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, prepareAlts,
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 setIdUnfolding, isDeadBinder,
26 idNewDemandInfo, setIdInfo,
27 setIdOccInfo, zapLamIdInfo, setOneShotLambda,
29 import OccName ( encodeFS )
30 import IdInfo ( OccInfo(..), isLoopBreaker,
35 import NewDemand ( isStrictDmd )
36 import DataCon ( dataConNumInstArgs, dataConRepStrictness )
38 import PprCore ( pprParendExpr, pprCoreExpr )
39 import CoreUnfold ( mkOtherCon, mkUnfolding, callSiteInline )
40 import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding,
41 exprIsConApp_maybe, mkPiTypes, findAlt,
42 exprType, exprIsValue,
43 exprOkForSpeculation, exprArity,
44 mkCoerce, mkSCC, mkInlineMe, mkAltExpr, applyTypeToArg
46 import Rules ( lookupRule )
47 import BasicTypes ( isMarkedStrict )
48 import CostCentre ( currentCCS )
49 import Type ( isUnLiftedType, seqType, tyConAppArgs, funArgTy,
50 splitFunTy_maybe, splitFunTy, eqType
52 import Subst ( mkSubst, substTy, substExpr,
53 isInScope, lookupIdSubst, simplIdInfo
55 import TysPrim ( realWorldStatePrimTy )
56 import PrelInfo ( realWorldPrimId )
57 import BasicTypes ( TopLevelFlag(..), isTopLevel,
61 import Maybe ( Maybe )
66 The guts of the simplifier is in this module, but the driver loop for
67 the simplifier is in SimplCore.lhs.
70 -----------------------------------------
71 *** IMPORTANT NOTE ***
72 -----------------------------------------
73 The simplifier used to guarantee that the output had no shadowing, but
74 it does not do so any more. (Actually, it never did!) The reason is
75 documented with simplifyArgs.
78 -----------------------------------------
79 *** IMPORTANT NOTE ***
80 -----------------------------------------
81 Many parts of the simplifier return a bunch of "floats" as well as an
82 expression. This is wrapped as a datatype SimplUtils.FloatsWith.
84 All "floats" are let-binds, not case-binds, but some non-rec lets may
85 be unlifted (with RHS ok-for-speculation).
89 -----------------------------------------
90 ORGANISATION OF FUNCTIONS
91 -----------------------------------------
93 - simplify all top-level binders
94 - for NonRec, call simplRecOrTopPair
95 - for Rec, call simplRecBind
98 ------------------------------
99 simplExpr (applied lambda) ==> simplNonRecBind
100 simplExpr (Let (NonRec ...) ..) ==> simplNonRecBind
101 simplExpr (Let (Rec ...) ..) ==> simplify binders; simplRecBind
103 ------------------------------
104 simplRecBind [binders already simplfied]
105 - use simplRecOrTopPair on each pair in turn
107 simplRecOrTopPair [binder already simplified]
108 Used for: recursive bindings (top level and nested)
109 top-level non-recursive bindings
111 - check for PreInlineUnconditionally
115 Used for: non-top-level non-recursive bindings
116 beta reductions (which amount to the same thing)
117 Because it can deal with strict arts, it takes a
118 "thing-inside" and returns an expression
120 - check for PreInlineUnconditionally
121 - simplify binder, including its IdInfo
130 simplNonRecX: [given a *simplified* RHS, but an *unsimplified* binder]
131 Used for: binding case-binder and constr args in a known-constructor case
132 - check for PreInLineUnconditionally
136 ------------------------------
137 simplLazyBind: [binder already simplified, RHS not]
138 Used for: recursive bindings (top level and nested)
139 top-level non-recursive bindings
140 non-top-level, but *lazy* non-recursive bindings
141 [must not be strict or unboxed]
142 Returns floats + an augmented environment, not an expression
143 - substituteIdInfo and add result to in-scope
144 [so that rules are available in rec rhs]
147 - float if exposes constructor or PAP
151 completeNonRecX: [binder and rhs both simplified]
152 - if the the thing needs case binding (unlifted and not ok-for-spec)
158 completeLazyBind: [given a simplified RHS]
159 [used for both rec and non-rec bindings, top level and not]
160 - try PostInlineUnconditionally
161 - add unfolding [this is the only place we add an unfolding]
166 Right hand sides and arguments
167 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
168 In many ways we want to treat
169 (a) the right hand side of a let(rec), and
170 (b) a function argument
171 in the same way. But not always! In particular, we would
172 like to leave these arguments exactly as they are, so they
173 will match a RULE more easily.
178 It's harder to make the rule match if we ANF-ise the constructor,
179 or eta-expand the PAP:
181 f (let { a = g x; b = h x } in (a,b))
184 On the other hand if we see the let-defns
189 then we *do* want to ANF-ise and eta-expand, so that p and q
190 can be safely inlined.
192 Even floating lets out is a bit dubious. For let RHS's we float lets
193 out if that exposes a value, so that the value can be inlined more vigorously.
196 r = let x = e in (x,x)
198 Here, if we float the let out we'll expose a nice constructor. We did experiments
199 that showed this to be a generally good thing. But it was a bad thing to float
200 lets out unconditionally, because that meant they got allocated more often.
202 For function arguments, there's less reason to expose a constructor (it won't
203 get inlined). Just possibly it might make a rule match, but I'm pretty skeptical.
204 So for the moment we don't float lets out of function arguments either.
209 For eta expansion, we want to catch things like
211 case e of (a,b) -> \x -> case a of (p,q) -> \y -> r
213 If the \x was on the RHS of a let, we'd eta expand to bring the two
214 lambdas together. And in general that's a good thing to do. Perhaps
215 we should eta expand wherever we find a (value) lambda? Then the eta
216 expansion at a let RHS can concentrate solely on the PAP case.
219 %************************************************************************
221 \subsection{Bindings}
223 %************************************************************************
226 simplTopBinds :: SimplEnv -> [InBind] -> SimplM [OutBind]
228 simplTopBinds env binds
229 = -- Put all the top-level binders into scope at the start
230 -- so that if a transformation rule has unexpectedly brought
231 -- anything into scope, then we don't get a complaint about that.
232 -- It's rather as if the top-level binders were imported.
233 simplRecBndrs env (bindersOfBinds binds) `thenSmpl` \ (env, bndrs') ->
234 simpl_binds env binds bndrs' `thenSmpl` \ (floats, _) ->
235 freeTick SimplifierDone `thenSmpl_`
236 returnSmpl (floatBinds floats)
238 -- We need to track the zapped top-level binders, because
239 -- they should have their fragile IdInfo zapped (notably occurrence info)
240 -- That's why we run down binds and bndrs' simultaneously.
241 simpl_binds :: SimplEnv -> [InBind] -> [OutId] -> SimplM (FloatsWith ())
242 simpl_binds env [] bs = ASSERT( null bs ) returnSmpl (emptyFloats env, ())
243 simpl_binds env (bind:binds) bs = simpl_bind env bind bs `thenSmpl` \ (floats,env) ->
244 addFloats env floats $ \env ->
245 simpl_binds env binds (drop_bs bind bs)
247 drop_bs (NonRec _ _) (_ : bs) = bs
248 drop_bs (Rec prs) bs = drop (length prs) bs
250 simpl_bind env (NonRec b r) (b':_) = simplRecOrTopPair env TopLevel b b' r
251 simpl_bind env (Rec pairs) bs' = simplRecBind env TopLevel pairs bs'
255 %************************************************************************
257 \subsection{simplNonRec}
259 %************************************************************************
261 simplNonRecBind is used for
262 * non-top-level non-recursive lets in expressions
266 * An unsimplified (binder, rhs) pair
267 * The env for the RHS. It may not be the same as the
268 current env because the bind might occur via (\x.E) arg
270 It uses the CPS form because the binding might be strict, in which
271 case we might discard the continuation:
272 let x* = error "foo" in (...x...)
274 It needs to turn unlifted bindings into a @case@. They can arise
275 from, say: (\x -> e) (4# + 3#)
278 simplNonRecBind :: SimplEnv
280 -> InExpr -> SimplEnv -- Arg, with its subst-env
281 -> OutType -- Type of thing computed by the context
282 -> (SimplEnv -> SimplM FloatsWithExpr) -- The body
283 -> SimplM FloatsWithExpr
285 simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
287 = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
290 simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
291 | preInlineUnconditionally env NotTopLevel bndr
292 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
293 thing_inside (extendSubst env bndr (ContEx (getSubstEnv rhs_se) rhs))
296 | isStrictDmd (idNewDemandInfo bndr) || isStrictType (idType bndr) -- A strict let
297 = -- Don't use simplBinder because that doesn't keep
298 -- fragile occurrence info in the substitution
299 simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
301 -- simplLetBndr doesn't deal with the IdInfo, so we must
302 -- do so here (c.f. simplLazyBind)
303 bndr'' = bndr' `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
304 env1 = modifyInScope env bndr'' bndr''
306 simplStrictArg AnRhs env1 rhs rhs_se (idType bndr') cont_ty $ \ env rhs1 ->
308 -- Now complete the binding and simplify the body
309 completeNonRecX env True {- strict -} bndr bndr'' rhs1 thing_inside
311 | otherwise -- Normal, lazy case
312 = -- Don't use simplBinder because that doesn't keep
313 -- fragile occurrence info in the substitution
314 simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
315 simplLazyBind env NotTopLevel NonRecursive
316 bndr bndr' rhs rhs_se `thenSmpl` \ (floats, env) ->
317 addFloats env floats thing_inside
320 A specialised variant of simplNonRec used when the RHS is already simplified, notably
321 in knownCon. It uses case-binding where necessary.
324 simplNonRecX :: SimplEnv
325 -> InId -- Old binder
326 -> OutExpr -- Simplified RHS
327 -> (SimplEnv -> SimplM FloatsWithExpr)
328 -> SimplM FloatsWithExpr
330 simplNonRecX env bndr new_rhs thing_inside
331 | needsCaseBinding (idType bndr) new_rhs
332 -- Make this test *before* the preInlineUnconditionally
333 -- Consider case I# (quotInt# x y) of
334 -- I# v -> let w = J# v in ...
335 -- If we gaily inline (quotInt# x y) for v, we end up building an
337 -- let w = J# (quotInt# x y) in ...
338 -- because quotInt# can fail.
339 = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
340 thing_inside env `thenSmpl` \ (floats, body) ->
341 returnSmpl (emptyFloats env, Case new_rhs bndr' [(DEFAULT, [], wrapFloats floats body)])
343 | preInlineUnconditionally env NotTopLevel bndr
344 -- This happens; for example, the case_bndr during case of
345 -- known constructor: case (a,b) of x { (p,q) -> ... }
346 -- Here x isn't mentioned in the RHS, so we don't want to
347 -- create the (dead) let-binding let x = (a,b) in ...
349 -- Similarly, single occurrences can be inlined vigourously
350 -- e.g. case (f x, g y) of (a,b) -> ....
351 -- If a,b occur once we can avoid constructing the let binding for them.
352 = thing_inside (extendSubst env bndr (ContEx emptySubstEnv new_rhs))
355 = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
356 completeNonRecX env False {- Non-strict; pessimistic -}
357 bndr bndr' new_rhs thing_inside
359 completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside
360 = mkAtomicArgs is_strict
361 True {- OK to float unlifted -}
362 new_rhs `thenSmpl` \ (aux_binds, rhs2) ->
364 -- Make the arguments atomic if necessary,
365 -- adding suitable bindings
366 addAtomicBindsE env (fromOL aux_binds) $ \ env ->
367 completeLazyBind env NotTopLevel
368 old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) ->
369 addFloats env floats thing_inside
373 %************************************************************************
375 \subsection{Lazy bindings}
377 %************************************************************************
379 simplRecBind is used for
380 * recursive bindings only
383 simplRecBind :: SimplEnv -> TopLevelFlag
384 -> [(InId, InExpr)] -> [OutId]
385 -> SimplM (FloatsWith SimplEnv)
386 simplRecBind env top_lvl pairs bndrs'
387 = go env pairs bndrs' `thenSmpl` \ (floats, env) ->
388 returnSmpl (flattenFloats floats, env)
390 go env [] _ = returnSmpl (emptyFloats env, env)
392 go env ((bndr, rhs) : pairs) (bndr' : bndrs')
393 = simplRecOrTopPair env top_lvl bndr bndr' rhs `thenSmpl` \ (floats, env) ->
394 addFloats env floats (\env -> go env pairs bndrs')
398 simplRecOrTopPair is used for
399 * recursive bindings (whether top level or not)
400 * top-level non-recursive bindings
402 It assumes the binder has already been simplified, but not its IdInfo.
405 simplRecOrTopPair :: SimplEnv
407 -> InId -> OutId -- Binder, both pre-and post simpl
408 -> InExpr -- The RHS and its environment
409 -> SimplM (FloatsWith SimplEnv)
411 simplRecOrTopPair env top_lvl bndr bndr' rhs
412 | preInlineUnconditionally env top_lvl bndr -- Check for unconditional inline
413 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
414 returnSmpl (emptyFloats env, extendSubst env bndr (ContEx (getSubstEnv env) rhs))
417 = simplLazyBind env top_lvl Recursive bndr bndr' rhs env
418 -- May not actually be recursive, but it doesn't matter
422 simplLazyBind is used for
423 * recursive bindings (whether top level or not)
424 * top-level non-recursive bindings
425 * non-top-level *lazy* non-recursive bindings
427 [Thus it deals with the lazy cases from simplNonRecBind, and all cases
428 from SimplRecOrTopBind]
431 1. It assumes that the binder is *already* simplified,
432 and is in scope, but not its IdInfo
434 2. It assumes that the binder type is lifted.
436 3. It does not check for pre-inline-unconditionallly;
437 that should have been done already.
440 simplLazyBind :: SimplEnv
441 -> TopLevelFlag -> RecFlag
442 -> InId -> OutId -- Binder, both pre-and post simpl
443 -> InExpr -> SimplEnv -- The RHS and its environment
444 -> SimplM (FloatsWith SimplEnv)
446 simplLazyBind env top_lvl is_rec bndr bndr' rhs rhs_se
447 = -- Substitute IdInfo on binder, in the light of earlier
448 -- substitutions in this very letrec, and extend the
449 -- in-scope env, so that the IdInfo for this binder extends
450 -- over the RHS for the binder itself.
452 -- This is important. Manuel found cases where he really, really
453 -- wanted a RULE for a recursive function to apply in that function's
454 -- own right-hand side.
456 -- NB: does no harm for non-recursive bindings
458 bndr'' = bndr' `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
459 env1 = modifyInScope env bndr'' bndr''
460 rhs_env = setInScope rhs_se env1
461 is_top_level = isTopLevel top_lvl
462 ok_float_unlifted = not is_top_level && isNonRec is_rec
463 rhs_cont = mkStop (idType bndr') AnRhs
465 -- Simplify the RHS; note the mkStop, which tells
466 -- the simplifier that this is the RHS of a let.
467 simplExprF rhs_env rhs rhs_cont `thenSmpl` \ (floats, rhs1) ->
469 -- If any of the floats can't be floated, give up now
470 -- (The allLifted predicate says True for empty floats.)
471 if (not ok_float_unlifted && not (allLifted floats)) then
472 completeLazyBind env1 top_lvl bndr bndr''
473 (wrapFloats floats rhs1)
476 -- ANF-ise a constructor or PAP rhs
477 mkAtomicArgs False {- Not strict -}
478 ok_float_unlifted rhs1 `thenSmpl` \ (aux_binds, rhs2) ->
480 -- If the result is a PAP, float the floats out, else wrap them
481 -- By this time it's already been ANF-ised (if necessary)
482 if isEmptyFloats floats && isNilOL aux_binds then -- Shortcut a common case
483 completeLazyBind env1 top_lvl bndr bndr'' rhs2
485 -- We use exprIsTrivial here because we want to reveal lone variables.
486 -- E.g. let { x = letrec { y = E } in y } in ...
487 -- Here we definitely want to float the y=E defn.
488 -- exprIsValue definitely isn't right for that.
490 -- BUT we can't use "exprIsCheap", because that causes a strictness bug.
491 -- x = let y* = E in case (scc y) of { T -> F; F -> T}
492 -- The case expression is 'cheap', but it's wrong to transform to
493 -- y* = E; x = case (scc y) of {...}
494 -- Either we must be careful not to float demanded non-values, or
495 -- we must use exprIsValue for the test, which ensures that the
496 -- thing is non-strict. I think. The WARN below tests for this.
497 else if is_top_level || exprIsTrivial rhs2 || exprIsValue rhs2 then
499 -- There's a subtlety here. There may be a binding (x* = e) in the
500 -- floats, where the '*' means 'will be demanded'. So is it safe
501 -- to float it out? Answer no, but it won't matter because
502 -- we only float if arg' is a WHNF,
503 -- and so there can't be any 'will be demanded' bindings in the floats.
505 WARN( any demanded_float (floatBinds floats),
506 ppr (filter demanded_float (floatBinds floats)) )
508 tick LetFloatFromLet `thenSmpl_` (
509 addFloats env1 floats $ \ env2 ->
510 addAtomicBinds env2 (fromOL aux_binds) $ \ env3 ->
511 completeLazyBind env3 top_lvl bndr bndr'' rhs2)
514 completeLazyBind env1 top_lvl bndr bndr'' (wrapFloats floats rhs1)
517 demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b))
518 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
519 demanded_float (Rec _) = False
524 %************************************************************************
526 \subsection{Completing a lazy binding}
528 %************************************************************************
531 * deals only with Ids, not TyVars
532 * takes an already-simplified binder and RHS
533 * is used for both recursive and non-recursive bindings
534 * is used for both top-level and non-top-level bindings
536 It does the following:
537 - tries discarding a dead binding
538 - tries PostInlineUnconditionally
539 - add unfolding [this is the only place we add an unfolding]
542 It does *not* attempt to do let-to-case. Why? Because it is used for
543 - top-level bindings (when let-to-case is impossible)
544 - many situations where the "rhs" is known to be a WHNF
545 (so let-to-case is inappropriate).
548 completeLazyBind :: SimplEnv
549 -> TopLevelFlag -- Flag stuck into unfolding
550 -> InId -- Old binder
551 -> OutId -- New binder
552 -> OutExpr -- Simplified RHS
553 -> SimplM (FloatsWith SimplEnv)
554 -- We return a new SimplEnv, because completeLazyBind may choose to do its work
555 -- by extending the substitution (e.g. let x = y in ...)
556 -- The new binding (if any) is returned as part of the floats.
557 -- NB: the returned SimplEnv has the right SubstEnv, but you should
558 -- (as usual) use the in-scope-env from the floats
560 completeLazyBind env top_lvl old_bndr new_bndr new_rhs
561 | postInlineUnconditionally env new_bndr occ_info new_rhs
562 = -- Drop the binding
563 tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
564 returnSmpl (emptyFloats env, extendSubst env old_bndr (DoneEx new_rhs))
565 -- Use the substitution to make quite, quite sure that the substitution
566 -- will happen, since we are going to discard the binding
571 new_bndr_info = idInfo new_bndr `setArityInfo` exprArity new_rhs
573 -- Add the unfolding *only* for non-loop-breakers
574 -- Making loop breakers not have an unfolding at all
575 -- means that we can avoid tests in exprIsConApp, for example.
576 -- This is important: if exprIsConApp says 'yes' for a recursive
577 -- thing, then we can get into an infinite loop
578 info_w_unf | loop_breaker = new_bndr_info
579 | otherwise = new_bndr_info `setUnfoldingInfo` unfolding
580 unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs
582 final_id = new_bndr `setIdInfo` info_w_unf
584 -- These seqs forces the Id, and hence its IdInfo,
585 -- and hence any inner substitutions
587 returnSmpl (unitFloat env final_id new_rhs, env)
590 loop_breaker = isLoopBreaker occ_info
591 old_info = idInfo old_bndr
592 occ_info = occInfo old_info
597 %************************************************************************
599 \subsection[Simplify-simplExpr]{The main function: simplExpr}
601 %************************************************************************
603 The reason for this OutExprStuff stuff is that we want to float *after*
604 simplifying a RHS, not before. If we do so naively we get quadratic
605 behaviour as things float out.
607 To see why it's important to do it after, consider this (real) example:
621 a -- Can't inline a this round, cos it appears twice
625 Each of the ==> steps is a round of simplification. We'd save a
626 whole round if we float first. This can cascade. Consider
631 let f = let d1 = ..d.. in \y -> e
635 in \x -> ...(\y ->e)...
637 Only in this second round can the \y be applied, and it
638 might do the same again.
642 simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
643 simplExpr env expr = simplExprC env expr (mkStop expr_ty' AnArg)
645 expr_ty' = substTy (getSubst env) (exprType expr)
646 -- The type in the Stop continuation, expr_ty', is usually not used
647 -- It's only needed when discarding continuations after finding
648 -- a function that returns bottom.
649 -- Hence the lazy substitution
652 simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
653 -- Simplify an expression, given a continuation
654 simplExprC env expr cont
655 = simplExprF env expr cont `thenSmpl` \ (floats, expr) ->
656 returnSmpl (wrapFloats floats expr)
658 simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM FloatsWithExpr
659 -- Simplify an expression, returning floated binds
661 simplExprF env (Var v) cont = simplVar env v cont
662 simplExprF env (Lit lit) cont = rebuild env (Lit lit) cont
663 simplExprF env expr@(Lam _ _) cont = simplLam env expr cont
664 simplExprF env (Note note expr) cont = simplNote env note expr cont
665 simplExprF env (App fun arg) cont = simplExprF env fun (ApplyTo NoDup arg env cont)
667 simplExprF env (Type ty) cont
668 = ASSERT( contIsRhsOrArg cont )
669 simplType env ty `thenSmpl` \ ty' ->
670 rebuild env (Type ty') cont
672 simplExprF env (Case scrut bndr alts) cont
673 | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
674 = -- Simplify the scrutinee with a Select continuation
675 simplExprF env scrut (Select NoDup bndr alts env cont)
678 = -- If case-of-case is off, simply simplify the case expression
679 -- in a vanilla Stop context, and rebuild the result around it
680 simplExprC env scrut case_cont `thenSmpl` \ case_expr' ->
681 rebuild env case_expr' cont
683 case_cont = Select NoDup bndr alts env (mkBoringStop (contResultType cont))
685 simplExprF env (Let (Rec pairs) body) cont
686 = simplRecBndrs env (map fst pairs) `thenSmpl` \ (env, bndrs') ->
687 -- NB: bndrs' don't have unfoldings or spec-envs
688 -- We add them as we go down, using simplPrags
690 simplRecBind env NotTopLevel pairs bndrs' `thenSmpl` \ (floats, env) ->
691 addFloats env floats $ \ env ->
692 simplExprF env body cont
694 -- A non-recursive let is dealt with by simplNonRecBind
695 simplExprF env (Let (NonRec bndr rhs) body) cont
696 = simplNonRecBind env bndr rhs env (contResultType cont) $ \ env ->
697 simplExprF env body cont
700 ---------------------------------
701 simplType :: SimplEnv -> InType -> SimplM OutType
702 -- Kept monadic just so we can do the seqType
704 = seqType new_ty `seq` returnSmpl new_ty
706 new_ty = substTy (getSubst env) ty
710 %************************************************************************
714 %************************************************************************
717 simplLam env fun cont
720 zap_it = mkLamBndrZapper fun (countArgs cont)
721 cont_ty = contResultType cont
723 -- Type-beta reduction
724 go env (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
725 = ASSERT( isTyVar bndr )
726 tick (BetaReduction bndr) `thenSmpl_`
727 simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' ->
728 go (extendSubst env bndr (DoneTy ty_arg')) body body_cont
730 -- Ordinary beta reduction
731 go env (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
732 = tick (BetaReduction bndr) `thenSmpl_`
733 simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env ->
734 go env body body_cont
736 -- Not enough args, so there are real lambdas left to put in the result
737 go env lam@(Lam _ _) cont
738 = simplLamBndrs env bndrs `thenSmpl` \ (env, bndrs') ->
739 simplExpr env body `thenSmpl` \ body' ->
740 mkLam env bndrs' body' cont `thenSmpl` \ (floats, new_lam) ->
741 addFloats env floats $ \ env ->
742 rebuild env new_lam cont
744 (bndrs,body) = collectBinders lam
746 -- Exactly enough args
747 go env expr cont = simplExprF env expr cont
749 mkLamBndrZapper :: CoreExpr -- Function
750 -> Int -- Number of args supplied, *including* type args
751 -> Id -> Id -- Use this to zap the binders
752 mkLamBndrZapper fun n_args
753 | n_args >= n_params fun = \b -> b -- Enough args
754 | otherwise = \b -> zapLamIdInfo b
756 -- NB: we count all the args incl type args
757 -- so we must count all the binders (incl type lambdas)
758 n_params (Note _ e) = n_params e
759 n_params (Lam b e) = 1 + n_params e
760 n_params other = 0::Int
764 %************************************************************************
768 %************************************************************************
771 simplNote env (Coerce to from) body cont
773 in_scope = getInScope env
775 addCoerce s1 k1 (CoerceIt t1 cont)
776 -- coerce T1 S1 (coerce S1 K1 e)
779 -- coerce T1 K1 e, otherwise
781 -- For example, in the initial form of a worker
782 -- we may find (coerce T (coerce S (\x.e))) y
783 -- and we'd like it to simplify to e[y/x] in one round
785 | t1 `eqType` k1 = cont -- The coerces cancel out
786 | otherwise = CoerceIt t1 cont -- They don't cancel, but
787 -- the inner one is redundant
789 addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
790 | Just (s1, s2) <- splitFunTy_maybe s1s2
791 -- (coerce (T1->T2) (S1->S2) F) E
793 -- coerce T2 S2 (F (coerce S1 T1 E))
795 -- t1t2 must be a function type, T1->T2
796 -- but s1s2 might conceivably not be
798 -- When we build the ApplyTo we can't mix the out-types
799 -- with the InExpr in the argument, so we simply substitute
800 -- to make it all consistent. It's a bit messy.
801 -- But it isn't a common case.
803 (t1,t2) = splitFunTy t1t2
804 new_arg = mkCoerce s1 t1 (substExpr (mkSubst in_scope (getSubstEnv arg_se)) arg)
806 ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont)
808 addCoerce to' _ cont = CoerceIt to' cont
810 simplType env to `thenSmpl` \ to' ->
811 simplType env from `thenSmpl` \ from' ->
812 simplExprF env body (addCoerce to' from' cont)
815 -- Hack: we only distinguish subsumed cost centre stacks for the purposes of
816 -- inlining. All other CCCSs are mapped to currentCCS.
817 simplNote env (SCC cc) e cont
818 = simplExpr (setEnclosingCC env currentCCS) e `thenSmpl` \ e' ->
819 rebuild env (mkSCC cc e') cont
821 simplNote env InlineCall e cont
822 = simplExprF env e (InlinePlease cont)
824 -- See notes with SimplMonad.inlineMode
825 simplNote env InlineMe e cont
826 | contIsRhsOrArg cont -- Totally boring continuation; see notes above
827 = -- Don't inline inside an INLINE expression
828 simplExpr (setMode inlineMode env ) e `thenSmpl` \ e' ->
829 rebuild env (mkInlineMe e') cont
831 | otherwise -- Dissolve the InlineMe note if there's
832 -- an interesting context of any kind to combine with
833 -- (even a type application -- anything except Stop)
834 = simplExprF env e cont
838 %************************************************************************
840 \subsection{Dealing with calls}
842 %************************************************************************
845 simplVar env var cont
846 = case lookupIdSubst (getSubst env) var of
847 DoneEx e -> simplExprF (zapSubstEnv env) e cont
848 ContEx se e -> simplExprF (setSubstEnv env se) e cont
849 DoneId var1 occ -> WARN( not (isInScope var1 (getSubst env)) && mustHaveLocalBinding var1,
850 text "simplVar:" <+> ppr var )
851 completeCall (zapSubstEnv env) var1 occ cont
852 -- The template is already simplified, so don't re-substitute.
853 -- This is VITAL. Consider
855 -- let y = \z -> ...x... in
857 -- We'll clone the inner \x, adding x->x' in the id_subst
858 -- Then when we inline y, we must *not* replace x by x' in
859 -- the inlined copy!!
861 ---------------------------------------------------------
862 -- Dealing with a call site
864 completeCall env var occ_info cont
865 = -- Simplify the arguments
866 getDOptsSmpl `thenSmpl` \ dflags ->
868 chkr = getSwitchChecker env
869 (args, call_cont, inline_call) = getContArgs chkr var cont
872 simplifyArgs env fn_ty args (contResultType call_cont) $ \ env args ->
874 -- Next, look for rules or specialisations that match
876 -- It's important to simplify the args first, because the rule-matcher
877 -- doesn't do substitution as it goes. We don't want to use subst_args
878 -- (defined in the 'where') because that throws away useful occurrence info,
879 -- and perhaps-very-important specialisations.
881 -- Some functions have specialisations *and* are strict; in this case,
882 -- we don't want to inline the wrapper of the non-specialised thing; better
883 -- to call the specialised thing instead.
884 -- We used to use the black-listing mechanism to ensure that inlining of
885 -- the wrapper didn't occur for things that have specialisations till a
886 -- later phase, so but now we just try RULES first
888 -- You might think that we shouldn't apply rules for a loop breaker:
889 -- doing so might give rise to an infinite loop, because a RULE is
890 -- rather like an extra equation for the function:
891 -- RULE: f (g x) y = x+y
894 -- But it's too drastic to disable rules for loop breakers.
895 -- Even the foldr/build rule would be disabled, because foldr
896 -- is recursive, and hence a loop breaker:
897 -- foldr k z (build g) = g k z
898 -- So it's up to the programmer: rules can cause divergence
901 in_scope = getInScope env
902 maybe_rule = case activeRule env of
903 Nothing -> Nothing -- No rules apply
904 Just act_fn -> lookupRule act_fn in_scope var args
907 Just (rule_name, rule_rhs) ->
908 tick (RuleFired rule_name) `thenSmpl_`
909 (if dopt Opt_D_dump_inlinings dflags then
910 pprTrace "Rule fired" (vcat [
911 text "Rule:" <+> ptext rule_name,
912 text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
913 text "After: " <+> pprCoreExpr rule_rhs,
914 text "Cont: " <+> ppr call_cont])
917 simplExprF env rule_rhs call_cont ;
919 Nothing -> -- No rules
921 -- Next, look for an inlining
923 arg_infos = [ interestingArg arg | arg <- args, isValArg arg]
925 interesting_cont = interestingCallContext (not (null args))
926 (not (null arg_infos))
929 active_inline = activeInline env var occ_info
930 maybe_inline = callSiteInline dflags active_inline inline_call occ_info
931 var arg_infos interesting_cont
933 case maybe_inline of {
934 Just unfolding -- There is an inlining!
935 -> tick (UnfoldingDone var) `thenSmpl_`
936 makeThatCall env var unfolding args call_cont
939 Nothing -> -- No inlining!
942 rebuild env (mkApps (Var var) args) call_cont
945 makeThatCall :: SimplEnv
947 -> InExpr -- Inlined function rhs
948 -> [OutExpr] -- Arguments, already simplified
949 -> SimplCont -- After the call
950 -> SimplM FloatsWithExpr
951 -- Similar to simplLam, but this time
952 -- the arguments are already simplified
953 makeThatCall orig_env var fun@(Lam _ _) args cont
954 = go orig_env fun args
956 zap_it = mkLamBndrZapper fun (length args)
958 -- Type-beta reduction
959 go env (Lam bndr body) (Type ty_arg : args)
960 = ASSERT( isTyVar bndr )
961 tick (BetaReduction bndr) `thenSmpl_`
962 go (extendSubst env bndr (DoneTy ty_arg)) body args
964 -- Ordinary beta reduction
965 go env (Lam bndr body) (arg : args)
966 = tick (BetaReduction bndr) `thenSmpl_`
967 simplNonRecX env (zap_it bndr) arg $ \ env ->
970 -- Not enough args, so there are real lambdas left to put in the result
972 = simplExprF env fun (pushContArgs orig_env args cont)
973 -- NB: orig_env; the correct environment to capture with
974 -- the arguments.... env has been augmented with substitutions
975 -- from the beta reductions.
977 makeThatCall env var fun args cont
978 = simplExprF env fun (pushContArgs env args cont)
982 %************************************************************************
984 \subsection{Arguments}
986 %************************************************************************
989 ---------------------------------------------------------
990 -- Simplifying the arguments of a call
992 simplifyArgs :: SimplEnv
993 -> OutType -- Type of the function
994 -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments
995 -> OutType -- Type of the continuation
996 -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr)
997 -> SimplM FloatsWithExpr
999 -- [CPS-like because of strict arguments]
1001 -- Simplify the arguments to a call.
1002 -- This part of the simplifier may break the no-shadowing invariant
1004 -- f (...(\a -> e)...) (case y of (a,b) -> e')
1005 -- where f is strict in its second arg
1006 -- If we simplify the innermost one first we get (...(\a -> e)...)
1007 -- Simplifying the second arg makes us float the case out, so we end up with
1008 -- case y of (a,b) -> f (...(\a -> e)...) e'
1009 -- So the output does not have the no-shadowing invariant. However, there is
1010 -- no danger of getting name-capture, because when the first arg was simplified
1011 -- we used an in-scope set that at least mentioned all the variables free in its
1012 -- static environment, and that is enough.
1014 -- We can't just do innermost first, or we'd end up with a dual problem:
1015 -- case x of (a,b) -> f e (...(\a -> e')...)
1017 -- I spent hours trying to recover the no-shadowing invariant, but I just could
1018 -- not think of an elegant way to do it. The simplifier is already knee-deep in
1019 -- continuations. We have to keep the right in-scope set around; AND we have
1020 -- to get the effect that finding (error "foo") in a strict arg position will
1021 -- discard the entire application and replace it with (error "foo"). Getting
1022 -- all this at once is TOO HARD!
1024 simplifyArgs env fn_ty args cont_ty thing_inside
1025 = go env fn_ty args thing_inside
1027 go env fn_ty [] thing_inside = thing_inside env []
1028 go env fn_ty (arg:args) thing_inside = simplifyArg env fn_ty arg cont_ty $ \ env arg' ->
1029 go env (applyTypeToArg fn_ty arg') args $ \ env args' ->
1030 thing_inside env (arg':args')
1032 simplifyArg env fn_ty (Type ty_arg, se, _) cont_ty thing_inside
1033 = simplType (setInScope se env) ty_arg `thenSmpl` \ new_ty_arg ->
1034 thing_inside env (Type new_ty_arg)
1036 simplifyArg env fn_ty (val_arg, arg_se, is_strict) cont_ty thing_inside
1038 = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside
1041 = simplExprF (setInScope arg_se env) val_arg
1042 (mkStop arg_ty AnArg) `thenSmpl` \ (floats, arg1) ->
1043 addFloats env floats $ \ env ->
1044 thing_inside env arg1
1046 arg_ty = funArgTy fn_ty
1049 simplStrictArg :: LetRhsFlag
1050 -> SimplEnv -- The env of the call
1051 -> InExpr -> SimplEnv -- The arg plus its env
1052 -> OutType -- arg_ty: type of the argument
1053 -> OutType -- cont_ty: Type of thing computed by the context
1054 -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr)
1055 -- Takes an expression of type rhs_ty,
1056 -- returns an expression of type cont_ty
1057 -- The env passed to this continuation is the
1058 -- env of the call, plus any new in-scope variables
1059 -> SimplM FloatsWithExpr -- An expression of type cont_ty
1061 simplStrictArg is_rhs call_env arg arg_env arg_ty cont_ty thing_inside
1062 = simplExprF (setInScope arg_env call_env) arg
1063 (ArgOf is_rhs arg_ty cont_ty (\ new_env -> thing_inside (setInScope call_env new_env)))
1064 -- Notice the way we use arg_env (augmented with in-scope vars from call_env)
1065 -- to simplify the argument
1066 -- and call-env (augmented with in-scope vars from the arg) to pass to the continuation
1070 %************************************************************************
1072 \subsection{mkAtomicArgs}
1074 %************************************************************************
1076 mkAtomicArgs takes a putative RHS, checks whether it's a PAP or
1077 constructor application and, if so, converts it to ANF, so that the
1078 resulting thing can be inlined more easily. Thus
1085 There are three sorts of binding context, specified by the two
1091 N N Top-level or recursive Only bind args of lifted type
1093 N Y Non-top-level and non-recursive, Bind args of lifted type, or
1094 but lazy unlifted-and-ok-for-speculation
1096 Y Y Non-top-level, non-recursive, Bind all args
1097 and strict (demanded)
1104 there is no point in transforming to
1106 x = case (y div# z) of r -> MkC r
1108 because the (y div# z) can't float out of the let. But if it was
1109 a *strict* let, then it would be a good thing to do. Hence the
1110 context information.
1113 mkAtomicArgs :: Bool -- A strict binding
1114 -> Bool -- OK to float unlifted args
1116 -> SimplM (OrdList (OutId,OutExpr), -- The floats (unusually) may include
1117 OutExpr) -- things that need case-binding,
1118 -- if the strict-binding flag is on
1120 mkAtomicArgs is_strict ok_float_unlifted rhs
1121 | (Var fun, args) <- collectArgs rhs, -- It's an application
1122 isDataConId fun || valArgCount args < idArity fun -- And it's a constructor or PAP
1123 = go fun nilOL [] args -- Have a go
1125 | otherwise = bale_out -- Give up
1128 bale_out = returnSmpl (nilOL, rhs)
1130 go fun binds rev_args []
1131 = returnSmpl (binds, mkApps (Var fun) (reverse rev_args))
1133 go fun binds rev_args (arg : args)
1134 | exprIsTrivial arg -- Easy case
1135 = go fun binds (arg:rev_args) args
1137 | not can_float_arg -- Can't make this arg atomic
1138 = bale_out -- ... so give up
1140 | otherwise -- Don't forget to do it recursively
1141 -- E.g. x = a:b:c:[]
1142 = mkAtomicArgs is_strict ok_float_unlifted arg `thenSmpl` \ (arg_binds, arg') ->
1143 newId FSLIT("a") arg_ty `thenSmpl` \ arg_id ->
1144 go fun ((arg_binds `snocOL` (arg_id,arg')) `appOL` binds)
1145 (Var arg_id : rev_args) args
1147 arg_ty = exprType arg
1148 can_float_arg = is_strict
1149 || not (isUnLiftedType arg_ty)
1150 || (ok_float_unlifted && exprOkForSpeculation arg)
1153 addAtomicBinds :: SimplEnv -> [(OutId,OutExpr)]
1154 -> (SimplEnv -> SimplM (FloatsWith a))
1155 -> SimplM (FloatsWith a)
1156 addAtomicBinds env [] thing_inside = thing_inside env
1157 addAtomicBinds env ((v,r):bs) thing_inside = addAuxiliaryBind env (NonRec v r) $ \ env ->
1158 addAtomicBinds env bs thing_inside
1160 addAtomicBindsE :: SimplEnv -> [(OutId,OutExpr)]
1161 -> (SimplEnv -> SimplM FloatsWithExpr)
1162 -> SimplM FloatsWithExpr
1163 -- Same again, but this time we're in an expression context,
1164 -- and may need to do some case bindings
1166 addAtomicBindsE env [] thing_inside
1168 addAtomicBindsE env ((v,r):bs) thing_inside
1169 | needsCaseBinding (idType v) r
1170 = addAtomicBindsE (addNewInScopeIds env [v]) bs thing_inside `thenSmpl` \ (floats, expr) ->
1171 WARN( exprIsTrivial expr, ppr v <+> pprCoreExpr expr )
1172 returnSmpl (emptyFloats env, Case r v [(DEFAULT,[], wrapFloats floats expr)])
1175 = addAuxiliaryBind env (NonRec v r) $ \ env ->
1176 addAtomicBindsE env bs thing_inside
1180 %************************************************************************
1182 \subsection{The main rebuilder}
1184 %************************************************************************
1187 rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr
1189 rebuild env expr (Stop _ _ _) = rebuildDone env expr
1190 rebuild env expr (ArgOf _ _ _ cont_fn) = cont_fn env expr
1191 rebuild env expr (CoerceIt to_ty cont) = rebuild env (mkCoerce to_ty (exprType expr) expr) cont
1192 rebuild env expr (InlinePlease cont) = rebuild env (Note InlineCall expr) cont
1193 rebuild env expr (Select _ bndr alts se cont) = rebuildCase (setInScope se env) expr bndr alts cont
1194 rebuild env expr (ApplyTo _ arg se cont) = rebuildApp (setInScope se env) expr arg cont
1196 rebuildApp env fun arg cont
1197 = simplExpr env arg `thenSmpl` \ arg' ->
1198 rebuild env (App fun arg') cont
1200 rebuildDone env expr = returnSmpl (emptyFloats env, expr)
1204 %************************************************************************
1206 \subsection{Functions dealing with a case}
1208 %************************************************************************
1210 Blob of helper functions for the "case-of-something-else" situation.
1213 ---------------------------------------------------------
1214 -- Eliminate the case if possible
1216 rebuildCase :: SimplEnv
1217 -> OutExpr -- Scrutinee
1218 -> InId -- Case binder
1219 -> [InAlt] -- Alternatives
1221 -> SimplM FloatsWithExpr
1223 rebuildCase env scrut case_bndr alts cont
1224 | Just (con,args) <- exprIsConApp_maybe scrut
1225 -- Works when the scrutinee is a variable with a known unfolding
1226 -- as well as when it's an explicit constructor application
1227 = knownCon env (DataAlt con) args case_bndr alts cont
1229 | Lit lit <- scrut -- No need for same treatment as constructors
1230 -- because literals are inlined more vigorously
1231 = knownCon env (LitAlt lit) [] case_bndr alts cont
1234 = prepareAlts scrut case_bndr alts `thenSmpl` \ (better_alts, handled_cons) ->
1236 -- Deal with the case binder, and prepare the continuation;
1237 -- The new subst_env is in place
1238 prepareCaseCont env better_alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1239 addFloats env floats $ \ env ->
1241 -- Deal with variable scrutinee
1242 simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr', zap_occ_info) ->
1244 -- Deal with the case alternatives
1245 simplAlts alt_env zap_occ_info handled_cons
1246 case_bndr' better_alts dup_cont `thenSmpl` \ alts' ->
1248 -- Put the case back together
1249 mkCase scrut case_bndr' alts' `thenSmpl` \ case_expr ->
1251 -- Notice that rebuildDone returns the in-scope set from env, not alt_env
1252 -- The case binder *not* scope over the whole returned case-expression
1253 rebuild env case_expr nondup_cont
1256 simplCaseBinder checks whether the scrutinee is a variable, v. If so,
1257 try to eliminate uses of v in the RHSs in favour of case_bndr; that
1258 way, there's a chance that v will now only be used once, and hence
1263 There is a time we *don't* want to do that, namely when
1264 -fno-case-of-case is on. This happens in the first simplifier pass,
1265 and enhances full laziness. Here's the bad case:
1266 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1267 If we eliminate the inner case, we trap it inside the I# v -> arm,
1268 which might prevent some full laziness happening. I've seen this
1269 in action in spectral/cichelli/Prog.hs:
1270 [(m,n) | m <- [1..max], n <- [1..max]]
1271 Hence the check for NoCaseOfCase.
1275 There is another situation when we don't want to do it. If we have
1277 case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
1278 ...other cases .... }
1280 We'll perform the binder-swap for the outer case, giving
1282 case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
1283 ...other cases .... }
1285 But there is no point in doing it for the inner case, because w1 can't
1286 be inlined anyway. Furthermore, doing the case-swapping involves
1287 zapping w2's occurrence info (see paragraphs that follow), and that
1288 forces us to bind w2 when doing case merging. So we get
1290 case x of w1 { A -> let w2 = w1 in e1
1291 B -> let w2 = w1 in e2
1292 ...other cases .... }
1294 This is plain silly in the common case where w2 is dead.
1296 Even so, I can't see a good way to implement this idea. I tried
1297 not doing the binder-swap if the scrutinee was already evaluated
1298 but that failed big-time:
1302 case v of w { MkT x ->
1303 case x of x1 { I# y1 ->
1304 case x of x2 { I# y2 -> ...
1306 Notice that because MkT is strict, x is marked "evaluated". But to
1307 eliminate the last case, we must either make sure that x (as well as
1308 x1) has unfolding MkT y1. THe straightforward thing to do is to do
1309 the binder-swap. So this whole note is a no-op.
1313 If we replace the scrutinee, v, by tbe case binder, then we have to nuke
1314 any occurrence info (eg IAmDead) in the case binder, because the
1315 case-binder now effectively occurs whenever v does. AND we have to do
1316 the same for the pattern-bound variables! Example:
1318 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1320 Here, b and p are dead. But when we move the argment inside the first
1321 case RHS, and eliminate the second case, we get
1323 case x or { (a,b) -> a b }
1325 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1326 happened. Hence the zap_occ_info function returned by simplCaseBinder
1329 simplCaseBinder env (Var v) case_bndr
1330 | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
1332 -- Failed try [see Note 2 above]
1333 -- not (isEvaldUnfolding (idUnfolding v))
1335 = simplBinder env (zap case_bndr) `thenSmpl` \ (env, case_bndr') ->
1336 returnSmpl (modifyInScope env v case_bndr', case_bndr', zap)
1337 -- We could extend the substitution instead, but it would be
1338 -- a hack because then the substitution wouldn't be idempotent
1339 -- any more (v is an OutId). And this just just as well.
1341 zap b = b `setIdOccInfo` NoOccInfo
1343 simplCaseBinder env other_scrut case_bndr
1344 = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') ->
1345 returnSmpl (env, case_bndr', \ bndr -> bndr) -- NoOp on bndr
1351 simplAlts :: SimplEnv
1352 -> (InId -> InId) -- Occ-info zapper
1353 -> [AltCon] -- Alternatives the scrutinee can't be
1354 -- in the default case
1355 -> OutId -- Case binder
1356 -> [InAlt] -> SimplCont
1357 -> SimplM [OutAlt] -- Includes the continuation
1359 simplAlts env zap_occ_info handled_cons case_bndr' alts cont'
1360 = mapSmpl simpl_alt alts
1362 inst_tys' = tyConAppArgs (idType case_bndr')
1364 simpl_alt (DEFAULT, _, rhs)
1366 -- In the default case we record the constructors that the
1367 -- case-binder *can't* be.
1368 -- We take advantage of any OtherCon info in the case scrutinee
1369 case_bndr_w_unf = case_bndr' `setIdUnfolding` mkOtherCon handled_cons
1370 env_with_unf = modifyInScope env case_bndr' case_bndr_w_unf
1372 simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
1373 returnSmpl (DEFAULT, [], rhs')
1375 simpl_alt (con, vs, rhs)
1376 = -- Deal with the pattern-bound variables
1377 -- Mark the ones that are in ! positions in the data constructor
1378 -- as certainly-evaluated.
1379 -- NB: it happens that simplBinders does *not* erase the OtherCon
1380 -- form of unfolding, so it's ok to add this info before
1381 -- doing simplBinders
1382 simplBinders env (add_evals con vs) `thenSmpl` \ (env, vs') ->
1384 -- Bind the case-binder to (con args)
1386 unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
1387 env_with_unf = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` unfolding)
1389 simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
1390 returnSmpl (con, vs', rhs')
1393 -- add_evals records the evaluated-ness of the bound variables of
1394 -- a case pattern. This is *important*. Consider
1395 -- data T = T !Int !Int
1397 -- case x of { T a b -> T (a+1) b }
1399 -- We really must record that b is already evaluated so that we don't
1400 -- go and re-evaluate it when constructing the result.
1402 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1403 add_evals other_con vs = vs
1405 cat_evals [] [] = []
1406 cat_evals (v:vs) (str:strs)
1407 | isTyVar v = v : cat_evals vs (str:strs)
1408 | isMarkedStrict str = evald_v : cat_evals vs strs
1409 | otherwise = zapped_v : cat_evals vs strs
1411 zapped_v = zap_occ_info v
1412 evald_v = zapped_v `setIdUnfolding` mkOtherCon []
1416 %************************************************************************
1418 \subsection{Known constructor}
1420 %************************************************************************
1422 We are a bit careful with occurrence info. Here's an example
1424 (\x* -> case x of (a*, b) -> f a) (h v, e)
1426 where the * means "occurs once". This effectively becomes
1427 case (h v, e) of (a*, b) -> f a)
1429 let a* = h v; b = e in f a
1433 All this should happen in one sweep.
1436 knownCon :: SimplEnv -> AltCon -> [OutExpr]
1437 -> InId -> [InAlt] -> SimplCont
1438 -> SimplM FloatsWithExpr
1440 knownCon env con args bndr alts cont
1441 = tick (KnownBranch bndr) `thenSmpl_`
1442 case findAlt con alts of
1443 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1444 simplNonRecX env bndr scrut $ \ env ->
1445 -- This might give rise to a binding with non-atomic args
1446 -- like x = Node (f x) (g x)
1447 -- but no harm will be done
1448 simplExprF env rhs cont
1451 LitAlt lit -> Lit lit
1452 DataAlt dc -> mkConApp dc args
1454 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1455 simplNonRecX env bndr (Lit lit) $ \ env ->
1456 simplExprF env rhs cont
1458 (DataAlt dc, bs, rhs) -> ASSERT( length bs + n_tys == length args )
1459 bind_args env bs (drop n_tys args) $ \ env ->
1461 con_app = mkConApp dc (take n_tys args ++ con_args)
1462 con_args = [substExpr (getSubst env) (varToCoreExpr b) | b <- bs]
1463 -- args are aready OutExprs, but bs are InIds
1465 simplNonRecX env bndr con_app $ \ env ->
1466 simplExprF env rhs cont
1468 n_tys = dataConNumInstArgs dc -- Non-existential type args
1470 bind_args env [] _ thing_inside = thing_inside env
1472 bind_args env (b:bs) (Type ty : args) thing_inside
1473 = bind_args (extendSubst env b (DoneTy ty)) bs args thing_inside
1475 bind_args env (b:bs) (arg : args) thing_inside
1476 = simplNonRecX env b arg $ \ env ->
1477 bind_args env bs args thing_inside
1481 %************************************************************************
1483 \subsection{Duplicating continuations}
1485 %************************************************************************
1488 prepareCaseCont :: SimplEnv
1489 -> [InAlt] -> SimplCont
1490 -> SimplM (FloatsWith (SimplCont,SimplCont))
1491 -- Return a duplicatable continuation, a non-duplicable part
1492 -- plus some extra bindings
1494 -- No need to make it duplicatable if there's only one alternative
1495 prepareCaseCont env [alt] cont = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
1496 prepareCaseCont env alts cont = mkDupableCont env cont
1500 mkDupableCont :: SimplEnv -> SimplCont
1501 -> SimplM (FloatsWith (SimplCont, SimplCont))
1503 mkDupableCont env cont
1504 | contIsDupable cont
1505 = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
1507 mkDupableCont env (CoerceIt ty cont)
1508 = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1509 returnSmpl (floats, (CoerceIt ty dup_cont, nondup_cont))
1511 mkDupableCont env (InlinePlease cont)
1512 = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1513 returnSmpl (floats, (InlinePlease dup_cont, nondup_cont))
1515 mkDupableCont env cont@(ArgOf _ arg_ty _ _)
1516 = returnSmpl (emptyFloats env, (mkBoringStop arg_ty, cont))
1517 -- Do *not* duplicate an ArgOf continuation
1518 -- Because ArgOf continuations are opaque, we gain nothing by
1519 -- propagating them into the expressions, and we do lose a lot.
1520 -- Here's an example:
1521 -- && (case x of { T -> F; F -> T }) E
1522 -- Now, && is strict so we end up simplifying the case with
1523 -- an ArgOf continuation. If we let-bind it, we get
1525 -- let $j = \v -> && v E
1526 -- in simplExpr (case x of { T -> F; F -> T })
1527 -- (ArgOf (\r -> $j r)
1528 -- And after simplifying more we get
1530 -- let $j = \v -> && v E
1531 -- in case of { T -> $j F; F -> $j T }
1532 -- Which is a Very Bad Thing
1534 -- The desire not to duplicate is the entire reason that
1535 -- mkDupableCont returns a pair of continuations.
1537 -- The original plan had:
1538 -- e.g. (...strict-fn...) [...hole...]
1540 -- let $j = \a -> ...strict-fn...
1541 -- in $j [...hole...]
1543 mkDupableCont env (ApplyTo _ arg se cont)
1544 = -- e.g. [...hole...] (...arg...)
1546 -- let a = ...arg...
1547 -- in [...hole...] a
1548 simplExpr (setInScope se env) arg `thenSmpl` \ arg' ->
1550 mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1551 addFloats env floats $ \ env ->
1553 if exprIsDupable arg' then
1554 returnSmpl (emptyFloats env, (ApplyTo OkToDup arg' (zapSubstEnv se) dup_cont, nondup_cont))
1556 newId FSLIT("a") (exprType arg') `thenSmpl` \ arg_id ->
1558 tick (CaseOfCase arg_id) `thenSmpl_`
1559 -- Want to tick here so that we go round again,
1560 -- and maybe copy or inline the code.
1561 -- Not strictly CaseOfCase, but never mind
1563 returnSmpl (unitFloat env arg_id arg',
1564 (ApplyTo OkToDup (Var arg_id) (zapSubstEnv se) dup_cont,
1566 -- But what if the arg should be case-bound?
1567 -- This has been this way for a long time, so I'll leave it,
1568 -- but I can't convince myself that it's right.
1571 mkDupableCont env (Select _ case_bndr alts se cont)
1572 = -- e.g. (case [...hole...] of { pi -> ei })
1574 -- let ji = \xij -> ei
1575 -- in case [...hole...] of { pi -> ji xij }
1576 tick (CaseOfCase case_bndr) `thenSmpl_`
1578 alt_env = setInScope se env
1580 prepareCaseCont alt_env alts cont `thenSmpl` \ (floats1, (dup_cont, nondup_cont)) ->
1581 addFloats alt_env floats1 $ \ alt_env ->
1583 simplBinder alt_env case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
1584 -- NB: simplBinder does not zap deadness occ-info, so
1585 -- a dead case_bndr' will still advertise its deadness
1586 -- This is really important because in
1587 -- case e of b { (# a,b #) -> ... }
1588 -- b is always dead, and indeed we are not allowed to bind b to (# a,b #),
1589 -- which might happen if e was an explicit unboxed pair and b wasn't marked dead.
1590 -- In the new alts we build, we have the new case binder, so it must retain
1593 mkDupableAlts alt_env case_bndr' alts dup_cont `thenSmpl` \ (floats2, alts') ->
1594 addFloats alt_env floats2 $ \ alt_env ->
1595 returnSmpl (emptyFloats alt_env,
1596 (Select OkToDup case_bndr' alts' (zapSubstEnv se)
1597 (mkBoringStop (contResultType dup_cont)),
1600 mkDupableAlts :: SimplEnv -> OutId -> [InAlt] -> SimplCont
1601 -> SimplM (FloatsWith [InAlt])
1602 -- Absorbs the continuation into the new alternatives
1604 mkDupableAlts env case_bndr' alts dupable_cont
1607 go env [] = returnSmpl (emptyFloats env, [])
1609 = mkDupableAlt env case_bndr' dupable_cont alt `thenSmpl` \ (floats1, alt') ->
1610 addFloats env floats1 $ \ env ->
1611 go env alts `thenSmpl` \ (floats2, alts') ->
1612 returnSmpl (floats2, alt' : alts')
1614 mkDupableAlt env case_bndr' cont alt@(con, bndrs, rhs)
1615 = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
1616 simplExprC env rhs cont `thenSmpl` \ rhs' ->
1618 if exprIsDupable rhs' then
1619 returnSmpl (emptyFloats env, (con, bndrs', rhs'))
1620 -- It is worth checking for a small RHS because otherwise we
1621 -- get extra let bindings that may cause an extra iteration of the simplifier to
1622 -- inline back in place. Quite often the rhs is just a variable or constructor.
1623 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1624 -- iterations because the version with the let bindings looked big, and so wasn't
1625 -- inlined, but after the join points had been inlined it looked smaller, and so
1628 -- NB: we have to check the size of rhs', not rhs.
1629 -- Duplicating a small InAlt might invalidate occurrence information
1630 -- However, if it *is* dupable, we return the *un* simplified alternative,
1631 -- because otherwise we'd need to pair it up with an empty subst-env....
1632 -- but we only have one env shared between all the alts.
1633 -- (Remember we must zap the subst-env before re-simplifying something).
1634 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1638 rhs_ty' = exprType rhs'
1639 used_bndrs' = filter (not . isDeadBinder) (case_bndr' : bndrs')
1640 -- The deadness info on the new binders is unscathed
1642 -- If we try to lift a primitive-typed something out
1643 -- for let-binding-purposes, we will *caseify* it (!),
1644 -- with potentially-disastrous strictness results. So
1645 -- instead we turn it into a function: \v -> e
1646 -- where v::State# RealWorld#. The value passed to this function
1647 -- is realworld#, which generates (almost) no code.
1649 -- There's a slight infelicity here: we pass the overall
1650 -- case_bndr to all the join points if it's used in *any* RHS,
1651 -- because we don't know its usage in each RHS separately
1653 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1654 -- we make the join point into a function whenever used_bndrs'
1655 -- is empty. This makes the join-point more CPR friendly.
1656 -- Consider: let j = if .. then I# 3 else I# 4
1657 -- in case .. of { A -> j; B -> j; C -> ... }
1659 -- Now CPR doesn't w/w j because it's a thunk, so
1660 -- that means that the enclosing function can't w/w either,
1661 -- which is a lose. Here's the example that happened in practice:
1662 -- kgmod :: Int -> Int -> Int
1663 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1667 -- I have seen a case alternative like this:
1668 -- True -> \v -> ...
1669 -- It's a bit silly to add the realWorld dummy arg in this case, making
1672 -- (the \v alone is enough to make CPR happy) but I think it's rare
1674 ( if null used_bndrs'
1675 then newId FSLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id ->
1676 returnSmpl ([rw_id], [Var realWorldPrimId])
1678 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs')
1679 ) `thenSmpl` \ (final_bndrs', final_args) ->
1681 -- See comment about "$j" name above
1682 newId (encodeFS SLIT("$j")) (mkPiTypes final_bndrs' rhs_ty') `thenSmpl` \ join_bndr ->
1683 -- Notice the funky mkPiTypes. If the contructor has existentials
1684 -- it's possible that the join point will be abstracted over
1685 -- type varaibles as well as term variables.
1686 -- Example: Suppose we have
1687 -- data T = forall t. C [t]
1689 -- case (case e of ...) of
1690 -- C t xs::[t] -> rhs
1691 -- We get the join point
1692 -- let j :: forall t. [t] -> ...
1693 -- j = /\t \xs::[t] -> rhs
1695 -- case (case e of ...) of
1696 -- C t xs::[t] -> j t xs
1698 -- We make the lambdas into one-shot-lambdas. The
1699 -- join point is sure to be applied at most once, and doing so
1700 -- prevents the body of the join point being floated out by
1701 -- the full laziness pass
1702 really_final_bndrs = map one_shot final_bndrs'
1703 one_shot v | isId v = setOneShotLambda v
1705 join_rhs = mkLams really_final_bndrs rhs'
1706 join_call = mkApps (Var join_bndr) final_args
1708 returnSmpl (unitFloat env join_bndr join_rhs, (con, bndrs', join_call))