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 PrelRules ( primOpRule, builtinRules ) where
13 #include "HsVersions.h"
16 import Rules ( ProtoCoreRule(..) )
17 import Id ( idUnfolding, mkWildId, isDataConId_maybe )
18 import Literal ( Literal(..), isLitLitLit, mkMachInt, mkMachWord
19 , inIntRange, inWordRange, literalType
20 , word2IntLit, int2WordLit, char2IntLit, int2CharLit
21 , float2IntLit, int2FloatLit, double2IntLit, int2DoubleLit
22 , addr2IntLit, int2AddrLit, float2DoubleLit, double2FloatLit
24 import PrimOp ( PrimOp(..), primOpOcc )
25 import TysWiredIn ( trueDataConId, falseDataConId )
26 import TyCon ( tyConDataCons, isEnumerationTyCon, isNewTyCon )
27 import DataCon ( DataCon, dataConTag, dataConRepArity, dataConTyCon, dataConId, fIRST_TAG )
28 import CoreUnfold ( maybeUnfoldingTemplate )
29 import CoreUtils ( exprIsValue, cheapEqExpr, exprIsConApp_maybe )
30 import Type ( splitTyConApp_maybe )
31 import OccName ( occNameUserString)
32 import ThinAir ( unpackCStringFoldrId )
33 import Maybes ( maybeToBool )
34 import Char ( ord, chr )
35 import Bits ( Bits(..) )
36 import PrelAddr ( intToWord, wordToInt )
37 import Word ( Word64 )
44 primOpRule :: PrimOp -> CoreRule
46 = BuiltinRule (primop_rule op)
48 op_name = _PK_ (occNameUserString (primOpOcc op))
49 op_name_case = op_name _APPEND_ SLIT("case")
51 -- ToDo: something for integer-shift ops?
54 primop_rule SeqOp = seqRule
55 primop_rule TagToEnumOp = tagToEnumRule
56 primop_rule DataToTagOp = dataToTagRule
59 primop_rule IntAddOp = twoLits (intOp2 (+) op_name)
60 primop_rule IntSubOp = twoLits (intOp2 (-) op_name)
61 primop_rule IntMulOp = twoLits (intOp2 (*) op_name)
62 primop_rule IntQuotOp = twoLits (intOp2Z quot op_name)
63 primop_rule IntRemOp = twoLits (intOp2Z rem op_name)
64 primop_rule IntNegOp = oneLit (negOp op_name)
67 primop_rule WordQuotOp = twoLits (wordOp2Z quot op_name)
68 primop_rule WordRemOp = twoLits (wordOp2Z rem op_name)
69 primop_rule AndOp = twoLits (wordBitOp2 (.&.) op_name)
70 primop_rule OrOp = twoLits (wordBitOp2 (.|.) op_name)
71 primop_rule XorOp = twoLits (wordBitOp2 xor op_name)
74 primop_rule Word2IntOp = oneLit (litCoerce word2IntLit op_name)
75 primop_rule Int2WordOp = oneLit (litCoerce int2WordLit op_name)
76 primop_rule OrdOp = oneLit (litCoerce char2IntLit op_name)
77 primop_rule ChrOp = oneLit (litCoerce int2CharLit op_name)
78 primop_rule Float2IntOp = oneLit (litCoerce float2IntLit op_name)
79 primop_rule Int2FloatOp = oneLit (litCoerce int2FloatLit op_name)
80 primop_rule Double2IntOp = oneLit (litCoerce double2IntLit op_name)
81 primop_rule Int2DoubleOp = oneLit (litCoerce int2DoubleLit op_name)
82 primop_rule Addr2IntOp = oneLit (litCoerce addr2IntLit op_name)
83 primop_rule Int2AddrOp = oneLit (litCoerce int2AddrLit op_name)
84 -- SUP: Not sure what the standard says about precision in the following 2 cases
85 primop_rule Float2DoubleOp = oneLit (litCoerce float2DoubleLit op_name)
86 primop_rule Double2FloatOp = oneLit (litCoerce double2FloatLit op_name)
89 primop_rule FloatAddOp = twoLits (floatOp2 (+) op_name)
90 primop_rule FloatSubOp = twoLits (floatOp2 (-) op_name)
91 primop_rule FloatMulOp = twoLits (floatOp2 (*) op_name)
92 primop_rule FloatDivOp = twoLits (floatOp2Z (/) op_name)
93 primop_rule FloatNegOp = oneLit (negOp op_name)
96 primop_rule DoubleAddOp = twoLits (doubleOp2 (+) op_name)
97 primop_rule DoubleSubOp = twoLits (doubleOp2 (-) op_name)
98 primop_rule DoubleMulOp = twoLits (doubleOp2 (*) op_name)
99 primop_rule DoubleDivOp = twoLits (doubleOp2Z (/) op_name)
100 primop_rule DoubleNegOp = oneLit (negOp op_name)
102 -- Relational operators
103 primop_rule IntEqOp = relop (==) `or_rule` litEq True op_name_case
104 primop_rule IntNeOp = relop (/=) `or_rule` litEq False op_name_case
105 primop_rule CharEqOp = relop (==) `or_rule` litEq True op_name_case
106 primop_rule CharNeOp = relop (/=) `or_rule` litEq False op_name_case
108 primop_rule IntGtOp = relop (>)
109 primop_rule IntGeOp = relop (>=)
110 primop_rule IntLeOp = relop (<=)
111 primop_rule IntLtOp = relop (<)
113 primop_rule CharGtOp = relop (>)
114 primop_rule CharGeOp = relop (>=)
115 primop_rule CharLeOp = relop (<=)
116 primop_rule CharLtOp = relop (<)
118 primop_rule FloatGtOp = relop (>)
119 primop_rule FloatGeOp = relop (>=)
120 primop_rule FloatLeOp = relop (<=)
121 primop_rule FloatLtOp = relop (<)
122 primop_rule FloatEqOp = relop (==)
123 primop_rule FloatNeOp = relop (/=)
125 primop_rule DoubleGtOp = relop (>)
126 primop_rule DoubleGeOp = relop (>=)
127 primop_rule DoubleLeOp = relop (<=)
128 primop_rule DoubleLtOp = relop (<)
129 primop_rule DoubleEqOp = relop (==)
130 primop_rule DoubleNeOp = relop (/=)
132 primop_rule WordGtOp = relop (>)
133 primop_rule WordGeOp = relop (>=)
134 primop_rule WordLeOp = relop (<=)
135 primop_rule WordLtOp = relop (<)
136 primop_rule WordEqOp = relop (==)
137 primop_rule WordNeOp = relop (/=)
139 primop_rule other = \args -> Nothing
142 relop cmp = twoLits (cmpOp (\ord -> ord `cmp` EQ) op_name)
143 -- Cunning. cmpOp compares the values to give an Ordering.
144 -- It applies its argument to that ordering value to turn
145 -- the ordering into a boolean value. (`cmp` EQ) is just the job.
148 %************************************************************************
150 \subsection{Doing the business}
152 %************************************************************************
156 In all these operations we might find a LitLit as an operand; that's
157 why we have the catch-all Nothing case.
160 --------------------------
161 litCoerce :: (Literal -> Literal) -> RuleName -> Literal -> Maybe (RuleName, CoreExpr)
162 litCoerce fn name lit | isLitLitLit lit = Nothing
163 | otherwise = Just (name, Lit (fn lit))
165 --------------------------
166 cmpOp :: (Ordering -> Bool) -> FAST_STRING -> Literal -> Literal -> Maybe (RuleName, CoreExpr)
170 done res | cmp res = Just (name, trueVal)
171 | otherwise = Just (name, falseVal)
173 -- These compares are at different types
174 go (MachChar i1) (MachChar i2) = done (i1 `compare` i2)
175 go (MachInt i1) (MachInt i2) = done (i1 `compare` i2)
176 go (MachInt64 i1) (MachInt64 i2) = done (i1 `compare` i2)
177 go (MachWord i1) (MachWord i2) = done (i1 `compare` i2)
178 go (MachWord64 i1) (MachWord64 i2) = done (i1 `compare` i2)
179 go (MachFloat i1) (MachFloat i2) = done (i1 `compare` i2)
180 go (MachDouble i1) (MachDouble i2) = done (i1 `compare` i2)
183 --------------------------
185 negOp name (MachFloat f) = Just (name, mkFloatVal (-f))
186 negOp name (MachDouble d) = Just (name, mkDoubleVal (-d))
187 negOp name l@(MachInt i) = intResult name (ppr l) (-i)
188 negOp name l = Nothing
190 --------------------------
191 intOp2 op name l1@(MachInt i1) l2@(MachInt i2)
192 = intResult name (ppr l1 <+> ppr l2) (i1 `op` i2)
193 intOp2 op name l1 l2 = Nothing -- Could find LitLit
195 intOp2Z op name (MachInt i1) (MachInt i2)
196 | i2 /= 0 = Just (name, mkIntVal (i1 `op` i2))
197 intOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
199 --------------------------
200 -- Integer is not an instance of Bits, so we operate on Word64
201 wordBitOp2 op name l1@(MachWord w1) l2@(MachWord w2)
202 = wordResult name (ppr l1 <+> ppr l2)
203 ((fromIntegral::Word64->Integer) (fromIntegral w1 `op` fromIntegral w2))
204 wordBitOp2 op name l1 l2 = Nothing -- Could find LitLit
206 wordOp2Z op name (MachWord w1) (MachWord w2)
207 | w2 /= 0 = Just (name, mkWordVal (w1 `op` w2))
208 wordOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
210 --------------------------
211 floatOp2 op name (MachFloat f1) (MachFloat f2)
212 = Just (name, mkFloatVal (f1 `op` f2))
213 floatOp2 op name l1 l2 = Nothing
215 floatOp2Z op name (MachFloat f1) (MachFloat f2)
216 | f1 /= 0 = Just (name, mkFloatVal (f1 `op` f2))
217 floatOp2Z op name l1 l2 = Nothing
219 --------------------------
220 doubleOp2 op name (MachDouble f1) (MachDouble f2)
221 = Just (name, mkDoubleVal (f1 `op` f2))
222 doubleOp2 op name l1 l2 = Nothing
224 doubleOp2Z op name (MachDouble f1) (MachDouble f2)
225 | f1 /= 0 = Just (name, mkDoubleVal (f1 `op` f2))
226 doubleOp2Z op name l1 l2 = Nothing
229 --------------------------
237 -- This is a Good Thing, because it allows case-of case things
238 -- to happen, and case-default absorption to happen. For
241 -- if (n ==# 3#) || (n ==# 4#) then e1 else e2
247 -- (modulo the usual precautions to avoid duplicating e1)
249 litEq :: Bool -- True <=> equality, False <=> inequality
252 litEq is_eq name [Lit lit, expr] = do_lit_eq is_eq name lit expr
253 litEq is_eq name [expr, Lit lit] = do_lit_eq is_eq name lit expr
254 litEq is_eq name other = Nothing
256 do_lit_eq is_eq name lit expr
257 = Just (name, Case expr (mkWildId (literalType lit))
258 [(LitAlt lit, [], val_if_eq),
259 (DEFAULT, [], val_if_neq)])
261 val_if_eq | is_eq = trueVal
262 | otherwise = falseVal
263 val_if_neq | is_eq = falseVal
264 | otherwise = trueVal
266 -- TODO: Merge intResult/wordResult
267 intResult name pp_args result
268 | not (inIntRange result)
269 -- Better tell the user that we've overflowed...
270 -- ..not that it stops us from actually folding!
272 = pprTrace "Warning:" (text "Integer overflow in:" <+> ppr name <+> pp_args)
273 Just (name, mkIntVal (squashInt result))
276 = Just (name, mkIntVal result)
278 wordResult name pp_args result
279 | not (inWordRange result)
280 -- Better tell the user that we've overflowed...
281 -- ..not that it stops us from actually folding!
283 = pprTrace "Warning:" (text "Word overflow in:" <+> ppr name <+> pp_args)
284 Just (name, mkWordVal (squashInt result))
287 = Just (name, mkWordVal result)
289 squashInt :: Integer -> Integer -- Squash into Int range
290 squashInt i = toInteger ((fromInteger i)::Int)
294 %************************************************************************
296 \subsection{Vaguely generic functions
298 %************************************************************************
301 type RuleFun = [CoreExpr] -> Maybe (RuleName, CoreExpr)
303 or_rule :: RuleFun -> RuleFun -> RuleFun
304 or_rule r1 r2 args = case r1 args of
305 Just stuff -> Just stuff
308 twoLits :: (Literal -> Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
309 twoLits rule [Lit l1, Lit l2] = rule l1 l2
310 twoLits rule other = Nothing
312 oneLit :: (Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
313 oneLit rule [Lit l1] = rule l1
314 oneLit rule other = Nothing
317 trueVal = Var trueDataConId
318 falseVal = Var falseDataConId
319 mkIntVal i = Lit (mkMachInt i)
320 mkWordVal w = Lit (mkMachWord w)
321 mkCharVal c = Lit (MachChar c)
322 mkFloatVal f = Lit (MachFloat f)
323 mkDoubleVal d = Lit (MachDouble d)
327 %************************************************************************
329 \subsection{Special rules for seq, tagToEnum, dataToTag}
331 %************************************************************************
333 In the parallel world, we use _seq_ to control the order in which
334 certain expressions will be evaluated. Operationally, the expression
335 ``_seq_ a b'' evaluates a and then evaluates b. We have an inlining
336 for _seq_ which translates _seq_ to:
338 _seq_ = /\ a b -> \ x::a y::b -> case seq# x of { 0# -> parError#; _ -> y }
340 Now, we know that the seq# primitive will never return 0#, but we
341 don't let the simplifier know that. We also use a special error
342 value, parError#, which is *not* a bottoming Id, so as far as the
343 simplifier is concerned, we have to evaluate seq# a before we know
344 whether or not y will be evaluated.
346 If we didn't have the extra case, then after inlining the compiler might
348 f p q = case seq# p of { _ -> p+q }
350 If it sees that, it can see that f is strict in q, and hence it might
351 evaluate q before p! The "0# ->" case prevents this happening.
352 By having the parError# branch we make sure that anything in the
353 other branch stays there!
355 This is fine, but we'd like to get rid of the extraneous code. Hence,
356 we *do* let the simplifier know that seq# is strict in its argument.
357 As a result, we hope that `a' will be evaluated before seq# is called.
358 At this point, we have a very special and magical simpification which
359 says that ``seq# a'' can be immediately simplified to `1#' if we
360 know that `a' is already evaluated.
362 NB: If we ever do case-floating, we have an extra worry:
365 a' -> let b' = case seq# a of { True -> b; False -> parError# }
371 a' -> let b' = case True of { True -> b; False -> parError# }
385 The second case must never be floated outside of the first!
388 seqRule [Type ty, arg] | exprIsValue arg = Just (SLIT("Seq"), mkIntVal 1)
389 seqRule other = Nothing
394 tagToEnumRule [Type ty, Lit (MachInt i)]
395 = ASSERT( isEnumerationTyCon tycon )
396 Just (SLIT("TagToEnum"), Var (dataConId dc))
399 constrs = tyConDataCons tycon
400 (dc:_) = [ dc | dc <- constrs, tag == dataConTag dc - fIRST_TAG ]
401 (Just (tycon,_)) = splitTyConApp_maybe ty
403 tagToEnumRule other = Nothing
406 For dataToTag#, we can reduce if either
408 (a) the argument is a constructor
409 (b) the argument is a variable whose unfolding is a known constructor
412 dataToTagRule [_, val_arg]
413 = case exprIsConApp_maybe val_arg of
414 Just (dc,_) -> ASSERT( not (isNewTyCon (dataConTyCon dc)) )
415 Just (SLIT("DataToTag"),
416 mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))
420 dataToTagRule other = Nothing
423 %************************************************************************
425 \subsection{Built in rules}
427 %************************************************************************
430 builtinRules :: [ProtoCoreRule]
431 -- Rules for non-primops that can't be expressed using a RULE pragma
433 = [ ProtoCoreRule False unpackCStringFoldrId
434 (BuiltinRule match_append_lit_str)
438 -- unpack "foo" c (unpack "baz" c n) = unpack "foobaz" c n
440 match_append_lit_str [Type ty1,
443 Var unpk `App` Type ty2
444 `App` Lit (MachStr s2)
448 | unpk == unpackCStringFoldrId &&
450 = ASSERT( ty1 == ty2 )
451 Just (SLIT("AppendLitString"),
452 Var unpk `App` Type ty1
453 `App` Lit (MachStr (s1 _APPEND_ s2))
457 match_append_lit_str other = Nothing