% % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998 % \section[ConFold]{Constant Folder} Conceptually, constant folding should be parameterized with the kind of target machine to get identical behaviour during compilation time and runtime. We cheat a little bit here... ToDo: check boundaries before folding, e.g. we can fold the Float addition (i1 + i2) only if it results in a valid Float. \begin{code}

    {-# OPTIONS -optc-DNON_POSIX_SOURCE #-}

    module PrelRules ( primOpRules, builtinRules ) where

    #include "HsVersions.h"

    import CoreSyn
    import MkCore
    import Id
    import Literal
    import PrimOp		( PrimOp(..), tagToEnumKey )
    import TysWiredIn
    import TyCon		( tyConDataCons_maybe, isEnumerationTyCon, isNewTyCon )
    import DataCon		( dataConTag, dataConTyCon, dataConWorkId, fIRST_TAG )
    import CoreUtils	( cheapEqExpr )
    import CoreUnfold	( exprIsConApp_maybe )
    import Type
    import OccName		( occNameFS )
    import PrelNames
    import Maybes		( orElse )
    import Name		( Name, nameOccName )
    import Outputable
    import FastString
    import StaticFlags      ( opt_SimplExcessPrecision )
    import Constants

    import Data.Bits as Bits
    import Data.Word	( Word )

\end{code} Note [Constant folding] ~~~~~~~~~~~~~~~~~~~~~~~ primOpRules generates the rewrite rules for each primop These rules do what is often called "constant folding" E.g. the rules for +# might say 4 +# 5 = 9 Well, of course you'd need a lot of rules if you did it like that, so we use a BuiltinRule instead, so that we can match in any two literal values. So the rule is really more like (Lit 4) +# (Lit y) = Lit (x+#y) where the (+#) on the rhs is done at compile time That is why these rules are built in here. Other rules which don't need to be built in are in GHC.Base. For example: x +# 0 = x \begin{code}

    primOpRules :: PrimOp -> Name -> [CoreRule]
    primOpRules op op_name = primop_rule op
      where
    	-- A useful shorthand
        one_lit   = oneLit  op_name
        two_lits  = twoLits op_name
        relop cmp = two_lits (cmpOp (\ord -> ord `cmp` EQ))
    	-- Cunning.  cmpOp compares the values to give an Ordering.
    	-- It applies its argument to that ordering value to turn
    	-- the ordering into a boolean value.  (`cmp` EQ) is just the job.

        -- ToDo:	something for integer-shift ops?
        --		NotOp

        primop_rule TagToEnumOp = mkBasicRule op_name 2 tagToEnumRule
        primop_rule DataToTagOp = mkBasicRule op_name 2 dataToTagRule

    	-- Int operations
        primop_rule IntAddOp    = two_lits (intOp2     (+))
        primop_rule IntSubOp    = two_lits (intOp2     (-))
        primop_rule IntMulOp    = two_lits (intOp2     (*))
        primop_rule IntQuotOp   = two_lits (intOp2Z    quot)
        primop_rule IntRemOp    = two_lits (intOp2Z    rem)
        primop_rule IntNegOp    = one_lit  negOp
        primop_rule ISllOp      = two_lits (intShiftOp2 Bits.shiftL)
        primop_rule ISraOp      = two_lits (intShiftOp2 Bits.shiftR)
        primop_rule ISrlOp      = two_lits (intShiftOp2 shiftRightLogical)

    	-- Word operations
        primop_rule WordAddOp   = two_lits (wordOp2    (+))
        primop_rule WordSubOp   = two_lits (wordOp2    (-))
        primop_rule WordMulOp   = two_lits (wordOp2    (*))
        primop_rule WordQuotOp  = two_lits (wordOp2Z   quot)
        primop_rule WordRemOp   = two_lits (wordOp2Z   rem)
        primop_rule AndOp       = two_lits (wordBitOp2 (.&.))
        primop_rule OrOp        = two_lits (wordBitOp2 (.|.))
        primop_rule XorOp       = two_lits (wordBitOp2 xor)
        primop_rule SllOp       = two_lits (wordShiftOp2 Bits.shiftL)
        primop_rule SrlOp       = two_lits (wordShiftOp2 shiftRightLogical)

    	-- coercions
        primop_rule Word2IntOp 	= one_lit (litCoerce word2IntLit)
        primop_rule Int2WordOp 	= one_lit (litCoerce int2WordLit)
        primop_rule Narrow8IntOp 	= one_lit (litCoerce narrow8IntLit)
        primop_rule Narrow16IntOp 	= one_lit (litCoerce narrow16IntLit)
        primop_rule Narrow32IntOp 	= one_lit (litCoerce narrow32IntLit)
        primop_rule Narrow8WordOp 	= one_lit (litCoerce narrow8WordLit)
        primop_rule Narrow16WordOp 	= one_lit (litCoerce narrow16WordLit)
        primop_rule Narrow32WordOp 	= one_lit (litCoerce narrow32WordLit)
        primop_rule OrdOp   	= one_lit (litCoerce char2IntLit)
        primop_rule ChrOp    	= one_lit (predLitCoerce litFitsInChar int2CharLit)
        primop_rule Float2IntOp	= one_lit (litCoerce float2IntLit)
        primop_rule Int2FloatOp	= one_lit (litCoerce int2FloatLit)
        primop_rule Double2IntOp	= one_lit (litCoerce double2IntLit)
        primop_rule Int2DoubleOp	= one_lit (litCoerce int2DoubleLit)
    	-- SUP: Not sure what the standard says about precision in the following 2 cases
        primop_rule Float2DoubleOp 	= one_lit (litCoerce float2DoubleLit)
        primop_rule Double2FloatOp 	= one_lit (litCoerce double2FloatLit)

    	-- Float
        primop_rule FloatAddOp   = two_lits (floatOp2  (+))
        primop_rule FloatSubOp   = two_lits (floatOp2  (-))
        primop_rule FloatMulOp   = two_lits (floatOp2  (*))
        primop_rule FloatDivOp   = two_lits (floatOp2Z (/))
        primop_rule FloatNegOp   = one_lit  negOp

    	-- Double
        primop_rule DoubleAddOp   = two_lits (doubleOp2  (+))
        primop_rule DoubleSubOp   = two_lits (doubleOp2  (-))
        primop_rule DoubleMulOp   = two_lits (doubleOp2  (*))
        primop_rule DoubleDivOp   = two_lits (doubleOp2Z (/))
        primop_rule DoubleNegOp   = one_lit  negOp

    	-- Relational operators
        primop_rule IntEqOp  = relop (==) ++ litEq op_name True
        primop_rule IntNeOp  = relop (/=) ++ litEq op_name False
        primop_rule CharEqOp = relop (==) ++ litEq op_name True
        primop_rule CharNeOp = relop (/=) ++ litEq op_name False

        primop_rule IntGtOp		= relop (>)
        primop_rule IntGeOp		= relop (>=)
        primop_rule IntLeOp		= relop (<=)
        primop_rule IntLtOp		= relop (<)

        primop_rule CharGtOp	= relop (>)
        primop_rule CharGeOp	= relop (>=)
        primop_rule CharLeOp	= relop (<=)
        primop_rule CharLtOp	= relop (<)

        primop_rule FloatGtOp	= relop (>)
        primop_rule FloatGeOp	= relop (>=)
        primop_rule FloatLeOp	= relop (<=)
        primop_rule FloatLtOp	= relop (<)
        primop_rule FloatEqOp	= relop (==)
        primop_rule FloatNeOp	= relop (/=)

        primop_rule DoubleGtOp	= relop (>)
        primop_rule DoubleGeOp	= relop (>=)
        primop_rule DoubleLeOp	= relop (<=)
        primop_rule DoubleLtOp	= relop (<)
        primop_rule DoubleEqOp	= relop (==)
        primop_rule DoubleNeOp	= relop (/=)

        primop_rule WordGtOp	= relop (>)
        primop_rule WordGeOp	= relop (>=)
        primop_rule WordLeOp	= relop (<=)
        primop_rule WordLtOp	= relop (<)
        primop_rule WordEqOp	= relop (==)
        primop_rule WordNeOp	= relop (/=)

        primop_rule _    		= []

\end{code} %************************************************************************ %* * \subsection{Doing the business} %* * %************************************************************************ ToDo: the reason these all return Nothing is because there used to be the possibility of an argument being a litlit. Litlits are now gone, so this could be cleaned up. \begin{code}

    --------------------------
    litCoerce :: (Literal -> Literal) -> Literal -> Maybe CoreExpr
    litCoerce fn lit = Just (Lit (fn lit))

    predLitCoerce :: (Literal -> Bool) -> (Literal -> Literal) -> Literal -> Maybe CoreExpr
    predLitCoerce p fn lit
       | p lit     = Just (Lit (fn lit))
       | otherwise = Nothing

    --------------------------
    cmpOp :: (Ordering -> Bool) -> Literal -> Literal -> Maybe CoreExpr
    cmpOp cmp l1 l2
      = go l1 l2
      where
        done res | cmp res   = Just trueVal
    	     | otherwise = Just falseVal

    	-- These compares are at different types
        go (MachChar i1)   (MachChar i2)   = done (i1 `compare` i2)
        go (MachInt i1)    (MachInt i2)    = done (i1 `compare` i2)
        go (MachInt64 i1)  (MachInt64 i2)  = done (i1 `compare` i2)
        go (MachWord i1)   (MachWord i2)   = done (i1 `compare` i2)
        go (MachWord64 i1) (MachWord64 i2) = done (i1 `compare` i2)
        go (MachFloat i1)  (MachFloat i2)  = done (i1 `compare` i2)
        go (MachDouble i1) (MachDouble i2) = done (i1 `compare` i2)
        go _               _               = Nothing

    --------------------------

    negOp :: Literal -> Maybe CoreExpr	-- Negate
    negOp (MachFloat 0.0)  = Nothing  -- can't represent -0.0 as a Rational
    negOp (MachFloat f)    = Just (mkFloatVal (-f))
    negOp (MachDouble 0.0) = Nothing
    negOp (MachDouble d)   = Just (mkDoubleVal (-d))
    negOp (MachInt i)      = intResult (-i)
    negOp _                = Nothing

    --------------------------
    intOp2 :: (Integer->Integer->Integer) -> Literal -> Literal -> Maybe CoreExpr
    intOp2 op (MachInt i1) (MachInt i2) = intResult (i1 `op` i2)
    intOp2 _  _            _            = Nothing -- Could find LitLit

    intOp2Z :: (Integer->Integer->Integer) -> Literal -> Literal -> Maybe CoreExpr
    -- Like intOp2, but Nothing if i2=0
    intOp2Z op (MachInt i1) (MachInt i2)
      | i2 /= 0 = intResult (i1 `op` i2)
    intOp2Z _ _ _ = Nothing		-- LitLit or zero dividend

    intShiftOp2 :: (Integer->Int->Integer) -> Literal -> Literal -> Maybe CoreExpr
    	-- Shifts take an Int; hence second arg of op is Int
    intShiftOp2 op (MachInt i1) (MachInt i2) = intResult (i1 `op` fromInteger i2)
    intShiftOp2 _  _            _            = Nothing

    shiftRightLogical :: Integer -> Int -> Integer
    -- Shift right, putting zeros in rather than sign-propagating as Bits.shiftR would do
    -- Do this by converting to Word and back.  Obviously this won't work for big
    -- values, but its ok as we use it here
    shiftRightLogical x n = fromIntegral (fromInteger x `shiftR` n :: Word)

    --------------------------
    wordOp2 :: (Integer->Integer->Integer) -> Literal -> Literal -> Maybe CoreExpr
    wordOp2 op (MachWord w1) (MachWord w2)
      = wordResult (w1 `op` w2)
    wordOp2 _ _ _ = Nothing		-- Could find LitLit

    wordOp2Z :: (Integer->Integer->Integer) -> Literal -> Literal -> Maybe CoreExpr
    wordOp2Z op (MachWord w1) (MachWord w2)
      | w2 /= 0 = wordResult (w1 `op` w2)
    wordOp2Z _ _ _ = Nothing	-- LitLit or zero dividend

    wordBitOp2 :: (Integer->Integer->Integer) -> Literal -> Literal
               -> Maybe CoreExpr
    wordBitOp2 op (MachWord w1) (MachWord w2)
      = wordResult (w1 `op` w2)
    wordBitOp2 _ _ _ = Nothing		-- Could find LitLit

    wordShiftOp2 :: (Integer->Int->Integer) -> Literal -> Literal -> Maybe CoreExpr
    	-- Shifts take an Int; hence second arg of op is Int
    wordShiftOp2 op (MachWord x) (MachInt n)
      = wordResult (x `op` fromInteger n)
    	-- Do the shift at type Integer
    wordShiftOp2 _ _ _ = Nothing

    --------------------------
    floatOp2 :: (Rational -> Rational -> Rational) -> Literal -> Literal
             -> Maybe (Expr CoreBndr)
    floatOp2  op (MachFloat f1) (MachFloat f2)
      = Just (mkFloatVal (f1 `op` f2))
    floatOp2 _ _ _ = Nothing

    floatOp2Z :: (Rational -> Rational -> Rational) -> Literal -> Literal
              -> Maybe (Expr CoreBndr)
    floatOp2Z op (MachFloat f1) (MachFloat f2)
      | (f1 /= 0 || f2 > 0)  -- see Note [negative zero]
      && f2 /= 0             -- avoid NaN and Infinity/-Infinity
      = Just (mkFloatVal (f1 `op` f2))
    floatOp2Z _ _ _ = Nothing

    --------------------------
    doubleOp2 :: (Rational -> Rational -> Rational) -> Literal -> Literal
              -> Maybe (Expr CoreBndr)
    doubleOp2  op (MachDouble f1) (MachDouble f2)
      = Just (mkDoubleVal (f1 `op` f2))
    doubleOp2 _ _ _ = Nothing

    doubleOp2Z :: (Rational -> Rational -> Rational) -> Literal -> Literal
               -> Maybe (Expr CoreBndr)
    doubleOp2Z op (MachDouble f1) (MachDouble f2)
      | (f1 /= 0 || f2 > 0)  -- see Note [negative zero]
      && f2 /= 0             -- avoid NaN and Infinity/-Infinity
      = Just (mkDoubleVal (f1 `op` f2))
      -- Note [negative zero] Avoid (0 / -d), otherwise 0/(-1) reduces to
      -- zero, but we might want to preserve the negative zero here which
      -- is representable in Float/Double but not in (normalised)
      -- Rational. (#3676) Perhaps we should generate (0 :% (-1)) instead?
    doubleOp2Z _ _ _ = Nothing

    --------------------------
    	-- This stuff turns
    	--	n ==# 3#
    	-- into
    	--	case n of
    	--	  3# -> True
    	--	  m  -> False
    	--
    	-- This is a Good Thing, because it allows case-of case things
    	-- to happen, and case-default absorption to happen.  For
    	-- example:
    	--
    	--	if (n ==# 3#) || (n ==# 4#) then e1 else e2
    	-- will transform to
    	--	case n of
    	--	  3# -> e1
    	--	  4# -> e1
    	--	  m  -> e2
    	-- (modulo the usual precautions to avoid duplicating e1)

    litEq :: Name
          -> Bool		-- True <=> equality, False <=> inequality
          -> [CoreRule]
    litEq op_name is_eq
      = [BuiltinRule { ru_name = occNameFS (nameOccName op_name)
    				`appendFS` (fsLit "->case"),
    		   ru_fn = op_name,
    		   ru_nargs = 2, ru_try = rule_fn }]
      where
        rule_fn _ [Lit lit, expr] = do_lit_eq lit expr
        rule_fn _ [expr, Lit lit] = do_lit_eq lit expr
        rule_fn _ _    	      = Nothing

        do_lit_eq lit expr
          = Just (mkWildCase expr (literalType lit) boolTy
    		    [(DEFAULT,    [], val_if_neq),
    		     (LitAlt lit, [], val_if_eq)])
        val_if_eq  | is_eq     = trueVal
       	       | otherwise = falseVal
        val_if_neq | is_eq     = falseVal
    	       | otherwise = trueVal

    -- Note that we *don't* warn the user about overflow. It's not done at
    -- runtime either, and compilation of completely harmless things like
    --    ((124076834 :: Word32) + (2147483647 :: Word32))
    -- would yield a warning. Instead we simply squash the value into the
    -- *target* Int/Word range.
    intResult :: Integer -> Maybe CoreExpr
    intResult result
      = Just (mkIntVal (toInteger (fromInteger result :: TargetInt)))

    wordResult :: Integer -> Maybe CoreExpr
    wordResult result
      = Just (mkWordVal (toInteger (fromInteger result :: TargetWord)))

\end{code} %************************************************************************ %* * \subsection{Vaguely generic functions %* * %************************************************************************ \begin{code}

    mkBasicRule :: Name -> Int
                -> (IdUnfoldingFun -> [CoreExpr] -> Maybe CoreExpr)
                -> [CoreRule]
    -- Gives the Rule the same name as the primop itself
    mkBasicRule op_name n_args rule_fn
      = [BuiltinRule { ru_name = occNameFS (nameOccName op_name),
    		   ru_fn = op_name,
    		   ru_nargs = n_args, ru_try = rule_fn }]

    oneLit :: Name -> (Literal -> Maybe CoreExpr)
           -> [CoreRule]
    oneLit op_name test
      = mkBasicRule op_name 1 rule_fn
      where
        rule_fn _ [Lit l1] = test (convFloating l1)
        rule_fn _ _        = Nothing

    twoLits :: Name -> (Literal -> Literal -> Maybe CoreExpr)
    	-> [CoreRule]
    twoLits op_name test
      = mkBasicRule op_name 2 rule_fn
      where
        rule_fn _ [Lit l1, Lit l2] = test (convFloating l1) (convFloating l2)
        rule_fn _ _                = Nothing

    -- When excess precision is not requested, cut down the precision of the
    -- Rational value to that of Float/Double. We confuse host architecture
    -- and target architecture here, but it's convenient (and wrong :-).
    convFloating :: Literal -> Literal
    convFloating (MachFloat  f) | not opt_SimplExcessPrecision =
       MachFloat  (toRational ((fromRational f) :: Float ))
    convFloating (MachDouble d) | not opt_SimplExcessPrecision =
       MachDouble (toRational ((fromRational d) :: Double))
    convFloating l = l

    trueVal, falseVal :: Expr CoreBndr
    trueVal       = Var trueDataConId
    falseVal      = Var falseDataConId
    mkIntVal :: Integer -> Expr CoreBndr
    mkIntVal    i = Lit (mkMachInt  i)
    mkWordVal :: Integer -> Expr CoreBndr
    mkWordVal   w = Lit (mkMachWord w)
    mkFloatVal :: Rational -> Expr CoreBndr
    mkFloatVal  f = Lit (convFloating (MachFloat  f))
    mkDoubleVal :: Rational -> Expr CoreBndr
    mkDoubleVal d = Lit (convFloating (MachDouble d))

\end{code} %************************************************************************ %* * \subsection{Special rules for seq, tagToEnum, dataToTag} %* * %************************************************************************ Note [tagToEnum#] ~~~~~~~~~~~~~~~~~ Nasty check to ensure that tagToEnum# is applied to a type that is an enumeration TyCon. Unification may refine the type later, but this check won't see that, alas. It's crude but it works. Here's are two cases that should fail f :: forall a. a f = tagToEnum# 0 -- Can't do tagToEnum# at a type variable g :: Int g = tagToEnum# 0 -- Int is not an enumeration We used to make this check in the type inference engine, but it's quite ugly to do so, because the delayed constraint solving means that we don't really know what's going on until the end. It's very much a corner case because we don't expect the user to call tagToEnum# at all; we merely generate calls in derived instances of Enum. So we compromise: a rewrite rule rewrites a bad instance of tagToEnum# to an error call, and emits a warning. \begin{code}

    tagToEnumRule :: IdUnfoldingFun -> [Expr CoreBndr] -> Maybe (Expr CoreBndr)
    -- If     data T a = A | B | C
    -- then   tag2Enum# (T ty) 2# -->  B ty
    tagToEnumRule _ [Type ty, Lit (MachInt i)]
      | Just (tycon, tc_args) <- splitTyConApp_maybe ty
      , isEnumerationTyCon tycon
      = case filter correct_tag (tyConDataCons_maybe tycon `orElse` []) of
    	[]	  -> Nothing	-- Abstract type
    	(dc:rest) -> ASSERT( null rest )
    		     Just (mkTyApps (Var (dataConWorkId dc)) tc_args)
      | otherwise 	  -- See Note [tagToEnum#]
      = WARN( True, ptext (sLit "tagToEnum# on non-enumeration type") <+> ppr ty )
        Just (mkRuntimeErrorApp rUNTIME_ERROR_ID ty "tagToEnum# on non-enumeration type")
      where
        correct_tag dc = (dataConTag dc - fIRST_TAG) == tag
        tag = fromInteger i

    tagToEnumRule _ _ = Nothing

\end{code} For dataToTag#, we can reduce if either (a) the argument is a constructor (b) the argument is a variable whose unfolding is a known constructor \begin{code}

    dataToTagRule :: IdUnfoldingFun -> [Expr CoreBndr] -> Maybe (Arg CoreBndr)
    dataToTagRule _ [Type ty1, Var tag_to_enum `App` Type ty2 `App` tag]
      | tag_to_enum `hasKey` tagToEnumKey
      , ty1 `coreEqType` ty2
      = Just tag	-- dataToTag (tagToEnum x)   ==>   x

    dataToTagRule id_unf [_, val_arg]
      | Just (dc,_,_) <- exprIsConApp_maybe id_unf val_arg
      = ASSERT( not (isNewTyCon (dataConTyCon dc)) )
        Just (mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))

    dataToTagRule _ _ = Nothing

\end{code} %************************************************************************ %* * \subsection{Built in rules} %* * %************************************************************************ Note [Scoping for Builtin rules] ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ When compiling a (base-package) module that defines one of the functions mentioned in the RHS of a built-in rule, there's a danger that we'll see f = ...(eq String x).... ....and lower down... eqString = ... Then a rewrite would give f = ...(eqString x)... ....and lower down... eqString = ... and lo, eqString is not in scope. This only really matters when we get to code generation. With -O we do a GlomBinds step that does a new SCC analysis on the whole set of bindings, which sorts out the dependency. Without -O we don't do any rule rewriting so again we are fine. (This whole thing doesn't show up for non-built-in rules because their dependencies are explicit.) \begin{code}

    builtinRules :: [CoreRule]
    -- Rules for non-primops that can't be expressed using a RULE pragma
    builtinRules
      = [ BuiltinRule { ru_name = fsLit "AppendLitString", ru_fn = unpackCStringFoldrName,
    		    ru_nargs = 4, ru_try = match_append_lit },
          BuiltinRule { ru_name = fsLit "EqString", ru_fn = eqStringName,
    		    ru_nargs = 2, ru_try = match_eq_string },
          BuiltinRule { ru_name = fsLit "Inline", ru_fn = inlineIdName,
    		    ru_nargs = 2, ru_try = match_inline }
        ]

    ---------------------------------------------------
    -- The rule is this:
    -- 	unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
    --      =  unpackFoldrCString# "foobaz" c n

    match_append_lit :: IdUnfoldingFun -> [Expr CoreBndr] -> Maybe (Expr CoreBndr)
    match_append_lit _ [Type ty1,
    		    Lit (MachStr s1),
    		    c1,
    		    Var unpk `App` Type ty2
    		  	     `App` Lit (MachStr s2)
    		  	     `App` c2
    		  	     `App` n
    		   ]
      | unpk `hasKey` unpackCStringFoldrIdKey &&
        c1 `cheapEqExpr` c2
      = ASSERT( ty1 `coreEqType` ty2 )
        Just (Var unpk `App` Type ty1
    		   `App` Lit (MachStr (s1 `appendFS` s2))
    		   `App` c1
    		   `App` n)

    match_append_lit _ _ = Nothing

    ---------------------------------------------------
    -- The rule is this:
    -- 	eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2

    match_eq_string :: IdUnfoldingFun -> [Expr CoreBndr] -> Maybe (Expr CoreBndr)
    match_eq_string _ [Var unpk1 `App` Lit (MachStr s1),
    		   Var unpk2 `App` Lit (MachStr s2)]
      | unpk1 `hasKey` unpackCStringIdKey,
        unpk2 `hasKey` unpackCStringIdKey
      = Just (if s1 == s2 then trueVal else falseVal)

    match_eq_string _ _ = Nothing

    ---------------------------------------------------
    -- The rule is this:
    --	inline f_ty (f a b c) = <f's unfolding> a b c
    -- (if f has an unfolding, EVEN if it's a loop breaker)
    --
    -- It's important to allow the argument to 'inline' to have args itself
    -- (a) because its more forgiving to allow the programmer to write
    --	 inline f a b c
    --   or  inline (f a b c)
    -- (b) because a polymorphic f wll get a type argument that the
    --     programmer can't avoid
    --
    -- Also, don't forget about 'inline's type argument!
    match_inline :: IdUnfoldingFun -> [Expr CoreBndr] -> Maybe (Expr CoreBndr)
    match_inline _ (Type _ : e : _)
      | (Var f, args1) <- collectArgs e,
        Just unf <- maybeUnfoldingTemplate (realIdUnfolding f)
        	     -- Ignore the IdUnfoldingFun here!
      = Just (mkApps unf args1)

    match_inline _ _ = Nothing

\end{code}