2 % (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
4 \section[SimplCore]{Driver for simplifying @Core@ programs}
7 module SimplCore ( core2core, simplifyExpr ) where
9 #include "HsVersions.h"
11 import CmdLineOpts ( CoreToDo(..), SimplifierSwitch(..),
12 SimplifierMode(..), DynFlags, DynFlag(..), dopt,
13 dopt_CoreToDo, buildCoreToDo
16 import CoreFVs ( ruleRhsFreeVars )
17 import TcIface ( loadImportedRules )
18 import HscTypes ( HscEnv(..), GhciMode(..),
19 ModGuts(..), ModGuts, Avails, availsToNameSet,
21 HomeModInfo(..), ExternalPackageState(..), hscEPS
23 import CSE ( cseProgram )
24 import Rules ( RuleBase, emptyRuleBase, ruleBaseIds,
25 extendRuleBaseList, pprRuleBase,
27 import Module ( moduleEnvElts )
28 import Name ( Name, isExternalName )
29 import NameSet ( elemNameSet )
30 import PprCore ( pprCoreBindings, pprCoreExpr )
31 import OccurAnal ( occurAnalyseBinds, occurAnalyseGlobalExpr )
32 import CoreUtils ( coreBindsSize )
33 import Simplify ( simplTopBinds, simplExpr )
34 import SimplUtils ( simplBinders )
36 import ErrUtils ( dumpIfSet, dumpIfSet_dyn, showPass )
37 import CoreLint ( endPass )
38 import FloatIn ( floatInwards )
39 import FloatOut ( floatOutwards )
40 import Id ( idName, setIdLocalExported )
42 import LiberateCase ( liberateCase )
43 import SAT ( doStaticArgs )
44 import Specialise ( specProgram)
45 import SpecConstr ( specConstrProgram)
46 import DmdAnal ( dmdAnalPgm )
47 import WorkWrap ( wwTopBinds )
49 import StrictAnal ( saBinds )
50 import CprAnalyse ( cprAnalyse )
53 import UniqSupply ( UniqSupply, mkSplitUniqSupply, splitUniqSupply )
54 import IO ( hPutStr, stderr )
57 import Maybes ( orElse )
58 import List ( partition )
61 %************************************************************************
63 \subsection{The driver for the simplifier}
65 %************************************************************************
73 mod_impl@(ModGuts { mg_exports = exports,
74 mg_binds = binds_in })
76 let dflags = hsc_dflags hsc_env
77 ghci_mode = hsc_mode hsc_env
79 | Just todo <- dopt_CoreToDo dflags = todo
80 | otherwise = buildCoreToDo dflags
82 us <- mkSplitUniqSupply 's'
83 let (cp_us, ru_us) = splitUniqSupply us
85 -- COMPUTE THE RULE BASE TO USE
86 (rule_base, local_rule_ids, orphan_rules)
87 <- prepareRules hsc_env mod_impl ru_us
89 -- PREPARE THE BINDINGS
90 let binds1 = updateBinders ghci_mode local_rule_ids
91 orphan_rules exports binds_in
94 (stats, processed_binds)
95 <- doCorePasses dflags rule_base (zeroSimplCount dflags) cp_us binds1 core_todos
97 dumpIfSet_dyn dflags Opt_D_dump_simpl_stats
98 "Grand total simplifier statistics"
102 -- We only return local orphan rules, i.e., local rules not attached to an Id
103 -- The bindings cotain more rules, embedded in the Ids
104 return (mod_impl { mg_binds = processed_binds, mg_rules = orphan_rules})
107 simplifyExpr :: DynFlags -- includes spec of what core-to-core passes to do
110 -- simplifyExpr is called by the driver to simplify an
111 -- expression typed in at the interactive prompt
112 simplifyExpr dflags expr
114 ; showPass dflags "Simplify"
116 ; us <- mkSplitUniqSupply 's'
118 ; let env = emptySimplEnv SimplGently [] emptyVarSet
119 (expr', _counts) = initSmpl dflags us (simplExprGently env expr)
121 ; dumpIfSet_dyn dflags Opt_D_dump_simpl "Simplified expression"
128 doCorePasses :: DynFlags
129 -> RuleBase -- the main rule base
130 -> SimplCount -- simplifier stats
131 -> UniqSupply -- uniques
132 -> [CoreBind] -- local binds in (with rules attached)
133 -> [CoreToDo] -- which passes to do
134 -> IO (SimplCount, [CoreBind]) -- stats, binds, local orphan rules
136 doCorePasses dflags rb stats us binds []
137 = return (stats, binds)
139 doCorePasses dflags rb stats us binds (to_do : to_dos)
141 let (us1, us2) = splitUniqSupply us
143 (stats1, binds1) <- doCorePass dflags rb us1 binds to_do
145 doCorePasses dflags rb (stats `plusSimplCount` stats1) us2 binds1 to_dos
147 doCorePass dfs rb us binds (CoreDoSimplify mode switches)
148 = _scc_ "Simplify" simplifyPgm dfs rb mode switches us binds
149 doCorePass dfs rb us binds CoreCSE
150 = _scc_ "CommonSubExpr" noStats dfs (cseProgram dfs binds)
151 doCorePass dfs rb us binds CoreLiberateCase
152 = _scc_ "LiberateCase" noStats dfs (liberateCase dfs binds)
153 doCorePass dfs rb us binds CoreDoFloatInwards
154 = _scc_ "FloatInwards" noStats dfs (floatInwards dfs binds)
155 doCorePass dfs rb us binds (CoreDoFloatOutwards f)
156 = _scc_ "FloatOutwards" noStats dfs (floatOutwards dfs f us binds)
157 doCorePass dfs rb us binds CoreDoStaticArgs
158 = _scc_ "StaticArgs" noStats dfs (doStaticArgs us binds)
159 doCorePass dfs rb us binds CoreDoStrictness
160 = _scc_ "Stranal" noStats dfs (dmdAnalPgm dfs binds)
161 doCorePass dfs rb us binds CoreDoWorkerWrapper
162 = _scc_ "WorkWrap" noStats dfs (wwTopBinds dfs us binds)
163 doCorePass dfs rb us binds CoreDoSpecialising
164 = _scc_ "Specialise" noStats dfs (specProgram dfs us binds)
165 doCorePass dfs rb us binds CoreDoSpecConstr
166 = _scc_ "SpecConstr" noStats dfs (specConstrProgram dfs us binds)
167 #ifdef OLD_STRICTNESS
168 doCorePass dfs rb us binds CoreDoOldStrictness
169 = _scc_ "OldStrictness" noStats dfs (doOldStrictness dfs binds)
171 doCorePass dfs rb us binds CoreDoPrintCore
172 = _scc_ "PrintCore" noStats dfs (printCore binds)
173 doCorePass dfs rb us binds CoreDoGlomBinds
174 = noStats dfs (glomBinds dfs binds)
175 doCorePass dfs rb us binds (CoreDoRuleCheck phase pat)
176 = noStats dfs (ruleCheck dfs phase pat binds)
177 doCorePass dfs rb us binds CoreDoNothing
178 = noStats dfs (return binds)
180 #ifdef OLD_STRICTNESS
181 doOldStrictness dfs binds
182 = do binds1 <- saBinds dfs binds
183 binds2 <- cprAnalyse dfs binds1
187 printCore binds = do dumpIfSet True "Print Core"
188 (pprCoreBindings binds)
191 ruleCheck dflags phase pat binds = do showPass dflags "RuleCheck"
192 printDump (ruleCheckProgram phase pat binds)
195 -- most passes return no stats and don't change rules
196 noStats dfs thing = do { binds <- thing; return (zeroSimplCount dfs, binds) }
202 %************************************************************************
204 \subsection{Dealing with rules}
206 %************************************************************************
208 -- prepareLocalRuleBase takes the CoreBinds and rules defined in this module.
209 -- It attaches those rules that are for local Ids to their binders, and
210 -- returns the remainder attached to Ids in an IdSet. It also returns
211 -- Ids mentioned on LHS of some rule; these should be blacklisted.
213 -- The rule Ids and LHS Ids are black-listed; that is, they aren't inlined
214 -- so that the opportunity to apply the rule isn't lost too soon
217 prepareRules :: HscEnv
220 -> IO (RuleBase, -- Full rule base
221 IdSet, -- Local rule Ids
222 [IdCoreRule]) -- Orphan rules defined in this module
224 prepareRules hsc_env@(HscEnv { hsc_dflags = dflags, hsc_HPT = hpt })
225 (ModGuts { mg_binds = binds, mg_rules = local_rules,
228 = do { pkg_rule_base <- loadImportedRules hsc_env deps
230 ; let env = emptySimplEnv SimplGently [] local_ids
231 (better_rules,_) = initSmpl dflags us (mapSmpl (simplRule env) local_rules)
233 ; let (local_rules, orphan_rules) = partition ((`elemVarSet` local_ids) . fst) better_rules
234 -- We use (`elemVarSet` local_ids) rather than isLocalId because
235 -- isLocalId isn't true of class methods.
236 -- If we miss any rules for Ids defined here, then we end up
237 -- giving the local decl a new Unique (because the in-scope-set is the
238 -- same as the rule-id set), and now the binding for the class method
239 -- doesn't have the same Unique as the one in the Class and the tc-env
240 -- Example: class Foo a where
242 -- {-# RULES "op" op x = x #-}
243 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
244 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
246 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hpt)
247 final_rule_base = extendRuleBaseList imp_rule_base orphan_rules
249 ; dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
250 (vcat [text "Local rules", pprRuleBase local_rule_base,
252 text "Imported rules", pprRuleBase final_rule_base])
254 ; return (final_rule_base, local_rule_ids, orphan_rules)
257 add_rules rule_base mod_info = extendRuleBaseList rule_base (md_rules (hm_details mod_info))
259 -- Boringly, we need to gather the in-scope set.
260 local_ids = foldr (unionVarSet . mkVarSet . bindersOf) emptyVarSet binds
263 updateBinders :: GhciMode
264 -> IdSet -- Locally defined ids with their Rules attached
265 -> [IdCoreRule] -- Orphan rules
266 -> Avails -- What is exported
267 -> [CoreBind] -> [CoreBind]
268 -- A horrible function
270 -- Update the binders of top-level bindings as follows
271 -- a) Attach the rules for each locally-defined Id to that Id.
272 -- b) Set the no-discard flag if either the Id is exported,
273 -- or it's mentioned in the RHS of a rule
275 -- You might wonder why exported Ids aren't already marked as such;
276 -- it's just because the type checker is rather busy already and
277 -- I didn't want to pass in yet another mapping.
280 -- - It makes the rules easier to look up
281 -- - It means that transformation rules and specialisations for
282 -- locally defined Ids are handled uniformly
283 -- - It keeps alive things that are referred to only from a rule
284 -- (the occurrence analyser knows about rules attached to Ids)
285 -- - It makes sure that, when we apply a rule, the free vars
286 -- of the RHS are more likely to be in scope
289 -- It means that the binding won't be discarded EVEN if the binding
290 -- ends up being trivial (v = w) -- the simplifier would usually just
291 -- substitute w for v throughout, but we don't apply the substitution to
292 -- the rules (maybe we should?), so this substitution would make the rule
295 updateBinders ghci_mode rule_ids orphan_rules exports binds
296 = map update_bndrs binds
298 update_bndrs (NonRec b r) = NonRec (update_bndr b) r
299 update_bndrs (Rec prs) = Rec [(update_bndr b, r) | (b,r) <- prs]
302 | dont_discard bndr = setIdLocalExported bndr_with_rules
303 | otherwise = bndr_with_rules
305 bndr_with_rules = lookupVarSet rule_ids bndr `orElse` bndr
307 orph_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) orphan_rules)
308 -- An orphan rule must keep alive the free vars
309 -- of its right-hand side.
310 -- Non-orphan rules are attached to the Id (bndr_with_rules above)
311 -- and that keeps the rhs free vars alive
313 dont_discard bndr = is_exported (idName bndr)
314 || bndr `elemVarSet` orph_rhs_fvs
316 -- In interactive mode, we don't want to discard any top-level
317 -- entities at all (eg. do not inline them away during
318 -- simplification), and retain them all in the TypeEnv so they are
319 -- available from the command line.
321 -- isExternalName separates the user-defined top-level names from those
322 -- introduced by the type checker.
323 is_exported :: Name -> Bool
324 is_exported | ghci_mode == Interactive = isExternalName
325 | otherwise = (`elemNameSet` export_fvs)
327 export_fvs = availsToNameSet exports
331 We must do some gentle simplification on the template (but not the RHS)
332 of each rule. The case that forced me to add this was the fold/build rule,
333 which without simplification looked like:
334 fold k z (build (/\a. g a)) ==> ...
335 This doesn't match unless you do eta reduction on the build argument.
338 simplRule env rule@(id, BuiltinRule _ _)
340 simplRule env rule@(id, Rule act name bndrs args rhs)
341 = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
342 mapSmpl (simplExprGently env) args `thenSmpl` \ args' ->
343 simplExprGently env rhs `thenSmpl` \ rhs' ->
344 returnSmpl (id, Rule act name bndrs' args' rhs')
346 -- It's important that simplExprGently does eta reduction.
347 -- For example, in a rule like:
348 -- augment g (build h)
349 -- we do not want to get
350 -- augment (\a. g a) (build h)
351 -- otherwise we don't match when given an argument like
354 -- The simplifier does indeed do eta reduction (it's in
355 -- Simplify.completeLam) but only if -O is on.
359 simplExprGently :: SimplEnv -> CoreExpr -> SimplM CoreExpr
360 -- Simplifies an expression
361 -- does occurrence analysis, then simplification
362 -- and repeats (twice currently) because one pass
363 -- alone leaves tons of crud.
364 -- Used (a) for user expressions typed in at the interactive prompt
365 -- (b) the LHS and RHS of a RULE
367 -- The name 'Gently' suggests that the SimplifierMode is SimplGently,
368 -- and in fact that is so.... but the 'Gently' in simplExprGently doesn't
369 -- enforce that; it just simplifies the expression twice
371 simplExprGently env expr
372 = simplExpr env (occurAnalyseGlobalExpr expr) `thenSmpl` \ expr1 ->
373 simplExpr env (occurAnalyseGlobalExpr expr1)
377 %************************************************************************
379 \subsection{Glomming}
381 %************************************************************************
384 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
385 -- Glom all binds together in one Rec, in case any
386 -- transformations have introduced any new dependencies
388 -- NB: the global invariant is this:
389 -- *** the top level bindings are never cloned, and are always unique ***
391 -- We sort them into dependency order, but applying transformation rules may
392 -- make something at the top refer to something at the bottom:
396 -- RULE: p (q x) = h x
398 -- Applying this rule makes f refer to h,
399 -- although it doesn't appear to in the source program.
400 -- This pass lets us control where it happens.
402 -- NOTICE that this cannot happen for rules whose head is a locally-defined
403 -- function. It only happens for rules whose head is an imported function
404 -- (p in the example above). So, for example, the rule had been
405 -- RULE: f (p x) = h x
406 -- then the rule for f would be attached to f itself (in its IdInfo)
407 -- by prepareLocalRuleBase and h would be regarded by the occurrency
408 -- analyser as free in f.
410 glomBinds dflags binds
411 = do { showPass dflags "GlomBinds" ;
412 let { recd_binds = [Rec (flattenBinds binds)] } ;
414 -- Not much point in printing the result...
415 -- just consumes output bandwidth
419 %************************************************************************
421 \subsection{The driver for the simplifier}
423 %************************************************************************
426 simplifyPgm :: DynFlags
429 -> [SimplifierSwitch]
431 -> [CoreBind] -- Input
432 -> IO (SimplCount, [CoreBind]) -- New bindings
434 simplifyPgm dflags rule_base
435 mode switches us binds
437 showPass dflags "Simplify";
439 (termination_msg, it_count, counts_out, binds')
440 <- iteration us 1 (zeroSimplCount dflags) binds;
442 dumpIfSet (dopt Opt_D_verbose_core2core dflags
443 && dopt Opt_D_dump_simpl_stats dflags)
444 "Simplifier statistics"
445 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
447 pprSimplCount counts_out]);
449 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
451 return (counts_out, binds')
454 phase_info = case mode of
455 SimplGently -> "gentle"
456 SimplPhase n -> show n
458 imported_rule_ids = ruleBaseIds rule_base
459 simpl_env = emptySimplEnv mode switches imported_rule_ids
460 sw_chkr = getSwitchChecker simpl_env
461 max_iterations = intSwitchSet sw_chkr MaxSimplifierIterations `orElse` 2
463 iteration us iteration_no counts binds
464 -- iteration_no is the number of the iteration we are
465 -- about to begin, with '1' for the first
466 | iteration_no > max_iterations -- Stop if we've run out of iterations
469 if max_iterations > 2 then
470 hPutStr stderr ("NOTE: Simplifier still going after " ++
471 show max_iterations ++
472 " iterations; bailing out.\n")
476 -- Subtract 1 from iteration_no to get the
477 -- number of iterations we actually completed
478 return ("Simplifier baled out", iteration_no - 1, counts, binds)
481 -- Try and force thunks off the binds; significantly reduces
482 -- space usage, especially with -O. JRS, 000620.
483 | let sz = coreBindsSize binds in sz == sz
485 -- Occurrence analysis
486 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
488 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
489 (pprCoreBindings tagged_binds);
492 -- We do this with a *case* not a *let* because lazy pattern
493 -- matching bit us with bad space leak!
494 -- With a let, we ended up with
499 -- case t of {(_,counts') -> if counts'=0 then ... }
500 -- So the conditional didn't force counts', because the
501 -- selection got duplicated. Sigh!
502 case initSmpl dflags us1 (simplTopBinds simpl_env tagged_binds) of {
503 (binds', counts') -> do {
504 -- The imported_rule_ids are used by initSmpl to initialise
505 -- the in-scope set. That way, the simplifier will change any
506 -- occurrences of the imported id to the one in the imported_rule_ids
507 -- set, which are decorated with their rules.
509 let { all_counts = counts `plusSimplCount` counts' ;
510 herald = "Simplifier phase " ++ phase_info ++
511 ", iteration " ++ show iteration_no ++
512 " out of " ++ show max_iterations
515 -- Stop if nothing happened; don't dump output
516 if isZeroSimplCount counts' then
517 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
520 -- Dump the result of this iteration
521 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations herald
522 (pprSimplCount counts') ;
524 endPass dflags herald Opt_D_dump_simpl_iterations binds' ;
527 iteration us2 (iteration_no + 1) all_counts binds'
530 (us1, us2) = splitUniqSupply us