2 % (c) The GRASP/AQUA Project, Glasgow University, 1993-1996
4 \section[Specialise]{Stamping out overloading, and (optionally) polymorphism}
13 #include "HsVersions.h"
15 import Id ( Id, DictVar, idType, mkUserLocal,
17 getIdSpecialisation, setIdSpecialisation,
19 IdSet, mkIdSet, addOneToIdSet, intersectIdSets, isEmptyIdSet,
20 emptyIdSet, unionIdSets, minusIdSet, unitIdSet, elementOfIdSet,
22 IdEnv, mkIdEnv, lookupIdEnv, addOneToIdEnv, delOneFromIdEnv
25 import Type ( Type, mkTyVarTy, splitSigmaTy, instantiateTy, isDictTy,
26 tyVarsOfType, tyVarsOfTypes, applyTys, mkForAllTys
28 import TyCon ( TyCon )
30 TyVarSet, mkTyVarSet, isEmptyTyVarSet, intersectTyVarSets,
31 elementOfTyVarSet, unionTyVarSets, emptyTyVarSet,
32 TyVarEnv, mkTyVarEnv, delFromTyVarEnv
35 import PprCore () -- Instances
36 import Name ( NamedThing(..), getSrcLoc )
37 import SpecEnv ( addToSpecEnv, lookupSpecEnv, specEnvValues )
39 import UniqSupply ( UniqSupply,
40 UniqSM, initUs, thenUs, returnUs, getUnique, mapUs
44 import Maybes ( MaybeErr(..), maybeToBool )
46 import List ( partition )
47 import Util ( zipEqual )
54 %************************************************************************
56 \subsection[notes-Specialise]{Implementation notes [SLPJ, Aug 18 1993]}
58 %************************************************************************
60 These notes describe how we implement specialisation to eliminate
61 overloading, and optionally to eliminate unboxed polymorphism, and
64 The specialisation pass is a partial evaluator which works on Core
65 syntax, complete with all the explicit dictionary application,
66 abstraction and construction as added by the type checker. The
67 existing type checker remains largely as it is.
69 One important thought: the {\em types} passed to an overloaded
70 function, and the {\em dictionaries} passed are mutually redundant.
71 If the same function is applied to the same type(s) then it is sure to
72 be applied to the same dictionary(s)---or rather to the same {\em
73 values}. (The arguments might look different but they will evaluate
76 Second important thought: we know that we can make progress by
77 treating dictionary arguments as static and worth specialising on. So
78 we can do without binding-time analysis, and instead specialise on
79 dictionary arguments and no others.
88 and suppose f is overloaded.
90 STEP 1: CALL-INSTANCE COLLECTION
92 We traverse <body>, accumulating all applications of f to types and
95 (Might there be partial applications, to just some of its types and
96 dictionaries? In principle yes, but in practice the type checker only
97 builds applications of f to all its types and dictionaries, so partial
98 applications could only arise as a result of transformation, and even
99 then I think it's unlikely. In any case, we simply don't accumulate such
100 partial applications.)
102 There's a choice of whether to collect details of all *polymorphic* functions
103 or simply all *overloaded* ones. How to sort this out?
104 Pass in a predicate on the function to say if it is "interesting"?
105 This is dependent on the user flags: SpecialiseOverloaded
111 So now we have a collection of calls to f:
115 Notice that f may take several type arguments. To avoid ambiguity, we
116 say that f is called at type t1/t2 and t3/t4.
118 We take equivalence classes using equality of the *types* (ignoring
119 the dictionary args, which as mentioned previously are redundant).
121 STEP 3: SPECIALISATION
123 For each equivalence class, choose a representative (f t1 t2 d1 d2),
124 and create a local instance of f, defined thus:
126 f@t1/t2 = <f_rhs> t1 t2 d1 d2
128 (f_rhs presumably has some big lambdas and dictionary lambdas, so lots
129 of simplification will now result.) Then we should recursively do
132 The new id has its own unique, but its print-name (if exported) has
133 an explicit representation of the instance types t1/t2.
135 Add this new id to f's IdInfo, to record that f has a specialised version.
137 Before doing any of this, check that f's IdInfo doesn't already
138 tell us about an existing instance of f at the required type/s.
139 (This might happen if specialisation was applied more than once, or
140 it might arise from user SPECIALIZE pragmas.)
144 Wait a minute! What if f is recursive? Then we can't just plug in
145 its right-hand side, can we?
147 But it's ok. The type checker *always* creates non-recursive definitions
148 for overloaded recursive functions. For example:
150 f x = f (x+x) -- Yes I know its silly
154 f a (d::Num a) = let p = +.sel a d
156 letrec fl (y::a) = fl (p y y)
160 We still have recusion for non-overloadd functions which we
161 speciailise, but the recursive call should get speciailised to the
162 same recursive version.
168 All this is crystal clear when the function is applied to *constant
169 types*; that is, types which have no type variables inside. But what if
170 it is applied to non-constant types? Suppose we find a call of f at type
171 t1/t2. There are two possibilities:
173 (a) The free type variables of t1, t2 are in scope at the definition point
174 of f. In this case there's no problem, we proceed just as before. A common
175 example is as follows. Here's the Haskell:
180 After typechecking we have
182 g a (d::Num a) (y::a) = let f b (d'::Num b) (x::b) = +.sel b d' x x
183 in +.sel a d (f a d y) (f a d y)
185 Notice that the call to f is at type type "a"; a non-constant type.
186 Both calls to f are at the same type, so we can specialise to give:
188 g a (d::Num a) (y::a) = let f@a (x::a) = +.sel a d x x
189 in +.sel a d (f@a y) (f@a y)
192 (b) The other case is when the type variables in the instance types
193 are *not* in scope at the definition point of f. The example we are
194 working with above is a good case. There are two instances of (+.sel a d),
195 but "a" is not in scope at the definition of +.sel. Can we do anything?
196 Yes, we can "common them up", a sort of limited common sub-expression deal.
199 g a (d::Num a) (y::a) = let +.sel@a = +.sel a d
200 f@a (x::a) = +.sel@a x x
201 in +.sel@a (f@a y) (f@a y)
203 This can save work, and can't be spotted by the type checker, because
204 the two instances of +.sel weren't originally at the same type.
208 * There are quite a few variations here. For example, the defn of
209 +.sel could be floated ouside the \y, to attempt to gain laziness.
210 It certainly mustn't be floated outside the \d because the d has to
213 * We don't want to inline f_rhs in this case, because
214 that will duplicate code. Just commoning up the call is the point.
216 * Nothing gets added to +.sel's IdInfo.
218 * Don't bother unless the equivalence class has more than one item!
220 Not clear whether this is all worth it. It is of course OK to
221 simply discard call-instances when passing a big lambda.
223 Polymorphism 2 -- Overloading
225 Consider a function whose most general type is
227 f :: forall a b. Ord a => [a] -> b -> b
229 There is really no point in making a version of g at Int/Int and another
230 at Int/Bool, because it's only instancing the type variable "a" which
231 buys us any efficiency. Since g is completely polymorphic in b there
232 ain't much point in making separate versions of g for the different
235 That suggests that we should identify which of g's type variables
236 are constrained (like "a") and which are unconstrained (like "b").
237 Then when taking equivalence classes in STEP 2, we ignore the type args
238 corresponding to unconstrained type variable. In STEP 3 we make
239 polymorphic versions. Thus:
241 f@t1/ = /\b -> <f_rhs> t1 b d1 d2
243 This seems pretty simple, and a Good Thing.
245 Polymorphism 3 -- Unboxed
248 If we are speciailising at unboxed types we must speciailise
249 regardless of the overloading constraint. In the exaple above it is
250 worth speciailising at types Int/Int#, Int/Bool# and a/Int#, Int#/Int#
253 Note that specialising an overloaded type at an uboxed type requires
254 an unboxed instance -- we cannot default to an unspecialised version!
261 f x = let g p q = p==q
267 Before specialisation, leaving out type abstractions we have
269 f df x = let g :: Eq a => a -> a -> Bool
271 h :: Num a => a -> a -> (a, Bool)
272 h dh r s = let deq = eqFromNum dh
273 in (+ dh r s, g deq r s)
277 After specialising h we get a specialised version of h, like this:
279 h' r s = let deq = eqFromNum df
280 in (+ df r s, g deq r s)
282 But we can't naively make an instance for g from this, because deq is not in scope
283 at the defn of g. Instead, we have to float out the (new) defn of deq
284 to widen its scope. Notice that this floating can't be done in advance -- it only
285 shows up when specialisation is done.
287 DELICATE MATTER: the way we tell a dictionary binding is by looking to
288 see if it has a Dict type. If the type has been "undictify'd", so that
289 it looks like a tuple, then the dictionary binding won't be floated, and
290 an opportunity to specialise might be lost.
292 User SPECIALIZE pragmas
293 ~~~~~~~~~~~~~~~~~~~~~~~
294 Specialisation pragmas can be digested by the type checker, and implemented
295 by adding extra definitions along with that of f, in the same way as before
297 f@t1/t2 = <f_rhs> t1 t2 d1 d2
299 Indeed the pragmas *have* to be dealt with by the type checker, because
300 only it knows how to build the dictionaries d1 and d2! For example
302 g :: Ord a => [a] -> [a]
303 {-# SPECIALIZE f :: [Tree Int] -> [Tree Int] #-}
305 Here, the specialised version of g is an application of g's rhs to the
306 Ord dictionary for (Tree Int), which only the type checker can conjure
307 up. There might not even *be* one, if (Tree Int) is not an instance of
308 Ord! (All the other specialision has suitable dictionaries to hand
311 Problem. The type checker doesn't have to hand a convenient <f_rhs>, because
312 it is buried in a complex (as-yet-un-desugared) binding group.
315 f@t1/t2 = f* t1 t2 d1 d2
317 where f* is the Id f with an IdInfo which says "inline me regardless!".
318 Indeed all the specialisation could be done in this way.
319 That in turn means that the simplifier has to be prepared to inline absolutely
320 any in-scope let-bound thing.
323 Again, the pragma should permit polymorphism in unconstrained variables:
325 h :: Ord a => [a] -> b -> b
326 {-# SPECIALIZE h :: [Int] -> b -> b #-}
328 We *insist* that all overloaded type variables are specialised to ground types,
329 (and hence there can be no context inside a SPECIALIZE pragma).
330 We *permit* unconstrained type variables to be specialised to
332 - or left as a polymorphic type variable
333 but nothing in between. So
335 {-# SPECIALIZE h :: [Int] -> [c] -> [c] #-}
337 is *illegal*. (It can be handled, but it adds complication, and gains the
341 SPECIALISING INSTANCE DECLARATIONS
342 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
345 instance Foo a => Foo [a] where
347 {-# SPECIALIZE instance Foo [Int] #-}
349 The original instance decl creates a dictionary-function
352 dfun.Foo.List :: forall a. Foo a -> Foo [a]
354 The SPECIALIZE pragma just makes a specialised copy, just as for
355 ordinary function definitions:
357 dfun.Foo.List@Int :: Foo [Int]
358 dfun.Foo.List@Int = dfun.Foo.List Int dFooInt
360 The information about what instance of the dfun exist gets added to
361 the dfun's IdInfo in the same way as a user-defined function too.
363 In fact, matters are a little bit more complicated than this.
364 When we make one of these specialised instances, we are defining
365 a constant dictionary, and so we want immediate access to its constant
366 methods and superclasses. Indeed, these constant methods and superclasses
367 must be in the IdInfo for the class selectors! We need help from the
368 typechecker to sort this out, perhaps by generating a separate IdInfo
371 Automatic instance decl specialisation?
372 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
373 Can instance decls be specialised automatically? It's tricky.
374 We could collect call-instance information for each dfun, but
375 then when we specialised their bodies we'd get new call-instances
376 for ordinary functions; and when we specialised their bodies, we might get
377 new call-instances of the dfuns, and so on. This all arises because of
378 the unrestricted mutual recursion between instance decls and value decls.
380 Furthermore, instance decls are usually exported and used non-locally,
381 so we'll want to compile enough to get those specialisations done.
383 Lastly, there's no such thing as a local instance decl, so we can
384 survive solely by spitting out *usage* information, and then reading that
385 back in as a pragma when next compiling the file. So for now,
386 we only specialise instance decls in response to pragmas.
388 That means that even if an instance decl ain't otherwise exported it
389 needs to be spat out as with a SPECIALIZE pragma. Furthermore, it needs
390 something to say which module defined the instance, so the usage info
391 can be fed into the right reqts info file. Blegh.
394 SPECIAILISING DATA DECLARATIONS
395 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
397 With unboxed specialisation (or full specialisation) we also require
398 data types (and their constructors) to be speciailised on unboxed
401 In addition to normal call instances we gather TyCon call instances at
402 unboxed types, determine equivalence classes for the locally defined
403 TyCons and build speciailised data constructor Ids for each TyCon and
404 substitute these in the Con calls.
406 We need the list of local TyCons to partition the TyCon instance info.
407 We pass out a FiniteMap from local TyCons to Specialised Instances to
408 give to the interface and code genertors.
410 N.B. The specialised data constructors reference the original data
411 constructor and type constructor which do not have the updated
412 specialisation info attached. Any specialisation info must be
413 extracted from the TyCon map returned.
416 SPITTING OUT USAGE INFORMATION
417 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
419 To spit out usage information we need to traverse the code collecting
420 call-instance information for all imported (non-prelude?) functions
421 and data types. Then we equivalence-class it and spit it out.
423 This is done at the top-level when all the call instances which escape
424 must be for imported functions and data types.
427 Partial specialisation by pragmas
428 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
429 What about partial specialisation:
431 k :: (Ord a, Eq b) => [a] -> b -> b -> [a]
432 {-# SPECIALIZE k :: Eq b => [Int] -> b -> b -> [a] #-}
436 {-# SPECIALIZE k :: Eq b => [Int] -> [b] -> [b] -> [a] #-}
438 Seems quite reasonable. Similar things could be done with instance decls:
440 instance (Foo a, Foo b) => Foo (a,b) where
442 {-# SPECIALIZE instance Foo a => Foo (a,Int) #-}
443 {-# SPECIALIZE instance Foo b => Foo (Int,b) #-}
445 Ho hum. Things are complex enough without this. I pass.
448 Requirements for the simplifer
449 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
450 The simplifier has to be able to take advantage of the specialisation.
452 * When the simplifier finds an application of a polymorphic f, it looks in
453 f's IdInfo in case there is a suitable instance to call instead. This converts
455 f t1 t2 d1 d2 ===> f_t1_t2
457 Note that the dictionaries get eaten up too!
459 * Dictionary selection operations on constant dictionaries must be
462 +.sel Int d ===> +Int
464 The obvious way to do this is in the same way as other specialised
465 calls: +.sel has inside it some IdInfo which tells that if it's applied
466 to the type Int then it should eat a dictionary and transform to +Int.
468 In short, dictionary selectors need IdInfo inside them for constant
471 * Exactly the same applies if a superclass dictionary is being
474 Eq.sel Int d ===> dEqInt
476 * Something similar applies to dictionary construction too. Suppose
477 dfun.Eq.List is the function taking a dictionary for (Eq a) to
478 one for (Eq [a]). Then we want
480 dfun.Eq.List Int d ===> dEq.List_Int
482 Where does the Eq [Int] dictionary come from? It is built in
483 response to a SPECIALIZE pragma on the Eq [a] instance decl.
485 In short, dfun Ids need IdInfo with a specialisation for each
486 constant instance of their instance declaration.
489 What does the specialisation IdInfo look like?
490 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
493 [Maybe Type] -- Instance types
494 Int -- No of dicts to eat
495 Id -- Specialised version
497 For example, if f has this SpecInfo:
499 SpecInfo [Just t1, Nothing, Just t3] 2 f'
503 f t1 t2 t3 d1 d2 ===> f t2
505 The "Nothings" identify type arguments in which the specialised
506 version is polymorphic.
508 What can't be done this way?
509 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
510 There is no way, post-typechecker, to get a dictionary for (say)
511 Eq a from a dictionary for Eq [a]. So if we find
515 we can't transform to
520 eqList :: (a->a->Bool) -> [a] -> [a] -> Bool
522 Of course, we currently have no way to automatically derive
523 eqList, nor to connect it to the Eq [a] instance decl, but you
524 can imagine that it might somehow be possible. Taking advantage
525 of this is permanently ruled out.
527 Still, this is no great hardship, because we intend to eliminate
528 overloading altogether anyway!
533 What about types/classes mentioned in SPECIALIZE pragmas spat out,
534 but not otherwise exported. Even if they are exported, what about
535 their original names.
537 Suggestion: use qualified names in pragmas, omitting module for
538 prelude and "this module".
545 f a (d::Num a) = let g = ...
547 ...(let d1::Ord a = Num.Ord.sel a d in g a d1)...
549 Here, g is only called at one type, but the dictionary isn't in scope at the
550 definition point for g. Usually the type checker would build a
551 definition for d1 which enclosed g, but the transformation system
552 might have moved d1's defn inward.
558 What should we do when a value is specialised to a *strict* unboxed value?
560 map_*_* f (x:xs) = let h = f x
564 Could convert let to case:
566 map_*_Int# f (x:xs) = case f x of h# ->
570 This may be undesirable since it forces evaluation here, but the value
571 may not be used in all branches of the body. In the general case this
572 transformation is impossible since the mutual recursion in a letrec
573 cannot be expressed as a case.
575 There is also a problem with top-level unboxed values, since our
576 implementation cannot handle unboxed values at the top level.
578 Solution: Lift the binding of the unboxed value and extract it when it
581 map_*_Int# f (x:xs) = let h = case (f x) of h# -> _Lift h#
586 Now give it to the simplifier and the _Lifting will be optimised away.
588 The benfit is that we have given the specialised "unboxed" values a
589 very simplep lifted semantics and then leave it up to the simplifier to
590 optimise it --- knowing that the overheads will be removed in nearly
593 In particular, the value will only be evaluted in the branches of the
594 program which use it, rather than being forced at the point where the
595 value is bound. For example:
597 filtermap_*_* p f (x:xs)
604 filtermap_*_Int# p f (x:xs)
605 = let h = case (f x) of h# -> _Lift h#
608 True -> case h of _Lift h#
612 The binding for h can still be inlined in the one branch and the
616 Question: When won't the _Lifting be eliminated?
618 Answer: When they at the top-level (where it is necessary) or when
619 inlining would duplicate work (or possibly code depending on
620 options). However, the _Lifting will still be eliminated if the
621 strictness analyser deems the lifted binding strict.
624 A note about non-tyvar dictionaries
625 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
626 Some Ids have types like
628 forall a,b,c. Eq a -> Ord [a] -> tau
630 This seems curious at first, because we usually only have dictionary
631 args whose types are of the form (C a) where a is a type variable.
632 But this doesn't hold for the functions arising from instance decls,
633 which sometimes get arguements with types of form (C (T a)) for some
636 Should we specialise wrt this compound-type dictionary? We used to say
638 "This is a heuristic judgement, as indeed is the fact that we
639 specialise wrt only dictionaries. We choose *not* to specialise
640 wrt compound dictionaries because at the moment the only place
641 they show up is in instance decls, where they are simply plugged
642 into a returned dictionary. So nothing is gained by specialising
645 But it is simpler and more uniform to specialise wrt these dicts too;
646 and in future GHC is likely to support full fledged type signatures
648 f ;: Eq [(a,b)] => ...
651 %************************************************************************
653 \subsubsection{The new specialiser}
655 %************************************************************************
657 Our basic game plan is this. For let(rec) bound function
658 f :: (C a, D c) => (a,b,c,d) -> Bool
660 * Find any specialised calls of f, (f ts ds), where
661 ts are the type arguments t1 .. t4, and
662 ds are the dictionary arguments d1 .. d2.
664 * Add a new definition for f1 (say):
666 f1 = /\ b d -> (..body of f..) t1 b t3 d d1 d2
668 Note that we abstract over the unconstrained type arguments.
672 [t1,b,t3,d] |-> \d1 d2 -> f1 b d
674 to the specialisations of f. This will be used by the
675 simplifier to replace calls
676 (f t1 t2 t3 t4) da db
678 (\d1 d1 -> f1 t2 t4) da db
680 All the stuff about how many dictionaries to discard, and what types
681 to apply the specialised function to, are handled by the fact that the
682 SpecEnv contains a template for the result of the specialisation.
684 We don't build *partial* specialisations for f. For example:
686 f :: Eq a => a -> a -> Bool
687 {-# SPECIALISE f :: (Eq b, Eq c) => (b,c) -> (b,c) -> Bool #-}
689 Here, little is gained by making a specialised copy of f.
690 There's a distinct danger that the specialised version would
691 first build a dictionary for (Eq b, Eq c), and then select the (==)
692 method from it! Even if it didn't, not a great deal is saved.
694 We do, however, generate polymorphic, but not overloaded, specialisations:
696 f :: Eq a => [a] -> b -> b -> b
697 {#- SPECIALISE f :: [Int] -> b -> b -> b #-}
699 Hence, the invariant is this:
701 *** no specialised version is overloaded ***
704 %************************************************************************
706 \subsubsection{The exported function}
708 %************************************************************************
711 specProgram :: UniqSupply -> [CoreBinding] -> [CoreBinding]
713 = initSM us (go binds `thenSM` \ (binds', _) ->
717 go [] = returnSM ([], emptyUDs)
718 go (bind:binds) = go binds `thenSM` \ (binds', uds) ->
719 specBind bind uds `thenSM` \ (bind', uds') ->
720 returnSM (bind' ++ binds', uds')
723 %************************************************************************
725 \subsubsection{@specExpr@: the main function}
727 %************************************************************************
730 specExpr :: CoreExpr -> SpecM (CoreExpr, UsageDetails)
732 ---------------- First the easy cases --------------------
733 specExpr e@(Var _) = returnSM (e, emptyUDs)
734 specExpr e@(Lit _) = returnSM (e, emptyUDs)
735 specExpr e@(Con _ _) = returnSM (e, emptyUDs)
736 specExpr e@(Prim _ _) = returnSM (e, emptyUDs)
738 specExpr (Coerce co ty body)
739 = specExpr body `thenSM` \ (body', uds) ->
740 returnSM (Coerce co ty body', uds)
742 specExpr (SCC cc body)
743 = specExpr body `thenSM` \ (body', uds) ->
744 returnSM (SCC cc body', uds)
747 ---------------- Applications might generate a call instance --------------------
748 specExpr e@(App fun arg)
751 go (App fun arg) args = go fun (arg:args)
752 go (Var f) args = returnSM (e, mkCallUDs f args)
753 go other args = specExpr other `thenSM` \ (e', uds) ->
754 returnSM (foldl App e' args, uds)
756 ---------------- Lambda/case require dumping of usage details --------------------
758 = specExpr body `thenSM` \ (body', uds) ->
760 (filtered_uds, body'') = dumpUDs bndrs uds body'
762 returnSM (foldr Lam body'' bndrs, filtered_uds)
764 (bndrs, body) = go [] e
766 -- More efficient to collect a group of binders together all at once
767 go bndrs (Lam bndr e) = go (bndr:bndrs) e
768 go bndrs e = (reverse bndrs, e)
771 specExpr (Case scrut alts)
772 = specExpr scrut `thenSM` \ (scrut', uds_scrut) ->
773 spec_alts alts `thenSM` \ (alts', uds_alts) ->
774 returnSM (Case scrut' alts', uds_scrut `plusUDs` uds_alts)
776 spec_alts (AlgAlts alts deflt)
777 = mapAndCombineSM spec_alg_alt alts `thenSM` \ (alts', uds1) ->
778 spec_deflt deflt `thenSM` \ (deflt', uds2) ->
779 returnSM (AlgAlts alts' deflt', uds1 `plusUDs` uds2)
781 spec_alts (PrimAlts alts deflt)
782 = mapAndCombineSM spec_prim_alt alts `thenSM` \ (alts', uds1) ->
783 spec_deflt deflt `thenSM` \ (deflt', uds2) ->
784 returnSM (PrimAlts alts' deflt', uds1 `plusUDs` uds2)
786 spec_alg_alt (con, args, rhs)
787 = specExpr rhs `thenSM` \ (rhs', uds) ->
789 (uds', rhs'') = dumpUDs (map ValBinder args) uds rhs'
791 returnSM ((con, args, rhs''), uds')
793 spec_prim_alt (lit, rhs)
794 = specExpr rhs `thenSM` \ (rhs', uds) ->
795 returnSM ((lit, rhs'), uds)
797 spec_deflt NoDefault = returnSM (NoDefault, emptyUDs)
798 spec_deflt (BindDefault arg rhs)
799 = specExpr rhs `thenSM` \ (rhs', uds) ->
801 (uds', rhs'') = dumpUDs [ValBinder arg] uds rhs'
803 returnSM (BindDefault arg rhs'', uds')
805 ---------------- Finally, let is the interesting case --------------------
806 specExpr (Let bind body)
807 = -- Deal with the body
808 specExpr body `thenSM` \ (body', body_uds) ->
810 -- Deal with the bindings
811 specBind bind body_uds `thenSM` \ (binds', uds) ->
814 returnSM (foldr Let body' binds', uds)
817 %************************************************************************
819 \subsubsection{Dealing with a binding}
821 %************************************************************************
824 specBind :: CoreBinding
825 -> UsageDetails -- Info on how the scope of the binding
826 -> SpecM ([CoreBinding], -- New bindings
827 UsageDetails) -- And info to pass upstream
829 specBind (NonRec bndr rhs) body_uds
830 | isDictTy (idType bndr)
831 = -- It's a dictionary binding
832 -- Pick it up and float it outwards.
833 specExpr rhs `thenSM` \ (rhs', rhs_uds) ->
835 all_uds = rhs_uds `plusUDs` addDictBind body_uds bndr rhs'
837 returnSM ([], all_uds)
840 = -- Deal with the RHS, specialising it according
841 -- to the calls found in the body
842 specDefn (calls body_uds) (bndr,rhs) `thenSM` \ ((bndr',rhs'), spec_defns, spec_uds) ->
844 (all_uds, (dict_binds, dump_calls))
845 = splitUDs [ValBinder bndr] (spec_uds `plusUDs` body_uds)
847 -- If we make specialisations then we Rec the whole lot together
848 -- If not, leave it as a NonRec
849 new_bind | null spec_defns = NonRec bndr' rhs'
850 | otherwise = Rec ((bndr',rhs'):spec_defns)
852 returnSM ( new_bind : dict_binds, all_uds )
854 specBind (Rec pairs) body_uds
855 = mapSM (specDefn (calls body_uds)) pairs `thenSM` \ stuff ->
857 (pairs', spec_defns_s, spec_uds_s) = unzip3 stuff
858 spec_defns = concat spec_defns_s
859 spec_uds = plusUDList spec_uds_s
860 (all_uds, (dict_binds, dump_calls))
861 = splitUDs (map (ValBinder . fst) pairs) (spec_uds `plusUDs` body_uds)
862 new_bind = Rec (spec_defns ++ pairs')
864 returnSM ( new_bind : dict_binds, all_uds )
866 specDefn :: CallDetails -- Info on how it is used in its scope
867 -> (Id, CoreExpr) -- The thing being bound and its un-processed RHS
868 -> SpecM ((Id, CoreExpr), -- The thing and its processed RHS
869 -- the Id may now have specialisations attached
870 [(Id,CoreExpr)], -- Extra, specialised bindings
871 UsageDetails -- Stuff to fling upwards from the RHS and its
872 ) -- specialised versions
874 specDefn calls (fn, rhs)
875 -- The first case is the interesting one
876 | n_tyvars == length rhs_tyvars -- Rhs of fn's defn has right number of big lambdas
877 && n_dicts <= length rhs_bndrs -- and enough dict args
878 && not (null calls_for_me) -- And there are some calls to specialise
879 = -- Specialise the body of the function
880 specExpr body `thenSM` \ (body', body_uds) ->
882 (float_uds, bound_uds@(dict_binds,_)) = splitUDs rhs_bndrs body_uds
885 -- Make a specialised version for each call in calls_for_me
886 mapSM (spec_call bound_uds) calls_for_me `thenSM` \ stuff ->
888 (spec_defns, spec_uds, spec_env_stuff) = unzip3 stuff
890 fn' = addIdSpecialisations fn spec_env_stuff
891 rhs' = foldr Lam (foldr Let body' dict_binds) rhs_bndrs
893 returnSM ((fn',rhs'),
895 float_uds `plusUDs` plusUDList spec_uds)
897 | otherwise -- No calls or RHS doesn't fit our preconceptions
898 = specExpr rhs `thenSM` \ (rhs', rhs_uds) ->
899 returnSM ((fn, rhs'), [], rhs_uds)
903 (tyvars, theta, tau) = splitSigmaTy fn_type
904 n_tyvars = length tyvars
905 n_dicts = length theta
906 mk_spec_tys call_ts = zipWith mk_spec_ty call_ts tyvars
908 mk_spec_ty (Just ty) _ = ty
909 mk_spec_ty Nothing tyvar = mkTyVarTy tyvar
911 (rhs_tyvars, rhs_ids, rhs_body) = collectBinders rhs
912 rhs_dicts = take n_dicts rhs_ids
913 rhs_bndrs = map TyBinder rhs_tyvars ++ map ValBinder rhs_dicts
914 body = mkValLam (drop n_dicts rhs_ids) rhs_body
915 -- Glue back on the non-dict lambdas
917 calls_for_me = case lookupFM calls fn of
919 Just cs -> fmToList cs
921 -- Filter out calls for which we already have a specialisation
922 calls_to_spec = filter spec_me calls_for_me
923 spec_me (call_ts, _) = not (maybeToBool (lookupSpecEnv id_spec_env (mk_spec_tys call_ts)))
924 id_spec_env = getIdSpecialisation fn
926 ----------------------------------------------------------
927 -- Specialise to one particular call pattern
928 spec_call :: ProtoUsageDetails -- From the original body, captured by
929 -- the dictionary lambdas
930 -> ([Maybe Type], [DictVar]) -- Call instance
931 -> SpecM ((Id,CoreExpr), -- Specialised definition
932 UsageDetails, -- Usage details from specialised body
933 ([TyVar], [Type], CoreExpr)) -- Info for the Id's SpecEnv
934 spec_call bound_uds (call_ts, call_ds)
935 = ASSERT( length call_ts == n_tyvars && length call_ds == n_dicts )
936 -- Calls are only recorded for properly-saturated applications
938 -- Supppose the call is for f [Just t1, Nothing, Just t3, Nothing] [d1, d2]
940 -- Construct the new binding
941 -- f1 = /\ b d -> (..rhs of f..) t1 b t3 d d1 d2
942 -- and the type of this binder
944 spec_tyvars = [tyvar | (tyvar, Nothing) <- tyvars `zip` call_ts]
945 spec_tys = mk_spec_tys call_ts
946 spec_rhs = mkTyLam spec_tyvars $
947 mkGenApp rhs (map TyArg spec_tys ++ map VarArg call_ds)
948 spec_id_ty = mkForAllTys spec_tyvars (instantiateTy ty_env tau)
949 ty_env = mkTyVarEnv (zipEqual "spec_call" tyvars spec_tys)
951 newIdSM fn spec_id_ty `thenSM` \ spec_f ->
954 -- Construct the stuff for f's spec env
955 -- [b,d] [t1,b,t3,d] |-> \d1 d2 -> f1 b d
957 spec_env_rhs = mkValLam call_ds $
958 mkTyApp (Var spec_f) $
959 map mkTyVarTy spec_tyvars
960 spec_env_info = (spec_tyvars, spec_tys, spec_env_rhs)
963 -- Specialise the UDs from f's RHS
965 -- Only the overloaded tyvars should be free in the uds
966 ty_env = [ (rhs_tyvar,ty)
967 | (rhs_tyvar, Just ty) <- zipEqual "specUDs1" rhs_tyvars call_ts
969 dict_env = zipEqual "specUDs2" rhs_dicts call_ds
971 specUDs ty_env dict_env bound_uds `thenSM` \ spec_uds ->
973 returnSM ((spec_f, spec_rhs),
979 %************************************************************************
981 \subsubsection{UsageDetails and suchlike}
983 %************************************************************************
986 type FreeDicts = IdSet
990 dict_binds :: !(Bag (DictVar, CoreExpr, TyVarSet, FreeDicts)),
991 -- Floated dictionary bindings
992 -- The order is important;
993 -- in ds1 `union` ds2, bindings in ds2 can depend on those in ds1
994 -- (Remember, Bags preserve order in GHC.)
995 -- The FreeDicts is the free vars of the RHS
997 calls :: !CallDetails
1000 emptyUDs = MkUD { dict_binds = emptyBag, calls = emptyFM }
1002 type ProtoUsageDetails = ([CoreBinding], -- Dict bindings
1003 [(Id, [Maybe Type], [DictVar])]
1006 ------------------------------------------------------------
1007 type CallDetails = FiniteMap Id CallInfo
1008 type CallInfo = FiniteMap [Maybe Type] -- Nothing => unconstrained type argument
1009 [DictVar] -- Dict args
1010 -- The finite maps eliminate duplicates
1011 -- The list of types and dictionaries is guaranteed to
1012 -- match the type of f
1014 callDetailsToList calls = [ (id,tys,dicts)
1015 | (id,fm) <- fmToList calls,
1016 (tys,dicts) <- fmToList fm
1019 listToCallDetails calls = foldr (unionCalls . singleCall) emptyFM calls
1021 unionCalls :: CallDetails -> CallDetails -> CallDetails
1022 unionCalls c1 c2 = plusFM_C plusFM c1 c2
1024 singleCall (id, tys, dicts) = unitFM id (unitFM tys dicts)
1028 || length spec_tys /= n_tyvars
1029 || length dicts /= n_dicts
1030 = emptyUDs -- Not overloaded
1033 = MkUD {dict_binds = emptyBag,
1034 calls = singleCall (f, spec_tys, dicts)
1037 (tyvars, theta, tau) = splitSigmaTy (idType f)
1038 constrained_tyvars = foldr (unionTyVarSets . tyVarsOfTypes . snd) emptyTyVarSet theta
1039 n_tyvars = length tyvars
1040 n_dicts = length theta
1042 spec_tys = [mk_spec_ty tv ty | (tv, TyArg ty) <- tyvars `zip` args]
1043 dicts = [d | (_, VarArg d) <- theta `zip` (drop n_tyvars args)]
1045 mk_spec_ty tyvar ty | tyvar `elementOfTyVarSet` constrained_tyvars
1050 ------------------------------------------------------------
1051 plusUDs :: UsageDetails -> UsageDetails -> UsageDetails
1052 plusUDs (MkUD {dict_binds = db1, calls = calls1})
1053 (MkUD {dict_binds = db2, calls = calls2})
1054 = MkUD {dict_binds, calls}
1056 dict_binds = db1 `unionBags` db2
1057 calls = calls1 `unionCalls` calls2
1059 plusUDList = foldr plusUDs emptyUDs
1061 mkDB dict rhs = (dict, rhs, db_ftvs, db_fvs)
1063 db_ftvs = tyVarsOfType (idType dict) -- Superset of RHS fvs
1064 db_fvs = dictRhsFVs rhs
1066 addDictBind uds dict rhs = uds { dict_binds = mkDB dict rhs `consBag` dict_binds uds }
1068 dumpUDs :: [CoreBinder]
1069 -> UsageDetails -> CoreExpr
1070 -> (UsageDetails, CoreExpr)
1071 dumpUDs bndrs uds body
1072 = (free_uds, foldr Let body dict_binds)
1074 (free_uds, (dict_binds, _)) = splitUDs bndrs uds
1076 splitUDs :: [CoreBinder]
1078 -> (UsageDetails, -- These don't mention the binders
1079 ProtoUsageDetails) -- These do
1081 splitUDs bndrs uds@(MkUD {dict_binds = orig_dbs,
1082 calls = orig_calls})
1084 = if isEmptyBag dump_dbs && null dump_calls then
1085 -- Common case: binder doesn't affect floats
1089 -- Binders bind some of the fvs of the floats
1090 (MkUD {dict_binds = free_dbs,
1091 calls = listToCallDetails free_calls},
1092 (bagToList dump_dbs, dump_calls)
1096 tyvar_set = mkTyVarSet [tv | TyBinder tv <- bndrs]
1097 id_set = mkIdSet [id | ValBinder id <- bndrs]
1099 (free_dbs, dump_dbs, dump_idset)
1100 = foldlBag dump_db (emptyBag, emptyBag, id_set) orig_dbs
1101 -- Important that it's foldl not foldr;
1102 -- we're accumulating the set of dumped ids in dump_set
1104 -- Filter out any calls that mention things that are being dumped
1105 -- Don't need to worry about the tyvars because the dicts will
1106 -- spot the captured ones; any fully polymorphic arguments will
1107 -- be Nothings in the call details
1108 orig_call_list = callDetailsToList orig_calls
1109 (dump_calls, free_calls) = partition captured orig_call_list
1110 captured (id,tys,dicts) = any (`elementOfIdSet` dump_idset) (id:dicts)
1112 dump_db (free_dbs, dump_dbs, dump_idset) db@(dict, rhs, ftvs, fvs)
1113 | isEmptyIdSet (dump_idset `intersectIdSets` fvs)
1114 && isEmptyTyVarSet (tyvar_set `intersectTyVarSets` ftvs)
1115 = (free_dbs `snocBag` db, dump_dbs, dump_idset)
1117 | otherwise -- Dump it
1118 = (free_dbs, dump_dbs `snocBag` NonRec dict rhs,
1119 dump_idset `addOneToIdSet` dict)
1122 Given a type and value substitution, specUDs creates a specialised copy of
1126 specUDs :: [(TyVar,Type)] -> [(DictVar,DictVar)] -> ProtoUsageDetails -> SpecM UsageDetails
1127 specUDs tv_env_list dict_env_list (dbs, calls)
1128 = specDBs dict_env dbs `thenSM` \ (dict_env', dbs') ->
1129 returnSM (MkUD { dict_binds = dbs',
1130 calls = listToCallDetails (map (inst_call dict_env') calls)
1133 tv_env = mkTyVarEnv tv_env_list
1134 dict_env = mkIdEnv dict_env_list
1136 inst_call dict_env (id, tys, dicts) = (id, map inst_maybe_ty tys,
1137 map (lookupId dict_env) dicts)
1139 inst_maybe_ty Nothing = Nothing
1140 inst_maybe_ty (Just ty) = Just (instantiateTy tv_env ty)
1143 = returnSM (dict_env, emptyBag)
1144 specDBs dict_env (NonRec dict rhs : dbs)
1145 = newIdSM dict (instantiateTy tv_env (idType dict)) `thenSM` \ dict' ->
1147 dict_env' = addOneToIdEnv dict_env dict dict'
1148 rhs' = instantiateDictRhs tv_env dict_env rhs
1150 specDBs dict_env' dbs `thenSM` \ (dict_env'', dbs') ->
1151 returnSM ( dict_env'', mkDB dict' rhs' `consBag` dbs' )
1154 %************************************************************************
1156 \subsubsection{Boring helper functions}
1158 %************************************************************************
1161 lookupId:: IdEnv Id -> Id -> Id
1162 lookupId env id = case lookupIdEnv env id of
1166 instantiateDictRhs :: TyVarEnv Type -> IdEnv Id -> CoreExpr -> CoreExpr
1167 -- Cheapo function for simple RHSs
1168 instantiateDictRhs ty_env id_env rhs
1171 go (App e1 (VarArg a)) = App (go e1) (VarArg (lookupId id_env a))
1172 go (App e1 (TyArg t)) = App (go e1) (TyArg (instantiateTy ty_env t))
1173 go (Var v) = Var (lookupId id_env v)
1176 dictRhsFVs :: CoreExpr -> IdSet
1177 -- Cheapo function for simple RHSs
1178 dictRhsFVs (App e1 (VarArg a)) = dictRhsFVs e1 `addOneToIdSet` a
1179 dictRhsFVs (App e1 (TyArg t)) = dictRhsFVs e1
1180 dictRhsFVs (Var v) = unitIdSet v
1181 dictRhsFVs (Lit l) = emptyIdSet
1184 addIdSpecialisations id spec_stuff
1185 = (if not (null errs) then
1186 pprTrace "Duplicate specialisations" (vcat (map ppr errs))
1189 setIdSpecialisation id new_spec_env
1191 (new_spec_env, errs) = foldr add (getIdSpecialisation id, []) spec_stuff
1193 add (tyvars, tys, template) (spec_env, errs)
1194 = case addToSpecEnv True spec_env tyvars tys template of
1195 Succeeded spec_env' -> (spec_env', errs)
1196 Failed err -> (spec_env, err:errs)
1198 -- Given an Id, isSpecVars returns all its specialisations.
1199 -- We extract these from its SpecEnv.
1200 -- This is used by the occurrence analyser and free-var finder;
1201 -- we regard an Id's specialisations as free in the Id's definition.
1203 idSpecVars :: Id -> [Id]
1205 = map get_spec (specEnvValues (getIdSpecialisation id))
1207 -- get_spec is another cheapo function like dictRhsFVs
1208 -- It knows what these specialisation temlates look like,
1209 -- and just goes for the jugular
1210 get_spec (App f _) = get_spec f
1211 get_spec (Lam _ b) = get_spec b
1212 get_spec (Var v) = v
1214 -- substSpecEnvRhs applies a substitution to the RHS's of a SpecEnv
1215 -- It's placed here because Specialise.lhs built that RHS, so
1216 -- it knows its structure. (Fully general subst
1218 substSpecEnvRhs te ve rhs
1221 go te ve (App f (TyArg ty)) = App (go te ve f) (TyArg (instantiateTy te ty))
1222 go te ve (App f (VarArg v)) = App (go te ve f) (case lookupIdEnv ve v of
1224 Nothing -> VarArg v)
1225 go te ve (Var v) = case lookupIdEnv ve v of
1226 Just (VarArg v') -> Var v'
1227 Just (LitArg l) -> Lit l
1230 -- These equations are a bit half baked, because
1231 -- they don't deal properly wih capture.
1232 -- But I'm sure it'll never matter... sigh.
1233 go te ve (Lam b@(TyBinder tyvar) e) = Lam b (go te' ve e)
1235 te' = delFromTyVarEnv te tyvar
1237 go te ve (Lam b@(ValBinder v) e) = Lam b (go te ve' e)
1239 ve' = delOneFromIdEnv ve v
1241 ----------------------------------------
1242 type SpecM a = UniqSM a
1246 getUniqSM = getUnique
1250 mapAndCombineSM f [] = returnSM ([], emptyUDs)
1251 mapAndCombineSM f (x:xs) = f x `thenSM` \ (y, uds1) ->
1252 mapAndCombineSM f xs `thenSM` \ (ys, uds2) ->
1253 returnSM (y:ys, uds1 `plusUDs` uds2)
1255 newIdSM old_id new_ty
1256 = getUnique `thenSM` \ uniq ->
1257 returnSM (mkUserLocal (getOccName old_id)