path: root/compiler/GHC/Stg/Syntax.hs

{-
(c) The GRASP/AQUA Project, Glasgow University, 1992-1998

Shared term graph (STG) syntax for spineless-tagless code generation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

This data type represents programs just before code generation (conversion to
@Cmm@): 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.
-}

{-# LANGUAGE CPP #-}
{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE LambdaCase #-}

module GHC.Stg.Syntax (
        StgArg(..),

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

        StgPass(..), BinderP, XRhsClosure, XLet, XLetNoEscape,
        NoExtFieldSilent, noExtFieldSilent,
        OutputablePass,

        UpdateFlag(..), isUpdatable,

        -- a set of synonyms for the vanilla parameterisation
        StgTopBinding, StgBinding, StgExpr, StgRhs, StgAlt,

        -- a set of synonyms for the code gen parameterisation
        CgStgTopBinding, CgStgBinding, CgStgExpr, CgStgRhs, CgStgAlt,

        -- a set of synonyms for the lambda lifting parameterisation
        LlStgTopBinding, LlStgBinding, LlStgExpr, LlStgRhs, LlStgAlt,

        -- a set of synonyms to distinguish in- and out variants
        InStgArg,  InStgTopBinding,  InStgBinding,  InStgExpr,  InStgRhs,  InStgAlt,
        OutStgArg, OutStgTopBinding, OutStgBinding, OutStgExpr, OutStgRhs, OutStgAlt,

        -- StgOp
        StgOp(..),

        -- utils
        stgRhsArity,
        isDllConApp,
        stgArgType,
        stripStgTicksTop, stripStgTicksTopE,
        stgCaseBndrInScope,
        bindersOf, bindersOfTop, bindersOfTopBinds,

        pprStgBinding, pprGenStgTopBindings, pprStgTopBindings
    ) where

#include "HsVersions.h"

import GhcPrelude

import CoreSyn     ( AltCon, Tickish )
import CostCentre  ( CostCentreStack )
import Data.ByteString ( ByteString )
import Data.Data   ( Data )
import Data.List   ( intersperse )
import DataCon
import GHC.Driver.Session
import ForeignCall ( ForeignCall )
import Id
import VarSet
import Literal     ( Literal, literalType )
import Module      ( Module )
import Outputable
import GHC.Driver.Packages    ( isDllName )
import GHC.Platform
import PprCore     ( {- instances -} )
import PrimOp      ( PrimOp, PrimCall )
import TyCon       ( PrimRep(..), TyCon )
import Type        ( Type )
import GHC.Types.RepType     ( typePrimRep1 )
import Util

import Data.List.NonEmpty ( NonEmpty, toList )

{-
************************************************************************
*                                                                      *
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@):
-}

-- | A top-level binding.
data GenStgTopBinding pass
-- See Note [CoreSyn top-level string literals]
  = StgTopLifted (GenStgBinding pass)
  | StgTopStringLit Id ByteString

data GenStgBinding pass
  = StgNonRec (BinderP pass) (GenStgRhs pass)
  | StgRec    [(BinderP pass, GenStgRhs pass)]

{-
************************************************************************
*                                                                      *
StgArg
*                                                                      *
************************************************************************
-}

data StgArg
  = StgVarArg  Id
  | StgLitArg  Literal

-- | Does this constructor application refer to anything in a different
-- *Windows* DLL?
-- If so, we can't allocate it statically
isDllConApp :: DynFlags -> Module -> DataCon -> [StgArg] -> Bool
isDllConApp dflags this_mod con args
 | platformOS (targetPlatform dflags) == OSMinGW32
    = isDllName dflags this_mod (dataConName con) || any is_dll_arg args
 | otherwise = False
  where
    -- NB: typePrimRep1 is legit because any free variables won't have
    -- unlifted type (there are no unlifted things at top level)
    is_dll_arg :: StgArg -> Bool
    is_dll_arg (StgVarArg v) =  isAddrRep (typePrimRep1 (idType v))
                             && isDllName dflags this_mod (idName v)
    is_dll_arg _             = False

-- True of machine addresses; these are the things that don't work across DLLs.
-- The key point here is that VoidRep comes out False, so that a top level
-- nullary GADT constructor is False for isDllConApp
--
--    data T a where
--      T1 :: T Int
--
-- gives
--
--    T1 :: forall a. (a~Int) -> T a
--
-- and hence the top-level binding
--
--    $WT1 :: T Int
--    $WT1 = T1 Int (Coercion (Refl Int))
--
-- The coercion argument here gets VoidRep
isAddrRep :: PrimRep -> Bool
isAddrRep AddrRep     = True
isAddrRep LiftedRep   = True
isAddrRep UnliftedRep = True
isAddrRep _           = False

-- | Type of an @StgArg@
--
-- Very half baked because we have lost the type arguments.
stgArgType :: StgArg -> Type
stgArgType (StgVarArg v)   = idType v
stgArgType (StgLitArg lit) = literalType lit


-- | Strip ticks of a given type from an STG expression.
stripStgTicksTop :: (Tickish Id -> Bool) -> GenStgExpr p -> ([Tickish Id], GenStgExpr p)
stripStgTicksTop p = go []
   where go ts (StgTick t e) | p t = go (t:ts) e
         go ts other               = (reverse ts, other)

-- | Strip ticks of a given type from an STG expression returning only the expression.
stripStgTicksTopE :: (Tickish Id -> Bool) -> GenStgExpr p -> GenStgExpr p
stripStgTicksTopE p = go
   where go (StgTick t e) | p t = go e
         go other               = other

-- | Given an alt type and whether the program is unarised, return whether the
-- case binder is in scope.
--
-- Case binders of unboxed tuple or unboxed sum type always dead after the
-- unariser has run. See Note [Post-unarisation invariants].
stgCaseBndrInScope :: AltType -> Bool {- ^ unarised? -} -> Bool
stgCaseBndrInScope alt_ty unarised =
    case alt_ty of
      AlgAlt _      -> True
      PrimAlt _     -> True
      MultiValAlt _ -> not unarised
      PolyAlt       -> True

{-
************************************************************************
*                                                                      *
STG expressions
*                                                                      *
************************************************************************

The @GenStgExpr@ data type is parameterised on binder and occurrence info, as
before.

************************************************************************
*                                                                      *
GenStgExpr
*                                                                      *
************************************************************************

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 []@.
-}

data GenStgExpr pass
  = StgApp
        Id       -- function
        [StgArg] -- arguments; may be empty

{-
************************************************************************
*                                                                      *
StgConApp and StgPrimApp --- saturated applications
*                                                                      *
************************************************************************

There are specialised forms of application, for constructors, primitives, and
literals.
-}

  | StgLit      Literal

        -- StgConApp is vital for returning unboxed tuples or sums
        -- which can't be let-bound
  | StgConApp   DataCon
                [StgArg] -- Saturated
                [Type]   -- See Note [Types in StgConApp] in GHC.Stg.Unarise

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

{-
************************************************************************
*                                                                      *
StgLam
*                                                                      *
************************************************************************

StgLam is used *only* during CoreToStg's work. Before CoreToStg has finished it
encodes (\x -> e) as (let f = \x -> e in f) TODO: Encode this via an extension
to GenStgExpr à la TTG.
-}

  | StgLam
        (NonEmpty (BinderP pass))
        StgExpr    -- Body of lambda

{-
************************************************************************
*                                                                      *
GenStgExpr: case-expressions
*                                                                      *
************************************************************************

This has the same boxed/unboxed business as Core case expressions.
-}

  | StgCase
        (GenStgExpr pass) -- the thing to examine
        (BinderP pass) -- binds the result of evaluating the scrutinee
        AltType
        [GenStgAlt pass]
                    -- The DEFAULT case is always *first*
                    -- if it is there at all

{-
************************************************************************
*                                                                      *
GenStgExpr: let(rec)-expressions
*                                                                      *
************************************************************************

The various forms of let(rec)-expression encode most of the interesting things
we want to do.

-   let-closure x = [free-vars] [args] expr in e

  is equivalent to

    let x = (\free-vars -> \args -> expr) free-vars

  @args@ may be empty (and is for most closures). It isn't under circumstances
  like this:

    let x = (\y -> y+z)

  This gets mangled to

    let-closure x = [z] [y] (y+z)

  The idea is that we compile code for @(y+z)@ in an environment in which @z@ is
  bound to an offset from Node, and `y` is bound to an offset from the stack
  pointer.

  (A let-closure is an @StgLet@ with a @StgRhsClosure@ RHS.)

-   let-constructor x = Constructor [args] in e

  (A let-constructor is an @StgLet@ with a @StgRhsCon@ RHS.)

- 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.

-   let-unboxed u = <an arbitrary arithmetic expression in unboxed values> in e

  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 ...)

- Advanced stuff here! Not to start with, but makes pattern matching generate
  more efficient code.

    let-escapes-not fail = expr
    in e'

  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:

    f x y = let z = huge-expression in
            if y==1 then z else
            if y==2 then z else
            1

  (A let-escapes-not is an @StgLetNoEscape@.)

- We may eventually want:

    let-literal x = Literal in e

And so the code for let(rec)-things:
-}

  | StgLet
        (XLet pass)
        (GenStgBinding pass)    -- right hand sides (see below)
        (GenStgExpr pass)       -- body

  | StgLetNoEscape
        (XLetNoEscape pass)
        (GenStgBinding pass)    -- right hand sides (see below)
        (GenStgExpr pass)       -- body

{-
*************************************************************************
*                                                                      *
GenStgExpr: hpc, scc and other debug annotations
*                                                                      *
*************************************************************************

Finally for @hpc@ expressions we introduce a new STG construct.
-}

  | StgTick
    (Tickish Id)
    (GenStgExpr pass)       -- sub expression

-- END of GenStgExpr

{-
************************************************************************
*                                                                      *
STG right-hand sides
*                                                                      *
************************************************************************

Here's the rest of the interesting stuff for @StgLet@s; the first flavour is for
closures:
-}

data GenStgRhs pass
  = StgRhsClosure
        (XRhsClosure pass) -- ^ Extension point for non-global free var
                           --   list just before 'CodeGen'.
        CostCentreStack    -- ^ CCS to be attached (default is CurrentCCS)
        !UpdateFlag        -- ^ 'ReEntrant' | 'Updatable' | 'SingleEntry'
        [BinderP pass]     -- ^ arguments; if empty, then not a function;
                           --   as above, order is important.
        (GenStgExpr pass)  -- ^ body

{-
An example may be in order.  Consider:

  let t = \x -> \y -> ... x ... y ... p ... q in e

Pulling out the free vars and stylising somewhat, we get the equivalent:

  let t = (\[p,q] -> \[x,y] -> ... x ... y ... p ...q) p q

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):
-}

  | 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. Never an unboxed tuple or sum, as those
                        -- are not allocated.
        [StgArg]        -- Args

-- | Used as a data type index for the stgSyn AST
data StgPass
  = Vanilla
  | LiftLams
  | CodeGen

-- | Like 'GHC.Hs.Extension.NoExtField', but with an 'Outputable' instance that
-- returns 'empty'.
data NoExtFieldSilent = NoExtFieldSilent
  deriving (Data, Eq, Ord)

instance Outputable NoExtFieldSilent where
  ppr _ = empty

-- | Used when constructing a term with an unused extension point that should
-- not appear in pretty-printed output at all.
noExtFieldSilent :: NoExtFieldSilent
noExtFieldSilent = NoExtFieldSilent
-- TODO: Maybe move this to GHC.Hs.Extension? I'm not sure about the
-- implications on build time...

-- TODO: Do we really want to the extension point type families to have a closed
-- domain?
type family BinderP (pass :: StgPass)
type instance BinderP 'Vanilla = Id
type instance BinderP 'CodeGen = Id

type family XRhsClosure (pass :: StgPass)
type instance XRhsClosure 'Vanilla = NoExtFieldSilent
-- | Code gen needs to track non-global free vars
type instance XRhsClosure 'CodeGen = DIdSet

type family XLet (pass :: StgPass)
type instance XLet 'Vanilla = NoExtFieldSilent
type instance XLet 'CodeGen = NoExtFieldSilent

type family XLetNoEscape (pass :: StgPass)
type instance XLetNoEscape 'Vanilla = NoExtFieldSilent
type instance XLetNoEscape 'CodeGen = NoExtFieldSilent

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

{-
************************************************************************
*                                                                      *
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 module
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.
-}

type GenStgAlt pass
  = (AltCon,          -- alts: data constructor,
     [BinderP pass],  -- constructor's parameters,
     GenStgExpr pass) -- ...right-hand side.

data AltType
  = PolyAlt             -- Polymorphic (a lifted type variable)
  | MultiValAlt Int     -- Multi value of this arity (unboxed tuple or sum)
                        -- the arity could indeed be 1 for unary unboxed tuple
                        -- or enum-like unboxed sums
  | AlgAlt      TyCon   -- Algebraic data type; the AltCons will be DataAlts
  | PrimAlt     PrimRep -- Primitive data type; the AltCons (if any) will be LitAlts

{-
************************************************************************
*                                                                      *
The Plain STG parameterisation
*                                                                      *
************************************************************************

This happens to be the only one we use at the moment.
-}

type StgTopBinding = GenStgTopBinding 'Vanilla
type StgBinding    = GenStgBinding    'Vanilla
type StgExpr       = GenStgExpr       'Vanilla
type StgRhs        = GenStgRhs        'Vanilla
type StgAlt        = GenStgAlt        'Vanilla

type LlStgTopBinding = GenStgTopBinding 'LiftLams
type LlStgBinding    = GenStgBinding    'LiftLams
type LlStgExpr       = GenStgExpr       'LiftLams
type LlStgRhs        = GenStgRhs        'LiftLams
type LlStgAlt        = GenStgAlt        'LiftLams

type CgStgTopBinding = GenStgTopBinding 'CodeGen
type CgStgBinding    = GenStgBinding    'CodeGen
type CgStgExpr       = GenStgExpr       'CodeGen
type CgStgRhs        = GenStgRhs        'CodeGen
type CgStgAlt        = GenStgAlt        'CodeGen

{- Many passes apply a substitution, and it's very handy to have type
   synonyms to remind us whether or not the substitution has been applied.
   See CoreSyn for precedence in Core land
-}

type InStgTopBinding  = StgTopBinding
type InStgBinding     = StgBinding
type InStgArg         = StgArg
type InStgExpr        = StgExpr
type InStgRhs         = StgRhs
type InStgAlt         = StgAlt
type OutStgTopBinding = StgTopBinding
type OutStgBinding    = StgBinding
type OutStgArg        = StgArg
type OutStgExpr       = StgExpr
type OutStgRhs        = StgRhs
type OutStgAlt        = StgAlt

{-

************************************************************************
*                                                                      *
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.
-}

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

{-
************************************************************************
*                                                                      *
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.
-}

data StgOp
  = StgPrimOp  PrimOp

  | StgPrimCallOp PrimCall

  | StgFCallOp ForeignCall Type
        -- The Type, which is obtained from the foreign import declaration
        -- itself, is needed by the stg-to-cmm pass to determine the offset to
        -- apply to unlifted boxed arguments in GHC.StgToCmm.Foreign. See Note
        -- [Unlifted boxed arguments to foreign calls]

{-
************************************************************************
*                                                                      *
Utilities
*                                                                      *
************************************************************************
-}

bindersOf :: BinderP a ~ Id => GenStgBinding a -> [Id]
bindersOf (StgNonRec binder _) = [binder]
bindersOf (StgRec pairs)       = [binder | (binder, _) <- pairs]

bindersOfTop :: BinderP a ~ Id => GenStgTopBinding a -> [Id]
bindersOfTop (StgTopLifted bind) = bindersOf bind
bindersOfTop (StgTopStringLit binder _) = [binder]

bindersOfTopBinds :: BinderP a ~ Id => [GenStgTopBinding a] -> [Id]
bindersOfTopBinds = foldr ((++) . bindersOfTop) []

{-
************************************************************************
*                                                                      *
Pretty-printing
*                                                                      *
************************************************************************

Robin Popplestone asked for semi-colon separators on STG binds; here's hoping he
likes terminators instead...  Ditto for case alternatives.
-}

type OutputablePass pass =
  ( Outputable (XLet pass)
  , Outputable (XLetNoEscape pass)
  , Outputable (XRhsClosure pass)
  , OutputableBndr (BinderP pass)
  )

pprGenStgTopBinding
  :: OutputablePass pass => GenStgTopBinding pass -> SDoc
pprGenStgTopBinding (StgTopStringLit bndr str)
  = hang (hsep [pprBndr LetBind bndr, equals])
        4 (pprHsBytes str <> semi)
pprGenStgTopBinding (StgTopLifted bind)
  = pprGenStgBinding bind

pprGenStgBinding
  :: OutputablePass pass => GenStgBinding pass -> SDoc

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

pprGenStgBinding (StgRec pairs)
  = vcat [ text "Rec {"
         , vcat (intersperse blankLine (map ppr_bind pairs))
         , text "end Rec }" ]
  where
    ppr_bind (bndr, expr)
      = hang (hsep [pprBndr LetBind bndr, equals])
             4 (ppr expr <> semi)

pprGenStgTopBindings
  :: (OutputablePass pass) => [GenStgTopBinding pass] -> SDoc
pprGenStgTopBindings binds
  = vcat $ intersperse blankLine (map pprGenStgTopBinding binds)

pprStgBinding :: StgBinding -> SDoc
pprStgBinding = pprGenStgBinding

pprStgTopBindings :: [StgTopBinding] -> SDoc
pprStgTopBindings = pprGenStgTopBindings

instance Outputable StgArg where
    ppr = pprStgArg

instance OutputablePass pass => Outputable (GenStgTopBinding pass) where
    ppr = pprGenStgTopBinding

instance OutputablePass pass => Outputable (GenStgBinding pass) where
    ppr = pprGenStgBinding

instance OutputablePass pass => Outputable (GenStgExpr pass) where
    ppr = pprStgExpr

instance OutputablePass pass => Outputable (GenStgRhs pass) where
    ppr rhs = pprStgRhs rhs

pprStgArg :: StgArg -> SDoc
pprStgArg (StgVarArg var) = ppr var
pprStgArg (StgLitArg con) = ppr con

pprStgExpr :: OutputablePass pass => GenStgExpr pass -> SDoc
-- special case
pprStgExpr (StgLit lit)     = ppr lit

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

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_list (map (pprBndr LambdaBind) (toList bndrs))
            <+> text "->",
         pprStgExpr body ]
  where ppr_list = brackets . fsep . punctuate comma

-- 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 [text "let { ", ppr bndr, ptext (sLit " = "),
                          ppr cc,
                          pp_binder_info bi,
                          text " [", whenPprDebug (interppSP free_vars), ptext (sLit "] \\"),
                          ppr upd_flag, text " [",
                          interppSP args, char ']'])
            8 (sep [hsep [ppr rhs, text "} in"]]))
      (ppr expr)
-}

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

pprStgExpr (StgLet ext bind expr@StgLet{})
  = ($$)
      (sep [hang (text "let" <+> ppr ext <+> text "{")
                2 (hsep [pprGenStgBinding bind, text "} in"])])
      (ppr expr)

-- general case
pprStgExpr (StgLet ext bind expr)
  = sep [hang (text "let" <+> ppr ext <+> text "{") 2 (pprGenStgBinding bind),
           hang (text "} in ") 2 (ppr expr)]

pprStgExpr (StgLetNoEscape ext bind expr)
  = sep [hang (text "let-no-escape" <+> ppr ext <+> text "{")
                2 (pprGenStgBinding bind),
           hang (text "} in ")
                2 (ppr expr)]

pprStgExpr (StgTick tickish expr)
  = sdocOption sdocSuppressTicks $ \case
      True  -> pprStgExpr expr
      False -> sep [ ppr tickish, pprStgExpr expr ]


-- Don't indent for a single case alternative.
pprStgExpr (StgCase expr bndr alt_type [alt])
  = sep [sep [text "case",
           nest 4 (hsep [pprStgExpr expr,
             whenPprDebug (dcolon <+> ppr alt_type)]),
           text "of", pprBndr CaseBind bndr, char '{'],
           pprStgAlt False alt,
           char '}']

pprStgExpr (StgCase expr bndr alt_type alts)
  = sep [sep [text "case",
           nest 4 (hsep [pprStgExpr expr,
             whenPprDebug (dcolon <+> ppr alt_type)]),
           text "of", pprBndr CaseBind bndr, char '{'],
           nest 2 (vcat (map (pprStgAlt True) alts)),
           char '}']


pprStgAlt :: OutputablePass pass => Bool -> GenStgAlt pass -> SDoc
pprStgAlt indent (con, params, expr)
  | indent    = hang altPattern 4 (ppr expr <> semi)
  | otherwise = sep [altPattern, ppr expr <> semi]
    where
      altPattern = (hsep [ppr con, sep (map (pprBndr CasePatBind) params), text "->"])


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

instance Outputable AltType where
  ppr PolyAlt         = text "Polymorphic"
  ppr (MultiValAlt n) = text "MultiAlt" <+> ppr n
  ppr (AlgAlt tc)     = text "Alg"    <+> ppr tc
  ppr (PrimAlt tc)    = text "Prim"   <+> ppr tc

pprStgRhs :: OutputablePass pass => GenStgRhs pass -> SDoc

pprStgRhs (StgRhsClosure ext cc upd_flag args body)
  = sdocWithDynFlags $ \dflags ->
    hang (hsep [if gopt Opt_SccProfilingOn dflags then ppr cc else empty,
                ppUnlessOption sdocSuppressStgExts (ppr ext),
                char '\\' <> ppr upd_flag, brackets (interppSP args)])
         4 (ppr body)

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