2 % (c) The University of Glasgow, 1994-2000
4 \section{Core pass to saturate constructors and PrimOps}
8 corePrepPgm, corePrepExpr
11 #include "HsVersions.h"
13 import CoreUtils( exprType, exprIsValue, etaExpand, exprArity, exprOkForSpeculation )
14 import CoreFVs ( exprFreeVars )
15 import CoreLint ( endPass )
17 import Type ( Type, applyTy, splitFunTy_maybe,
18 isUnLiftedType, isUnboxedTupleType, seqType )
19 import NewDemand ( Demand, isStrictDmd, lazyDmd, StrictSig(..), DmdType(..) )
20 import Var ( Var, Id, setVarUnique )
23 import Id ( mkSysLocal, idType, idNewDemandInfo, idArity, setIdUnfolding, setIdType,
24 isFCallId, isGlobalId, isImplicitId,
25 isLocalId, hasNoBinding, idNewStrictness,
26 idUnfolding, isDataConWorkId_maybe, isPrimOpId_maybe
28 import DataCon ( isVanillaDataCon )
29 import PrimOp ( PrimOp( DataToTagOp ) )
30 import HscTypes ( TypeEnv, typeEnvElts, TyThing( AnId ) )
31 import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel,
39 import Util ( listLengthCmp )
43 -- ---------------------------------------------------------------------------
45 -- ---------------------------------------------------------------------------
47 The goal of this pass is to prepare for code generation.
49 1. Saturate constructor and primop applications.
51 2. Convert to A-normal form:
53 * Use case for strict arguments:
54 f E ==> case E of x -> f x
57 * Use let for non-trivial lazy arguments
58 f E ==> let x = E in f x
59 (were f is lazy and x is non-trivial)
61 3. Similarly, convert any unboxed lets into cases.
62 [I'm experimenting with leaving 'ok-for-speculation'
63 rhss in let-form right up to this point.]
65 4. Ensure that lambdas only occur as the RHS of a binding
66 (The code generator can't deal with anything else.)
68 5. [Not any more; nuked Jun 2002] Do the seq/par munging.
70 6. Clone all local Ids.
71 This means that all such Ids are unique, rather than the
72 weaker guarantee of no clashes which the simplifier provides.
73 And that is what the code generator needs.
75 We don't clone TyVars. The code gen doesn't need that,
76 and doing so would be tiresome because then we'd need
77 to substitute in types.
80 7. Give each dynamic CCall occurrence a fresh unique; this is
81 rather like the cloning step above.
83 8. Inject bindings for the "implicit" Ids:
84 * Constructor wrappers
87 We want curried definitions for all of these in case they
88 aren't inlined by some caller.
90 This is all done modulo type applications and abstractions, so that
91 when type erasure is done for conversion to STG, we don't end up with
92 any trivial or useless bindings.
96 -- -----------------------------------------------------------------------------
98 -- -----------------------------------------------------------------------------
101 corePrepPgm :: DynFlags -> [CoreBind] -> TypeEnv -> IO [CoreBind]
102 corePrepPgm dflags binds types
103 = do showPass dflags "CorePrep"
104 us <- mkSplitUniqSupply 's'
106 let implicit_binds = mkImplicitBinds types
107 -- NB: we must feed mkImplicitBinds through corePrep too
108 -- so that they are suitably cloned and eta-expanded
110 binds_out = initUs_ us (
111 corePrepTopBinds binds `thenUs` \ floats1 ->
112 corePrepTopBinds implicit_binds `thenUs` \ floats2 ->
113 returnUs (deFloatTop (floats1 `appendFloats` floats2))
116 endPass dflags "CorePrep" Opt_D_dump_prep binds_out
119 corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
120 corePrepExpr dflags expr
121 = do showPass dflags "CorePrep"
122 us <- mkSplitUniqSupply 's'
123 let new_expr = initUs_ us (corePrepAnExpr emptyCorePrepEnv expr)
124 dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep"
129 -- -----------------------------------------------------------------------------
131 -- -----------------------------------------------------------------------------
133 Create any necessary "implicit" bindings (data constructors etc).
135 * Constructor workers
136 * Constructor wrappers
137 * Data type record selectors
140 In the latter three cases, the Id contains the unfolding to use for
141 the binding. In the case of data con workers we create the rather
142 strange (non-recursive!) binding
144 $wC = \x y -> $wC x y
146 i.e. a curried constructor that allocates. This means that we can
147 treat the worker for a constructor like any other function in the rest
148 of the compiler. The point here is that CoreToStg will generate a
149 StgConApp for the RHS, rather than a call to the worker (which would
150 give a loop). As Lennart says: the ice is thin here, but it works.
152 Hmm. Should we create bindings for dictionary constructors? They are
153 always fully applied, and the bindings are just there to support
154 partial applications. But it's easier to let them through.
157 mkImplicitBinds type_env
158 = [ NonRec id (get_unfolding id)
159 | AnId id <- typeEnvElts type_env, isImplicitId id ]
160 -- The type environment already contains all the implicit Ids,
161 -- so we just filter them out
163 -- The etaExpand is so that the manifest arity of the
164 -- binding matches its claimed arity, which is an
165 -- invariant of top level bindings going into the code gen
167 get_unfolding id -- See notes above
168 | Just data_con <- isDataConWorkId_maybe id = Var id -- The ice is thin here, but it works
169 -- CorePrep will eta-expand it
170 | otherwise = unfoldingTemplate (idUnfolding id)
175 -- ---------------------------------------------------------------------------
176 -- Dealing with bindings
177 -- ---------------------------------------------------------------------------
179 data FloatingBind = FloatLet CoreBind
180 | FloatCase Id CoreExpr Bool
181 -- The bool indicates "ok-for-speculation"
183 data Floats = Floats OkToSpec (OrdList FloatingBind)
185 -- Can we float these binds out of the rhs of a let? We cache this decision
186 -- to avoid having to recompute it in a non-linear way when there are
187 -- deeply nested lets.
189 = NotOkToSpec -- definitely not
191 | IfUnboxedOk -- only if floating an unboxed binding is ok
193 emptyFloats :: Floats
194 emptyFloats = Floats OkToSpec nilOL
196 addFloat :: Floats -> FloatingBind -> Floats
197 addFloat (Floats ok_to_spec floats) new_float
198 = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
200 check (FloatLet _) = OkToSpec
201 check (FloatCase _ _ ok_for_spec)
202 | ok_for_spec = IfUnboxedOk
203 | otherwise = NotOkToSpec
204 -- The ok-for-speculation flag says that it's safe to
205 -- float this Case out of a let, and thereby do it more eagerly
206 -- We need the top-level flag because it's never ok to float
207 -- an unboxed binding to the top level
209 unitFloat :: FloatingBind -> Floats
210 unitFloat = addFloat emptyFloats
212 appendFloats :: Floats -> Floats -> Floats
213 appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
214 = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
216 concatFloats :: [Floats] -> Floats
217 concatFloats = foldr appendFloats emptyFloats
219 combine NotOkToSpec _ = NotOkToSpec
220 combine _ NotOkToSpec = NotOkToSpec
221 combine IfUnboxedOk _ = IfUnboxedOk
222 combine _ IfUnboxedOk = IfUnboxedOk
223 combine _ _ = OkToSpec
225 instance Outputable FloatingBind where
226 ppr (FloatLet bind) = text "FloatLet" <+> ppr bind
227 ppr (FloatCase b rhs spec) = text "FloatCase" <+> ppr b <+> ppr spec <+> equals <+> ppr rhs
229 deFloatTop :: Floats -> [CoreBind]
230 -- For top level only; we don't expect any FloatCases
231 deFloatTop (Floats _ floats)
232 = foldrOL get [] floats
234 get (FloatLet b) bs = b:bs
235 get b bs = pprPanic "corePrepPgm" (ppr b)
237 allLazy :: TopLevelFlag -> RecFlag -> Floats -> Bool
238 allLazy top_lvl is_rec (Floats ok_to_spec _)
242 IfUnboxedOk -> isNotTopLevel top_lvl && isNonRec is_rec
244 -- ---------------------------------------------------------------------------
246 -- ---------------------------------------------------------------------------
248 corePrepTopBinds :: [CoreBind] -> UniqSM Floats
249 corePrepTopBinds binds
250 = go emptyCorePrepEnv binds
252 go env [] = returnUs emptyFloats
253 go env (bind : binds) = corePrepTopBind env bind `thenUs` \ (env', bind') ->
254 go env' binds `thenUs` \ binds' ->
255 returnUs (bind' `appendFloats` binds')
257 -- NB: we do need to float out of top-level bindings
258 -- Consider x = length [True,False]
264 -- We return a *list* of bindings, because we may start with
266 -- where x is demanded, in which case we want to finish with
269 -- And then x will actually end up case-bound
271 -- What happens to the CafInfo on the floated bindings? By
272 -- default, all the CafInfos will be set to MayHaveCafRefs,
275 -- This might be pessimistic, because eg. s1 & s2
276 -- might not refer to any CAFs and the GC will end up doing
277 -- more traversal than is necessary, but it's still better
278 -- than not floating the bindings at all, because then
279 -- the GC would have to traverse the structure in the heap
280 -- instead. Given this, we decided not to try to get
281 -- the CafInfo on the floated bindings correct, because
282 -- it looks difficult.
284 --------------------------------
285 corePrepTopBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
286 corePrepTopBind env (NonRec bndr rhs)
287 = cloneBndr env bndr `thenUs` \ (env', bndr') ->
288 corePrepRhs TopLevel NonRecursive env (bndr, rhs) `thenUs` \ (floats, rhs') ->
289 returnUs (env', addFloat floats (FloatLet (NonRec bndr' rhs')))
291 corePrepTopBind env (Rec pairs) = corePrepRecPairs TopLevel env pairs
293 --------------------------------
294 corePrepBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
295 -- This one is used for *local* bindings
296 corePrepBind env (NonRec bndr rhs)
297 = etaExpandRhs bndr rhs `thenUs` \ rhs1 ->
298 corePrepExprFloat env rhs1 `thenUs` \ (floats, rhs2) ->
299 cloneBndr env bndr `thenUs` \ (_, bndr') ->
300 mkLocalNonRec bndr' (bdrDem bndr) floats rhs2 `thenUs` \ (floats', bndr'') ->
301 -- We want bndr'' in the envt, because it records
302 -- the evaluated-ness of the binder
303 returnUs (extendCorePrepEnv env bndr bndr'', floats')
305 corePrepBind env (Rec pairs) = corePrepRecPairs NotTopLevel env pairs
307 --------------------------------
308 corePrepRecPairs :: TopLevelFlag -> CorePrepEnv
309 -> [(Id,CoreExpr)] -- Recursive bindings
310 -> UniqSM (CorePrepEnv, Floats)
311 -- Used for all recursive bindings, top level and otherwise
312 corePrepRecPairs lvl env pairs
313 = cloneBndrs env (map fst pairs) `thenUs` \ (env', bndrs') ->
314 mapAndUnzipUs (corePrepRhs lvl Recursive env') pairs `thenUs` \ (floats_s, rhss') ->
315 returnUs (env', unitFloat (FloatLet (Rec (flatten (concatFloats floats_s) bndrs' rhss'))))
317 -- Flatten all the floats, and the currrent
318 -- group into a single giant Rec
319 flatten (Floats _ floats) bndrs rhss = foldrOL get (bndrs `zip` rhss) floats
321 get (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
322 get (FloatLet (Rec prs1)) prs2 = prs1 ++ prs2
324 --------------------------------
325 corePrepRhs :: TopLevelFlag -> RecFlag
326 -> CorePrepEnv -> (Id, CoreExpr)
327 -> UniqSM (Floats, CoreExpr)
328 -- Used for top-level bindings, and local recursive bindings
329 corePrepRhs top_lvl is_rec env (bndr, rhs)
330 = etaExpandRhs bndr rhs `thenUs` \ rhs' ->
331 corePrepExprFloat env rhs' `thenUs` \ floats_w_rhs ->
332 floatRhs top_lvl is_rec bndr floats_w_rhs
335 -- ---------------------------------------------------------------------------
336 -- Making arguments atomic (function args & constructor args)
337 -- ---------------------------------------------------------------------------
339 -- This is where we arrange that a non-trivial argument is let-bound
340 corePrepArg :: CorePrepEnv -> CoreArg -> RhsDemand
341 -> UniqSM (Floats, CoreArg)
342 corePrepArg env arg dem
343 = corePrepExprFloat env arg `thenUs` \ (floats, arg') ->
344 if exprIsTrivial arg'
345 then returnUs (floats, arg')
346 else newVar (exprType arg') `thenUs` \ v ->
347 mkLocalNonRec v dem floats arg' `thenUs` \ (floats', v') ->
348 returnUs (floats', Var v')
350 -- version that doesn't consider an scc annotation to be trivial.
351 exprIsTrivial (Var v) = True
352 exprIsTrivial (Type _) = True
353 exprIsTrivial (Lit lit) = True
354 exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
355 exprIsTrivial (Note (SCC _) e) = False
356 exprIsTrivial (Note _ e) = exprIsTrivial e
357 exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
358 exprIsTrivial other = False
360 -- ---------------------------------------------------------------------------
361 -- Dealing with expressions
362 -- ---------------------------------------------------------------------------
364 corePrepAnExpr :: CorePrepEnv -> CoreExpr -> UniqSM CoreExpr
365 corePrepAnExpr env expr
366 = corePrepExprFloat env expr `thenUs` \ (floats, expr) ->
370 corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
374 -- e = let bs in e' (semantically, that is!)
377 -- f (g x) ===> ([v = g x], f v)
379 corePrepExprFloat env (Var v)
380 = fiddleCCall v `thenUs` \ v1 ->
382 v2 = lookupCorePrepEnv env v1
384 maybeSaturate v2 (Var v2) 0 emptyFloats (idType v2)
386 corePrepExprFloat env expr@(Type _)
387 = returnUs (emptyFloats, expr)
389 corePrepExprFloat env expr@(Lit lit)
390 = returnUs (emptyFloats, expr)
392 corePrepExprFloat env (Let bind body)
393 = corePrepBind env bind `thenUs` \ (env', new_binds) ->
394 corePrepExprFloat env' body `thenUs` \ (floats, new_body) ->
395 returnUs (new_binds `appendFloats` floats, new_body)
397 corePrepExprFloat env (Note n@(SCC _) expr)
398 = corePrepAnExpr env expr `thenUs` \ expr1 ->
399 deLamFloat expr1 `thenUs` \ (floats, expr2) ->
400 returnUs (floats, Note n expr2)
402 corePrepExprFloat env (Note other_note expr)
403 = corePrepExprFloat env expr `thenUs` \ (floats, expr') ->
404 returnUs (floats, Note other_note expr')
406 corePrepExprFloat env expr@(Lam _ _)
407 = cloneBndrs env bndrs `thenUs` \ (env', bndrs') ->
408 corePrepAnExpr env' body `thenUs` \ body' ->
409 returnUs (emptyFloats, mkLams bndrs' body')
411 (bndrs,body) = collectBinders expr
413 corePrepExprFloat env (Case scrut bndr ty alts)
414 = corePrepExprFloat env scrut `thenUs` \ (floats1, scrut1) ->
415 deLamFloat scrut1 `thenUs` \ (floats2, scrut2) ->
417 bndr1 = bndr `setIdUnfolding` evaldUnfolding
418 -- Record that the case binder is evaluated in the alternatives
420 cloneBndr env bndr1 `thenUs` \ (env', bndr2) ->
421 mapUs (sat_alt env') alts `thenUs` \ alts' ->
422 returnUs (floats1 `appendFloats` floats2 , Case scrut2 bndr2 ty alts')
424 sat_alt env (con, bs, rhs)
426 env1 = setGadt env con
428 cloneBndrs env1 bs `thenUs` \ (env2, bs') ->
429 corePrepAnExpr env2 rhs `thenUs` \ rhs1 ->
430 deLam rhs1 `thenUs` \ rhs2 ->
431 returnUs (con, bs', rhs2)
433 corePrepExprFloat env expr@(App _ _)
434 = collect_args expr 0 `thenUs` \ (app, (head,depth), ty, floats, ss) ->
435 ASSERT(null ss) -- make sure we used all the strictness info
437 -- Now deal with the function
439 Var fn_id -> maybeSaturate fn_id app depth floats ty
440 _other -> returnUs (floats, app)
444 -- Deconstruct and rebuild the application, floating any non-atomic
445 -- arguments to the outside. We collect the type of the expression,
446 -- the head of the application, and the number of actual value arguments,
447 -- all of which are used to possibly saturate this application if it
448 -- has a constructor or primop at the head.
452 -> Int -- current app depth
453 -> UniqSM (CoreExpr, -- the rebuilt expression
454 (CoreExpr,Int), -- the head of the application,
455 -- and no. of args it was applied to
456 Type, -- type of the whole expr
457 Floats, -- any floats we pulled out
458 [Demand]) -- remaining argument demands
460 collect_args (App fun arg@(Type arg_ty)) depth
461 = collect_args fun depth `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
462 returnUs (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
464 collect_args (App fun arg) depth
465 = collect_args fun (depth+1) `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
467 (ss1, ss_rest) = case ss of
468 (ss1:ss_rest) -> (ss1, ss_rest)
470 (arg_ty, res_ty) = expectJust "corePrepExprFloat:collect_args" $
471 splitFunTy_maybe fun_ty
473 corePrepArg env arg (mkDemTy ss1 arg_ty) `thenUs` \ (fs, arg') ->
474 returnUs (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest)
476 collect_args (Var v) depth
477 = fiddleCCall v `thenUs` \ v1 ->
479 v2 = lookupCorePrepEnv env v1
481 returnUs (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts)
483 stricts = case idNewStrictness v of
484 StrictSig (DmdType _ demands _)
485 | listLengthCmp demands depth /= GT -> demands
486 -- length demands <= depth
488 -- If depth < length demands, then we have too few args to
489 -- satisfy strictness info so we have to ignore all the
490 -- strictness info, e.g. + (error "urk")
491 -- Here, we can't evaluate the arg strictly, because this
492 -- partial application might be seq'd
495 collect_args (Note (Coerce ty1 ty2) fun) depth
496 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
497 returnUs (Note (Coerce ty1 ty2) fun', hd, ty1, floats, ss)
499 collect_args (Note note fun) depth
501 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
502 returnUs (Note note fun', hd, fun_ty, floats, ss)
504 -- N-variable fun, better let-bind it
505 -- ToDo: perhaps we can case-bind rather than let-bind this closure,
506 -- since it is sure to be evaluated.
507 collect_args fun depth
508 = corePrepExprFloat env fun `thenUs` \ (fun_floats, fun') ->
509 newVar ty `thenUs` \ fn_id ->
510 mkLocalNonRec fn_id onceDem fun_floats fun' `thenUs` \ (floats, fn_id') ->
511 returnUs (Var fn_id', (Var fn_id', depth), ty, floats, [])
515 ignore_note (CoreNote _) = True
516 ignore_note InlineCall = True
517 ignore_note InlineMe = True
518 ignore_note _other = False
519 -- We don't ignore SCCs, since they require some code generation
521 ------------------------------------------------------------------------------
522 -- Building the saturated syntax
523 -- ---------------------------------------------------------------------------
525 -- maybeSaturate deals with saturating primops and constructors
526 -- The type is the type of the entire application
527 maybeSaturate :: Id -> CoreExpr -> Int -> Floats -> Type -> UniqSM (Floats, CoreExpr)
528 maybeSaturate fn expr n_args floats ty
529 | hasNoBinding fn = saturate_it
530 | otherwise = returnUs (floats, expr)
532 fn_arity = idArity fn
533 excess_arity = fn_arity - n_args
534 saturate_it = getUniquesUs `thenUs` \ us ->
535 let expr' = etaExpand excess_arity us expr ty in
536 case isPrimOpId_maybe fn of
537 Just DataToTagOp -> hack_data2tag expr'
538 other -> returnUs (floats, expr')
540 -- Ensure that the argument of DataToTagOp is evaluated
541 hack_data2tag app@(Var _fn `App` _ty `App` Var arg_id)
542 | isEvaldUnfolding (idUnfolding arg_id) -- Includes nullary constructors
543 = returnUs (floats, app) -- The arg is evaluated
544 hack_data2tag app@(Var fn `App` Type ty `App` arg)
545 | otherwise -- Arg not evaluated, so evaluate it
546 = newVar ty `thenUs` \ arg_id1 ->
547 let arg_id2 = setIdUnfolding arg_id1 evaldUnfolding
548 new_float = FloatCase arg_id2 arg False
550 returnUs (addFloat floats new_float,
551 Var fn `App` Type ty `App` Var arg_id2)
554 -- ---------------------------------------------------------------------------
555 -- Precipitating the floating bindings
556 -- ---------------------------------------------------------------------------
558 floatRhs :: TopLevelFlag -> RecFlag
560 -> (Floats, CoreExpr) -- Rhs: let binds in body
561 -> UniqSM (Floats, -- Floats out of this bind
562 CoreExpr) -- Final Rhs
564 floatRhs top_lvl is_rec bndr (floats, rhs)
565 | isTopLevel top_lvl || exprIsValue rhs, -- Float to expose value or
566 allLazy top_lvl is_rec floats -- at top level
567 = -- Why the test for allLazy?
568 -- v = f (x `divInt#` y)
569 -- we don't want to float the case, even if f has arity 2,
570 -- because floating the case would make it evaluated too early
571 returnUs (floats, rhs)
574 -- Don't float; the RHS isn't a value
575 = mkBinds floats rhs `thenUs` \ rhs' ->
576 returnUs (emptyFloats, rhs')
578 -- mkLocalNonRec is used only for *nested*, *non-recursive* bindings
579 mkLocalNonRec :: Id -> RhsDemand -- Lhs: id with demand
580 -> Floats -> CoreExpr -- Rhs: let binds in body
581 -> UniqSM (Floats, Id) -- The new Id may have an evaldUnfolding,
582 -- to record that it's been evaluated
584 mkLocalNonRec bndr dem floats rhs
585 | isUnLiftedType (idType bndr)
586 -- If this is an unlifted binding, we always make a case for it.
587 = ASSERT( not (isUnboxedTupleType (idType bndr)) )
589 float = FloatCase bndr rhs (exprOkForSpeculation rhs)
591 returnUs (addFloat floats float, evald_bndr)
594 -- It's a strict let so we definitely float all the bindings
595 = let -- Don't make a case for a value binding,
596 -- even if it's strict. Otherwise we get
597 -- case (\x -> e) of ...!
598 float | exprIsValue rhs = FloatLet (NonRec bndr rhs)
599 | otherwise = FloatCase bndr rhs (exprOkForSpeculation rhs)
601 returnUs (addFloat floats float, evald_bndr)
604 = floatRhs NotTopLevel NonRecursive bndr (floats, rhs) `thenUs` \ (floats', rhs') ->
605 returnUs (addFloat floats' (FloatLet (NonRec bndr rhs')),
606 if exprIsValue rhs' then evald_bndr else bndr)
609 evald_bndr = bndr `setIdUnfolding` evaldUnfolding
610 -- Record if the binder is evaluated
613 mkBinds :: Floats -> CoreExpr -> UniqSM CoreExpr
614 mkBinds (Floats _ binds) body
615 | isNilOL binds = returnUs body
616 | otherwise = deLam body `thenUs` \ body' ->
617 returnUs (foldrOL mk_bind body' binds)
619 mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
620 mk_bind (FloatLet bind) body = Let bind body
622 etaExpandRhs bndr rhs
623 = -- Eta expand to match the arity claimed by the binder
624 -- Remember, after CorePrep we must not change arity
626 -- Eta expansion might not have happened already,
627 -- because it is done by the simplifier only when
628 -- there at least one lambda already.
630 -- NB1:we could refrain when the RHS is trivial (which can happen
631 -- for exported things). This would reduce the amount of code
632 -- generated (a little) and make things a little words for
633 -- code compiled without -O. The case in point is data constructor
636 -- NB2: we have to be careful that the result of etaExpand doesn't
637 -- invalidate any of the assumptions that CorePrep is attempting
638 -- to establish. One possible cause is eta expanding inside of
639 -- an SCC note - we're now careful in etaExpand to make sure the
640 -- SCC is pushed inside any new lambdas that are generated.
642 -- NB3: It's important to do eta expansion, and *then* ANF-ising
643 -- f = /\a -> g (h 3) -- h has arity 2
644 -- If we ANF first we get
645 -- f = /\a -> let s = h 3 in g s
646 -- and now eta expansion gives
647 -- f = /\a -> \ y -> (let s = h 3 in g s) y
648 -- which is horrible.
649 -- Eta expanding first gives
650 -- f = /\a -> \y -> let s = h 3 in g s y
652 getUniquesUs `thenUs` \ us ->
653 returnUs (etaExpand arity us rhs (idType bndr))
655 -- For a GlobalId, take the Arity from the Id.
656 -- It was set in CoreTidy and must not change
657 -- For all others, just expand at will
658 arity | isGlobalId bndr = idArity bndr
659 | otherwise = exprArity rhs
661 -- ---------------------------------------------------------------------------
662 -- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
663 -- We arrange that they only show up as the RHS of a let(rec)
664 -- ---------------------------------------------------------------------------
666 deLam :: CoreExpr -> UniqSM CoreExpr
668 deLamFloat expr `thenUs` \ (floats, expr) ->
672 deLamFloat :: CoreExpr -> UniqSM (Floats, CoreExpr)
673 -- Remove top level lambdas by let-bindinig
675 deLamFloat (Note n expr)
676 = -- You can get things like
677 -- case e of { p -> coerce t (\s -> ...) }
678 deLamFloat expr `thenUs` \ (floats, expr') ->
679 returnUs (floats, Note n expr')
682 | null bndrs = returnUs (emptyFloats, expr)
684 = case tryEta bndrs body of
685 Just no_lam_result -> returnUs (emptyFloats, no_lam_result)
686 Nothing -> newVar (exprType expr) `thenUs` \ fn ->
687 returnUs (unitFloat (FloatLet (NonRec fn expr)),
690 (bndrs,body) = collectBinders expr
692 -- Why try eta reduction? Hasn't the simplifier already done eta?
693 -- But the simplifier only eta reduces if that leaves something
694 -- trivial (like f, or f Int). But for deLam it would be enough to
695 -- get to a partial application, like (map f).
697 tryEta bndrs expr@(App _ _)
698 | ok_to_eta_reduce f &&
700 and (zipWith ok bndrs last_args) &&
701 not (any (`elemVarSet` fvs_remaining) bndrs)
702 = Just remaining_expr
704 (f, args) = collectArgs expr
705 remaining_expr = mkApps f remaining_args
706 fvs_remaining = exprFreeVars remaining_expr
707 (remaining_args, last_args) = splitAt n_remaining args
708 n_remaining = length args - length bndrs
710 ok bndr (Var arg) = bndr == arg
711 ok bndr other = False
713 -- we can't eta reduce something which must be saturated.
714 ok_to_eta_reduce (Var f) = not (hasNoBinding f)
715 ok_to_eta_reduce _ = False --safe. ToDo: generalise
717 tryEta bndrs (Let bind@(NonRec b r) body)
718 | not (any (`elemVarSet` fvs) bndrs)
719 = case tryEta bndrs body of
720 Just e -> Just (Let bind e)
725 tryEta bndrs _ = Nothing
729 -- -----------------------------------------------------------------------------
731 -- -----------------------------------------------------------------------------
735 = RhsDemand { isStrict :: Bool, -- True => used at least once
736 isOnceDem :: Bool -- True => used at most once
739 mkDem :: Demand -> Bool -> RhsDemand
740 mkDem strict once = RhsDemand (isStrictDmd strict) once
742 mkDemTy :: Demand -> Type -> RhsDemand
743 mkDemTy strict ty = RhsDemand (isStrictDmd strict)
746 bdrDem :: Id -> RhsDemand
747 bdrDem id = mkDem (idNewDemandInfo id)
750 -- safeDem :: RhsDemand
751 -- safeDem = RhsDemand False False -- always safe to use this
754 onceDem = RhsDemand False True -- used at most once
760 %************************************************************************
764 %************************************************************************
767 -- ---------------------------------------------------------------------------
769 -- ---------------------------------------------------------------------------
771 data CorePrepEnv = CPE (IdEnv Id) -- Clone local Ids
772 Bool -- True <=> inside a GADT case; see Note [GADT]
776 -- Be careful with cloning inside GADTs. For example,
777 -- /\a. \f::a. \x::T a. case x of { T -> f True; ... }
778 -- The case on x may refine the type of f to be a function type.
779 -- Without this type refinement, exprType (f True) may simply fail,
782 -- Solution: remember when we are inside a potentially-type-refining case,
783 -- and in that situation use the type from the old occurrence
784 -- when looking up occurrences
786 emptyCorePrepEnv :: CorePrepEnv
787 emptyCorePrepEnv = CPE emptyVarEnv False
789 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
790 extendCorePrepEnv (CPE env gadt) id id' = CPE (extendVarEnv env id id') gadt
792 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
793 -- See Note [GADT] above
794 lookupCorePrepEnv (CPE env gadt) id
795 = case lookupVarEnv env id of
797 Just id' | gadt -> setIdType id' (idType id)
800 setGadt :: CorePrepEnv -> AltCon -> CorePrepEnv
801 setGadt env@(CPE id_env _) (DataAlt data_con) | not (isVanillaDataCon data_con) = CPE id_env True
802 setGadt env other = env
805 ------------------------------------------------------------------------------
807 -- ---------------------------------------------------------------------------
809 cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
810 cloneBndrs env bs = mapAccumLUs cloneBndr env bs
812 cloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
815 = getUniqueUs `thenUs` \ uniq ->
817 bndr' = setVarUnique bndr uniq
819 returnUs (extendCorePrepEnv env bndr bndr', bndr')
821 | otherwise -- Top level things, which we don't want
822 -- to clone, have become GlobalIds by now
823 -- And we don't clone tyvars
824 = returnUs (env, bndr)
827 ------------------------------------------------------------------------------
828 -- Cloning ccall Ids; each must have a unique name,
829 -- to give the code generator a handle to hang it on
830 -- ---------------------------------------------------------------------------
832 fiddleCCall :: Id -> UniqSM Id
834 | isFCallId id = getUniqueUs `thenUs` \ uniq ->
835 returnUs (id `setVarUnique` uniq)
836 | otherwise = returnUs id
838 ------------------------------------------------------------------------------
839 -- Generating new binders
840 -- ---------------------------------------------------------------------------
842 newVar :: Type -> UniqSM Id
845 getUniqueUs `thenUs` \ uniq ->
846 returnUs (mkSysLocal FSLIT("sat") uniq ty)