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
22 , inIntRange, inWordRange, literalType
23 , word2IntLit, int2WordLit, char2IntLit, int2CharLit
24 , float2IntLit, int2FloatLit, double2IntLit, int2DoubleLit
25 , addr2IntLit, int2AddrLit, float2DoubleLit, double2FloatLit
27 import RdrName ( RdrName )
28 import PrimOp ( PrimOp(..), primOpOcc )
29 import TysWiredIn ( trueDataConId, falseDataConId )
30 import TyCon ( tyConDataConsIfAvailable, isEnumerationTyCon, isNewTyCon )
31 import DataCon ( dataConTag, dataConTyCon, dataConId, fIRST_TAG )
32 import CoreUtils ( exprIsValue, cheapEqExpr, exprIsConApp_maybe )
33 import Type ( splitTyConApp_maybe )
34 import OccName ( occNameUserString)
35 import PrelNames ( unpackCStringFoldr_RDR )
36 import Unique ( unpackCStringFoldrIdKey, hasKey )
37 import Bits ( Bits(..) )
38 import Word ( Word64 )
40 import CmdLineOpts ( opt_SimplExcessPrecision )
45 primOpRule :: PrimOp -> CoreRule
47 = BuiltinRule (primop_rule op)
49 op_name = _PK_ (occNameUserString (primOpOcc op))
50 op_name_case = op_name _APPEND_ SLIT("->case")
52 -- ToDo: something for integer-shift ops?
55 primop_rule SeqOp = seqRule
56 primop_rule TagToEnumOp = tagToEnumRule
57 primop_rule DataToTagOp = dataToTagRule
60 primop_rule IntAddOp = twoLits (intOp2 (+) op_name)
61 primop_rule IntSubOp = twoLits (intOp2 (-) op_name)
62 primop_rule IntMulOp = twoLits (intOp2 (*) op_name)
63 primop_rule IntQuotOp = twoLits (intOp2Z quot op_name)
64 primop_rule IntRemOp = twoLits (intOp2Z rem op_name)
65 primop_rule IntNegOp = oneLit (negOp op_name)
68 primop_rule WordQuotOp = twoLits (wordOp2Z quot op_name)
69 primop_rule WordRemOp = twoLits (wordOp2Z rem op_name)
70 #if __GLASGOW_HASKELL__ >= 407
71 primop_rule AndOp = twoLits (wordBitOp2 (.&.) op_name)
72 primop_rule OrOp = twoLits (wordBitOp2 (.|.) op_name)
73 primop_rule XorOp = twoLits (wordBitOp2 xor op_name)
77 primop_rule Word2IntOp = oneLit (litCoerce word2IntLit op_name)
78 primop_rule Int2WordOp = oneLit (litCoerce int2WordLit op_name)
79 primop_rule OrdOp = oneLit (litCoerce char2IntLit op_name)
80 primop_rule ChrOp = oneLit (litCoerce int2CharLit op_name)
81 primop_rule Float2IntOp = oneLit (litCoerce float2IntLit op_name)
82 primop_rule Int2FloatOp = oneLit (litCoerce int2FloatLit op_name)
83 primop_rule Double2IntOp = oneLit (litCoerce double2IntLit op_name)
84 primop_rule Int2DoubleOp = oneLit (litCoerce int2DoubleLit op_name)
85 primop_rule Addr2IntOp = oneLit (litCoerce addr2IntLit op_name)
86 primop_rule Int2AddrOp = oneLit (litCoerce int2AddrLit op_name)
87 -- SUP: Not sure what the standard says about precision in the following 2 cases
88 primop_rule Float2DoubleOp = oneLit (litCoerce float2DoubleLit op_name)
89 primop_rule Double2FloatOp = oneLit (litCoerce double2FloatLit op_name)
92 primop_rule FloatAddOp = twoLits (floatOp2 (+) op_name)
93 primop_rule FloatSubOp = twoLits (floatOp2 (-) op_name)
94 primop_rule FloatMulOp = twoLits (floatOp2 (*) op_name)
95 primop_rule FloatDivOp = twoLits (floatOp2Z (/) op_name)
96 primop_rule FloatNegOp = oneLit (negOp op_name)
99 primop_rule DoubleAddOp = twoLits (doubleOp2 (+) op_name)
100 primop_rule DoubleSubOp = twoLits (doubleOp2 (-) op_name)
101 primop_rule DoubleMulOp = twoLits (doubleOp2 (*) op_name)
102 primop_rule DoubleDivOp = twoLits (doubleOp2Z (/) op_name)
103 primop_rule DoubleNegOp = oneLit (negOp op_name)
105 -- Relational operators
106 primop_rule IntEqOp = relop (==) `or_rule` litEq True op_name_case
107 primop_rule IntNeOp = relop (/=) `or_rule` litEq False op_name_case
108 primop_rule CharEqOp = relop (==) `or_rule` litEq True op_name_case
109 primop_rule CharNeOp = relop (/=) `or_rule` litEq False op_name_case
111 primop_rule IntGtOp = relop (>)
112 primop_rule IntGeOp = relop (>=)
113 primop_rule IntLeOp = relop (<=)
114 primop_rule IntLtOp = relop (<)
116 primop_rule CharGtOp = relop (>)
117 primop_rule CharGeOp = relop (>=)
118 primop_rule CharLeOp = relop (<=)
119 primop_rule CharLtOp = relop (<)
121 primop_rule FloatGtOp = relop (>)
122 primop_rule FloatGeOp = relop (>=)
123 primop_rule FloatLeOp = relop (<=)
124 primop_rule FloatLtOp = relop (<)
125 primop_rule FloatEqOp = relop (==)
126 primop_rule FloatNeOp = relop (/=)
128 primop_rule DoubleGtOp = relop (>)
129 primop_rule DoubleGeOp = relop (>=)
130 primop_rule DoubleLeOp = relop (<=)
131 primop_rule DoubleLtOp = relop (<)
132 primop_rule DoubleEqOp = relop (==)
133 primop_rule DoubleNeOp = relop (/=)
135 primop_rule WordGtOp = relop (>)
136 primop_rule WordGeOp = relop (>=)
137 primop_rule WordLeOp = relop (<=)
138 primop_rule WordLtOp = relop (<)
139 primop_rule WordEqOp = relop (==)
140 primop_rule WordNeOp = relop (/=)
142 primop_rule other = \args -> Nothing
145 relop cmp = twoLits (cmpOp (\ord -> ord `cmp` EQ) op_name)
146 -- Cunning. cmpOp compares the values to give an Ordering.
147 -- It applies its argument to that ordering value to turn
148 -- the ordering into a boolean value. (`cmp` EQ) is just the job.
151 %************************************************************************
153 \subsection{Doing the business}
155 %************************************************************************
159 In all these operations we might find a LitLit as an operand; that's
160 why we have the catch-all Nothing case.
163 --------------------------
164 litCoerce :: (Literal -> Literal) -> RuleName -> Literal -> Maybe (RuleName, CoreExpr)
165 litCoerce fn name lit | isLitLitLit lit = Nothing
166 | otherwise = Just (name, Lit (fn lit))
168 --------------------------
169 cmpOp :: (Ordering -> Bool) -> FAST_STRING -> Literal -> Literal -> Maybe (RuleName, CoreExpr)
173 done res | cmp res = Just (name, trueVal)
174 | otherwise = Just (name, falseVal)
176 -- These compares are at different types
177 go (MachChar i1) (MachChar i2) = done (i1 `compare` i2)
178 go (MachInt i1) (MachInt i2) = done (i1 `compare` i2)
179 go (MachInt64 i1) (MachInt64 i2) = done (i1 `compare` i2)
180 go (MachWord i1) (MachWord i2) = done (i1 `compare` i2)
181 go (MachWord64 i1) (MachWord64 i2) = done (i1 `compare` i2)
182 go (MachFloat i1) (MachFloat i2) = done (i1 `compare` i2)
183 go (MachDouble i1) (MachDouble i2) = done (i1 `compare` i2)
186 --------------------------
188 negOp name (MachFloat f) = Just (name, mkFloatVal (-f))
189 negOp name (MachDouble d) = Just (name, mkDoubleVal (-d))
190 negOp name l@(MachInt i) = intResult name (-i)
191 negOp name l = Nothing
193 --------------------------
194 intOp2 op name l1@(MachInt i1) l2@(MachInt i2)
195 = intResult name (i1 `op` i2)
196 intOp2 op name l1 l2 = Nothing -- Could find LitLit
198 intOp2Z op name (MachInt i1) (MachInt i2)
199 | i2 /= 0 = Just (name, mkIntVal (i1 `op` i2))
200 intOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
202 --------------------------
203 -- Integer is not an instance of Bits, so we operate on Word64
204 wordBitOp2 op name l1@(MachWord w1) l2@(MachWord w2)
205 = Just (name, mkWordVal ((fromIntegral::Word64->Integer) (fromIntegral w1 `op` fromIntegral w2)))
206 wordBitOp2 op name l1 l2 = Nothing -- Could find LitLit
208 wordOp2Z op name (MachWord w1) (MachWord w2)
209 | w2 /= 0 = Just (name, mkWordVal (w1 `op` w2))
210 wordOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
212 --------------------------
213 floatOp2 op name (MachFloat f1) (MachFloat f2)
214 = Just (name, mkFloatVal (f1 `op` f2))
215 floatOp2 op name l1 l2 = Nothing
217 floatOp2Z op name (MachFloat f1) (MachFloat f2)
218 | f2 /= 0 = Just (name, mkFloatVal (f1 `op` f2))
219 floatOp2Z op name l1 l2 = Nothing
221 --------------------------
222 doubleOp2 op name (MachDouble f1) (MachDouble f2)
223 = Just (name, mkDoubleVal (f1 `op` f2))
224 doubleOp2 op name l1 l2 = Nothing
226 doubleOp2Z op name (MachDouble f1) (MachDouble f2)
227 | f2 /= 0 = Just (name, mkDoubleVal (f1 `op` f2))
228 doubleOp2Z op name l1 l2 = Nothing
231 --------------------------
239 -- This is a Good Thing, because it allows case-of case things
240 -- to happen, and case-default absorption to happen. For
243 -- if (n ==# 3#) || (n ==# 4#) then e1 else e2
249 -- (modulo the usual precautions to avoid duplicating e1)
251 litEq :: Bool -- True <=> equality, False <=> inequality
254 litEq is_eq name [Lit lit, expr] = do_lit_eq is_eq name lit expr
255 litEq is_eq name [expr, Lit lit] = do_lit_eq is_eq name lit expr
256 litEq is_eq name other = Nothing
258 do_lit_eq is_eq name lit expr
259 = Just (name, Case expr (mkWildId (literalType lit))
260 [(LitAlt lit, [], val_if_eq),
261 (DEFAULT, [], val_if_neq)])
263 val_if_eq | is_eq = trueVal
264 | otherwise = falseVal
265 val_if_neq | is_eq = falseVal
266 | otherwise = trueVal
268 -- Note that we *don't* warn the user about overflow. It's not done at
269 -- runtime either, and compilation of completely harmless things like
270 -- ((124076834 :: Word32) + (2147483647 :: Word32))
271 -- would yield a warning. Instead we simply squash the value into the
272 -- Int range, but not in a way suitable for cross-compiling... :-(
273 intResult :: RuleName -> Integer -> Maybe (RuleName, CoreExpr)
274 intResult name result
275 = Just (name, mkIntVal (toInteger ((fromInteger result)::Int)))
279 %************************************************************************
281 \subsection{Vaguely generic functions
283 %************************************************************************
286 type RuleFun = [CoreExpr] -> Maybe (RuleName, CoreExpr)
288 or_rule :: RuleFun -> RuleFun -> RuleFun
289 or_rule r1 r2 args = maybe (r2 args) Just (r1 args) -- i.e.: r1 args `mplus` r2 args
291 twoLits :: (Literal -> Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
292 twoLits rule [Lit l1, Lit l2] = rule (convFloating l1) (convFloating l2)
293 twoLits rule other = Nothing
295 oneLit :: (Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
296 oneLit rule [Lit l1] = rule (convFloating l1)
297 oneLit rule other = Nothing
299 -- When excess precision is not requested, cut down the precision of the
300 -- Rational value to that of Float/Double. We confuse host architecture
301 -- and target architecture here, but it's convenient (and wrong :-).
302 convFloating :: Literal -> Literal
303 convFloating (MachFloat f) | not opt_SimplExcessPrecision =
304 MachFloat (toRational ((fromRational f) :: Float ))
305 convFloating (MachDouble d) | not opt_SimplExcessPrecision =
306 MachDouble (toRational ((fromRational d) :: Double))
310 trueVal = Var trueDataConId
311 falseVal = Var falseDataConId
312 mkIntVal i = Lit (mkMachInt i)
313 mkWordVal w = Lit (mkMachWord w)
314 mkCharVal c = Lit (MachChar c)
315 mkFloatVal f = Lit (convFloating (MachFloat f))
316 mkDoubleVal d = Lit (convFloating (MachDouble d))
320 %************************************************************************
322 \subsection{Special rules for seq, tagToEnum, dataToTag}
324 %************************************************************************
326 In the parallel world, we use _seq_ to control the order in which
327 certain expressions will be evaluated. Operationally, the expression
328 ``_seq_ a b'' evaluates a and then evaluates b. We have an inlining
329 for _seq_ which translates _seq_ to:
331 _seq_ = /\ a b -> \ x::a y::b -> case seq# x of { 0# -> parError#; _ -> y }
333 Now, we know that the seq# primitive will never return 0#, but we
334 don't let the simplifier know that. We also use a special error
335 value, parError#, which is *not* a bottoming Id, so as far as the
336 simplifier is concerned, we have to evaluate seq# a before we know
337 whether or not y will be evaluated.
339 If we didn't have the extra case, then after inlining the compiler might
341 f p q = case seq# p of { _ -> p+q }
343 If it sees that, it can see that f is strict in q, and hence it might
344 evaluate q before p! The "0# ->" case prevents this happening.
345 By having the parError# branch we make sure that anything in the
346 other branch stays there!
348 This is fine, but we'd like to get rid of the extraneous code. Hence,
349 we *do* let the simplifier know that seq# is strict in its argument.
350 As a result, we hope that `a' will be evaluated before seq# is called.
351 At this point, we have a very special and magical simpification which
352 says that ``seq# a'' can be immediately simplified to `1#' if we
353 know that `a' is already evaluated.
355 NB: If we ever do case-floating, we have an extra worry:
358 a' -> let b' = case seq# a of { True -> b; False -> parError# }
364 a' -> let b' = case True of { True -> b; False -> parError# }
378 The second case must never be floated outside of the first!
381 seqRule [Type ty, arg] | exprIsValue arg = Just (SLIT("Seq"), mkIntVal 1)
382 seqRule other = Nothing
387 tagToEnumRule [Type ty, Lit (MachInt i)]
388 = ASSERT( isEnumerationTyCon tycon )
389 case filter correct_tag (tyConDataConsIfAvailable tycon) of
392 [] -> Nothing -- Abstract type
393 (dc:rest) -> ASSERT( null rest )
394 Just (SLIT("TagToEnum"), Var (dataConId dc))
396 correct_tag dc = (dataConTag dc - fIRST_TAG) == tag
398 (Just (tycon,_)) = splitTyConApp_maybe ty
400 tagToEnumRule other = Nothing
403 For dataToTag#, we can reduce if either
405 (a) the argument is a constructor
406 (b) the argument is a variable whose unfolding is a known constructor
409 dataToTagRule [_, val_arg]
410 = case exprIsConApp_maybe val_arg of
411 Just (dc,_) -> ASSERT( not (isNewTyCon (dataConTyCon dc)) )
412 Just (SLIT("DataToTag"),
413 mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))
417 dataToTagRule other = Nothing
420 %************************************************************************
422 \subsection{Built in rules}
424 %************************************************************************
427 builtinRules :: [(RdrName, CoreRule)]
428 -- Rules for non-primops that can't be expressed using a RULE pragma
430 = [ (unpackCStringFoldr_RDR, BuiltinRule match_append_lit_str)
434 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n) = unpackFoldrCString# "foobaz" c n
436 match_append_lit_str [Type ty1,
439 Var unpk `App` Type ty2
440 `App` Lit (MachStr s2)
444 | unpk `hasKey` unpackCStringFoldrIdKey &&
446 = ASSERT( ty1 == ty2 )
447 Just (SLIT("AppendLitString"),
448 Var unpk `App` Type ty1
449 `App` Lit (MachStr (s1 _APPEND_ s2))
453 match_append_lit_str other = Nothing