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)
39 -- ---------------------------------------------------------------------------
41 -- ---------------------------------------------------------------------------
43 The goal of this pass is to prepare for code generation.
45 1. Saturate constructor and primop applications.
47 2. Convert to A-normal form; that is, function arguments
50 * Use case for strict arguments:
51 f E ==> case E of x -> f x
54 * Use let for non-trivial lazy arguments
55 f E ==> let x = E in f x
56 (were f is lazy and x is non-trivial)
58 3. Similarly, convert any unboxed lets into cases.
59 [I'm experimenting with leaving 'ok-for-speculation'
60 rhss in let-form right up to this point.]
62 4. Ensure that lambdas only occur as the RHS of a binding
63 (The code generator can't deal with anything else.)
65 5. [Not any more; nuked Jun 2002] Do the seq/par munging.
67 6. Clone all local Ids.
68 This means that all such Ids are unique, rather than the
69 weaker guarantee of no clashes which the simplifier provides.
70 And that is what the code generator needs.
72 We don't clone TyVars. The code gen doesn't need that,
73 and doing so would be tiresome because then we'd need
74 to substitute in types.
77 7. Give each dynamic CCall occurrence a fresh unique; this is
78 rather like the cloning step above.
80 8. Inject bindings for the "implicit" Ids:
81 * Constructor wrappers
84 We want curried definitions for all of these in case they
85 aren't inlined by some caller.
87 This is all done modulo type applications and abstractions, so that
88 when type erasure is done for conversion to STG, we don't end up with
89 any trivial or useless bindings.
93 -- -----------------------------------------------------------------------------
95 -- -----------------------------------------------------------------------------
98 corePrepPgm :: DynFlags -> [CoreBind] -> [TyCon] -> IO [CoreBind]
99 corePrepPgm dflags binds data_tycons
100 = do showPass dflags "CorePrep"
101 us <- mkSplitUniqSupply 's'
103 let implicit_binds = mkDataConWorkers data_tycons
104 -- NB: we must feed mkImplicitBinds through corePrep too
105 -- so that they are suitably cloned and eta-expanded
107 binds_out = initUs_ us (
108 corePrepTopBinds binds `thenUs` \ floats1 ->
109 corePrepTopBinds implicit_binds `thenUs` \ floats2 ->
110 returnUs (deFloatTop (floats1 `appendFloats` floats2))
113 endPass dflags "CorePrep" Opt_D_dump_prep binds_out
116 corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
117 corePrepExpr dflags expr
118 = do showPass dflags "CorePrep"
119 us <- mkSplitUniqSupply 's'
120 let new_expr = initUs_ us (corePrepAnExpr emptyCorePrepEnv expr)
121 dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep"
126 -- -----------------------------------------------------------------------------
128 -- -----------------------------------------------------------------------------
130 Create any necessary "implicit" bindings for data con workers. We
131 create the rather strange (non-recursive!) binding
133 $wC = \x y -> $wC x y
135 i.e. a curried constructor that allocates. This means that we can
136 treat the worker for a constructor like any other function in the rest
137 of the compiler. The point here is that CoreToStg will generate a
138 StgConApp for the RHS, rather than a call to the worker (which would
139 give a loop). As Lennart says: the ice is thin here, but it works.
141 Hmm. Should we create bindings for dictionary constructors? They are
142 always fully applied, and the bindings are just there to support
143 partial applications. But it's easier to let them through.
146 mkDataConWorkers data_tycons
147 = [ NonRec id (Var id) -- The ice is thin here, but it works
148 | tycon <- data_tycons, -- CorePrep will eta-expand it
149 data_con <- tyConDataCons tycon,
150 let id = dataConWorkId data_con ]
155 -- ---------------------------------------------------------------------------
156 -- Dealing with bindings
157 -- ---------------------------------------------------------------------------
159 data FloatingBind = FloatLet CoreBind
160 | FloatCase Id CoreExpr Bool
161 -- The bool indicates "ok-for-speculation"
163 data Floats = Floats OkToSpec (OrdList FloatingBind)
165 -- Can we float these binds out of the rhs of a let? We cache this decision
166 -- to avoid having to recompute it in a non-linear way when there are
167 -- deeply nested lets.
169 = NotOkToSpec -- definitely not
171 | IfUnboxedOk -- only if floating an unboxed binding is ok
173 emptyFloats :: Floats
174 emptyFloats = Floats OkToSpec nilOL
176 addFloat :: Floats -> FloatingBind -> Floats
177 addFloat (Floats ok_to_spec floats) new_float
178 = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
180 check (FloatLet _) = OkToSpec
181 check (FloatCase _ _ ok_for_spec)
182 | ok_for_spec = IfUnboxedOk
183 | otherwise = NotOkToSpec
184 -- The ok-for-speculation flag says that it's safe to
185 -- float this Case out of a let, and thereby do it more eagerly
186 -- We need the top-level flag because it's never ok to float
187 -- an unboxed binding to the top level
189 unitFloat :: FloatingBind -> Floats
190 unitFloat = addFloat emptyFloats
192 appendFloats :: Floats -> Floats -> Floats
193 appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
194 = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
196 concatFloats :: [Floats] -> Floats
197 concatFloats = foldr appendFloats emptyFloats
199 combine NotOkToSpec _ = NotOkToSpec
200 combine _ NotOkToSpec = NotOkToSpec
201 combine IfUnboxedOk _ = IfUnboxedOk
202 combine _ IfUnboxedOk = IfUnboxedOk
203 combine _ _ = OkToSpec
205 instance Outputable FloatingBind where
206 ppr (FloatLet bind) = text "FloatLet" <+> ppr bind
207 ppr (FloatCase b rhs spec) = text "FloatCase" <+> ppr b <+> ppr spec <+> equals <+> ppr rhs
209 deFloatTop :: Floats -> [CoreBind]
210 -- For top level only; we don't expect any FloatCases
211 deFloatTop (Floats _ floats)
212 = foldrOL get [] floats
214 get (FloatLet b) bs = b:bs
215 get b bs = pprPanic "corePrepPgm" (ppr b)
217 allLazy :: TopLevelFlag -> RecFlag -> Floats -> Bool
218 allLazy top_lvl is_rec (Floats ok_to_spec _)
222 IfUnboxedOk -> isNotTopLevel top_lvl && isNonRec is_rec
224 -- ---------------------------------------------------------------------------
226 -- ---------------------------------------------------------------------------
228 corePrepTopBinds :: [CoreBind] -> UniqSM Floats
229 corePrepTopBinds binds
230 = go emptyCorePrepEnv binds
232 go env [] = returnUs emptyFloats
233 go env (bind : binds) = corePrepTopBind env bind `thenUs` \ (env', bind') ->
234 go env' binds `thenUs` \ binds' ->
235 returnUs (bind' `appendFloats` binds')
237 -- NB: we do need to float out of top-level bindings
238 -- Consider x = length [True,False]
244 -- We return a *list* of bindings, because we may start with
246 -- where x is demanded, in which case we want to finish with
249 -- And then x will actually end up case-bound
251 -- What happens to the CafInfo on the floated bindings? By
252 -- default, all the CafInfos will be set to MayHaveCafRefs,
255 -- This might be pessimistic, because eg. s1 & s2
256 -- might not refer to any CAFs and the GC will end up doing
257 -- more traversal than is necessary, but it's still better
258 -- than not floating the bindings at all, because then
259 -- the GC would have to traverse the structure in the heap
260 -- instead. Given this, we decided not to try to get
261 -- the CafInfo on the floated bindings correct, because
262 -- it looks difficult.
264 --------------------------------
265 corePrepTopBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
266 corePrepTopBind env (NonRec bndr rhs)
267 = cloneBndr env bndr `thenUs` \ (env', bndr') ->
268 corePrepRhs TopLevel NonRecursive env (bndr, rhs) `thenUs` \ (floats, rhs') ->
269 returnUs (env', addFloat floats (FloatLet (NonRec bndr' rhs')))
271 corePrepTopBind env (Rec pairs) = corePrepRecPairs TopLevel env pairs
273 --------------------------------
274 corePrepBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
275 -- This one is used for *local* bindings
276 corePrepBind env (NonRec bndr rhs)
277 = etaExpandRhs bndr rhs `thenUs` \ rhs1 ->
278 corePrepExprFloat env rhs1 `thenUs` \ (floats, rhs2) ->
279 cloneBndr env bndr `thenUs` \ (_, bndr') ->
280 mkLocalNonRec bndr' (bdrDem bndr) floats rhs2 `thenUs` \ (floats', bndr'') ->
281 -- We want bndr'' in the envt, because it records
282 -- the evaluated-ness of the binder
283 returnUs (extendCorePrepEnv env bndr bndr'', floats')
285 corePrepBind env (Rec pairs) = corePrepRecPairs NotTopLevel env pairs
287 --------------------------------
288 corePrepRecPairs :: TopLevelFlag -> CorePrepEnv
289 -> [(Id,CoreExpr)] -- Recursive bindings
290 -> UniqSM (CorePrepEnv, Floats)
291 -- Used for all recursive bindings, top level and otherwise
292 corePrepRecPairs lvl env pairs
293 = cloneBndrs env (map fst pairs) `thenUs` \ (env', bndrs') ->
294 mapAndUnzipUs (corePrepRhs lvl Recursive env') pairs `thenUs` \ (floats_s, rhss') ->
295 returnUs (env', unitFloat (FloatLet (Rec (flatten (concatFloats floats_s) bndrs' rhss'))))
297 -- Flatten all the floats, and the currrent
298 -- group into a single giant Rec
299 flatten (Floats _ floats) bndrs rhss = foldrOL get (bndrs `zip` rhss) floats
301 get (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
302 get (FloatLet (Rec prs1)) prs2 = prs1 ++ prs2
303 get b prs2 = pprPanic "corePrepRecPairs" (ppr b)
305 --------------------------------
306 corePrepRhs :: TopLevelFlag -> RecFlag
307 -> CorePrepEnv -> (Id, CoreExpr)
308 -> UniqSM (Floats, CoreExpr)
309 -- Used for top-level bindings, and local recursive bindings
310 corePrepRhs top_lvl is_rec env (bndr, rhs)
311 = etaExpandRhs bndr rhs `thenUs` \ rhs' ->
312 corePrepExprFloat env rhs' `thenUs` \ floats_w_rhs ->
313 floatRhs top_lvl is_rec bndr floats_w_rhs
316 -- ---------------------------------------------------------------------------
317 -- Making arguments atomic (function args & constructor args)
318 -- ---------------------------------------------------------------------------
320 -- This is where we arrange that a non-trivial argument is let-bound
321 corePrepArg :: CorePrepEnv -> CoreArg -> RhsDemand
322 -> UniqSM (Floats, CoreArg)
323 corePrepArg env arg dem
324 = corePrepExprFloat env arg `thenUs` \ (floats, arg') ->
325 if exprIsTrivial arg'
326 then returnUs (floats, arg')
327 else newVar (exprType arg') `thenUs` \ v ->
328 mkLocalNonRec v dem floats arg' `thenUs` \ (floats', v') ->
329 returnUs (floats', Var v')
331 -- version that doesn't consider an scc annotation to be trivial.
332 exprIsTrivial (Var v) = True
333 exprIsTrivial (Type _) = True
334 exprIsTrivial (Lit lit) = True
335 exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
336 exprIsTrivial (Note (SCC _) e) = False
337 exprIsTrivial (Note _ e) = exprIsTrivial e
338 exprIsTrivial (Cast e co) = exprIsTrivial e
339 exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
340 exprIsTrivial other = False
342 -- ---------------------------------------------------------------------------
343 -- Dealing with expressions
344 -- ---------------------------------------------------------------------------
346 corePrepAnExpr :: CorePrepEnv -> CoreExpr -> UniqSM CoreExpr
347 corePrepAnExpr env expr
348 = corePrepExprFloat env expr `thenUs` \ (floats, expr) ->
352 corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
356 -- e = let bs in e' (semantically, that is!)
359 -- f (g x) ===> ([v = g x], f v)
361 corePrepExprFloat env (Var v)
362 = fiddleCCall v `thenUs` \ v1 ->
364 v2 = lookupCorePrepEnv env v1
366 maybeSaturate v2 (Var v2) 0 emptyFloats (idType v2)
368 corePrepExprFloat env expr@(Type _)
369 = returnUs (emptyFloats, expr)
371 corePrepExprFloat env expr@(Lit lit)
372 = returnUs (emptyFloats, expr)
374 corePrepExprFloat env (Let bind body)
375 = corePrepBind env bind `thenUs` \ (env', new_binds) ->
376 corePrepExprFloat env' body `thenUs` \ (floats, new_body) ->
377 returnUs (new_binds `appendFloats` floats, new_body)
379 corePrepExprFloat env (Note n@(SCC _) expr)
380 = corePrepAnExpr env expr `thenUs` \ expr1 ->
381 deLamFloat expr1 `thenUs` \ (floats, expr2) ->
382 returnUs (floats, Note n expr2)
384 corePrepExprFloat env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
385 | Just (TickBox {}) <- isTickBoxOp_maybe id
386 = corePrepAnExpr env expr `thenUs` \ expr1 ->
387 deLamFloat expr1 `thenUs` \ (floats, expr2) ->
388 return (floats, Case (Var id) bndr ty [(DEFAULT,[],expr2)])
390 corePrepExprFloat env (Note other_note expr)
391 = corePrepExprFloat env expr `thenUs` \ (floats, expr') ->
392 returnUs (floats, Note other_note expr')
394 corePrepExprFloat env (Cast expr co)
395 = corePrepExprFloat env expr `thenUs` \ (floats, expr') ->
396 returnUs (floats, Cast expr' co)
398 corePrepExprFloat env expr@(Lam _ _)
399 = cloneBndrs env bndrs `thenUs` \ (env', bndrs') ->
400 corePrepAnExpr env' body `thenUs` \ body' ->
401 returnUs (emptyFloats, mkLams bndrs' body')
403 (bndrs,body) = collectBinders expr
405 corePrepExprFloat env (Case scrut bndr ty alts)
406 = corePrepExprFloat env scrut `thenUs` \ (floats1, scrut1) ->
407 deLamFloat scrut1 `thenUs` \ (floats2, scrut2) ->
409 bndr1 = bndr `setIdUnfolding` evaldUnfolding
410 -- Record that the case binder is evaluated in the alternatives
412 cloneBndr env bndr1 `thenUs` \ (env', bndr2) ->
413 mapUs (sat_alt env') alts `thenUs` \ alts' ->
414 returnUs (floats1 `appendFloats` floats2 , Case scrut2 bndr2 ty alts')
416 sat_alt env (con, bs, rhs)
417 = cloneBndrs env bs `thenUs` \ (env2, bs') ->
418 corePrepAnExpr env2 rhs `thenUs` \ rhs1 ->
419 deLam rhs1 `thenUs` \ rhs2 ->
420 returnUs (con, bs', rhs2)
422 corePrepExprFloat env expr@(App _ _)
423 = collect_args expr 0 `thenUs` \ (app, (head,depth), ty, floats, ss) ->
424 ASSERT(null ss) -- make sure we used all the strictness info
426 -- Now deal with the function
428 Var fn_id -> maybeSaturate fn_id app depth floats ty
429 _other -> returnUs (floats, app)
433 -- Deconstruct and rebuild the application, floating any non-atomic
434 -- arguments to the outside. We collect the type of the expression,
435 -- the head of the application, and the number of actual value arguments,
436 -- all of which are used to possibly saturate this application if it
437 -- has a constructor or primop at the head.
441 -> Int -- current app depth
442 -> UniqSM (CoreExpr, -- the rebuilt expression
443 (CoreExpr,Int), -- the head of the application,
444 -- and no. of args it was applied to
445 Type, -- type of the whole expr
446 Floats, -- any floats we pulled out
447 [Demand]) -- remaining argument demands
449 collect_args (App fun arg@(Type arg_ty)) depth
450 = collect_args fun depth `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
451 returnUs (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
453 collect_args (App fun arg) depth
454 = collect_args fun (depth+1) `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
456 (ss1, ss_rest) = case ss of
457 (ss1:ss_rest) -> (ss1, ss_rest)
459 (arg_ty, res_ty) = expectJust "corePrepExprFloat:collect_args" $
460 splitFunTy_maybe fun_ty
462 corePrepArg env arg (mkDemTy ss1 arg_ty) `thenUs` \ (fs, arg') ->
463 returnUs (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest)
465 collect_args (Var v) depth
466 = fiddleCCall v `thenUs` \ v1 ->
468 v2 = lookupCorePrepEnv env v1
470 returnUs (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts)
472 stricts = case idNewStrictness v of
473 StrictSig (DmdType _ demands _)
474 | listLengthCmp demands depth /= GT -> demands
475 -- length demands <= depth
477 -- If depth < length demands, then we have too few args to
478 -- satisfy strictness info so we have to ignore all the
479 -- strictness info, e.g. + (error "urk")
480 -- Here, we can't evaluate the arg strictly, because this
481 -- partial application might be seq'd
483 collect_args (Cast fun co) depth
484 = let (_ty1,ty2) = coercionKind co in
485 collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
486 returnUs (Cast fun' co, hd, ty2, floats, ss)
488 collect_args (Note note fun) depth
489 | ignore_note note -- Drop these notes altogether
490 -- They aren't used by the code generator
491 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
492 returnUs (fun', hd, fun_ty, floats, ss)
494 -- N-variable fun, better let-bind it
495 -- ToDo: perhaps we can case-bind rather than let-bind this closure,
496 -- since it is sure to be evaluated.
497 collect_args fun depth
498 = corePrepExprFloat env fun `thenUs` \ (fun_floats, fun') ->
499 newVar ty `thenUs` \ fn_id ->
500 mkLocalNonRec fn_id onceDem fun_floats fun' `thenUs` \ (floats, fn_id') ->
501 returnUs (Var fn_id', (Var fn_id', depth), ty, floats, [])
505 ignore_note (CoreNote _) = True
506 ignore_note InlineMe = True
507 ignore_note _other = False
508 -- We don't ignore SCCs, since they require some code generation
510 ------------------------------------------------------------------------------
511 -- Building the saturated syntax
512 -- ---------------------------------------------------------------------------
514 -- maybeSaturate deals with saturating primops and constructors
515 -- The type is the type of the entire application
516 maybeSaturate :: Id -> CoreExpr -> Int -> Floats -> Type -> UniqSM (Floats, CoreExpr)
517 maybeSaturate fn expr n_args floats ty
518 | Just DataToTagOp <- isPrimOpId_maybe fn -- DataToTag must have an evaluated arg
519 -- A gruesome special case
520 = saturate_it `thenUs` \ sat_expr ->
522 -- OK, now ensure that the arg is evaluated.
523 -- But (sigh) take into account the lambdas we've now introduced
525 (eta_bndrs, eta_body) = collectBinders sat_expr
527 eval_data2tag_arg eta_body `thenUs` \ (eta_floats, eta_body') ->
528 if null eta_bndrs then
529 returnUs (floats `appendFloats` eta_floats, eta_body')
531 mkBinds eta_floats eta_body' `thenUs` \ eta_body'' ->
532 returnUs (floats, mkLams eta_bndrs eta_body'')
534 | hasNoBinding fn = saturate_it `thenUs` \ sat_expr ->
535 returnUs (floats, sat_expr)
537 | otherwise = returnUs (floats, expr)
540 fn_arity = idArity fn
541 excess_arity = fn_arity - n_args
543 saturate_it :: UniqSM CoreExpr
544 saturate_it | excess_arity == 0 = returnUs expr
545 | otherwise = getUniquesUs `thenUs` \ us ->
546 returnUs (etaExpand excess_arity us expr ty)
548 -- Ensure that the argument of DataToTagOp is evaluated
549 eval_data2tag_arg :: CoreExpr -> UniqSM (Floats, CoreExpr)
550 eval_data2tag_arg app@(fun `App` arg)
551 | exprIsHNF arg -- Includes nullary constructors
552 = returnUs (emptyFloats, app) -- The arg is evaluated
553 | otherwise -- Arg not evaluated, so evaluate it
554 = newVar (exprType arg) `thenUs` \ arg_id ->
556 arg_id1 = setIdUnfolding arg_id evaldUnfolding
558 returnUs (unitFloat (FloatCase arg_id1 arg False ),
559 fun `App` Var arg_id1)
561 eval_data2tag_arg (Note note app) -- Scc notes can appear
562 = eval_data2tag_arg app `thenUs` \ (floats, app') ->
563 returnUs (floats, Note note app')
565 eval_data2tag_arg other -- Should not happen
566 = pprPanic "eval_data2tag" (ppr other)
569 -- ---------------------------------------------------------------------------
570 -- Precipitating the floating bindings
571 -- ---------------------------------------------------------------------------
573 floatRhs :: TopLevelFlag -> RecFlag
575 -> (Floats, CoreExpr) -- Rhs: let binds in body
576 -> UniqSM (Floats, -- Floats out of this bind
577 CoreExpr) -- Final Rhs
579 floatRhs top_lvl is_rec bndr (floats, rhs)
580 | isTopLevel top_lvl || exprIsHNF rhs, -- Float to expose value or
581 allLazy top_lvl is_rec floats -- at top level
582 = -- Why the test for allLazy?
583 -- v = f (x `divInt#` y)
584 -- we don't want to float the case, even if f has arity 2,
585 -- because floating the case would make it evaluated too early
586 returnUs (floats, rhs)
589 -- Don't float; the RHS isn't a value
590 = mkBinds floats rhs `thenUs` \ rhs' ->
591 returnUs (emptyFloats, rhs')
593 -- mkLocalNonRec is used only for *nested*, *non-recursive* bindings
594 mkLocalNonRec :: Id -> RhsDemand -- Lhs: id with demand
595 -> Floats -> CoreExpr -- Rhs: let binds in body
596 -> UniqSM (Floats, Id) -- The new Id may have an evaldUnfolding,
597 -- to record that it's been evaluated
599 mkLocalNonRec bndr dem floats rhs
600 | isUnLiftedType (idType bndr)
601 -- If this is an unlifted binding, we always make a case for it.
602 = ASSERT( not (isUnboxedTupleType (idType bndr)) )
604 float = FloatCase bndr rhs (exprOkForSpeculation rhs)
606 returnUs (addFloat floats float, evald_bndr)
609 -- It's a strict let so we definitely float all the bindings
610 = let -- Don't make a case for a value binding,
611 -- even if it's strict. Otherwise we get
612 -- case (\x -> e) of ...!
613 float | exprIsHNF rhs = FloatLet (NonRec bndr rhs)
614 | otherwise = FloatCase bndr rhs (exprOkForSpeculation rhs)
616 returnUs (addFloat floats float, evald_bndr)
619 = floatRhs NotTopLevel NonRecursive bndr (floats, rhs) `thenUs` \ (floats', rhs') ->
620 returnUs (addFloat floats' (FloatLet (NonRec bndr rhs')),
621 if exprIsHNF rhs' then evald_bndr else bndr)
624 evald_bndr = bndr `setIdUnfolding` evaldUnfolding
625 -- Record if the binder is evaluated
628 mkBinds :: Floats -> CoreExpr -> UniqSM CoreExpr
629 mkBinds (Floats _ binds) body
630 | isNilOL binds = returnUs body
631 | otherwise = deLam body `thenUs` \ body' ->
632 -- Lambdas are not allowed as the body of a 'let'
633 returnUs (foldrOL mk_bind body' binds)
635 mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
636 mk_bind (FloatLet bind) body = Let bind body
638 etaExpandRhs bndr rhs
639 = -- Eta expand to match the arity claimed by the binder
640 -- Remember, after CorePrep we must not change arity
642 -- Eta expansion might not have happened already,
643 -- because it is done by the simplifier only when
644 -- there at least one lambda already.
646 -- NB1:we could refrain when the RHS is trivial (which can happen
647 -- for exported things). This would reduce the amount of code
648 -- generated (a little) and make things a little words for
649 -- code compiled without -O. The case in point is data constructor
652 -- NB2: we have to be careful that the result of etaExpand doesn't
653 -- invalidate any of the assumptions that CorePrep is attempting
654 -- to establish. One possible cause is eta expanding inside of
655 -- an SCC note - we're now careful in etaExpand to make sure the
656 -- SCC is pushed inside any new lambdas that are generated.
658 -- NB3: It's important to do eta expansion, and *then* ANF-ising
659 -- f = /\a -> g (h 3) -- h has arity 2
660 -- If we ANF first we get
661 -- f = /\a -> let s = h 3 in g s
662 -- and now eta expansion gives
663 -- f = /\a -> \ y -> (let s = h 3 in g s) y
664 -- which is horrible.
665 -- Eta expanding first gives
666 -- f = /\a -> \y -> let s = h 3 in g s y
668 getUniquesUs `thenUs` \ us ->
669 returnUs (etaExpand arity us rhs (idType bndr))
671 -- For a GlobalId, take the Arity from the Id.
672 -- It was set in CoreTidy and must not change
673 -- For all others, just expand at will
674 arity | isGlobalId bndr = idArity bndr
675 | otherwise = exprArity rhs
677 -- ---------------------------------------------------------------------------
678 -- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
679 -- We arrange that they only show up as the RHS of a let(rec)
680 -- ---------------------------------------------------------------------------
682 deLam :: CoreExpr -> UniqSM CoreExpr
683 -- Takes an expression that may be a lambda,
684 -- and returns one that definitely isn't:
685 -- (\x.e) ==> let f = \x.e in f
687 deLamFloat expr `thenUs` \ (floats, expr) ->
691 deLamFloat :: CoreExpr -> UniqSM (Floats, CoreExpr)
692 -- Remove top level lambdas by let-bindinig
694 deLamFloat (Note n expr)
695 = -- You can get things like
696 -- case e of { p -> coerce t (\s -> ...) }
697 deLamFloat expr `thenUs` \ (floats, expr') ->
698 returnUs (floats, Note n expr')
700 deLamFloat (Cast e co)
701 = deLamFloat e `thenUs` \ (floats, e') ->
702 returnUs (floats, Cast e' co)
705 | null bndrs = returnUs (emptyFloats, expr)
707 = case tryEta bndrs body of
708 Just no_lam_result -> returnUs (emptyFloats, no_lam_result)
709 Nothing -> newVar (exprType expr) `thenUs` \ fn ->
710 returnUs (unitFloat (FloatLet (NonRec fn expr)),
713 (bndrs,body) = collectBinders expr
715 -- Why try eta reduction? Hasn't the simplifier already done eta?
716 -- But the simplifier only eta reduces if that leaves something
717 -- trivial (like f, or f Int). But for deLam it would be enough to
718 -- get to a partial application:
719 -- \xs. map f xs ==> map f
721 tryEta bndrs expr@(App _ _)
722 | ok_to_eta_reduce f &&
724 and (zipWith ok bndrs last_args) &&
725 not (any (`elemVarSet` fvs_remaining) bndrs)
726 = Just remaining_expr
728 (f, args) = collectArgs expr
729 remaining_expr = mkApps f remaining_args
730 fvs_remaining = exprFreeVars remaining_expr
731 (remaining_args, last_args) = splitAt n_remaining args
732 n_remaining = length args - length bndrs
734 ok bndr (Var arg) = bndr == arg
735 ok bndr other = False
737 -- we can't eta reduce something which must be saturated.
738 ok_to_eta_reduce (Var f) = not (hasNoBinding f)
739 ok_to_eta_reduce _ = False --safe. ToDo: generalise
741 tryEta bndrs (Let bind@(NonRec b r) body)
742 | not (any (`elemVarSet` fvs) bndrs)
743 = case tryEta bndrs body of
744 Just e -> Just (Let bind e)
749 tryEta bndrs _ = Nothing
753 -- -----------------------------------------------------------------------------
755 -- -----------------------------------------------------------------------------
759 = RhsDemand { isStrict :: Bool, -- True => used at least once
760 isOnceDem :: Bool -- True => used at most once
763 mkDem :: Demand -> Bool -> RhsDemand
764 mkDem strict once = RhsDemand (isStrictDmd strict) once
766 mkDemTy :: Demand -> Type -> RhsDemand
767 mkDemTy strict ty = RhsDemand (isStrictDmd strict)
770 bdrDem :: Id -> RhsDemand
771 bdrDem id = mkDem (idNewDemandInfo id)
774 -- safeDem :: RhsDemand
775 -- safeDem = RhsDemand False False -- always safe to use this
778 onceDem = RhsDemand False True -- used at most once
784 %************************************************************************
788 %************************************************************************
791 -- ---------------------------------------------------------------------------
793 -- ---------------------------------------------------------------------------
795 data CorePrepEnv = CPE (IdEnv Id) -- Clone local Ids
797 emptyCorePrepEnv :: CorePrepEnv
798 emptyCorePrepEnv = CPE emptyVarEnv
800 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
801 extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')
803 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
804 lookupCorePrepEnv (CPE env) id
805 = case lookupVarEnv env id of
809 ------------------------------------------------------------------------------
811 -- ---------------------------------------------------------------------------
813 cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
814 cloneBndrs env bs = mapAccumLUs cloneBndr env bs
816 cloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
819 = getUniqueUs `thenUs` \ uniq ->
821 bndr' = setVarUnique bndr uniq
823 returnUs (extendCorePrepEnv env bndr bndr', bndr')
825 | otherwise -- Top level things, which we don't want
826 -- to clone, have become GlobalIds by now
827 -- And we don't clone tyvars
828 = returnUs (env, bndr)
831 ------------------------------------------------------------------------------
832 -- Cloning ccall Ids; each must have a unique name,
833 -- to give the code generator a handle to hang it on
834 -- ---------------------------------------------------------------------------
836 fiddleCCall :: Id -> UniqSM Id
838 | isFCallId id = getUniqueUs `thenUs` \ uniq ->
839 returnUs (id `setVarUnique` uniq)
840 | otherwise = returnUs id
842 ------------------------------------------------------------------------------
843 -- Generating new binders
844 -- ---------------------------------------------------------------------------
846 newVar :: Type -> UniqSM Id
849 getUniqueUs `thenUs` \ uniq ->
850 returnUs (mkSysLocal FSLIT("sat") uniq ty)