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 PrelNames ( lazyIdKey, hasKey )
18 import CoreMonad ( endPass, CoreToDo(..) )
42 import Data.List ( mapAccumL )
46 -- ---------------------------------------------------------------------------
48 -- ---------------------------------------------------------------------------
50 The goal of this pass is to prepare for code generation.
52 1. Saturate constructor and primop applications.
54 2. Convert to A-normal form; that is, function arguments
57 * Use case for strict arguments:
58 f E ==> case E of x -> f x
61 * Use let for non-trivial lazy arguments
62 f E ==> let x = E in f x
63 (were f is lazy and x is non-trivial)
65 3. Similarly, convert any unboxed lets into cases.
66 [I'm experimenting with leaving 'ok-for-speculation'
67 rhss in let-form right up to this point.]
69 4. Ensure that *value* lambdas only occur as the RHS of a binding
70 (The code generator can't deal with anything else.)
71 Type lambdas are ok, however, because the code gen discards them.
73 5. [Not any more; nuked Jun 2002] Do the seq/par munging.
75 6. Clone all local Ids.
76 This means that all such Ids are unique, rather than the
77 weaker guarantee of no clashes which the simplifier provides.
78 And that is what the code generator needs.
80 We don't clone TyVars. The code gen doesn't need that,
81 and doing so would be tiresome because then we'd need
82 to substitute in types.
85 7. Give each dynamic CCall occurrence a fresh unique; this is
86 rather like the cloning step above.
88 8. Inject bindings for the "implicit" Ids:
89 * Constructor wrappers
91 We want curried definitions for all of these in case they
92 aren't inlined by some caller.
94 9. Replace (lazy e) by e. See Note [lazyId magic] in MkId.lhs
96 This is all done modulo type applications and abstractions, so that
97 when type erasure is done for conversion to STG, we don't end up with
98 any trivial or useless bindings.
103 Here is the syntax of the Core produced by CorePrep:
106 triv ::= lit | var | triv ty | /\a. triv | triv |> co
109 app ::= lit | var | app triv | app ty | app |> co
113 | let(rec) x = rhs in body -- Boxed only
114 | case body of pat -> body
118 Right hand sides (only place where lambdas can occur)
119 rhs ::= /\a.rhs | \x.rhs | body
121 We define a synonym for each of these non-terminals. Functions
122 with the corresponding name produce a result in that syntax.
125 type CpeTriv = CoreExpr -- Non-terminal 'triv'
126 type CpeApp = CoreExpr -- Non-terminal 'app'
127 type CpeBody = CoreExpr -- Non-terminal 'body'
128 type CpeRhs = CoreExpr -- Non-terminal 'rhs'
131 %************************************************************************
135 %************************************************************************
138 corePrepPgm :: DynFlags -> [CoreBind] -> [TyCon] -> IO [CoreBind]
139 corePrepPgm dflags binds data_tycons = do
140 showPass dflags "CorePrep"
141 us <- mkSplitUniqSupply 's'
143 let implicit_binds = mkDataConWorkers data_tycons
144 -- NB: we must feed mkImplicitBinds through corePrep too
145 -- so that they are suitably cloned and eta-expanded
147 binds_out = initUs_ us $ do
148 floats1 <- corePrepTopBinds binds
149 floats2 <- corePrepTopBinds implicit_binds
150 return (deFloatTop (floats1 `appendFloats` floats2))
152 endPass dflags CorePrep binds_out []
155 corePrepExpr :: DynFlags -> CoreExpr -> IO CoreExpr
156 corePrepExpr dflags expr = do
157 showPass dflags "CorePrep"
158 us <- mkSplitUniqSupply 's'
159 let new_expr = initUs_ us (cpeBodyNF emptyCorePrepEnv expr)
160 dumpIfSet_dyn dflags Opt_D_dump_prep "CorePrep" (ppr new_expr)
163 corePrepTopBinds :: [CoreBind] -> UniqSM Floats
164 -- Note [Floating out of top level bindings]
165 corePrepTopBinds binds
166 = go emptyCorePrepEnv binds
168 go _ [] = return emptyFloats
169 go env (bind : binds) = do (env', bind') <- cpeBind TopLevel env bind
170 binds' <- go env' binds
171 return (bind' `appendFloats` binds')
173 mkDataConWorkers :: [TyCon] -> [CoreBind]
174 -- See Note [Data constructor workers]
175 mkDataConWorkers data_tycons
176 = [ NonRec id (Var id) -- The ice is thin here, but it works
177 | tycon <- data_tycons, -- CorePrep will eta-expand it
178 data_con <- tyConDataCons tycon,
179 let id = dataConWorkId data_con ]
182 Note [Floating out of top level bindings]
183 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
184 NB: we do need to float out of top-level bindings
185 Consider x = length [True,False]
191 We return a *list* of bindings, because we may start with
193 where x is demanded, in which case we want to finish with
196 And then x will actually end up case-bound
198 Note [CafInfo and floating]
199 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
200 What happens when we try to float bindings to the top level? At this
201 point all the CafInfo is supposed to be correct, and we must make certain
202 that is true of the new top-level bindings. There are two cases
205 a) The top-level binding is marked asCafRefs. In that case we are
206 basically fine. The floated bindings had better all be lazy lets,
207 so they can float to top level, but they'll all have HasCafRefs
208 (the default) which is safe.
210 b) The top-level binding is marked NoCafRefs. This really happens
211 Example. CoreTidy produces
212 $fApplicativeSTM [NoCafRefs] = D:Alternative retry# ...blah...
213 Now CorePrep has to eta-expand to
214 $fApplicativeSTM = let sat = \xy. retry x y
215 in D:Alternative sat ...blah...
217 sat [NoCafRefs] = \xy. retry x y
218 $fApplicativeSTM [NoCafRefs] = D:Alternative sat ...blah...
220 So, gruesomely, we must set the NoCafRefs flag on the sat bindings,
221 *and* substutite the modified 'sat' into the old RHS.
223 It should be the case that 'sat' is itself [NoCafRefs] (a value, no
224 cafs) else the original top-level binding would not itself have been
225 marked [NoCafRefs]. The DEBUG check in CoreToStg for
226 consistentCafInfo will find this.
228 This is all very gruesome and horrible. It would be better to figure
229 out CafInfo later, after CorePrep. We'll do that in due course.
230 Meanwhile this horrible hack works.
233 Note [Data constructor workers]
234 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
235 Create any necessary "implicit" bindings for data con workers. We
236 create the rather strange (non-recursive!) binding
238 $wC = \x y -> $wC x y
240 i.e. a curried constructor that allocates. This means that we can
241 treat the worker for a constructor like any other function in the rest
242 of the compiler. The point here is that CoreToStg will generate a
243 StgConApp for the RHS, rather than a call to the worker (which would
244 give a loop). As Lennart says: the ice is thin here, but it works.
246 Hmm. Should we create bindings for dictionary constructors? They are
247 always fully applied, and the bindings are just there to support
248 partial applications. But it's easier to let them through.
251 %************************************************************************
255 %************************************************************************
258 cpeBind :: TopLevelFlag
259 -> CorePrepEnv -> CoreBind
260 -> UniqSM (CorePrepEnv, Floats)
261 cpeBind top_lvl env (NonRec bndr rhs)
262 = do { (_, bndr1) <- cloneBndr env bndr
263 ; let is_strict = isStrictDmd (idDemandInfo bndr)
264 is_unlifted = isUnLiftedType (idType bndr)
265 ; (floats, bndr2, rhs2) <- cpePair top_lvl NonRecursive
266 (is_strict || is_unlifted)
268 ; let new_float = mkFloat is_strict is_unlifted bndr2 rhs2
270 -- We want bndr'' in the envt, because it records
271 -- the evaluated-ness of the binder
272 ; return (extendCorePrepEnv env bndr bndr2,
273 addFloat floats new_float) }
275 cpeBind top_lvl env (Rec pairs)
276 = do { let (bndrs,rhss) = unzip pairs
277 ; (env', bndrs1) <- cloneBndrs env (map fst pairs)
278 ; stuff <- zipWithM (cpePair top_lvl Recursive False env') bndrs1 rhss
280 ; let (floats_s, bndrs2, rhss2) = unzip3 stuff
281 all_pairs = foldrOL add_float (bndrs1 `zip` rhss2)
282 (concatFloats floats_s)
283 ; return (extendCorePrepEnvList env (bndrs `zip` bndrs2),
284 unitFloat (FloatLet (Rec all_pairs))) }
286 -- Flatten all the floats, and the currrent
287 -- group into a single giant Rec
288 add_float (FloatLet (NonRec b r)) prs2 = (b,r) : prs2
289 add_float (FloatLet (Rec prs1)) prs2 = prs1 ++ prs2
290 add_float b _ = pprPanic "cpeBind" (ppr b)
293 cpePair :: TopLevelFlag -> RecFlag -> RhsDemand
294 -> CorePrepEnv -> Id -> CoreExpr
295 -> UniqSM (Floats, Id, CpeRhs)
296 -- Used for all bindings
297 cpePair top_lvl is_rec is_strict_or_unlifted env bndr rhs
298 = do { (floats1, rhs1) <- cpeRhsE env rhs
300 -- See if we are allowed to float this stuff out of the RHS
301 ; (floats2, rhs2) <- float_from_rhs floats1 rhs1
303 -- Make the arity match up
305 <- if manifestArity rhs1 <= arity
306 then return (floats2, cpeEtaExpand arity rhs2)
307 else WARN(True, text "CorePrep: silly extra arguments:" <+> ppr bndr)
308 -- Note [Silly extra arguments]
309 (do { v <- newVar (idType bndr)
310 ; let float = mkFloat False False v rhs2
311 ; return (addFloat floats2 float, cpeEtaExpand arity (Var v)) })
313 -- Record if the binder is evaluated
314 ; let bndr' | exprIsHNF rhs' = bndr `setIdUnfolding` evaldUnfolding
317 ; return (floats3, bndr', rhs') }
319 arity = idArity bndr -- We must match this arity
321 ---------------------
322 float_from_rhs floats rhs
323 | isEmptyFloats floats = return (emptyFloats, rhs)
324 | isTopLevel top_lvl = float_top floats rhs
325 | otherwise = float_nested floats rhs
327 ---------------------
328 float_nested floats rhs
329 | wantFloatNested is_rec is_strict_or_unlifted floats rhs
330 = return (floats, rhs)
331 | otherwise = dont_float floats rhs
333 ---------------------
334 float_top floats rhs -- Urhgh! See Note [CafInfo and floating]
335 | mayHaveCafRefs (idCafInfo bndr)
337 = return (floats, rhs)
339 -- So the top-level binding is marked NoCafRefs
340 | Just (floats', rhs') <- canFloatFromNoCaf floats rhs
341 = return (floats', rhs')
344 = dont_float floats rhs
346 ---------------------
347 dont_float floats rhs
348 -- Non-empty floats, but do not want to float from rhs
349 -- So wrap the rhs in the floats
350 -- But: rhs1 might have lambdas, and we can't
351 -- put them inside a wrapBinds
352 = do { body <- rhsToBodyNF rhs
353 ; return (emptyFloats, wrapBinds floats body) }
355 {- Note [Silly extra arguments]
356 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
359 We *must* match the arity on the Id, so we have to generate
363 It's a bizarre case: why is the arity on the Id wrong? Reason
364 (in the days of __inline_me__):
365 f{arity=0} = __inline_me__ (let v = expensive in \xy. e)
366 When InlineMe notes go away this won't happen any more. But
367 it seems good for CorePrep to be robust.
370 -- ---------------------------------------------------------------------------
371 -- CpeRhs: produces a result satisfying CpeRhs
372 -- ---------------------------------------------------------------------------
374 cpeRhsE :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs)
378 -- e = let bs in e' (semantically, that is!)
381 -- f (g x) ===> ([v = g x], f v)
383 cpeRhsE _env expr@(Type _) = return (emptyFloats, expr)
384 cpeRhsE _env expr@(Lit _) = return (emptyFloats, expr)
385 cpeRhsE env expr@(Var {}) = cpeApp env expr
387 cpeRhsE env (Var f `App` _ `App` arg)
388 | f `hasKey` lazyIdKey -- Replace (lazy a) by a
389 = cpeRhsE env arg -- See Note [lazyId magic] in MkId
391 cpeRhsE env expr@(App {}) = cpeApp env expr
393 cpeRhsE env (Let bind expr)
394 = do { (env', new_binds) <- cpeBind NotTopLevel env bind
395 ; (floats, body) <- cpeRhsE env' expr
396 ; return (new_binds `appendFloats` floats, body) }
398 cpeRhsE env (Note note expr)
401 | otherwise -- Just SCCs actually
402 = do { body <- cpeBodyNF env expr
403 ; return (emptyFloats, Note note body) }
405 cpeRhsE env (Cast expr co)
406 = do { (floats, expr') <- cpeRhsE env expr
407 ; return (floats, Cast expr' co) }
409 cpeRhsE env expr@(Lam {})
410 = do { let (bndrs,body) = collectBinders expr
411 ; (env', bndrs') <- cloneBndrs env bndrs
412 ; body' <- cpeBodyNF env' body
413 ; return (emptyFloats, mkLams bndrs' body') }
415 cpeRhsE env (Case (Var id) bndr ty [(DEFAULT,[],expr)])
416 | Just (TickBox {}) <- isTickBoxOp_maybe id
417 = do { body <- cpeBodyNF env expr
418 ; return (emptyFloats, Case (Var id) bndr ty [(DEFAULT,[],body)]) }
420 cpeRhsE env (Case scrut bndr ty alts)
421 = do { (floats, scrut') <- cpeBody env scrut
422 ; let bndr1 = bndr `setIdUnfolding` evaldUnfolding
423 -- Record that the case binder is evaluated in the alternatives
424 ; (env', bndr2) <- cloneBndr env bndr1
425 ; alts' <- mapM (sat_alt env') alts
426 ; return (floats, Case scrut' bndr2 ty alts') }
428 sat_alt env (con, bs, rhs)
429 = do { (env2, bs') <- cloneBndrs env bs
430 ; rhs' <- cpeBodyNF env2 rhs
431 ; return (con, bs', rhs') }
433 -- ---------------------------------------------------------------------------
434 -- CpeBody: produces a result satisfying CpeBody
435 -- ---------------------------------------------------------------------------
437 cpeBodyNF :: CorePrepEnv -> CoreExpr -> UniqSM CpeBody
439 = do { (floats, body) <- cpeBody env expr
440 ; return (wrapBinds floats body) }
443 cpeBody :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeBody)
445 = do { (floats1, rhs) <- cpeRhsE env expr
446 ; (floats2, body) <- rhsToBody rhs
447 ; return (floats1 `appendFloats` floats2, body) }
450 rhsToBodyNF :: CpeRhs -> UniqSM CpeBody
451 rhsToBodyNF rhs = do { (floats,body) <- rhsToBody rhs
452 ; return (wrapBinds floats body) }
455 rhsToBody :: CpeRhs -> UniqSM (Floats, CpeBody)
456 -- Remove top level lambdas by let-binding
458 rhsToBody (Note n expr)
459 -- You can get things like
460 -- case e of { p -> coerce t (\s -> ...) }
461 = do { (floats, expr') <- rhsToBody expr
462 ; return (floats, Note n expr') }
464 rhsToBody (Cast e co)
465 = do { (floats, e') <- rhsToBody e
466 ; return (floats, Cast e' co) }
468 rhsToBody expr@(Lam {})
469 | Just no_lam_result <- tryEtaReducePrep bndrs body
470 = return (emptyFloats, no_lam_result)
471 | all isTyCoVar bndrs -- Type lambdas are ok
472 = return (emptyFloats, expr)
473 | otherwise -- Some value lambdas
474 = do { fn <- newVar (exprType expr)
475 ; let rhs = cpeEtaExpand (exprArity expr) expr
476 float = FloatLet (NonRec fn rhs)
477 ; return (unitFloat float, Var fn) }
479 (bndrs,body) = collectBinders expr
481 rhsToBody expr = return (emptyFloats, expr)
485 -- ---------------------------------------------------------------------------
486 -- CpeApp: produces a result satisfying CpeApp
487 -- ---------------------------------------------------------------------------
489 cpeApp :: CorePrepEnv -> CoreExpr -> UniqSM (Floats, CpeRhs)
490 -- May return a CpeRhs because of saturating primops
492 = do { (app, (head,depth), _, floats, ss) <- collect_args expr 0
493 ; MASSERT(null ss) -- make sure we used all the strictness info
495 -- Now deal with the function
497 Var fn_id -> do { sat_app <- maybeSaturate fn_id app depth
498 ; return (floats, sat_app) }
499 _other -> return (floats, app) }
502 -- Deconstruct and rebuild the application, floating any non-atomic
503 -- arguments to the outside. We collect the type of the expression,
504 -- the head of the application, and the number of actual value arguments,
505 -- all of which are used to possibly saturate this application if it
506 -- has a constructor or primop at the head.
510 -> Int -- Current app depth
511 -> UniqSM (CpeApp, -- The rebuilt expression
512 (CoreExpr,Int), -- The head of the application,
513 -- and no. of args it was applied to
514 Type, -- Type of the whole expr
515 Floats, -- Any floats we pulled out
516 [Demand]) -- Remaining argument demands
518 collect_args (App fun arg@(Type arg_ty)) depth
519 = do { (fun',hd,fun_ty,floats,ss) <- collect_args fun depth
520 ; return (App fun' arg, hd, applyTy fun_ty arg_ty, floats, ss) }
522 collect_args (App fun arg) depth
523 = do { (fun',hd,fun_ty,floats,ss) <- collect_args fun (depth+1)
525 (ss1, ss_rest) = case ss of
526 (ss1:ss_rest) -> (ss1, ss_rest)
528 (arg_ty, res_ty) = expectJust "cpeBody:collect_args" $
529 splitFunTy_maybe fun_ty
531 ; (fs, arg') <- cpeArg env (isStrictDmd ss1) arg arg_ty
532 ; return (App fun' arg', hd, res_ty, fs `appendFloats` floats, ss_rest) }
534 collect_args (Var v) depth
535 = do { v1 <- fiddleCCall v
536 ; let v2 = lookupCorePrepEnv env v1
537 ; return (Var v2, (Var v2, depth), idType v2, emptyFloats, stricts) }
539 stricts = case idStrictness v of
540 StrictSig (DmdType _ demands _)
541 | listLengthCmp demands depth /= GT -> demands
542 -- length demands <= depth
544 -- If depth < length demands, then we have too few args to
545 -- satisfy strictness info so we have to ignore all the
546 -- strictness info, e.g. + (error "urk")
547 -- Here, we can't evaluate the arg strictly, because this
548 -- partial application might be seq'd
550 collect_args (Cast fun co) depth
551 = do { let (_ty1,ty2) = coercionKind co
552 ; (fun', hd, _, floats, ss) <- collect_args fun depth
553 ; return (Cast fun' co, hd, ty2, floats, ss) }
555 collect_args (Note note fun) depth
556 | ignoreNote note -- Drop these notes altogether
557 = collect_args fun depth -- They aren't used by the code generator
559 -- N-variable fun, better let-bind it
560 collect_args fun depth
561 = do { (fun_floats, fun') <- cpeArg env True fun ty
562 -- The True says that it's sure to be evaluated,
563 -- so we'll end up case-binding it
564 ; return (fun', (fun', depth), ty, fun_floats, []) }
568 -- ---------------------------------------------------------------------------
569 -- CpeArg: produces a result satisfying CpeArg
570 -- ---------------------------------------------------------------------------
572 -- This is where we arrange that a non-trivial argument is let-bound
573 cpeArg :: CorePrepEnv -> RhsDemand -> CoreArg -> Type
574 -> UniqSM (Floats, CpeTriv)
575 cpeArg env is_strict arg arg_ty
576 | cpe_ExprIsTrivial arg -- Do not eta expand etc a trivial argument
577 = cpeBody env arg -- Must still do substitution though
579 = do { (floats1, arg1) <- cpeRhsE env arg -- arg1 can be a lambda
580 ; (floats2, arg2) <- if want_float floats1 arg1
581 then return (floats1, arg1)
582 else do { body1 <- rhsToBodyNF arg1
583 ; return (emptyFloats, wrapBinds floats1 body1) }
584 -- Else case: arg1 might have lambdas, and we can't
585 -- put them inside a wrapBinds
588 ; let arg3 = cpeEtaExpand (exprArity arg2) arg2
589 arg_float = mkFloat is_strict is_unlifted v arg3
590 ; return (addFloat floats2 arg_float, Var v) }
592 is_unlifted = isUnLiftedType arg_ty
593 want_float = wantFloatNested NonRecursive (is_strict || is_unlifted)
596 Note [Floating unlifted arguments]
597 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
598 Consider C (let v* = expensive in v)
600 where the "*" indicates "will be demanded". Usually v will have been
601 inlined by now, but let's suppose it hasn't (see Trac #2756). Then we
604 let v* = expensive in C v
606 because that has different strictness. Hence the use of 'allLazy'.
607 (NB: the let v* turns into a FloatCase, in mkLocalNonRec.)
610 ------------------------------------------------------------------------------
611 -- Building the saturated syntax
612 -- ---------------------------------------------------------------------------
614 maybeSaturate deals with saturating primops and constructors
615 The type is the type of the entire application
618 maybeSaturate :: Id -> CpeApp -> Int -> UniqSM CpeRhs
619 maybeSaturate fn expr n_args
620 | Just DataToTagOp <- isPrimOpId_maybe fn -- DataToTag must have an evaluated arg
621 -- A gruesome special case
622 = saturateDataToTag sat_expr
624 | hasNoBinding fn -- There's no binding
630 fn_arity = idArity fn
631 excess_arity = fn_arity - n_args
632 sat_expr = cpeEtaExpand excess_arity expr
635 saturateDataToTag :: CpeApp -> UniqSM CpeApp
636 -- Horrid: ensure that the arg of data2TagOp is evaluated
637 -- (data2tag x) --> (case x of y -> data2tag y)
638 -- (yuk yuk) take into account the lambdas we've now introduced
639 saturateDataToTag sat_expr
640 = do { let (eta_bndrs, eta_body) = collectBinders sat_expr
641 ; eta_body' <- eval_data2tag_arg eta_body
642 ; return (mkLams eta_bndrs eta_body') }
644 eval_data2tag_arg :: CpeApp -> UniqSM CpeBody
645 eval_data2tag_arg app@(fun `App` arg)
646 | exprIsHNF arg -- Includes nullary constructors
647 = return app -- The arg is evaluated
648 | otherwise -- Arg not evaluated, so evaluate it
649 = do { arg_id <- newVar (exprType arg)
650 ; let arg_id1 = setIdUnfolding arg_id evaldUnfolding
651 ; return (Case arg arg_id1 (exprType app)
652 [(DEFAULT, [], fun `App` Var arg_id1)]) }
654 eval_data2tag_arg (Note note app) -- Scc notes can appear
655 = do { app' <- eval_data2tag_arg app
656 ; return (Note note app') }
658 eval_data2tag_arg other -- Should not happen
659 = pprPanic "eval_data2tag" (ppr other)
665 %************************************************************************
667 Simple CoreSyn operations
669 %************************************************************************
672 -- We don't ignore SCCs, since they require some code generation
673 ignoreNote :: Note -> Bool
674 -- Tells which notes to drop altogether; they are ignored by code generation
675 -- Do not ignore SCCs!
676 -- It's important that we do drop InlineMe notes; for example
677 -- unzip = __inline_me__ (/\ab. foldr (..) (..))
678 -- Here unzip gets arity 1 so we'll eta-expand it. But we don't
680 -- unzip = /\ab \xs. (__inline_me__ ...) a b xs
681 ignoreNote (CoreNote _) = True
682 ignoreNote _other = False
685 cpe_ExprIsTrivial :: CoreExpr -> Bool
686 -- Version that doesn't consider an scc annotation to be trivial.
687 cpe_ExprIsTrivial (Var _) = True
688 cpe_ExprIsTrivial (Type _) = True
689 cpe_ExprIsTrivial (Lit _) = True
690 cpe_ExprIsTrivial (App e arg) = isTypeArg arg && cpe_ExprIsTrivial e
691 cpe_ExprIsTrivial (Note n e) = notSccNote n && cpe_ExprIsTrivial e
692 cpe_ExprIsTrivial (Cast e _) = cpe_ExprIsTrivial e
693 cpe_ExprIsTrivial (Lam b body) | isTyCoVar b = cpe_ExprIsTrivial body
694 cpe_ExprIsTrivial _ = False
697 -- -----------------------------------------------------------------------------
699 -- -----------------------------------------------------------------------------
702 ~~~~~~~~~~~~~~~~~~~~~
703 Eta expand to match the arity claimed by the binder Remember,
704 CorePrep must not change arity
706 Eta expansion might not have happened already, because it is done by
707 the simplifier only when there at least one lambda already.
709 NB1:we could refrain when the RHS is trivial (which can happen
710 for exported things). This would reduce the amount of code
711 generated (a little) and make things a little words for
712 code compiled without -O. The case in point is data constructor
715 NB2: we have to be careful that the result of etaExpand doesn't
716 invalidate any of the assumptions that CorePrep is attempting
717 to establish. One possible cause is eta expanding inside of
718 an SCC note - we're now careful in etaExpand to make sure the
719 SCC is pushed inside any new lambdas that are generated.
721 Note [Eta expansion and the CorePrep invariants]
722 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
723 It turns out to be much much easier to do eta expansion
724 *after* the main CorePrep stuff. But that places constraints
725 on the eta expander: given a CpeRhs, it must return a CpeRhs.
727 For example here is what we do not want:
728 f = /\a -> g (h 3) -- h has arity 2
730 f = /\a -> let s = h 3 in g s
731 and now we do NOT want eta expansion to give
732 f = /\a -> \ y -> (let s = h 3 in g s) y
734 Instead CoreArity.etaExpand gives
735 f = /\a -> \y -> let s = h 3 in g s y
738 cpeEtaExpand :: Arity -> CpeRhs -> CpeRhs
739 cpeEtaExpand arity expr
741 | otherwise = etaExpand arity expr
744 -- -----------------------------------------------------------------------------
746 -- -----------------------------------------------------------------------------
748 Why try eta reduction? Hasn't the simplifier already done eta?
749 But the simplifier only eta reduces if that leaves something
750 trivial (like f, or f Int). But for deLam it would be enough to
751 get to a partial application:
752 case x of { p -> \xs. map f xs }
753 ==> case x of { p -> map f }
756 tryEtaReducePrep :: [CoreBndr] -> CoreExpr -> Maybe CoreExpr
757 tryEtaReducePrep bndrs expr@(App _ _)
758 | ok_to_eta_reduce f &&
760 and (zipWith ok bndrs last_args) &&
761 not (any (`elemVarSet` fvs_remaining) bndrs)
762 = Just remaining_expr
764 (f, args) = collectArgs expr
765 remaining_expr = mkApps f remaining_args
766 fvs_remaining = exprFreeVars remaining_expr
767 (remaining_args, last_args) = splitAt n_remaining args
768 n_remaining = length args - length bndrs
770 ok bndr (Var arg) = bndr == arg
773 -- we can't eta reduce something which must be saturated.
774 ok_to_eta_reduce (Var f) = not (hasNoBinding f)
775 ok_to_eta_reduce _ = False --safe. ToDo: generalise
777 tryEtaReducePrep bndrs (Let bind@(NonRec _ r) body)
778 | not (any (`elemVarSet` fvs) bndrs)
779 = case tryEtaReducePrep bndrs body of
780 Just e -> Just (Let bind e)
785 tryEtaReducePrep _ _ = Nothing
789 -- -----------------------------------------------------------------------------
791 -- -----------------------------------------------------------------------------
794 type RhsDemand = Bool -- True => used strictly; hence not top-level, non-recursive
797 %************************************************************************
801 %************************************************************************
805 = FloatLet CoreBind -- Rhs of bindings are CpeRhss
806 -- They are always of lifted type;
807 -- unlifted ones are done with FloatCase
811 Bool -- The bool indicates "ok-for-speculation"
813 data Floats = Floats OkToSpec (OrdList FloatingBind)
815 instance Outputable FloatingBind where
816 ppr (FloatLet b) = ppr b
817 ppr (FloatCase b r ok) = brackets (ppr ok) <+> ppr b <+> equals <+> ppr r
819 instance Outputable Floats where
820 ppr (Floats flag fs) = ptext (sLit "Floats") <> brackets (ppr flag) <+>
821 braces (vcat (map ppr (fromOL fs)))
823 instance Outputable OkToSpec where
824 ppr OkToSpec = ptext (sLit "OkToSpec")
825 ppr IfUnboxedOk = ptext (sLit "IfUnboxedOk")
826 ppr NotOkToSpec = ptext (sLit "NotOkToSpec")
828 -- Can we float these binds out of the rhs of a let? We cache this decision
829 -- to avoid having to recompute it in a non-linear way when there are
830 -- deeply nested lets.
832 = OkToSpec -- Lazy bindings of lifted type
833 | IfUnboxedOk -- A mixture of lazy lifted bindings and n
834 -- ok-to-speculate unlifted bindings
835 | NotOkToSpec -- Some not-ok-to-speculate unlifted bindings
837 mkFloat :: Bool -> Bool -> Id -> CpeRhs -> FloatingBind
838 mkFloat is_strict is_unlifted bndr rhs
839 | use_case = FloatCase bndr rhs (exprOkForSpeculation rhs)
840 | otherwise = FloatLet (NonRec bndr rhs)
842 use_case = is_unlifted || is_strict && not (exprIsHNF rhs)
843 -- Don't make a case for a value binding,
844 -- even if it's strict. Otherwise we get
845 -- case (\x -> e) of ...!
847 emptyFloats :: Floats
848 emptyFloats = Floats OkToSpec nilOL
850 isEmptyFloats :: Floats -> Bool
851 isEmptyFloats (Floats _ bs) = isNilOL bs
853 wrapBinds :: Floats -> CpeBody -> CpeBody
854 wrapBinds (Floats _ binds) body
855 = foldrOL mk_bind body binds
857 mk_bind (FloatCase bndr rhs _) body = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
858 mk_bind (FloatLet bind) body = Let bind body
860 addFloat :: Floats -> FloatingBind -> Floats
861 addFloat (Floats ok_to_spec floats) new_float
862 = Floats (combine ok_to_spec (check new_float)) (floats `snocOL` new_float)
864 check (FloatLet _) = OkToSpec
865 check (FloatCase _ _ ok_for_spec)
866 | ok_for_spec = IfUnboxedOk
867 | otherwise = NotOkToSpec
868 -- The ok-for-speculation flag says that it's safe to
869 -- float this Case out of a let, and thereby do it more eagerly
870 -- We need the top-level flag because it's never ok to float
871 -- an unboxed binding to the top level
873 unitFloat :: FloatingBind -> Floats
874 unitFloat = addFloat emptyFloats
876 appendFloats :: Floats -> Floats -> Floats
877 appendFloats (Floats spec1 floats1) (Floats spec2 floats2)
878 = Floats (combine spec1 spec2) (floats1 `appOL` floats2)
880 concatFloats :: [Floats] -> OrdList FloatingBind
881 concatFloats = foldr (\ (Floats _ bs1) bs2 -> appOL bs1 bs2) nilOL
883 combine :: OkToSpec -> OkToSpec -> OkToSpec
884 combine NotOkToSpec _ = NotOkToSpec
885 combine _ NotOkToSpec = NotOkToSpec
886 combine IfUnboxedOk _ = IfUnboxedOk
887 combine _ IfUnboxedOk = IfUnboxedOk
888 combine _ _ = OkToSpec
890 deFloatTop :: Floats -> [CoreBind]
891 -- For top level only; we don't expect any FloatCases
892 deFloatTop (Floats _ floats)
893 = foldrOL get [] floats
895 get (FloatLet b) bs = b:bs
896 get b _ = pprPanic "corePrepPgm" (ppr b)
898 -------------------------------------------
899 canFloatFromNoCaf :: Floats -> CpeRhs -> Maybe (Floats, CpeRhs)
900 -- Note [CafInfo and floating]
901 canFloatFromNoCaf (Floats ok_to_spec fs) rhs
902 | OkToSpec <- ok_to_spec -- Worth trying
903 , Just (subst, fs') <- go (emptySubst, nilOL) (fromOL fs)
904 = Just (Floats OkToSpec fs', subst_expr subst rhs)
908 subst_expr = substExpr (text "CorePrep")
910 go :: (Subst, OrdList FloatingBind) -> [FloatingBind]
911 -> Maybe (Subst, OrdList FloatingBind)
913 go (subst, fbs_out) [] = Just (subst, fbs_out)
915 go (subst, fbs_out) (FloatLet (NonRec b r) : fbs_in)
917 = go (subst', fbs_out `snocOL` new_fb) fbs_in
919 (subst', b') = set_nocaf_bndr subst b
920 new_fb = FloatLet (NonRec b' (subst_expr subst r))
922 go (subst, fbs_out) (FloatLet (Rec prs) : fbs_in)
924 = go (subst', fbs_out `snocOL` new_fb) fbs_in
927 (subst', bs') = mapAccumL set_nocaf_bndr subst bs
928 rs' = map (subst_expr subst') rs
929 new_fb = FloatLet (Rec (bs' `zip` rs'))
931 go _ _ = Nothing -- Encountered a caffy binding
934 set_nocaf_bndr subst bndr
935 = (extendIdSubst subst bndr (Var bndr'), bndr')
937 bndr' = bndr `setIdCafInfo` NoCafRefs
940 rhs_ok :: CoreExpr -> Bool
941 -- We can only float to top level from a NoCaf thing if
942 -- the new binding is static. However it can't mention
943 -- any non-static things or it would *already* be Caffy
944 rhs_ok = rhsIsStatic (\_ -> False)
946 wantFloatNested :: RecFlag -> Bool -> Floats -> CpeRhs -> Bool
947 wantFloatNested is_rec strict_or_unlifted floats rhs
948 = isEmptyFloats floats
949 || strict_or_unlifted
950 || (allLazyNested is_rec floats && exprIsHNF rhs)
951 -- Why the test for allLazyNested?
952 -- v = f (x `divInt#` y)
953 -- we don't want to float the case, even if f has arity 2,
954 -- because floating the case would make it evaluated too early
956 allLazyTop :: Floats -> Bool
957 allLazyTop (Floats OkToSpec _) = True
960 allLazyNested :: RecFlag -> Floats -> Bool
961 allLazyNested _ (Floats OkToSpec _) = True
962 allLazyNested _ (Floats NotOkToSpec _) = False
963 allLazyNested is_rec (Floats IfUnboxedOk _) = isNonRec is_rec
967 %************************************************************************
971 %************************************************************************
974 -- ---------------------------------------------------------------------------
976 -- ---------------------------------------------------------------------------
978 data CorePrepEnv = CPE (IdEnv Id) -- Clone local Ids
980 emptyCorePrepEnv :: CorePrepEnv
981 emptyCorePrepEnv = CPE emptyVarEnv
983 extendCorePrepEnv :: CorePrepEnv -> Id -> Id -> CorePrepEnv
984 extendCorePrepEnv (CPE env) id id' = CPE (extendVarEnv env id id')
986 extendCorePrepEnvList :: CorePrepEnv -> [(Id,Id)] -> CorePrepEnv
987 extendCorePrepEnvList (CPE env) prs = CPE (extendVarEnvList env prs)
989 lookupCorePrepEnv :: CorePrepEnv -> Id -> Id
990 lookupCorePrepEnv (CPE env) id
991 = case lookupVarEnv env id of
995 ------------------------------------------------------------------------------
997 -- ---------------------------------------------------------------------------
999 cloneBndrs :: CorePrepEnv -> [Var] -> UniqSM (CorePrepEnv, [Var])
1000 cloneBndrs env bs = mapAccumLM cloneBndr env bs
1002 cloneBndr :: CorePrepEnv -> Var -> UniqSM (CorePrepEnv, Var)
1005 = do bndr' <- setVarUnique bndr <$> getUniqueM
1006 return (extendCorePrepEnv env bndr bndr', bndr')
1008 | otherwise -- Top level things, which we don't want
1009 -- to clone, have become GlobalIds by now
1010 -- And we don't clone tyvars
1011 = return (env, bndr)
1014 ------------------------------------------------------------------------------
1015 -- Cloning ccall Ids; each must have a unique name,
1016 -- to give the code generator a handle to hang it on
1017 -- ---------------------------------------------------------------------------
1019 fiddleCCall :: Id -> UniqSM Id
1021 | isFCallId id = (id `setVarUnique`) <$> getUniqueM
1022 | otherwise = return id
1024 ------------------------------------------------------------------------------
1025 -- Generating new binders
1026 -- ---------------------------------------------------------------------------
1028 newVar :: Type -> UniqSM Id
1030 = seqType ty `seq` do
1032 return (mkSysLocal (fsLit "sat") uniq ty)