2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[ConFold]{Constant Folder}
7 check boundaries before folding, e.g. we can fold the Float addition
8 (i1 + i2) only if it results in a valid Float.
11 module ConFold ( tryPrimOp ) where
13 #include "HsVersions.h"
16 import Id ( getIdUnfolding )
17 import Const ( mkMachInt, mkMachWord, Literal(..), Con(..) )
18 import PrimOp ( PrimOp(..) )
20 import TysWiredIn ( trueDataCon, falseDataCon )
21 import TyCon ( tyConDataCons, isEnumerationTyCon, isNewTyCon )
22 import DataCon ( dataConTag, dataConTyCon, fIRST_TAG )
23 import Const ( conOkForAlt )
24 import CoreUnfold ( maybeUnfoldingTemplate )
25 import CoreUtils ( exprIsValue )
26 import Type ( splitTyConApp_maybe )
28 import Maybes ( maybeToBool )
29 import Char ( ord, chr )
34 tryPrimOp :: PrimOp -> [CoreArg] -- op arg1 ... argn
35 -- Args are already simplified
36 -> Maybe CoreExpr -- Nothing => no transformation
37 -- Just e => transforms to e
40 In the parallel world, we use _seq_ to control the order in which
41 certain expressions will be evaluated. Operationally, the expression
42 ``_seq_ a b'' evaluates a and then evaluates b. We have an inlining
43 for _seq_ which translates _seq_ to:
45 _seq_ = /\ a b -> \ x::a y::b -> case seq# x of { 0# -> parError#; _ -> y }
47 Now, we know that the seq# primitive will never return 0#, but we
48 don't let the simplifier know that. We also use a special error
49 value, parError#, which is *not* a bottoming Id, so as far as the
50 simplifier is concerned, we have to evaluate seq# a before we know
51 whether or not y will be evaluated.
53 If we didn't have the extra case, then after inlining the compiler might
55 f p q = case seq# p of { _ -> p+q }
57 If it sees that, it can see that f is strict in q, and hence it might
58 evaluate q before p! The "0# ->" case prevents this happening.
59 By having the parError# branch we make sure that anything in the
60 other branch stays there!
62 This is fine, but we'd like to get rid of the extraneous code. Hence,
63 we *do* let the simplifier know that seq# is strict in its argument.
64 As a result, we hope that `a' will be evaluated before seq# is called.
65 At this point, we have a very special and magical simpification which
66 says that ``seq# a'' can be immediately simplified to `1#' if we
67 know that `a' is already evaluated.
69 NB: If we ever do case-floating, we have an extra worry:
72 a' -> let b' = case seq# a of { True -> b; False -> parError# }
78 a' -> let b' = case True of { True -> b; False -> parError# }
92 The second case must never be floated outside of the first!
95 tryPrimOp SeqOp [Type ty, arg]
97 = Just (Con (Literal (mkMachInt 1)) [])
101 tryPrimOp TagToEnumOp [Type ty, Con (Literal (MachInt i _)) _]
102 | isEnumerationTyCon tycon = Just (Con (DataCon dc) [])
103 | otherwise = panic "tryPrimOp: tagToEnum# on non-enumeration type"
104 where tag = fromInteger i
105 constrs = tyConDataCons tycon
106 (dc:_) = [ dc | dc <- constrs, tag == dataConTag dc - fIRST_TAG ]
107 (Just (tycon,_)) = splitTyConApp_maybe ty
110 For dataToTag#, we can reduce if either
112 (a) the argument is a constructor
113 (b) the argument is a variable whose unfolding is a known constructor
116 tryPrimOp DataToTagOp [Type ty, Con (DataCon dc) _]
117 = Just (Con (Literal (mkMachInt (toInteger (dataConTag dc - fIRST_TAG)))) [])
118 tryPrimOp DataToTagOp [Type ty, Var x]
119 | maybeToBool maybe_constr
120 = ASSERT( not (isNewTyCon (dataConTyCon dc)) )
121 Just (Con (Literal (mkMachInt (toInteger (dataConTag dc - fIRST_TAG)))) [])
123 maybe_constr = case maybeUnfoldingTemplate (getIdUnfolding x) of
124 Just (Con (DataCon dc) _) -> Just dc
126 Just dc = maybe_constr
132 [Con (Literal (MachChar char_lit)) _] -> oneCharLit op char_lit
133 [Con (Literal (MachInt int_lit signed)) _] -> (if signed then oneIntLit else oneWordLit)
135 [Con (Literal (MachFloat float_lit)) _] -> oneFloatLit op float_lit
136 [Con (Literal (MachDouble double_lit)) _] -> oneDoubleLit op double_lit
137 [Con (Literal other_lit) _] -> oneLit op other_lit
139 [Con (Literal (MachChar char_lit1)) _,
140 Con (Literal (MachChar char_lit2)) _] -> twoCharLits op char_lit1 char_lit2
142 [Con (Literal (MachInt int_lit1 True)) _, -- both *signed* literals
143 Con (Literal (MachInt int_lit2 True)) _] -> twoIntLits op int_lit1 int_lit2
145 [Con (Literal (MachInt int_lit1 False)) _, -- both *unsigned* literals
146 Con (Literal (MachInt int_lit2 False)) _] -> twoWordLits op int_lit1 int_lit2
148 [Con (Literal (MachInt int_lit1 False)) _, -- unsigned+signed (shift ops)
149 Con (Literal (MachInt int_lit2 True)) _] -> oneWordOneIntLit op int_lit1 int_lit2
151 [Con (Literal (MachFloat float_lit1)) _,
152 Con (Literal (MachFloat float_lit2)) _] -> twoFloatLits op float_lit1 float_lit2
154 [Con (Literal (MachDouble double_lit1)) _,
155 Con (Literal (MachDouble double_lit2)) _] -> twoDoubleLits op double_lit1 double_lit2
157 [Con (Literal lit) _, Var var] -> litVar op lit var
158 [Var var, Con (Literal lit) _] -> litVar op lit var
164 return_char c = Just (Con (Literal (MachChar c)) [])
165 return_int i = Just (Con (Literal (mkMachInt i)) [])
166 return_word i = Just (Con (Literal (mkMachWord i)) [])
167 return_float f = Just (Con (Literal (MachFloat f)) [])
168 return_double d = Just (Con (Literal (MachDouble d)) [])
169 return_lit lit = Just (Con (Literal lit) [])
171 return_bool True = Just trueVal
172 return_bool False = Just falseVal
174 return_prim_case var lit val_if_eq val_if_neq
175 = Just (Case (Var var) var [(Literal lit, [], val_if_eq),
176 (DEFAULT, [], val_if_neq)])
178 --------- Ints --------------
179 oneIntLit IntNegOp i = return_int (-i)
180 oneIntLit ChrOp i = return_char (chr (fromInteger i))
181 -- SIGH: these two cause trouble in unfoldery
182 -- as we can't distinguish unsigned literals in interfaces (ToDo?)
183 -- oneIntLit Int2WordOp i = ASSERT( i>=0 ) return_word i
184 -- oneIntLit Int2AddrOp i = ASSERT( i>=0 ) return_lit (MachAddr i)
185 oneIntLit Int2FloatOp i = return_float (fromInteger i)
186 oneIntLit Int2DoubleOp i = return_double (fromInteger i)
187 oneIntLit _ _ = {-trace "oneIntLit: giving up"-} give_up
189 oneWordLit Word2IntOp w = {-lazy:ASSERT( w<= maxInt)-} return_int w
190 -- oneWordLit NotOp w = ??? ToDo: sort-of a pain
191 oneWordLit _ _ = {-trace "oneIntLit: giving up"-} give_up
193 twoIntLits IntAddOp i1 i2 = checkRange (i1+i2)
194 twoIntLits IntSubOp i1 i2 = checkRange (i1-i2)
195 twoIntLits IntMulOp i1 i2 = checkRange (i1*i2)
196 twoIntLits IntQuotOp i1 i2 | i2 /= 0 = return_int (i1 `quot` i2)
197 twoIntLits IntRemOp i1 i2 | i2 /= 0 = return_int (i1 `rem` i2)
198 twoIntLits IntGtOp i1 i2 = return_bool (i1 > i2)
199 twoIntLits IntGeOp i1 i2 = return_bool (i1 >= i2)
200 twoIntLits IntEqOp i1 i2 = return_bool (i1 == i2)
201 twoIntLits IntNeOp i1 i2 = return_bool (i1 /= i2)
202 twoIntLits IntLtOp i1 i2 = return_bool (i1 < i2)
203 twoIntLits IntLeOp i1 i2 = return_bool (i1 <= i2)
204 -- ToDo: something for integer-shift ops?
205 twoIntLits _ _ _ = give_up
207 twoWordLits WordGtOp w1 w2 = return_bool (w1 > w2)
208 twoWordLits WordGeOp w1 w2 = return_bool (w1 >= w2)
209 twoWordLits WordEqOp w1 w2 = return_bool (w1 == w2)
210 twoWordLits WordNeOp w1 w2 = return_bool (w1 /= w2)
211 twoWordLits WordLtOp w1 w2 = return_bool (w1 < w2)
212 twoWordLits WordLeOp w1 w2 = return_bool (w1 <= w2)
213 -- ToDo: something for AndOp, OrOp?
214 twoWordLits _ _ _ = give_up
216 -- ToDo: something for shifts
217 oneWordOneIntLit _ _ _ = give_up
219 --------- Floats --------------
220 oneFloatLit FloatNegOp f = return_float (-f)
221 -- hard to do float ops in Rationals ?? (WDP 94/10) ToDo
222 oneFloatLit _ _ = give_up
224 twoFloatLits FloatGtOp f1 f2 = return_bool (f1 > f2)
225 twoFloatLits FloatGeOp f1 f2 = return_bool (f1 >= f2)
226 twoFloatLits FloatEqOp f1 f2 = return_bool (f1 == f2)
227 twoFloatLits FloatNeOp f1 f2 = return_bool (f1 /= f2)
228 twoFloatLits FloatLtOp f1 f2 = return_bool (f1 < f2)
229 twoFloatLits FloatLeOp f1 f2 = return_bool (f1 <= f2)
230 twoFloatLits FloatAddOp f1 f2 = return_float (f1 + f2)
231 twoFloatLits FloatSubOp f1 f2 = return_float (f1 - f2)
232 twoFloatLits FloatMulOp f1 f2 = return_float (f1 * f2)
233 twoFloatLits FloatDivOp f1 f2 | f2 /= 0 = return_float (f1 / f2)
234 twoFloatLits _ _ _ = give_up
236 --------- Doubles --------------
237 oneDoubleLit DoubleNegOp d = return_double (-d)
238 oneDoubleLit _ _ = give_up
240 twoDoubleLits DoubleGtOp d1 d2 = return_bool (d1 > d2)
241 twoDoubleLits DoubleGeOp d1 d2 = return_bool (d1 >= d2)
242 twoDoubleLits DoubleEqOp d1 d2 = return_bool (d1 == d2)
243 twoDoubleLits DoubleNeOp d1 d2 = return_bool (d1 /= d2)
244 twoDoubleLits DoubleLtOp d1 d2 = return_bool (d1 < d2)
245 twoDoubleLits DoubleLeOp d1 d2 = return_bool (d1 <= d2)
246 twoDoubleLits DoubleAddOp d1 d2 = return_double (d1 + d2)
247 twoDoubleLits DoubleSubOp d1 d2 = return_double (d1 - d2)
248 twoDoubleLits DoubleMulOp d1 d2 = return_double (d1 * d2)
249 twoDoubleLits DoubleDivOp d1 d2 | d2 /= 0 = return_double (d1 / d2)
250 twoDoubleLits _ _ _ = give_up
252 --------- Characters --------------
253 oneCharLit OrdOp c = return_int (fromInt (ord c))
254 oneCharLit _ _ = give_up
256 twoCharLits CharGtOp c1 c2 = return_bool (c1 > c2)
257 twoCharLits CharGeOp c1 c2 = return_bool (c1 >= c2)
258 twoCharLits CharEqOp c1 c2 = return_bool (c1 == c2)
259 twoCharLits CharNeOp c1 c2 = return_bool (c1 /= c2)
260 twoCharLits CharLtOp c1 c2 = return_bool (c1 < c2)
261 twoCharLits CharLeOp c1 c2 = return_bool (c1 <= c2)
262 twoCharLits _ _ _ = give_up
264 --------- Miscellaneous --------------
265 oneLit Addr2IntOp (MachAddr i) = return_int (fromInteger i)
266 oneLit op lit = give_up
268 --------- Equality and inequality for Int/Char --------------
276 -- This is a Good Thing, because it allows case-of case things
277 -- to happen, and case-default absorption to happen. For
280 -- if (n ==# 3#) || (n ==# 4#) then e1 else e2
286 -- (modulo the usual precautions to avoid duplicating e1)
288 litVar IntEqOp lit var = return_prim_case var lit trueVal falseVal
289 litVar IntNeOp lit var = return_prim_case var lit falseVal trueVal
290 litVar CharEqOp lit var = return_prim_case var lit trueVal falseVal
291 litVar CharNeOp lit var = return_prim_case var lit falseVal trueVal
292 litVar other_op lit var = give_up
295 checkRange :: Integer -> Maybe CoreExpr
297 | (val > fromInt maxInt) || (val < fromInt minInt) =
298 -- Better tell the user that we've overflowed...
299 pprTrace "Warning:" (text "Integer overflow in expression: " <>
300 ppr ((mkPrimApp op args)::CoreExpr)) $
301 -- ..not that it stops us from actually folding!
302 -- ToDo: a SrcLoc would be nice.
304 | otherwise = return_int val
306 trueVal = Con (DataCon trueDataCon) []
307 falseVal = Con (DataCon falseDataCon) []