2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[SimplCore]{Driver for simplifying @Core@ programs}
8 -- The above warning supression flag is a temporary kludge.
9 -- While working on this module you are encouraged to remove it and fix
10 -- any warnings in the module. See
11 -- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
14 module SimplCore ( core2core, simplifyExpr ) where
16 #include "HsVersions.h"
18 import DynFlags ( DynFlags, DynFlag(..), dopt )
22 import CSE ( cseProgram )
23 import Rules ( RuleBase, emptyRuleBase, mkRuleBase, unionRuleBase,
24 extendRuleBaseList, pprRuleBase, pprRulesForUser,
25 ruleCheckProgram, rulesOfBinds,
26 addSpecInfo, addIdSpecialisations )
27 import PprCore ( pprCoreBindings, pprCoreExpr, pprRules )
28 import OccurAnal ( occurAnalysePgm, occurAnalyseExpr )
30 import CoreUtils ( coreBindsSize )
31 import Simplify ( simplTopBinds, simplExpr )
32 import SimplUtils ( simplEnvForGHCi, simplEnvForRules )
36 import qualified ErrUtils as Err
38 import FloatIn ( floatInwards )
39 import FloatOut ( floatOutwards )
43 import TyCon ( tyConDataCons )
44 import Class ( classSelIds )
45 import BasicTypes ( CompilerPhase, isActive, isDefaultInlinePragma )
48 import NameEnv ( lookupNameEnv )
49 import LiberateCase ( liberateCase )
50 import SAT ( doStaticArgs )
51 import Specialise ( specProgram)
52 import SpecConstr ( specConstrProgram)
53 import DmdAnal ( dmdAnalPgm )
54 import WorkWrap ( wwTopBinds )
55 import Vectorise ( vectorise )
59 import UniqSupply ( UniqSupply, mkSplitUniqSupply, splitUniqSupply )
67 %************************************************************************
69 \subsection{The driver for the simplifier}
71 %************************************************************************
78 core2core hsc_env guts = do
79 let dflags = hsc_dflags hsc_env
81 us <- mkSplitUniqSupply 's'
82 let (cp_us, ru_us) = splitUniqSupply us
84 -- COMPUTE THE RULE BASE TO USE
85 -- See Note [Overall plumbing for rules] in Rules.lhs
86 (hpt_rule_base, guts1) <- prepareRules hsc_env guts ru_us
88 -- Get the module out of the current HscEnv so we can retrieve it from the monad.
89 -- This is very convienent for the users of the monad (e.g. plugins do not have to
90 -- consume the ModGuts to find the module) but somewhat ugly because mg_module may
91 -- _theoretically_ be changed during the Core pipeline (it's part of ModGuts), which
92 -- would mean our cached value would go out of date.
93 let mod = mg_module guts
94 (guts2, stats) <- runCoreM hsc_env hpt_rule_base cp_us mod $ do
95 -- FIND BUILT-IN PASSES
96 let builtin_core_todos = getCoreToDo dflags
99 doCorePasses builtin_core_todos guts1
101 Err.dumpIfSet_dyn dflags Opt_D_dump_simpl_stats
102 "Grand total simplifier statistics"
103 (pprSimplCount stats)
108 type CorePass = CoreToDo
110 simplifyExpr :: DynFlags -- includes spec of what core-to-core passes to do
113 -- simplifyExpr is called by the driver to simplify an
114 -- expression typed in at the interactive prompt
116 -- Also used by Template Haskell
117 simplifyExpr dflags expr
119 ; Err.showPass dflags "Simplify"
121 ; us <- mkSplitUniqSupply 's'
123 ; let (expr', _counts) = initSmpl dflags emptyRuleBase emptyFamInstEnvs us $
124 simplExprGently simplEnvForGHCi expr
126 ; Err.dumpIfSet_dyn dflags Opt_D_dump_simpl "Simplified expression"
132 doCorePasses :: [CorePass] -> ModGuts -> CoreM ModGuts
133 doCorePasses passes guts
134 = foldM do_pass guts passes
136 do_pass guts CoreDoNothing = return guts
137 do_pass guts (CoreDoPasses ps) = doCorePasses ps guts
139 = do { dflags <- getDynFlags
140 ; liftIO $ showPass dflags pass
141 ; guts' <- doCorePass pass guts
142 ; liftIO $ endPass dflags pass (mg_binds guts') (mg_rules guts')
145 doCorePass :: CorePass -> ModGuts -> CoreM ModGuts
146 doCorePass pass@(CoreDoSimplify {}) = {-# SCC "Simplify" #-}
149 doCorePass CoreCSE = {-# SCC "CommonSubExpr" #-}
152 doCorePass CoreLiberateCase = {-# SCC "LiberateCase" #-}
155 doCorePass CoreDoFloatInwards = {-# SCC "FloatInwards" #-}
158 doCorePass (CoreDoFloatOutwards f) = {-# SCC "FloatOutwards" #-}
159 doPassDUM (floatOutwards f)
161 doCorePass CoreDoStaticArgs = {-# SCC "StaticArgs" #-}
164 doCorePass CoreDoStrictness = {-# SCC "Stranal" #-}
167 doCorePass CoreDoWorkerWrapper = {-# SCC "WorkWrap" #-}
170 doCorePass CoreDoSpecialising = {-# SCC "Specialise" #-}
173 doCorePass CoreDoSpecConstr = {-# SCC "SpecConstr" #-}
176 doCorePass (CoreDoVectorisation be) = {-# SCC "Vectorise" #-}
179 doCorePass CoreDoGlomBinds = doPassDM glomBinds
180 doCorePass CoreDoPrintCore = observe printCore
181 doCorePass (CoreDoRuleCheck phase pat) = ruleCheck phase pat
182 doCorePass CoreDoNothing = return
183 doCorePass (CoreDoPasses passes) = doCorePasses passes
186 %************************************************************************
188 \subsection{Core pass combinators}
190 %************************************************************************
193 printCore _ binds = Err.dumpIfSet True "Print Core" (pprCoreBindings binds)
195 ruleCheck :: CompilerPhase -> String -> ModGuts -> CoreM ModGuts
196 ruleCheck current_phase pat guts = do
198 dflags <- getDynFlags
199 liftIO $ Err.showPass dflags "RuleCheck"
200 liftIO $ printDump (ruleCheckProgram current_phase pat rb (mg_binds guts))
204 doPassDMS :: (DynFlags -> [CoreBind] -> IO (SimplCount, [CoreBind])) -> ModGuts -> CoreM ModGuts
205 doPassDMS do_pass = doPassM $ \binds -> do
206 dflags <- getDynFlags
207 liftIOWithCount $ do_pass dflags binds
209 doPassDUM :: (DynFlags -> UniqSupply -> [CoreBind] -> IO [CoreBind]) -> ModGuts -> CoreM ModGuts
210 doPassDUM do_pass = doPassM $ \binds -> do
211 dflags <- getDynFlags
212 us <- getUniqueSupplyM
213 liftIO $ do_pass dflags us binds
215 doPassDM :: (DynFlags -> [CoreBind] -> IO [CoreBind]) -> ModGuts -> CoreM ModGuts
216 doPassDM do_pass = doPassDUM (\dflags -> const (do_pass dflags))
218 doPassD :: (DynFlags -> [CoreBind] -> [CoreBind]) -> ModGuts -> CoreM ModGuts
219 doPassD do_pass = doPassDM (\dflags -> return . do_pass dflags)
221 doPassDU :: (DynFlags -> UniqSupply -> [CoreBind] -> [CoreBind]) -> ModGuts -> CoreM ModGuts
222 doPassDU do_pass = doPassDUM (\dflags us -> return . do_pass dflags us)
224 doPassU :: (UniqSupply -> [CoreBind] -> [CoreBind]) -> ModGuts -> CoreM ModGuts
225 doPassU do_pass = doPassDU (const do_pass)
227 -- Most passes return no stats and don't change rules: these combinators
228 -- let us lift them to the full blown ModGuts+CoreM world
229 doPassM :: Monad m => ([CoreBind] -> m [CoreBind]) -> ModGuts -> m ModGuts
230 doPassM bind_f guts = do
231 binds' <- bind_f (mg_binds guts)
232 return (guts { mg_binds = binds' })
234 doPassMG :: Monad m => (ModGuts -> m [CoreBind]) -> ModGuts -> m ModGuts
235 doPassMG bind_f guts = do
236 binds' <- bind_f guts
237 return (guts { mg_binds = binds' })
239 doPass :: ([CoreBind] -> [CoreBind]) -> ModGuts -> CoreM ModGuts
240 doPass bind_f guts = return $ guts { mg_binds = bind_f (mg_binds guts) }
242 -- Observer passes just peek; don't modify the bindings at all
243 observe :: (DynFlags -> [CoreBind] -> IO a) -> ModGuts -> CoreM ModGuts
244 observe do_pass = doPassM $ \binds -> do
245 dflags <- getDynFlags
246 liftIO $ do_pass dflags binds
251 %************************************************************************
255 %************************************************************************
257 -- prepareLocalRuleBase takes the CoreBinds and rules defined in this module.
258 -- It attaches those rules that are for local Ids to their binders, and
259 -- returns the remainder attached to Ids in an IdSet.
262 prepareRules :: HscEnv
265 -> IO (RuleBase, -- Rule base for imported things, incl
266 -- (a) rules defined in this module (orphans)
267 -- (b) rules from other modules in home package
268 -- but not things from other packages
270 ModGuts) -- Modified fields are
271 -- (a) Bindings have rules attached,
272 -- and INLINE rules simplified
273 -- (b) Rules are now just orphan rules
275 prepareRules hsc_env@(HscEnv { hsc_dflags = dflags, hsc_HPT = hpt })
276 guts@(ModGuts { mg_binds = binds, mg_deps = deps
277 , mg_rules = local_rules, mg_rdr_env = rdr_env })
279 = do { us <- mkSplitUniqSupply 'w'
281 ; let -- Simplify the local rules; boringly, we need to make an in-scope set
282 -- from the local binders, to avoid warnings from Simplify.simplVar
283 local_ids = mkInScopeSet (mkVarSet (bindersOfBinds binds))
284 env = setInScopeSet simplEnvForRules local_ids
285 (simpl_rules, _) = initSmpl dflags emptyRuleBase emptyFamInstEnvs us $
286 mapM (simplRule env) local_rules
288 ; let (rules_for_locals, rules_for_imps) = partition isLocalRule simpl_rules
290 home_pkg_rules = hptRules hsc_env (dep_mods deps)
291 hpt_rule_base = mkRuleBase home_pkg_rules
292 binds_w_rules = updateBinders rules_for_locals binds
295 ; Err.dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
296 (withPprStyle (mkUserStyle (mkPrintUnqualified dflags rdr_env) AllTheWay) $
297 vcat [text "Local rules for local Ids", pprRules simpl_rules,
299 text "Local rules for imported Ids", pprRuleBase hpt_rule_base])
301 ; return (hpt_rule_base, guts { mg_binds = binds_w_rules,
302 mg_rules = rules_for_imps })
305 -- Note [Attach rules to local ids]
306 -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
307 -- Find the rules for locally-defined Ids; then we can attach them
308 -- to the binders in the top-level bindings
311 -- - It makes the rules easier to look up
312 -- - It means that transformation rules and specialisations for
313 -- locally defined Ids are handled uniformly
314 -- - It keeps alive things that are referred to only from a rule
315 -- (the occurrence analyser knows about rules attached to Ids)
316 -- - It makes sure that, when we apply a rule, the free vars
317 -- of the RHS are more likely to be in scope
318 -- - The imported rules are carried in the in-scope set
319 -- which is extended on each iteration by the new wave of
320 -- local binders; any rules which aren't on the binding will
321 -- thereby get dropped
323 updateBinders :: [CoreRule] -> [CoreBind] -> [CoreBind]
324 updateBinders rules_for_locals binds
325 = map update_bind binds
327 local_rules = extendRuleBaseList emptyRuleBase rules_for_locals
329 update_bind (NonRec b r) = NonRec (add_rules b) r
330 update_bind (Rec prs) = Rec (mapFst add_rules prs)
332 -- See Note [Attach rules to local ids]
333 -- NB: the binder might have some existing rules,
334 -- arising from specialisation pragmas
336 | Just rules <- lookupNameEnv local_rules (idName bndr)
337 = bndr `addIdSpecialisations` rules
342 Note [Simplifying the left-hand side of a RULE]
343 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
344 We must do some gentle simplification on the lhs (template) of each
345 rule. The case that forced me to add this was the fold/build rule,
346 which without simplification looked like:
347 fold k z (build (/\a. g a)) ==> ...
348 This doesn't match unless you do eta reduction on the build argument.
349 Similarly for a LHS like
351 we do not want to get
352 augment (\a. g a) (build h)
353 otherwise we don't match when given an argument like
354 augment (\a. h a a) (build h)
356 The simplifier does indeed do eta reduction (it's in
357 Simplify.completeLam) but only if -O is on.
360 simplRule :: SimplEnv -> CoreRule -> SimplM CoreRule
361 simplRule env rule@(BuiltinRule {})
363 simplRule env rule@(Rule { ru_bndrs = bndrs, ru_args = args, ru_rhs = rhs })
364 = do (env, bndrs') <- simplBinders env bndrs
365 args' <- mapM (simplExprGently env) args
366 rhs' <- simplExprGently env rhs
367 return (rule { ru_bndrs = bndrs', ru_args = args'
368 , ru_rhs = occurAnalyseExpr rhs' })
372 simplExprGently :: SimplEnv -> CoreExpr -> SimplM CoreExpr
373 -- Simplifies an expression
374 -- does occurrence analysis, then simplification
375 -- and repeats (twice currently) because one pass
376 -- alone leaves tons of crud.
377 -- Used (a) for user expressions typed in at the interactive prompt
378 -- (b) the LHS and RHS of a RULE
379 -- (c) Template Haskell splices
381 -- The name 'Gently' suggests that the SimplifierMode is SimplGently,
382 -- and in fact that is so.... but the 'Gently' in simplExprGently doesn't
383 -- enforce that; it just simplifies the expression twice
385 -- It's important that simplExprGently does eta reduction; see
386 -- Note [Simplifying the left-hand side of a RULE] above. The
387 -- simplifier does indeed do eta reduction (it's in Simplify.completeLam)
388 -- but only if -O is on.
390 simplExprGently env expr = do
391 expr1 <- simplExpr env (occurAnalyseExpr expr)
392 simplExpr env (occurAnalyseExpr expr1)
396 %************************************************************************
398 \subsection{Glomming}
400 %************************************************************************
403 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
404 -- Glom all binds together in one Rec, in case any
405 -- transformations have introduced any new dependencies
407 -- NB: the global invariant is this:
408 -- *** the top level bindings are never cloned, and are always unique ***
410 -- We sort them into dependency order, but applying transformation rules may
411 -- make something at the top refer to something at the bottom:
415 -- RULE: p (q x) = h x
417 -- Applying this rule makes f refer to h,
418 -- although it doesn't appear to in the source program.
419 -- This pass lets us control where it happens.
421 -- NOTICE that this cannot happen for rules whose head is a locally-defined
422 -- function. It only happens for rules whose head is an imported function
423 -- (p in the example above). So, for example, the rule had been
424 -- RULE: f (p x) = h x
425 -- then the rule for f would be attached to f itself (in its IdInfo)
426 -- by prepareLocalRuleBase and h would be regarded by the occurrency
427 -- analyser as free in f.
429 glomBinds dflags binds
430 = do { Err.showPass dflags "GlomBinds" ;
431 let { recd_binds = [Rec (flattenBinds binds)] } ;
433 -- Not much point in printing the result...
434 -- just consumes output bandwidth
438 %************************************************************************
440 \subsection{The driver for the simplifier}
442 %************************************************************************
445 simplifyPgm :: CoreToDo -> ModGuts -> CoreM ModGuts
446 simplifyPgm pass guts
447 = do { hsc_env <- getHscEnv
448 ; us <- getUniqueSupplyM
451 simplifyPgmIO pass hsc_env us rb guts }
453 simplifyPgmIO :: CoreToDo
458 -> IO (SimplCount, ModGuts) -- New bindings
460 simplifyPgmIO pass@(CoreDoSimplify mode max_iterations switches)
461 hsc_env us hpt_rule_base
462 guts@(ModGuts { mg_binds = binds, mg_rules = rules
463 , mg_fam_inst_env = fam_inst_env })
465 (termination_msg, it_count, counts_out, guts')
466 <- do_iteration us 1 (zeroSimplCount dflags) binds rules ;
468 Err.dumpIfSet (dump_phase && dopt Opt_D_dump_simpl_stats dflags)
469 "Simplifier statistics for following pass"
470 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
472 pprSimplCount counts_out]);
474 return (counts_out, guts')
477 dflags = hsc_dflags hsc_env
478 dump_phase = dumpSimplPhase dflags mode
479 sw_chkr = isAmongSimpl switches
480 do_iteration :: UniqSupply
481 -> Int -- Counts iterations
482 -> SimplCount -- Logs optimisations performed
483 -> [CoreBind] -- Bindings in
484 -> [CoreRule] -- and orphan rules
485 -> IO (String, Int, SimplCount, ModGuts)
487 do_iteration us iteration_no counts binds rules
488 -- iteration_no is the number of the iteration we are
489 -- about to begin, with '1' for the first
490 | iteration_no > max_iterations -- Stop if we've run out of iterations
491 = WARN(debugIsOn && (max_iterations > 2),
492 text ("Simplifier still going after " ++
493 show max_iterations ++
494 " iterations; bailing out. Size = " ++ show (coreBindsSize binds) ++ "\n" ))
495 -- Subtract 1 from iteration_no to get the
496 -- number of iterations we actually completed
497 return ("Simplifier bailed out", iteration_no - 1, counts,
498 guts { mg_binds = binds, mg_rules = rules })
500 -- Try and force thunks off the binds; significantly reduces
501 -- space usage, especially with -O. JRS, 000620.
502 | let sz = coreBindsSize binds in sz == sz
504 -- Occurrence analysis
505 let { tagged_binds = {-# SCC "OccAnal" #-} occurAnalysePgm binds rules } ;
506 Err.dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
507 (pprCoreBindings tagged_binds);
509 -- Get any new rules, and extend the rule base
510 -- See Note [Overall plumbing for rules] in Rules.lhs
511 -- We need to do this regularly, because simplification can
512 -- poke on IdInfo thunks, which in turn brings in new rules
513 -- behind the scenes. Otherwise there's a danger we'll simply
514 -- miss the rules for Ids hidden inside imported inlinings
515 eps <- hscEPS hsc_env ;
516 let { rule_base1 = unionRuleBase hpt_rule_base (eps_rule_base eps)
517 ; rule_base2 = extendRuleBaseList rule_base1 rules
518 ; simpl_env = mkSimplEnv sw_chkr mode
519 ; simpl_binds = {-# SCC "SimplTopBinds" #-}
520 simplTopBinds simpl_env tagged_binds
521 ; fam_envs = (eps_fam_inst_env eps, fam_inst_env) } ;
523 -- Simplify the program
524 -- We do this with a *case* not a *let* because lazy pattern
525 -- matching bit us with bad space leak!
526 -- With a let, we ended up with
531 -- case t of {(_,counts') -> if counts'=0 then ... }
532 -- So the conditional didn't force counts', because the
533 -- selection got duplicated. Sigh!
534 case initSmpl dflags rule_base2 fam_envs us1 simpl_binds of {
535 (env1, counts1) -> do {
537 let { all_counts = counts `plusSimplCount` counts1
538 ; binds1 = getFloats env1
539 ; rules1 = substRulesForImportedIds (mkCoreSubst (text "imp-rules") env1) rules
542 -- Stop if nothing happened; don't dump output
543 if isZeroSimplCount counts1 then
544 return ("Simplifier reached fixed point", iteration_no, all_counts,
545 guts { mg_binds = binds1, mg_rules = rules1 })
547 -- Short out indirections
548 -- We do this *after* at least one run of the simplifier
549 -- because indirection-shorting uses the export flag on *occurrences*
550 -- and that isn't guaranteed to be ok until after the first run propagates
551 -- stuff from the binding site to its occurrences
553 -- ToDo: alas, this means that indirection-shorting does not happen at all
554 -- if the simplifier does nothing (not common, I know, but unsavoury)
555 let { binds2 = {-# SCC "ZapInd" #-} shortOutIndirections binds1 } ;
557 -- Dump the result of this iteration
558 end_iteration dflags pass iteration_no counts1 binds2 rules1 ;
561 do_iteration us2 (iteration_no + 1) all_counts binds2 rules1
564 (us1, us2) = splitUniqSupply us
567 end_iteration :: DynFlags -> CoreToDo -> Int
568 -> SimplCount -> [CoreBind] -> [CoreRule] -> IO ()
569 -- Same as endIteration but with simplifier counts
570 end_iteration dflags pass iteration_no counts binds rules
571 = do { dumpIfSet (dopt Opt_D_dump_simpl_iterations dflags)
572 pass (ptext (sLit "Simplifier counts"))
573 (pprSimplCount counts)
575 ; endIteration dflags pass iteration_no binds rules }
579 %************************************************************************
581 Shorting out indirections
583 %************************************************************************
587 x_local = <expression>
591 where x_exported is exported, and x_local is not, then we replace it with this:
593 x_exported = <expression>
597 Without this we never get rid of the x_exported = x_local thing. This
598 save a gratuitous jump (from \tr{x_exported} to \tr{x_local}), and
599 makes strictness information propagate better. This used to happen in
600 the final phase, but it's tidier to do it here.
602 Note [Transferring IdInfo]
603 ~~~~~~~~~~~~~~~~~~~~~~~~~~
604 We want to propagage any useful IdInfo on x_local to x_exported.
606 STRICTNESS: if we have done strictness analysis, we want the strictness info on
607 x_local to transfer to x_exported. Hence the copyIdInfo call.
609 RULES: we want to *add* any RULES for x_local to x_exported.
612 Note [Messing up the exported Id's RULES]
613 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
614 We must be careful about discarding (obviously) or even merging the
615 RULES on the exported Id. The example that went bad on me at one stage
618 iterate :: (a -> a) -> a -> [a]
620 iterate = iterateList
622 iterateFB c f x = x `c` iterateFB c f (f x)
623 iterateList f x = x : iterateList f (f x)
627 "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
628 "iterateFB" iterateFB (:) = iterateList
631 This got shorted out to:
633 iterateList :: (a -> a) -> a -> [a]
634 iterateList = iterate
636 iterateFB c f x = x `c` iterateFB c f (f x)
637 iterate f x = x : iterate f (f x)
640 "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
641 "iterateFB" iterateFB (:) = iterate
644 And now we get an infinite loop in the rule system
645 iterate f x -> build (\cn -> iterateFB c f x)
650 use rule switching-off pragmas to get rid
651 of iterateList in the first place
653 But in principle the user *might* want rules that only apply to the Id
654 he says. And inline pragmas are similar
658 Then we do not want to get rid of the NOINLINE.
660 Hence hasShortableIdinfo.
663 Note [Rules and indirection-zapping]
664 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
665 Problem: what if x_exported has a RULE that mentions something in ...bindings...?
666 Then the things mentioned can be out of scope! Solution
667 a) Make sure that in this pass the usage-info from x_exported is
668 available for ...bindings...
669 b) If there are any such RULES, rec-ify the entire top-level.
670 It'll get sorted out next time round
674 If more than one exported thing is equal to a local thing (i.e., the
675 local thing really is shared), then we do one only:
678 x_exported1 = x_local
679 x_exported2 = x_local
683 x_exported2 = x_exported1
686 We rely on prior eta reduction to simplify things like
688 x_exported = /\ tyvars -> x_local tyvars
692 Hence,there's a possibility of leaving unchanged something like this:
695 x_exported1 = x_local Int
697 By the time we've thrown away the types in STG land this
698 could be eliminated. But I don't think it's very common
699 and it's dangerous to do this fiddling in STG land
700 because we might elminate a binding that's mentioned in the
701 unfolding for something.
704 type IndEnv = IdEnv Id -- Maps local_id -> exported_id
706 shortOutIndirections :: [CoreBind] -> [CoreBind]
707 shortOutIndirections binds
708 | isEmptyVarEnv ind_env = binds
709 | no_need_to_flatten = binds' -- See Note [Rules and indirect-zapping]
710 | otherwise = [Rec (flattenBinds binds')] -- for this no_need_to_flatten stuff
712 ind_env = makeIndEnv binds
713 exp_ids = varSetElems ind_env -- These exported Ids are the subjects
714 exp_id_set = mkVarSet exp_ids -- of the indirection-elimination
715 no_need_to_flatten = all (null . specInfoRules . idSpecialisation) exp_ids
716 binds' = concatMap zap binds
718 zap (NonRec bndr rhs) = [NonRec b r | (b,r) <- zapPair (bndr,rhs)]
719 zap (Rec pairs) = [Rec (concatMap zapPair pairs)]
722 | bndr `elemVarSet` exp_id_set = []
723 | Just exp_id <- lookupVarEnv ind_env bndr = [(transferIdInfo exp_id bndr, rhs),
725 | otherwise = [(bndr,rhs)]
727 makeIndEnv :: [CoreBind] -> IndEnv
729 = foldr add_bind emptyVarEnv binds
731 add_bind :: CoreBind -> IndEnv -> IndEnv
732 add_bind (NonRec exported_id rhs) env = add_pair (exported_id, rhs) env
733 add_bind (Rec pairs) env = foldr add_pair env pairs
735 add_pair :: (Id,CoreExpr) -> IndEnv -> IndEnv
736 add_pair (exported_id, Var local_id) env
737 | shortMeOut env exported_id local_id = extendVarEnv env local_id exported_id
738 add_pair (exported_id, rhs) env
742 shortMeOut ind_env exported_id local_id
743 -- The if-then-else stuff is just so I can get a pprTrace to see
744 -- how often I don't get shorting out becuase of IdInfo stuff
745 = if isExportedId exported_id && -- Only if this is exported
747 isLocalId local_id && -- Only if this one is defined in this
748 -- module, so that we *can* change its
749 -- binding to be the exported thing!
751 not (isExportedId local_id) && -- Only if this one is not itself exported,
752 -- since the transformation will nuke it
754 not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
756 if hasShortableIdInfo exported_id
757 then True -- See Note [Messing up the exported Id's IdInfo]
758 else WARN( True, ptext (sLit "Not shorting out:") <+> ppr exported_id )
764 hasShortableIdInfo :: Id -> Bool
765 -- True if there is no user-attached IdInfo on exported_id,
766 -- so we can safely discard it
767 -- See Note [Messing up the exported Id's IdInfo]
768 hasShortableIdInfo id
769 = isEmptySpecInfo (specInfo info)
770 && isDefaultInlinePragma (inlinePragInfo info)
775 transferIdInfo :: Id -> Id -> Id
776 -- See Note [Transferring IdInfo]
778 -- lcl_id = e; exp_id = lcl_id
779 -- and lcl_id has useful IdInfo, we don't want to discard it by going
780 -- gbl_id = e; lcl_id = gbl_id
781 -- Instead, transfer IdInfo from lcl_id to exp_id
782 -- Overwriting, rather than merging, seems to work ok.
783 transferIdInfo exported_id local_id
784 = modifyIdInfo transfer exported_id
786 local_info = idInfo local_id
787 transfer exp_info = exp_info `setStrictnessInfo` strictnessInfo local_info
788 `setUnfoldingInfo` unfoldingInfo local_info
789 `setInlinePragInfo` inlinePragInfo local_info
790 `setSpecInfo` addSpecInfo (specInfo exp_info) new_info
791 new_info = setSpecInfoHead (idName exported_id)
792 (specInfo local_info)
793 -- Remember to set the function-name field of the
794 -- rules as we transfer them from one function to another