2 % (c) The AQUA Project, Glasgow University, 1993-1998
4 \section[Simplify]{The main module of the simplifier}
7 module Simplify ( simplTopBinds, simplExpr ) where
9 #include "HsVersions.h"
11 import CmdLineOpts ( dopt, DynFlag(Opt_D_dump_inlinings),
15 import SimplUtils ( mkCase, mkLam, newId,
16 simplBinder, simplBinders, simplLamBndrs, simplRecBndrs, simplLetBndr,
17 SimplCont(..), DupFlag(..), LetRhsFlag(..),
18 mkStop, mkBoringStop, pushContArgs,
19 contResultType, countArgs, contIsDupable, contIsRhsOrArg,
20 getContArgs, interestingCallContext, interestingArg, isStrictType
22 import Var ( mustHaveLocalBinding )
24 import Id ( Id, idType, idInfo, idArity, isDataConId,
25 idUnfolding, setIdUnfolding, isDeadBinder,
26 idNewDemandInfo, setIdInfo,
27 setIdOccInfo, zapLamIdInfo, setOneShotLambda,
29 import IdInfo ( OccInfo(..), isLoopBreaker,
34 import NewDemand ( isStrictDmd )
35 import DataCon ( dataConNumInstArgs, dataConRepStrictness )
37 import PprCore ( pprParendExpr, pprCoreExpr )
38 import CoreUnfold ( mkOtherCon, mkUnfolding, otherCons, callSiteInline )
39 import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding,
40 exprIsConApp_maybe, mkPiTypes, findAlt,
41 exprType, coreAltsType, exprIsValue,
42 exprOkForSpeculation, exprArity, findDefault,
43 mkCoerce, mkSCC, mkInlineMe, mkAltExpr, applyTypeToArg
45 import Rules ( lookupRule )
46 import BasicTypes ( isMarkedStrict )
47 import CostCentre ( currentCCS )
48 import Type ( isUnLiftedType, seqType, mkFunTy, tyConAppArgs, funArgTy,
49 funResultTy, splitFunTy_maybe, splitFunTy, eqType
51 import Subst ( mkSubst, substTy, substExpr,
52 isInScope, lookupIdSubst, simplIdInfo
54 import TysPrim ( realWorldStatePrimTy )
55 import PrelInfo ( realWorldPrimId )
56 import BasicTypes ( TopLevelFlag(..), isTopLevel,
60 import Maybe ( Maybe )
65 The guts of the simplifier is in this module, but the driver loop for
66 the simplifier is in SimplCore.lhs.
69 -----------------------------------------
70 *** IMPORTANT NOTE ***
71 -----------------------------------------
72 The simplifier used to guarantee that the output had no shadowing, but
73 it does not do so any more. (Actually, it never did!) The reason is
74 documented with simplifyArgs.
77 -----------------------------------------
78 *** IMPORTANT NOTE ***
79 -----------------------------------------
80 Many parts of the simplifier return a bunch of "floats" as well as an
81 expression. This is wrapped as a datatype SimplUtils.FloatsWith.
83 All "floats" are let-binds, not case-binds, but some non-rec lets may
84 be unlifted (with RHS ok-for-speculation).
88 -----------------------------------------
89 ORGANISATION OF FUNCTIONS
90 -----------------------------------------
92 - simplify all top-level binders
93 - for NonRec, call simplRecOrTopPair
94 - for Rec, call simplRecBind
97 ------------------------------
98 simplExpr (applied lambda) ==> simplNonRecBind
99 simplExpr (Let (NonRec ...) ..) ==> simplNonRecBind
100 simplExpr (Let (Rec ...) ..) ==> simplify binders; simplRecBind
102 ------------------------------
103 simplRecBind [binders already simplfied]
104 - use simplRecOrTopPair on each pair in turn
106 simplRecOrTopPair [binder already simplified]
107 Used for: recursive bindings (top level and nested)
108 top-level non-recursive bindings
110 - check for PreInlineUnconditionally
114 Used for: non-top-level non-recursive bindings
115 beta reductions (which amount to the same thing)
116 Because it can deal with strict arts, it takes a
117 "thing-inside" and returns an expression
119 - check for PreInlineUnconditionally
120 - simplify binder, including its IdInfo
129 simplNonRecX: [given a *simplified* RHS, but an *unsimplified* binder]
130 Used for: binding case-binder and constr args in a known-constructor case
131 - check for PreInLineUnconditionally
135 ------------------------------
136 simplLazyBind: [binder already simplified, RHS not]
137 Used for: recursive bindings (top level and nested)
138 top-level non-recursive bindings
139 non-top-level, but *lazy* non-recursive bindings
140 [must not be strict or unboxed]
141 Returns floats + an augmented environment, not an expression
142 - substituteIdInfo and add result to in-scope
143 [so that rules are available in rec rhs]
146 - float if exposes constructor or PAP
150 completeNonRecX: [binder and rhs both simplified]
151 - if the the thing needs case binding (unlifted and not ok-for-spec)
157 completeLazyBind: [given a simplified RHS]
158 [used for both rec and non-rec bindings, top level and not]
159 - try PostInlineUnconditionally
160 - add unfolding [this is the only place we add an unfolding]
165 Right hand sides and arguments
166 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
167 In many ways we want to treat
168 (a) the right hand side of a let(rec), and
169 (b) a function argument
170 in the same way. But not always! In particular, we would
171 like to leave these arguments exactly as they are, so they
172 will match a RULE more easily.
177 It's harder to make the rule match if we ANF-ise the constructor,
178 or eta-expand the PAP:
180 f (let { a = g x; b = h x } in (a,b))
183 On the other hand if we see the let-defns
188 then we *do* want to ANF-ise and eta-expand, so that p and q
189 can be safely inlined.
191 Even floating lets out is a bit dubious. For let RHS's we float lets
192 out if that exposes a value, so that the value can be inlined more vigorously.
195 r = let x = e in (x,x)
197 Here, if we float the let out we'll expose a nice constructor. We did experiments
198 that showed this to be a generally good thing. But it was a bad thing to float
199 lets out unconditionally, because that meant they got allocated more often.
201 For function arguments, there's less reason to expose a constructor (it won't
202 get inlined). Just possibly it might make a rule match, but I'm pretty skeptical.
203 So for the moment we don't float lets out of function arguments either.
208 For eta expansion, we want to catch things like
210 case e of (a,b) -> \x -> case a of (p,q) -> \y -> r
212 If the \x was on the RHS of a let, we'd eta expand to bring the two
213 lambdas together. And in general that's a good thing to do. Perhaps
214 we should eta expand wherever we find a (value) lambda? Then the eta
215 expansion at a let RHS can concentrate solely on the PAP case.
218 %************************************************************************
220 \subsection{Bindings}
222 %************************************************************************
225 simplTopBinds :: SimplEnv -> [InBind] -> SimplM [OutBind]
227 simplTopBinds env binds
228 = -- Put all the top-level binders into scope at the start
229 -- so that if a transformation rule has unexpectedly brought
230 -- anything into scope, then we don't get a complaint about that.
231 -- It's rather as if the top-level binders were imported.
232 simplRecBndrs env (bindersOfBinds binds) `thenSmpl` \ (env, bndrs') ->
233 simpl_binds env binds bndrs' `thenSmpl` \ (floats, _) ->
234 freeTick SimplifierDone `thenSmpl_`
235 returnSmpl (floatBinds floats)
237 -- We need to track the zapped top-level binders, because
238 -- they should have their fragile IdInfo zapped (notably occurrence info)
239 -- That's why we run down binds and bndrs' simultaneously.
240 simpl_binds :: SimplEnv -> [InBind] -> [OutId] -> SimplM (FloatsWith ())
241 simpl_binds env [] bs = ASSERT( null bs ) returnSmpl (emptyFloats env, ())
242 simpl_binds env (bind:binds) bs = simpl_bind env bind bs `thenSmpl` \ (floats,env) ->
243 addFloats env floats $ \env ->
244 simpl_binds env binds (drop_bs bind bs)
246 drop_bs (NonRec _ _) (_ : bs) = bs
247 drop_bs (Rec prs) bs = drop (length prs) bs
249 simpl_bind env (NonRec b r) (b':_) = simplRecOrTopPair env TopLevel b b' r
250 simpl_bind env (Rec pairs) bs' = simplRecBind env TopLevel pairs bs'
254 %************************************************************************
256 \subsection{simplNonRec}
258 %************************************************************************
260 simplNonRecBind is used for
261 * non-top-level non-recursive lets in expressions
265 * An unsimplified (binder, rhs) pair
266 * The env for the RHS. It may not be the same as the
267 current env because the bind might occur via (\x.E) arg
269 It uses the CPS form because the binding might be strict, in which
270 case we might discard the continuation:
271 let x* = error "foo" in (...x...)
273 It needs to turn unlifted bindings into a @case@. They can arise
274 from, say: (\x -> e) (4# + 3#)
277 simplNonRecBind :: SimplEnv
279 -> InExpr -> SimplEnv -- Arg, with its subst-env
280 -> OutType -- Type of thing computed by the context
281 -> (SimplEnv -> SimplM FloatsWithExpr) -- The body
282 -> SimplM FloatsWithExpr
284 simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
286 = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
289 simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
290 | preInlineUnconditionally env NotTopLevel bndr
291 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
292 thing_inside (extendSubst env bndr (ContEx (getSubstEnv rhs_se) rhs))
295 | isStrictDmd (idNewDemandInfo bndr) || isStrictType (idType bndr) -- A strict let
296 = -- Don't use simplBinder because that doesn't keep
297 -- fragile occurrence in the substitution
298 simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
299 simplStrictArg AnRhs env rhs rhs_se (idType bndr') cont_ty $ \ env rhs1 ->
301 -- Now complete the binding and simplify the body
302 completeNonRecX env True {- strict -} bndr bndr' rhs1 thing_inside
304 | otherwise -- Normal, lazy case
305 = -- Don't use simplBinder because that doesn't keep
306 -- fragile occurrence in the substitution
307 simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
308 simplLazyBind env NotTopLevel NonRecursive
309 bndr bndr' rhs rhs_se `thenSmpl` \ (floats, env) ->
310 addFloats env floats thing_inside
313 A specialised variant of simplNonRec used when the RHS is already simplified, notably
314 in knownCon. It uses case-binding where necessary.
317 simplNonRecX :: SimplEnv
318 -> InId -- Old binder
319 -> OutExpr -- Simplified RHS
320 -> (SimplEnv -> SimplM FloatsWithExpr)
321 -> SimplM FloatsWithExpr
323 simplNonRecX env bndr new_rhs thing_inside
324 | preInlineUnconditionally env NotTopLevel bndr
325 -- This happens; for example, the case_bndr during case of
326 -- known constructor: case (a,b) of x { (p,q) -> ... }
327 -- Here x isn't mentioned in the RHS, so we don't want to
328 -- create the (dead) let-binding let x = (a,b) in ...
330 -- Similarly, single occurrences can be inlined vigourously
331 -- e.g. case (f x, g y) of (a,b) -> ....
332 -- If a,b occur once we can avoid constructing the let binding for them.
333 = thing_inside (extendSubst env bndr (ContEx emptySubstEnv new_rhs))
336 = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
337 completeNonRecX env False {- Non-strict; pessimistic -}
338 bndr bndr' new_rhs thing_inside
340 completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside
341 | needsCaseBinding (idType new_bndr) new_rhs
342 = thing_inside env `thenSmpl` \ (floats, body) ->
343 returnSmpl (emptyFloats env, Case new_rhs new_bndr [(DEFAULT, [], wrapFloats floats body)])
346 = mkAtomicArgs is_strict
347 True {- OK to float unlifted -}
348 new_rhs `thenSmpl` \ (aux_binds, rhs2) ->
350 -- Make the arguments atomic if necessary,
351 -- adding suitable bindings
352 addAtomicBindsE env (fromOL aux_binds) $ \ env ->
353 completeLazyBind env NotTopLevel
354 old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) ->
355 addFloats env floats thing_inside
359 %************************************************************************
361 \subsection{Lazy bindings}
363 %************************************************************************
365 simplRecBind is used for
366 * recursive bindings only
369 simplRecBind :: SimplEnv -> TopLevelFlag
370 -> [(InId, InExpr)] -> [OutId]
371 -> SimplM (FloatsWith SimplEnv)
372 simplRecBind env top_lvl pairs bndrs'
373 = go env pairs bndrs' `thenSmpl` \ (floats, env) ->
374 returnSmpl (flattenFloats floats, env)
376 go env [] _ = returnSmpl (emptyFloats env, env)
378 go env ((bndr, rhs) : pairs) (bndr' : bndrs')
379 = simplRecOrTopPair env top_lvl bndr bndr' rhs `thenSmpl` \ (floats, env) ->
380 addFloats env floats (\env -> go env pairs bndrs')
384 simplRecOrTopPair is used for
385 * recursive bindings (whether top level or not)
386 * top-level non-recursive bindings
388 It assumes the binder has already been simplified, but not its IdInfo.
391 simplRecOrTopPair :: SimplEnv
393 -> InId -> OutId -- Binder, both pre-and post simpl
394 -> InExpr -- The RHS and its environment
395 -> SimplM (FloatsWith SimplEnv)
397 simplRecOrTopPair env top_lvl bndr bndr' rhs
398 | preInlineUnconditionally env top_lvl bndr -- Check for unconditional inline
399 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
400 returnSmpl (emptyFloats env, extendSubst env bndr (ContEx (getSubstEnv env) rhs))
403 = simplLazyBind env top_lvl Recursive bndr bndr' rhs env
404 -- May not actually be recursive, but it doesn't matter
408 simplLazyBind is used for
409 * recursive bindings (whether top level or not)
410 * top-level non-recursive bindings
411 * non-top-level *lazy* non-recursive bindings
413 [Thus it deals with the lazy cases from simplNonRecBind, and all cases
414 from SimplRecOrTopBind]
417 1. It assumes that the binder is *already* simplified,
418 and is in scope, but not its IdInfo
420 2. It assumes that the binder type is lifted.
422 3. It does not check for pre-inline-unconditionallly;
423 that should have been done already.
426 simplLazyBind :: SimplEnv
427 -> TopLevelFlag -> RecFlag
428 -> InId -> OutId -- Binder, both pre-and post simpl
429 -> InExpr -> SimplEnv -- The RHS and its environment
430 -> SimplM (FloatsWith SimplEnv)
432 simplLazyBind env top_lvl is_rec bndr bndr' rhs rhs_se
433 = -- Substitute IdInfo on binder, in the light of earlier
434 -- substitutions in this very letrec, and extend the
435 -- in-scope env, so that the IdInfo for this binder extends
436 -- over the RHS for the binder itself.
438 -- This is important. Manuel found cases where he really, really
439 -- wanted a RULE for a recursive function to apply in that function's
440 -- own right-hand side.
442 -- NB: does no harm for non-recursive bindings
444 is_top_level = isTopLevel top_lvl
445 bndr_ty' = idType bndr'
446 bndr'' = simplIdInfo (getSubst rhs_se) (idInfo bndr) bndr'
447 env1 = modifyInScope env bndr'' bndr''
448 rhs_env = setInScope rhs_se env1
449 ok_float_unlifted = not is_top_level && isNonRec is_rec
450 rhs_cont = mkStop bndr_ty' AnRhs
452 -- Simplify the RHS; note the mkStop, which tells
453 -- the simplifier that this is the RHS of a let.
454 simplExprF rhs_env rhs rhs_cont `thenSmpl` \ (floats, rhs1) ->
456 -- If any of the floats can't be floated, give up now
457 -- (The allLifted predicate says True for empty floats.)
458 if (not ok_float_unlifted && not (allLifted floats)) then
459 completeLazyBind env1 top_lvl bndr bndr''
460 (wrapFloats floats rhs1)
463 -- ANF-ise a constructor or PAP rhs
464 mkAtomicArgs False {- Not strict -}
465 ok_float_unlifted rhs1 `thenSmpl` \ (aux_binds, rhs2) ->
467 -- If the result is a PAP, float the floats out, else wrap them
468 -- By this time it's already been ANF-ised (if necessary)
469 if isEmptyFloats floats && isNilOL aux_binds then -- Shortcut a common case
470 completeLazyBind env1 top_lvl bndr bndr'' rhs2
472 -- We use exprIsTrivial here because we want to reveal lone variables.
473 -- E.g. let { x = letrec { y = E } in y } in ...
474 -- Here we definitely want to float the y=E defn.
475 -- exprIsValue definitely isn't right for that.
477 -- BUT we can't use "exprIsCheap", because that causes a strictness bug.
478 -- x = let y* = E in case (scc y) of { T -> F; F -> T}
479 -- The case expression is 'cheap', but it's wrong to transform to
480 -- y* = E; x = case (scc y) of {...}
481 -- Either we must be careful not to float demanded non-values, or
482 -- we must use exprIsValue for the test, which ensures that the
483 -- thing is non-strict. I think. The WARN below tests for this.
484 else if is_top_level || exprIsTrivial rhs2 || exprIsValue rhs2 then
486 -- There's a subtlety here. There may be a binding (x* = e) in the
487 -- floats, where the '*' means 'will be demanded'. So is it safe
488 -- to float it out? Answer no, but it won't matter because
489 -- we only float if arg' is a WHNF,
490 -- and so there can't be any 'will be demanded' bindings in the floats.
492 WARN( any demanded_float (floatBinds floats),
493 ppr (filter demanded_float (floatBinds floats)) )
495 tick LetFloatFromLet `thenSmpl_` (
496 addFloats env1 floats $ \ env2 ->
497 addAtomicBinds env2 (fromOL aux_binds) $ \ env3 ->
498 completeLazyBind env3 top_lvl bndr bndr'' rhs2)
501 completeLazyBind env1 top_lvl bndr bndr'' (wrapFloats floats rhs1)
504 demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b))
505 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
506 demanded_float (Rec _) = False
511 %************************************************************************
513 \subsection{Completing a lazy binding}
515 %************************************************************************
518 * deals only with Ids, not TyVars
519 * takes an already-simplified binder and RHS
520 * is used for both recursive and non-recursive bindings
521 * is used for both top-level and non-top-level bindings
523 It does the following:
524 - tries discarding a dead binding
525 - tries PostInlineUnconditionally
526 - add unfolding [this is the only place we add an unfolding]
529 It does *not* attempt to do let-to-case. Why? Because it is used for
530 - top-level bindings (when let-to-case is impossible)
531 - many situations where the "rhs" is known to be a WHNF
532 (so let-to-case is inappropriate).
535 completeLazyBind :: SimplEnv
536 -> TopLevelFlag -- Flag stuck into unfolding
537 -> InId -- Old binder
538 -> OutId -- New binder
539 -> OutExpr -- Simplified RHS
540 -> SimplM (FloatsWith SimplEnv)
541 -- We return a new SimplEnv, because completeLazyBind may choose to do its work
542 -- by extending the substitution (e.g. let x = y in ...)
543 -- The new binding (if any) is returned as part of the floats.
544 -- NB: the returned SimplEnv has the right SubstEnv, but you should
545 -- (as usual) use the in-scope-env from the floats
547 completeLazyBind env top_lvl old_bndr new_bndr new_rhs
548 | postInlineUnconditionally env new_bndr loop_breaker new_rhs
549 = -- Drop the binding
550 tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
551 returnSmpl (emptyFloats env, extendSubst env old_bndr (DoneEx new_rhs))
552 -- Use the substitution to make quite, quite sure that the substitution
553 -- will happen, since we are going to discard the binding
558 new_bndr_info = idInfo new_bndr `setArityInfo` exprArity new_rhs
560 -- Add the unfolding *only* for non-loop-breakers
561 -- Making loop breakers not have an unfolding at all
562 -- means that we can avoid tests in exprIsConApp, for example.
563 -- This is important: if exprIsConApp says 'yes' for a recursive
564 -- thing, then we can get into an infinite loop
565 info_w_unf | loop_breaker = new_bndr_info
566 | otherwise = new_bndr_info `setUnfoldingInfo` unfolding
567 unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs
569 final_id = new_bndr `setIdInfo` info_w_unf
571 -- These seqs forces the Id, and hence its IdInfo,
572 -- and hence any inner substitutions
574 returnSmpl (unitFloat env final_id new_rhs, env)
577 loop_breaker = isLoopBreaker occ_info
578 old_info = idInfo old_bndr
579 occ_info = occInfo old_info
584 %************************************************************************
586 \subsection[Simplify-simplExpr]{The main function: simplExpr}
588 %************************************************************************
590 The reason for this OutExprStuff stuff is that we want to float *after*
591 simplifying a RHS, not before. If we do so naively we get quadratic
592 behaviour as things float out.
594 To see why it's important to do it after, consider this (real) example:
608 a -- Can't inline a this round, cos it appears twice
612 Each of the ==> steps is a round of simplification. We'd save a
613 whole round if we float first. This can cascade. Consider
618 let f = let d1 = ..d.. in \y -> e
622 in \x -> ...(\y ->e)...
624 Only in this second round can the \y be applied, and it
625 might do the same again.
629 simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
630 simplExpr env expr = simplExprC env expr (mkStop expr_ty' AnArg)
632 expr_ty' = substTy (getSubst env) (exprType expr)
633 -- The type in the Stop continuation, expr_ty', is usually not used
634 -- It's only needed when discarding continuations after finding
635 -- a function that returns bottom.
636 -- Hence the lazy substitution
639 simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
640 -- Simplify an expression, given a continuation
641 simplExprC env expr cont
642 = simplExprF env expr cont `thenSmpl` \ (floats, expr) ->
643 returnSmpl (wrapFloats floats expr)
645 simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM FloatsWithExpr
646 -- Simplify an expression, returning floated binds
648 simplExprF env (Var v) cont = simplVar env v cont
649 simplExprF env (Lit lit) cont = rebuild env (Lit lit) cont
650 simplExprF env expr@(Lam _ _) cont = simplLam env expr cont
651 simplExprF env (Note note expr) cont = simplNote env note expr cont
652 simplExprF env (App fun arg) cont = simplExprF env fun (ApplyTo NoDup arg env cont)
654 simplExprF env (Type ty) cont
655 = ASSERT( contIsRhsOrArg cont )
656 simplType env ty `thenSmpl` \ ty' ->
657 rebuild env (Type ty') cont
659 simplExprF env (Case scrut bndr alts) cont
660 | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
661 = -- Simplify the scrutinee with a Select continuation
662 simplExprF env scrut (Select NoDup bndr alts env cont)
665 = -- If case-of-case is off, simply simplify the case expression
666 -- in a vanilla Stop context, and rebuild the result around it
667 simplExprC env scrut case_cont `thenSmpl` \ case_expr' ->
668 rebuild env case_expr' cont
670 case_cont = Select NoDup bndr alts env (mkBoringStop (contResultType cont))
672 simplExprF env (Let (Rec pairs) body) cont
673 = simplRecBndrs env (map fst pairs) `thenSmpl` \ (env, bndrs') ->
674 -- NB: bndrs' don't have unfoldings or spec-envs
675 -- We add them as we go down, using simplPrags
677 simplRecBind env NotTopLevel pairs bndrs' `thenSmpl` \ (floats, env) ->
678 addFloats env floats $ \ env ->
679 simplExprF env body cont
681 -- A non-recursive let is dealt with by simplNonRecBind
682 simplExprF env (Let (NonRec bndr rhs) body) cont
683 = simplNonRecBind env bndr rhs env (contResultType cont) $ \ env ->
684 simplExprF env body cont
687 ---------------------------------
688 simplType :: SimplEnv -> InType -> SimplM OutType
689 -- Kept monadic just so we can do the seqType
691 = seqType new_ty `seq` returnSmpl new_ty
693 new_ty = substTy (getSubst env) ty
697 %************************************************************************
701 %************************************************************************
704 simplLam env fun cont
707 zap_it = mkLamBndrZapper fun (countArgs cont)
708 cont_ty = contResultType cont
710 -- Type-beta reduction
711 go env (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
712 = ASSERT( isTyVar bndr )
713 tick (BetaReduction bndr) `thenSmpl_`
714 simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' ->
715 go (extendSubst env bndr (DoneTy ty_arg')) body body_cont
717 -- Ordinary beta reduction
718 go env (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
719 = tick (BetaReduction bndr) `thenSmpl_`
720 simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env ->
721 go env body body_cont
723 -- Not enough args, so there are real lambdas left to put in the result
724 go env lam@(Lam _ _) cont
725 = simplLamBndrs env bndrs `thenSmpl` \ (env, bndrs') ->
726 simplExpr env body `thenSmpl` \ body' ->
727 mkLam env bndrs' body' cont `thenSmpl` \ (floats, new_lam) ->
728 addFloats env floats $ \ env ->
729 rebuild env new_lam cont
731 (bndrs,body) = collectBinders lam
733 -- Exactly enough args
734 go env expr cont = simplExprF env expr cont
736 mkLamBndrZapper :: CoreExpr -- Function
737 -> Int -- Number of args supplied, *including* type args
738 -> Id -> Id -- Use this to zap the binders
739 mkLamBndrZapper fun n_args
740 | n_args >= n_params fun = \b -> b -- Enough args
741 | otherwise = \b -> zapLamIdInfo b
743 -- NB: we count all the args incl type args
744 -- so we must count all the binders (incl type lambdas)
745 n_params (Note _ e) = n_params e
746 n_params (Lam b e) = 1 + n_params e
747 n_params other = 0::Int
751 %************************************************************************
755 %************************************************************************
758 simplNote env (Coerce to from) body cont
760 in_scope = getInScope env
762 addCoerce s1 k1 (CoerceIt t1 cont)
763 -- coerce T1 S1 (coerce S1 K1 e)
766 -- coerce T1 K1 e, otherwise
768 -- For example, in the initial form of a worker
769 -- we may find (coerce T (coerce S (\x.e))) y
770 -- and we'd like it to simplify to e[y/x] in one round
772 | t1 `eqType` k1 = cont -- The coerces cancel out
773 | otherwise = CoerceIt t1 cont -- They don't cancel, but
774 -- the inner one is redundant
776 addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
777 | Just (s1, s2) <- splitFunTy_maybe s1s2
778 -- (coerce (T1->T2) (S1->S2) F) E
780 -- coerce T2 S2 (F (coerce S1 T1 E))
782 -- t1t2 must be a function type, T1->T2
783 -- but s1s2 might conceivably not be
785 -- When we build the ApplyTo we can't mix the out-types
786 -- with the InExpr in the argument, so we simply substitute
787 -- to make it all consistent. It's a bit messy.
788 -- But it isn't a common case.
790 (t1,t2) = splitFunTy t1t2
791 new_arg = mkCoerce s1 t1 (substExpr (mkSubst in_scope (getSubstEnv arg_se)) arg)
793 ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont)
795 addCoerce to' _ cont = CoerceIt to' cont
797 simplType env to `thenSmpl` \ to' ->
798 simplType env from `thenSmpl` \ from' ->
799 simplExprF env body (addCoerce to' from' cont)
802 -- Hack: we only distinguish subsumed cost centre stacks for the purposes of
803 -- inlining. All other CCCSs are mapped to currentCCS.
804 simplNote env (SCC cc) e cont
805 = simplExpr (setEnclosingCC env currentCCS) e `thenSmpl` \ e' ->
806 rebuild env (mkSCC cc e') cont
808 simplNote env InlineCall e cont
809 = simplExprF env e (InlinePlease cont)
811 -- See notes with SimplMonad.inlineMode
812 simplNote env InlineMe e cont
813 | contIsRhsOrArg cont -- Totally boring continuation; see notes above
814 = -- Don't inline inside an INLINE expression
815 simplExpr (setMode inlineMode env ) e `thenSmpl` \ e' ->
816 rebuild env (mkInlineMe e') cont
818 | otherwise -- Dissolve the InlineMe note if there's
819 -- an interesting context of any kind to combine with
820 -- (even a type application -- anything except Stop)
821 = simplExprF env e cont
825 %************************************************************************
827 \subsection{Dealing with calls}
829 %************************************************************************
832 simplVar env var cont
833 = case lookupIdSubst (getSubst env) var of
834 DoneEx e -> simplExprF (zapSubstEnv env) e cont
835 ContEx se e -> simplExprF (setSubstEnv env se) e cont
836 DoneId var1 occ -> WARN( not (isInScope var1 (getSubst env)) && mustHaveLocalBinding var1,
837 text "simplVar:" <+> ppr var )
838 completeCall (zapSubstEnv env) var1 occ cont
839 -- The template is already simplified, so don't re-substitute.
840 -- This is VITAL. Consider
842 -- let y = \z -> ...x... in
844 -- We'll clone the inner \x, adding x->x' in the id_subst
845 -- Then when we inline y, we must *not* replace x by x' in
846 -- the inlined copy!!
848 ---------------------------------------------------------
849 -- Dealing with a call site
851 completeCall env var occ_info cont
852 = -- Simplify the arguments
853 getDOptsSmpl `thenSmpl` \ dflags ->
855 chkr = getSwitchChecker env
856 (args, call_cont, inline_call) = getContArgs chkr var cont
859 simplifyArgs env fn_ty args (contResultType call_cont) $ \ env args ->
861 -- Next, look for rules or specialisations that match
863 -- It's important to simplify the args first, because the rule-matcher
864 -- doesn't do substitution as it goes. We don't want to use subst_args
865 -- (defined in the 'where') because that throws away useful occurrence info,
866 -- and perhaps-very-important specialisations.
868 -- Some functions have specialisations *and* are strict; in this case,
869 -- we don't want to inline the wrapper of the non-specialised thing; better
870 -- to call the specialised thing instead.
871 -- We used to use the black-listing mechanism to ensure that inlining of
872 -- the wrapper didn't occur for things that have specialisations till a
873 -- later phase, so but now we just try RULES first
875 -- You might think that we shouldn't apply rules for a loop breaker:
876 -- doing so might give rise to an infinite loop, because a RULE is
877 -- rather like an extra equation for the function:
878 -- RULE: f (g x) y = x+y
881 -- But it's too drastic to disable rules for loop breakers.
882 -- Even the foldr/build rule would be disabled, because foldr
883 -- is recursive, and hence a loop breaker:
884 -- foldr k z (build g) = g k z
885 -- So it's up to the programmer: rules can cause divergence
888 in_scope = getInScope env
889 maybe_rule = case activeRule env of
890 Nothing -> Nothing -- No rules apply
891 Just act_fn -> lookupRule act_fn in_scope var args
894 Just (rule_name, rule_rhs) ->
895 tick (RuleFired rule_name) `thenSmpl_`
896 (if dopt Opt_D_dump_inlinings dflags then
897 pprTrace "Rule fired" (vcat [
898 text "Rule:" <+> ptext rule_name,
899 text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
900 text "After: " <+> pprCoreExpr rule_rhs,
901 text "Cont: " <+> ppr call_cont])
904 simplExprF env rule_rhs call_cont ;
906 Nothing -> -- No rules
908 -- Next, look for an inlining
910 arg_infos = [ interestingArg arg | arg <- args, isValArg arg]
912 interesting_cont = interestingCallContext (not (null args))
913 (not (null arg_infos))
916 active_inline = activeInline env var occ_info
917 maybe_inline = callSiteInline dflags active_inline inline_call occ_info
918 var arg_infos interesting_cont
920 case maybe_inline of {
921 Just unfolding -- There is an inlining!
922 -> tick (UnfoldingDone var) `thenSmpl_`
923 makeThatCall env var unfolding args call_cont
926 Nothing -> -- No inlining!
929 rebuild env (mkApps (Var var) args) call_cont
932 makeThatCall :: SimplEnv
934 -> InExpr -- Inlined function rhs
935 -> [OutExpr] -- Arguments, already simplified
936 -> SimplCont -- After the call
937 -> SimplM FloatsWithExpr
938 -- Similar to simplLam, but this time
939 -- the arguments are already simplified
940 makeThatCall orig_env var fun@(Lam _ _) args cont
941 = go orig_env fun args
943 zap_it = mkLamBndrZapper fun (length args)
945 -- Type-beta reduction
946 go env (Lam bndr body) (Type ty_arg : args)
947 = ASSERT( isTyVar bndr )
948 tick (BetaReduction bndr) `thenSmpl_`
949 go (extendSubst env bndr (DoneTy ty_arg)) body args
951 -- Ordinary beta reduction
952 go env (Lam bndr body) (arg : args)
953 = tick (BetaReduction bndr) `thenSmpl_`
954 simplNonRecX env (zap_it bndr) arg $ \ env ->
957 -- Not enough args, so there are real lambdas left to put in the result
959 = simplExprF env fun (pushContArgs orig_env args cont)
960 -- NB: orig_env; the correct environment to capture with
961 -- the arguments.... env has been augmented with substitutions
962 -- from the beta reductions.
964 makeThatCall env var fun args cont
965 = simplExprF env fun (pushContArgs env args cont)
969 %************************************************************************
971 \subsection{Arguments}
973 %************************************************************************
976 ---------------------------------------------------------
977 -- Simplifying the arguments of a call
979 simplifyArgs :: SimplEnv
980 -> OutType -- Type of the function
981 -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments
982 -> OutType -- Type of the continuation
983 -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr)
984 -> SimplM FloatsWithExpr
986 -- [CPS-like because of strict arguments]
988 -- Simplify the arguments to a call.
989 -- This part of the simplifier may break the no-shadowing invariant
991 -- f (...(\a -> e)...) (case y of (a,b) -> e')
992 -- where f is strict in its second arg
993 -- If we simplify the innermost one first we get (...(\a -> e)...)
994 -- Simplifying the second arg makes us float the case out, so we end up with
995 -- case y of (a,b) -> f (...(\a -> e)...) e'
996 -- So the output does not have the no-shadowing invariant. However, there is
997 -- no danger of getting name-capture, because when the first arg was simplified
998 -- we used an in-scope set that at least mentioned all the variables free in its
999 -- static environment, and that is enough.
1001 -- We can't just do innermost first, or we'd end up with a dual problem:
1002 -- case x of (a,b) -> f e (...(\a -> e')...)
1004 -- I spent hours trying to recover the no-shadowing invariant, but I just could
1005 -- not think of an elegant way to do it. The simplifier is already knee-deep in
1006 -- continuations. We have to keep the right in-scope set around; AND we have
1007 -- to get the effect that finding (error "foo") in a strict arg position will
1008 -- discard the entire application and replace it with (error "foo"). Getting
1009 -- all this at once is TOO HARD!
1011 simplifyArgs env fn_ty args cont_ty thing_inside
1012 = go env fn_ty args thing_inside
1014 go env fn_ty [] thing_inside = thing_inside env []
1015 go env fn_ty (arg:args) thing_inside = simplifyArg env fn_ty arg cont_ty $ \ env arg' ->
1016 go env (applyTypeToArg fn_ty arg') args $ \ env args' ->
1017 thing_inside env (arg':args')
1019 simplifyArg env fn_ty (Type ty_arg, se, _) cont_ty thing_inside
1020 = simplType (setInScope se env) ty_arg `thenSmpl` \ new_ty_arg ->
1021 thing_inside env (Type new_ty_arg)
1023 simplifyArg env fn_ty (val_arg, arg_se, is_strict) cont_ty thing_inside
1025 = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside
1028 = simplExprF (setInScope arg_se env) val_arg
1029 (mkStop arg_ty AnArg) `thenSmpl` \ (floats, arg1) ->
1030 addFloats env floats $ \ env ->
1031 thing_inside env arg1
1033 arg_ty = funArgTy fn_ty
1036 simplStrictArg :: LetRhsFlag
1037 -> SimplEnv -- The env of the call
1038 -> InExpr -> SimplEnv -- The arg plus its env
1039 -> OutType -- arg_ty: type of the argument
1040 -> OutType -- cont_ty: Type of thing computed by the context
1041 -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr)
1042 -- Takes an expression of type rhs_ty,
1043 -- returns an expression of type cont_ty
1044 -- The env passed to this continuation is the
1045 -- env of the call, plus any new in-scope variables
1046 -> SimplM FloatsWithExpr -- An expression of type cont_ty
1048 simplStrictArg is_rhs call_env arg arg_env arg_ty cont_ty thing_inside
1049 = simplExprF (setInScope arg_env call_env) arg
1050 (ArgOf is_rhs arg_ty cont_ty (\ new_env -> thing_inside (setInScope call_env new_env)))
1051 -- Notice the way we use arg_env (augmented with in-scope vars from call_env)
1052 -- to simplify the argument
1053 -- and call-env (augmented with in-scope vars from the arg) to pass to the continuation
1057 %************************************************************************
1059 \subsection{mkAtomicArgs}
1061 %************************************************************************
1063 mkAtomicArgs takes a putative RHS, checks whether it's a PAP or
1064 constructor application and, if so, converts it to ANF, so that the
1065 resulting thing can be inlined more easily. Thus
1072 There are three sorts of binding context, specified by the two
1078 N N Top-level or recursive Only bind args of lifted type
1080 N Y Non-top-level and non-recursive, Bind args of lifted type, or
1081 but lazy unlifted-and-ok-for-speculation
1083 Y Y Non-top-level, non-recursive, Bind all args
1084 and strict (demanded)
1091 there is no point in transforming to
1093 x = case (y div# z) of r -> MkC r
1095 because the (y div# z) can't float out of the let. But if it was
1096 a *strict* let, then it would be a good thing to do. Hence the
1097 context information.
1100 mkAtomicArgs :: Bool -- A strict binding
1101 -> Bool -- OK to float unlifted args
1103 -> SimplM (OrdList (OutId,OutExpr), -- The floats (unusually) may include
1104 OutExpr) -- things that need case-binding,
1105 -- if the strict-binding flag is on
1107 mkAtomicArgs is_strict ok_float_unlifted rhs
1108 | (Var fun, args) <- collectArgs rhs, -- It's an application
1109 isDataConId fun || valArgCount args < idArity fun -- And it's a constructor or PAP
1110 = go fun nilOL [] args -- Have a go
1112 | otherwise = bale_out -- Give up
1115 bale_out = returnSmpl (nilOL, rhs)
1117 go fun binds rev_args []
1118 = returnSmpl (binds, mkApps (Var fun) (reverse rev_args))
1120 go fun binds rev_args (arg : args)
1121 | exprIsTrivial arg -- Easy case
1122 = go fun binds (arg:rev_args) args
1124 | not can_float_arg -- Can't make this arg atomic
1125 = bale_out -- ... so give up
1127 | otherwise -- Don't forget to do it recursively
1128 -- E.g. x = a:b:c:[]
1129 = mkAtomicArgs is_strict ok_float_unlifted arg `thenSmpl` \ (arg_binds, arg') ->
1130 newId SLIT("a") arg_ty `thenSmpl` \ arg_id ->
1131 go fun ((arg_binds `snocOL` (arg_id,arg')) `appOL` binds)
1132 (Var arg_id : rev_args) args
1134 arg_ty = exprType arg
1135 can_float_arg = is_strict
1136 || not (isUnLiftedType arg_ty)
1137 || (ok_float_unlifted && exprOkForSpeculation arg)
1140 addAtomicBinds :: SimplEnv -> [(OutId,OutExpr)]
1141 -> (SimplEnv -> SimplM (FloatsWith a))
1142 -> SimplM (FloatsWith a)
1143 addAtomicBinds env [] thing_inside = thing_inside env
1144 addAtomicBinds env ((v,r):bs) thing_inside = addAuxiliaryBind env (NonRec v r) $ \ env ->
1145 addAtomicBinds env bs thing_inside
1147 addAtomicBindsE :: SimplEnv -> [(OutId,OutExpr)]
1148 -> (SimplEnv -> SimplM FloatsWithExpr)
1149 -> SimplM FloatsWithExpr
1150 -- Same again, but this time we're in an expression context,
1151 -- and may need to do some case bindings
1153 addAtomicBindsE env [] thing_inside
1155 addAtomicBindsE env ((v,r):bs) thing_inside
1156 | needsCaseBinding (idType v) r
1157 = addAtomicBindsE (addNewInScopeIds env [v]) bs thing_inside `thenSmpl` \ (floats, expr) ->
1158 WARN( exprIsTrivial expr, ppr v <+> pprCoreExpr expr )
1159 returnSmpl (emptyFloats env, Case r v [(DEFAULT,[], wrapFloats floats expr)])
1162 = addAuxiliaryBind env (NonRec v r) $ \ env ->
1163 addAtomicBindsE env bs thing_inside
1167 %************************************************************************
1169 \subsection{The main rebuilder}
1171 %************************************************************************
1174 rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr
1176 rebuild env expr (Stop _ _ _) = rebuildDone env expr
1177 rebuild env expr (ArgOf _ _ _ cont_fn) = cont_fn env expr
1178 rebuild env expr (CoerceIt to_ty cont) = rebuild env (mkCoerce to_ty (exprType expr) expr) cont
1179 rebuild env expr (InlinePlease cont) = rebuild env (Note InlineCall expr) cont
1180 rebuild env expr (Select _ bndr alts se cont) = rebuildCase (setInScope se env) expr bndr alts cont
1181 rebuild env expr (ApplyTo _ arg se cont) = rebuildApp (setInScope se env) expr arg cont
1183 rebuildApp env fun arg cont
1184 = simplExpr env arg `thenSmpl` \ arg' ->
1185 rebuild env (App fun arg') cont
1187 rebuildDone env expr = returnSmpl (emptyFloats env, expr)
1191 %************************************************************************
1193 \subsection{Functions dealing with a case}
1195 %************************************************************************
1197 Blob of helper functions for the "case-of-something-else" situation.
1200 ---------------------------------------------------------
1201 -- Eliminate the case if possible
1203 rebuildCase :: SimplEnv
1204 -> OutExpr -- Scrutinee
1205 -> InId -- Case binder
1206 -> [InAlt] -- Alternatives
1208 -> SimplM FloatsWithExpr
1210 rebuildCase env scrut case_bndr alts cont
1211 | Just (con,args) <- exprIsConApp_maybe scrut
1212 -- Works when the scrutinee is a variable with a known unfolding
1213 -- as well as when it's an explicit constructor application
1214 = knownCon env (DataAlt con) args case_bndr alts cont
1216 | Lit lit <- scrut -- No need for same treatment as constructors
1217 -- because literals are inlined more vigorously
1218 = knownCon env (LitAlt lit) [] case_bndr alts cont
1221 = -- Prepare case alternatives
1222 -- Filter out alternatives that can't possibly match
1224 impossible_cons = case scrut of
1225 Var v -> otherCons (idUnfolding v)
1227 better_alts = case impossible_cons of
1229 other -> [alt | alt@(con,_,_) <- alts,
1230 not (con `elem` impossible_cons)]
1232 -- "handled_cons" are handled either by the context,
1233 -- or by a branch in this case expression
1234 -- Don't add DEFAULT to the handled_cons!!
1235 (alts_wo_default, _) = findDefault better_alts
1236 handled_cons = impossible_cons ++ [con | (con,_,_) <- alts_wo_default]
1239 -- Deal with the case binder, and prepare the continuation;
1240 -- The new subst_env is in place
1241 prepareCaseCont env better_alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1242 addFloats env floats $ \ env ->
1244 -- Deal with variable scrutinee
1245 simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr', zap_occ_info) ->
1247 -- Deal with the case alternatives
1248 simplAlts alt_env zap_occ_info handled_cons
1249 case_bndr' better_alts dup_cont `thenSmpl` \ alts' ->
1251 -- Put the case back together
1252 mkCase scrut handled_cons case_bndr' alts' `thenSmpl` \ case_expr ->
1254 -- Notice that rebuildDone returns the in-scope set from env, not alt_env
1255 -- The case binder *not* scope over the whole returned case-expression
1256 rebuild env case_expr nondup_cont
1259 simplCaseBinder checks whether the scrutinee is a variable, v. If so,
1260 try to eliminate uses of v in the RHSs in favour of case_bndr; that
1261 way, there's a chance that v will now only be used once, and hence
1266 There is a time we *don't* want to do that, namely when
1267 -fno-case-of-case is on. This happens in the first simplifier pass,
1268 and enhances full laziness. Here's the bad case:
1269 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1270 If we eliminate the inner case, we trap it inside the I# v -> arm,
1271 which might prevent some full laziness happening. I've seen this
1272 in action in spectral/cichelli/Prog.hs:
1273 [(m,n) | m <- [1..max], n <- [1..max]]
1274 Hence the check for NoCaseOfCase.
1278 There is another situation when we don't want to do it. If we have
1280 case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
1281 ...other cases .... }
1283 We'll perform the binder-swap for the outer case, giving
1285 case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
1286 ...other cases .... }
1288 But there is no point in doing it for the inner case,
1289 because w1 can't be inlined anyway. Furthermore, doing the case-swapping
1290 involves zapping w2's occurrence info (see paragraphs that follow),
1291 and that forces us to bind w2 when doing case merging. So we get
1293 case x of w1 { A -> let w2 = w1 in e1
1294 B -> let w2 = w1 in e2
1295 ...other cases .... }
1297 This is plain silly in the common case where w2 is dead.
1299 Even so, I can't see a good way to implement this idea. I tried
1300 not doing the binder-swap if the scrutinee was already evaluated
1301 but that failed big-time:
1305 case v of w { MkT x ->
1306 case x of x1 { I# y1 ->
1307 case x of x2 { I# y2 -> ...
1309 Notice that because MkT is strict, x is marked "evaluated". But to
1310 eliminate the last case, we must either make sure that x (as well as
1311 x1) has unfolding MkT y1. THe straightforward thing to do is to do
1312 the binder-swap. So this whole note is a no-op.
1316 If we replace the scrutinee, v, by tbe case binder, then we have to nuke
1317 any occurrence info (eg IAmDead) in the case binder, because the
1318 case-binder now effectively occurs whenever v does. AND we have to do
1319 the same for the pattern-bound variables! Example:
1321 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1323 Here, b and p are dead. But when we move the argment inside the first
1324 case RHS, and eliminate the second case, we get
1326 case x or { (a,b) -> a b }
1328 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1329 happened. Hence the zap_occ_info function returned by simplCaseBinder
1332 simplCaseBinder env (Var v) case_bndr
1333 | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
1335 -- Failed try [see Note 2 above]
1336 -- not (isEvaldUnfolding (idUnfolding v))
1338 = simplBinder env (zap case_bndr) `thenSmpl` \ (env, case_bndr') ->
1339 returnSmpl (modifyInScope env v case_bndr', case_bndr', zap)
1340 -- We could extend the substitution instead, but it would be
1341 -- a hack because then the substitution wouldn't be idempotent
1342 -- any more (v is an OutId). And this just just as well.
1344 zap b = b `setIdOccInfo` NoOccInfo
1346 simplCaseBinder env other_scrut case_bndr
1347 = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') ->
1348 returnSmpl (env, case_bndr', \ bndr -> bndr) -- NoOp on bndr
1354 simplAlts :: SimplEnv
1355 -> (InId -> InId) -- Occ-info zapper
1356 -> [AltCon] -- Alternatives the scrutinee can't be
1357 -- in the default case
1358 -> OutId -- Case binder
1359 -> [InAlt] -> SimplCont
1360 -> SimplM [OutAlt] -- Includes the continuation
1362 simplAlts env zap_occ_info handled_cons case_bndr' alts cont'
1363 = mapSmpl simpl_alt alts
1365 inst_tys' = tyConAppArgs (idType case_bndr')
1367 simpl_alt (DEFAULT, _, rhs)
1369 -- In the default case we record the constructors that the
1370 -- case-binder *can't* be.
1371 -- We take advantage of any OtherCon info in the case scrutinee
1372 case_bndr_w_unf = case_bndr' `setIdUnfolding` mkOtherCon handled_cons
1373 env_with_unf = modifyInScope env case_bndr' case_bndr_w_unf
1375 simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
1376 returnSmpl (DEFAULT, [], rhs')
1378 simpl_alt (con, vs, rhs)
1379 = -- Deal with the pattern-bound variables
1380 -- Mark the ones that are in ! positions in the data constructor
1381 -- as certainly-evaluated.
1382 -- NB: it happens that simplBinders does *not* erase the OtherCon
1383 -- form of unfolding, so it's ok to add this info before
1384 -- doing simplBinders
1385 simplBinders env (add_evals con vs) `thenSmpl` \ (env, vs') ->
1387 -- Bind the case-binder to (con args)
1389 unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
1390 env_with_unf = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` unfolding)
1392 simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
1393 returnSmpl (con, vs', rhs')
1396 -- add_evals records the evaluated-ness of the bound variables of
1397 -- a case pattern. This is *important*. Consider
1398 -- data T = T !Int !Int
1400 -- case x of { T a b -> T (a+1) b }
1402 -- We really must record that b is already evaluated so that we don't
1403 -- go and re-evaluate it when constructing the result.
1405 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1406 add_evals other_con vs = vs
1408 cat_evals [] [] = []
1409 cat_evals (v:vs) (str:strs)
1410 | isTyVar v = v : cat_evals vs (str:strs)
1411 | isMarkedStrict str = evald_v : cat_evals vs strs
1412 | otherwise = zapped_v : cat_evals vs strs
1414 zapped_v = zap_occ_info v
1415 evald_v = zapped_v `setIdUnfolding` mkOtherCon []
1419 %************************************************************************
1421 \subsection{Known constructor}
1423 %************************************************************************
1425 We are a bit careful with occurrence info. Here's an example
1427 (\x* -> case x of (a*, b) -> f a) (h v, e)
1429 where the * means "occurs once". This effectively becomes
1430 case (h v, e) of (a*, b) -> f a)
1432 let a* = h v; b = e in f a
1436 All this should happen in one sweep.
1439 knownCon :: SimplEnv -> AltCon -> [OutExpr]
1440 -> InId -> [InAlt] -> SimplCont
1441 -> SimplM FloatsWithExpr
1443 knownCon env con args bndr alts cont
1444 = tick (KnownBranch bndr) `thenSmpl_`
1445 case findAlt con alts of
1446 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1447 simplNonRecX env bndr scrut $ \ env ->
1448 -- This might give rise to a binding with non-atomic args
1449 -- like x = Node (f x) (g x)
1450 -- but no harm will be done
1451 simplExprF env rhs cont
1454 LitAlt lit -> Lit lit
1455 DataAlt dc -> mkConApp dc args
1457 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1458 simplNonRecX env bndr (Lit lit) $ \ env ->
1459 simplExprF env rhs cont
1461 (DataAlt dc, bs, rhs) -> ASSERT( length bs + n_tys == length args )
1462 bind_args env bs (drop n_tys args) $ \ env ->
1464 con_app = mkConApp dc (take n_tys args ++ con_args)
1465 con_args = [substExpr (getSubst env) (varToCoreExpr b) | b <- bs]
1466 -- args are aready OutExprs, but bs are InIds
1468 simplNonRecX env bndr con_app $ \ env ->
1469 simplExprF env rhs cont
1471 n_tys = dataConNumInstArgs dc -- Non-existential type args
1473 bind_args env [] _ thing_inside = thing_inside env
1475 bind_args env (b:bs) (Type ty : args) thing_inside
1476 = bind_args (extendSubst env b (DoneTy ty)) bs args thing_inside
1478 bind_args env (b:bs) (arg : args) thing_inside
1479 = simplNonRecX env b arg $ \ env ->
1480 bind_args env bs args thing_inside
1484 %************************************************************************
1486 \subsection{Duplicating continuations}
1488 %************************************************************************
1491 prepareCaseCont :: SimplEnv
1492 -> [InAlt] -> SimplCont
1493 -> SimplM (FloatsWith (SimplCont,SimplCont))
1494 -- Return a duplicatable continuation, a non-duplicable part
1495 -- plus some extra bindings
1497 -- No need to make it duplicatable if there's only one alternative
1498 prepareCaseCont env [alt] cont = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
1499 prepareCaseCont env alts cont = mkDupableCont env cont
1503 mkDupableCont :: SimplEnv -> SimplCont
1504 -> SimplM (FloatsWith (SimplCont, SimplCont))
1506 mkDupableCont env cont
1507 | contIsDupable cont
1508 = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
1510 mkDupableCont env (CoerceIt ty cont)
1511 = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1512 returnSmpl (floats, (CoerceIt ty dup_cont, nondup_cont))
1514 mkDupableCont env (InlinePlease cont)
1515 = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1516 returnSmpl (floats, (InlinePlease dup_cont, nondup_cont))
1518 mkDupableCont env cont@(ArgOf _ arg_ty _ _)
1519 = returnSmpl (emptyFloats env, (mkBoringStop arg_ty, cont))
1520 -- Do *not* duplicate an ArgOf continuation
1521 -- Because ArgOf continuations are opaque, we gain nothing by
1522 -- propagating them into the expressions, and we do lose a lot.
1523 -- Here's an example:
1524 -- && (case x of { T -> F; F -> T }) E
1525 -- Now, && is strict so we end up simplifying the case with
1526 -- an ArgOf continuation. If we let-bind it, we get
1528 -- let $j = \v -> && v E
1529 -- in simplExpr (case x of { T -> F; F -> T })
1530 -- (ArgOf (\r -> $j r)
1531 -- And after simplifying more we get
1533 -- let $j = \v -> && v E
1534 -- in case of { T -> $j F; F -> $j T }
1535 -- Which is a Very Bad Thing
1537 -- The desire not to duplicate is the entire reason that
1538 -- mkDupableCont returns a pair of continuations.
1540 -- The original plan had:
1541 -- e.g. (...strict-fn...) [...hole...]
1543 -- let $j = \a -> ...strict-fn...
1544 -- in $j [...hole...]
1546 mkDupableCont env (ApplyTo _ arg se cont)
1547 = -- e.g. [...hole...] (...arg...)
1549 -- let a = ...arg...
1550 -- in [...hole...] a
1551 simplExpr (setInScope se env) arg `thenSmpl` \ arg' ->
1553 mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1554 addFloats env floats $ \ env ->
1556 if exprIsDupable arg' then
1557 returnSmpl (emptyFloats env, (ApplyTo OkToDup arg' (zapSubstEnv se) dup_cont, nondup_cont))
1559 newId SLIT("a") (exprType arg') `thenSmpl` \ arg_id ->
1561 tick (CaseOfCase arg_id) `thenSmpl_`
1562 -- Want to tick here so that we go round again,
1563 -- and maybe copy or inline the code.
1564 -- Not strictly CaseOfCase, but never mind
1566 returnSmpl (unitFloat env arg_id arg',
1567 (ApplyTo OkToDup (Var arg_id) (zapSubstEnv se) dup_cont,
1569 -- But what if the arg should be case-bound?
1570 -- This has been this way for a long time, so I'll leave it,
1571 -- but I can't convince myself that it's right.
1574 mkDupableCont env (Select _ case_bndr alts se cont)
1575 = -- e.g. (case [...hole...] of { pi -> ei })
1577 -- let ji = \xij -> ei
1578 -- in case [...hole...] of { pi -> ji xij }
1579 tick (CaseOfCase case_bndr) `thenSmpl_`
1581 alt_env = setInScope se env
1583 prepareCaseCont alt_env alts cont `thenSmpl` \ (floats1, (dup_cont, nondup_cont)) ->
1584 addFloats alt_env floats1 $ \ alt_env ->
1586 simplBinder alt_env case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
1587 -- NB: simplBinder does not zap deadness occ-info, so
1588 -- a dead case_bndr' will still advertise its deadness
1589 -- This is really important because in
1590 -- case e of b { (# a,b #) -> ... }
1591 -- b is always dead, and indeed we are not allowed to bind b to (# a,b #),
1592 -- which might happen if e was an explicit unboxed pair and b wasn't marked dead.
1593 -- In the new alts we build, we have the new case binder, so it must retain
1596 mkDupableAlts alt_env case_bndr' alts dup_cont `thenSmpl` \ (floats2, alts') ->
1597 addFloats alt_env floats2 $ \ alt_env ->
1598 returnSmpl (emptyFloats alt_env,
1599 (Select OkToDup case_bndr' alts' (zapSubstEnv se)
1600 (mkBoringStop (contResultType dup_cont)),
1603 mkDupableAlts :: SimplEnv -> OutId -> [InAlt] -> SimplCont
1604 -> SimplM (FloatsWith [InAlt])
1605 -- Absorbs the continuation into the new alternatives
1607 mkDupableAlts env case_bndr' alts dupable_cont
1610 go env [] = returnSmpl (emptyFloats env, [])
1612 = mkDupableAlt env case_bndr' dupable_cont alt `thenSmpl` \ (floats1, alt') ->
1613 addFloats env floats1 $ \ env ->
1614 go env alts `thenSmpl` \ (floats2, alts') ->
1615 returnSmpl (floats2, alt' : alts')
1617 mkDupableAlt env case_bndr' cont alt@(con, bndrs, rhs)
1618 = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
1619 simplExprC env rhs cont `thenSmpl` \ rhs' ->
1621 if exprIsDupable rhs' then
1622 returnSmpl (emptyFloats env, (con, bndrs', rhs'))
1623 -- It is worth checking for a small RHS because otherwise we
1624 -- get extra let bindings that may cause an extra iteration of the simplifier to
1625 -- inline back in place. Quite often the rhs is just a variable or constructor.
1626 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1627 -- iterations because the version with the let bindings looked big, and so wasn't
1628 -- inlined, but after the join points had been inlined it looked smaller, and so
1631 -- NB: we have to check the size of rhs', not rhs.
1632 -- Duplicating a small InAlt might invalidate occurrence information
1633 -- However, if it *is* dupable, we return the *un* simplified alternative,
1634 -- because otherwise we'd need to pair it up with an empty subst-env....
1635 -- but we only have one env shared between all the alts.
1636 -- (Remember we must zap the subst-env before re-simplifying something).
1637 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1641 rhs_ty' = exprType rhs'
1642 used_bndrs' = filter (not . isDeadBinder) (case_bndr' : bndrs')
1643 -- The deadness info on the new binders is unscathed
1645 -- If we try to lift a primitive-typed something out
1646 -- for let-binding-purposes, we will *caseify* it (!),
1647 -- with potentially-disastrous strictness results. So
1648 -- instead we turn it into a function: \v -> e
1649 -- where v::State# RealWorld#. The value passed to this function
1650 -- is realworld#, which generates (almost) no code.
1652 -- There's a slight infelicity here: we pass the overall
1653 -- case_bndr to all the join points if it's used in *any* RHS,
1654 -- because we don't know its usage in each RHS separately
1656 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1657 -- we make the join point into a function whenever used_bndrs'
1658 -- is empty. This makes the join-point more CPR friendly.
1659 -- Consider: let j = if .. then I# 3 else I# 4
1660 -- in case .. of { A -> j; B -> j; C -> ... }
1662 -- Now CPR doesn't w/w j because it's a thunk, so
1663 -- that means that the enclosing function can't w/w either,
1664 -- which is a lose. Here's the example that happened in practice:
1665 -- kgmod :: Int -> Int -> Int
1666 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1670 -- I have seen a case alternative like this:
1671 -- True -> \v -> ...
1672 -- It's a bit silly to add the realWorld dummy arg in this case, making
1675 -- (the \v alone is enough to make CPR happy) but I think it's rare
1677 ( if null used_bndrs'
1678 then newId SLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id ->
1679 returnSmpl ([rw_id], [Var realWorldPrimId])
1681 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs')
1682 ) `thenSmpl` \ (final_bndrs', final_args) ->
1684 -- See comment about "$j" name above
1685 newId SLIT("$j") (mkPiTypes final_bndrs' rhs_ty') `thenSmpl` \ join_bndr ->
1686 -- Notice the funky mkPiTypes. If the contructor has existentials
1687 -- it's possible that the join point will be abstracted over
1688 -- type varaibles as well as term variables.
1689 -- Example: Suppose we have
1690 -- data T = forall t. C [t]
1692 -- case (case e of ...) of
1693 -- C t xs::[t] -> rhs
1694 -- We get the join point
1695 -- let j :: forall t. [t] -> ...
1696 -- j = /\t \xs::[t] -> rhs
1698 -- case (case e of ...) of
1699 -- C t xs::[t] -> j t xs
1701 -- We make the lambdas into one-shot-lambdas. The
1702 -- join point is sure to be applied at most once, and doing so
1703 -- prevents the body of the join point being floated out by
1704 -- the full laziness pass
1705 really_final_bndrs = map one_shot final_bndrs'
1706 one_shot v | isId v = setOneShotLambda v
1708 join_rhs = mkLams really_final_bndrs rhs'
1709 join_call = mkApps (Var join_bndr) final_args
1711 returnSmpl (unitFloat env join_bndr join_rhs, (con, bndrs', join_call))