite these stack slots
        	    	    	    	    	--  *Doesn't* include binders of the let(rec).

    	(GenStgLiveVars occ)		-- Live in the right hand sides (only)
    					-- These are the ones which must be saved on
    					-- the stack if they aren't there already
        	    	    	    	    	--  *Does* include binders of the let(rec) if recursive.

    	(GenStgBinding bndr occ)	-- right hand sides (see below)
    	(GenStgExpr bndr occ)		-- body

\end{code} %************************************************************************ %* * \subsubsection{@GenStgExpr@: @scc@ expressions} %* * %************************************************************************ Finally for @scc@ expressions we introduce a new STG construct. \begin{code}

      | StgSCC
    	CostCentre		-- label of SCC expression
    	(GenStgExpr bndr occ)	-- scc expression

\end{code} %************************************************************************ %* * \subsubsection{@GenStgExpr@: @hpc@ expressions} %* * %************************************************************************ Finally for @scc@ expressions we introduce a new STG construct. \begin{code}

      | StgTick
        Module			-- the module of the source of this tick
        Int				-- tick number
        (GenStgExpr bndr occ)	-- sub expression
      -- end of GenStgExpr

\end{code} %************************************************************************ %* * \subsection{STG right-hand sides} %* * %************************************************************************ Here's the rest of the interesting stuff for @StgLet@s; the first flavour is for closures: \begin{code}

    data GenStgRhs bndr occ
      = StgRhsClosure
    	CostCentreStack		-- CCS to be attached (default is CurrentCCS)
    	StgBinderInfo		-- Info about how this binder is used (see below)
    	[occ]			-- non-global free vars; a list, rather than
    				-- a set, because order is important
    	!UpdateFlag		-- ReEntrant | Updatable | SingleEntry
    	SRT 			-- The SRT reference
    	[bndr]			-- arguments; if empty, then not a function;
    				-- as above, order is important.
    	(GenStgExpr bndr occ)	-- body

\end{code} An example may be in order. Consider: \begin{verbatim} let t = \x -> \y -> ... x ... y ... p ... q in e \end{verbatim} Pulling out the free vars and stylising somewhat, we get the equivalent: \begin{verbatim} let t = (\[p,q] -> \[x,y] -> ... x ... y ... p ...q) p q \end{verbatim} Stg-operationally, the @[x,y]@ are on the stack, the @[p,q]@ are offsets from @Node@ into the closure, and the code ptr for the closure will be exactly that in parentheses above. The second flavour of right-hand-side is for constructors (simple but important): \begin{code}

      | StgRhsCon
    	CostCentreStack		-- CCS to be attached (default is CurrentCCS).
    				-- Top-level (static) ones will end up with
    				-- DontCareCCS, because we don't count static
    				-- data in heap profiles, and we don't set CCCS
    				-- from static closure.
    	DataCon			-- constructor
    	[GenStgArg occ]	-- args

\end{code} \begin{code}

    stgRhsArity :: StgRhs -> Int
    stgRhsArity (StgRhsClosure _ _ _ _ _ bndrs _)
      = ASSERT( all isId bndrs ) length bndrs
      -- The arity never includes type parameters, but they should have gone by now
    stgRhsArity (StgRhsCon _ _ _) = 0

\end{code} \begin{code}

    stgBindHasCafRefs :: GenStgBinding bndr Id -> Bool
    stgBindHasCafRefs (StgNonRec _ rhs) = rhsHasCafRefs rhs
    stgBindHasCafRefs (StgRec binds)    = any rhsHasCafRefs (map snd binds)

    rhsHasCafRefs :: GenStgRhs bndr Id -> Bool
    rhsHasCafRefs (StgRhsClosure _ _ _ upd srt _ _)
      = isUpdatable upd || nonEmptySRT srt
    rhsHasCafRefs (StgRhsCon _ _ args)
      = any stgArgHasCafRefs args

    stgArgHasCafRefs :: GenStgArg Id -> Bool
    stgArgHasCafRefs (StgVarArg id) = mayHaveCafRefs (idCafInfo id)
    stgArgHasCafRefs _ = False

\end{code} Here's the @StgBinderInfo@ type, and its combining op: \begin{code}

    data StgBinderInfo
      = NoStgBinderInfo
      | SatCallsOnly	-- All occurrences are *saturated* *function* calls
    			-- This means we don't need to build an info table and
    			-- slow entry code for the thing
    			-- Thunks never get this value

    noBinderInfo, stgUnsatOcc, stgSatOcc :: StgBinderInfo
    noBinderInfo = NoStgBinderInfo
    stgUnsatOcc  = NoStgBinderInfo
    stgSatOcc    = SatCallsOnly

    satCallsOnly :: StgBinderInfo -> Bool
    satCallsOnly SatCallsOnly    = True
    satCallsOnly NoStgBinderInfo = False

    combineStgBinderInfo :: StgBinderInfo -> StgBinderInfo -> StgBinderInfo
    combineStgBinderInfo SatCallsOnly SatCallsOnly = SatCallsOnly
    combineStgBinderInfo _            _            = NoStgBinderInfo

    --------------
    pp_binder_info :: StgBinderInfo -> SDoc
    pp_binder_info NoStgBinderInfo = empty
    pp_binder_info SatCallsOnly    = ptext (sLit "sat-only")

\end{code} %************************************************************************ %* * \subsection[Stg-case-alternatives]{STG case alternatives} %* * %************************************************************************ Very like in @CoreSyntax@ (except no type-world stuff). The type constructor is guaranteed not to be abstract; that is, we can see its representation. This is important because the code generator uses it to determine return conventions etc. But it's not trivial where there's a moduule loop involved, because some versions of a type constructor might not have all the constructors visible. So mkStgAlgAlts (in CoreToStg) ensures that it gets the TyCon from the constructors or literals (which are guaranteed to have the Real McCoy) rather than from the scrutinee type. \begin{code}

    type GenStgAlt bndr occ
      = (AltCon,		-- alts: data constructor,
         [bndr],		-- constructor's parameters,
         [Bool],		-- "use mask", same length as
    			-- parameters; a True in a
    			-- param's position if it is
    			-- used in the ...
         GenStgExpr bndr occ)	-- ...right-hand side.

    data AltType
      = PolyAlt		-- Polymorphic (a type variable)
      | UbxTupAlt TyCon	-- Unboxed tuple
      | AlgAlt    TyCon	-- Algebraic data type; the AltCons will be DataAlts
      | PrimAlt   TyCon	-- Primitive data type; the AltCons will be LitAlts

\end{code} %************************************************************************ %* * \subsection[Stg]{The Plain STG parameterisation} %* * %************************************************************************ This happens to be the only one we use at the moment. \begin{code}

    type StgBinding     = GenStgBinding	Id Id
    type StgArg         = GenStgArg		Id
    type StgLiveVars    = GenStgLiveVars	Id
    type StgExpr        = GenStgExpr	Id Id
    type StgRhs         = GenStgRhs		Id Id
    type StgAlt	    = GenStgAlt		Id Id

\end{code} %************************************************************************ %* * \subsubsection[UpdateFlag-datatype]{@UpdateFlag@} %* * %************************************************************************ This is also used in @LambdaFormInfo@ in the @ClosureInfo@ module. A @ReEntrant@ closure may be entered multiple times, but should not be updated or blackholed. An @Updatable@ closure should be updated after evaluation (and may be blackholed during evaluation). A @SingleEntry@ closure will only be entered once, and so need not be updated but may safely be blackholed. \begin{code}

    data UpdateFlag = ReEntrant | Updatable | SingleEntry

    instance Outputable UpdateFlag where
        ppr u
          = char (case u of { ReEntrant -> 'r';  Updatable -> 'u';  SingleEntry -> 's' })

    isUpdatable :: UpdateFlag -> Bool
    isUpdatable ReEntrant   = False
    isUpdatable SingleEntry = False
    isUpdatable Updatable   = True

\end{code} %************************************************************************ %* * \subsubsection{StgOp} %* * %************************************************************************ An StgOp allows us to group together PrimOps and ForeignCalls. It's quite useful to move these around together, notably in StgOpApp and COpStmt. \begin{code}

    data StgOp = StgPrimOp  PrimOp

               | StgPrimCallOp PrimCall

    	   | StgFCallOp ForeignCall Unique
    		-- The Unique is occasionally needed by the C pretty-printer
    		-- (which lacks a unique supply), notably when generating a
    		-- typedef for foreign-export-dynamic

\end{code} %************************************************************************ %* * \subsubsection[Static Reference Tables]{@SRT@} %* * %************************************************************************ There is one SRT per top-level function group. Each local binding and case expression within this binding group has a subrange of the whole SRT, expressed as an offset and length. In CoreToStg we collect the list of CafRefs at each SRT site, which is later converted into the length and offset form by the SRT pass. \begin{code}

    data SRT = NoSRT
    	 | SRTEntries IdSet
    		-- generated by CoreToStg
             | SRT !Int{-offset-} !Int{-length-} !Bitmap{-bitmap-}
    		-- generated by computeSRTs

    nonEmptySRT :: SRT -> Bool
    nonEmptySRT NoSRT           = False
    nonEmptySRT (SRTEntries vs) = not (isEmptyVarSet vs)
    nonEmptySRT _               = True

    pprSRT :: SRT -> SDoc
    pprSRT (NoSRT)          = ptext (sLit "_no_srt_")
    pprSRT (SRTEntries ids) = text "SRT:" <> ppr ids
    pprSRT (SRT off _ _)    = parens (ppr off <> comma <> text "*bitmap*")

\end{code} %************************************************************************ %* * \subsection[Stg-pretty-printing]{Pretty-printing} %* * %************************************************************************ Robin Popplestone asked for semi-colon separators on STG binds; here's hoping he likes terminators instead... Ditto for case alternatives. \begin{code}

    pprGenStgBinding :: (Outputable bndr, Outputable bdee, Ord bdee)
    		 => GenStgBinding bndr bdee -> SDoc

    pprGenStgBinding (StgNonRec bndr rhs)
      = hang (hsep [ppr bndr, equals])
        	4 ((<>) (ppr rhs) semi)

    pprGenStgBinding (StgRec pairs)
      = vcat ((ifPprDebug (ptext (sLit "{- StgRec (begin) -}"))) :
    	   (map (ppr_bind) pairs) ++ [(ifPprDebug (ptext (sLit "{- StgRec (end) -}")))])
      where
        ppr_bind (bndr, expr)
          = hang (hsep [ppr bndr, equals])
    	     4 ((<>) (ppr expr) semi)

    pprStgBinding  :: StgBinding -> SDoc
    pprStgBinding  bind  = pprGenStgBinding bind

    pprStgBindings :: [StgBinding] -> SDoc
    pprStgBindings binds = vcat (map pprGenStgBinding binds)

    pprGenStgBindingWithSRT
    	:: (Outputable bndr, Outputable bdee, Ord bdee)
    	=> (GenStgBinding bndr bdee,[(Id,[Id])]) -> SDoc

    pprGenStgBindingWithSRT (bind,srts)
      = vcat (pprGenStgBinding bind : map pprSRT srts)
      where pprSRT (id,srt) =
    	   ptext (sLit "SRT") <> parens (ppr id) <> ptext (sLit ": ") <> ppr srt

    pprStgBindingsWithSRTs :: [(StgBinding,[(Id,[Id])])] -> SDoc
    pprStgBindingsWithSRTs binds = vcat (map pprGenStgBindingWithSRT binds)

\end{code} \begin{code}

    instance (Outputable bdee) => Outputable (GenStgArg bdee) where
        ppr = pprStgArg

    instance (Outputable bndr, Outputable bdee, Ord bdee)
    		=> Outputable (GenStgBinding bndr bdee) where
        ppr = pprGenStgBinding

    instance (Outputable bndr, Outputable bdee, Ord bdee)
    		=> Outputable (GenStgExpr bndr bdee) where
        ppr = pprStgExpr

    instance (Outputable bndr, Outputable bdee, Ord bdee)
    		=> Outputable (GenStgRhs bndr bdee) where
        ppr rhs = pprStgRhs rhs

\end{code} \begin{code}

    pprStgArg :: (Outputable bdee) => GenStgArg bdee -> SDoc

    pprStgArg (StgVarArg var) = ppr var
    pprStgArg (StgLitArg con) = ppr con
    pprStgArg (StgTypeArg ty) = char '@' <+> ppr ty

\end{code} \begin{code}

    pprStgExpr :: (Outputable bndr, Outputable bdee, Ord bdee)
    	   => GenStgExpr bndr bdee -> SDoc
    -- special case
    pprStgExpr (StgLit lit)     = ppr lit

    -- general case
    pprStgExpr (StgApp func args)
      = hang (ppr func)
    	 4 (sep (map (ppr) args))

\end{code} \begin{code}

    pprStgExpr (StgConApp con args)
      = hsep [ ppr con, brackets (interppSP args)]

    pprStgExpr (StgOpApp op args _)
      = hsep [ pprStgOp op, brackets (interppSP args)]

    pprStgExpr (StgLam _ bndrs body)
      =sep [ char '\\' <+> ppr bndrs <+> ptext (sLit "->"),
    	 pprStgExpr body ]

\end{code} \begin{code}

    -- special case: let v = <very specific thing>
    --		 in
    --		 let ...
    --		 in
    --		 ...
    --
    -- Very special!  Suspicious! (SLPJ)

    {-
    pprStgExpr (StgLet srt (StgNonRec bndr (StgRhsClosure cc bi free_vars upd_flag args rhs))
    		    	expr@(StgLet _ _))
      = ($$)
          (hang (hcat [ptext (sLit "let { "), ppr bndr, ptext (sLit " = "),
    			  ppr cc,
    			  pp_binder_info bi,
    			  ptext (sLit " ["), ifPprDebug (interppSP free_vars), ptext (sLit "] \\"),
    			  ppr upd_flag, ptext (sLit " ["),
    			  interppSP args, char ']'])
    	    8 (sep [hsep [ppr rhs, ptext (sLit "} in")]]))
          (ppr expr)
    -}

    -- special case: let ... in let ...

    pprStgExpr (StgLet bind expr@(StgLet _ _))
      = ($$)
          (sep [hang (ptext (sLit "let {"))
    	 	2 (hsep [pprGenStgBinding bind, ptext (sLit "} in")])])
          (ppr expr)

    -- general case
    pprStgExpr (StgLet bind expr)
      = sep [hang (ptext (sLit "let {")) 2 (pprGenStgBinding bind),
    	   hang (ptext (sLit "} in ")) 2 (ppr expr)]

    pprStgExpr (StgLetNoEscape lvs_whole lvs_rhss bind expr)
      = sep [hang (ptext (sLit "let-no-escape {"))
    	    	2 (pprGenStgBinding bind),
    	   hang ((<>) (ptext (sLit "} in "))
    		   (ifPprDebug (
    		    nest 4 (
    		      hcat [ptext  (sLit "-- lvs: ["), interppSP (uniqSetToList lvs_whole),
    			     ptext (sLit "]; rhs lvs: ["), interppSP (uniqSetToList lvs_rhss),
    			     char ']']))))
    		2 (ppr expr)]

    pprStgExpr (StgSCC cc expr)
      = sep [ hsep [ptext (sLit "_scc_"), ppr cc],
    	  pprStgExpr expr ]

    pprStgExpr (StgTick m n expr)
      = sep [ hsep [ptext (sLit "_tick_"),  pprModule m,text (show n)],
    	  pprStgExpr expr ]

    pprStgExpr (StgCase expr lvs_whole lvs_rhss bndr srt alt_type alts)
      = sep [sep [ptext (sLit "case"),
    	   nest 4 (hsep [pprStgExpr expr,
    	     ifPprDebug (dcolon <+> ppr alt_type)]),
    	   ptext (sLit "of"), ppr bndr, char '{'],
    	   ifPprDebug (
    	   nest 4 (
    	     hcat [ptext  (sLit "-- lvs: ["), interppSP (uniqSetToList lvs_whole),
    		    ptext (sLit "]; rhs lvs: ["), interppSP (uniqSetToList lvs_rhss),
    		    ptext (sLit "]; "),
    		    pprMaybeSRT srt])),
    	   nest 2 (vcat (map pprStgAlt alts)),
    	   char '}']

    pprStgAlt :: (Outputable bndr, Outputable occ, Ord occ)
              => GenStgAlt bndr occ -> SDoc
    pprStgAlt (con, params, _use_mask, expr)
      = hang (hsep [ppr con, interppSP params, ptext (sLit "->")])
    	 4 (ppr expr <> semi)

    pprStgOp :: StgOp -> SDoc
    pprStgOp (StgPrimOp  op)   = ppr op
    pprStgOp (StgPrimCallOp op)= ppr op
    pprStgOp (StgFCallOp op _) = ppr op

    instance Outputable AltType where
      ppr PolyAlt 	     = ptext (sLit "Polymorphic")
      ppr (UbxTupAlt tc) = ptext (sLit "UbxTup") <+> ppr tc
      ppr (AlgAlt tc)    = ptext (sLit "Alg")    <+> ppr tc
      ppr (PrimAlt tc)   = ptext (sLit "Prim")   <+> ppr tc

\end{code} \begin{code}

    #ifdef DEBUG
    pprStgLVs :: Outputable occ => GenStgLiveVars occ -> SDoc
    pprStgLVs lvs
      = getPprStyle $ \ sty ->
        if userStyle sty || isEmptyUniqSet lvs then
    	empty
        else
    	hcat [text "{-lvs:", interpp'SP (uniqSetToList lvs), text "-}"]
    #endif

\end{code} \begin{code}

    pprStgRhs :: (Outputable bndr, Outputable bdee, Ord bdee)
    	  => GenStgRhs bndr bdee -> SDoc

    -- special case
    pprStgRhs (StgRhsClosure cc bi [free_var] upd_flag srt [{-no args-}] (StgApp func []))
      = hcat [ ppr cc,
    	   pp_binder_info bi,
    	   brackets (ifPprDebug (ppr free_var)),
    	   ptext (sLit " \\"), ppr upd_flag, pprMaybeSRT srt, ptext (sLit " [] "), ppr func ]

    -- general case
    pprStgRhs (StgRhsClosure cc bi free_vars upd_flag srt args body)
      = hang (hsep [if opt_SccProfilingOn then ppr cc else empty,
    		pp_binder_info bi,
    		ifPprDebug (brackets (interppSP free_vars)),
    		char '\\' <> ppr upd_flag, pprMaybeSRT srt, brackets (interppSP args)])
    	 4 (ppr body)

    pprStgRhs (StgRhsCon cc con args)
      = hcat [ ppr cc,
    	   space, ppr con, ptext (sLit "! "), brackets (interppSP args)]

    pprMaybeSRT :: SRT -> SDoc
    pprMaybeSRT (NoSRT) = empty
    pprMaybeSRT srt     = ptext (sLit "srt:") <> pprSRT srt

\end{code}