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, exprIsHNF, etaExpand, exprArity, exprOkForSpeculation )
14 import CoreFVs ( exprFreeVars )
15 import CoreLint ( endPass )
17 import Type ( Type, applyTy, splitFunTy_maybe,
18 isUnLiftedType, isUnboxedTupleType, seqType )
19 import TyCon ( TyCon, tyConDataCons )
20 import NewDemand ( Demand, isStrictDmd, lazyDmd, StrictSig(..), DmdType(..) )
21 import Var ( Var, Id, setVarUnique )
24 import Id ( mkSysLocal, idType, idNewDemandInfo, idArity, setIdUnfolding, setIdType,
25 isFCallId, isGlobalId,
26 isLocalId, hasNoBinding, idNewStrictness,
29 import DataCon ( isVanillaDataCon, dataConWorkId )
30 import PrimOp ( PrimOp( DataToTagOp ) )
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] -> [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 (Lam b body) | isTyVar b = exprIsTrivial body
342 exprIsTrivial other = False
344 -- ---------------------------------------------------------------------------
345 -- Dealing with expressions
346 -- ---------------------------------------------------------------------------
348 corePrepAnExpr :: CorePrepEnv -> CoreExpr -> UniqSM CoreExpr
349 corePrepAnExpr env expr
350 = corePrepExprFloat env expr `thenUs` \ (floats, expr) ->
354 corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
358 -- e = let bs in e' (semantically, that is!)
361 -- f (g x) ===> ([v = g x], f v)
363 corePrepExprFloat env (Var v)
364 = fiddleCCall v `thenUs` \ v1 ->
366 v2 = lookupCorePrepEnv env v1
368 maybeSaturate v2 (Var v2) 0 emptyFloats (idType v2)
370 corePrepExprFloat env expr@(Type _)
371 = returnUs (emptyFloats, expr)
373 corePrepExprFloat env expr@(Lit lit)
374 = returnUs (emptyFloats, expr)
376 corePrepExprFloat env (Let bind body)
377 = corePrepBind env bind `thenUs` \ (env', new_binds) ->
378 corePrepExprFloat env' body `thenUs` \ (floats, new_body) ->
379 returnUs (new_binds `appendFloats` floats, new_body)
381 corePrepExprFloat env (Note n@(SCC _) expr)
382 = corePrepAnExpr env expr `thenUs` \ expr1 ->
383 deLamFloat expr1 `thenUs` \ (floats, expr2) ->
384 returnUs (floats, Note n expr2)
386 corePrepExprFloat env (Note other_note expr)
387 = corePrepExprFloat env expr `thenUs` \ (floats, expr') ->
388 returnUs (floats, Note other_note expr')
390 corePrepExprFloat env expr@(Lam _ _)
391 = cloneBndrs env bndrs `thenUs` \ (env', bndrs') ->
392 corePrepAnExpr env' body `thenUs` \ body' ->
393 returnUs (emptyFloats, mkLams bndrs' body')
395 (bndrs,body) = collectBinders expr
397 corePrepExprFloat env (Case scrut bndr ty alts)
398 = corePrepExprFloat env scrut `thenUs` \ (floats1, scrut1) ->
399 deLamFloat scrut1 `thenUs` \ (floats2, scrut2) ->
401 bndr1 = bndr `setIdUnfolding` evaldUnfolding
402 -- Record that the case binder is evaluated in the alternatives
404 cloneBndr env bndr1 `thenUs` \ (env', bndr2) ->
405 mapUs (sat_alt env') alts `thenUs` \ alts' ->
406 returnUs (floats1 `appendFloats` floats2 , Case scrut2 bndr2 ty alts')
408 sat_alt env (con, bs, rhs)
410 env1 = setGadt env con
412 cloneBndrs env1 bs `thenUs` \ (env2, bs') ->
413 corePrepAnExpr env2 rhs `thenUs` \ rhs1 ->
414 deLam rhs1 `thenUs` \ rhs2 ->
415 returnUs (con, bs', rhs2)
417 corePrepExprFloat env expr@(App _ _)
418 = collect_args expr 0 `thenUs` \ (app, (head,depth), ty, floats, ss) ->
419 ASSERT(null ss) -- make sure we used all the strictness info
421 -- Now deal with the function
423 Var fn_id -> maybeSaturate fn_id app depth floats ty
424 _other -> returnUs (floats, app)
428 -- Deconstruct and rebuild the application, floating any non-atomic
429 -- arguments to the outside. We collect the type of the expression,
430 -- the head of the application, and the number of actual value arguments,
431 -- all of which are used to possibly saturate this application if it
432 -- has a constructor or primop at the head.
436 -> Int -- current app depth
437 -> UniqSM (CoreExpr, -- the rebuilt expression
438 (CoreExpr,Int), -- the head of the application,
439 -- and no. of args it was applied to
440 Type, -- type of the whole expr
441 Floats, -- any floats we pulled out
442 [Demand]) -- remaining argument demands
444 collect_args (App fun arg@(Type arg_ty)) depth
445 = collect_args fun depth `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
446 returnUs (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
448 collect_args (App fun arg) depth
449 = collect_args fun (depth+1) `thenUs` \ (fun',hd,fun_ty,floats,ss) ->
451 (ss1, ss_rest) = case ss of
452 (ss1:ss_rest) -> (ss1, ss_rest)
454 (arg_ty, res_ty) = expectJust "corePrepExprFloat:collect_args" $
455 splitFunTy_maybe fun_ty
457 corePrepArg env arg (mkDemTy ss1 arg_ty) `thenUs` \ (fs, arg') ->
458 returnUs (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest)
460 collect_args (Var v) depth
461 = fiddleCCall v `thenUs` \ v1 ->
463 v2 = lookupCorePrepEnv env v1
465 returnUs (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts)
467 stricts = case idNewStrictness v of
468 StrictSig (DmdType _ demands _)
469 | listLengthCmp demands depth /= GT -> demands
470 -- length demands <= depth
472 -- If depth < length demands, then we have too few args to
473 -- satisfy strictness info so we have to ignore all the
474 -- strictness info, e.g. + (error "urk")
475 -- Here, we can't evaluate the arg strictly, because this
476 -- partial application might be seq'd
479 collect_args (Note (Coerce ty1 ty2) fun) depth
480 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
481 returnUs (Note (Coerce ty1 ty2) fun', hd, ty1, floats, ss)
483 collect_args (Note note fun) depth
484 | ignore_note note -- Drop these notes altogether
485 -- They aren't used by the code generator
486 = collect_args fun depth `thenUs` \ (fun', hd, fun_ty, floats, ss) ->
487 returnUs (fun', hd, fun_ty, floats, ss)
489 -- N-variable fun, better let-bind it
490 -- ToDo: perhaps we can case-bind rather than let-bind this closure,
491 -- since it is sure to be evaluated.
492 collect_args fun depth
493 = corePrepExprFloat env fun `thenUs` \ (fun_floats, fun') ->
494 newVar ty `thenUs` \ fn_id ->
495 mkLocalNonRec fn_id onceDem fun_floats fun' `thenUs` \ (floats, fn_id') ->
496 returnUs (Var fn_id', (Var fn_id', depth), ty, floats, [])
500 ignore_note (CoreNote _) = True
501 ignore_note InlineMe = True
502 ignore_note _other = False
503 -- We don't ignore SCCs, since they require some code generation
505 ------------------------------------------------------------------------------
506 -- Building the saturated syntax
507 -- ---------------------------------------------------------------------------
509 -- maybeSaturate deals with saturating primops and constructors
510 -- The type is the type of the entire application
511 maybeSaturate :: Id -> CoreExpr -> Int -> Floats -> Type -> UniqSM (Floats, CoreExpr)
512 maybeSaturate fn expr n_args floats ty
513 | Just DataToTagOp <- isPrimOpId_maybe fn -- DataToTag must have an evaluated arg
514 -- A gruesome special case
515 = saturate_it `thenUs` \ sat_expr ->
517 -- OK, now ensure that the arg is evaluated.
518 -- But (sigh) take into account the lambdas we've now introduced
520 (eta_bndrs, eta_body) = collectBinders sat_expr
522 eval_data2tag_arg eta_body `thenUs` \ (eta_floats, eta_body') ->
523 if null eta_bndrs then
524 returnUs (floats `appendFloats` eta_floats, eta_body')
526 mkBinds eta_floats eta_body' `thenUs` \ eta_body'' ->
527 returnUs (floats, mkLams eta_bndrs eta_body'')
529 | hasNoBinding fn = saturate_it `thenUs` \ sat_expr ->
530 returnUs (floats, sat_expr)
532 | otherwise = returnUs (floats, expr)
535 fn_arity = idArity fn
536 excess_arity = fn_arity - n_args
538 saturate_it :: UniqSM CoreExpr
539 saturate_it | excess_arity == 0 = returnUs expr
540 | otherwise = getUniquesUs `thenUs` \ us ->
541 returnUs (etaExpand excess_arity us expr ty)
543 -- Ensure that the argument of DataToTagOp is evaluated
544 eval_data2tag_arg :: CoreExpr -> UniqSM (Floats, CoreExpr)
545 eval_data2tag_arg app@(fun `App` arg)
546 | exprIsHNF arg -- Includes nullary constructors
547 = returnUs (emptyFloats, app) -- The arg is evaluated
548 | otherwise -- Arg not evaluated, so evaluate it
549 = newVar (exprType arg) `thenUs` \ arg_id ->
551 arg_id1 = setIdUnfolding arg_id evaldUnfolding
553 returnUs (unitFloat (FloatCase arg_id1 arg False ),
554 fun `App` Var arg_id1)
556 eval_data2tag_arg (Note note app) -- Scc notes can appear
557 = eval_data2tag_arg app `thenUs` \ (floats, app') ->
558 returnUs (floats, Note note app')
560 eval_data2tag_arg other -- Should not happen
561 = pprPanic "eval_data2tag" (ppr other)
564 -- ---------------------------------------------------------------------------
565 -- Precipitating the floating bindings
566 -- ---------------------------------------------------------------------------
568 floatRhs :: TopLevelFlag -> RecFlag
570 -> (Floats, CoreExpr) -- Rhs: let binds in body
571 -> UniqSM (Floats, -- Floats out of this bind
572 CoreExpr) -- Final Rhs
574 floatRhs top_lvl is_rec bndr (floats, rhs)
575 | isTopLevel top_lvl || exprIsHNF rhs, -- Float to expose value or
576 allLazy top_lvl is_rec floats -- at top level
577 = -- Why the test for allLazy?
578 -- v = f (x `divInt#` y)
579 -- we don't want to float the case, even if f has arity 2,
580 -- because floating the case would make it evaluated too early
581 returnUs (floats, rhs)
584 -- Don't float; the RHS isn't a value
585 = mkBinds floats rhs `thenUs` \ rhs' ->
586 returnUs (emptyFloats, rhs')
588 -- mkLocalNonRec is used only for *nested*, *non-recursive* bindings
589 mkLocalNonRec :: Id -> RhsDemand -- Lhs: id with demand
590 -> Floats -> CoreExpr -- Rhs: let binds in body
591 -> UniqSM (Floats, Id) -- The new Id may have an evaldUnfolding,
592 -- to record that it's been evaluated
594 mkLocalNonRec bndr dem floats rhs
595 | isUnLiftedType (idType bndr)
596 -- If this is an unlifted binding, we always make a case for it.
597 = ASSERT( not (isUnboxedTupleType (idType bndr)) )
599 float = FloatCase bndr rhs (exprOkForSpeculation rhs)
601 returnUs (addFloat floats float, evald_bndr)
604 -- It's a strict let so we definitely float all the bindings
605 = let -- Don't make a case for a value binding,
606 -- even if it's strict. Otherwise we get
607 -- case (\x -> e) of ...!
608 float | exprIsHNF rhs = FloatLet (NonRec bndr rhs)
609 | otherwise = FloatCase bndr rhs (exprOkForSpeculation rhs)
611 returnUs (addFloat floats float, evald_bndr)
614 = floatRhs NotTopLevel NonRecursive bndr (floats, rhs) `thenUs` \ (floats', rhs') ->
615 returnUs (addFloat floats' (FloatLet (NonRec bndr rhs')),
616 if exprIsHNF rhs' then evald_bndr else bndr)
619 evald_bndr = bndr `setIdUnfolding` evaldUnfolding
620 -- Record if the binder is evaluated
623 mkBinds :: Floats -> CoreExpr -> UniqSM CoreExpr
624 mkBinds (Floats _ binds) body
625 | isNilOL binds = returnUs body
626 | otherwise = deLam body `thenUs` \ body' ->
627 -- Lambdas are not allowed as the body of a 'let'
628 returnUs (foldrOL mk_bind body' binds)
630 mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
631 mk_bind (FloatLet bind) body = Let bind body
633 etaExpandRhs bndr rhs
634 = -- Eta expand to match the arity claimed by the binder
635 -- Remember, after CorePrep we must not change arity
637 -- Eta expansion might not have happened already,
638 -- because it is done by the simplifier only when
639 -- there at least one lambda already.
641 -- NB1:we could refrain when the RHS is trivial (which can happen
642 -- for exported things). This would reduce the amount of code
643 -- generated (a little) and make things a little words for
644 -- code compiled without -O. The case in point is data constructor
647 -- NB2: we have to be careful that the result of etaExpand doesn't
648 -- invalidate any of the assumptions that CorePrep is attempting
649 -- to establish. One possible cause is eta expanding inside of
650 -- an SCC note - we're now careful in etaExpand to make sure the
651 -- SCC is pushed inside any new lambdas that are generated.
653 -- NB3: It's important to do eta expansion, and *then* ANF-ising
654 -- f = /\a -> g (h 3) -- h has arity 2
655 -- If we ANF first we get
656 -- f = /\a -> let s = h 3 in g s
657 -- and now eta expansion gives
658 -- f = /\a -> \ y -> (let s = h 3 in g s) y
659 -- which is horrible.
660 -- Eta expanding first gives
661 -- f = /\a -> \y -> let s = h 3 in g s y
663 getUniquesUs `thenUs` \ us ->
664 returnUs (etaExpand arity us rhs (idType bndr))
666 -- For a GlobalId, take the Arity from the Id.
667 -- It was set in CoreTidy and must not change
668 -- For all others, just expand at will
669 arity | isGlobalId bndr = idArity bndr
670 | otherwise = exprArity rhs
672 -- ---------------------------------------------------------------------------
673 -- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
674 -- We arrange that they only show up as the RHS of a let(rec)
675 -- ---------------------------------------------------------------------------
677 deLam :: CoreExpr -> UniqSM CoreExpr
679 deLamFloat expr `thenUs` \ (floats, expr) ->
683 deLamFloat :: CoreExpr -> UniqSM (Floats, CoreExpr)
684 -- Remove top level lambdas by let-bindinig
686 deLamFloat (Note n expr)
687 = -- You can get things like
688 -- case e of { p -> coerce t (\s -> ...) }
689 deLamFloat expr `thenUs` \ (floats, expr') ->
690 returnUs (floats, Note n expr')
693 | null bndrs = returnUs (emptyFloats, expr)
695 = case tryEta bndrs body of
696 Just no_lam_result -> returnUs (emptyFloats, no_lam_result)
697 Nothing -> newVar (exprType expr) `thenUs` \ fn ->
698 returnUs (unitFloat (FloatLet (NonRec fn expr)),
701 (bndrs,body) = collectBinders expr
703 -- Why try eta reduction? Hasn't the simplifier already done eta?
704 -- But the simplifier only eta reduces if that leaves something
705 -- trivial (like f, or f Int). But for deLam it would be enough to
706 -- get to a partial application, like (map f).
708 tryEta bndrs expr@(App _ _)
709 | ok_to_eta_reduce f &&
711 and (zipWith ok bndrs last_args) &&
712 not (any (`elemVarSet` fvs_remaining) bndrs)
713 = Just remaining_expr
715 (f, args) = collectArgs expr
716 remaining_expr = mkApps f remaining_args
717 fvs_remaining = exprFreeVars remaining_expr
718 (remaining_args, last_args) = splitAt n_remaining args
719 n_remaining = length args - length bndrs
721 ok bndr (Var arg) = bndr == arg
722 ok bndr other = False
724 -- we can't eta reduce something which must be saturated.
725 ok_to_eta_reduce (Var f) = not (hasNoBinding f)
726 ok_to_eta_reduce _ = False --safe. ToDo: generalise
728 tryEta bndrs (Let bind@(NonRec b r) body)
729 | not (any (`elemVarSet` fvs) bndrs)
730 = case tryEta bndrs body of
731 Just e -> Just (Let bind e)
736 tryEta bndrs _ = Nothing
740 -- -----------------------------------------------------------------------------
742 -- -----------------------------------------------------------------------------
746 = RhsDemand { isStrict :: Bool, -- True => used at least once
747 isOnceDem :: Bool -- True => used at most once
750 mkDem :: Demand -> Bool -> RhsDemand
751 mkDem strict once = RhsDemand (isStrictDmd strict) once
753 mkDemTy :: Demand -> Type -> RhsDemand
754 mkDemTy strict ty = RhsDemand (isStrictDmd strict)
757 bdrDem :: Id -> RhsDemand
758 bdrDem id = mkDem (idNewDemandInfo id)
761 -- safeDem :: RhsDemand
762 -- safeDem = RhsDemand False False -- always safe to use this
765 onceDem = RhsDemand False True -- used at most once
771 %************************************************************************
775 %************************************************************************
778 -- ---------------------------------------------------------------------------
780 -- ---------------------------------------------------------------------------
782 data CorePrepEnv = CPE (IdEnv Id) -- Clone local Ids
783 Bool -- True <=> inside a GADT case; see Note [GADT]
787 -- Be careful with cloning inside GADTs. For example,
788 -- /\a. \f::a. \x::T a. case x of { T -> f True; ... }
789 -- The case on x may refine the type of f to be a function type.
790 -- Without this type refinement, exprType (f True) may simply fail,
793 -- Solution: remember when we are inside a potentially-type-refining case,
794 -- and in that situation use the type from the old occurrence
795 -- when looking up occurrences
797 emptyCorePrepEnv :: CorePrepEnv
798 emptyCorePrepEnv = CPE emptyVarEnv False
800 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
801 extendCorePrepEnv (CPE env gadt) id id' = CPE (extendVarEnv env id id') gadt
803 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
804 -- See Note [GADT] above
805 lookupCorePrepEnv (CPE env gadt) id
806 = case lookupVarEnv env id of
808 Just id' | gadt -> setIdType id' (idType id)
811 setGadt :: CorePrepEnv -> AltCon -> CorePrepEnv
812 setGadt env@(CPE id_env _) (DataAlt data_con) | not (isVanillaDataCon data_con) = CPE id_env True
813 setGadt env other = env
816 ------------------------------------------------------------------------------
818 -- ---------------------------------------------------------------------------
820 cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
821 cloneBndrs env bs = mapAccumLUs cloneBndr env bs
823 cloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
826 = getUniqueUs `thenUs` \ uniq ->
828 bndr' = setVarUnique bndr uniq
830 returnUs (extendCorePrepEnv env bndr bndr', bndr')
832 | otherwise -- Top level things, which we don't want
833 -- to clone, have become GlobalIds by now
834 -- And we don't clone tyvars
835 = returnUs (env, bndr)
838 ------------------------------------------------------------------------------
839 -- Cloning ccall Ids; each must have a unique name,
840 -- to give the code generator a handle to hang it on
841 -- ---------------------------------------------------------------------------
843 fiddleCCall :: Id -> UniqSM Id
845 | isFCallId id = getUniqueUs `thenUs` \ uniq ->
846 returnUs (id `setVarUnique` uniq)
847 | otherwise = returnUs id
849 ------------------------------------------------------------------------------
850 -- Generating new binders
851 -- ---------------------------------------------------------------------------
853 newVar :: Type -> UniqSM Id
856 getUniqueUs `thenUs` \ uniq ->
857 returnUs (mkSysLocal FSLIT("sat") uniq ty)