path: root/compiler/deSugar/DsCCall.lhs

%
% (c) The University of Glasgow 2006
% (c) The AQUA Project, Glasgow University, 1994-1998
%

Desugaring foreign calls

\begin{code}
{-# OPTIONS -fno-warn-tabs #-}
-- The above warning supression flag is a temporary kludge.
-- While working on this module you are encouraged to remove it and
-- detab the module (please do the detabbing in a separate patch). See
--     http://ghc.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#TabsvsSpaces
-- for details

module DsCCall 
	( dsCCall
	, mkFCall
	, unboxArg
	, boxResult
	, resultWrapper
	) where

#include "HsVersions.h"


import CoreSyn

import DsMonad

import CoreUtils
import MkCore
import Var
import MkId
import Maybes
import ForeignCall
import DataCon

import TcType
import Type
import Coercion
import PrimOp
import TysPrim
import TyCon
import TysWiredIn
import BasicTypes
import Literal
import PrelNames
import VarSet
import DynFlags
import Outputable
import Util
\end{code}

Desugaring of @ccall@s consists of adding some state manipulation,
unboxing any boxed primitive arguments and boxing the result if
desired.

The state stuff just consists of adding in
@PrimIO (\ s -> case s of { S# s# -> ... })@ in an appropriate place.

The unboxing is straightforward, as all information needed to unbox is
available from the type.  For each boxed-primitive argument, we
transform:
\begin{verbatim}
   _ccall_ foo [ r, t1, ... tm ] e1 ... em
   |
   |
   V
   case e1 of { T1# x1# ->
   ...
   case em of { Tm# xm# -> xm#
   ccall# foo [ r, t1#, ... tm# ] x1# ... xm#
   } ... }
\end{verbatim}

The reboxing of a @_ccall_@ result is a bit tricker: the types don't
contain information about the state-pairing functions so we have to
keep a list of \tr{(type, s-p-function)} pairs.  We transform as
follows:
\begin{verbatim}
   ccall# foo [ r, t1#, ... tm# ] e1# ... em#
   |
   |
   V
   \ s# -> case (ccall# foo [ r, t1#, ... tm# ] s# e1# ... em#) of
	  (StateAnd<r># result# state#) -> (R# result#, realWorld#)
\end{verbatim}

\begin{code}
dsCCall :: CLabelString	-- C routine to invoke
	-> [CoreExpr]	-- Arguments (desugared)
	-> Safety	-- Safety of the call
	-> Type		-- Type of the result: IO t
	-> DsM CoreExpr	-- Result, of type ???

dsCCall lbl args may_gc result_ty
  = do (unboxed_args, arg_wrappers) <- mapAndUnzipM unboxArg args
       (ccall_result_ty, res_wrapper) <- boxResult result_ty
       uniq <- newUnique
       dflags <- getDynFlags
       let
           target = StaticTarget lbl Nothing True
           the_fcall    = CCall (CCallSpec target CCallConv may_gc)
           the_prim_app = mkFCall dflags uniq the_fcall unboxed_args ccall_result_ty
       return (foldr ($) (res_wrapper the_prim_app) arg_wrappers)

mkFCall :: DynFlags -> Unique -> ForeignCall 
	-> [CoreExpr] 	-- Args
	-> Type 	-- Result type
	-> CoreExpr
-- Construct the ccall.  The only tricky bit is that the ccall Id should have
-- no free vars, so if any of the arg tys do we must give it a polymorphic type.
-- 	[I forget *why* it should have no free vars!]
-- For example:
--	mkCCall ... [s::StablePtr (a->b), x::Addr, c::Char]
--
-- Here we build a ccall thus
--	(ccallid::(forall a b.  StablePtr (a -> b) -> Addr -> Char -> IO Addr))
--			a b s x c
mkFCall dflags uniq the_fcall val_args res_ty
  = mkApps (mkVarApps (Var the_fcall_id) tyvars) val_args
  where
    arg_tys = map exprType val_args
    body_ty = (mkFunTys arg_tys res_ty)
    tyvars  = varSetElems (tyVarsOfType body_ty)
    ty 	    = mkForAllTys tyvars body_ty
    the_fcall_id = mkFCallId dflags uniq the_fcall ty
\end{code}

\begin{code}
unboxArg :: CoreExpr			-- The supplied argument
	 -> DsM (CoreExpr,		-- To pass as the actual argument
		 CoreExpr -> CoreExpr	-- Wrapper to unbox the arg
		)
-- Example: if the arg is e::Int, unboxArg will return
--	(x#::Int#, \W. case x of I# x# -> W)
-- where W is a CoreExpr that probably mentions x#

unboxArg arg
  -- Primtive types: nothing to unbox
  | isPrimitiveType arg_ty
  = return (arg, \body -> body)

  -- Recursive newtypes
  | Just(_rep_ty, co) <- splitNewTypeRepCo_maybe arg_ty
  = unboxArg (mkCast arg co)
      
  -- Booleans
  | Just tc <- tyConAppTyCon_maybe arg_ty, 
    tc `hasKey` boolTyConKey
  = do dflags <- getDynFlags
       prim_arg <- newSysLocalDs intPrimTy
       return (Var prim_arg,
              \ body -> Case (mkWildCase arg arg_ty intPrimTy
                                       [(DataAlt falseDataCon,[],mkIntLit dflags 0),
                                        (DataAlt trueDataCon, [],mkIntLit dflags 1)])
                                        -- In increasing tag order!
                             prim_arg
                             (exprType body) 
                             [(DEFAULT,[],body)])

  -- Data types with a single constructor, which has a single, primitive-typed arg
  -- This deals with Int, Float etc; also Ptr, ForeignPtr
  | is_product_type && data_con_arity == 1 
  = ASSERT2(isUnLiftedType data_con_arg_ty1, pprType arg_ty)
                        -- Typechecker ensures this
    do case_bndr <- newSysLocalDs arg_ty
       prim_arg <- newSysLocalDs data_con_arg_ty1
       return (Var prim_arg,
               \ body -> Case arg case_bndr (exprType body) [(DataAlt data_con,[prim_arg],body)]
              )

  -- Byte-arrays, both mutable and otherwise; hack warning
  -- We're looking for values of type ByteArray, MutableByteArray
  --	data ByteArray          ix = ByteArray        ix ix ByteArray#
  --	data MutableByteArray s ix = MutableByteArray ix ix (MutableByteArray# s)
  | is_product_type &&
    data_con_arity == 3 &&
    maybeToBool maybe_arg3_tycon &&
    (arg3_tycon ==  byteArrayPrimTyCon ||
     arg3_tycon ==  mutableByteArrayPrimTyCon)
  = do case_bndr <- newSysLocalDs arg_ty
       vars@[_l_var, _r_var, arr_cts_var] <- newSysLocalsDs data_con_arg_tys
       return (Var arr_cts_var,
               \ body -> Case arg case_bndr (exprType body) [(DataAlt data_con,vars,body)]
              )

  | otherwise
  = do l <- getSrcSpanDs
       pprPanic "unboxArg: " (ppr l <+> ppr arg_ty)
  where
    arg_ty					= exprType arg
    maybe_product_type 			   	= splitDataProductType_maybe arg_ty
    is_product_type			   	= maybeToBool maybe_product_type
    Just (_, _, data_con, data_con_arg_tys)	= maybe_product_type
    data_con_arity				= dataConSourceArity data_con
    (data_con_arg_ty1 : _)			= data_con_arg_tys

    (_ : _ : data_con_arg_ty3 : _) = data_con_arg_tys
    maybe_arg3_tycon    	   = tyConAppTyCon_maybe data_con_arg_ty3
    Just arg3_tycon		   = maybe_arg3_tycon
\end{code}


\begin{code}
boxResult :: Type
	  -> DsM (Type, CoreExpr -> CoreExpr)

-- Takes the result of the user-level ccall: 
--	either (IO t), 
--	or maybe just t for an side-effect-free call
-- Returns a wrapper for the primitive ccall itself, along with the
-- type of the result of the primitive ccall.  This result type
-- will be of the form  
--	State# RealWorld -> (# State# RealWorld, t' #)
-- where t' is the unwrapped form of t.  If t is simply (), then
-- the result type will be 
--	State# RealWorld -> (# State# RealWorld #)

boxResult result_ty
  | Just (io_tycon, io_res_ty) <- tcSplitIOType_maybe result_ty
	-- isIOType_maybe handles the case where the type is a 
	-- simple wrapping of IO.  E.g.
	-- 	newtype Wrap a = W (IO a)
	-- No coercion necessary because its a non-recursive newtype
	-- (If we wanted to handle a *recursive* newtype too, we'd need
	-- another case, and a coercion.)
   	-- The result is IO t, so wrap the result in an IO constructor
  = do	{ res <- resultWrapper io_res_ty
	; let extra_result_tys 
		= case res of
		     (Just ty,_) 
		       | isUnboxedTupleType ty 
		       -> let Just ls = tyConAppArgs_maybe ty in tail ls
		     _ -> []

	      return_result state anss
		= mkConApp (tupleCon UnboxedTuple (2 + length extra_result_tys))
	         	   (map Type (realWorldStatePrimTy : io_res_ty : extra_result_tys)
			      ++ (state : anss)) 

	; (ccall_res_ty, the_alt) <- mk_alt return_result res

	; state_id <- newSysLocalDs realWorldStatePrimTy
	; let io_data_con = head (tyConDataCons io_tycon)
	      toIOCon     = dataConWrapId io_data_con

	      wrap the_call =
			      mkApps (Var toIOCon)
			    	     [ Type io_res_ty, 
			    	       Lam state_id $
			    	       mkWildCase (App the_call (Var state_id))
			    	     	     ccall_res_ty
			                     (coreAltType the_alt) 
			    	     	     [the_alt]
			    	     ]

	; return (realWorldStatePrimTy `mkFunTy` ccall_res_ty, wrap) }

boxResult result_ty
  = do -- It isn't IO, so do unsafePerformIO
       -- It's not conveniently available, so we inline it
       res <- resultWrapper result_ty
       (ccall_res_ty, the_alt) <- mk_alt return_result res
       let
           wrap = \ the_call -> mkWildCase (App the_call (Var realWorldPrimId)) 
                                     	   ccall_res_ty
                                     	   (coreAltType the_alt)
                                     	   [the_alt]
       return (realWorldStatePrimTy `mkFunTy` ccall_res_ty, wrap)
  where
    return_result _ [ans] = ans
    return_result _ _     = panic "return_result: expected single result"


mk_alt :: (Expr Var -> [Expr Var] -> Expr Var)
       -> (Maybe Type, Expr Var -> Expr Var)
       -> DsM (Type, (AltCon, [Id], Expr Var))
mk_alt return_result (Nothing, wrap_result)
  = do -- The ccall returns ()
       state_id <- newSysLocalDs realWorldStatePrimTy
       let
             the_rhs = return_result (Var state_id) 
                                     [wrap_result (panic "boxResult")]

             ccall_res_ty = mkTyConApp unboxedSingletonTyCon [realWorldStatePrimTy]
             the_alt      = (DataAlt unboxedSingletonDataCon, [state_id], the_rhs)
       
       return (ccall_res_ty, the_alt)

mk_alt return_result (Just prim_res_ty, wrap_result)
    		-- The ccall returns a non-() value
  | isUnboxedTupleType prim_res_ty= do
    let
        Just ls = tyConAppArgs_maybe prim_res_ty
        arity = 1 + length ls
    args_ids@(result_id:as) <- mapM newSysLocalDs ls
    state_id <- newSysLocalDs realWorldStatePrimTy
    let
        the_rhs = return_result (Var state_id) 
                                (wrap_result (Var result_id) : map Var as)
        ccall_res_ty = mkTyConApp (tupleTyCon UnboxedTuple arity)
                                  (realWorldStatePrimTy : ls)
        the_alt      = ( DataAlt (tupleCon UnboxedTuple arity)
                       , (state_id : args_ids)
                       , the_rhs
                       )
    return (ccall_res_ty, the_alt)

  | otherwise = do
    result_id <- newSysLocalDs prim_res_ty
    state_id <- newSysLocalDs realWorldStatePrimTy
    let
        the_rhs = return_result (Var state_id) 
                                [wrap_result (Var result_id)]
        ccall_res_ty = mkTyConApp unboxedPairTyCon [realWorldStatePrimTy, prim_res_ty]
        the_alt      = (DataAlt unboxedPairDataCon, [state_id, result_id], the_rhs)
    return (ccall_res_ty, the_alt)


resultWrapper :: Type
              -> DsM (Maybe Type,               -- Type of the expected result, if any
                      CoreExpr -> CoreExpr)     -- Wrapper for the result 
-- resultWrapper deals with the result *value*
-- E.g. foreign import foo :: Int -> IO T
-- Then resultWrapper deals with marshalling the 'T' part
resultWrapper result_ty
  -- Base case 1: primitive types
  | isPrimitiveType result_ty
  = return (Just result_ty, \e -> e)

  -- Base case 2: the unit type ()
  | Just (tc,_) <- maybe_tc_app, tc `hasKey` unitTyConKey
  = return (Nothing, \_ -> Var unitDataConId)

  -- Base case 3: the boolean type
  | Just (tc,_) <- maybe_tc_app, tc `hasKey` boolTyConKey
  = do
    dflags <- getDynFlags
    return
     (Just intPrimTy, \e -> mkWildCase e intPrimTy
                                   boolTy
                                   [(DEFAULT                    ,[],Var trueDataConId ),
                                    (LitAlt (mkMachInt dflags 0),[],Var falseDataConId)])

  -- Recursive newtypes
  | Just (rep_ty, co) <- splitNewTypeRepCo_maybe result_ty
  = do (maybe_ty, wrapper) <- resultWrapper rep_ty
       return (maybe_ty, \e -> mkCast (wrapper e) (mkSymCo co))

  -- The type might contain foralls (eg. for dummy type arguments,
  -- referring to 'Ptr a' is legal).
  | Just (tyvar, rest) <- splitForAllTy_maybe result_ty
  = do (maybe_ty, wrapper) <- resultWrapper rest
       return (maybe_ty, \e -> Lam tyvar (wrapper e))

  -- Data types with a single constructor, which has a single arg
  -- This includes types like Ptr and ForeignPtr
  | Just (tycon, tycon_arg_tys, data_con, data_con_arg_tys) <- splitDataProductType_maybe result_ty,
    dataConSourceArity data_con == 1
  = do dflags <- getDynFlags
       let
           (unwrapped_res_ty : _) = data_con_arg_tys
           narrow_wrapper         = maybeNarrow dflags tycon
       (maybe_ty, wrapper) <- resultWrapper unwrapped_res_ty
       return
         (maybe_ty, \e -> mkApps (Var (dataConWrapId data_con)) 
                                 (map Type tycon_arg_tys ++ [wrapper (narrow_wrapper e)]))

  | otherwise
  = pprPanic "resultWrapper" (ppr result_ty)
  where
    maybe_tc_app = splitTyConApp_maybe result_ty

-- When the result of a foreign call is smaller than the word size, we
-- need to sign- or zero-extend the result up to the word size.  The C
-- standard appears to say that this is the responsibility of the
-- caller, not the callee.

maybeNarrow :: DynFlags -> TyCon -> (CoreExpr -> CoreExpr)
maybeNarrow dflags tycon
  | tycon `hasKey` int8TyConKey   = \e -> App (Var (mkPrimOpId Narrow8IntOp)) e
  | tycon `hasKey` int16TyConKey  = \e -> App (Var (mkPrimOpId Narrow16IntOp)) e
  | tycon `hasKey` int32TyConKey
	 && wORD_SIZE dflags > 4         = \e -> App (Var (mkPrimOpId Narrow32IntOp)) e

  | tycon `hasKey` word8TyConKey  = \e -> App (Var (mkPrimOpId Narrow8WordOp)) e
  | tycon `hasKey` word16TyConKey = \e -> App (Var (mkPrimOpId Narrow16WordOp)) e
  | tycon `hasKey` word32TyConKey
	 && wORD_SIZE dflags > 4         = \e -> App (Var (mkPrimOpId Narrow32WordOp)) e
  | otherwise			  = id
\end{code}