2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[ConFold]{Constant Folder}
6 Conceptually, constant folding should be parameterized with the kind
7 of target machine to get identical behaviour during compilation time
8 and runtime. We cheat a little bit here...
11 check boundaries before folding, e.g. we can fold the Float addition
12 (i1 + i2) only if it results in a valid Float.
15 module PrelRules ( primOpRule, builtinRules ) where
17 #include "HsVersions.h"
20 import Id ( mkWildId )
21 import Literal ( Literal(..), isLitLitLit, mkMachInt, mkMachWord
23 , word2IntLit, int2WordLit, char2IntLit, int2CharLit
24 , float2IntLit, int2FloatLit, double2IntLit, int2DoubleLit
25 , addr2IntLit, int2AddrLit, float2DoubleLit, double2FloatLit
27 import PrimOp ( PrimOp(..), primOpOcc )
28 import TysWiredIn ( trueDataConId, falseDataConId )
29 import TyCon ( tyConDataConsIfAvailable, isEnumerationTyCon, isNewTyCon )
30 import DataCon ( dataConTag, dataConTyCon, dataConId, fIRST_TAG )
31 import CoreUtils ( exprIsValue, cheapEqExpr, exprIsConApp_maybe )
32 import Type ( splitTyConApp_maybe )
33 import OccName ( occNameUserString)
34 import PrelNames ( unpackCStringFoldrName, unpackCStringFoldrIdKey, hasKey )
36 import Bits ( Bits(..) )
37 import Word ( Word64 )
39 import CmdLineOpts ( opt_SimplExcessPrecision )
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 #if __GLASGOW_HASKELL__ >= 407
70 primop_rule AndOp = twoLits (wordBitOp2 (.&.) op_name)
71 primop_rule OrOp = twoLits (wordBitOp2 (.|.) op_name)
72 primop_rule XorOp = twoLits (wordBitOp2 xor op_name)
76 primop_rule Word2IntOp = oneLit (litCoerce word2IntLit op_name)
77 primop_rule Int2WordOp = oneLit (litCoerce int2WordLit op_name)
78 primop_rule OrdOp = oneLit (litCoerce char2IntLit op_name)
79 primop_rule ChrOp = oneLit (litCoerce int2CharLit op_name)
80 primop_rule Float2IntOp = oneLit (litCoerce float2IntLit op_name)
81 primop_rule Int2FloatOp = oneLit (litCoerce int2FloatLit op_name)
82 primop_rule Double2IntOp = oneLit (litCoerce double2IntLit op_name)
83 primop_rule Int2DoubleOp = oneLit (litCoerce int2DoubleLit op_name)
84 primop_rule Addr2IntOp = oneLit (litCoerce addr2IntLit op_name)
85 primop_rule Int2AddrOp = oneLit (litCoerce int2AddrLit op_name)
86 -- SUP: Not sure what the standard says about precision in the following 2 cases
87 primop_rule Float2DoubleOp = oneLit (litCoerce float2DoubleLit op_name)
88 primop_rule Double2FloatOp = oneLit (litCoerce double2FloatLit op_name)
91 primop_rule FloatAddOp = twoLits (floatOp2 (+) op_name)
92 primop_rule FloatSubOp = twoLits (floatOp2 (-) op_name)
93 primop_rule FloatMulOp = twoLits (floatOp2 (*) op_name)
94 primop_rule FloatDivOp = twoLits (floatOp2Z (/) op_name)
95 primop_rule FloatNegOp = oneLit (negOp op_name)
98 primop_rule DoubleAddOp = twoLits (doubleOp2 (+) op_name)
99 primop_rule DoubleSubOp = twoLits (doubleOp2 (-) op_name)
100 primop_rule DoubleMulOp = twoLits (doubleOp2 (*) op_name)
101 primop_rule DoubleDivOp = twoLits (doubleOp2Z (/) op_name)
102 primop_rule DoubleNegOp = oneLit (negOp op_name)
104 -- Relational operators
105 primop_rule IntEqOp = relop (==) `or_rule` litEq True op_name_case
106 primop_rule IntNeOp = relop (/=) `or_rule` litEq False op_name_case
107 primop_rule CharEqOp = relop (==) `or_rule` litEq True op_name_case
108 primop_rule CharNeOp = relop (/=) `or_rule` litEq False op_name_case
110 primop_rule IntGtOp = relop (>)
111 primop_rule IntGeOp = relop (>=)
112 primop_rule IntLeOp = relop (<=)
113 primop_rule IntLtOp = relop (<)
115 primop_rule CharGtOp = relop (>)
116 primop_rule CharGeOp = relop (>=)
117 primop_rule CharLeOp = relop (<=)
118 primop_rule CharLtOp = relop (<)
120 primop_rule FloatGtOp = relop (>)
121 primop_rule FloatGeOp = relop (>=)
122 primop_rule FloatLeOp = relop (<=)
123 primop_rule FloatLtOp = relop (<)
124 primop_rule FloatEqOp = relop (==)
125 primop_rule FloatNeOp = relop (/=)
127 primop_rule DoubleGtOp = relop (>)
128 primop_rule DoubleGeOp = relop (>=)
129 primop_rule DoubleLeOp = relop (<=)
130 primop_rule DoubleLtOp = relop (<)
131 primop_rule DoubleEqOp = relop (==)
132 primop_rule DoubleNeOp = relop (/=)
134 primop_rule WordGtOp = relop (>)
135 primop_rule WordGeOp = relop (>=)
136 primop_rule WordLeOp = relop (<=)
137 primop_rule WordLtOp = relop (<)
138 primop_rule WordEqOp = relop (==)
139 primop_rule WordNeOp = relop (/=)
141 primop_rule other = \args -> Nothing
144 relop cmp = twoLits (cmpOp (\ord -> ord `cmp` EQ) op_name)
145 -- Cunning. cmpOp compares the values to give an Ordering.
146 -- It applies its argument to that ordering value to turn
147 -- the ordering into a boolean value. (`cmp` EQ) is just the job.
150 %************************************************************************
152 \subsection{Doing the business}
154 %************************************************************************
158 In all these operations we might find a LitLit as an operand; that's
159 why we have the catch-all Nothing case.
162 --------------------------
163 litCoerce :: (Literal -> Literal) -> RuleName -> Literal -> Maybe (RuleName, CoreExpr)
164 litCoerce fn name lit | isLitLitLit lit = Nothing
165 | otherwise = Just (name, Lit (fn lit))
167 --------------------------
168 cmpOp :: (Ordering -> Bool) -> FAST_STRING -> Literal -> Literal -> Maybe (RuleName, CoreExpr)
172 done res | cmp res = Just (name, trueVal)
173 | otherwise = Just (name, falseVal)
175 -- These compares are at different types
176 go (MachChar i1) (MachChar i2) = done (i1 `compare` i2)
177 go (MachInt i1) (MachInt i2) = done (i1 `compare` i2)
178 go (MachInt64 i1) (MachInt64 i2) = done (i1 `compare` i2)
179 go (MachWord i1) (MachWord i2) = done (i1 `compare` i2)
180 go (MachWord64 i1) (MachWord64 i2) = done (i1 `compare` i2)
181 go (MachFloat i1) (MachFloat i2) = done (i1 `compare` i2)
182 go (MachDouble i1) (MachDouble i2) = done (i1 `compare` i2)
185 --------------------------
187 negOp name (MachFloat f) = Just (name, mkFloatVal (-f))
188 negOp name (MachDouble d) = Just (name, mkDoubleVal (-d))
189 negOp name l@(MachInt i) = intResult name (-i)
190 negOp name l = Nothing
192 --------------------------
193 intOp2 op name l1@(MachInt i1) l2@(MachInt i2)
194 = intResult name (i1 `op` i2)
195 intOp2 op name l1 l2 = Nothing -- Could find LitLit
197 intOp2Z op name (MachInt i1) (MachInt i2)
198 | i2 /= 0 = Just (name, mkIntVal (i1 `op` i2))
199 intOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
201 --------------------------
202 -- Integer is not an instance of Bits, so we operate on Word64
203 wordBitOp2 op name l1@(MachWord w1) l2@(MachWord w2)
204 = Just (name, mkWordVal ((fromIntegral::Word64->Integer) (fromIntegral w1 `op` fromIntegral w2)))
205 wordBitOp2 op name l1 l2 = Nothing -- Could find LitLit
207 wordOp2Z op name (MachWord w1) (MachWord w2)
208 | w2 /= 0 = Just (name, mkWordVal (w1 `op` w2))
209 wordOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
211 --------------------------
212 floatOp2 op name (MachFloat f1) (MachFloat f2)
213 = Just (name, mkFloatVal (f1 `op` f2))
214 floatOp2 op name l1 l2 = Nothing
216 floatOp2Z op name (MachFloat f1) (MachFloat f2)
217 | f2 /= 0 = Just (name, mkFloatVal (f1 `op` f2))
218 floatOp2Z op name l1 l2 = Nothing
220 --------------------------
221 doubleOp2 op name (MachDouble f1) (MachDouble f2)
222 = Just (name, mkDoubleVal (f1 `op` f2))
223 doubleOp2 op name l1 l2 = Nothing
225 doubleOp2Z op name (MachDouble f1) (MachDouble f2)
226 | f2 /= 0 = Just (name, mkDoubleVal (f1 `op` f2))
227 doubleOp2Z op name l1 l2 = Nothing
230 --------------------------
238 -- This is a Good Thing, because it allows case-of case things
239 -- to happen, and case-default absorption to happen. For
242 -- if (n ==# 3#) || (n ==# 4#) then e1 else e2
248 -- (modulo the usual precautions to avoid duplicating e1)
250 litEq :: Bool -- True <=> equality, False <=> inequality
253 litEq is_eq name [Lit lit, expr] = do_lit_eq is_eq name lit expr
254 litEq is_eq name [expr, Lit lit] = do_lit_eq is_eq name lit expr
255 litEq is_eq name other = Nothing
257 do_lit_eq is_eq name lit expr
258 = Just (name, Case expr (mkWildId (literalType lit))
259 [(LitAlt lit, [], val_if_eq),
260 (DEFAULT, [], val_if_neq)])
262 val_if_eq | is_eq = trueVal
263 | otherwise = falseVal
264 val_if_neq | is_eq = falseVal
265 | otherwise = trueVal
267 -- Note that we *don't* warn the user about overflow. It's not done at
268 -- runtime either, and compilation of completely harmless things like
269 -- ((124076834 :: Word32) + (2147483647 :: Word32))
270 -- would yield a warning. Instead we simply squash the value into the
271 -- Int range, but not in a way suitable for cross-compiling... :-(
272 intResult :: RuleName -> Integer -> Maybe (RuleName, CoreExpr)
273 intResult name result
274 = Just (name, mkIntVal (toInteger ((fromInteger result)::Int)))
278 %************************************************************************
280 \subsection{Vaguely generic functions
282 %************************************************************************
285 type RuleFun = [CoreExpr] -> Maybe (RuleName, CoreExpr)
287 or_rule :: RuleFun -> RuleFun -> RuleFun
288 or_rule r1 r2 args = maybe (r2 args) Just (r1 args) -- i.e.: r1 args `mplus` r2 args
290 twoLits :: (Literal -> Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
291 twoLits rule [Lit l1, Lit l2] = rule (convFloating l1) (convFloating l2)
292 twoLits rule other = Nothing
294 oneLit :: (Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
295 oneLit rule [Lit l1] = rule (convFloating l1)
296 oneLit rule other = Nothing
298 -- When excess precision is not requested, cut down the precision of the
299 -- Rational value to that of Float/Double. We confuse host architecture
300 -- and target architecture here, but it's convenient (and wrong :-).
301 convFloating :: Literal -> Literal
302 convFloating (MachFloat f) | not opt_SimplExcessPrecision =
303 MachFloat (toRational ((fromRational f) :: Float ))
304 convFloating (MachDouble d) | not opt_SimplExcessPrecision =
305 MachDouble (toRational ((fromRational d) :: Double))
309 trueVal = Var trueDataConId
310 falseVal = Var falseDataConId
311 mkIntVal i = Lit (mkMachInt i)
312 mkWordVal w = Lit (mkMachWord w)
313 mkFloatVal f = Lit (convFloating (MachFloat f))
314 mkDoubleVal d = Lit (convFloating (MachDouble d))
318 %************************************************************************
320 \subsection{Special rules for seq, tagToEnum, dataToTag}
322 %************************************************************************
324 In the parallel world, we use _seq_ to control the order in which
325 certain expressions will be evaluated. Operationally, the expression
326 ``_seq_ a b'' evaluates a and then evaluates b. We have an inlining
327 for _seq_ which translates _seq_ to:
329 _seq_ = /\ a b -> \ x::a y::b -> case seq# x of { 0# -> parError#; _ -> y }
331 Now, we know that the seq# primitive will never return 0#, but we
332 don't let the simplifier know that. We also use a special error
333 value, parError#, which is *not* a bottoming Id, so as far as the
334 simplifier is concerned, we have to evaluate seq# a before we know
335 whether or not y will be evaluated.
337 If we didn't have the extra case, then after inlining the compiler might
339 f p q = case seq# p of { _ -> p+q }
341 If it sees that, it can see that f is strict in q, and hence it might
342 evaluate q before p! The "0# ->" case prevents this happening.
343 By having the parError# branch we make sure that anything in the
344 other branch stays there!
346 This is fine, but we'd like to get rid of the extraneous code. Hence,
347 we *do* let the simplifier know that seq# is strict in its argument.
348 As a result, we hope that `a' will be evaluated before seq# is called.
349 At this point, we have a very special and magical simpification which
350 says that ``seq# a'' can be immediately simplified to `1#' if we
351 know that `a' is already evaluated.
353 NB: If we ever do case-floating, we have an extra worry:
356 a' -> let b' = case seq# a of { True -> b; False -> parError# }
362 a' -> let b' = case True of { True -> b; False -> parError# }
376 The second case must never be floated outside of the first!
379 seqRule [Type ty, arg] | exprIsValue arg = Just (SLIT("Seq"), mkIntVal 1)
380 seqRule other = Nothing
385 tagToEnumRule [Type ty, Lit (MachInt i)]
386 = ASSERT( isEnumerationTyCon tycon )
387 case filter correct_tag (tyConDataConsIfAvailable tycon) of
390 [] -> Nothing -- Abstract type
391 (dc:rest) -> ASSERT( null rest )
392 Just (SLIT("TagToEnum"), Var (dataConId dc))
394 correct_tag dc = (dataConTag dc - fIRST_TAG) == tag
396 (Just (tycon,_)) = splitTyConApp_maybe ty
398 tagToEnumRule other = Nothing
401 For dataToTag#, we can reduce if either
403 (a) the argument is a constructor
404 (b) the argument is a variable whose unfolding is a known constructor
407 dataToTagRule [_, val_arg]
408 = case exprIsConApp_maybe val_arg of
409 Just (dc,_) -> ASSERT( not (isNewTyCon (dataConTyCon dc)) )
410 Just (SLIT("DataToTag"),
411 mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))
415 dataToTagRule other = Nothing
418 %************************************************************************
420 \subsection{Built in rules}
422 %************************************************************************
425 builtinRules :: [(Name, CoreRule)]
426 -- Rules for non-primops that can't be expressed using a RULE pragma
428 = [ (unpackCStringFoldrName, BuiltinRule match_append_lit_str)
433 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n) = unpackFoldrCString# "foobaz" c n
435 match_append_lit_str [Type ty1,
438 Var unpk `App` Type ty2
439 `App` Lit (MachStr s2)
443 | unpk `hasKey` unpackCStringFoldrIdKey &&
445 = ASSERT( ty1 == ty2 )
446 Just (SLIT("AppendLitString"),
447 Var unpk `App` Type ty1
448 `App` Lit (MachStr (s1 _APPEND_ s2))
452 match_append_lit_str other = Nothing