2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[SpecConstr]{Specialise over constructors}
11 #include "HsVersions.h"
14 import CoreLint ( showPass, endPass )
15 import CoreUtils ( exprType, mkPiTypes )
16 import CoreFVs ( exprsFreeVars )
17 import CoreSubst ( Subst, mkSubst, substExpr )
18 import CoreTidy ( tidyRules )
19 import PprCore ( pprRules )
20 import WwLib ( mkWorkerArgs )
21 import DataCon ( dataConRepArity, isVanillaDataCon )
22 import Type ( tyConAppArgs, tyVarsOfTypes )
23 import Rules ( matchN )
24 import Unify ( coreRefineTys )
25 import Id ( Id, idName, idType, isDataConWorkId_maybe,
26 mkUserLocal, mkSysLocal, idUnfolding, isLocalId )
30 import Name ( nameOccName, nameSrcLoc )
31 import Rules ( addIdSpecialisations, mkLocalRule, rulesOfBinds )
32 import OccName ( mkSpecOcc )
33 import ErrUtils ( dumpIfSet_dyn )
34 import DynFlags ( DynFlags, DynFlag(..) )
35 import BasicTypes ( Activation(..) )
36 import Maybes ( orElse, catMaybes, isJust )
37 import Util ( zipWithEqual, lengthAtLeast, notNull )
38 import List ( nubBy, partition )
45 -----------------------------------------------------
47 -----------------------------------------------------
52 drop n (x:xs) = drop (n-1) xs
54 After the first time round, we could pass n unboxed. This happens in
55 numerical code too. Here's what it looks like in Core:
57 drop n xs = case xs of
62 _ -> drop (I# (n# -# 1#)) xs
64 Notice that the recursive call has an explicit constructor as argument.
65 Noticing this, we can make a specialised version of drop
67 RULE: drop (I# n#) xs ==> drop' n# xs
69 drop' n# xs = let n = I# n# in ...orig RHS...
71 Now the simplifier will apply the specialisation in the rhs of drop', giving
73 drop' n# xs = case xs of
77 _ -> drop (n# -# 1#) xs
81 We'd also like to catch cases where a parameter is carried along unchanged,
82 but evaluated each time round the loop:
84 f i n = if i>0 || i>n then i else f (i*2) n
86 Here f isn't strict in n, but we'd like to avoid evaluating it each iteration.
87 In Core, by the time we've w/wd (f is strict in i) we get
89 f i# n = case i# ># 0 of
91 True -> case n of n' { I# n# ->
94 True -> f (i# *# 2#) n'
96 At the call to f, we see that the argument, n is know to be (I# n#),
97 and n is evaluated elsewhere in the body of f, so we can play the same
103 We must be careful not to allocate the same constructor twice. Consider
104 f p = (...(case p of (a,b) -> e)...p...,
105 ...let t = (r,s) in ...t...(f t)...)
106 At the recursive call to f, we can see that t is a pair. But we do NOT want
107 to make a specialised copy:
108 f' a b = let p = (a,b) in (..., ...)
109 because now t is allocated by the caller, then r and s are passed to the
110 recursive call, which allocates the (r,s) pair again.
113 (a) the argument p is used in other than a case-scrutinsation way.
114 (b) the argument to the call is not a 'fresh' tuple; you have to
115 look into its unfolding to see that it's a tuple
117 Hence the "OR" part of Note [Good arguments] below.
119 ALTERNATIVE: pass both boxed and unboxed versions. This no longer saves
120 allocation, but does perhaps save evals. In the RULE we'd have
123 f (I# x#) = f' (I# x#) x#
125 If at the call site the (I# x) was an unfolding, then we'd have to
126 rely on CSE to eliminate the duplicate allocation.... This alternative
127 doesn't look attractive enough to pursue.
130 Note [Good arguments]
131 ~~~~~~~~~~~~~~~~~~~~~
134 * A self-recursive function. Ignore mutual recursion for now,
135 because it's less common, and the code is simpler for self-recursion.
139 a) At a recursive call, one or more parameters is an explicit
140 constructor application
142 That same parameter is scrutinised by a case somewhere in
143 the RHS of the function
147 b) At a recursive call, one or more parameters has an unfolding
148 that is an explicit constructor application
150 That same parameter is scrutinised by a case somewhere in
151 the RHS of the function
153 Those are the only uses of the parameter (see Note [Reboxing])
156 What to abstract over
157 ~~~~~~~~~~~~~~~~~~~~~
158 There's a bit of a complication with type arguments. If the call
161 f p = ...f ((:) [a] x xs)...
163 then our specialised function look like
165 f_spec x xs = let p = (:) [a] x xs in ....as before....
167 This only makes sense if either
168 a) the type variable 'a' is in scope at the top of f, or
169 b) the type variable 'a' is an argument to f (and hence fs)
171 Actually, (a) may hold for value arguments too, in which case
172 we may not want to pass them. Supose 'x' is in scope at f's
173 defn, but xs is not. Then we'd like
175 f_spec xs = let p = (:) [a] x xs in ....as before....
177 Similarly (b) may hold too. If x is already an argument at the
178 call, no need to pass it again.
180 Finally, if 'a' is not in scope at the call site, we could abstract
181 it as we do the term variables:
183 f_spec a x xs = let p = (:) [a] x xs in ...as before...
185 So the grand plan is:
187 * abstract the call site to a constructor-only pattern
188 e.g. C x (D (f p) (g q)) ==> C s1 (D s2 s3)
190 * Find the free variables of the abstracted pattern
192 * Pass these variables, less any that are in scope at
193 the fn defn. But see Note [Shadowing] below.
196 NOTICE that we only abstract over variables that are not in scope,
197 so we're in no danger of shadowing variables used in "higher up"
203 In this pass we gather up usage information that may mention variables
204 that are bound between the usage site and the definition site; or (more
205 seriously) may be bound to something different at the definition site.
208 f x = letrec g y v = let x = ...
211 Since 'x' is in scope at the call site, we may make a rewrite rule that
213 RULE forall a,b. g (a,b) x = ...
214 But this rule will never match, because it's really a different 'x' at
215 the call site -- and that difference will be manifest by the time the
216 simplifier gets to it. [A worry: the simplifier doesn't *guarantee*
217 no-shadowing, so perhaps it may not be distinct?]
219 Anyway, the rule isn't actually wrong, it's just not useful. One possibility
220 is to run deShadowBinds before running SpecConstr, but instead we run the
221 simplifier. That gives the simplest possible program for SpecConstr to
222 chew on; and it virtually guarantees no shadowing.
224 Note [Specialising for constant parameters]
225 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
226 This one is about specialising on a *constant* (but not necessarily
227 constructor) argument
229 foo :: Int -> (Int -> Int) -> Int
231 foo m f = foo (f m) (+1)
235 lvl_rmV :: GHC.Base.Int -> GHC.Base.Int
237 \ (ds_dlk :: GHC.Base.Int) ->
238 case ds_dlk of wild_alH { GHC.Base.I# x_alG ->
239 GHC.Base.I# (GHC.Prim.+# x_alG 1)
241 T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
244 \ (ww_sme :: GHC.Prim.Int#) (w_smg :: GHC.Base.Int -> GHC.Base.Int) ->
245 case ww_sme of ds_Xlw {
247 case w_smg (GHC.Base.I# ds_Xlw) of w1_Xmo { GHC.Base.I# ww1_Xmz ->
248 T.$wfoo ww1_Xmz lvl_rmV
253 The recursive call has lvl_rmV as its argument, so we could create a specialised copy
254 with that argument baked in; that is, not passed at all. Now it can perhaps be inlined.
256 When is this worth it? Call the constant 'lvl'
257 - If 'lvl' has an unfolding that is a constructor, see if the corresponding
258 parameter is scrutinised anywhere in the body.
260 - If 'lvl' has an unfolding that is a inlinable function, see if the corresponding
261 parameter is applied (...to enough arguments...?)
263 Also do this is if the function has RULES?
267 Note [Specialising for lambda parameters]
268 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
269 foo :: Int -> (Int -> Int) -> Int
271 foo m f = foo (f m) (\n -> n-m)
273 This is subtly different from the previous one in that we get an
274 explicit lambda as the argument:
276 T.$wfoo :: GHC.Prim.Int# -> (GHC.Base.Int -> GHC.Base.Int) ->
279 \ (ww_sm8 :: GHC.Prim.Int#) (w_sma :: GHC.Base.Int -> GHC.Base.Int) ->
280 case ww_sm8 of ds_Xlr {
282 case w_sma (GHC.Base.I# ds_Xlr) of w1_Xmf { GHC.Base.I# ww1_Xmq ->
285 (\ (n_ad3 :: GHC.Base.Int) ->
286 case n_ad3 of wild_alB { GHC.Base.I# x_alA ->
287 GHC.Base.I# (GHC.Prim.-# x_alA ds_Xlr)
293 I wonder if SpecConstr couldn't be extended to handle this? After all,
294 lambda is a sort of constructor for functions and perhaps it already
295 has most of the necessary machinery?
297 Furthermore, there's an immediate win, because you don't need to allocate the lamda
298 at the call site; and if perchance it's called in the recursive call, then you
299 may avoid allocating it altogether. Just like for constructors.
301 Looks cool, but probably rare...but it might be easy to implement.
303 -----------------------------------------------------
304 Stuff not yet handled
305 -----------------------------------------------------
307 Here are notes arising from Roman's work that I don't want to lose.
313 foo :: Int -> T Int -> Int
315 foo x t | even x = case t of { T n -> foo (x-n) t }
316 | otherwise = foo (x-1) t
318 SpecConstr does no specialisation, because the second recursive call
319 looks like a boxed use of the argument. A pity.
321 $wfoo_sFw :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
323 \ (ww_sFo [Just L] :: GHC.Prim.Int#) (w_sFq [Just L] :: T.T GHC.Base.Int) ->
324 case ww_sFo of ds_Xw6 [Just L] {
326 case GHC.Prim.remInt# ds_Xw6 2 of wild1_aEF [Dead Just A] {
327 __DEFAULT -> $wfoo_sFw (GHC.Prim.-# ds_Xw6 1) w_sFq;
329 case w_sFq of wild_Xy [Just L] { T.T n_ad5 [Just U(L)] ->
330 case n_ad5 of wild1_aET [Just A] { GHC.Base.I# y_aES [Just L] ->
331 $wfoo_sFw (GHC.Prim.-# ds_Xw6 y_aES) wild_Xy
337 data a :*: b = !a :*: !b
340 foo :: (Int :*: T Int) -> Int
342 foo (x :*: t) | even x = case t of { T n -> foo ((x-n) :*: t) }
343 | otherwise = foo ((x-1) :*: t)
345 Very similar to the previous one, except that the parameters are now in
346 a strict tuple. Before SpecConstr, we have
348 $wfoo_sG3 :: GHC.Prim.Int# -> T.T GHC.Base.Int -> GHC.Prim.Int#
350 \ (ww_sFU [Just L] :: GHC.Prim.Int#) (ww_sFW [Just L] :: T.T
352 case ww_sFU of ds_Xws [Just L] {
354 case GHC.Prim.remInt# ds_Xws 2 of wild1_aEZ [Dead Just A] {
356 case ww_sFW of tpl_B2 [Just L] { T.T a_sFo [Just A] ->
357 $wfoo_sG3 (GHC.Prim.-# ds_Xws 1) tpl_B2 -- $wfoo1
360 case ww_sFW of wild_XB [Just A] { T.T n_ad7 [Just S(L)] ->
361 case n_ad7 of wild1_aFd [Just L] { GHC.Base.I# y_aFc [Just L] ->
362 $wfoo_sG3 (GHC.Prim.-# ds_Xws y_aFc) wild_XB -- $wfoo2
366 We get two specialisations:
367 "SC:$wfoo1" [0] __forall {a_sFB :: GHC.Base.Int sc_sGC :: GHC.Prim.Int#}
368 Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int a_sFB)
369 = Foo.$s$wfoo1 a_sFB sc_sGC ;
370 "SC:$wfoo2" [0] __forall {y_aFp :: GHC.Prim.Int# sc_sGC :: GHC.Prim.Int#}
371 Foo.$wfoo sc_sGC (Foo.T @ GHC.Base.Int (GHC.Base.I# y_aFp))
372 = Foo.$s$wfoo y_aFp sc_sGC ;
374 But perhaps the first one isn't good. After all, we know that tpl_B2 is
375 a T (I# x) really, because T is strict and Int has one constructor. (We can't
376 unbox the strict fields, becuase T is polymorphic!)
380 %************************************************************************
382 \subsection{Top level wrapper stuff}
384 %************************************************************************
387 specConstrProgram :: DynFlags -> UniqSupply -> [CoreBind] -> IO [CoreBind]
388 specConstrProgram dflags us binds
390 showPass dflags "SpecConstr"
392 let (binds', _) = initUs us (go emptyScEnv binds)
394 endPass dflags "SpecConstr" Opt_D_dump_spec binds'
396 dumpIfSet_dyn dflags Opt_D_dump_rules "Top-level specialisations"
397 (pprRules (tidyRules emptyTidyEnv (rulesOfBinds binds')))
401 go env [] = returnUs []
402 go env (bind:binds) = scBind env bind `thenUs` \ (env', _, bind') ->
403 go env' binds `thenUs` \ binds' ->
404 returnUs (bind' : binds')
408 %************************************************************************
410 \subsection{Environment: goes downwards}
412 %************************************************************************
415 data ScEnv = SCE { scope :: InScopeEnv,
416 -- Binds all non-top-level variables in scope
421 type InScopeEnv = VarEnv HowBound
423 type ConstrEnv = IdEnv ConValue
424 data ConValue = CV AltCon [CoreArg]
425 -- Variables known to be bound to a constructor
426 -- in a particular case alternative
429 instance Outputable ConValue where
430 ppr (CV con args) = ppr con <+> interpp'SP args
432 refineConstrEnv :: Subst -> ConstrEnv -> ConstrEnv
433 -- The substitution is a type substitution only
434 refineConstrEnv subst env = mapVarEnv refine_con_value env
436 refine_con_value (CV con args) = CV con (map (substExpr subst) args)
438 emptyScEnv = SCE { scope = emptyVarEnv, cons = emptyVarEnv }
440 data HowBound = RecFun -- These are the recursive functions for which
441 -- we seek interesting call patterns
443 | RecArg -- These are those functions' arguments; we are
444 -- interested to see if those arguments are scrutinised
446 | Other -- We track all others so we know what's in scope
447 -- This is used in spec_one to check what needs to be
448 -- passed as a parameter and what is in scope at the
449 -- function definition site
451 instance Outputable HowBound where
452 ppr RecFun = text "RecFun"
453 ppr RecArg = text "RecArg"
454 ppr Other = text "Other"
456 lookupScopeEnv env v = lookupVarEnv (scope env) v
458 extendBndrs env bndrs = env { scope = extendVarEnvList (scope env) [(b,Other) | b <- bndrs] }
459 extendBndr env bndr = env { scope = extendVarEnv (scope env) bndr Other }
464 -- we want to bind b, and perhaps scrut too, to (C x y)
465 extendCaseBndrs :: ScEnv -> Id -> CoreExpr -> AltCon -> [Var] -> ScEnv
466 extendCaseBndrs env case_bndr scrut DEFAULT alt_bndrs
467 = extendBndrs env (case_bndr : alt_bndrs)
469 extendCaseBndrs env case_bndr scrut con@(LitAlt lit) alt_bndrs
470 = ASSERT( null alt_bndrs ) extendAlt env case_bndr scrut (CV con []) []
472 extendCaseBndrs env case_bndr scrut con@(DataAlt data_con) alt_bndrs
473 | isVanillaDataCon data_con
474 = extendAlt env case_bndr scrut (CV con vanilla_args) alt_bndrs
477 = extendAlt env1 case_bndr scrut (CV con gadt_args) alt_bndrs
479 vanilla_args = map Type (tyConAppArgs (idType case_bndr)) ++
480 map varToCoreExpr alt_bndrs
482 gadt_args = map (substExpr subst . varToCoreExpr) alt_bndrs
483 -- This call generates some bogus warnings from substExpr,
484 -- because it's inconvenient to put all the Ids in scope
485 -- Will be fixed when we move to FC
487 (alt_tvs, _) = span isTyVar alt_bndrs
488 Just (tv_subst, is_local) = coreRefineTys data_con alt_tvs (idType case_bndr)
489 subst = mkSubst in_scope tv_subst emptyVarEnv -- No Id substitition
490 in_scope = mkInScopeSet (tyVarsOfTypes (varEnvElts tv_subst))
492 env1 | is_local = env
493 | otherwise = env { cons = refineConstrEnv subst (cons env) }
496 extendAlt :: ScEnv -> Id -> CoreExpr -> ConValue -> [Var] -> ScEnv
497 extendAlt env case_bndr scrut val alt_bndrs
499 env1 = SCE { scope = extendVarEnvList (scope env) [(b,Other) | b <- case_bndr : alt_bndrs],
500 cons = extendVarEnv (cons env) case_bndr val }
503 Var v -> -- Bind the scrutinee in the ConstrEnv if it's a variable
504 -- Also forget if the scrutinee is a RecArg, because we're
505 -- now in the branch of a case, and we don't want to
506 -- record a non-scrutinee use of v if we have
507 -- case v of { (a,b) -> ...(f v)... }
508 SCE { scope = extendVarEnv (scope env1) v Other,
509 cons = extendVarEnv (cons env1) v val }
512 -- When we encounter a recursive function binding
514 -- we want to extend the scope env with bindings
515 -- that record that f is a RecFn and x,y are RecArgs
516 extendRecBndr env fn bndrs
517 = env { scope = scope env `extendVarEnvList`
518 ((fn,RecFun): [(bndr,RecArg) | bndr <- bndrs]) }
522 %************************************************************************
524 \subsection{Usage information: flows upwards}
526 %************************************************************************
531 calls :: !(IdEnv ([Call])), -- Calls
532 -- The functions are a subset of the
533 -- RecFuns in the ScEnv
535 occs :: !(IdEnv ArgOcc) -- Information on argument occurrences
536 } -- The variables are a subset of the
537 -- RecArg in the ScEnv
539 type Call = (ConstrEnv, [CoreArg])
540 -- The arguments of the call, together with the
541 -- env giving the constructor bindings at the call site
543 nullUsage = SCU { calls = emptyVarEnv, occs = emptyVarEnv }
545 combineUsage u1 u2 = SCU { calls = plusVarEnv_C (++) (calls u1) (calls u2),
546 occs = plusVarEnv_C combineOcc (occs u1) (occs u2) }
548 combineUsages [] = nullUsage
549 combineUsages us = foldr1 combineUsage us
551 lookupOcc :: ScUsage -> Var -> (ScUsage, ArgOcc)
552 lookupOcc (SCU { calls = sc_calls, occs = sc_occs }) bndr
553 = (SCU {calls = sc_calls, occs = delVarEnv sc_occs bndr},
554 lookupVarEnv sc_occs bndr `orElse` NoOcc)
556 lookupOccs :: ScUsage -> [Var] -> (ScUsage, [ArgOcc])
557 lookupOccs (SCU { calls = sc_calls, occs = sc_occs }) bndrs
558 = (SCU {calls = sc_calls, occs = delVarEnvList sc_occs bndrs},
559 [lookupVarEnv sc_occs b `orElse` NoOcc | b <- bndrs])
561 data ArgOcc = NoOcc -- Doesn't occur at all; or a type argument
562 | UnkOcc -- Used in some unknown way
564 | ScrutOcc (UniqFM [ArgOcc]) -- Only taken apart or applied
565 -- ScrutOcc emptyUFM for functions, literals
566 -- ScrutOcc subs for data constructors;
567 -- the [ArgOcc] gives usage of the *value* components,
568 -- The domain of the UniqFM is the Unique of the data constructor
570 | BothOcc -- Definitely taken apart, *and* perhaps used in some other way
573 instance Outputable ArgOcc where
574 ppr (ScrutOcc xs) = ptext SLIT("scrut-occ") <+> ppr xs
575 ppr UnkOcc = ptext SLIT("unk-occ")
576 ppr BothOcc = ptext SLIT("both-occ")
577 ppr NoOcc = ptext SLIT("no-occ")
579 combineOcc NoOcc occ = occ
580 combineOcc occ NoOcc = occ
581 combineOcc (ScrutOcc xs) (ScrutOcc ys) = ScrutOcc (plusUFM_C combineOccs xs ys)
582 combineOcc UnkOcc UnkOcc = UnkOcc
583 combineOcc _ _ = BothOcc
585 combineOccs :: [ArgOcc] -> [ArgOcc] -> [ArgOcc]
586 combineOccs xs ys = zipWithEqual "combineOccs" combineOcc xs ys
588 subOccs :: ArgOcc -> AltCon -> [ArgOcc]
589 -- Find usage of components of data con; returns [UnkOcc...] if unknown
590 subOccs (ScrutOcc fm) (DataAlt dc) = lookupUFM fm dc `orElse` repeat UnkOcc
591 subOccs other dc = repeat UnkOcc
595 %************************************************************************
597 \subsection{The main recursive function}
599 %************************************************************************
601 The main recursive function gathers up usage information, and
602 creates specialised versions of functions.
605 scExpr :: ScEnv -> CoreExpr -> UniqSM (ScUsage, CoreExpr)
606 -- The unique supply is needed when we invent
607 -- a new name for the specialised function and its args
609 scExpr env e@(Type t) = returnUs (nullUsage, e)
610 scExpr env e@(Lit l) = returnUs (nullUsage, e)
611 scExpr env e@(Var v) = returnUs (varUsage env v UnkOcc, e)
612 scExpr env (Note n e) = scExpr env e `thenUs` \ (usg,e') ->
613 returnUs (usg, Note n e')
614 scExpr env (Lam b e) = scExpr (extendBndr env b) e `thenUs` \ (usg,e') ->
615 returnUs (usg, Lam b e')
617 scExpr env (Case scrut b ty alts)
618 = do { (alt_usgs, alt_occs, alts') <- mapAndUnzip3Us sc_alt alts
619 ; let (alt_usg, b_occ) = lookupOcc (combineUsages alt_usgs) b
620 scrut_occ = foldr combineOcc b_occ alt_occs
621 -- The combined usage of the scrutinee is given
622 -- by scrut_occ, which is passed to scScrut, which
623 -- in turn treats a bare-variable scrutinee specially
624 ; (scrut_usg, scrut') <- scScrut env scrut scrut_occ
625 ; return (alt_usg `combineUsage` scrut_usg,
626 Case scrut' b ty alts') }
629 = do { let env1 = extendCaseBndrs env b scrut con bs
630 ; (usg,rhs') <- scExpr env1 rhs
631 ; let (usg', arg_occs) = lookupOccs usg bs
632 scrut_occ = case con of
633 DataAlt dc -> ScrutOcc (unitUFM dc arg_occs)
634 other -> ScrutOcc emptyUFM
635 ; return (usg', scrut_occ, (con,bs,rhs')) }
637 scExpr env (Let bind body)
638 = scBind env bind `thenUs` \ (env', bind_usg, bind') ->
639 scExpr env' body `thenUs` \ (body_usg, body') ->
640 returnUs (bind_usg `combineUsage` body_usg, Let bind' body')
642 scExpr env e@(App _ _)
643 = do { let (fn, args) = collectArgs e
644 ; (fn_usg, fn') <- scScrut env fn (ScrutOcc emptyUFM)
645 -- Process the function too. It's almost always a variable,
646 -- but not always. In particular, if this pass follows float-in,
647 -- which it may, we can get
648 -- (let f = ...f... in f) arg1 arg2
649 -- We use scScrut to record the fact that the function is called
650 -- Perhpas we should check that it has at least one value arg,
651 -- but currently we don't bother
653 ; (arg_usgs, args') <- mapAndUnzipUs (scExpr env) args
654 ; let call_usg = case fn of
655 Var f | Just RecFun <- lookupScopeEnv env f
656 -> SCU { calls = unitVarEnv f [(cons env, args)],
659 ; return (combineUsages arg_usgs `combineUsage` fn_usg
660 `combineUsage` call_usg,
664 ----------------------
665 scScrut :: ScEnv -> CoreExpr -> ArgOcc -> UniqSM (ScUsage, CoreExpr)
666 -- Used for the scrutinee of a case,
667 -- or the function of an application
668 scScrut env e@(Var v) occ = returnUs (varUsage env v occ, e)
669 scScrut env e occ = scExpr env e
672 ----------------------
673 scBind :: ScEnv -> CoreBind -> UniqSM (ScEnv, ScUsage, CoreBind)
674 scBind env (Rec [(fn,rhs)])
676 = scExpr env_fn_body body `thenUs` \ (usg, body') ->
677 specialise env fn bndrs body' usg `thenUs` \ (rules, spec_prs) ->
678 -- Note body': the specialised copies should be based on the
679 -- optimised version of the body, in case there were
680 -- nested functions inside.
682 SCU { calls = calls, occs = occs } = usg
684 returnUs (extendBndr env fn, -- For the body of the letrec, just
685 -- extend the env with Other to record
686 -- that it's in scope; no funny RecFun business
687 SCU { calls = calls `delVarEnv` fn, occs = occs `delVarEnvList` val_bndrs},
688 Rec ((fn `addIdSpecialisations` rules, mkLams bndrs body') : spec_prs))
690 (bndrs,body) = collectBinders rhs
691 val_bndrs = filter isId bndrs
692 env_fn_body = extendRecBndr env fn bndrs
695 = mapAndUnzipUs do_one prs `thenUs` \ (usgs, prs') ->
696 returnUs (extendBndrs env (map fst prs), combineUsages usgs, Rec prs')
698 do_one (bndr,rhs) = scExpr env rhs `thenUs` \ (usg, rhs') ->
699 returnUs (usg, (bndr,rhs'))
701 scBind env (NonRec bndr rhs)
702 = scExpr env rhs `thenUs` \ (usg, rhs') ->
703 returnUs (extendBndr env bndr, usg, NonRec bndr rhs')
705 ----------------------
707 | Just RecArg <- lookupScopeEnv env v = SCU { calls = emptyVarEnv,
708 occs = unitVarEnv v use }
709 | otherwise = nullUsage
713 %************************************************************************
715 \subsection{The specialiser}
717 %************************************************************************
722 -> [CoreBndr] -> CoreExpr -- Its RHS
723 -> ScUsage -- Info on usage
724 -> UniqSM ([CoreRule], -- Rules
725 [(Id,CoreExpr)]) -- Bindings
727 specialise env fn bndrs body body_usg
728 = do { let (_, bndr_occs) = lookupOccs body_usg bndrs
730 ; mb_calls <- mapM (callToPats (scope env) bndr_occs)
731 (lookupVarEnv (calls body_usg) fn `orElse` [])
733 ; let good_calls :: [([Var], [CoreArg])]
734 good_calls = catMaybes mb_calls
735 in_scope = mkInScopeSet $ unionVarSets $
736 [ exprsFreeVars pats `delVarSetList` vs
737 | (vs,pats) <- good_calls ]
738 uniq_calls = nubBy (same_call in_scope) good_calls
740 mapAndUnzipUs (spec_one env fn (mkLams bndrs body))
741 (uniq_calls `zip` [1..]) }
743 -- Two calls are the same if they match both ways
744 same_call in_scope (vs1,as1)(vs2,as2)
745 = isJust (matchN in_scope vs1 as1 as2)
746 && isJust (matchN in_scope vs2 as2 as1)
748 callToPats :: InScopeEnv -> [ArgOcc] -> Call
749 -> UniqSM (Maybe ([Var], [CoreExpr]))
750 -- The VarSet is the variables to quantify over in the rule
751 -- The [CoreExpr] are the argument patterns for the rule
752 callToPats in_scope bndr_occs (con_env, args)
753 | length args < length bndr_occs -- Check saturated
756 = do { prs <- argsToPats in_scope con_env (args `zip` bndr_occs)
757 ; let (good_pats, pats) = unzip prs
758 pat_fvs = varSetElems (exprsFreeVars pats)
759 qvars = filter (not . (`elemVarEnv` in_scope)) pat_fvs
760 -- Quantify over variables that are not in sccpe
761 -- See Note [Shadowing] at the top
764 then return (Just (qvars, pats))
765 else return Nothing }
767 ---------------------
770 -> CoreExpr -- Rhs of the original function
771 -> (([Var], [CoreArg]), Int)
772 -> UniqSM (CoreRule, (Id,CoreExpr)) -- Rule and binding
774 -- spec_one creates a specialised copy of the function, together
775 -- with a rule for using it. I'm very proud of how short this
776 -- function is, considering what it does :-).
782 f = /\b \y::[(a,b)] -> ....f (b,c) ((:) (a,(b,c)) (x,v) (h w))...
783 [c::*, v::(b,c) are presumably bound by the (...) part]
785 f_spec = /\ b c \ v::(b,c) hw::[(a,(b,c))] ->
786 (...entire RHS of f...) (b,c) ((:) (a,(b,c)) (x,v) hw)
788 RULE: forall b::* c::*, -- Note, *not* forall a, x
792 f (b,c) ((:) (a,(b,c)) (x,v) hw) = f_spec b c v hw
795 spec_one env fn rhs ((vars_to_bind, pats), rule_number)
796 = getUniqueUs `thenUs` \ spec_uniq ->
799 fn_loc = nameSrcLoc fn_name
800 spec_occ = mkSpecOcc (nameOccName fn_name)
802 -- Put the type variables first; the type of a term
803 -- variable may mention a type variable
804 (tvs, ids) = partition isTyVar vars_to_bind
806 spec_body = mkApps rhs pats
807 body_ty = exprType spec_body
809 (spec_lam_args, spec_call_args) = mkWorkerArgs bndrs body_ty
810 -- Usual w/w hack to avoid generating
811 -- a spec_rhs of unlifted type and no args
813 rule_name = mkFastString ("SC:" ++ showSDoc (ppr fn <> int rule_number))
814 spec_rhs = mkLams spec_lam_args spec_body
815 spec_id = mkUserLocal spec_occ spec_uniq (mkPiTypes spec_lam_args body_ty) fn_loc
816 rule_rhs = mkVarApps (Var spec_id) spec_call_args
817 rule = mkLocalRule rule_name specConstrActivation fn_name bndrs pats rule_rhs
819 returnUs (rule, (spec_id, spec_rhs))
821 -- In which phase should the specialise-constructor rules be active?
822 -- Originally I made them always-active, but Manuel found that
823 -- this defeated some clever user-written rules. So Plan B
824 -- is to make them active only in Phase 0; after all, currently,
825 -- the specConstr transformation is only run after the simplifier
826 -- has reached Phase 0. In general one would want it to be
827 -- flag-controllable, but for now I'm leaving it baked in
829 specConstrActivation :: Activation
830 specConstrActivation = ActiveAfter 0 -- Baked in; see comments above
833 %************************************************************************
835 \subsection{Argument analysis}
837 %************************************************************************
839 This code deals with analysing call-site arguments to see whether
840 they are constructor applications.
842 ---------------------
843 good_arg :: ConstrEnv -> IdEnv ArgOcc -> (CoreBndr, CoreArg) -> Bool
844 -- See Note [Good arguments] above
845 good_arg con_env arg_occs (bndr, arg)
846 = case is_con_app_maybe con_env arg of
847 Just _ -> bndr_usg_ok arg_occs bndr arg
850 bndr_usg_ok :: IdEnv ArgOcc -> Var -> CoreArg -> Bool
851 bndr_usg_ok arg_occs bndr arg
852 = case lookupVarEnv arg_occs bndr of
853 Just ScrutOcc -> True -- Used only by case scrutiny
854 Just Both -> case arg of -- Used by case and elsewhere
855 App _ _ -> True -- so the arg should be an explicit con app
857 other -> False -- Not used, or used wonkily
861 -- argToPat takes an actual argument, and returns an abstracted
862 -- version, consisting of just the "constructor skeleton" of the
863 -- argument, with non-constructor sub-expression replaced by new
864 -- placeholder variables. For example:
865 -- C a (D (f x) (g y)) ==> C p1 (D p2 p3)
867 argToPat :: InScopeEnv -- What's in scope at the fn defn site
868 -> ConstrEnv -- ConstrEnv at the call site
869 -> CoreArg -- A call arg (or component thereof)
871 -> UniqSM (Bool, CoreArg)
872 -- Returns (interesting, pat),
873 -- where pat is the pattern derived from the argument
874 -- intersting=True if the pattern is non-trivial (not a variable or type)
875 -- E.g. x:xs --> (True, x:xs)
876 -- f xs --> (False, w) where w is a fresh wildcard
877 -- (f xs, 'c') --> (True, (w, 'c')) where w is a fresh wildcard
878 -- \x. x+y --> (True, \x. x+y)
879 -- lvl7 --> (True, lvl7) if lvl7 is bound
880 -- somewhere further out
882 argToPat in_scope con_env arg@(Type ty) arg_occ
883 = return (False, arg)
885 argToPat in_scope con_env (Var v) arg_occ -- Don't uniqify existing vars,
886 = return (interesting, Var v) -- so that we can spot when we pass them twice
888 interesting = not (isLocalId v) || v `elemVarEnv` in_scope
890 argToPat in_scope con_env arg arg_occ
894 is_value_lam (Lam v e) -- Spot a value lambda, even if
895 | isId v = True -- it is inside a type lambda
896 | otherwise = is_value_lam e
897 is_value_lam other = False
899 argToPat in_scope con_env arg arg_occ
900 | Just (CV dc args) <- is_con_app_maybe con_env arg
902 ScrutOcc _ -> True -- Used only by case scrutinee
903 BothOcc -> case arg of -- Used by case scrut
904 App {} -> True -- ...and elsewhere...
906 other -> False -- No point; the arg is not decomposed
907 = do { args' <- argsToPats in_scope con_env (args `zip` subOccs arg_occ dc)
908 ; return (True, mk_con_app dc (map snd args')) }
910 argToPat in_scope con_env arg arg_occ
911 = do { uniq <- getUniqueUs
912 ; let id = mkSysLocal FSLIT("sc") uniq (exprType arg)
913 ; return (False, Var id) }
915 argsToPats :: InScopeEnv -> ConstrEnv
916 -> [(CoreArg, ArgOcc)]
917 -> UniqSM [(Bool, CoreArg)]
918 argsToPats in_scope con_env args
921 do_one (arg,occ) = argToPat in_scope con_env arg occ
926 is_con_app_maybe :: ConstrEnv -> CoreExpr -> Maybe ConValue
927 is_con_app_maybe env (Var v)
928 = case lookupVarEnv env v of
929 Just stuff -> Just stuff
930 -- You might think we could look in the idUnfolding here
931 -- but that doesn't take account of which branch of a
932 -- case we are in, which is the whole point
934 Nothing | isCheapUnfolding unf
935 -> is_con_app_maybe env (unfoldingTemplate unf)
938 -- However we do want to consult the unfolding
939 -- as well, for let-bound constructors!
943 is_con_app_maybe env (Lit lit)
944 = Just (CV (LitAlt lit) [])
946 is_con_app_maybe env expr
947 = case collectArgs expr of
948 (Var fun, args) | Just con <- isDataConWorkId_maybe fun,
949 args `lengthAtLeast` dataConRepArity con
950 -- Might be > because the arity excludes type args
951 -> Just (CV (DataAlt con) args)
955 mk_con_app :: AltCon -> [CoreArg] -> CoreExpr
956 mk_con_app (LitAlt lit) [] = Lit lit
957 mk_con_app (DataAlt con) args = mkConApp con args