2 % (c) The University of Glasgow, 1994-2006
5 Core pass to saturate constructors and PrimOps
9 corePrepPgm, corePrepExpr
12 #include "HsVersions.h"
14 import CoreUtils hiding (exprIsTrivial)
42 -- ---------------------------------------------------------------------------
44 -- ---------------------------------------------------------------------------
46 The goal of this pass is to prepare for code generation.
48 1. Saturate constructor and primop applications.
50 2. Convert to A-normal form; that is, function arguments
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] -> [TyCon] -> IO [CoreBind]
102 corePrepPgm dflags binds data_tycons
103 = do showPass dflags "CorePrep"
104 us <- mkSplitUniqSupply 's'
106 let implicit_binds = mkDataConWorkers data_tycons
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 for data con workers. We
134 create the rather strange (non-recursive!) binding
136 $wC = \x y -> $wC x y
138 i.e. a curried constructor that allocates. This means that we can
139 treat the worker for a constructor like any other function in the rest
140 of the compiler. The point here is that CoreToStg will generate a
141 StgConApp for the RHS, rather than a call to the worker (which would
142 give a loop). As Lennart says: the ice is thin here, but it works.
144 Hmm. Should we create bindings for dictionary constructors? They are
145 always fully applied, and the bindings are just there to support
146 partial applications. But it's easier to let them through.
149 mkDataConWorkers data_tycons
150 = [ NonRec id (Var id) -- The ice is thin here, but it works
151 | tycon <- data_tycons, -- CorePrep will eta-expand it
152 data_con <- tyConDataCons tycon,
153 let id = dataConWorkId data_con ]
158 -- ---------------------------------------------------------------------------
159 -- Dealing with bindings
160 -- ---------------------------------------------------------------------------
162 data FloatingBind = FloatLet CoreBind
163 | FloatCase Id CoreExpr Bool
164 -- The bool indicates "ok-for-speculation"
166 data Floats = Floats OkToSpec (OrdList FloatingBind)
168 -- Can we float these binds out of the rhs of a let? We cache this decision
169 -- to avoid having to recompute it in a non-linear way when there are
170 -- deeply nested lets.
172 = NotOkToSpec -- definitely not
174 | IfUnboxedOk -- only if floating an unboxed binding is ok
176 emptyFloats :: Floats
177 emptyFloats = Floats OkToSpec nilOL
179 addFloat :: Floats -> FloatingBind -> Floats
180 addFloat (Floats ok_to_spec floats) new_float
181 = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
183 check (FloatLet _) = OkToSpec
184 check (FloatCase _ _ ok_for_spec)
185 | ok_for_spec = IfUnboxedOk
186 | otherwise = NotOkToSpec
187 -- The ok-for-speculation flag says that it's safe to
188 -- float this Case out of a let, and thereby do it more eagerly
189 -- We need the top-level flag because it's never ok to float
190 -- an unboxed binding to the top level
192 unitFloat :: FloatingBind -> Floats
193 unitFloat = addFloat emptyFloats
195 appendFloats :: Floats -> Floats -> Floats
196 appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
197 = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
199 concatFloats :: [Floats] -> Floats
200 concatFloats = foldr appendFloats emptyFloats
202 combine NotOkToSpec _ = NotOkToSpec
203 combine _ NotOkToSpec = NotOkToSpec
204 combine IfUnboxedOk _ = IfUnboxedOk
205 combine _ IfUnboxedOk = IfUnboxedOk
206 combine _ _ = OkToSpec
208 instance Outputable FloatingBind where
209 ppr (FloatLet bind) = text "FloatLet" <+> ppr bind
210 ppr (FloatCase b rhs spec) = text "FloatCase" <+> ppr b <+> ppr spec <+> equals <+> ppr rhs
212 deFloatTop :: Floats -> [CoreBind]
213 -- For top level only; we don't expect any FloatCases
214 deFloatTop (Floats _ floats)
215 = foldrOL get [] floats
217 get (FloatLet b) bs = b:bs
218 get b bs = pprPanic "corePrepPgm" (ppr b)
220 allLazy :: TopLevelFlag -> RecFlag -> Floats -> Bool
221 allLazy top_lvl is_rec (Floats ok_to_spec _)
225 IfUnboxedOk -> isNotTopLevel top_lvl && isNonRec is_rec
227 -- ---------------------------------------------------------------------------
229 -- ---------------------------------------------------------------------------
231 corePrepTopBinds :: [CoreBind] -> UniqSM Floats
232 corePrepTopBinds binds
233 = go emptyCorePrepEnv binds
235 go env [] = returnUs emptyFloats
236 go env (bind : binds) = corePrepTopBind env bind `thenUs` \ (env', bind') ->
237 go env' binds `thenUs` \ binds' ->
238 returnUs (bind' `appendFloats` binds')
240 -- NB: we do need to float out of top-level bindings
241 -- Consider x = length [True,False]
247 -- We return a *list* of bindings, because we may start with
249 -- where x is demanded, in which case we want to finish with
252 -- And then x will actually end up case-bound
254 -- What happens to the CafInfo on the floated bindings? By
255 -- default, all the CafInfos will be set to MayHaveCafRefs,
258 -- This might be pessimistic, because eg. s1 & s2
259 -- might not refer to any CAFs and the GC will end up doing
260 -- more traversal than is necessary, but it's still better
261 -- than not floating the bindings at all, because then
262 -- the GC would have to traverse the structure in the heap
263 -- instead. Given this, we decided not to try to get
264 -- the CafInfo on the floated bindings correct, because
265 -- it looks difficult.
267 --------------------------------
268 corePrepTopBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
269 corePrepTopBind env (NonRec bndr rhs)
270 = cloneBndr env bndr `thenUs` \ (env', bndr') ->
271 corePrepRhs TopLevel NonRecursive env (bndr, rhs) `thenUs` \ (floats, rhs') ->
272 returnUs (env', addFloat floats (FloatLet (NonRec bndr' rhs')))
274 corePrepTopBind env (Rec pairs) = corePrepRecPairs TopLevel env pairs
276 --------------------------------
277 corePrepBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
278 -- This one is used for *local* bindings
279 corePrepBind env (NonRec bndr rhs)
280 = etaExpandRhs bndr rhs `thenUs` \ rhs1 ->
281 corePrepExprFloat env rhs1 `thenUs` \ (floats, rhs2) ->
282 cloneBndr env bndr `thenUs` \ (_, bndr') ->
283 mkLocalNonRec bndr' (bdrDem bndr) floats rhs2 `thenUs` \ (floats', bndr'') ->
284 -- We want bndr'' in the envt, because it records
285 -- the evaluated-ness of the binder
286 returnUs (extendCorePrepEnv env bndr bndr'', floats')
288 corePrepBind env (Rec pairs) = corePrepRecPairs NotTopLevel env pairs
290 --------------------------------
291 corePrepRecPairs :: TopLevelFlag -> CorePrepEnv
292 -> [(Id,CoreExpr)] -- Recursive bindings
293 -> UniqSM (CorePrepEnv, Floats)
294 -- Used for all recursive bindings, top level and otherwise
295 corePrepRecPairs lvl env pairs
296 = cloneBndrs env (map fst pairs) `thenUs` \ (env', bndrs') ->
297 mapAndUnzipUs (corePrepRhs lvl Recursive env') pairs `thenUs` \ (floats_s, rhss') ->
298 returnUs (env', unitFloat (FloatLet (Rec (flatten (concatFloats floats_s) bndrs' rhss'))))
300 -- Flatten all the floats, and the currrent
301 -- group into a single giant Rec
302 flatten (Floats _ floats) bndrs rhss = foldrOL get (bndrs `zip` rhss) floats
304 get (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
305 get (FloatLet (Rec prs1)) prs2 = prs1 ++ prs2
306 get b prs2 = pprPanic "corePrepRecPairs" (ppr b)
308 --------------------------------
309 corePrepRhs :: TopLevelFlag -> RecFlag
310 -> CorePrepEnv -> (Id, CoreExpr)
311 -> UniqSM (Floats, CoreExpr)
312 -- Used for top-level bindings, and local recursive bindings
313 corePrepRhs top_lvl is_rec env (bndr, rhs)
314 = etaExpandRhs bndr rhs `thenUs` \ rhs' ->
315 corePrepExprFloat env rhs' `thenUs` \ floats_w_rhs ->
316 floatRhs top_lvl is_rec bndr floats_w_rhs
319 -- ---------------------------------------------------------------------------
320 -- Making arguments atomic (function args & constructor args)
321 -- ---------------------------------------------------------------------------
323 -- This is where we arrange that a non-trivial argument is let-bound
324 corePrepArg :: CorePrepEnv -> CoreArg -> RhsDemand
325 -> UniqSM (Floats, CoreArg)
326 corePrepArg env arg dem
327 = corePrepExprFloat env arg `thenUs` \ (floats, arg') ->
328 if exprIsTrivial arg'
329 then returnUs (floats, arg')
330 else newVar (exprType arg') `thenUs` \ v ->
331 mkLocalNonRec v dem floats arg' `thenUs` \ (floats', v') ->
332 returnUs (floats', Var v')
334 -- version that doesn't consider an scc annotation to be trivial.
335 exprIsTrivial (Var v) = True
336 exprIsTrivial (Type _) = True
337 exprIsTrivial (Lit lit) = True
338 exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
339 exprIsTrivial (Note (SCC _) e) = False
340 exprIsTrivial (Note _ e) = exprIsTrivial e
341 exprIsTrivial (Cast e co) = exprIsTrivial e
342 exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
343 exprIsTrivial other = False
345 -- ---------------------------------------------------------------------------
346 -- Dealing with expressions
347 -- ---------------------------------------------------------------------------
349 corePrepAnExpr :: CorePrepEnv -> CoreExpr -> UniqSM CoreExpr
350 corePrepAnExpr env expr
351 = corePrepExprFloat env expr `thenUs` \ (floats, expr) ->
355 corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
359 -- e = let bs in e' (semantically, that is!)
362 -- f (g x) ===> ([v = g x], f v)
364 corePrepExprFloat env (Var v)
365 = fiddleCCall v `thenUs` \ v1 ->
367 v2 = lookupCorePrepEnv env v1
369 maybeSaturate v2 (Var v2) 0 emptyFloats (idType v2)
371 corePrepExprFloat env expr@(Type _)
372 = returnUs (emptyFloats, expr)
374 corePrepExprFloat env expr@(Lit lit)
375 = returnUs (emptyFloats, expr)
377 corePrepExprFloat env (Let bind body)
378 = corePrepBind env bind `thenUs` \ (env', new_binds) ->
379 corePrepExprFloat env' body `thenUs` \ (floats, new_body) ->
380 returnUs (new_binds `appendFloats` floats, new_body)
382 corePrepExprFloat env (Note n@(SCC _) expr)
383 = corePrepAnExpr env expr `thenUs` \ expr1 ->
384 deLamFloat expr1 `thenUs` \ (floats, expr2) ->
385 returnUs (floats, Note n expr2)
387 corePrepExprFloat env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
388 | Just (TickBox {}) <- isTickBoxOp_maybe id
389 = corePrepAnExpr env expr `thenUs` \ expr1 ->
390 deLamFloat expr1 `thenUs` \ (floats, expr2) ->
391 return (floats, Case (Var id) bndr ty [(DEFAULT,[],expr2)])
393 corePrepExprFloat env (Note other_note expr)
394 = corePrepExprFloat env expr `thenUs` \ (floats, expr') ->
395 returnUs (floats, Note other_note expr')
397 corePrepExprFloat env (Cast expr co)
398 = corePrepExprFloat env expr `thenUs` \ (floats, expr') ->
399 returnUs (floats, Cast expr' co)
401 corePrepExprFloat env expr@(Lam _ _)
402 = cloneBndrs env bndrs `thenUs` \ (env', bndrs') ->
403 corePrepAnExpr env' body `thenUs` \ body' ->
404 returnUs (emptyFloats, mkLams bndrs' body')
406 (bndrs,body) = collectBinders expr
408 corePrepExprFloat env (Case scrut bndr ty alts)
409 = corePrepExprFloat env scrut `thenUs` \ (floats1, scrut1) ->
410 deLamFloat scrut1 `thenUs` \ (floats2, scrut2) ->
412 bndr1 = bndr `setIdUnfolding` evaldUnfolding
413 -- Record that the case binder is evaluated in the alternatives
415 cloneBndr env bndr1 `thenUs` \ (env', bndr2) ->
416 mapUs (sat_alt env') alts `thenUs` \ alts' ->
417 returnUs (floats1 `appendFloats` floats2 , Case scrut2 bndr2 ty alts')
419 sat_alt env (con, bs, rhs)
420 = cloneBndrs env bs `thenUs` \ (env2, bs') ->
421 corePrepAnExpr env2 rhs `thenUs` \ rhs1 ->
422 deLam rhs1 `thenUs` \ rhs2 ->
423 returnUs (con, bs', rhs2)
425 corePrepExprFloat env expr@(App _ _)
426 = collect_args expr 0 `thenUs` \ (app, (head,depth), ty, floats, ss) ->
427 ASSERT(null ss) -- make sure we used all the strictness info
429 -- Now deal with the function
431 Var fn_id -> maybeSaturate fn_id app depth floats ty
432 _other -> returnUs (floats, app)
436 -- Deconstruct and rebuild the application, floating any non-atomic
437 -- arguments to the outside. We collect the type of the expression,
438 -- the head of the application, and the number of actual value arguments,
439 -- all of which are used to possibly saturate this application if it
440 -- has a constructor or primop at the head.
444 -> Int -- current app depth
445 -> UniqSM (CoreExpr, -- the rebuilt expression
446 (CoreExpr,Int), -- the head of the application,
447 -- and no. of args it was applied to
448 Type, -- type of the whole expr
449 Floats, -- any floats we pulled out
450 [Demand]) -- remaining argument demands
452 collect_args (App fun arg@(Type arg_ty)) depth
453 = collect_args fun depth `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
454 returnUs (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
456 collect_args (App fun arg) depth
457 = collect_args fun (depth+1) `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
459 (ss1, ss_rest) = case ss of
460 (ss1:ss_rest) -> (ss1, ss_rest)
462 (arg_ty, res_ty) = expectJust "corePrepExprFloat:collect_args" $
463 splitFunTy_maybe fun_ty
465 corePrepArg env arg (mkDemTy ss1 arg_ty) `thenUs` \ (fs, arg') ->
466 returnUs (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest)
468 collect_args (Var v) depth
469 = fiddleCCall v `thenUs` \ v1 ->
471 v2 = lookupCorePrepEnv env v1
473 returnUs (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts)
475 stricts = case idNewStrictness v of
476 StrictSig (DmdType _ demands _)
477 | listLengthCmp demands depth /= GT -> demands
478 -- length demands <= depth
480 -- If depth < length demands, then we have too few args to
481 -- satisfy strictness info so we have to ignore all the
482 -- strictness info, e.g. + (error "urk")
483 -- Here, we can't evaluate the arg strictly, because this
484 -- partial application might be seq'd
486 collect_args (Cast fun co) depth
487 = let (_ty1,ty2) = coercionKind co in
488 collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
489 returnUs (Cast fun' co, hd, ty2, floats, ss)
491 collect_args (Note note fun) depth
492 | ignore_note note -- Drop these notes altogether
493 -- They aren't used by the code generator
494 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
495 returnUs (fun', hd, fun_ty, floats, ss)
497 -- N-variable fun, better let-bind it
498 -- ToDo: perhaps we can case-bind rather than let-bind this closure,
499 -- since it is sure to be evaluated.
500 collect_args fun depth
501 = corePrepExprFloat env fun `thenUs` \ (fun_floats, fun') ->
502 newVar ty `thenUs` \ fn_id ->
503 mkLocalNonRec fn_id onceDem fun_floats fun' `thenUs` \ (floats, fn_id') ->
504 returnUs (Var fn_id', (Var fn_id', depth), ty, floats, [])
508 ignore_note (CoreNote _) = True
509 ignore_note InlineMe = True
510 ignore_note _other = False
511 -- We don't ignore SCCs, since they require some code generation
513 ------------------------------------------------------------------------------
514 -- Building the saturated syntax
515 -- ---------------------------------------------------------------------------
517 -- maybeSaturate deals with saturating primops and constructors
518 -- The type is the type of the entire application
519 maybeSaturate :: Id -> CoreExpr -> Int -> Floats -> Type -> UniqSM (Floats, CoreExpr)
520 maybeSaturate fn expr n_args floats ty
521 | Just DataToTagOp <- isPrimOpId_maybe fn -- DataToTag must have an evaluated arg
522 -- A gruesome special case
523 = saturate_it `thenUs` \ sat_expr ->
525 -- OK, now ensure that the arg is evaluated.
526 -- But (sigh) take into account the lambdas we've now introduced
528 (eta_bndrs, eta_body) = collectBinders sat_expr
530 eval_data2tag_arg eta_body `thenUs` \ (eta_floats, eta_body') ->
531 if null eta_bndrs then
532 returnUs (floats `appendFloats` eta_floats, eta_body')
534 mkBinds eta_floats eta_body' `thenUs` \ eta_body'' ->
535 returnUs (floats, mkLams eta_bndrs eta_body'')
537 | hasNoBinding fn = saturate_it `thenUs` \ sat_expr ->
538 returnUs (floats, sat_expr)
540 | otherwise = returnUs (floats, expr)
543 fn_arity = idArity fn
544 excess_arity = fn_arity - n_args
546 saturate_it :: UniqSM CoreExpr
547 saturate_it | excess_arity == 0 = returnUs expr
548 | otherwise = getUniquesUs `thenUs` \ us ->
549 returnUs (etaExpand excess_arity us expr ty)
551 -- Ensure that the argument of DataToTagOp is evaluated
552 eval_data2tag_arg :: CoreExpr -> UniqSM (Floats, CoreExpr)
553 eval_data2tag_arg app@(fun `App` arg)
554 | exprIsHNF arg -- Includes nullary constructors
555 = returnUs (emptyFloats, app) -- The arg is evaluated
556 | otherwise -- Arg not evaluated, so evaluate it
557 = newVar (exprType arg) `thenUs` \ arg_id ->
559 arg_id1 = setIdUnfolding arg_id evaldUnfolding
561 returnUs (unitFloat (FloatCase arg_id1 arg False ),
562 fun `App` Var arg_id1)
564 eval_data2tag_arg (Note note app) -- Scc notes can appear
565 = eval_data2tag_arg app `thenUs` \ (floats, app') ->
566 returnUs (floats, Note note app')
568 eval_data2tag_arg other -- Should not happen
569 = pprPanic "eval_data2tag" (ppr other)
572 -- ---------------------------------------------------------------------------
573 -- Precipitating the floating bindings
574 -- ---------------------------------------------------------------------------
576 floatRhs :: TopLevelFlag -> RecFlag
578 -> (Floats, CoreExpr) -- Rhs: let binds in body
579 -> UniqSM (Floats, -- Floats out of this bind
580 CoreExpr) -- Final Rhs
582 floatRhs top_lvl is_rec bndr (floats, rhs)
583 | isTopLevel top_lvl || exprIsHNF rhs, -- Float to expose value or
584 allLazy top_lvl is_rec floats -- at top level
585 = -- Why the test for allLazy?
586 -- v = f (x `divInt#` y)
587 -- we don't want to float the case, even if f has arity 2,
588 -- because floating the case would make it evaluated too early
589 returnUs (floats, rhs)
592 -- Don't float; the RHS isn't a value
593 = mkBinds floats rhs `thenUs` \ rhs' ->
594 returnUs (emptyFloats, rhs')
596 -- mkLocalNonRec is used only for *nested*, *non-recursive* bindings
597 mkLocalNonRec :: Id -> RhsDemand -- Lhs: id with demand
598 -> Floats -> CoreExpr -- Rhs: let binds in body
599 -> UniqSM (Floats, Id) -- The new Id may have an evaldUnfolding,
600 -- to record that it's been evaluated
602 mkLocalNonRec bndr dem floats rhs
603 | isUnLiftedType (idType bndr)
604 -- If this is an unlifted binding, we always make a case for it.
605 = ASSERT( not (isUnboxedTupleType (idType bndr)) )
607 float = FloatCase bndr rhs (exprOkForSpeculation rhs)
609 returnUs (addFloat floats float, evald_bndr)
612 -- It's a strict let so we definitely float all the bindings
613 = let -- Don't make a case for a value binding,
614 -- even if it's strict. Otherwise we get
615 -- case (\x -> e) of ...!
616 float | exprIsHNF rhs = FloatLet (NonRec bndr rhs)
617 | otherwise = FloatCase bndr rhs (exprOkForSpeculation rhs)
619 returnUs (addFloat floats float, evald_bndr)
622 = floatRhs NotTopLevel NonRecursive bndr (floats, rhs) `thenUs` \ (floats', rhs') ->
623 returnUs (addFloat floats' (FloatLet (NonRec bndr rhs')),
624 if exprIsHNF rhs' then evald_bndr else bndr)
627 evald_bndr = bndr `setIdUnfolding` evaldUnfolding
628 -- Record if the binder is evaluated
631 mkBinds :: Floats -> CoreExpr -> UniqSM CoreExpr
632 mkBinds (Floats _ binds) body
633 | isNilOL binds = returnUs body
634 | otherwise = deLam body `thenUs` \ body' ->
635 -- Lambdas are not allowed as the body of a 'let'
636 returnUs (foldrOL mk_bind body' binds)
638 mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
639 mk_bind (FloatLet bind) body = Let bind body
641 etaExpandRhs bndr rhs
642 = -- Eta expand to match the arity claimed by the binder
643 -- Remember, after CorePrep we must not change arity
645 -- Eta expansion might not have happened already,
646 -- because it is done by the simplifier only when
647 -- there at least one lambda already.
649 -- NB1:we could refrain when the RHS is trivial (which can happen
650 -- for exported things). This would reduce the amount of code
651 -- generated (a little) and make things a little words for
652 -- code compiled without -O. The case in point is data constructor
655 -- NB2: we have to be careful that the result of etaExpand doesn't
656 -- invalidate any of the assumptions that CorePrep is attempting
657 -- to establish. One possible cause is eta expanding inside of
658 -- an SCC note - we're now careful in etaExpand to make sure the
659 -- SCC is pushed inside any new lambdas that are generated.
661 -- NB3: It's important to do eta expansion, and *then* ANF-ising
662 -- f = /\a -> g (h 3) -- h has arity 2
663 -- If we ANF first we get
664 -- f = /\a -> let s = h 3 in g s
665 -- and now eta expansion gives
666 -- f = /\a -> \ y -> (let s = h 3 in g s) y
667 -- which is horrible.
668 -- Eta expanding first gives
669 -- f = /\a -> \y -> let s = h 3 in g s y
671 getUniquesUs `thenUs` \ us ->
672 returnUs (etaExpand arity us rhs (idType bndr))
674 -- For a GlobalId, take the Arity from the Id.
675 -- It was set in CoreTidy and must not change
676 -- For all others, just expand at will
677 arity | isGlobalId bndr = idArity bndr
678 | otherwise = exprArity rhs
680 -- ---------------------------------------------------------------------------
681 -- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
682 -- We arrange that they only show up as the RHS of a let(rec)
683 -- ---------------------------------------------------------------------------
685 deLam :: CoreExpr -> UniqSM CoreExpr
686 -- Takes an expression that may be a lambda,
687 -- and returns one that definitely isn't:
688 -- (\x.e) ==> let f = \x.e in f
690 deLamFloat expr `thenUs` \ (floats, expr) ->
694 deLamFloat :: CoreExpr -> UniqSM (Floats, CoreExpr)
695 -- Remove top level lambdas by let-bindinig
697 deLamFloat (Note n expr)
698 = -- You can get things like
699 -- case e of { p -> coerce t (\s -> ...) }
700 deLamFloat expr `thenUs` \ (floats, expr') ->
701 returnUs (floats, Note n expr')
703 deLamFloat (Cast e co)
704 = deLamFloat e `thenUs` \ (floats, e') ->
705 returnUs (floats, Cast e' co)
708 | null bndrs = returnUs (emptyFloats, expr)
710 = case tryEta bndrs body of
711 Just no_lam_result -> returnUs (emptyFloats, no_lam_result)
712 Nothing -> newVar (exprType expr) `thenUs` \ fn ->
713 returnUs (unitFloat (FloatLet (NonRec fn expr)),
716 (bndrs,body) = collectBinders expr
718 -- Why try eta reduction? Hasn't the simplifier already done eta?
719 -- But the simplifier only eta reduces if that leaves something
720 -- trivial (like f, or f Int). But for deLam it would be enough to
721 -- get to a partial application:
722 -- \xs. map f xs ==> map f
724 tryEta bndrs expr@(App _ _)
725 | ok_to_eta_reduce f &&
727 and (zipWith ok bndrs last_args) &&
728 not (any (`elemVarSet` fvs_remaining) bndrs)
729 = Just remaining_expr
731 (f, args) = collectArgs expr
732 remaining_expr = mkApps f remaining_args
733 fvs_remaining = exprFreeVars remaining_expr
734 (remaining_args, last_args) = splitAt n_remaining args
735 n_remaining = length args - length bndrs
737 ok bndr (Var arg) = bndr == arg
738 ok bndr other = False
740 -- we can't eta reduce something which must be saturated.
741 ok_to_eta_reduce (Var f) = not (hasNoBinding f)
742 ok_to_eta_reduce _ = False --safe. ToDo: generalise
744 tryEta bndrs (Let bind@(NonRec b r) body)
745 | not (any (`elemVarSet` fvs) bndrs)
746 = case tryEta bndrs body of
747 Just e -> Just (Let bind e)
752 tryEta bndrs _ = Nothing
756 -- -----------------------------------------------------------------------------
758 -- -----------------------------------------------------------------------------
762 = RhsDemand { isStrict :: Bool, -- True => used at least once
763 isOnceDem :: Bool -- True => used at most once
766 mkDem :: Demand -> Bool -> RhsDemand
767 mkDem strict once = RhsDemand (isStrictDmd strict) once
769 mkDemTy :: Demand -> Type -> RhsDemand
770 mkDemTy strict ty = RhsDemand (isStrictDmd strict)
773 bdrDem :: Id -> RhsDemand
774 bdrDem id = mkDem (idNewDemandInfo id)
777 -- safeDem :: RhsDemand
778 -- safeDem = RhsDemand False False -- always safe to use this
781 onceDem = RhsDemand False True -- used at most once
787 %************************************************************************
791 %************************************************************************
794 -- ---------------------------------------------------------------------------
796 -- ---------------------------------------------------------------------------
798 data CorePrepEnv = CPE (IdEnv Id) -- Clone local Ids
800 emptyCorePrepEnv :: CorePrepEnv
801 emptyCorePrepEnv = CPE emptyVarEnv
803 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
804 extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')
806 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
807 lookupCorePrepEnv (CPE env) id
808 = case lookupVarEnv env id of
812 ------------------------------------------------------------------------------
814 -- ---------------------------------------------------------------------------
816 cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
817 cloneBndrs env bs = mapAccumLUs cloneBndr env bs
819 cloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
822 = getUniqueUs `thenUs` \ uniq ->
824 bndr' = setVarUnique bndr uniq
826 returnUs (extendCorePrepEnv env bndr bndr', bndr')
828 | otherwise -- Top level things, which we don't want
829 -- to clone, have become GlobalIds by now
830 -- And we don't clone tyvars
831 = returnUs (env, bndr)
834 ------------------------------------------------------------------------------
835 -- Cloning ccall Ids; each must have a unique name,
836 -- to give the code generator a handle to hang it on
837 -- ---------------------------------------------------------------------------
839 fiddleCCall :: Id -> UniqSM Id
841 | isFCallId id = getUniqueUs `thenUs` \ uniq ->
842 returnUs (id `setVarUnique` uniq)
843 | otherwise = returnUs id
845 ------------------------------------------------------------------------------
846 -- Generating new binders
847 -- ---------------------------------------------------------------------------
849 newVar :: Type -> UniqSM Id
852 getUniqueUs `thenUs` \ uniq ->
853 returnUs (mkSysLocal FSLIT("sat") uniq ty)