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
24 , intToInt8Lit, intToInt16Lit, intToInt32Lit
25 , wordToWord8Lit, wordToWord16Lit, wordToWord32Lit
26 , char2IntLit, int2CharLit
27 , float2IntLit, int2FloatLit, double2IntLit, int2DoubleLit
28 , addr2IntLit, int2AddrLit, float2DoubleLit, double2FloatLit
30 import PrimOp ( PrimOp(..), primOpOcc )
31 import TysWiredIn ( trueDataConId, falseDataConId )
32 import TyCon ( tyConDataConsIfAvailable, isEnumerationTyCon, isNewTyCon )
33 import DataCon ( dataConTag, dataConTyCon, dataConId, fIRST_TAG )
34 import CoreUtils ( exprIsValue, cheapEqExpr, exprIsConApp_maybe )
35 import Type ( tyConAppTyCon )
36 import OccName ( occNameUserString)
37 import PrelNames ( unpackCStringFoldrName, unpackCStringFoldrIdKey, hasKey )
39 import Bits ( Bits(..) )
40 #if __GLASGOW_HASKELL__ >= 500
43 import Word ( Word64 )
46 import CmdLineOpts ( opt_SimplExcessPrecision )
51 primOpRule :: PrimOp -> Maybe CoreRule
52 primOpRule op = fmap BuiltinRule (primop_rule op)
54 op_name = _PK_ (occNameUserString (primOpOcc op))
55 op_name_case = op_name _APPEND_ SLIT("->case")
57 -- ToDo: something for integer-shift ops?
60 primop_rule SeqOp = Just seqRule
61 primop_rule TagToEnumOp = Just tagToEnumRule
62 primop_rule DataToTagOp = Just dataToTagRule
65 primop_rule IntAddOp = Just (twoLits (intOp2 (+) op_name))
66 primop_rule IntSubOp = Just (twoLits (intOp2 (-) op_name))
67 primop_rule IntMulOp = Just (twoLits (intOp2 (*) op_name))
68 primop_rule IntQuotOp = Just (twoLits (intOp2Z quot op_name))
69 primop_rule IntRemOp = Just (twoLits (intOp2Z rem op_name))
70 primop_rule IntNegOp = Just (oneLit (negOp op_name))
73 #if __GLASGOW_HASKELL__ >= 500
74 primop_rule WordAddOp = Just (twoLits (wordOp2 (+) op_name))
75 primop_rule WordSubOp = Just (twoLits (wordOp2 (-) op_name))
76 primop_rule WordMulOp = Just (twoLits (wordOp2 (*) op_name))
78 primop_rule WordQuotOp = Just (twoLits (wordOp2Z quot op_name))
79 primop_rule WordRemOp = Just (twoLits (wordOp2Z rem op_name))
80 #if __GLASGOW_HASKELL__ >= 407
81 primop_rule AndOp = Just (twoLits (wordBitOp2 (.&.) op_name))
82 primop_rule OrOp = Just (twoLits (wordBitOp2 (.|.) op_name))
83 primop_rule XorOp = Just (twoLits (wordBitOp2 xor op_name))
87 primop_rule Word2IntOp = Just (oneLit (litCoerce word2IntLit op_name))
88 primop_rule Int2WordOp = Just (oneLit (litCoerce int2WordLit op_name))
89 primop_rule IntToInt8Op = Just (oneLit (litCoerce intToInt8Lit op_name))
90 primop_rule IntToInt16Op = Just (oneLit (litCoerce intToInt16Lit op_name))
91 primop_rule IntToInt32Op = Just (oneLit (litCoerce intToInt32Lit op_name))
92 primop_rule WordToWord8Op = Just (oneLit (litCoerce wordToWord8Lit op_name))
93 primop_rule WordToWord16Op = Just (oneLit (litCoerce wordToWord16Lit op_name))
94 primop_rule WordToWord32Op = Just (oneLit (litCoerce wordToWord32Lit op_name))
95 primop_rule OrdOp = Just (oneLit (litCoerce char2IntLit op_name))
96 primop_rule ChrOp = Just (oneLit (litCoerce int2CharLit op_name))
97 primop_rule Float2IntOp = Just (oneLit (litCoerce float2IntLit op_name))
98 primop_rule Int2FloatOp = Just (oneLit (litCoerce int2FloatLit op_name))
99 primop_rule Double2IntOp = Just (oneLit (litCoerce double2IntLit op_name))
100 primop_rule Int2DoubleOp = Just (oneLit (litCoerce int2DoubleLit op_name))
101 primop_rule Addr2IntOp = Just (oneLit (litCoerce addr2IntLit op_name))
102 primop_rule Int2AddrOp = Just (oneLit (litCoerce int2AddrLit op_name))
103 -- SUP: Not sure what the standard says about precision in the following 2 cases
104 primop_rule Float2DoubleOp = Just (oneLit (litCoerce float2DoubleLit op_name))
105 primop_rule Double2FloatOp = Just (oneLit (litCoerce double2FloatLit op_name))
108 primop_rule FloatAddOp = Just (twoLits (floatOp2 (+) op_name))
109 primop_rule FloatSubOp = Just (twoLits (floatOp2 (-) op_name))
110 primop_rule FloatMulOp = Just (twoLits (floatOp2 (*) op_name))
111 primop_rule FloatDivOp = Just (twoLits (floatOp2Z (/) op_name))
112 primop_rule FloatNegOp = Just (oneLit (negOp op_name))
115 primop_rule DoubleAddOp = Just (twoLits (doubleOp2 (+) op_name))
116 primop_rule DoubleSubOp = Just (twoLits (doubleOp2 (-) op_name))
117 primop_rule DoubleMulOp = Just (twoLits (doubleOp2 (*) op_name))
118 primop_rule DoubleDivOp = Just (twoLits (doubleOp2Z (/) op_name))
119 primop_rule DoubleNegOp = Just (oneLit (negOp op_name))
121 -- Relational operators
122 primop_rule IntEqOp = Just (relop (==) `or_rule` litEq True op_name_case)
123 primop_rule IntNeOp = Just (relop (/=) `or_rule` litEq False op_name_case)
124 primop_rule CharEqOp = Just (relop (==) `or_rule` litEq True op_name_case)
125 primop_rule CharNeOp = Just (relop (/=) `or_rule` litEq False op_name_case)
127 primop_rule IntGtOp = Just (relop (>))
128 primop_rule IntGeOp = Just (relop (>=))
129 primop_rule IntLeOp = Just (relop (<=))
130 primop_rule IntLtOp = Just (relop (<))
132 primop_rule CharGtOp = Just (relop (>))
133 primop_rule CharGeOp = Just (relop (>=))
134 primop_rule CharLeOp = Just (relop (<=))
135 primop_rule CharLtOp = Just (relop (<))
137 primop_rule FloatGtOp = Just (relop (>))
138 primop_rule FloatGeOp = Just (relop (>=))
139 primop_rule FloatLeOp = Just (relop (<=))
140 primop_rule FloatLtOp = Just (relop (<))
141 primop_rule FloatEqOp = Just (relop (==))
142 primop_rule FloatNeOp = Just (relop (/=))
144 primop_rule DoubleGtOp = Just (relop (>))
145 primop_rule DoubleGeOp = Just (relop (>=))
146 primop_rule DoubleLeOp = Just (relop (<=))
147 primop_rule DoubleLtOp = Just (relop (<))
148 primop_rule DoubleEqOp = Just (relop (==))
149 primop_rule DoubleNeOp = Just (relop (/=))
151 primop_rule WordGtOp = Just (relop (>))
152 primop_rule WordGeOp = Just (relop (>=))
153 primop_rule WordLeOp = Just (relop (<=))
154 primop_rule WordLtOp = Just (relop (<))
155 primop_rule WordEqOp = Just (relop (==))
156 primop_rule WordNeOp = Just (relop (/=))
158 primop_rule other = Nothing
161 relop cmp = twoLits (cmpOp (\ord -> ord `cmp` EQ) op_name)
162 -- Cunning. cmpOp compares the values to give an Ordering.
163 -- It applies its argument to that ordering value to turn
164 -- the ordering into a boolean value. (`cmp` EQ) is just the job.
167 %************************************************************************
169 \subsection{Doing the business}
171 %************************************************************************
175 In all these operations we might find a LitLit as an operand; that's
176 why we have the catch-all Nothing case.
179 --------------------------
180 litCoerce :: (Literal -> Literal) -> RuleName -> Literal -> Maybe (RuleName, CoreExpr)
181 litCoerce fn name lit | isLitLitLit lit = Nothing
182 | otherwise = Just (name, Lit (fn lit))
184 --------------------------
185 cmpOp :: (Ordering -> Bool) -> FAST_STRING -> Literal -> Literal -> Maybe (RuleName, CoreExpr)
189 done res | cmp res = Just (name, trueVal)
190 | otherwise = Just (name, falseVal)
192 -- These compares are at different types
193 go (MachChar i1) (MachChar i2) = done (i1 `compare` i2)
194 go (MachInt i1) (MachInt i2) = done (i1 `compare` i2)
195 go (MachInt64 i1) (MachInt64 i2) = done (i1 `compare` i2)
196 go (MachWord i1) (MachWord i2) = done (i1 `compare` i2)
197 go (MachWord64 i1) (MachWord64 i2) = done (i1 `compare` i2)
198 go (MachFloat i1) (MachFloat i2) = done (i1 `compare` i2)
199 go (MachDouble i1) (MachDouble i2) = done (i1 `compare` i2)
202 --------------------------
204 negOp name (MachFloat f) = Just (name, mkFloatVal (-f))
205 negOp name (MachDouble d) = Just (name, mkDoubleVal (-d))
206 negOp name (MachInt i) = intResult name (-i)
207 negOp name l = Nothing
209 --------------------------
210 intOp2 op name (MachInt i1) (MachInt i2)
211 = intResult name (i1 `op` i2)
212 intOp2 op name l1 l2 = Nothing -- Could find LitLit
214 intOp2Z op name (MachInt i1) (MachInt i2)
215 | i2 /= 0 = Just (name, mkIntVal (i1 `op` i2))
216 intOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
218 --------------------------
219 #if __GLASGOW_HASKELL__ >= 500
220 wordOp2 op name (MachWord w1) (MachWord w2)
221 = wordResult name (w1 `op` w2)
222 wordOp2 op name l1 l2 = Nothing -- Could find LitLit
225 wordOp2Z op name (MachWord w1) (MachWord w2)
226 | w2 /= 0 = Just (name, mkWordVal (w1 `op` w2))
227 wordOp2Z op name l1 l2 = Nothing -- LitLit or zero dividend
229 #if __GLASGOW_HASKELL__ >= 500
230 wordBitOp2 op name l1@(MachWord w1) l2@(MachWord w2)
231 = Just (name, mkWordVal (w1 `op` w2))
233 -- Integer is not an instance of Bits, so we operate on Word64
234 wordBitOp2 op name l1@(MachWord w1) l2@(MachWord w2)
235 = Just (name, mkWordVal ((fromIntegral::Word64->Integer) (fromIntegral w1 `op` fromIntegral w2)))
237 wordBitOp2 op name l1 l2 = Nothing -- Could find LitLit
239 --------------------------
240 floatOp2 op name (MachFloat f1) (MachFloat f2)
241 = Just (name, mkFloatVal (f1 `op` f2))
242 floatOp2 op name l1 l2 = Nothing
244 floatOp2Z op name (MachFloat f1) (MachFloat f2)
245 | f2 /= 0 = Just (name, mkFloatVal (f1 `op` f2))
246 floatOp2Z op name l1 l2 = Nothing
248 --------------------------
249 doubleOp2 op name (MachDouble f1) (MachDouble f2)
250 = Just (name, mkDoubleVal (f1 `op` f2))
251 doubleOp2 op name l1 l2 = Nothing
253 doubleOp2Z op name (MachDouble f1) (MachDouble f2)
254 | f2 /= 0 = Just (name, mkDoubleVal (f1 `op` f2))
255 doubleOp2Z op name l1 l2 = Nothing
258 --------------------------
266 -- This is a Good Thing, because it allows case-of case things
267 -- to happen, and case-default absorption to happen. For
270 -- if (n ==# 3#) || (n ==# 4#) then e1 else e2
276 -- (modulo the usual precautions to avoid duplicating e1)
278 litEq :: Bool -- True <=> equality, False <=> inequality
281 litEq is_eq name [Lit lit, expr] = do_lit_eq is_eq name lit expr
282 litEq is_eq name [expr, Lit lit] = do_lit_eq is_eq name lit expr
283 litEq is_eq name other = Nothing
285 do_lit_eq is_eq name lit expr
286 = Just (name, Case expr (mkWildId (literalType lit))
287 [(LitAlt lit, [], val_if_eq),
288 (DEFAULT, [], val_if_neq)])
290 val_if_eq | is_eq = trueVal
291 | otherwise = falseVal
292 val_if_neq | is_eq = falseVal
293 | otherwise = trueVal
295 -- Note that we *don't* warn the user about overflow. It's not done at
296 -- runtime either, and compilation of completely harmless things like
297 -- ((124076834 :: Word32) + (2147483647 :: Word32))
298 -- would yield a warning. Instead we simply squash the value into the
299 -- Int range, but not in a way suitable for cross-compiling... :-(
300 intResult :: RuleName -> Integer -> Maybe (RuleName, CoreExpr)
301 intResult name result
302 = Just (name, mkIntVal (toInteger (fromInteger result :: Int)))
304 #if __GLASGOW_HASKELL__ >= 500
305 wordResult :: RuleName -> Integer -> Maybe (RuleName, CoreExpr)
306 wordResult name result
307 = Just (name, mkWordVal (toInteger (fromInteger result :: Word)))
312 %************************************************************************
314 \subsection{Vaguely generic functions
316 %************************************************************************
319 type RuleFun = [CoreExpr] -> Maybe (RuleName, CoreExpr)
321 or_rule :: RuleFun -> RuleFun -> RuleFun
322 or_rule r1 r2 args = maybe (r2 args) Just (r1 args) -- i.e.: r1 args `mplus` r2 args
324 twoLits :: (Literal -> Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
325 twoLits rule [Lit l1, Lit l2] = rule (convFloating l1) (convFloating l2)
326 twoLits rule _ = Nothing
328 oneLit :: (Literal -> Maybe (RuleName, CoreExpr)) -> RuleFun
329 oneLit rule [Lit l1] = rule (convFloating l1)
330 oneLit rule _ = Nothing
332 -- When excess precision is not requested, cut down the precision of the
333 -- Rational value to that of Float/Double. We confuse host architecture
334 -- and target architecture here, but it's convenient (and wrong :-).
335 convFloating :: Literal -> Literal
336 convFloating (MachFloat f) | not opt_SimplExcessPrecision =
337 MachFloat (toRational ((fromRational f) :: Float ))
338 convFloating (MachDouble d) | not opt_SimplExcessPrecision =
339 MachDouble (toRational ((fromRational d) :: Double))
343 trueVal = Var trueDataConId
344 falseVal = Var falseDataConId
345 mkIntVal i = Lit (mkMachInt i)
346 mkWordVal w = Lit (mkMachWord w)
347 mkFloatVal f = Lit (convFloating (MachFloat f))
348 mkDoubleVal d = Lit (convFloating (MachDouble d))
352 %************************************************************************
354 \subsection{Special rules for seq, tagToEnum, dataToTag}
356 %************************************************************************
358 In the parallel world, we use _seq_ to control the order in which
359 certain expressions will be evaluated. Operationally, the expression
360 ``_seq_ a b'' evaluates a and then evaluates b. We have an inlining
361 for _seq_ which translates _seq_ to:
363 _seq_ = /\ a b -> \ x::a y::b -> case seq# x of { 0# -> parError#; _ -> y }
365 Now, we know that the seq# primitive will never return 0#, but we
366 don't let the simplifier know that. We also use a special error
367 value, parError#, which is *not* a bottoming Id, so as far as the
368 simplifier is concerned, we have to evaluate seq# a before we know
369 whether or not y will be evaluated.
371 If we didn't have the extra case, then after inlining the compiler might
373 f p q = case seq# p of { _ -> p+q }
375 If it sees that, it can see that f is strict in q, and hence it might
376 evaluate q before p! The "0# ->" case prevents this happening.
377 By having the parError# branch we make sure that anything in the
378 other branch stays there!
380 This is fine, but we'd like to get rid of the extraneous code. Hence,
381 we *do* let the simplifier know that seq# is strict in its argument.
382 As a result, we hope that `a' will be evaluated before seq# is called.
383 At this point, we have a very special and magical simpification which
384 says that ``seq# a'' can be immediately simplified to `1#' if we
385 know that `a' is already evaluated.
387 NB: If we ever do case-floating, we have an extra worry:
390 a' -> let b' = case seq# a of { True -> b; False -> parError# }
396 a' -> let b' = case True of { True -> b; False -> parError# }
410 The second case must never be floated outside of the first!
413 seqRule [Type ty, arg] | exprIsValue arg = Just (SLIT("Seq"), mkIntVal 1)
414 seqRule other = Nothing
419 tagToEnumRule [Type ty, Lit (MachInt i)]
420 = ASSERT( isEnumerationTyCon tycon )
421 case filter correct_tag (tyConDataConsIfAvailable tycon) of
424 [] -> Nothing -- Abstract type
425 (dc:rest) -> ASSERT( null rest )
426 Just (SLIT("TagToEnum"), Var (dataConId dc))
428 correct_tag dc = (dataConTag dc - fIRST_TAG) == tag
430 tycon = tyConAppTyCon ty
432 tagToEnumRule other = Nothing
435 For dataToTag#, we can reduce if either
437 (a) the argument is a constructor
438 (b) the argument is a variable whose unfolding is a known constructor
441 dataToTagRule [_, val_arg]
442 = case exprIsConApp_maybe val_arg of
443 Just (dc,_) -> ASSERT( not (isNewTyCon (dataConTyCon dc)) )
444 Just (SLIT("DataToTag"),
445 mkIntVal (toInteger (dataConTag dc - fIRST_TAG)))
449 dataToTagRule other = Nothing
452 %************************************************************************
454 \subsection{Built in rules}
456 %************************************************************************
459 builtinRules :: [(Name, CoreRule)]
460 -- Rules for non-primops that can't be expressed using a RULE pragma
462 = [ (unpackCStringFoldrName, BuiltinRule match_append_lit_str)
467 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n) = unpackFoldrCString# "foobaz" c n
469 match_append_lit_str [Type ty1,
472 Var unpk `App` Type ty2
473 `App` Lit (MachStr s2)
477 | unpk `hasKey` unpackCStringFoldrIdKey &&
479 = ASSERT( ty1 == ty2 )
480 Just (SLIT("AppendLitString"),
481 Var unpk `App` Type ty1
482 `App` Lit (MachStr (s1 _APPEND_ s2))
486 match_append_lit_str other = Nothing