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 ( cleverMkPrimApp ) 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 )
22 import Char ( ord, chr )
27 cleverMkPrimApp :: PrimOp -> [CoreArg] -> CoreExpr
30 In the parallel world, we use _seq_ to control the order in which
31 certain expressions will be evaluated. Operationally, the expression
32 ``_seq_ a b'' evaluates a and then evaluates b. We have an inlining
33 for _seq_ which translates _seq_ to:
35 _seq_ = /\ a b -> \ x::a y::b -> case seq# x of { 0# -> parError#; _ -> y }
37 Now, we know that the seq# primitive will never return 0#, but we
38 don't let the simplifier know that. We also use a special error
39 value, parError#, which is *not* a bottoming Id, so as far as the
40 simplifier is concerned, we have to evaluate seq# a before we know
41 whether or not y will be evaluated.
43 If we didn't have the extra case, then after inlining the compiler might
45 f p q = case seq# p of { _ -> p+q }
47 If it sees that, it can see that f is strict in q, and hence it might
48 evaluate q before p! The "0# ->" case prevents this happening.
49 By having the parError# branch we make sure that anything in the
50 other branch stays there!
52 This is fine, but we'd like to get rid of the extraneous code. Hence,
53 we *do* let the simplifier know that seq# is strict in its argument.
54 As a result, we hope that `a' will be evaluated before seq# is called.
55 At this point, we have a very special and magical simpification which
56 says that ``seq# a'' can be immediately simplified to `1#' if we
57 know that `a' is already evaluated.
59 NB: If we ever do case-floating, we have an extra worry:
62 a' -> let b' = case seq# a of { True -> b; False -> parError# }
68 a' -> let b' = case True of { True -> b; False -> parError# }
82 The second case must never be floated outside of the first!
85 cleverMkPrimApp SeqOp [Type ty, Con (Literal lit) _]
86 = Con (Literal (mkMachInt 1)) []
88 cleverMkPrimApp SeqOp args@[Type ty, Var var]
89 | isEvaluated (getIdUnfolding var) = Con (Literal (mkMachInt 1)) []) -- var is eval'd
90 | otherwise = Con (PrimOp op) args -- var not eval'd
94 cleverMkPrimApp op args
96 [Con (Literal (MachChar char_lit)) _] -> oneCharLit op char_lit
97 [Con (Literal (MachInt int_lit signed)) _] -> (if signed then oneIntLit else oneWordLit)
99 [Con (Literal (MachFloat float_lit)) _] -> oneFloatLit op float_lit
100 [Con (Literal (MachDouble double_lit)) _] -> oneDoubleLit op double_lit
101 [Con (Literal other_lit) _] -> oneLit op other_lit
103 [Con (Literal (MachChar char_lit1)) _,
104 Con (Literal (MachChar char_lit2)) _] -> twoCharLits op char_lit1 char_lit2
106 [Con (Literal (MachInt int_lit1 True)) _, -- both *signed* literals
107 Con (Literal (MachInt int_lit2 True)) _] -> twoIntLits op int_lit1 int_lit2
109 [Con (Literal (MachInt int_lit1 False)) _, -- both *unsigned* literals
110 Con (Literal (MachInt int_lit2 False)) _] -> twoWordLits op int_lit1 int_lit2
112 [Con (Literal (MachInt int_lit1 False)) _, -- unsigned+signed (shift ops)
113 Con (Literal (MachInt int_lit2 True)) _] -> oneWordOneIntLit op int_lit1 int_lit2
115 [Con (Literal (MachFloat float_lit1)) _,
116 Con (Literal (MachFloat float_lit2)) _] -> twoFloatLits op float_lit1 float_lit2
118 [Con (Literal (MachDouble double_lit1)) _,
119 Con (Literal (MachDouble double_lit2)) _] -> twoDoubleLits op double_lit1 double_lit2
121 [Con (Literal lit) _, Var var] -> litVar op lit var
122 [Var var, Con (Literal lit) _] -> litVar op lit var
126 give_up = Con (PrimOp op) args
128 return_char c = Con (Literal (MachChar c)) []
129 return_int i = Con (Literal (mkMachInt i)) []
130 return_word i = Con (Literal (mkMachWord i)) []
131 return_float f = Con (Literal (MachFloat f)) []
132 return_double d = Con (Literal (MachDouble d)) []
133 return_lit lit = Con (Literal lit) []
135 return_bool True = trueVal
136 return_bool False = falseVal
138 return_prim_case var lit val_if_eq val_if_neq
139 = Case (Var var) var [(Literal lit, [], val_if_eq),
140 (DEFAULT, [], val_if_neq)]
142 --------- Ints --------------
143 oneIntLit IntNegOp i = return_int (-i)
144 oneIntLit ChrOp i = return_char (chr (fromInteger i))
145 -- SIGH: these two cause trouble in unfoldery
146 -- as we can't distinguish unsigned literals in interfaces (ToDo?)
147 -- oneIntLit Int2WordOp i = ASSERT( i>=0 ) return_word i
148 -- oneIntLit Int2AddrOp i = ASSERT( i>=0 ) return_lit (MachAddr i)
149 oneIntLit Int2FloatOp i = return_float (fromInteger i)
150 oneIntLit Int2DoubleOp i = return_double (fromInteger i)
151 oneIntLit _ _ = {-trace "oneIntLit: giving up"-} give_up
153 oneWordLit Word2IntOp w = {-lazy:ASSERT( w<= maxInt)-} return_int w
154 -- oneWordLit NotOp w = ??? ToDo: sort-of a pain
155 oneWordLit _ _ = {-trace "oneIntLit: giving up"-} give_up
157 twoIntLits IntAddOp i1 i2 = checkRange (i1+i2)
158 twoIntLits IntSubOp i1 i2 = checkRange (i1-i2)
159 twoIntLits IntMulOp i1 i2 = checkRange (i1*i2)
160 twoIntLits IntQuotOp i1 i2 | i2 /= 0 = return_int (i1 `quot` i2)
161 twoIntLits IntRemOp i1 i2 | i2 /= 0 = return_int (i1 `rem` i2)
162 twoIntLits IntGtOp i1 i2 = return_bool (i1 > i2)
163 twoIntLits IntGeOp i1 i2 = return_bool (i1 >= i2)
164 twoIntLits IntEqOp i1 i2 = return_bool (i1 == i2)
165 twoIntLits IntNeOp i1 i2 = return_bool (i1 /= i2)
166 twoIntLits IntLtOp i1 i2 = return_bool (i1 < i2)
167 twoIntLits IntLeOp i1 i2 = return_bool (i1 <= i2)
168 -- ToDo: something for integer-shift ops?
169 twoIntLits _ _ _ = give_up
171 twoWordLits WordGtOp w1 w2 = return_bool (w1 > w2)
172 twoWordLits WordGeOp w1 w2 = return_bool (w1 >= w2)
173 twoWordLits WordEqOp w1 w2 = return_bool (w1 == w2)
174 twoWordLits WordNeOp w1 w2 = return_bool (w1 /= w2)
175 twoWordLits WordLtOp w1 w2 = return_bool (w1 < w2)
176 twoWordLits WordLeOp w1 w2 = return_bool (w1 <= w2)
177 -- ToDo: something for AndOp, OrOp?
178 twoWordLits _ _ _ = give_up
180 -- ToDo: something for shifts
181 oneWordOneIntLit _ _ _ = give_up
183 --------- Floats --------------
184 oneFloatLit FloatNegOp f = return_float (-f)
185 -- hard to do float ops in Rationals ?? (WDP 94/10) ToDo
186 oneFloatLit _ _ = give_up
188 twoFloatLits FloatGtOp f1 f2 = return_bool (f1 > f2)
189 twoFloatLits FloatGeOp f1 f2 = return_bool (f1 >= f2)
190 twoFloatLits FloatEqOp f1 f2 = return_bool (f1 == f2)
191 twoFloatLits FloatNeOp f1 f2 = return_bool (f1 /= f2)
192 twoFloatLits FloatLtOp f1 f2 = return_bool (f1 < f2)
193 twoFloatLits FloatLeOp f1 f2 = return_bool (f1 <= f2)
194 twoFloatLits FloatAddOp f1 f2 = return_float (f1 + f2)
195 twoFloatLits FloatSubOp f1 f2 = return_float (f1 - f2)
196 twoFloatLits FloatMulOp f1 f2 = return_float (f1 * f2)
197 twoFloatLits FloatDivOp f1 f2 | f2 /= 0 = return_float (f1 / f2)
198 twoFloatLits _ _ _ = give_up
200 --------- Doubles --------------
201 oneDoubleLit DoubleNegOp d = return_double (-d)
202 oneDoubleLit _ _ = give_up
204 twoDoubleLits DoubleGtOp d1 d2 = return_bool (d1 > d2)
205 twoDoubleLits DoubleGeOp d1 d2 = return_bool (d1 >= d2)
206 twoDoubleLits DoubleEqOp d1 d2 = return_bool (d1 == d2)
207 twoDoubleLits DoubleNeOp d1 d2 = return_bool (d1 /= d2)
208 twoDoubleLits DoubleLtOp d1 d2 = return_bool (d1 < d2)
209 twoDoubleLits DoubleLeOp d1 d2 = return_bool (d1 <= d2)
210 twoDoubleLits DoubleAddOp d1 d2 = return_double (d1 + d2)
211 twoDoubleLits DoubleSubOp d1 d2 = return_double (d1 - d2)
212 twoDoubleLits DoubleMulOp d1 d2 = return_double (d1 * d2)
213 twoDoubleLits DoubleDivOp d1 d2 | d2 /= 0 = return_double (d1 / d2)
214 twoDoubleLits _ _ _ = give_up
216 --------- Characters --------------
217 oneCharLit OrdOp c = return_int (fromInt (ord c))
218 oneCharLit _ _ = give_up
220 twoCharLits CharGtOp c1 c2 = return_bool (c1 > c2)
221 twoCharLits CharGeOp c1 c2 = return_bool (c1 >= c2)
222 twoCharLits CharEqOp c1 c2 = return_bool (c1 == c2)
223 twoCharLits CharNeOp c1 c2 = return_bool (c1 /= c2)
224 twoCharLits CharLtOp c1 c2 = return_bool (c1 < c2)
225 twoCharLits CharLeOp c1 c2 = return_bool (c1 <= c2)
226 twoCharLits _ _ _ = give_up
228 --------- Miscellaneous --------------
229 oneLit Addr2IntOp (MachAddr i) = return_int (fromInteger i)
230 oneLit op lit = give_up
232 --------- Equality and inequality for Int/Char --------------
240 -- This is a Good Thing, because it allows case-of case things
241 -- to happen, and case-default absorption to happen. For
244 -- if (n ==# 3#) || (n ==# 4#) then e1 else e2
250 -- (modulo the usual precautions to avoid duplicating e1)
252 litVar IntEqOp lit var = return_prim_case var lit trueVal falseVal
253 litVar IntNeOp lit var = return_prim_case var lit falseVal trueVal
254 litVar CharEqOp lit var = return_prim_case var lit trueVal falseVal
255 litVar CharNeOp lit var = return_prim_case var lit falseVal trueVal
256 litVar other_op lit var = give_up
259 checkRange :: Integer -> CoreExpr
261 | (val > fromInt maxInt) || (val < fromInt minInt) =
262 -- Better tell the user that we've overflowed...
263 pprTrace "Warning:" (text "Integer overflow in expression: " <>
264 ppr ((mkPrimApp op args)::CoreExpr)) $
265 -- ..not that it stops us from actually folding!
266 -- ToDo: a SrcLoc would be nice.
268 | otherwise = return_int val
270 trueVal = Con (DataCon trueDataCon) []
271 falseVal = Con (DataCon falseDataCon) []