2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[CoreUtils]{Utility functions on @Core@ syntax}
8 coreExprType, coreAltsType,
10 exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
12 exprOkForSpeculation, exprIsBig, hashExpr,
13 exprArity, exprEtaExpandArity,
14 cheapEqExpr, eqExpr, applyTypeToArgs
17 #include "HsVersions.h"
20 import {-# SOURCE #-} CoreUnfold ( isEvaldUnfolding )
22 import GlaExts -- For `xori`
25 import PprCore ( pprCoreExpr )
26 import Var ( IdOrTyVar, isId, isTyVar )
29 import Name ( isLocallyDefined, hashName )
30 import Const ( Con(..), isWHNFCon, conIsTrivial, conIsCheap, conIsDupable,
33 import PrimOp ( primOpOkForSpeculation, primOpStrictness )
34 import Id ( Id, idType, setIdType, idUnique, idAppIsBottom,
35 getIdArity, idName, isPrimitiveId_maybe,
36 getIdSpecialisation, setIdSpecialisation,
37 getInlinePragma, setInlinePragma,
38 getIdUnfolding, setIdUnfolding, idInfo
40 import IdInfo ( arityLowerBound, InlinePragInfo(..), lbvarInfo, LBVarInfo(..) )
41 import Type ( Type, mkFunTy, mkForAllTy,
42 splitFunTy_maybe, tyVarsOfType, tyVarsOfTypes,
43 isNotUsgTy, mkUsgTy, unUsgTy, UsageAnn(..),
44 tidyTyVar, applyTys, isUnLiftedType
46 import Demand ( isPrim, isLazy )
47 import Unique ( buildIdKey, augmentIdKey )
48 import Util ( zipWithEqual, mapAccumL )
50 import TysPrim ( alphaTy ) -- Debugging only
54 %************************************************************************
56 \subsection{Find the type of a Core atom/expression}
58 %************************************************************************
61 coreExprType :: CoreExpr -> Type
63 coreExprType (Var var) = idType var
64 coreExprType (Let _ body) = coreExprType body
65 coreExprType (Case _ _ alts) = coreAltsType alts
66 coreExprType (Note (Coerce ty _) e) = ty -- **! should take usage from e
67 coreExprType (Note (TermUsg u) e) = mkUsgTy u (unUsgTy (coreExprType e))
68 coreExprType (Note other_note e) = coreExprType e
69 coreExprType e@(Con con args) = ASSERT2( all (\ a -> case a of { Type ty -> isNotUsgTy ty; _ -> True }) args, ppr e)
70 applyTypeToArgs e (conType con) args
72 coreExprType (Lam binder expr)
73 | isId binder = (case (lbvarInfo . idInfo) binder of
74 IsOneShotLambda -> mkUsgTy UsOnce
76 idType binder `mkFunTy` coreExprType expr
77 | isTyVar binder = mkForAllTy binder (coreExprType expr)
79 coreExprType e@(App _ _)
80 = case collectArgs e of
81 (fun, args) -> applyTypeToArgs e (coreExprType fun) args
83 coreExprType other = pprTrace "coreExprType" (pprCoreExpr other) alphaTy
85 coreAltsType :: [CoreAlt] -> Type
86 coreAltsType ((_,_,rhs) : _) = coreExprType rhs
90 -- The first argument is just for debugging
91 applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
92 applyTypeToArgs e op_ty [] = op_ty
94 applyTypeToArgs e op_ty (Type ty : args)
95 = -- Accumulate type arguments so we can instantiate all at once
96 ASSERT2( all isNotUsgTy tys, ppr e <+> text "of" <+> ppr op_ty <+> text "to" <+> ppr (Type ty : args) <+> text "i.e." <+> ppr tys )
97 applyTypeToArgs e (applyTys op_ty tys) rest_args
99 (tys, rest_args) = go [ty] args
100 go tys (Type ty : args) = go (ty:tys) args
101 go tys rest_args = (reverse tys, rest_args)
103 applyTypeToArgs e op_ty (other_arg : args)
104 = case (splitFunTy_maybe op_ty) of
105 Just (_, res_ty) -> applyTypeToArgs e res_ty args
106 Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e)
109 %************************************************************************
111 \subsection{Figuring out things about expressions}
113 %************************************************************************
115 @exprIsTrivial@ is true of expressions we are unconditionally
116 happy to duplicate; simple variables and constants,
117 and type applications.
119 @exprIsBottom@ is true of expressions that are guaranteed to diverge
123 exprIsTrivial (Type _) = True
124 exprIsTrivial (Var v) = True
125 exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
126 exprIsTrivial (Note _ e) = exprIsTrivial e
127 exprIsTrivial (Con con args) = conIsTrivial con && all isTypeArg args
128 exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
129 exprIsTrivial other = False
133 @exprIsDupable@ is true of expressions that can be duplicated at a modest
134 cost in code size. This will only happen in different case
135 branches, so there's no issue about duplicating work.
137 That is, exprIsDupable returns True of (f x) even if
138 f is very very expensive to call.
140 Its only purpose is to avoid fruitless let-binding
141 and then inlining of case join points
145 exprIsDupable (Type _) = True
146 exprIsDupable (Con con args) = conIsDupable con &&
147 all exprIsDupable args &&
148 valArgCount args <= dupAppSize
150 exprIsDupable (Note _ e) = exprIsDupable e
151 exprIsDupable expr = case collectArgs expr of
152 (Var f, args) -> all exprIsDupable args && valArgCount args <= dupAppSize
156 dupAppSize = 4 -- Size of application we are prepared to duplicate
159 @exprIsCheap@ looks at a Core expression and returns \tr{True} if
160 it is obviously in weak head normal form, or is cheap to get to WHNF.
161 [Note that that's not the same as exprIsDupable; an expression might be
162 big, and hence not dupable, but still cheap.]
164 By ``cheap'' we mean a computation we're willing to:
165 push inside a lambda, or
166 inline at more than one place
167 That might mean it gets evaluated more than once, instead of being
168 shared. The main examples of things which aren't WHNF but are
174 where e, and all the ei are cheap; and
179 where e and b are cheap; and
183 where op is a cheap primitive operator
187 Notice that a variable is considered 'cheap': we can push it inside a lambda,
188 because sharing will make sure it is only evaluated once.
191 exprIsCheap :: CoreExpr -> Bool
192 exprIsCheap (Type _) = True
193 exprIsCheap (Var _) = True
194 exprIsCheap (Con con args) = conIsCheap con && all exprIsCheap args
195 exprIsCheap (Note _ e) = exprIsCheap e
196 exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e
197 exprIsCheap other_expr -- look for manifest partial application
198 = case collectArgs other_expr of
199 (f, args) -> isPap f (valArgCount args) && all exprIsCheap args
203 isPap :: CoreExpr -- Function
204 -> Int -- Number of value args
206 isPap (Var f) n_val_args
207 = idAppIsBottom f n_val_args
208 -- Application of a function which
209 -- always gives bottom; we treat this as
210 -- a WHNF, because it certainly doesn't
211 -- need to be shared!
213 || n_val_args == 0 -- Just a type application of
214 -- a variable (f t1 t2 t3)
217 || n_val_args < arityLowerBound (getIdArity f)
219 isPap fun n_val_args = False
222 exprOkForSpeculation returns True of an expression that it is
224 * safe to evaluate even if normal order eval might not
225 evaluate the expression at all, or
227 * safe *not* to evaluate even if normal order would do so
231 the expression guarantees to terminate,
233 without raising an exception,
234 without causing a side effect (e.g. writing a mutable variable)
237 let x = case y# +# 1# of { r# -> I# r# }
240 case y# +# 1# of { r# ->
245 We can only do this if the (y+1) is ok for speculation: it has no
246 side effects, and can't diverge or raise an exception.
249 exprOkForSpeculation :: CoreExpr -> Bool
250 exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
251 exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
253 exprOkForSpeculation (Con (Literal _) args) = True
254 exprOkForSpeculation (Con (DataCon _) args) = True
255 -- The strictness of the constructor has already
256 -- been expressed by its "wrapper", so we don't need
257 -- to take the arguments into account
259 exprOkForSpeculation (Con (PrimOp op) args)
260 = prim_op_ok_for_spec op args
262 exprOkForSpeculation (App fun arg) -- Might be application of a primop
265 go (App fun arg) args = go fun (arg:args)
266 go (Var v) args = case isPrimitiveId_maybe v of
267 Just op -> prim_op_ok_for_spec op args
269 go other args = False
271 exprOkForSpeculation other = False -- Conservative
273 prim_op_ok_for_spec op args
274 = primOpOkForSpeculation op &&
275 and (zipWith ok (filter isValArg args) (fst (primOpStrictness op)))
277 ok arg demand | isLazy demand = True
278 | otherwise = exprOkForSpeculation arg
283 exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
284 exprIsBottom e = go 0 e
286 -- n is the number of args
287 go n (Note _ e) = go n e
288 go n (Let _ e) = go n e
289 go n (Case e _ _) = go 0 e -- Just check the scrut
290 go n (App e _) = go (n+1) e
291 go n (Var v) = idAppIsBottom v n
292 go n (Con _ _) = False
293 go n (Lam _ _) = False
296 @exprIsValue@ returns true for expressions that are certainly *already*
297 evaluated to WHNF. This is used to decide wether it's ok to change
298 case x of _ -> e ===> e
300 and to decide whether it's safe to discard a `seq`
302 So, it does *not* treat variables as evaluated, unless they say they are
305 exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
306 exprIsValue (Type ty) = True -- Types are honorary Values; we don't mind
308 exprIsValue (Var v) = isEvaldUnfolding (getIdUnfolding v)
309 exprIsValue (Lam b e) = isId b || exprIsValue e
310 exprIsValue (Note _ e) = exprIsValue e
311 exprIsValue (Let _ e) = False
312 exprIsValue (Case _ _ _) = False
313 exprIsValue (Con con _) = isWHNFCon con
314 exprIsValue e@(App _ _) = case collectArgs e of
315 (Var v, args) -> fun_arity > valArgCount args
317 fun_arity = arityLowerBound (getIdArity v)
322 exprArity :: CoreExpr -> Int -- How many value lambdas are at the top
323 exprArity (Lam b e) | isTyVar b = exprArity e
324 | otherwise = 1 + exprArity e
326 exprArity (Note note e) | ok_note note = exprArity e
328 ok_note (Coerce _ _) = True
329 -- We *do* look through coerces when getting arities.
330 -- Reason: arities are to do with *representation* and
332 ok_note InlineMe = True
333 ok_note InlineCall = True
334 ok_note other = False
335 -- SCC and TermUsg might be over-conservative?
342 exprEtaExpandArity :: CoreExpr -> Int -- The number of args the thing can be applied to
343 -- without doing much work
344 -- This is used when eta expanding
345 -- e ==> \xy -> e x y
347 -- It returns 1 (or more) to:
348 -- case x of p -> \s -> ...
349 -- because for I/O ish things we really want to get that \s to the top.
350 -- We are prepared to evaluate x each time round the loop in order to get that
351 -- Hence "generous" arity
353 exprEtaExpandArity (Var v) = arityLowerBound (getIdArity v)
354 exprEtaExpandArity (Lam x e)
355 | isId x = 1 + exprEtaExpandArity e
356 | otherwise = exprEtaExpandArity e
357 exprEtaExpandArity (Let bind body)
358 | all exprIsCheap (rhssOfBind bind) = exprEtaExpandArity body
359 exprEtaExpandArity (Case scrut _ alts)
360 | exprIsCheap scrut = min_zero [exprEtaExpandArity rhs | (_,_,rhs) <- alts]
362 exprEtaExpandArity (Note note e)
363 | ok_note note = exprEtaExpandArity e
365 ok_note (Coerce _ _) = True
366 ok_note InlineCall = True
367 ok_note other = False
368 -- Notice that we do not look through __inline_me__
369 -- This one is a bit more surprising, but consider
370 -- f = _inline_me (\x -> e)
371 -- We DO NOT want to eta expand this to
372 -- f = \x -> (_inline_me (\x -> e)) x
373 -- because the _inline_me gets dropped now it is applied,
378 exprEtaExpandArity other = 0 -- Could do better for applications
380 min_zero :: [Int] -> Int -- Find the minimum, but zero is the smallest
381 min_zero (x:xs) = go x xs
383 go 0 xs = 0 -- Nothing beats zero
385 go min (x:xs) | x < min = go x xs
386 | otherwise = go min xs
391 %************************************************************************
393 \subsection{Equality}
395 %************************************************************************
397 @cheapEqExpr@ is a cheap equality test which bales out fast!
398 True => definitely equal
399 False => may or may not be equal
402 cheapEqExpr :: Expr b -> Expr b -> Bool
404 cheapEqExpr (Var v1) (Var v2) = v1==v2
405 cheapEqExpr (Con con1 args1) (Con con2 args2)
407 and (zipWithEqual "cheapEqExpr" cheapEqExpr args1 args2)
409 cheapEqExpr (App f1 a1) (App f2 a2)
410 = f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
412 cheapEqExpr (Type t1) (Type t2) = t1 == t2
414 cheapEqExpr _ _ = False
416 exprIsBig :: Expr b -> Bool
417 -- Returns True of expressions that are too big to be compared by cheapEqExpr
418 exprIsBig (Var v) = False
419 exprIsBig (Type t) = False
420 exprIsBig (App f a) = exprIsBig f || exprIsBig a
421 exprIsBig (Con _ args) = any exprIsBig args
422 exprIsBig other = True
427 eqExpr :: CoreExpr -> CoreExpr -> Bool
428 -- Works ok at more general type, but only needed at CoreExpr
430 = eq emptyVarEnv e1 e2
432 -- The "env" maps variables in e1 to variables in ty2
433 -- So when comparing lambdas etc,
434 -- we in effect substitute v2 for v1 in e1 before continuing
435 eq env (Var v1) (Var v2) = case lookupVarEnv env v1 of
436 Just v1' -> v1' == v2
439 eq env (Con c1 es1) (Con c2 es2) = c1 == c2 && eq_list env es1 es2
440 eq env (App f1 a1) (App f2 a2) = eq env f1 f2 && eq env a1 a2
441 eq env (Lam v1 e1) (Lam v2 e2) = eq (extendVarEnv env v1 v2) e1 e2
442 eq env (Let (NonRec v1 r1) e1)
443 (Let (NonRec v2 r2) e2) = eq env r1 r2 && eq (extendVarEnv env v1 v2) e1 e2
444 eq env (Let (Rec ps1) e1)
445 (Let (Rec ps2) e2) = length ps1 == length ps2 &&
446 and (zipWith eq_rhs ps1 ps2) &&
449 env' = extendVarEnvList env [(v1,v2) | ((v1,_),(v2,_)) <- zip ps1 ps2]
450 eq_rhs (_,r1) (_,r2) = eq env' r1 r2
451 eq env (Case e1 v1 a1)
452 (Case e2 v2 a2) = eq env e1 e2 &&
453 length a1 == length a2 &&
454 and (zipWith (eq_alt env') a1 a2)
456 env' = extendVarEnv env v1 v2
458 eq env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && eq env e1 e2
459 eq env (Type t1) (Type t2) = t1 == t2
462 eq_list env [] [] = True
463 eq_list env (e1:es1) (e2:es2) = eq env e1 e2 && eq_list env es1 es2
464 eq_list env es1 es2 = False
466 eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 &&
467 eq (extendVarEnvList env (vs1 `zip` vs2)) r1 r2
469 eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
470 eq_note env (Coerce t1 f1) (Coerce t2 f2) = t1==t2 && f1==f2
471 eq_note env InlineCall InlineCall = True
472 eq_note env other1 other2 = False
475 %************************************************************************
479 %************************************************************************
482 hashExpr :: CoreExpr -> Int
483 hashExpr e = abs (hash_expr e)
484 -- Negative numbers kill UniqFM
486 hash_expr (Note _ e) = hash_expr e
487 hash_expr (Let (NonRec b r) e) = hashId b
488 hash_expr (Let (Rec ((b,r):_)) e) = hashId b
489 hash_expr (Case _ b _) = hashId b
490 hash_expr (App f e) = hash_expr f + fast_hash_expr e
491 hash_expr (Var v) = hashId v
492 hash_expr (Con con args) = foldr ((+) . fast_hash_expr) (hashCon con) args
493 hash_expr (Lam b _) = hashId b
494 hash_expr (Type t) = trace "hash_expr: type" 0 -- Shouldn't happen
496 fast_hash_expr (Var v) = hashId v
497 fast_hash_expr (Con con args) = fast_hash_args args con
498 fast_hash_expr (App f (Type _)) = fast_hash_expr f
499 fast_hash_expr (App f a) = fast_hash_expr a
500 fast_hash_expr (Lam b _) = hashId b
501 fast_hash_expr other = 0
503 fast_hash_args [] con = hashCon con
504 fast_hash_args (Type t : args) con = fast_hash_args args con
505 fast_hash_args (arg : args) con = fast_hash_expr arg
508 hashId id = hashName (idName id)