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, 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, tyConAppArgs, funArgTy,
49 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 info in the substitution
298 simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
300 -- simplLetBndr doesn't deal with the IdInfo, so we must
301 -- do so here (c.f. simplLazyBind)
302 bndr'' = bndr' `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
303 env1 = modifyInScope env bndr'' bndr''
305 simplStrictArg AnRhs env1 rhs rhs_se (idType bndr') cont_ty $ \ env rhs1 ->
307 -- Now complete the binding and simplify the body
308 completeNonRecX env True {- strict -} bndr bndr'' rhs1 thing_inside
310 | otherwise -- Normal, lazy case
311 = -- Don't use simplBinder because that doesn't keep
312 -- fragile occurrence info in the substitution
313 simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
314 simplLazyBind env NotTopLevel NonRecursive
315 bndr bndr' rhs rhs_se `thenSmpl` \ (floats, env) ->
316 addFloats env floats thing_inside
319 A specialised variant of simplNonRec used when the RHS is already simplified, notably
320 in knownCon. It uses case-binding where necessary.
323 simplNonRecX :: SimplEnv
324 -> InId -- Old binder
325 -> OutExpr -- Simplified RHS
326 -> (SimplEnv -> SimplM FloatsWithExpr)
327 -> SimplM FloatsWithExpr
329 simplNonRecX env bndr new_rhs thing_inside
330 | needsCaseBinding (idType bndr) new_rhs
331 -- Make this test *before* the preInlineUnconditionally
332 -- Consider case I# (quotInt# x y) of
333 -- I# v -> let w = J# v in ...
334 -- If we gaily inline (quotInt# x y) for v, we end up building an
336 -- let w = J# (quotInt# x y) in ...
337 -- because quotInt# can fail.
338 = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
339 thing_inside env `thenSmpl` \ (floats, body) ->
340 returnSmpl (emptyFloats env, Case new_rhs bndr' [(DEFAULT, [], wrapFloats floats body)])
342 | preInlineUnconditionally env NotTopLevel bndr
343 -- This happens; for example, the case_bndr during case of
344 -- known constructor: case (a,b) of x { (p,q) -> ... }
345 -- Here x isn't mentioned in the RHS, so we don't want to
346 -- create the (dead) let-binding let x = (a,b) in ...
348 -- Similarly, single occurrences can be inlined vigourously
349 -- e.g. case (f x, g y) of (a,b) -> ....
350 -- If a,b occur once we can avoid constructing the let binding for them.
351 = thing_inside (extendSubst env bndr (ContEx emptySubstEnv new_rhs))
354 = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
355 completeNonRecX env False {- Non-strict; pessimistic -}
356 bndr bndr' new_rhs thing_inside
358 completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside
359 = mkAtomicArgs is_strict
360 True {- OK to float unlifted -}
361 new_rhs `thenSmpl` \ (aux_binds, rhs2) ->
363 -- Make the arguments atomic if necessary,
364 -- adding suitable bindings
365 addAtomicBindsE env (fromOL aux_binds) $ \ env ->
366 completeLazyBind env NotTopLevel
367 old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) ->
368 addFloats env floats thing_inside
372 %************************************************************************
374 \subsection{Lazy bindings}
376 %************************************************************************
378 simplRecBind is used for
379 * recursive bindings only
382 simplRecBind :: SimplEnv -> TopLevelFlag
383 -> [(InId, InExpr)] -> [OutId]
384 -> SimplM (FloatsWith SimplEnv)
385 simplRecBind env top_lvl pairs bndrs'
386 = go env pairs bndrs' `thenSmpl` \ (floats, env) ->
387 returnSmpl (flattenFloats floats, env)
389 go env [] _ = returnSmpl (emptyFloats env, env)
391 go env ((bndr, rhs) : pairs) (bndr' : bndrs')
392 = simplRecOrTopPair env top_lvl bndr bndr' rhs `thenSmpl` \ (floats, env) ->
393 addFloats env floats (\env -> go env pairs bndrs')
397 simplRecOrTopPair is used for
398 * recursive bindings (whether top level or not)
399 * top-level non-recursive bindings
401 It assumes the binder has already been simplified, but not its IdInfo.
404 simplRecOrTopPair :: SimplEnv
406 -> InId -> OutId -- Binder, both pre-and post simpl
407 -> InExpr -- The RHS and its environment
408 -> SimplM (FloatsWith SimplEnv)
410 simplRecOrTopPair env top_lvl bndr bndr' rhs
411 | preInlineUnconditionally env top_lvl bndr -- Check for unconditional inline
412 = tick (PreInlineUnconditionally bndr) `thenSmpl_`
413 returnSmpl (emptyFloats env, extendSubst env bndr (ContEx (getSubstEnv env) rhs))
416 = simplLazyBind env top_lvl Recursive bndr bndr' rhs env
417 -- May not actually be recursive, but it doesn't matter
421 simplLazyBind is used for
422 * recursive bindings (whether top level or not)
423 * top-level non-recursive bindings
424 * non-top-level *lazy* non-recursive bindings
426 [Thus it deals with the lazy cases from simplNonRecBind, and all cases
427 from SimplRecOrTopBind]
430 1. It assumes that the binder is *already* simplified,
431 and is in scope, but not its IdInfo
433 2. It assumes that the binder type is lifted.
435 3. It does not check for pre-inline-unconditionallly;
436 that should have been done already.
439 simplLazyBind :: SimplEnv
440 -> TopLevelFlag -> RecFlag
441 -> InId -> OutId -- Binder, both pre-and post simpl
442 -> InExpr -> SimplEnv -- The RHS and its environment
443 -> SimplM (FloatsWith SimplEnv)
445 simplLazyBind env top_lvl is_rec bndr bndr' rhs rhs_se
446 = -- Substitute IdInfo on binder, in the light of earlier
447 -- substitutions in this very letrec, and extend the
448 -- in-scope env, so that the IdInfo for this binder extends
449 -- over the RHS for the binder itself.
451 -- This is important. Manuel found cases where he really, really
452 -- wanted a RULE for a recursive function to apply in that function's
453 -- own right-hand side.
455 -- NB: does no harm for non-recursive bindings
457 bndr'' = bndr' `setIdInfo` simplIdInfo (getSubst env) (idInfo bndr)
458 env1 = modifyInScope env bndr'' bndr''
459 rhs_env = setInScope rhs_se env1
460 is_top_level = isTopLevel top_lvl
461 ok_float_unlifted = not is_top_level && isNonRec is_rec
462 rhs_cont = mkStop (idType bndr') AnRhs
464 -- Simplify the RHS; note the mkStop, which tells
465 -- the simplifier that this is the RHS of a let.
466 simplExprF rhs_env rhs rhs_cont `thenSmpl` \ (floats, rhs1) ->
468 -- If any of the floats can't be floated, give up now
469 -- (The allLifted predicate says True for empty floats.)
470 if (not ok_float_unlifted && not (allLifted floats)) then
471 completeLazyBind env1 top_lvl bndr bndr''
472 (wrapFloats floats rhs1)
475 -- ANF-ise a constructor or PAP rhs
476 mkAtomicArgs False {- Not strict -}
477 ok_float_unlifted rhs1 `thenSmpl` \ (aux_binds, rhs2) ->
479 -- If the result is a PAP, float the floats out, else wrap them
480 -- By this time it's already been ANF-ised (if necessary)
481 if isEmptyFloats floats && isNilOL aux_binds then -- Shortcut a common case
482 completeLazyBind env1 top_lvl bndr bndr'' rhs2
484 -- We use exprIsTrivial here because we want to reveal lone variables.
485 -- E.g. let { x = letrec { y = E } in y } in ...
486 -- Here we definitely want to float the y=E defn.
487 -- exprIsValue definitely isn't right for that.
489 -- BUT we can't use "exprIsCheap", because that causes a strictness bug.
490 -- x = let y* = E in case (scc y) of { T -> F; F -> T}
491 -- The case expression is 'cheap', but it's wrong to transform to
492 -- y* = E; x = case (scc y) of {...}
493 -- Either we must be careful not to float demanded non-values, or
494 -- we must use exprIsValue for the test, which ensures that the
495 -- thing is non-strict. I think. The WARN below tests for this.
496 else if is_top_level || exprIsTrivial rhs2 || exprIsValue rhs2 then
498 -- There's a subtlety here. There may be a binding (x* = e) in the
499 -- floats, where the '*' means 'will be demanded'. So is it safe
500 -- to float it out? Answer no, but it won't matter because
501 -- we only float if arg' is a WHNF,
502 -- and so there can't be any 'will be demanded' bindings in the floats.
504 WARN( any demanded_float (floatBinds floats),
505 ppr (filter demanded_float (floatBinds floats)) )
507 tick LetFloatFromLet `thenSmpl_` (
508 addFloats env1 floats $ \ env2 ->
509 addAtomicBinds env2 (fromOL aux_binds) $ \ env3 ->
510 completeLazyBind env3 top_lvl bndr bndr'' rhs2)
513 completeLazyBind env1 top_lvl bndr bndr'' (wrapFloats floats rhs1)
516 demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b))
517 -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
518 demanded_float (Rec _) = False
523 %************************************************************************
525 \subsection{Completing a lazy binding}
527 %************************************************************************
530 * deals only with Ids, not TyVars
531 * takes an already-simplified binder and RHS
532 * is used for both recursive and non-recursive bindings
533 * is used for both top-level and non-top-level bindings
535 It does the following:
536 - tries discarding a dead binding
537 - tries PostInlineUnconditionally
538 - add unfolding [this is the only place we add an unfolding]
541 It does *not* attempt to do let-to-case. Why? Because it is used for
542 - top-level bindings (when let-to-case is impossible)
543 - many situations where the "rhs" is known to be a WHNF
544 (so let-to-case is inappropriate).
547 completeLazyBind :: SimplEnv
548 -> TopLevelFlag -- Flag stuck into unfolding
549 -> InId -- Old binder
550 -> OutId -- New binder
551 -> OutExpr -- Simplified RHS
552 -> SimplM (FloatsWith SimplEnv)
553 -- We return a new SimplEnv, because completeLazyBind may choose to do its work
554 -- by extending the substitution (e.g. let x = y in ...)
555 -- The new binding (if any) is returned as part of the floats.
556 -- NB: the returned SimplEnv has the right SubstEnv, but you should
557 -- (as usual) use the in-scope-env from the floats
559 completeLazyBind env top_lvl old_bndr new_bndr new_rhs
560 | postInlineUnconditionally env new_bndr occ_info new_rhs
561 = -- Drop the binding
562 tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
563 returnSmpl (emptyFloats env, extendSubst env old_bndr (DoneEx new_rhs))
564 -- Use the substitution to make quite, quite sure that the substitution
565 -- will happen, since we are going to discard the binding
570 new_bndr_info = idInfo new_bndr `setArityInfo` exprArity new_rhs
572 -- Add the unfolding *only* for non-loop-breakers
573 -- Making loop breakers not have an unfolding at all
574 -- means that we can avoid tests in exprIsConApp, for example.
575 -- This is important: if exprIsConApp says 'yes' for a recursive
576 -- thing, then we can get into an infinite loop
577 info_w_unf | loop_breaker = new_bndr_info
578 | otherwise = new_bndr_info `setUnfoldingInfo` unfolding
579 unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs
581 final_id = new_bndr `setIdInfo` info_w_unf
583 -- These seqs forces the Id, and hence its IdInfo,
584 -- and hence any inner substitutions
586 returnSmpl (unitFloat env final_id new_rhs, env)
589 loop_breaker = isLoopBreaker occ_info
590 old_info = idInfo old_bndr
591 occ_info = occInfo old_info
596 %************************************************************************
598 \subsection[Simplify-simplExpr]{The main function: simplExpr}
600 %************************************************************************
602 The reason for this OutExprStuff stuff is that we want to float *after*
603 simplifying a RHS, not before. If we do so naively we get quadratic
604 behaviour as things float out.
606 To see why it's important to do it after, consider this (real) example:
620 a -- Can't inline a this round, cos it appears twice
624 Each of the ==> steps is a round of simplification. We'd save a
625 whole round if we float first. This can cascade. Consider
630 let f = let d1 = ..d.. in \y -> e
634 in \x -> ...(\y ->e)...
636 Only in this second round can the \y be applied, and it
637 might do the same again.
641 simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
642 simplExpr env expr = simplExprC env expr (mkStop expr_ty' AnArg)
644 expr_ty' = substTy (getSubst env) (exprType expr)
645 -- The type in the Stop continuation, expr_ty', is usually not used
646 -- It's only needed when discarding continuations after finding
647 -- a function that returns bottom.
648 -- Hence the lazy substitution
651 simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
652 -- Simplify an expression, given a continuation
653 simplExprC env expr cont
654 = simplExprF env expr cont `thenSmpl` \ (floats, expr) ->
655 returnSmpl (wrapFloats floats expr)
657 simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM FloatsWithExpr
658 -- Simplify an expression, returning floated binds
660 simplExprF env (Var v) cont = simplVar env v cont
661 simplExprF env (Lit lit) cont = rebuild env (Lit lit) cont
662 simplExprF env expr@(Lam _ _) cont = simplLam env expr cont
663 simplExprF env (Note note expr) cont = simplNote env note expr cont
664 simplExprF env (App fun arg) cont = simplExprF env fun (ApplyTo NoDup arg env cont)
666 simplExprF env (Type ty) cont
667 = ASSERT( contIsRhsOrArg cont )
668 simplType env ty `thenSmpl` \ ty' ->
669 rebuild env (Type ty') cont
671 simplExprF env (Case scrut bndr alts) cont
672 | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
673 = -- Simplify the scrutinee with a Select continuation
674 simplExprF env scrut (Select NoDup bndr alts env cont)
677 = -- If case-of-case is off, simply simplify the case expression
678 -- in a vanilla Stop context, and rebuild the result around it
679 simplExprC env scrut case_cont `thenSmpl` \ case_expr' ->
680 rebuild env case_expr' cont
682 case_cont = Select NoDup bndr alts env (mkBoringStop (contResultType cont))
684 simplExprF env (Let (Rec pairs) body) cont
685 = simplRecBndrs env (map fst pairs) `thenSmpl` \ (env, bndrs') ->
686 -- NB: bndrs' don't have unfoldings or spec-envs
687 -- We add them as we go down, using simplPrags
689 simplRecBind env NotTopLevel pairs bndrs' `thenSmpl` \ (floats, env) ->
690 addFloats env floats $ \ env ->
691 simplExprF env body cont
693 -- A non-recursive let is dealt with by simplNonRecBind
694 simplExprF env (Let (NonRec bndr rhs) body) cont
695 = simplNonRecBind env bndr rhs env (contResultType cont) $ \ env ->
696 simplExprF env body cont
699 ---------------------------------
700 simplType :: SimplEnv -> InType -> SimplM OutType
701 -- Kept monadic just so we can do the seqType
703 = seqType new_ty `seq` returnSmpl new_ty
705 new_ty = substTy (getSubst env) ty
709 %************************************************************************
713 %************************************************************************
716 simplLam env fun cont
719 zap_it = mkLamBndrZapper fun (countArgs cont)
720 cont_ty = contResultType cont
722 -- Type-beta reduction
723 go env (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
724 = ASSERT( isTyVar bndr )
725 tick (BetaReduction bndr) `thenSmpl_`
726 simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' ->
727 go (extendSubst env bndr (DoneTy ty_arg')) body body_cont
729 -- Ordinary beta reduction
730 go env (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
731 = tick (BetaReduction bndr) `thenSmpl_`
732 simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env ->
733 go env body body_cont
735 -- Not enough args, so there are real lambdas left to put in the result
736 go env lam@(Lam _ _) cont
737 = simplLamBndrs env bndrs `thenSmpl` \ (env, bndrs') ->
738 simplExpr env body `thenSmpl` \ body' ->
739 mkLam env bndrs' body' cont `thenSmpl` \ (floats, new_lam) ->
740 addFloats env floats $ \ env ->
741 rebuild env new_lam cont
743 (bndrs,body) = collectBinders lam
745 -- Exactly enough args
746 go env expr cont = simplExprF env expr cont
748 mkLamBndrZapper :: CoreExpr -- Function
749 -> Int -- Number of args supplied, *including* type args
750 -> Id -> Id -- Use this to zap the binders
751 mkLamBndrZapper fun n_args
752 | n_args >= n_params fun = \b -> b -- Enough args
753 | otherwise = \b -> zapLamIdInfo b
755 -- NB: we count all the args incl type args
756 -- so we must count all the binders (incl type lambdas)
757 n_params (Note _ e) = n_params e
758 n_params (Lam b e) = 1 + n_params e
759 n_params other = 0::Int
763 %************************************************************************
767 %************************************************************************
770 simplNote env (Coerce to from) body cont
772 in_scope = getInScope env
774 addCoerce s1 k1 (CoerceIt t1 cont)
775 -- coerce T1 S1 (coerce S1 K1 e)
778 -- coerce T1 K1 e, otherwise
780 -- For example, in the initial form of a worker
781 -- we may find (coerce T (coerce S (\x.e))) y
782 -- and we'd like it to simplify to e[y/x] in one round
784 | t1 `eqType` k1 = cont -- The coerces cancel out
785 | otherwise = CoerceIt t1 cont -- They don't cancel, but
786 -- the inner one is redundant
788 addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
789 | Just (s1, s2) <- splitFunTy_maybe s1s2
790 -- (coerce (T1->T2) (S1->S2) F) E
792 -- coerce T2 S2 (F (coerce S1 T1 E))
794 -- t1t2 must be a function type, T1->T2
795 -- but s1s2 might conceivably not be
797 -- When we build the ApplyTo we can't mix the out-types
798 -- with the InExpr in the argument, so we simply substitute
799 -- to make it all consistent. It's a bit messy.
800 -- But it isn't a common case.
802 (t1,t2) = splitFunTy t1t2
803 new_arg = mkCoerce s1 t1 (substExpr (mkSubst in_scope (getSubstEnv arg_se)) arg)
805 ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont)
807 addCoerce to' _ cont = CoerceIt to' cont
809 simplType env to `thenSmpl` \ to' ->
810 simplType env from `thenSmpl` \ from' ->
811 simplExprF env body (addCoerce to' from' cont)
814 -- Hack: we only distinguish subsumed cost centre stacks for the purposes of
815 -- inlining. All other CCCSs are mapped to currentCCS.
816 simplNote env (SCC cc) e cont
817 = simplExpr (setEnclosingCC env currentCCS) e `thenSmpl` \ e' ->
818 rebuild env (mkSCC cc e') cont
820 simplNote env InlineCall e cont
821 = simplExprF env e (InlinePlease cont)
823 -- See notes with SimplMonad.inlineMode
824 simplNote env InlineMe e cont
825 | contIsRhsOrArg cont -- Totally boring continuation; see notes above
826 = -- Don't inline inside an INLINE expression
827 simplExpr (setMode inlineMode env ) e `thenSmpl` \ e' ->
828 rebuild env (mkInlineMe e') cont
830 | otherwise -- Dissolve the InlineMe note if there's
831 -- an interesting context of any kind to combine with
832 -- (even a type application -- anything except Stop)
833 = simplExprF env e cont
837 %************************************************************************
839 \subsection{Dealing with calls}
841 %************************************************************************
844 simplVar env var cont
845 = case lookupIdSubst (getSubst env) var of
846 DoneEx e -> simplExprF (zapSubstEnv env) e cont
847 ContEx se e -> simplExprF (setSubstEnv env se) e cont
848 DoneId var1 occ -> WARN( not (isInScope var1 (getSubst env)) && mustHaveLocalBinding var1,
849 text "simplVar:" <+> ppr var )
850 completeCall (zapSubstEnv env) var1 occ cont
851 -- The template is already simplified, so don't re-substitute.
852 -- This is VITAL. Consider
854 -- let y = \z -> ...x... in
856 -- We'll clone the inner \x, adding x->x' in the id_subst
857 -- Then when we inline y, we must *not* replace x by x' in
858 -- the inlined copy!!
860 ---------------------------------------------------------
861 -- Dealing with a call site
863 completeCall env var occ_info cont
864 = -- Simplify the arguments
865 getDOptsSmpl `thenSmpl` \ dflags ->
867 chkr = getSwitchChecker env
868 (args, call_cont, inline_call) = getContArgs chkr var cont
871 simplifyArgs env fn_ty args (contResultType call_cont) $ \ env args ->
873 -- Next, look for rules or specialisations that match
875 -- It's important to simplify the args first, because the rule-matcher
876 -- doesn't do substitution as it goes. We don't want to use subst_args
877 -- (defined in the 'where') because that throws away useful occurrence info,
878 -- and perhaps-very-important specialisations.
880 -- Some functions have specialisations *and* are strict; in this case,
881 -- we don't want to inline the wrapper of the non-specialised thing; better
882 -- to call the specialised thing instead.
883 -- We used to use the black-listing mechanism to ensure that inlining of
884 -- the wrapper didn't occur for things that have specialisations till a
885 -- later phase, so but now we just try RULES first
887 -- You might think that we shouldn't apply rules for a loop breaker:
888 -- doing so might give rise to an infinite loop, because a RULE is
889 -- rather like an extra equation for the function:
890 -- RULE: f (g x) y = x+y
893 -- But it's too drastic to disable rules for loop breakers.
894 -- Even the foldr/build rule would be disabled, because foldr
895 -- is recursive, and hence a loop breaker:
896 -- foldr k z (build g) = g k z
897 -- So it's up to the programmer: rules can cause divergence
900 in_scope = getInScope env
901 maybe_rule = case activeRule env of
902 Nothing -> Nothing -- No rules apply
903 Just act_fn -> lookupRule act_fn in_scope var args
906 Just (rule_name, rule_rhs) ->
907 tick (RuleFired rule_name) `thenSmpl_`
908 (if dopt Opt_D_dump_inlinings dflags then
909 pprTrace "Rule fired" (vcat [
910 text "Rule:" <+> ptext rule_name,
911 text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
912 text "After: " <+> pprCoreExpr rule_rhs,
913 text "Cont: " <+> ppr call_cont])
916 simplExprF env rule_rhs call_cont ;
918 Nothing -> -- No rules
920 -- Next, look for an inlining
922 arg_infos = [ interestingArg arg | arg <- args, isValArg arg]
924 interesting_cont = interestingCallContext (not (null args))
925 (not (null arg_infos))
928 active_inline = activeInline env var occ_info
929 maybe_inline = callSiteInline dflags active_inline inline_call occ_info
930 var arg_infos interesting_cont
932 case maybe_inline of {
933 Just unfolding -- There is an inlining!
934 -> tick (UnfoldingDone var) `thenSmpl_`
935 makeThatCall env var unfolding args call_cont
938 Nothing -> -- No inlining!
941 rebuild env (mkApps (Var var) args) call_cont
944 makeThatCall :: SimplEnv
946 -> InExpr -- Inlined function rhs
947 -> [OutExpr] -- Arguments, already simplified
948 -> SimplCont -- After the call
949 -> SimplM FloatsWithExpr
950 -- Similar to simplLam, but this time
951 -- the arguments are already simplified
952 makeThatCall orig_env var fun@(Lam _ _) args cont
953 = go orig_env fun args
955 zap_it = mkLamBndrZapper fun (length args)
957 -- Type-beta reduction
958 go env (Lam bndr body) (Type ty_arg : args)
959 = ASSERT( isTyVar bndr )
960 tick (BetaReduction bndr) `thenSmpl_`
961 go (extendSubst env bndr (DoneTy ty_arg)) body args
963 -- Ordinary beta reduction
964 go env (Lam bndr body) (arg : args)
965 = tick (BetaReduction bndr) `thenSmpl_`
966 simplNonRecX env (zap_it bndr) arg $ \ env ->
969 -- Not enough args, so there are real lambdas left to put in the result
971 = simplExprF env fun (pushContArgs orig_env args cont)
972 -- NB: orig_env; the correct environment to capture with
973 -- the arguments.... env has been augmented with substitutions
974 -- from the beta reductions.
976 makeThatCall env var fun args cont
977 = simplExprF env fun (pushContArgs env args cont)
981 %************************************************************************
983 \subsection{Arguments}
985 %************************************************************************
988 ---------------------------------------------------------
989 -- Simplifying the arguments of a call
991 simplifyArgs :: SimplEnv
992 -> OutType -- Type of the function
993 -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments
994 -> OutType -- Type of the continuation
995 -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr)
996 -> SimplM FloatsWithExpr
998 -- [CPS-like because of strict arguments]
1000 -- Simplify the arguments to a call.
1001 -- This part of the simplifier may break the no-shadowing invariant
1003 -- f (...(\a -> e)...) (case y of (a,b) -> e')
1004 -- where f is strict in its second arg
1005 -- If we simplify the innermost one first we get (...(\a -> e)...)
1006 -- Simplifying the second arg makes us float the case out, so we end up with
1007 -- case y of (a,b) -> f (...(\a -> e)...) e'
1008 -- So the output does not have the no-shadowing invariant. However, there is
1009 -- no danger of getting name-capture, because when the first arg was simplified
1010 -- we used an in-scope set that at least mentioned all the variables free in its
1011 -- static environment, and that is enough.
1013 -- We can't just do innermost first, or we'd end up with a dual problem:
1014 -- case x of (a,b) -> f e (...(\a -> e')...)
1016 -- I spent hours trying to recover the no-shadowing invariant, but I just could
1017 -- not think of an elegant way to do it. The simplifier is already knee-deep in
1018 -- continuations. We have to keep the right in-scope set around; AND we have
1019 -- to get the effect that finding (error "foo") in a strict arg position will
1020 -- discard the entire application and replace it with (error "foo"). Getting
1021 -- all this at once is TOO HARD!
1023 simplifyArgs env fn_ty args cont_ty thing_inside
1024 = go env fn_ty args thing_inside
1026 go env fn_ty [] thing_inside = thing_inside env []
1027 go env fn_ty (arg:args) thing_inside = simplifyArg env fn_ty arg cont_ty $ \ env arg' ->
1028 go env (applyTypeToArg fn_ty arg') args $ \ env args' ->
1029 thing_inside env (arg':args')
1031 simplifyArg env fn_ty (Type ty_arg, se, _) cont_ty thing_inside
1032 = simplType (setInScope se env) ty_arg `thenSmpl` \ new_ty_arg ->
1033 thing_inside env (Type new_ty_arg)
1035 simplifyArg env fn_ty (val_arg, arg_se, is_strict) cont_ty thing_inside
1037 = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside
1040 = simplExprF (setInScope arg_se env) val_arg
1041 (mkStop arg_ty AnArg) `thenSmpl` \ (floats, arg1) ->
1042 addFloats env floats $ \ env ->
1043 thing_inside env arg1
1045 arg_ty = funArgTy fn_ty
1048 simplStrictArg :: LetRhsFlag
1049 -> SimplEnv -- The env of the call
1050 -> InExpr -> SimplEnv -- The arg plus its env
1051 -> OutType -- arg_ty: type of the argument
1052 -> OutType -- cont_ty: Type of thing computed by the context
1053 -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr)
1054 -- Takes an expression of type rhs_ty,
1055 -- returns an expression of type cont_ty
1056 -- The env passed to this continuation is the
1057 -- env of the call, plus any new in-scope variables
1058 -> SimplM FloatsWithExpr -- An expression of type cont_ty
1060 simplStrictArg is_rhs call_env arg arg_env arg_ty cont_ty thing_inside
1061 = simplExprF (setInScope arg_env call_env) arg
1062 (ArgOf is_rhs arg_ty cont_ty (\ new_env -> thing_inside (setInScope call_env new_env)))
1063 -- Notice the way we use arg_env (augmented with in-scope vars from call_env)
1064 -- to simplify the argument
1065 -- and call-env (augmented with in-scope vars from the arg) to pass to the continuation
1069 %************************************************************************
1071 \subsection{mkAtomicArgs}
1073 %************************************************************************
1075 mkAtomicArgs takes a putative RHS, checks whether it's a PAP or
1076 constructor application and, if so, converts it to ANF, so that the
1077 resulting thing can be inlined more easily. Thus
1084 There are three sorts of binding context, specified by the two
1090 N N Top-level or recursive Only bind args of lifted type
1092 N Y Non-top-level and non-recursive, Bind args of lifted type, or
1093 but lazy unlifted-and-ok-for-speculation
1095 Y Y Non-top-level, non-recursive, Bind all args
1096 and strict (demanded)
1103 there is no point in transforming to
1105 x = case (y div# z) of r -> MkC r
1107 because the (y div# z) can't float out of the let. But if it was
1108 a *strict* let, then it would be a good thing to do. Hence the
1109 context information.
1112 mkAtomicArgs :: Bool -- A strict binding
1113 -> Bool -- OK to float unlifted args
1115 -> SimplM (OrdList (OutId,OutExpr), -- The floats (unusually) may include
1116 OutExpr) -- things that need case-binding,
1117 -- if the strict-binding flag is on
1119 mkAtomicArgs is_strict ok_float_unlifted rhs
1120 | (Var fun, args) <- collectArgs rhs, -- It's an application
1121 isDataConId fun || valArgCount args < idArity fun -- And it's a constructor or PAP
1122 = go fun nilOL [] args -- Have a go
1124 | otherwise = bale_out -- Give up
1127 bale_out = returnSmpl (nilOL, rhs)
1129 go fun binds rev_args []
1130 = returnSmpl (binds, mkApps (Var fun) (reverse rev_args))
1132 go fun binds rev_args (arg : args)
1133 | exprIsTrivial arg -- Easy case
1134 = go fun binds (arg:rev_args) args
1136 | not can_float_arg -- Can't make this arg atomic
1137 = bale_out -- ... so give up
1139 | otherwise -- Don't forget to do it recursively
1140 -- E.g. x = a:b:c:[]
1141 = mkAtomicArgs is_strict ok_float_unlifted arg `thenSmpl` \ (arg_binds, arg') ->
1142 newId SLIT("a") arg_ty `thenSmpl` \ arg_id ->
1143 go fun ((arg_binds `snocOL` (arg_id,arg')) `appOL` binds)
1144 (Var arg_id : rev_args) args
1146 arg_ty = exprType arg
1147 can_float_arg = is_strict
1148 || not (isUnLiftedType arg_ty)
1149 || (ok_float_unlifted && exprOkForSpeculation arg)
1152 addAtomicBinds :: SimplEnv -> [(OutId,OutExpr)]
1153 -> (SimplEnv -> SimplM (FloatsWith a))
1154 -> SimplM (FloatsWith a)
1155 addAtomicBinds env [] thing_inside = thing_inside env
1156 addAtomicBinds env ((v,r):bs) thing_inside = addAuxiliaryBind env (NonRec v r) $ \ env ->
1157 addAtomicBinds env bs thing_inside
1159 addAtomicBindsE :: SimplEnv -> [(OutId,OutExpr)]
1160 -> (SimplEnv -> SimplM FloatsWithExpr)
1161 -> SimplM FloatsWithExpr
1162 -- Same again, but this time we're in an expression context,
1163 -- and may need to do some case bindings
1165 addAtomicBindsE env [] thing_inside
1167 addAtomicBindsE env ((v,r):bs) thing_inside
1168 | needsCaseBinding (idType v) r
1169 = addAtomicBindsE (addNewInScopeIds env [v]) bs thing_inside `thenSmpl` \ (floats, expr) ->
1170 WARN( exprIsTrivial expr, ppr v <+> pprCoreExpr expr )
1171 returnSmpl (emptyFloats env, Case r v [(DEFAULT,[], wrapFloats floats expr)])
1174 = addAuxiliaryBind env (NonRec v r) $ \ env ->
1175 addAtomicBindsE env bs thing_inside
1179 %************************************************************************
1181 \subsection{The main rebuilder}
1183 %************************************************************************
1186 rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr
1188 rebuild env expr (Stop _ _ _) = rebuildDone env expr
1189 rebuild env expr (ArgOf _ _ _ cont_fn) = cont_fn env expr
1190 rebuild env expr (CoerceIt to_ty cont) = rebuild env (mkCoerce to_ty (exprType expr) expr) cont
1191 rebuild env expr (InlinePlease cont) = rebuild env (Note InlineCall expr) cont
1192 rebuild env expr (Select _ bndr alts se cont) = rebuildCase (setInScope se env) expr bndr alts cont
1193 rebuild env expr (ApplyTo _ arg se cont) = rebuildApp (setInScope se env) expr arg cont
1195 rebuildApp env fun arg cont
1196 = simplExpr env arg `thenSmpl` \ arg' ->
1197 rebuild env (App fun arg') cont
1199 rebuildDone env expr = returnSmpl (emptyFloats env, expr)
1203 %************************************************************************
1205 \subsection{Functions dealing with a case}
1207 %************************************************************************
1209 Blob of helper functions for the "case-of-something-else" situation.
1212 ---------------------------------------------------------
1213 -- Eliminate the case if possible
1215 rebuildCase :: SimplEnv
1216 -> OutExpr -- Scrutinee
1217 -> InId -- Case binder
1218 -> [InAlt] -- Alternatives
1220 -> SimplM FloatsWithExpr
1222 rebuildCase env scrut case_bndr alts cont
1223 | Just (con,args) <- exprIsConApp_maybe scrut
1224 -- Works when the scrutinee is a variable with a known unfolding
1225 -- as well as when it's an explicit constructor application
1226 = knownCon env (DataAlt con) args case_bndr alts cont
1228 | Lit lit <- scrut -- No need for same treatment as constructors
1229 -- because literals are inlined more vigorously
1230 = knownCon env (LitAlt lit) [] case_bndr alts cont
1233 = -- Prepare case alternatives
1234 -- Filter out alternatives that can't possibly match
1236 impossible_cons = case scrut of
1237 Var v -> otherCons (idUnfolding v)
1239 better_alts = case impossible_cons of
1241 other -> [alt | alt@(con,_,_) <- alts,
1242 not (con `elem` impossible_cons)]
1244 -- "handled_cons" are handled either by the context,
1245 -- or by a branch in this case expression
1246 -- Don't add DEFAULT to the handled_cons!!
1247 (alts_wo_default, _) = findDefault better_alts
1248 handled_cons = impossible_cons ++ [con | (con,_,_) <- alts_wo_default]
1251 -- Deal with the case binder, and prepare the continuation;
1252 -- The new subst_env is in place
1253 prepareCaseCont env better_alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1254 addFloats env floats $ \ env ->
1256 -- Deal with variable scrutinee
1257 simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr', zap_occ_info) ->
1259 -- Deal with the case alternatives
1260 simplAlts alt_env zap_occ_info handled_cons
1261 case_bndr' better_alts dup_cont `thenSmpl` \ alts' ->
1263 -- Put the case back together
1264 mkCase scrut handled_cons case_bndr' alts' `thenSmpl` \ case_expr ->
1266 -- Notice that rebuildDone returns the in-scope set from env, not alt_env
1267 -- The case binder *not* scope over the whole returned case-expression
1268 rebuild env case_expr nondup_cont
1271 simplCaseBinder checks whether the scrutinee is a variable, v. If so,
1272 try to eliminate uses of v in the RHSs in favour of case_bndr; that
1273 way, there's a chance that v will now only be used once, and hence
1278 There is a time we *don't* want to do that, namely when
1279 -fno-case-of-case is on. This happens in the first simplifier pass,
1280 and enhances full laziness. Here's the bad case:
1281 f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
1282 If we eliminate the inner case, we trap it inside the I# v -> arm,
1283 which might prevent some full laziness happening. I've seen this
1284 in action in spectral/cichelli/Prog.hs:
1285 [(m,n) | m <- [1..max], n <- [1..max]]
1286 Hence the check for NoCaseOfCase.
1290 There is another situation when we don't want to do it. If we have
1292 case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
1293 ...other cases .... }
1295 We'll perform the binder-swap for the outer case, giving
1297 case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
1298 ...other cases .... }
1300 But there is no point in doing it for the inner case, because w1 can't
1301 be inlined anyway. Furthermore, doing the case-swapping involves
1302 zapping w2's occurrence info (see paragraphs that follow), and that
1303 forces us to bind w2 when doing case merging. So we get
1305 case x of w1 { A -> let w2 = w1 in e1
1306 B -> let w2 = w1 in e2
1307 ...other cases .... }
1309 This is plain silly in the common case where w2 is dead.
1311 Even so, I can't see a good way to implement this idea. I tried
1312 not doing the binder-swap if the scrutinee was already evaluated
1313 but that failed big-time:
1317 case v of w { MkT x ->
1318 case x of x1 { I# y1 ->
1319 case x of x2 { I# y2 -> ...
1321 Notice that because MkT is strict, x is marked "evaluated". But to
1322 eliminate the last case, we must either make sure that x (as well as
1323 x1) has unfolding MkT y1. THe straightforward thing to do is to do
1324 the binder-swap. So this whole note is a no-op.
1328 If we replace the scrutinee, v, by tbe case binder, then we have to nuke
1329 any occurrence info (eg IAmDead) in the case binder, because the
1330 case-binder now effectively occurs whenever v does. AND we have to do
1331 the same for the pattern-bound variables! Example:
1333 (case x of { (a,b) -> a }) (case x of { (p,q) -> q })
1335 Here, b and p are dead. But when we move the argment inside the first
1336 case RHS, and eliminate the second case, we get
1338 case x or { (a,b) -> a b }
1340 Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
1341 happened. Hence the zap_occ_info function returned by simplCaseBinder
1344 simplCaseBinder env (Var v) case_bndr
1345 | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
1347 -- Failed try [see Note 2 above]
1348 -- not (isEvaldUnfolding (idUnfolding v))
1350 = simplBinder env (zap case_bndr) `thenSmpl` \ (env, case_bndr') ->
1351 returnSmpl (modifyInScope env v case_bndr', case_bndr', zap)
1352 -- We could extend the substitution instead, but it would be
1353 -- a hack because then the substitution wouldn't be idempotent
1354 -- any more (v is an OutId). And this just just as well.
1356 zap b = b `setIdOccInfo` NoOccInfo
1358 simplCaseBinder env other_scrut case_bndr
1359 = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') ->
1360 returnSmpl (env, case_bndr', \ bndr -> bndr) -- NoOp on bndr
1366 simplAlts :: SimplEnv
1367 -> (InId -> InId) -- Occ-info zapper
1368 -> [AltCon] -- Alternatives the scrutinee can't be
1369 -- in the default case
1370 -> OutId -- Case binder
1371 -> [InAlt] -> SimplCont
1372 -> SimplM [OutAlt] -- Includes the continuation
1374 simplAlts env zap_occ_info handled_cons case_bndr' alts cont'
1375 = mapSmpl simpl_alt alts
1377 inst_tys' = tyConAppArgs (idType case_bndr')
1379 simpl_alt (DEFAULT, _, rhs)
1381 -- In the default case we record the constructors that the
1382 -- case-binder *can't* be.
1383 -- We take advantage of any OtherCon info in the case scrutinee
1384 case_bndr_w_unf = case_bndr' `setIdUnfolding` mkOtherCon handled_cons
1385 env_with_unf = modifyInScope env case_bndr' case_bndr_w_unf
1387 simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
1388 returnSmpl (DEFAULT, [], rhs')
1390 simpl_alt (con, vs, rhs)
1391 = -- Deal with the pattern-bound variables
1392 -- Mark the ones that are in ! positions in the data constructor
1393 -- as certainly-evaluated.
1394 -- NB: it happens that simplBinders does *not* erase the OtherCon
1395 -- form of unfolding, so it's ok to add this info before
1396 -- doing simplBinders
1397 simplBinders env (add_evals con vs) `thenSmpl` \ (env, vs') ->
1399 -- Bind the case-binder to (con args)
1401 unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys')
1402 env_with_unf = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` unfolding)
1404 simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' ->
1405 returnSmpl (con, vs', rhs')
1408 -- add_evals records the evaluated-ness of the bound variables of
1409 -- a case pattern. This is *important*. Consider
1410 -- data T = T !Int !Int
1412 -- case x of { T a b -> T (a+1) b }
1414 -- We really must record that b is already evaluated so that we don't
1415 -- go and re-evaluate it when constructing the result.
1417 add_evals (DataAlt dc) vs = cat_evals vs (dataConRepStrictness dc)
1418 add_evals other_con vs = vs
1420 cat_evals [] [] = []
1421 cat_evals (v:vs) (str:strs)
1422 | isTyVar v = v : cat_evals vs (str:strs)
1423 | isMarkedStrict str = evald_v : cat_evals vs strs
1424 | otherwise = zapped_v : cat_evals vs strs
1426 zapped_v = zap_occ_info v
1427 evald_v = zapped_v `setIdUnfolding` mkOtherCon []
1431 %************************************************************************
1433 \subsection{Known constructor}
1435 %************************************************************************
1437 We are a bit careful with occurrence info. Here's an example
1439 (\x* -> case x of (a*, b) -> f a) (h v, e)
1441 where the * means "occurs once". This effectively becomes
1442 case (h v, e) of (a*, b) -> f a)
1444 let a* = h v; b = e in f a
1448 All this should happen in one sweep.
1451 knownCon :: SimplEnv -> AltCon -> [OutExpr]
1452 -> InId -> [InAlt] -> SimplCont
1453 -> SimplM FloatsWithExpr
1455 knownCon env con args bndr alts cont
1456 = tick (KnownBranch bndr) `thenSmpl_`
1457 case findAlt con alts of
1458 (DEFAULT, bs, rhs) -> ASSERT( null bs )
1459 simplNonRecX env bndr scrut $ \ env ->
1460 -- This might give rise to a binding with non-atomic args
1461 -- like x = Node (f x) (g x)
1462 -- but no harm will be done
1463 simplExprF env rhs cont
1466 LitAlt lit -> Lit lit
1467 DataAlt dc -> mkConApp dc args
1469 (LitAlt lit, bs, rhs) -> ASSERT( null bs )
1470 simplNonRecX env bndr (Lit lit) $ \ env ->
1471 simplExprF env rhs cont
1473 (DataAlt dc, bs, rhs) -> ASSERT( length bs + n_tys == length args )
1474 bind_args env bs (drop n_tys args) $ \ env ->
1476 con_app = mkConApp dc (take n_tys args ++ con_args)
1477 con_args = [substExpr (getSubst env) (varToCoreExpr b) | b <- bs]
1478 -- args are aready OutExprs, but bs are InIds
1480 simplNonRecX env bndr con_app $ \ env ->
1481 simplExprF env rhs cont
1483 n_tys = dataConNumInstArgs dc -- Non-existential type args
1485 bind_args env [] _ thing_inside = thing_inside env
1487 bind_args env (b:bs) (Type ty : args) thing_inside
1488 = bind_args (extendSubst env b (DoneTy ty)) bs args thing_inside
1490 bind_args env (b:bs) (arg : args) thing_inside
1491 = simplNonRecX env b arg $ \ env ->
1492 bind_args env bs args thing_inside
1496 %************************************************************************
1498 \subsection{Duplicating continuations}
1500 %************************************************************************
1503 prepareCaseCont :: SimplEnv
1504 -> [InAlt] -> SimplCont
1505 -> SimplM (FloatsWith (SimplCont,SimplCont))
1506 -- Return a duplicatable continuation, a non-duplicable part
1507 -- plus some extra bindings
1509 -- No need to make it duplicatable if there's only one alternative
1510 prepareCaseCont env [alt] cont = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
1511 prepareCaseCont env alts cont = mkDupableCont env cont
1515 mkDupableCont :: SimplEnv -> SimplCont
1516 -> SimplM (FloatsWith (SimplCont, SimplCont))
1518 mkDupableCont env cont
1519 | contIsDupable cont
1520 = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
1522 mkDupableCont env (CoerceIt ty cont)
1523 = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1524 returnSmpl (floats, (CoerceIt ty dup_cont, nondup_cont))
1526 mkDupableCont env (InlinePlease cont)
1527 = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1528 returnSmpl (floats, (InlinePlease dup_cont, nondup_cont))
1530 mkDupableCont env cont@(ArgOf _ arg_ty _ _)
1531 = returnSmpl (emptyFloats env, (mkBoringStop arg_ty, cont))
1532 -- Do *not* duplicate an ArgOf continuation
1533 -- Because ArgOf continuations are opaque, we gain nothing by
1534 -- propagating them into the expressions, and we do lose a lot.
1535 -- Here's an example:
1536 -- && (case x of { T -> F; F -> T }) E
1537 -- Now, && is strict so we end up simplifying the case with
1538 -- an ArgOf continuation. If we let-bind it, we get
1540 -- let $j = \v -> && v E
1541 -- in simplExpr (case x of { T -> F; F -> T })
1542 -- (ArgOf (\r -> $j r)
1543 -- And after simplifying more we get
1545 -- let $j = \v -> && v E
1546 -- in case of { T -> $j F; F -> $j T }
1547 -- Which is a Very Bad Thing
1549 -- The desire not to duplicate is the entire reason that
1550 -- mkDupableCont returns a pair of continuations.
1552 -- The original plan had:
1553 -- e.g. (...strict-fn...) [...hole...]
1555 -- let $j = \a -> ...strict-fn...
1556 -- in $j [...hole...]
1558 mkDupableCont env (ApplyTo _ arg se cont)
1559 = -- e.g. [...hole...] (...arg...)
1561 -- let a = ...arg...
1562 -- in [...hole...] a
1563 simplExpr (setInScope se env) arg `thenSmpl` \ arg' ->
1565 mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
1566 addFloats env floats $ \ env ->
1568 if exprIsDupable arg' then
1569 returnSmpl (emptyFloats env, (ApplyTo OkToDup arg' (zapSubstEnv se) dup_cont, nondup_cont))
1571 newId SLIT("a") (exprType arg') `thenSmpl` \ arg_id ->
1573 tick (CaseOfCase arg_id) `thenSmpl_`
1574 -- Want to tick here so that we go round again,
1575 -- and maybe copy or inline the code.
1576 -- Not strictly CaseOfCase, but never mind
1578 returnSmpl (unitFloat env arg_id arg',
1579 (ApplyTo OkToDup (Var arg_id) (zapSubstEnv se) dup_cont,
1581 -- But what if the arg should be case-bound?
1582 -- This has been this way for a long time, so I'll leave it,
1583 -- but I can't convince myself that it's right.
1586 mkDupableCont env (Select _ case_bndr alts se cont)
1587 = -- e.g. (case [...hole...] of { pi -> ei })
1589 -- let ji = \xij -> ei
1590 -- in case [...hole...] of { pi -> ji xij }
1591 tick (CaseOfCase case_bndr) `thenSmpl_`
1593 alt_env = setInScope se env
1595 prepareCaseCont alt_env alts cont `thenSmpl` \ (floats1, (dup_cont, nondup_cont)) ->
1596 addFloats alt_env floats1 $ \ alt_env ->
1598 simplBinder alt_env case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
1599 -- NB: simplBinder does not zap deadness occ-info, so
1600 -- a dead case_bndr' will still advertise its deadness
1601 -- This is really important because in
1602 -- case e of b { (# a,b #) -> ... }
1603 -- b is always dead, and indeed we are not allowed to bind b to (# a,b #),
1604 -- which might happen if e was an explicit unboxed pair and b wasn't marked dead.
1605 -- In the new alts we build, we have the new case binder, so it must retain
1608 mkDupableAlts alt_env case_bndr' alts dup_cont `thenSmpl` \ (floats2, alts') ->
1609 addFloats alt_env floats2 $ \ alt_env ->
1610 returnSmpl (emptyFloats alt_env,
1611 (Select OkToDup case_bndr' alts' (zapSubstEnv se)
1612 (mkBoringStop (contResultType dup_cont)),
1615 mkDupableAlts :: SimplEnv -> OutId -> [InAlt] -> SimplCont
1616 -> SimplM (FloatsWith [InAlt])
1617 -- Absorbs the continuation into the new alternatives
1619 mkDupableAlts env case_bndr' alts dupable_cont
1622 go env [] = returnSmpl (emptyFloats env, [])
1624 = mkDupableAlt env case_bndr' dupable_cont alt `thenSmpl` \ (floats1, alt') ->
1625 addFloats env floats1 $ \ env ->
1626 go env alts `thenSmpl` \ (floats2, alts') ->
1627 returnSmpl (floats2, alt' : alts')
1629 mkDupableAlt env case_bndr' cont alt@(con, bndrs, rhs)
1630 = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
1631 simplExprC env rhs cont `thenSmpl` \ rhs' ->
1633 if exprIsDupable rhs' then
1634 returnSmpl (emptyFloats env, (con, bndrs', rhs'))
1635 -- It is worth checking for a small RHS because otherwise we
1636 -- get extra let bindings that may cause an extra iteration of the simplifier to
1637 -- inline back in place. Quite often the rhs is just a variable or constructor.
1638 -- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
1639 -- iterations because the version with the let bindings looked big, and so wasn't
1640 -- inlined, but after the join points had been inlined it looked smaller, and so
1643 -- NB: we have to check the size of rhs', not rhs.
1644 -- Duplicating a small InAlt might invalidate occurrence information
1645 -- However, if it *is* dupable, we return the *un* simplified alternative,
1646 -- because otherwise we'd need to pair it up with an empty subst-env....
1647 -- but we only have one env shared between all the alts.
1648 -- (Remember we must zap the subst-env before re-simplifying something).
1649 -- Rather than do this we simply agree to re-simplify the original (small) thing later.
1653 rhs_ty' = exprType rhs'
1654 used_bndrs' = filter (not . isDeadBinder) (case_bndr' : bndrs')
1655 -- The deadness info on the new binders is unscathed
1657 -- If we try to lift a primitive-typed something out
1658 -- for let-binding-purposes, we will *caseify* it (!),
1659 -- with potentially-disastrous strictness results. So
1660 -- instead we turn it into a function: \v -> e
1661 -- where v::State# RealWorld#. The value passed to this function
1662 -- is realworld#, which generates (almost) no code.
1664 -- There's a slight infelicity here: we pass the overall
1665 -- case_bndr to all the join points if it's used in *any* RHS,
1666 -- because we don't know its usage in each RHS separately
1668 -- We used to say "&& isUnLiftedType rhs_ty'" here, but now
1669 -- we make the join point into a function whenever used_bndrs'
1670 -- is empty. This makes the join-point more CPR friendly.
1671 -- Consider: let j = if .. then I# 3 else I# 4
1672 -- in case .. of { A -> j; B -> j; C -> ... }
1674 -- Now CPR doesn't w/w j because it's a thunk, so
1675 -- that means that the enclosing function can't w/w either,
1676 -- which is a lose. Here's the example that happened in practice:
1677 -- kgmod :: Int -> Int -> Int
1678 -- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
1682 -- I have seen a case alternative like this:
1683 -- True -> \v -> ...
1684 -- It's a bit silly to add the realWorld dummy arg in this case, making
1687 -- (the \v alone is enough to make CPR happy) but I think it's rare
1689 ( if null used_bndrs'
1690 then newId SLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id ->
1691 returnSmpl ([rw_id], [Var realWorldPrimId])
1693 returnSmpl (used_bndrs', map varToCoreExpr used_bndrs')
1694 ) `thenSmpl` \ (final_bndrs', final_args) ->
1696 -- See comment about "$j" name above
1697 newId SLIT("$j") (mkPiTypes final_bndrs' rhs_ty') `thenSmpl` \ join_bndr ->
1698 -- Notice the funky mkPiTypes. If the contructor has existentials
1699 -- it's possible that the join point will be abstracted over
1700 -- type varaibles as well as term variables.
1701 -- Example: Suppose we have
1702 -- data T = forall t. C [t]
1704 -- case (case e of ...) of
1705 -- C t xs::[t] -> rhs
1706 -- We get the join point
1707 -- let j :: forall t. [t] -> ...
1708 -- j = /\t \xs::[t] -> rhs
1710 -- case (case e of ...) of
1711 -- C t xs::[t] -> j t xs
1713 -- We make the lambdas into one-shot-lambdas. The
1714 -- join point is sure to be applied at most once, and doing so
1715 -- prevents the body of the join point being floated out by
1716 -- the full laziness pass
1717 really_final_bndrs = map one_shot final_bndrs'
1718 one_shot v | isId v = setOneShotLambda v
1720 join_rhs = mkLams really_final_bndrs rhs'
1721 join_call = mkApps (Var join_bndr) final_args
1723 returnSmpl (unitFloat env join_bndr join_rhs, (con, bndrs', join_call))