2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[Demand]{@Demand@: the amount of demand on a value}
8 Demand(..), Keepity(..),
9 mkSeq, topDmd, lazyDmd, seqDmd, evalDmd, isStrictDmd, defer,
11 DmdType(..), topDmdType, botDmdType, mkDmdType, mkTopDmdType,
12 dmdTypeDepth, dmdTypeRes,
14 DmdResult(..), isBotRes, returnsCPR,
16 StrictSig(..), mkStrictSig, topSig, botSig,
17 splitStrictSig, strictSigResInfo,
18 pprIfaceStrictSig, appIsBottom, isBottomingSig
21 #include "HsVersions.h"
23 import BasicTypes ( Arity )
24 import VarEnv ( VarEnv, emptyVarEnv )
25 import UniqFM ( ufmToList )
30 %************************************************************************
32 \subsection{Demand types}
34 %************************************************************************
37 data DmdType = DmdType
38 DmdEnv -- Demand on explicitly-mentioned
40 [Demand] -- Demand on arguments
41 DmdResult -- Nature of result
43 -- IMPORTANT INVARIANT
44 -- The default demand on free variables not in the DmdEnv is:
45 -- DmdResult = BotRes <=> Bot
46 -- DmdResult = TopRes/ResCPR <=> Abs
48 type DmdEnv = VarEnv Demand
50 data DmdResult = TopRes -- Nothing known
51 | RetCPR -- Returns a constructed product
52 | BotRes -- Diverges or errors
54 -- Equality for fixpoints
55 -- Show needed for Show in Lex.Token (sigh)
57 -- Equality needed for fixpoints in DmdAnal
58 instance Eq DmdType where
59 (==) (DmdType fv1 ds1 res1)
60 (DmdType fv2 ds2 res2) = ufmToList fv1 == ufmToList fv2
61 && ds1 == ds2 && res1 == res2
63 instance Outputable DmdType where
64 ppr (DmdType fv ds res)
65 = hsep [text "DmdType",
66 hcat (map ppr ds) <> ppr res,
67 if null fv_elts then empty
68 else braces (fsep (map pp_elt fv_elts))]
70 pp_elt (uniq, dmd) = ppr uniq <> text "->" <> ppr dmd
71 fv_elts = ufmToList fv
73 instance Outputable DmdResult where
74 ppr TopRes = empty -- Keep these distinct from Demand letters
75 ppr RetCPR = char 'm' -- so that we can print strictness sigs as
76 ppr BotRes = char 'b' -- dddr
79 emptyDmdEnv = emptyVarEnv
80 topDmdType = DmdType emptyDmdEnv [] TopRes
81 botDmdType = DmdType emptyDmdEnv [] BotRes
83 isBotRes :: DmdResult -> Bool
84 isBotRes BotRes = True
85 isBotRes other = False
87 returnsCPR :: DmdResult -> Bool
88 returnsCPR RetCPR = True
89 returnsCPR other = False
91 mkDmdType :: DmdEnv -> [Demand] -> DmdResult -> DmdType
92 mkDmdType fv ds res = DmdType fv ds res
94 mkTopDmdType :: [Demand] -> DmdResult -> DmdType
95 mkTopDmdType ds res = DmdType emptyDmdEnv ds res
97 dmdTypeDepth :: DmdType -> Arity
98 dmdTypeDepth (DmdType _ ds _) = length ds
100 dmdTypeRes :: DmdType -> DmdResult
101 dmdTypeRes (DmdType _ _ res_ty) = res_ty
105 %************************************************************************
107 \subsection{Strictness signature
109 %************************************************************************
111 In a let-bound Id we record its strictness info.
112 In principle, this strictness info is a demand transformer, mapping
113 a demand on the Id into a DmdType, which gives
114 a) the free vars of the Id's value
115 b) the Id's arguments
116 c) an indication of the result of applying
117 the Id to its arguments
119 However, in fact we store in the Id an extremely emascuated demand transfomer,
122 (Nevertheless we dignify StrictSig as a distinct type.)
124 This DmdType gives the demands unleashed by the Id when it is applied
125 to as many arguments as are given in by the arg demands in the DmdType.
127 For example, the demand transformer described by the DmdType
128 DmdType {x -> U(LL)} [V,A] Top
129 says that when the function is applied to two arguments, it
130 unleashes demand U(LL) on the free var x, V on the first arg,
133 If this same function is applied to one arg, all we can say is
134 that it uses x with U*(LL), and its arg with demand L.
137 newtype StrictSig = StrictSig DmdType
140 instance Outputable StrictSig where
141 ppr (StrictSig ty) = ppr ty
143 instance Show StrictSig where
144 show (StrictSig ty) = showSDoc (ppr ty)
146 mkStrictSig :: DmdType -> StrictSig
147 mkStrictSig dmd_ty = StrictSig dmd_ty
149 splitStrictSig :: StrictSig -> ([Demand], DmdResult)
150 splitStrictSig (StrictSig (DmdType _ dmds res)) = (dmds, res)
152 strictSigResInfo :: StrictSig -> DmdResult
153 strictSigResInfo (StrictSig (DmdType _ _ res)) = res
155 topSig = StrictSig topDmdType
156 botSig = StrictSig botDmdType
158 -- appIsBottom returns true if an application to n args would diverge
159 appIsBottom (StrictSig (DmdType _ ds BotRes)) n = n >= length ds
160 appIsBottom _ _ = False
162 isBottomingSig (StrictSig (DmdType _ _ BotRes)) = True
163 isBottomingSig _ = False
165 pprIfaceStrictSig :: StrictSig -> SDoc
166 -- Used for printing top-level strictness pragmas in interface files
167 pprIfaceStrictSig (StrictSig (DmdType _ dmds res))
168 = hcat (map ppr dmds) <> ppr res
172 %************************************************************************
176 %************************************************************************
180 = Lazy -- L; used for unlifted types too, so that
184 | Call Demand -- C(d)
186 | Seq Keepity -- S/U/D(ds)
187 [Demand] -- S(ds) = L `both` U(ds)
188 -- D(ds) = A `lub` U(ds)
189 -- *** Invariant: these demands are never Bot or Abs
190 -- *** Invariant: if all demands are Abs, get []
195 -- Equality needed for fixpoints in DmdAnal
197 data Keepity = Keep | Drop | Defer
200 mkSeq :: Keepity -> [Demand] -> Demand
201 mkSeq k ds | all is_absent ds = Seq k []
202 | otherwise = Seq k ds
207 defer :: Demand -> Demand
208 -- Computes (Abs `lub` d)
209 -- For the Bot case consider
210 -- f x y = if ... then x else error x
211 -- Then for y we get Abs `lub` Bot, and we really
215 defer (Seq Keep ds) = Lazy
216 defer (Seq _ ds) = Seq Defer ds
219 topDmd, lazyDmd, seqDmd :: Demand
220 topDmd = Lazy -- The most uninformative demand
222 seqDmd = Seq Keep [] -- Polymorphic seq demand
225 isStrictDmd :: Demand -> Bool
226 isStrictDmd Bot = True
227 isStrictDmd Err = True
228 isStrictDmd (Seq Drop _) = True -- But not Defer!
229 isStrictDmd (Seq Keep _) = True
230 isStrictDmd Eval = True
231 isStrictDmd (Call _) = True
232 isStrictDmd other = False
234 instance Outputable Demand where
240 ppr (Call d) = char 'C' <> parens (ppr d)
241 ppr (Seq k []) = ppr k
242 ppr (Seq k ds) = ppr k <> parens (hcat (map ppr ds))
244 instance Outputable Keepity where