2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[SpecConstr]{Specialise over constructors}
7 -- The above warning supression flag is a temporary kludge.
8 -- While working on this module you are encouraged to remove it and fix
9 -- any warnings in the module. See
10 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
17 #include "HsVersions.h"
22 import CoreUnfold ( couldBeSmallEnoughToInline )
23 import CoreLint ( showPass, endPass )
24 import CoreFVs ( exprsFreeVars )
25 import WwLib ( mkWorkerArgs )
26 import DataCon ( dataConRepArity, dataConUnivTyVars )
29 import Type hiding( substTy )
35 import OccName ( mkSpecOcc )
36 import ErrUtils ( dumpIfSet_dyn )
37 import DynFlags ( DynFlags(..), DynFlag(..) )
38 import StaticFlags ( opt_PprStyle_Debug )
39 import StaticFlags ( opt_SpecInlineJoinPoints )
40 import BasicTypes ( Activation(..) )
41 import Maybes ( orElse, catMaybes, isJust, isNothing )
43 import List ( nubBy, partition )
49 import Control.Monad ( zipWithM )
52 -----------------------------------------------------
54 -----------------------------------------------------
59 drop n (x:xs) = drop (n-1) xs
61 After the first time round, we could pass n unboxed. This happens in
62 numerical code too. Here's what it looks like in Core:
64 drop n xs = case xs of
69 _ -> drop (I# (n# -# 1#)) xs
71 Notice that the recursive call has an explicit constructor as argument.
72 Noticing this, we can make a specialised version of drop
74 RULE: drop (I# n#) xs ==> drop' n# xs
76 drop' n# xs = let n = I# n# in ...orig RHS...
78 Now the simplifier will apply the specialisation in the rhs of drop', giving
80 drop' n# xs = case xs of
84 _ -> drop (n# -# 1#) xs
88 We'd also like to catch cases where a parameter is carried along unchanged,
89 but evaluated each time round the loop:
91 f i n = if i>0 || i>n then i else f (i*2) n
93 Here f isn't strict in n, but we'd like to avoid evaluating it each iteration.
94 In Core, by the time we've w/wd (f is strict in i) we get
96 f i# n = case i# ># 0 of
98 True -> case n of n' { I# n# ->
101 True -> f (i# *# 2#) n'
103 At the call to f, we see that the argument, n is know to be (I# n#),
104 and n is evaluated elsewhere in the body of f, so we can play the same
110 We must be careful not to allocate the same constructor twice. Consider
111 f p = (...(case p of (a,b) -> e)...p...,
112 ...let t = (r,s) in ...t...(f t)...)
113 At the recursive call to f, we can see that t is a pair. But we do NOT want
114 to make a specialised copy:
115 f' a b = let p = (a,b) in (..., ...)
116 because now t is allocated by the caller, then r and s are passed to the
117 recursive call, which allocates the (r,s) pair again.
120 (a) the argument p is used in other than a case-scrutinsation way.
121 (b) the argument to the call is not a 'fresh' tuple; you have to
122 look into its unfolding to see that it's a tuple
124 Hence the "OR" part of Note [Good arguments] below.
126 ALTERNATIVE 2: pass both boxed and unboxed versions. This no longer saves
127 allocation, but does perhaps save evals. In the RULE we'd have
130 f (I# x#) = f' (I# x#) x#
132 If at the call site the (I# x) was an unfolding, then we'd have to
133 rely on CSE to eliminate the duplicate allocation.... This alternative
134 doesn't look attractive enough to pursue.
136 ALTERNATIVE 3: ignore the reboxing problem. The trouble is that
137 the conservative reboxing story prevents many useful functions from being
138 specialised. Example:
139 foo :: Maybe Int -> Int -> Int
141 foo x@(Just m) n = foo x (n-m)
142 Here the use of 'x' will clearly not require boxing in the specialised function.
144 The strictness analyser has the same problem, in fact. Example:
146 If we pass just 'a' and 'b' to the worker, it might need to rebox the
147 pair to create (a,b). A more sophisticated analysis might figure out
148 precisely the cases in which this could happen, but the strictness
149 analyser does no such analysis; it just passes 'a' and 'b', and hopes
152 So my current choice is to make SpecConstr similarly aggressive, and
153 ignore the bad potential of reboxing.
156 Note [Good arguments]
157 ~~~~~~~~~~~~~~~~~~~~~
160 * A self-recursive function. Ignore mutual recursion for now,
161 because it's less common, and the code is simpler for self-recursion.
165 a) At a recursive call, one or more parameters is an explicit
166 constructor application
168 That same parameter is scrutinised by a case somewhere in
169 the RHS of the function
173 b) At a recursive call, one or more parameters has an unfolding
174 that is an explicit constructor application
176 That same parameter is scrutinised by a case somewhere in
177 the RHS of the function
179 Those are the only uses of the parameter (see Note [Reboxing])
182 What to abstract over
183 ~~~~~~~~~~~~~~~~~~~~~
184 There's a bit of a complication with type arguments. If the call
187 f p = ...f ((:) [a] x xs)...
189 then our specialised function look like
191 f_spec x xs = let p = (:) [a] x xs in ....as before....
193 This only makes sense if either
194 a) the type variable 'a' is in scope at the top of f, or
195 b) the type variable 'a' is an argument to f (and hence fs)
197 Actually, (a) may hold for value arguments too, in which case
198 we may not want to pass them. Supose 'x' is in scope at f's
199 defn, but xs is not. Then we'd like
201 f_spec xs = let p = (:) [a] x xs in ....as before....
203 Similarly (b) may hold too. If x is already an argument at the
204 call, no need to pass it again.
206 Finally, if 'a' is not in scope at the call site, we could abstract
207 it as we do the term variables:
209 f_spec a x xs = let p = (:) [a] x xs in ...as before...
211 So the grand plan is:
213 * abstract the call site to a constructor-only pattern
214 e.g. C x (D (f p) (g q)) ==> C s1 (D s2 s3)
216 * Find the free variables of the abstracted pattern
218 * Pass these variables, less any that are in scope at
219 the fn defn. But see Note [Shadowing] below.
222 NOTICE that we only abstract over variables that are not in scope,
223 so we're in no danger of shadowing variables used in "higher up"
229 In this pass we gather up usage information that may mention variables
230 that are bound between the usage site and the definition site; or (more
231 seriously) may be bound to something different at the definition site.
234 f x = letrec g y v = let x = ...
237 Since 'x' is in scope at the call site, we may make a rewrite rule that
239 RULE forall a,b. g (a,b) x = ...
240 But this rule will never match, because it's really a different 'x' at
241 the call site -- and that difference will be manifest by the time the
242 simplifier gets to it. [A worry: the simplifier doesn't *guarantee*
243 no-shadowing, so perhaps it may not be distinct?]
245 Anyway, the rule isn't actually wrong, it's just not useful. One possibility
246 is to run deShadowBinds before running SpecConstr, but instead we run the
247 simplifier. That gives the simplest possible program for SpecConstr to
248 chew on; and it virtually guarantees no shadowing.
250 Note [Specialising for constant parameters]
251 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
252 This one is about specialising on a *constant* (but not necessarily
253 constructor) argument
255 foo :: Int -> (Int -> Int) -> Int
257 foo m f = foo (f m) (+1)
261 lvl_rmV :: GHC.Base.Int -> GHC.Base.Int
263 \ (ds_dlk :: GHC.Base.Int) ->
264 case ds_dlk of wild_alH { GHC.Base.I# x_alG ->
265 GHC.Base.I# (GHC.Prim.+# x_alG 1)
267 T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
270 \ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) ->
271 case ww_sme of ds_Xlw {
273 case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz ->
274 T.$wfoo ww1_Xmz lvl_rmV
279 The recursive call has lvl_rmV as its argument, so we could create a specialised copy
280 with that argument baked in; that is, not passed at all. Now it can perhaps be inlined.
282 When is this worth it? Call the constant 'lvl'
283 - If 'lvl' has an unfolding that is a constructor, see if the corresponding
284 parameter is scrutinised anywhere in the body.
286 - If 'lvl' has an unfolding that is a inlinable function, see if the corresponding
287 parameter is applied (...to enough arguments...?)
289 Also do this is if the function has RULES?
293 Note [Specialising for lambda parameters]
294 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
295 foo :: Int -> (Int -> Int) -> Int
297 foo m f = foo (f m) (\n -> n-m)
299 This is subtly different from the previous one in that we get an
300 explicit lambda as the argument:
302 T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
305 \ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) ->
306 case ww_sm8 of ds_Xlr {
308 case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq ->
311 (\ (n_ad3 :: GHC.Base.Int) ->
312 case n_ad3 of wild_alB { GHC.Base.I# x_alA ->
313 GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr)
319 I wonder if SpecConstr couldn't be extended to handle this? After all,
320 lambda is a sort of constructor for functions and perhaps it already
321 has most of the necessary machinery?
323 Furthermore, there's an immediate win, because you don't need to allocate the lamda
324 at the call site; and if perchance it's called in the recursive call, then you
325 may avoid allocating it altogether. Just like for constructors.
327 Looks cool, but probably rare...but it might be easy to implement.
330 Note [SpecConstr for casts]
331 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
334 data instance T Int = T Int
339 go (T n) = go (T (n-1))
341 The recursive call ends up looking like
342 go (T (I# ...) `cast` g)
343 So we want to spot the construtor application inside the cast.
344 That's why we have the Cast case in argToPat
346 Note [Local recursive groups]
347 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
348 For a *local* recursive group, we can see all the calls to the
349 function, so we seed the specialisation loop from the calls in the
350 body, not from the calls in the RHS. Consider:
352 bar m n = foo n (n,n) (n,n) (n,n) (n,n)
356 | n > 3000 = case p of { (p1,p2) -> foo (n-1) (p2,p1) q r s }
357 | n > 2000 = case q of { (q1,q2) -> foo (n-1) p (q2,q1) r s }
358 | n > 1000 = case r of { (r1,r2) -> foo (n-1) p q (r2,r1) s }
359 | otherwise = case s of { (s1,s2) -> foo (n-1) p q r (s2,s1) }
361 If we start with the RHSs of 'foo', we get lots and lots of specialisations,
362 most of which are not needed. But if we start with the (single) call
363 in the rhs of 'bar' we get exactly one fully-specialised copy, and all
364 the recursive calls go to this fully-specialised copy. Indeed, the original
365 function is later collected as dead code. This is very important in
366 specialising the loops arising from stream fusion, for example in NDP where
367 we were getting literally hundreds of (mostly unused) specialisations of
370 -----------------------------------------------------
371 Stuff not yet handled
372 -----------------------------------------------------
374 Here are notes arising from Roman's work that I don't want to lose.
380 foo :: Int -> T Int -> Int
382 foo x t | even x = case t of { T n -> foo (x-n) t }
383 | otherwise = foo (x-1) t
385 SpecConstr does no specialisation, because the second recursive call
386 looks like a boxed use of the argument. A pity.
388 $wfoo_sFw :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
390 \ (ww_sFo [Just L] :: GHC.Prim.Int#) (w_sFq [Just L] :: T.T GHC.Base.Int) ->
391 case ww_sFo of ds_Xw6 [Just L] {
393 case GHC.Prim.remInt# ds_Xw6 2 of wild1_aEF [Dead Just A] {
394 __DEFAULT -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 1) w_sFq;
396 case w_sFq of wild_Xy [Just L] { T.T n_ad5 [Just U(L)] ->
397 case n_ad5 of wild1_aET [Just A] { GHC.Base.I# y_aES [Just L] ->
398 $wfoo_sFw (GHC.Prim.-# ds_Xw6 y_aES) wild_Xy
404 data a :*: b = !a :*: !b
407 foo :: (Int :*: T Int) -> Int
409 foo (x :*: t) | even x = case t of { T n -> foo ((x-n) :*: t) }
410 | otherwise = foo ((x-1) :*: t)
412 Very similar to the previous one, except that the parameters are now in
413 a strict tuple. Before SpecConstr, we have
415 $wfoo_sG3 :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
417 \ (ww_sFU [Just L] :: GHC.Prim.Int#) (ww_sFW [Just L] :: T.T
419 case ww_sFU of ds_Xws [Just L] {
421 case GHC.Prim.remInt# ds_Xws 2 of wild1_aEZ [Dead Just A] {
423 case ww_sFW of tpl_B2 [Just L] { T.T a_sFo [Just A] ->
424 $wfoo_sG3 (GHC.Prim.-# ds_Xws 1) tpl_B2 -- $wfoo1
427 case ww_sFW of wild_XB [Just A] { T.T n_ad7 [Just S(L)] ->
428 case n_ad7 of wild1_aFd [Just L] { GHC.Base.I# y_aFc [Just L] ->
429 $wfoo_sG3 (GHC.Prim.-# ds_Xws y_aFc) wild_XB -- $wfoo2
433 We get two specialisations:
434 "SC:$wfoo1" [0] __forall {a_sFB :: GHC.Base.Int sc_sGC :: GHC.Prim.Int#}
435 Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int a_sFB)
436 = Foo.$s$wfoo1 a_sFB sc_sGC ;
437 "SC:$wfoo2" [0] __forall {y_aFp :: GHC.Prim.Int# sc_sGC :: GHC.Prim.Int#}
438 Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int (GHC.Base.I# y_aFp))
439 = Foo.$s$wfoo y_aFp sc_sGC ;
441 But perhaps the first one isn't good. After all, we know that tpl_B2 is
442 a T (I# x) really, because T is strict and Int has one constructor. (We can't
443 unbox the strict fields, becuase T is polymorphic!)
447 %************************************************************************
449 \subsection{Top level wrapper stuff}
451 %************************************************************************
454 specConstrProgram :: DynFlags -> UniqSupply -> [CoreBind] -> IO [CoreBind]
455 specConstrProgram dflags us binds
457 showPass dflags "SpecConstr"
459 let (binds', _) = initUs us (go (initScEnv dflags) binds)
461 endPass dflags "SpecConstr" Opt_D_dump_spec binds'
463 dumpIfSet_dyn dflags Opt_D_dump_rules "Top-level specialisations"
464 (pprRulesForUser (rulesOfBinds binds'))
469 go env (bind:binds) = do (env', bind') <- scTopBind env bind
470 binds' <- go env' binds
471 return (bind' : binds')
475 %************************************************************************
477 \subsection{Environment: goes downwards}
479 %************************************************************************
482 data ScEnv = SCE { sc_size :: Maybe Int, -- Size threshold
483 sc_count :: Maybe Int, -- Max # of specialisations for any one fn
485 sc_subst :: Subst, -- Current substitution
486 -- Maps InIds to OutExprs
488 sc_how_bound :: HowBoundEnv,
489 -- Binds interesting non-top-level variables
490 -- Domain is OutVars (*after* applying the substitution)
493 -- Domain is OutIds (*after* applying the substitution)
494 -- Used even for top-level bindings (but not imported ones)
497 ---------------------
498 -- As we go, we apply a substitution (sc_subst) to the current term
499 type InExpr = CoreExpr -- _Before_ applying the subst
501 type OutExpr = CoreExpr -- _After_ applying the subst
505 ---------------------
506 type HowBoundEnv = VarEnv HowBound -- Domain is OutVars
508 ---------------------
509 type ValueEnv = IdEnv Value -- Domain is OutIds
510 data Value = ConVal AltCon [CoreArg] -- _Saturated_ constructors
511 | LambdaVal -- Inlinable lambdas or PAPs
513 instance Outputable Value where
514 ppr (ConVal con args) = ppr con <+> interpp'SP args
515 ppr LambdaVal = ptext (sLit "<Lambda>")
517 ---------------------
518 initScEnv :: DynFlags -> ScEnv
520 = SCE { sc_size = specConstrThreshold dflags,
521 sc_count = specConstrCount dflags,
522 sc_subst = emptySubst,
523 sc_how_bound = emptyVarEnv,
524 sc_vals = emptyVarEnv }
526 data HowBound = RecFun -- These are the recursive functions for which
527 -- we seek interesting call patterns
529 | RecArg -- These are those functions' arguments, or their sub-components;
530 -- we gather occurrence information for these
532 instance Outputable HowBound where
533 ppr RecFun = text "RecFun"
534 ppr RecArg = text "RecArg"
536 lookupHowBound :: ScEnv -> Id -> Maybe HowBound
537 lookupHowBound env id = lookupVarEnv (sc_how_bound env) id
539 scSubstId :: ScEnv -> Id -> CoreExpr
540 scSubstId env v = lookupIdSubst (sc_subst env) v
542 scSubstTy :: ScEnv -> Type -> Type
543 scSubstTy env ty = substTy (sc_subst env) ty
545 zapScSubst :: ScEnv -> ScEnv
546 zapScSubst env = env { sc_subst = zapSubstEnv (sc_subst env) }
548 extendScInScope :: ScEnv -> [Var] -> ScEnv
549 -- Bring the quantified variables into scope
550 extendScInScope env qvars = env { sc_subst = extendInScopeList (sc_subst env) qvars }
552 -- Extend the substitution
553 extendScSubst :: ScEnv -> Var -> OutExpr -> ScEnv
554 extendScSubst env var expr = env { sc_subst = extendSubst (sc_subst env) var expr }
556 extendScSubstList :: ScEnv -> [(Var,OutExpr)] -> ScEnv
557 extendScSubstList env prs = env { sc_subst = extendSubstList (sc_subst env) prs }
559 extendHowBound :: ScEnv -> [Var] -> HowBound -> ScEnv
560 extendHowBound env bndrs how_bound
561 = env { sc_how_bound = extendVarEnvList (sc_how_bound env)
562 [(bndr,how_bound) | bndr <- bndrs] }
564 extendBndrsWith :: HowBound -> ScEnv -> [Var] -> (ScEnv, [Var])
565 extendBndrsWith how_bound env bndrs
566 = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndrs')
568 (subst', bndrs') = substBndrs (sc_subst env) bndrs
569 hb_env' = sc_how_bound env `extendVarEnvList`
570 [(bndr,how_bound) | bndr <- bndrs']
572 extendBndrWith :: HowBound -> ScEnv -> Var -> (ScEnv, Var)
573 extendBndrWith how_bound env bndr
574 = (env { sc_subst = subst', sc_how_bound = hb_env' }, bndr')
576 (subst', bndr') = substBndr (sc_subst env) bndr
577 hb_env' = extendVarEnv (sc_how_bound env) bndr' how_bound
579 extendRecBndrs :: ScEnv -> [Var] -> (ScEnv, [Var])
580 extendRecBndrs env bndrs = (env { sc_subst = subst' }, bndrs')
582 (subst', bndrs') = substRecBndrs (sc_subst env) bndrs
584 extendBndr :: ScEnv -> Var -> (ScEnv, Var)
585 extendBndr env bndr = (env { sc_subst = subst' }, bndr')
587 (subst', bndr') = substBndr (sc_subst env) bndr
589 extendValEnv :: ScEnv -> Id -> Maybe Value -> ScEnv
590 extendValEnv env _ Nothing = env
591 extendValEnv env id (Just cv) = env { sc_vals = extendVarEnv (sc_vals env) id cv }
593 extendCaseBndrs :: ScEnv -> Id -> AltCon -> [Var] -> (ScEnv, [Var])
597 -- we want to bind b, to (C x y)
598 -- NB1: Extends only the sc_vals part of the envt
599 -- NB2: Kill the dead-ness info on the pattern binders x,y, since
600 -- they are potentially made alive by the [b -> C x y] binding
601 extendCaseBndrs env case_bndr con alt_bndrs
602 | isDeadBinder case_bndr
605 = (env1, map zap alt_bndrs)
606 -- NB: We used to bind v too, if scrut = (Var v); but
607 -- the simplifer has already done this so it seems
608 -- redundant to do so here
610 -- Var v -> extendValEnv env1 v cval
613 zap v | isTyVar v = v -- See NB2 above
614 | otherwise = zapIdOccInfo v
615 env1 = extendValEnv env case_bndr cval
618 LitAlt {} -> Just (ConVal con [])
619 DataAlt {} -> Just (ConVal con vanilla_args)
621 vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
622 varsToCoreExprs alt_bndrs
626 %************************************************************************
628 \subsection{Usage information: flows upwards}
630 %************************************************************************
635 scu_calls :: CallEnv, -- Calls
636 -- The functions are a subset of the
637 -- RecFuns in the ScEnv
639 scu_occs :: !(IdEnv ArgOcc) -- Information on argument occurrences
640 } -- The domain is OutIds
642 type CallEnv = IdEnv [Call]
643 type Call = (ValueEnv, [CoreArg])
644 -- The arguments of the call, together with the
645 -- env giving the constructor bindings at the call site
648 nullUsage = SCU { scu_calls = emptyVarEnv, scu_occs = emptyVarEnv }
650 combineCalls :: CallEnv -> CallEnv -> CallEnv
651 combineCalls = plusVarEnv_C (++)
653 combineUsage :: ScUsage -> ScUsage -> ScUsage
654 combineUsage u1 u2 = SCU { scu_calls = combineCalls (scu_calls u1) (scu_calls u2),
655 scu_occs = plusVarEnv_C combineOcc (scu_occs u1) (scu_occs u2) }
657 combineUsages :: [ScUsage] -> ScUsage
658 combineUsages [] = nullUsage
659 combineUsages us = foldr1 combineUsage us
661 lookupOcc :: ScUsage -> OutVar -> (ScUsage, ArgOcc)
662 lookupOcc (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndr
663 = (SCU {scu_calls = sc_calls, scu_occs = delVarEnv sc_occs bndr},
664 lookupVarEnv sc_occs bndr `orElse` NoOcc)
666 lookupOccs :: ScUsage -> [OutVar] -> (ScUsage, [ArgOcc])
667 lookupOccs (SCU { scu_calls = sc_calls, scu_occs = sc_occs }) bndrs
668 = (SCU {scu_calls = sc_calls, scu_occs = delVarEnvList sc_occs bndrs},
669 [lookupVarEnv sc_occs b `orElse` NoOcc | b <- bndrs])
671 data ArgOcc = NoOcc -- Doesn't occur at all; or a type argument
672 | UnkOcc -- Used in some unknown way
674 | ScrutOcc (UniqFM [ArgOcc]) -- See Note [ScrutOcc]
676 | BothOcc -- Definitely taken apart, *and* perhaps used in some other way
680 An occurrence of ScrutOcc indicates that the thing, or a `cast` version of the thing,
681 is *only* taken apart or applied.
683 Functions, literal: ScrutOcc emptyUFM
684 Data constructors: ScrutOcc subs,
686 where (subs :: UniqFM [ArgOcc]) gives usage of the *pattern-bound* components,
687 The domain of the UniqFM is the Unique of the data constructor
689 The [ArgOcc] is the occurrences of the *pattern-bound* components
690 of the data structure. E.g.
691 data T a = forall b. MkT a b (b->a)
692 A pattern binds b, x::a, y::b, z::b->a, but not 'a'!
696 instance Outputable ArgOcc where
697 ppr (ScrutOcc xs) = ptext (sLit "scrut-occ") <> ppr xs
698 ppr UnkOcc = ptext (sLit "unk-occ")
699 ppr BothOcc = ptext (sLit "both-occ")
700 ppr NoOcc = ptext (sLit "no-occ")
702 -- Experimentally, this vesion of combineOcc makes ScrutOcc "win", so
703 -- that if the thing is scrutinised anywhere then we get to see that
704 -- in the overall result, even if it's also used in a boxed way
705 -- This might be too agressive; see Note [Reboxing] Alternative 3
706 combineOcc :: ArgOcc -> ArgOcc -> ArgOcc
707 combineOcc NoOcc occ = occ
708 combineOcc occ NoOcc = occ
709 combineOcc (ScrutOcc xs) (ScrutOcc ys) = ScrutOcc (plusUFM_C combineOccs xs ys)
710 combineOcc _occ (ScrutOcc ys) = ScrutOcc ys
711 combineOcc (ScrutOcc xs) _occ = ScrutOcc xs
712 combineOcc UnkOcc UnkOcc = UnkOcc
713 combineOcc _ _ = BothOcc
715 combineOccs :: [ArgOcc] -> [ArgOcc] -> [ArgOcc]
716 combineOccs xs ys = zipWithEqual "combineOccs" combineOcc xs ys
718 setScrutOcc :: ScEnv -> ScUsage -> OutExpr -> ArgOcc -> ScUsage
719 -- _Overwrite_ the occurrence info for the scrutinee, if the scrutinee
720 -- is a variable, and an interesting variable
721 setScrutOcc env usg (Cast e _) occ = setScrutOcc env usg e occ
722 setScrutOcc env usg (Note _ e) occ = setScrutOcc env usg e occ
723 setScrutOcc env usg (Var v) occ
724 | Just RecArg <- lookupHowBound env v = usg { scu_occs = extendVarEnv (scu_occs usg) v occ }
726 setScrutOcc _env usg _other _occ -- Catch-all
729 conArgOccs :: ArgOcc -> AltCon -> [ArgOcc]
730 -- Find usage of components of data con; returns [UnkOcc...] if unknown
731 -- See Note [ScrutOcc] for the extra UnkOccs in the vanilla datacon case
733 conArgOccs (ScrutOcc fm) (DataAlt dc)
734 | Just pat_arg_occs <- lookupUFM fm dc
735 = [UnkOcc | _ <- dataConUnivTyVars dc] ++ pat_arg_occs
737 conArgOccs _other _con = repeat UnkOcc
740 %************************************************************************
742 \subsection{The main recursive function}
744 %************************************************************************
746 The main recursive function gathers up usage information, and
747 creates specialised versions of functions.
750 scExpr, scExpr' :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr)
751 -- The unique supply is needed when we invent
752 -- a new name for the specialised function and its args
754 scExpr env e = scExpr' env e
757 scExpr' env (Var v) = case scSubstId env v of
758 Var v' -> return (varUsage env v' UnkOcc, Var v')
759 e' -> scExpr (zapScSubst env) e'
761 scExpr' env (Type t) = return (nullUsage, Type (scSubstTy env t))
762 scExpr' _ e@(Lit {}) = return (nullUsage, e)
763 scExpr' env (Note n e) = do (usg,e') <- scExpr env e
764 return (usg, Note n e')
765 scExpr' env (Cast e co) = do (usg, e') <- scExpr env e
766 return (usg, Cast e' (scSubstTy env co))
767 scExpr' env e@(App _ _) = scApp env (collectArgs e)
768 scExpr' env (Lam b e) = do let (env', b') = extendBndr env b
769 (usg, e') <- scExpr env' e
770 return (usg, Lam b' e')
772 scExpr' env (Case scrut b ty alts)
773 = do { (scrut_usg, scrut') <- scExpr env scrut
774 ; case isValue (sc_vals env) scrut' of
775 Just (ConVal con args) -> sc_con_app con args scrut'
776 _other -> sc_vanilla scrut_usg scrut'
779 sc_con_app con args scrut' -- Known constructor; simplify
780 = do { let (_, bs, rhs) = findAlt con alts
781 alt_env' = extendScSubstList env ((b,scrut') : bs `zip` trimConArgs con args)
782 ; scExpr alt_env' rhs }
784 sc_vanilla scrut_usg scrut' -- Normal case
785 = do { let (alt_env,b') = extendBndrWith RecArg env b
786 -- Record RecArg for the components
788 ; (alt_usgs, alt_occs, alts')
789 <- mapAndUnzip3M (sc_alt alt_env scrut' b') alts
791 ; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b'
792 scrut_occ = foldr combineOcc b_occ alt_occs
793 scrut_usg' = setScrutOcc env scrut_usg scrut' scrut_occ
794 -- The combined usage of the scrutinee is given
795 -- by scrut_occ, which is passed to scScrut, which
796 -- in turn treats a bare-variable scrutinee specially
798 ; return (alt_usg `combineUsage` scrut_usg',
799 Case scrut' b' (scSubstTy env ty) alts') }
801 sc_alt env _scrut' b' (con,bs,rhs)
802 = do { let (env1, bs1) = extendBndrsWith RecArg env bs
803 (env2, bs2) = extendCaseBndrs env1 b' con bs1
804 ; (usg,rhs') <- scExpr env2 rhs
805 ; let (usg', arg_occs) = lookupOccs usg bs2
806 scrut_occ = case con of
807 DataAlt dc -> ScrutOcc (unitUFM dc arg_occs)
808 _ -> ScrutOcc emptyUFM
809 ; return (usg', scrut_occ, (con, bs2, rhs')) }
811 scExpr' env (Let (NonRec bndr rhs) body)
812 | isTyVar bndr -- Type-lets may be created by doBeta
813 = scExpr' (extendScSubst env bndr rhs) body
815 = do { let (body_env, bndr') = extendBndr env bndr
816 ; (rhs_usg, (_, args', rhs_body', _)) <- scRecRhs env (bndr',rhs)
817 ; let rhs' = mkLams args' rhs_body'
819 ; if not opt_SpecInlineJoinPoints || null args' || isEmptyVarEnv (scu_calls rhs_usg) then do
821 let body_env2 = extendValEnv body_env bndr' (isValue (sc_vals env) rhs')
822 -- Record if the RHS is a value
823 ; (body_usg, body') <- scExpr body_env2 body
824 ; return (body_usg `combineUsage` rhs_usg, Let (NonRec bndr' rhs') body') }
825 else -- For now, just brutally inline the join point
826 do { let body_env2 = extendScSubst env bndr rhs'
827 ; scExpr body_env2 body } }
831 do { -- Join-point case
832 let body_env2 = extendHowBound body_env [bndr'] RecFun
833 -- If the RHS of this 'let' contains calls
834 -- to recursive functions that we're trying
835 -- to specialise, then treat this let too
836 -- as one to specialise
837 ; (body_usg, body') <- scExpr body_env2 body
839 ; (spec_usg, _, specs) <- specialise env (scu_calls body_usg) ([], rhs_info)
841 ; return (body_usg { scu_calls = scu_calls body_usg `delVarEnv` bndr' }
842 `combineUsage` rhs_usg `combineUsage` spec_usg,
843 mkLets [NonRec b r | (b,r) <- specInfoBinds rhs_info specs] body')
847 -- A *local* recursive group: see Note [Local recursive groups]
848 scExpr' env (Let (Rec prs) body)
849 = do { let (bndrs,rhss) = unzip prs
850 (rhs_env1,bndrs') = extendRecBndrs env bndrs
851 rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
853 ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
854 ; (body_usg, body') <- scExpr rhs_env2 body
856 -- NB: start specLoop from body_usg
857 ; (spec_usg, specs) <- specLoop rhs_env2 (scu_calls body_usg) rhs_infos nullUsage
858 [SI [] 0 (Just usg) | usg <- rhs_usgs]
860 ; let all_usg = spec_usg `combineUsage` body_usg
861 bind' = Rec (concat (zipWith specInfoBinds rhs_infos specs))
863 ; return (all_usg { scu_calls = scu_calls all_usg `delVarEnvList` bndrs' },
866 -----------------------------------
867 scApp :: ScEnv -> (InExpr, [InExpr]) -> UniqSM (ScUsage, CoreExpr)
869 scApp env (Var fn, args) -- Function is a variable
870 = ASSERT( not (null args) )
871 do { args_w_usgs <- mapM (scExpr env) args
872 ; let (arg_usgs, args') = unzip args_w_usgs
873 arg_usg = combineUsages arg_usgs
874 ; case scSubstId env fn of
875 fn'@(Lam {}) -> scExpr (zapScSubst env) (doBeta fn' args')
876 -- Do beta-reduction and try again
878 Var fn' -> return (arg_usg `combineUsage` fn_usg, mkApps (Var fn') args')
880 fn_usg = case lookupHowBound env fn' of
881 Just RecFun -> SCU { scu_calls = unitVarEnv fn' [(sc_vals env, args')],
882 scu_occs = emptyVarEnv }
883 Just RecArg -> SCU { scu_calls = emptyVarEnv,
884 scu_occs = unitVarEnv fn' (ScrutOcc emptyUFM) }
888 other_fn' -> return (arg_usg, mkApps other_fn' args') }
889 -- NB: doing this ignores any usage info from the substituted
890 -- function, but I don't think that matters. If it does
893 doBeta :: OutExpr -> [OutExpr] -> OutExpr
894 -- ToDo: adjust for System IF
895 doBeta (Lam bndr body) (arg : args) = Let (NonRec bndr arg) (doBeta body args)
896 doBeta fn args = mkApps fn args
898 -- The function is almost always a variable, but not always.
899 -- In particular, if this pass follows float-in,
900 -- which it may, we can get
901 -- (let f = ...f... in f) arg1 arg2
902 scApp env (other_fn, args)
903 = do { (fn_usg, fn') <- scExpr env other_fn
904 ; (arg_usgs, args') <- mapAndUnzipM (scExpr env) args
905 ; return (combineUsages arg_usgs `combineUsage` fn_usg, mkApps fn' args') }
907 ----------------------
908 scTopBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, CoreBind)
909 scTopBind env (Rec prs)
910 | Just threshold <- sc_size env
911 , not (all (couldBeSmallEnoughToInline threshold) rhss)
913 = do { let (rhs_env,bndrs') = extendRecBndrs env bndrs
914 ; (_, rhss') <- mapAndUnzipM (scExpr rhs_env) rhss
915 ; return (rhs_env, Rec (bndrs' `zip` rhss')) }
916 | otherwise -- Do specialisation
917 = do { let (rhs_env1,bndrs') = extendRecBndrs env bndrs
918 rhs_env2 = extendHowBound rhs_env1 bndrs' RecFun
920 ; (rhs_usgs, rhs_infos) <- mapAndUnzipM (scRecRhs rhs_env2) (bndrs' `zip` rhss)
921 ; let rhs_usg = combineUsages rhs_usgs
923 ; (_, specs) <- specLoop rhs_env2 (scu_calls rhs_usg) rhs_infos nullUsage
924 [SI [] 0 Nothing | _ <- bndrs]
926 ; return (rhs_env1, -- For the body of the letrec, delete the RecFun business
927 Rec (concat (zipWith specInfoBinds rhs_infos specs))) }
929 (bndrs,rhss) = unzip prs
931 scTopBind env (NonRec bndr rhs)
932 = do { (_, rhs') <- scExpr env rhs
933 ; let (env1, bndr') = extendBndr env bndr
934 env2 = extendValEnv env1 bndr' (isValue (sc_vals env) rhs')
935 ; return (env2, NonRec bndr' rhs') }
937 ----------------------
938 scRecRhs :: ScEnv -> (OutId, InExpr) -> UniqSM (ScUsage, RhsInfo)
939 scRecRhs env (bndr,rhs)
940 = do { let (arg_bndrs,body) = collectBinders rhs
941 (body_env, arg_bndrs') = extendBndrsWith RecArg env arg_bndrs
942 ; (body_usg, body') <- scExpr body_env body
943 ; let (rhs_usg, arg_occs) = lookupOccs body_usg arg_bndrs'
944 ; return (rhs_usg, (bndr, arg_bndrs', body', arg_occs)) }
946 -- The arg_occs says how the visible,
947 -- lambda-bound binders of the RHS are used
948 -- (including the TyVar binders)
949 -- Two pats are the same if they match both ways
951 ----------------------
952 specInfoBinds :: RhsInfo -> SpecInfo -> [(Id,CoreExpr)]
953 specInfoBinds (fn, args, body, _) (SI specs _ _)
954 = [(id,rhs) | OS _ _ id rhs <- specs] ++
955 [(fn `addIdSpecialisations` rules, mkLams args body)]
957 rules = [r | OS _ r _ _ <- specs]
959 ----------------------
960 varUsage :: ScEnv -> OutVar -> ArgOcc -> ScUsage
962 | Just RecArg <- lookupHowBound env v = SCU { scu_calls = emptyVarEnv
963 , scu_occs = unitVarEnv v use }
964 | otherwise = nullUsage
968 %************************************************************************
970 The specialiser itself
972 %************************************************************************
975 type RhsInfo = (OutId, [OutVar], OutExpr, [ArgOcc])
976 -- Info about the *original* RHS of a binding we are specialising
977 -- Original binding f = \xs.body
978 -- Plus info about usage of arguments
980 data SpecInfo = SI [OneSpec] -- The specialisations we have generated
981 Int -- Length of specs; used for numbering them
982 (Maybe ScUsage) -- Nothing => we have generated specialisations
983 -- from calls in the *original* RHS
984 -- Just cs => we haven't, and this is the usage
985 -- of the original RHS
987 -- One specialisation: Rule plus definition
988 data OneSpec = OS CallPat -- Call pattern that generated this specialisation
989 CoreRule -- Rule connecting original id with the specialisation
990 OutId OutExpr -- Spec id + its rhs
996 -> ScUsage -> [SpecInfo] -- One per binder; acccumulating parameter
997 -> UniqSM (ScUsage, [SpecInfo]) -- ...ditto...
998 specLoop env all_calls rhs_infos usg_so_far specs_so_far
999 = do { specs_w_usg <- zipWithM (specialise env all_calls) rhs_infos specs_so_far
1000 ; let (new_usg_s, all_specs) = unzip specs_w_usg
1001 new_usg = combineUsages new_usg_s
1002 new_calls = scu_calls new_usg
1003 all_usg = usg_so_far `combineUsage` new_usg
1004 ; if isEmptyVarEnv new_calls then
1005 return (all_usg, all_specs)
1007 specLoop env new_calls rhs_infos all_usg all_specs }
1011 -> CallEnv -- Info on calls
1013 -> SpecInfo -- Original RHS plus patterns dealt with
1014 -> UniqSM (ScUsage, SpecInfo) -- New specialised versions and their usage
1016 -- Note: the rhs here is the optimised version of the original rhs
1017 -- So when we make a specialised copy of the RHS, we're starting
1018 -- from an RHS whose nested functions have been optimised already.
1020 specialise env bind_calls (fn, arg_bndrs, body, arg_occs)
1021 spec_info@(SI specs spec_count mb_unspec)
1022 | notNull arg_bndrs, -- Only specialise functions
1023 Just all_calls <- lookupVarEnv bind_calls fn
1024 = do { (boring_call, pats) <- callsToPats env specs arg_occs all_calls
1025 -- ; pprTrace "specialise" (vcat [ppr fn <+> ppr arg_occs,
1026 -- text "calls" <+> ppr all_calls,
1027 -- text "good pats" <+> ppr pats]) $
1030 -- Bale out if too many specialisations
1031 -- Rather a hacky way to do so, but it'll do for now
1032 ; let spec_count' = length pats + spec_count
1033 ; case sc_count env of
1034 Just max | spec_count' > max
1035 -> WARN( True, msg ) return (nullUsage, spec_info)
1037 msg = vcat [ sep [ ptext (sLit "SpecConstr: specialisation of") <+> quotes (ppr fn)
1038 , nest 2 (ptext (sLit "limited by bound of")) <+> int max ]
1039 , ptext (sLit "Use -fspec-constr-count=n to set the bound")
1041 extra | not opt_PprStyle_Debug = ptext (sLit "Use -dppr-debug to see specialisations")
1042 | otherwise = ptext (sLit "Specialisations:") <+> ppr (pats ++ [p | OS p _ _ _ <- specs])
1044 _normal_case -> do {
1046 (spec_usgs, new_specs) <- mapAndUnzipM (spec_one env fn arg_bndrs body)
1047 (pats `zip` [spec_count..])
1049 ; let spec_usg = combineUsages spec_usgs
1050 (new_usg, mb_unspec')
1052 Just rhs_usg | boring_call -> (spec_usg `combineUsage` rhs_usg, Nothing)
1053 _ -> (spec_usg, mb_unspec)
1055 ; return (new_usg, SI (new_specs ++ specs) spec_count' mb_unspec') } }
1057 = return (nullUsage, spec_info) -- The boring case
1060 ---------------------
1062 -> OutId -- Function
1063 -> [Var] -- Lambda-binders of RHS; should match patterns
1064 -> CoreExpr -- Body of the original function
1066 -> UniqSM (ScUsage, OneSpec) -- Rule and binding
1068 -- spec_one creates a specialised copy of the function, together
1069 -- with a rule for using it. I'm very proud of how short this
1070 -- function is, considering what it does :-).
1076 f = /\b \y::[(a,b)] -> ....f (b,c) ((:) (a,(b,c)) (x,v) (h w))...
1077 [c::*, v::(b,c) are presumably bound by the (...) part]
1079 f_spec = /\ b c \ v::(b,c) hw::[(a,(b,c))] ->
1080 (...entire body of f...) [b -> (b,c),
1081 y -> ((:) (a,(b,c)) (x,v) hw)]
1083 RULE: forall b::* c::*, -- Note, *not* forall a, x
1087 f (b,c) ((:) (a,(b,c)) (x,v) hw) = f_spec b c v hw
1090 spec_one env fn arg_bndrs body (call_pat@(qvars, pats), rule_number)
1091 = do { -- Specialise the body
1092 let spec_env = extendScSubstList (extendScInScope env qvars)
1093 (arg_bndrs `zip` pats)
1094 ; (spec_usg, spec_body) <- scExpr spec_env body
1096 -- ; pprTrace "spec_one" (ppr fn <+> vcat [text "pats" <+> ppr pats,
1097 -- text "calls" <+> (ppr (scu_calls spec_usg))])
1100 -- And build the results
1101 ; spec_uniq <- getUniqueUs
1102 ; let (spec_lam_args, spec_call_args) = mkWorkerArgs qvars body_ty
1103 -- Usual w/w hack to avoid generating
1104 -- a spec_rhs of unlifted type and no args
1107 fn_loc = nameSrcSpan fn_name
1108 spec_occ = mkSpecOcc (nameOccName fn_name)
1109 rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
1110 spec_rhs = mkLams spec_lam_args spec_body
1111 spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc
1112 body_ty = exprType spec_body
1113 rule_rhs = mkVarApps (Var spec_id) spec_call_args
1114 rule = mkLocalRule rule_name specConstrActivation fn_name qvars pats rule_rhs
1115 ; return (spec_usg, OS call_pat rule spec_id spec_rhs) }
1117 -- In which phase should the specialise-constructor rules be active?
1118 -- Originally I made them always-active, but Manuel found that
1119 -- this defeated some clever user-written rules. So Plan B
1120 -- is to make them active only in Phase 0; after all, currently,
1121 -- the specConstr transformation is only run after the simplifier
1122 -- has reached Phase 0. In general one would want it to be
1123 -- flag-controllable, but for now I'm leaving it baked in
1125 specConstrActivation :: Activation
1126 specConstrActivation = ActiveAfter 0 -- Baked in; see comments above
1129 %************************************************************************
1131 \subsection{Argument analysis}
1133 %************************************************************************
1135 This code deals with analysing call-site arguments to see whether
1136 they are constructor applications.
1140 type CallPat = ([Var], [CoreExpr]) -- Quantified variables and arguments
1143 callsToPats :: ScEnv -> [OneSpec] -> [ArgOcc] -> [Call] -> UniqSM (Bool, [CallPat])
1144 -- Result has no duplicate patterns,
1145 -- nor ones mentioned in done_pats
1146 -- Bool indicates that there was at least one boring pattern
1147 callsToPats env done_specs bndr_occs calls
1148 = do { mb_pats <- mapM (callToPats env bndr_occs) calls
1150 ; let good_pats :: [([Var], [CoreArg])]
1151 good_pats = catMaybes mb_pats
1152 done_pats = [p | OS p _ _ _ <- done_specs]
1153 is_done p = any (samePat p) done_pats
1155 ; return (any isNothing mb_pats,
1156 filterOut is_done (nubBy samePat good_pats)) }
1158 callToPats :: ScEnv -> [ArgOcc] -> Call -> UniqSM (Maybe CallPat)
1159 -- The [Var] is the variables to quantify over in the rule
1160 -- Type variables come first, since they may scope
1161 -- over the following term variables
1162 -- The [CoreExpr] are the argument patterns for the rule
1163 callToPats env bndr_occs (con_env, args)
1164 | length args < length bndr_occs -- Check saturated
1167 = do { let in_scope = substInScope (sc_subst env)
1168 ; prs <- argsToPats in_scope con_env (args `zip` bndr_occs)
1169 ; let (interesting_s, pats) = unzip prs
1170 pat_fvs = varSetElems (exprsFreeVars pats)
1171 qvars = filterOut (`elemInScopeSet` in_scope) pat_fvs
1172 -- Quantify over variables that are not in sccpe
1174 -- See Note [Shadowing] at the top
1176 (tvs, ids) = partition isTyVar qvars
1178 -- Put the type variables first; the type of a term
1179 -- variable may mention a type variable
1181 ; -- pprTrace "callToPats" (ppr args $$ ppr prs $$ ppr bndr_occs) $
1183 then return (Just (qvars', pats))
1184 else return Nothing }
1186 -- argToPat takes an actual argument, and returns an abstracted
1187 -- version, consisting of just the "constructor skeleton" of the
1188 -- argument, with non-constructor sub-expression replaced by new
1189 -- placeholder variables. For example:
1190 -- C a (D (f x) (g y)) ==> C p1 (D p2 p3)
1192 argToPat :: InScopeSet -- What's in scope at the fn defn site
1193 -> ValueEnv -- ValueEnv at the call site
1194 -> CoreArg -- A call arg (or component thereof)
1196 -> UniqSM (Bool, CoreArg)
1197 -- Returns (interesting, pat),
1198 -- where pat is the pattern derived from the argument
1199 -- intersting=True if the pattern is non-trivial (not a variable or type)
1200 -- E.g. x:xs --> (True, x:xs)
1201 -- f xs --> (False, w) where w is a fresh wildcard
1202 -- (f xs, 'c') --> (True, (w, 'c')) where w is a fresh wildcard
1203 -- \x. x+y --> (True, \x. x+y)
1204 -- lvl7 --> (True, lvl7) if lvl7 is bound
1205 -- somewhere further out
1207 argToPat _in_scope _val_env arg@(Type {}) _arg_occ
1208 = return (False, arg)
1210 argToPat in_scope val_env (Note _ arg) arg_occ
1211 = argToPat in_scope val_env arg arg_occ
1212 -- Note [Notes in call patterns]
1213 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1214 -- Ignore Notes. In particular, we want to ignore any InlineMe notes
1215 -- Perhaps we should not ignore profiling notes, but I'm going to
1216 -- ride roughshod over them all for now.
1217 --- See Note [Notes in RULE matching] in Rules
1219 argToPat in_scope val_env (Let _ arg) arg_occ
1220 = argToPat in_scope val_env arg arg_occ
1221 -- Look through let expressions
1222 -- e.g. f (let v = rhs in \y -> ...v...)
1223 -- Here we can specialise for f (\y -> ...)
1224 -- because the rule-matcher will look through the let.
1226 argToPat in_scope val_env (Cast arg co) arg_occ
1227 = do { (interesting, arg') <- argToPat in_scope val_env arg arg_occ
1228 ; let (ty1,ty2) = coercionKind co
1229 ; if not interesting then
1232 { -- Make a wild-card pattern for the coercion
1234 ; let co_name = mkSysTvName uniq (fsLit "sg")
1235 co_var = mkCoVar co_name (mkCoKind ty1 ty2)
1236 ; return (interesting, Cast arg' (mkTyVarTy co_var)) } }
1238 {- Disabling lambda specialisation for now
1239 It's fragile, and the spec_loop can be infinite
1240 argToPat in_scope val_env arg arg_occ
1242 = return (True, arg)
1244 is_value_lam (Lam v e) -- Spot a value lambda, even if
1245 | isId v = True -- it is inside a type lambda
1246 | otherwise = is_value_lam e
1247 is_value_lam other = False
1250 -- Check for a constructor application
1251 -- NB: this *precedes* the Var case, so that we catch nullary constrs
1252 argToPat in_scope val_env arg arg_occ
1253 | Just (ConVal dc args) <- isValue val_env arg
1255 ScrutOcc _ -> True -- Used only by case scrutinee
1256 BothOcc -> case arg of -- Used elsewhere
1257 App {} -> True -- see Note [Reboxing]
1259 _other -> False -- No point; the arg is not decomposed
1260 = do { args' <- argsToPats in_scope val_env (args `zip` conArgOccs arg_occ dc)
1261 ; return (True, mk_con_app dc (map snd args')) }
1263 -- Check if the argument is a variable that
1264 -- is in scope at the function definition site
1265 -- It's worth specialising on this if
1266 -- (a) it's used in an interesting way in the body
1267 -- (b) we know what its value is
1268 argToPat in_scope val_env (Var v) arg_occ
1269 | case arg_occ of { UnkOcc -> False; _other -> True }, -- (a)
1271 = return (True, Var v)
1274 | isLocalId v = v `elemInScopeSet` in_scope
1275 && isJust (lookupVarEnv val_env v)
1276 -- Local variables have values in val_env
1277 | otherwise = isValueUnfolding (idUnfolding v)
1278 -- Imports have unfoldings
1280 -- I'm really not sure what this comment means
1281 -- And by not wild-carding we tend to get forall'd
1282 -- variables that are in soope, which in turn can
1283 -- expose the weakness in let-matching
1284 -- See Note [Matching lets] in Rules
1286 -- Check for a variable bound inside the function.
1287 -- Don't make a wild-card, because we may usefully share
1288 -- e.g. f a = let x = ... in f (x,x)
1289 -- NB: this case follows the lambda and con-app cases!!
1290 -- argToPat _in_scope _val_env (Var v) _arg_occ
1291 -- = return (False, Var v)
1292 -- SLPJ : disabling this to avoid proliferation of versions
1293 -- also works badly when thinking about seeding the loop
1294 -- from the body of the let
1295 -- f x y = letrec g z = ... in g (x,y)
1296 -- We don't want to specialise for that *particular* x,y
1298 -- The default case: make a wild-card
1299 argToPat _in_scope _val_env arg _arg_occ
1300 = wildCardPat (exprType arg)
1302 wildCardPat :: Type -> UniqSM (Bool, CoreArg)
1303 wildCardPat ty = do { uniq <- getUniqueUs
1304 ; let id = mkSysLocal (fsLit "sc") uniq ty
1305 ; return (False, Var id) }
1307 argsToPats :: InScopeSet -> ValueEnv
1308 -> [(CoreArg, ArgOcc)]
1309 -> UniqSM [(Bool, CoreArg)]
1310 argsToPats in_scope val_env args
1313 do_one (arg,occ) = argToPat in_scope val_env arg occ
1318 isValue :: ValueEnv -> CoreExpr -> Maybe Value
1319 isValue _env (Lit lit)
1320 = Just (ConVal (LitAlt lit) [])
1323 | Just stuff <- lookupVarEnv env v
1324 = Just stuff -- You might think we could look in the idUnfolding here
1325 -- but that doesn't take account of which branch of a
1326 -- case we are in, which is the whole point
1328 | not (isLocalId v) && isCheapUnfolding unf
1329 = isValue env (unfoldingTemplate unf)
1332 -- However we do want to consult the unfolding
1333 -- as well, for let-bound constructors!
1335 isValue env (Lam b e)
1336 | isTyVar b = case isValue env e of
1337 Just _ -> Just LambdaVal
1339 | otherwise = Just LambdaVal
1341 isValue _env expr -- Maybe it's a constructor application
1342 | (Var fun, args) <- collectArgs expr
1343 = case isDataConWorkId_maybe fun of
1345 Just con | args `lengthAtLeast` dataConRepArity con
1346 -- Check saturated; might be > because the
1347 -- arity excludes type args
1348 -> Just (ConVal (DataAlt con) args)
1350 _other | valArgCount args < idArity fun
1351 -- Under-applied function
1352 -> Just LambdaVal -- Partial application
1356 isValue _env _expr = Nothing
1358 mk_con_app :: AltCon -> [CoreArg] -> CoreExpr
1359 mk_con_app (LitAlt lit) [] = Lit lit
1360 mk_con_app (DataAlt con) args = mkConApp con args
1361 mk_con_app _other _args = panic "SpecConstr.mk_con_app"
1363 samePat :: CallPat -> CallPat -> Bool
1364 samePat (vs1, as1) (vs2, as2)
1367 same (Var v1) (Var v2)
1368 | v1 `elem` vs1 = v2 `elem` vs2
1369 | v2 `elem` vs2 = False
1370 | otherwise = v1 == v2
1372 same (Lit l1) (Lit l2) = l1==l2
1373 same (App f1 a1) (App f2 a2) = same f1 f2 && same a1 a2
1375 same (Type {}) (Type {}) = True -- Note [Ignore type differences]
1376 same (Note _ e1) e2 = same e1 e2 -- Ignore casts and notes
1377 same (Cast e1 _) e2 = same e1 e2
1378 same e1 (Note _ e2) = same e1 e2
1379 same e1 (Cast e2 _) = same e1 e2
1381 same e1 e2 = WARN( bad e1 || bad e2, ppr e1 $$ ppr e2)
1382 False -- Let, lambda, case should not occur
1383 bad (Case {}) = True
1389 Note [Ignore type differences]
1390 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1391 We do not want to generate specialisations where the call patterns
1392 differ only in their type arguments! Not only is it utterly useless,
1393 but it also means that (with polymorphic recursion) we can generate
1394 an infinite number of specialisations. Example is Data.Sequence.adjustTree,