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)
41 -- ---------------------------------------------------------------------------
43 -- ---------------------------------------------------------------------------
45 The goal of this pass is to prepare for code generation.
47 1. Saturate constructor and primop applications.
49 2. Convert to A-normal form; that is, function arguments
52 * Use case for strict arguments:
53 f E ==> case E of x -> f x
56 * Use let for non-trivial lazy arguments
57 f E ==> let x = E in f x
58 (were f is lazy and x is non-trivial)
60 3. Similarly, convert any unboxed lets into cases.
61 [I'm experimenting with leaving 'ok-for-speculation'
62 rhss in let-form right up to this point.]
64 4. Ensure that lambdas only occur as the RHS of a binding
65 (The code generator can't deal with anything else.)
67 5. [Not any more; nuked Jun 2002] Do the seq/par munging.
69 6. Clone all local Ids.
70 This means that all such Ids are unique, rather than the
71 weaker guarantee of no clashes which the simplifier provides.
72 And that is what the code generator needs.
74 We don't clone TyVars. The code gen doesn't need that,
75 and doing so would be tiresome because then we'd need
76 to substitute in types.
79 7. Give each dynamic CCall occurrence a fresh unique; this is
80 rather like the cloning step above.
82 8. Inject bindings for the "implicit" Ids:
83 * Constructor wrappers
86 We want curried definitions for all of these in case they
87 aren't inlined by some caller.
89 This is all done modulo type applications and abstractions, so that
90 when type erasure is done for conversion to STG, we don't end up with
91 any trivial or useless bindings.
95 -- -----------------------------------------------------------------------------
97 -- -----------------------------------------------------------------------------
100 corePrepPgm :: DynFlags -> [CoreBind] -> [TyCon] -> IO [CoreBind]
101 corePrepPgm dflags binds data_tycons = do
102 showPass dflags "CorePrep"
103 us <- mkSplitUniqSupply 's'
105 let implicit_binds = mkDataConWorkers data_tycons
106 -- NB: we must feed mkImplicitBinds through corePrep too
107 -- so that they are suitably cloned and eta-expanded
109 binds_out = initUs_ us $ do
110 floats1 <- corePrepTopBinds binds
111 floats2 <- corePrepTopBinds implicit_binds
112 return (deFloatTop (floats1 `appendFloats` floats2))
114 endPass dflags "CorePrep" Opt_D_dump_prep binds_out
117 corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
118 corePrepExpr dflags expr = do
119 showPass dflags "CorePrep"
120 us <- mkSplitUniqSupply 's'
121 let new_expr = initUs_ us (corePrepAnExpr emptyCorePrepEnv expr)
122 dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep" (ppr new_expr)
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 :: [TyCon] -> [CoreBind]
147 mkDataConWorkers data_tycons
148 = [ NonRec id (Var id) -- The ice is thin here, but it works
149 | tycon <- data_tycons, -- CorePrep will eta-expand it
150 data_con <- tyConDataCons tycon,
151 let id = dataConWorkId data_con ]
156 -- ---------------------------------------------------------------------------
157 -- Dealing with bindings
158 -- ---------------------------------------------------------------------------
160 data FloatingBind = FloatLet CoreBind
161 | FloatCase Id CoreExpr Bool
162 -- The bool indicates "ok-for-speculation"
164 data Floats = Floats OkToSpec (OrdList FloatingBind)
166 -- Can we float these binds out of the rhs of a let? We cache this decision
167 -- to avoid having to recompute it in a non-linear way when there are
168 -- deeply nested lets.
170 = NotOkToSpec -- definitely not
172 | IfUnboxedOk -- only if floating an unboxed binding is ok
174 emptyFloats :: Floats
175 emptyFloats = Floats OkToSpec nilOL
177 addFloat :: Floats -> FloatingBind -> Floats
178 addFloat (Floats ok_to_spec floats) new_float
179 = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
181 check (FloatLet _) = OkToSpec
182 check (FloatCase _ _ ok_for_spec)
183 | ok_for_spec = IfUnboxedOk
184 | otherwise = NotOkToSpec
185 -- The ok-for-speculation flag says that it's safe to
186 -- float this Case out of a let, and thereby do it more eagerly
187 -- We need the top-level flag because it's never ok to float
188 -- an unboxed binding to the top level
190 unitFloat :: FloatingBind -> Floats
191 unitFloat = addFloat emptyFloats
193 appendFloats :: Floats -> Floats -> Floats
194 appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
195 = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
197 concatFloats :: [Floats] -> Floats
198 concatFloats = foldr appendFloats emptyFloats
200 combine :: OkToSpec -> OkToSpec -> OkToSpec
201 combine NotOkToSpec _ = NotOkToSpec
202 combine _ NotOkToSpec = NotOkToSpec
203 combine IfUnboxedOk _ = IfUnboxedOk
204 combine _ IfUnboxedOk = IfUnboxedOk
205 combine _ _ = OkToSpec
207 instance Outputable FloatingBind where
208 ppr (FloatLet bind) = text "FloatLet" <+> ppr bind
209 ppr (FloatCase b rhs spec) = text "FloatCase" <+> ppr b <+> ppr spec <+> equals <+> ppr rhs
211 deFloatTop :: Floats -> [CoreBind]
212 -- For top level only; we don't expect any FloatCases
213 deFloatTop (Floats _ floats)
214 = foldrOL get [] floats
216 get (FloatLet b) bs = b:bs
217 get b _ = pprPanic "corePrepPgm" (ppr b)
219 allLazy :: TopLevelFlag -> RecFlag -> Floats -> Bool
220 allLazy top_lvl is_rec (Floats ok_to_spec _)
224 IfUnboxedOk -> isNotTopLevel top_lvl && isNonRec is_rec
226 -- ---------------------------------------------------------------------------
228 -- ---------------------------------------------------------------------------
230 corePrepTopBinds :: [CoreBind] -> UniqSM Floats
231 corePrepTopBinds binds
232 = go emptyCorePrepEnv binds
234 go _ [] = return emptyFloats
235 go env (bind : binds) = do (env', bind') <- corePrepTopBind env bind
236 binds' <- go env' binds
237 return (bind' `appendFloats` binds')
239 -- NB: we do need to float out of top-level bindings
240 -- Consider x = length [True,False]
246 -- We return a *list* of bindings, because we may start with
248 -- where x is demanded, in which case we want to finish with
251 -- And then x will actually end up case-bound
253 -- What happens to the CafInfo on the floated bindings? By
254 -- default, all the CafInfos will be set to MayHaveCafRefs,
257 -- This might be pessimistic, because eg. s1 & s2
258 -- might not refer to any CAFs and the GC will end up doing
259 -- more traversal than is necessary, but it's still better
260 -- than not floating the bindings at all, because then
261 -- the GC would have to traverse the structure in the heap
262 -- instead. Given this, we decided not to try to get
263 -- the CafInfo on the floated bindings correct, because
264 -- it looks difficult.
266 --------------------------------
267 corePrepTopBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
268 corePrepTopBind env (NonRec bndr rhs) = do
269 (env', bndr') <- cloneBndr env bndr
270 (floats, rhs') <- corePrepRhs TopLevel NonRecursive env (bndr, rhs)
271 return (env', addFloat floats (FloatLet (NonRec bndr' rhs')))
273 corePrepTopBind env (Rec pairs) = corePrepRecPairs TopLevel env pairs
275 --------------------------------
276 corePrepBind :: CorePrepEnv -> CoreBind -> UniqSM (CorePrepEnv, Floats)
277 -- This one is used for *local* bindings
278 corePrepBind env (NonRec bndr rhs) = do
279 (floats, rhs2) <- corePrepExprFloat env rhs
280 (_, bndr') <- cloneBndr env bndr
281 (floats', bndr'') <- mkLocalNonRec bndr' (bdrDem bndr) floats rhs2
282 -- We want bndr'' in the envt, because it records
283 -- the evaluated-ness of the binder
284 return (extendCorePrepEnv env bndr bndr'', floats')
286 corePrepBind env (Rec pairs) = corePrepRecPairs NotTopLevel env pairs
288 --------------------------------
289 corePrepRecPairs :: TopLevelFlag -> CorePrepEnv
290 -> [(Id,CoreExpr)] -- Recursive bindings
291 -> UniqSM (CorePrepEnv, Floats)
292 -- Used for all recursive bindings, top level and otherwise
293 corePrepRecPairs lvl env pairs = do
294 (env', bndrs') <- cloneBndrs env (map fst pairs)
295 (floats_s, rhss') <- mapAndUnzipM (corePrepRhs lvl Recursive env') pairs
296 return (env', unitFloat (FloatLet (Rec (flatten (concatFloats floats_s) bndrs' rhss'))))
298 -- Flatten all the floats, and the currrent
299 -- group into a single giant Rec
300 flatten (Floats _ floats) bndrs rhss = foldrOL get (bndrs `zip` rhss) floats
302 get (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
303 get (FloatLet (Rec prs1)) prs2 = prs1 ++ prs2
304 get b _ = pprPanic "corePrepRecPairs" (ppr b)
306 --------------------------------
307 corePrepRhs :: TopLevelFlag -> RecFlag
308 -> CorePrepEnv -> (Id, CoreExpr)
309 -> UniqSM (Floats, CoreExpr)
310 -- Used for top-level bindings, and local recursive bindings
311 corePrepRhs top_lvl is_rec env (bndr, rhs) = do
312 floats_w_rhs <- corePrepExprFloat env 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 = do { (floats, arg') <- corePrepExprFloat env arg
325 ; if exprIsTrivial arg' && allLazy NotTopLevel NonRecursive floats
326 -- Note [Floating unlifted arguments]
327 then return (floats, arg')
328 else do { v <- newVar (exprType arg')
329 -- Note [Eta expand arguments]
330 ; (floats', v') <- mkLocalNonRec v dem floats arg'
331 ; return (floats', Var v') } }
333 -- version that doesn't consider an scc annotation to be trivial.
334 exprIsTrivial :: CoreExpr -> Bool
335 exprIsTrivial (Var _) = True
336 exprIsTrivial (Type _) = True
337 exprIsTrivial (Lit _) = True
338 exprIsTrivial (App e arg) = isTypeArg arg && exprIsTrivial e
339 exprIsTrivial (Note (SCC _) _) = False
340 exprIsTrivial (Note _ e) = exprIsTrivial e
341 exprIsTrivial (Cast e _) = exprIsTrivial e
342 exprIsTrivial (Lam b body) | isTyVar b = exprIsTrivial body
343 exprIsTrivial _ = False
346 Note [Floating unlifted arguments]
347 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
348 Consider C (let v* = expensive in v)
350 where the "*" indicates "will be demanded". Usually v will have been
351 inlined by now, but let's suppose it hasn't (see Trac #2756). Then we
354 let v* = expensive in C v
356 because that has different strictness. Hence the use of 'allLazy'.
357 (NB: the let v* turns into a FloatCase, in mkLocalNonRec.)
361 -- ---------------------------------------------------------------------------
362 -- Dealing with expressions
363 -- ---------------------------------------------------------------------------
365 corePrepAnExpr :: CorePrepEnv -> CoreExpr -> UniqSM CoreExpr
366 corePrepAnExpr env expr = do
367 (floats, expr) <- corePrepExprFloat env expr
371 corePrepExprFloat :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CoreExpr)
375 -- e = let bs in e' (semantically, that is!)
378 -- f (g x) ===> ([v = g x], f v)
380 corePrepExprFloat env (Var v) = do
383 v2 = lookupCorePrepEnv env v1
384 maybeSaturate v2 (Var v2) 0 emptyFloats (idType v2)
386 corePrepExprFloat _env expr@(Type _)
387 = return (emptyFloats, expr)
389 corePrepExprFloat _env expr@(Lit _)
390 = return (emptyFloats, expr)
392 corePrepExprFloat env (Let bind body) = do
393 (env', new_binds) <- corePrepBind env bind
394 (floats, new_body) <- corePrepExprFloat env' body
395 return (new_binds `appendFloats` floats, new_body)
397 corePrepExprFloat env (Note n@(SCC _) expr) = do
398 expr1 <- corePrepAnExpr env expr
399 (floats, expr2) <- deLamFloat expr1
400 return (floats, Note n expr2)
402 corePrepExprFloat env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
403 | Just (TickBox {}) <- isTickBoxOp_maybe id = do
404 expr1 <- corePrepAnExpr env expr
405 (floats, expr2) <- deLamFloat expr1
406 return (floats, Case (Var id) bndr ty [(DEFAULT,[],expr2)])
408 corePrepExprFloat env (Note other_note expr) = do
409 (floats, expr') <- corePrepExprFloat env expr
410 return (floats, Note other_note expr')
412 corePrepExprFloat env (Cast expr co) = do
413 (floats, expr') <- corePrepExprFloat env expr
414 return (floats, Cast expr' co)
416 corePrepExprFloat env expr@(Lam _ _) = do
417 (env', bndrs') <- cloneBndrs env bndrs
418 body' <- corePrepAnExpr env' body
419 return (emptyFloats, mkLams bndrs' body')
421 (bndrs,body) = collectBinders expr
423 corePrepExprFloat env (Case scrut bndr ty alts) = do
424 (floats1, scrut1) <- corePrepExprFloat env scrut
425 (floats2, scrut2) <- deLamFloat scrut1
427 bndr1 = bndr `setIdUnfolding` evaldUnfolding
428 -- Record that the case binder is evaluated in the alternatives
429 (env', bndr2) <- cloneBndr env bndr1
430 alts' <- mapM (sat_alt env') alts
431 return (floats1 `appendFloats` floats2 , Case scrut2 bndr2 ty alts')
433 sat_alt env (con, bs, rhs) = do
434 (env2, bs') <- cloneBndrs env bs
435 rhs1 <- corePrepAnExpr env2 rhs
437 return (con, bs', rhs2)
439 corePrepExprFloat env expr@(App _ _) = do
440 (app, (head,depth), ty, floats, ss) <- collect_args expr 0
441 MASSERT(null ss) -- make sure we used all the strictness info
443 -- Now deal with the function
445 Var fn_id -> maybeSaturate fn_id app depth floats ty
446 _other -> return (floats, app)
450 -- Deconstruct and rebuild the application, floating any non-atomic
451 -- arguments to the outside. We collect the type of the expression,
452 -- the head of the application, and the number of actual value arguments,
453 -- all of which are used to possibly saturate this application if it
454 -- has a constructor or primop at the head.
458 -> Int -- current app depth
459 -> UniqSM (CoreExpr, -- the rebuilt expression
460 (CoreExpr,Int), -- the head of the application,
461 -- and no. of args it was applied to
462 Type, -- type of the whole expr
463 Floats, -- any floats we pulled out
464 [Demand]) -- remaining argument demands
466 collect_args (App fun arg@(Type arg_ty)) depth = do
467 (fun',hd,fun_ty,floats,ss) <- collect_args fun depth
468 return (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss)
470 collect_args (App fun arg) depth = do
471 (fun',hd,fun_ty,floats,ss) <- collect_args fun (depth+1)
473 (ss1, ss_rest) = case ss of
474 (ss1:ss_rest) -> (ss1, ss_rest)
476 (arg_ty, res_ty) = expectJust "corePrepExprFloat:collect_args" $
477 splitFunTy_maybe fun_ty
479 (fs, arg') <- corePrepArg env arg (mkDemTy ss1 arg_ty)
480 return (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest)
482 collect_args (Var v) depth = do
484 let v2 = lookupCorePrepEnv env v1
485 return (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts)
487 stricts = case idNewStrictness v of
488 StrictSig (DmdType _ demands _)
489 | listLengthCmp demands depth /= GT -> demands
490 -- length demands <= depth
492 -- If depth < length demands, then we have too few args to
493 -- satisfy strictness info so we have to ignore all the
494 -- strictness info, e.g. + (error "urk")
495 -- Here, we can't evaluate the arg strictly, because this
496 -- partial application might be seq'd
498 collect_args (Cast fun co) depth = do
499 let (_ty1,ty2) = coercionKind co
500 (fun', hd, _, floats, ss) <- collect_args fun depth
501 return (Cast fun' co, hd, ty2, floats, ss)
503 collect_args (Note note fun) depth
504 | ignore_note note = do -- Drop these notes altogether
505 -- They aren't used by the code generator
506 (fun', hd, fun_ty, floats, ss) <- collect_args fun depth
507 return (fun', hd, fun_ty, floats, ss)
509 -- N-variable fun, better let-bind it
510 -- ToDo: perhaps we can case-bind rather than let-bind this closure,
511 -- since it is sure to be evaluated.
512 collect_args fun depth = do
513 (fun_floats, fun') <- corePrepExprFloat env fun
515 (floats, fn_id') <- mkLocalNonRec fn_id onceDem fun_floats fun'
516 return (Var fn_id', (Var fn_id', depth), ty, floats, [])
520 ignore_note (CoreNote _) = True
521 ignore_note _other = False
522 -- We don't ignore SCCs, since they require some code generation
524 ------------------------------------------------------------------------------
525 -- Building the saturated syntax
526 -- ---------------------------------------------------------------------------
528 -- maybeSaturate deals with saturating primops and constructors
529 -- The type is the type of the entire application
530 maybeSaturate :: Id -> CoreExpr -> Int -> Floats -> Type -> UniqSM (Floats, CoreExpr)
531 maybeSaturate fn expr n_args floats ty
532 | Just DataToTagOp <- isPrimOpId_maybe fn -- DataToTag must have an evaluated arg
533 -- A gruesome special case
534 = do sat_expr <- saturate_it
536 -- OK, now ensure that the arg is evaluated.
537 -- But (sigh) take into account the lambdas we've now introduced
538 let (eta_bndrs, eta_body) = collectBinders sat_expr
539 (eta_floats, eta_body') <- eval_data2tag_arg eta_body
540 if null eta_bndrs then
541 return (floats `appendFloats` eta_floats, eta_body')
543 eta_body'' <- mkBinds eta_floats eta_body'
544 return (floats, mkLams eta_bndrs eta_body'')
546 | hasNoBinding fn = do sat_expr <- saturate_it
547 return (floats, sat_expr)
549 | otherwise = return (floats, expr)
552 fn_arity = idArity fn
553 excess_arity = fn_arity - n_args
555 saturate_it :: UniqSM CoreExpr
556 saturate_it | excess_arity == 0 = return expr
557 | otherwise = do us <- getUniquesM
558 return (etaExpand excess_arity us expr ty)
560 -- Ensure that the argument of DataToTagOp is evaluated
561 eval_data2tag_arg :: CoreExpr -> UniqSM (Floats, CoreExpr)
562 eval_data2tag_arg app@(fun `App` arg)
563 | exprIsHNF arg -- Includes nullary constructors
564 = return (emptyFloats, app) -- The arg is evaluated
565 | otherwise -- Arg not evaluated, so evaluate it
566 = do arg_id <- newVar (exprType arg)
568 arg_id1 = setIdUnfolding arg_id evaldUnfolding
569 return (unitFloat (FloatCase arg_id1 arg False ),
570 fun `App` Var arg_id1)
572 eval_data2tag_arg (Note note app) -- Scc notes can appear
573 = do (floats, app') <- eval_data2tag_arg app
574 return (floats, Note note app')
576 eval_data2tag_arg other -- Should not happen
577 = pprPanic "eval_data2tag" (ppr other)
580 -- ---------------------------------------------------------------------------
581 -- Precipitating the floating bindings
582 -- ---------------------------------------------------------------------------
584 floatRhs :: TopLevelFlag -> RecFlag
586 -> (Floats, CoreExpr) -- Rhs: let binds in body
587 -> UniqSM (Floats, -- Floats out of this bind
588 CoreExpr) -- Final Rhs
590 floatRhs top_lvl is_rec bndr (floats, rhs)
591 | isTopLevel top_lvl || exprIsHNF rhs, -- Float to expose value or
592 allLazy top_lvl is_rec floats -- at top level
593 = -- Why the test for allLazy?
594 -- v = f (x `divInt#` y)
595 -- we don't want to float the case, even if f has arity 2,
596 -- because floating the case would make it evaluated too early
597 do { us <- getUniquesM
598 ; let eta_rhs = etaExpand arity us rhs (idType bndr)
599 -- For a GlobalId, take the Arity from the Id.
600 -- It was set in CoreTidy and must not change
601 -- For all others, just expand at will
602 -- See Note [Eta expansion]
603 arity | isGlobalId bndr = idArity bndr
604 | otherwise = exprArity rhs
605 ; return (floats, eta_rhs) }
608 -- Don't float; the RHS isn't a value
609 rhs' <- mkBinds floats rhs
610 return (emptyFloats, rhs')
614 ~~~~~~~~~~~~~~~~~~~~~
615 Eta expand to match the arity claimed by the binder Remember,
616 CorePrep must not change arity
618 Eta expansion might not have happened already, because it is done by
619 the simplifier only when there at least one lambda already.
621 NB1:we could refrain when the RHS is trivial (which can happen
622 for exported things). This would reduce the amount of code
623 generated (a little) and make things a little words for
624 code compiled without -O. The case in point is data constructor
627 NB2: we have to be careful that the result of etaExpand doesn't
628 invalidate any of the assumptions that CorePrep is attempting
629 to establish. One possible cause is eta expanding inside of
630 an SCC note - we're now careful in etaExpand to make sure the
631 SCC is pushed inside any new lambdas that are generated.
633 NB3: It's important to do eta expansion, and *then* ANF-ising
634 f = /\a -> g (h 3) -- h has arity 2
635 If we ANF first we get
636 f = /\a -> let s = h 3 in g s
637 and now eta expansion gives
638 f = /\a -> \ y -> (let s = h 3 in g s) y
640 Eta expanding first gives
641 f = /\a -> \y -> let s = h 3 in g s y
644 -- mkLocalNonRec is used only for *nested*, *non-recursive* bindings
645 mkLocalNonRec :: Id -> RhsDemand -- Lhs: id with demand
646 -> Floats -> CoreExpr -- Rhs: let binds in body
647 -> UniqSM (Floats, Id) -- The new Id may have an evaldUnfolding,
648 -- to record that it's been evaluated
650 mkLocalNonRec bndr dem floats rhs
651 | isUnLiftedType (idType bndr)
652 -- If this is an unlifted binding, we always make a case for it.
653 = ASSERT( not (isUnboxedTupleType (idType bndr)) )
655 float = FloatCase bndr rhs (exprOkForSpeculation rhs)
657 return (addFloat floats float, evald_bndr)
660 -- It's a strict let so we definitely float all the bindings
661 = let -- Don't make a case for a value binding,
662 -- even if it's strict. Otherwise we get
663 -- case (\x -> e) of ...!
664 float | exprIsHNF rhs = FloatLet (NonRec bndr rhs)
665 | otherwise = FloatCase bndr rhs (exprOkForSpeculation rhs)
667 return (addFloat floats float, evald_bndr)
670 = do (floats', rhs') <- floatRhs NotTopLevel NonRecursive bndr (floats, rhs)
671 return (addFloat floats' (FloatLet (NonRec bndr rhs')),
672 if exprIsHNF rhs' then evald_bndr else bndr)
675 evald_bndr = bndr `setIdUnfolding` evaldUnfolding
676 -- Record if the binder is evaluated
679 mkBinds :: Floats -> CoreExpr -> UniqSM CoreExpr
680 mkBinds (Floats _ binds) body
681 | isNilOL binds = return body
682 | otherwise = do body' <- deLam body
683 -- Lambdas are not allowed as the body of a 'let'
684 return (foldrOL mk_bind body' binds)
686 mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
687 mk_bind (FloatLet bind) body = Let bind body
690 -- ---------------------------------------------------------------------------
691 -- Eliminate Lam as a non-rhs (STG doesn't have such a thing)
692 -- We arrange that they only show up as the RHS of a let(rec)
693 -- ---------------------------------------------------------------------------
695 deLam :: CoreExpr -> UniqSM CoreExpr
696 -- Takes an expression that may be a lambda,
697 -- and returns one that definitely isn't:
698 -- (\x.e) ==> let f = \x.e in f
700 (floats, expr) <- deLamFloat expr
704 deLamFloat :: CoreExpr -> UniqSM (Floats, CoreExpr)
705 -- Remove top level lambdas by let-bindinig
707 deLamFloat (Note n expr) = do
708 -- You can get things like
709 -- case e of { p -> coerce t (\s -> ...) }
710 (floats, expr') <- deLamFloat expr
711 return (floats, Note n expr')
713 deLamFloat (Cast e co) = do
714 (floats, e') <- deLamFloat e
715 return (floats, Cast e' co)
718 | null bndrs = return (emptyFloats, expr)
720 = case tryEta bndrs body of
721 Just no_lam_result -> return (emptyFloats, no_lam_result)
722 Nothing -> do fn <- newVar (exprType expr)
723 return (unitFloat (FloatLet (NonRec fn expr)),
726 (bndrs,body) = collectBinders expr
728 -- Why try eta reduction? Hasn't the simplifier already done eta?
729 -- But the simplifier only eta reduces if that leaves something
730 -- trivial (like f, or f Int). But for deLam it would be enough to
731 -- get to a partial application:
732 -- \xs. map f xs ==> map f
734 tryEta :: [CoreBndr] -> CoreExpr -> Maybe CoreExpr
735 tryEta bndrs expr@(App _ _)
736 | ok_to_eta_reduce f &&
738 and (zipWith ok bndrs last_args) &&
739 not (any (`elemVarSet` fvs_remaining) bndrs)
740 = Just remaining_expr
742 (f, args) = collectArgs expr
743 remaining_expr = mkApps f remaining_args
744 fvs_remaining = exprFreeVars remaining_expr
745 (remaining_args, last_args) = splitAt n_remaining args
746 n_remaining = length args - length bndrs
748 ok bndr (Var arg) = bndr == arg
751 -- we can't eta reduce something which must be saturated.
752 ok_to_eta_reduce (Var f) = not (hasNoBinding f)
753 ok_to_eta_reduce _ = False --safe. ToDo: generalise
755 tryEta bndrs (Let bind@(NonRec _ r) body)
756 | not (any (`elemVarSet` fvs) bndrs)
757 = case tryEta bndrs body of
758 Just e -> Just (Let bind e)
767 -- -----------------------------------------------------------------------------
769 -- -----------------------------------------------------------------------------
773 = RhsDemand { isStrict :: Bool, -- True => used at least once
774 _isOnceDem :: Bool -- True => used at most once
777 mkDem :: Demand -> Bool -> RhsDemand
778 mkDem strict once = RhsDemand (isStrictDmd strict) once
780 mkDemTy :: Demand -> Type -> RhsDemand
781 mkDemTy strict _ty = RhsDemand (isStrictDmd strict)
784 bdrDem :: Id -> RhsDemand
785 bdrDem id = mkDem (idNewDemandInfo id)
788 -- safeDem :: RhsDemand
789 -- safeDem = RhsDemand False False -- always safe to use this
792 onceDem = RhsDemand False True -- used at most once
798 %************************************************************************
802 %************************************************************************
805 -- ---------------------------------------------------------------------------
807 -- ---------------------------------------------------------------------------
809 data CorePrepEnv = CPE (IdEnv Id) -- Clone local Ids
811 emptyCorePrepEnv :: CorePrepEnv
812 emptyCorePrepEnv = CPE emptyVarEnv
814 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
815 extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')
817 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
818 lookupCorePrepEnv (CPE env) id
819 = case lookupVarEnv env id of
823 ------------------------------------------------------------------------------
825 -- ---------------------------------------------------------------------------
827 cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
828 cloneBndrs env bs = mapAccumLM cloneBndr env bs
830 cloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
833 = do bndr' <- setVarUnique bndr <$> getUniqueM
834 return (extendCorePrepEnv env bndr bndr', bndr')
836 | otherwise -- Top level things, which we don't want
837 -- to clone, have become GlobalIds by now
838 -- And we don't clone tyvars
842 ------------------------------------------------------------------------------
843 -- Cloning ccall Ids; each must have a unique name,
844 -- to give the code generator a handle to hang it on
845 -- ---------------------------------------------------------------------------
847 fiddleCCall :: Id -> UniqSM Id
849 | isFCallId id = (id `setVarUnique`) <$> getUniqueM
850 | otherwise = return id
852 ------------------------------------------------------------------------------
853 -- Generating new binders
854 -- ---------------------------------------------------------------------------
856 newVar :: Type -> UniqSM Id
858 = seqType ty `seq` do
860 return (mkSysLocal (fsLit "sat") uniq ty)