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,
16 import CoreFVs ( ruleRhsFreeVars )
17 import HscTypes ( HscEnv(..), GhciMode(..),
18 ModGuts(..), ModGuts, Avails, availsToNameSet,
19 PackageRuleBase, HomePackageTable, ModDetails(..),
22 import CSE ( cseProgram )
23 import Rules ( RuleBase, emptyRuleBase, ruleBaseFVs, ruleBaseIds,
24 extendRuleBaseList, addRuleBaseFVs, pprRuleBase,
26 import Module ( moduleEnvElts )
27 import Name ( Name, isExternalName )
28 import NameSet ( elemNameSet )
29 import PprCore ( pprCoreBindings, pprCoreExpr )
30 import OccurAnal ( occurAnalyseBinds, occurAnalyseGlobalExpr )
31 import CoreUtils ( coreBindsSize )
32 import Simplify ( simplTopBinds, simplExpr )
33 import SimplUtils ( simplBinders )
35 import ErrUtils ( dumpIfSet, dumpIfSet_dyn, showPass )
36 import CoreLint ( endPass )
37 import FloatIn ( floatInwards )
38 import FloatOut ( floatOutwards )
39 import Id ( idName, setIdLocalExported )
41 import LiberateCase ( liberateCase )
42 import SAT ( doStaticArgs )
43 import Specialise ( specProgram)
44 import SpecConstr ( specConstrProgram)
45 import DmdAnal ( dmdAnalPgm )
46 import WorkWrap ( wwTopBinds )
48 import StrictAnal ( saBinds )
49 import CprAnalyse ( cprAnalyse )
52 import UniqSupply ( UniqSupply, mkSplitUniqSupply, splitUniqSupply )
53 import IO ( hPutStr, stderr )
56 import Maybes ( orElse )
57 import List ( partition )
60 %************************************************************************
62 \subsection{The driver for the simplifier}
64 %************************************************************************
72 core2core hsc_env pkg_rule_base
73 mod_impl@(ModGuts { mg_exports = exports,
75 mg_rules = rules_in })
77 let dflags = hsc_dflags hsc_env
79 ghci_mode = hsc_mode hsc_env
80 core_todos = dopt_CoreToDo 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, rule_rhs_fvs)
87 <- prepareRules dflags pkg_rule_base hpt ru_us binds_in rules_in
89 -- PREPARE THE BINDINGS
90 let binds1 = updateBinders ghci_mode local_rule_ids
91 rule_rhs_fvs 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 :: DynFlags -> PackageRuleBase -> HomePackageTable
220 -> [IdCoreRule] -- Local rules
221 -> IO (RuleBase, -- Full rule base
222 IdSet, -- Local rule Ids
223 [IdCoreRule], -- Orphan rules
224 IdSet) -- RHS free vars of all rules
226 prepareRules dflags pkg_rule_base hpt us binds local_rules
227 = do { let env = emptySimplEnv SimplGently [] local_ids
228 (better_rules,_) = initSmpl dflags us (mapSmpl (simplRule env) local_rules)
230 ; let (local_rules, orphan_rules) = partition ((`elemVarSet` local_ids) . fst) better_rules
231 -- We use (`elemVarSet` local_ids) rather than isLocalId because
232 -- isLocalId isn't true of class methods.
233 -- If we miss any rules for Ids defined here, then we end up
234 -- giving the local decl a new Unique (because the in-scope-set is the
235 -- same as the rule-id set), and now the binding for the class method
236 -- doesn't have the same Unique as the one in the Class and the tc-env
237 -- Example: class Foo a where
239 -- {-# RULES "op" op x = x #-}
241 rule_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) better_rules)
242 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
243 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
244 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hpt)
245 rule_base = extendRuleBaseList imp_rule_base orphan_rules
246 final_rule_base = addRuleBaseFVs rule_base (ruleBaseFVs local_rule_base)
247 -- The last step black-lists the free vars of local rules too
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, rule_rhs_fvs)
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 -> IdSet -- Ids free in the RHS of local 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 rule_rhs_fvs 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 dont_discard bndr = is_exported (idName bndr)
308 || bndr `elemVarSet` rule_rhs_fvs
310 -- In interactive mode, we don't want to discard any top-level
311 -- entities at all (eg. do not inline them away during
312 -- simplification), and retain them all in the TypeEnv so they are
313 -- available from the command line.
315 -- isExternalName separates the user-defined top-level names from those
316 -- introduced by the type checker.
317 is_exported :: Name -> Bool
318 is_exported | ghci_mode == Interactive = isExternalName
319 | otherwise = (`elemNameSet` export_fvs)
321 export_fvs = availsToNameSet exports
325 We must do some gentle simplification on the template (but not the RHS)
326 of each rule. The case that forced me to add this was the fold/build rule,
327 which without simplification looked like:
328 fold k z (build (/\a. g a)) ==> ...
329 This doesn't match unless you do eta reduction on the build argument.
332 simplRule env rule@(id, BuiltinRule _ _)
334 simplRule env rule@(id, Rule act name bndrs args rhs)
335 = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
336 mapSmpl (simplExprGently env) args `thenSmpl` \ args' ->
337 simplExprGently env rhs `thenSmpl` \ rhs' ->
338 returnSmpl (id, Rule act name bndrs' args' rhs')
340 -- It's important that simplExprGently does eta reduction.
341 -- For example, in a rule like:
342 -- augment g (build h)
343 -- we do not want to get
344 -- augment (\a. g a) (build h)
345 -- otherwise we don't match when given an argument like
348 -- The simplifier does indeed do eta reduction (it's in
349 -- Simplify.completeLam) but only if -O is on.
353 simplExprGently :: SimplEnv -> CoreExpr -> SimplM CoreExpr
354 -- Simplifies an expression
355 -- does occurrence analysis, then simplification
356 -- and repeats (twice currently) because one pass
357 -- alone leaves tons of crud.
358 -- Used (a) for user expressions typed in at the interactive prompt
359 -- (b) the LHS and RHS of a RULE
361 -- The name 'Gently' suggests that the SimplifierMode is SimplGently,
362 -- and in fact that is so.... but the 'Gently' in simplExprGently doesn't
363 -- enforce that; it just simplifies the expression twice
365 simplExprGently env expr
366 = simplExpr env (occurAnalyseGlobalExpr expr) `thenSmpl` \ expr1 ->
367 simplExpr env (occurAnalyseGlobalExpr expr1)
371 %************************************************************************
373 \subsection{Glomming}
375 %************************************************************************
378 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
379 -- Glom all binds together in one Rec, in case any
380 -- transformations have introduced any new dependencies
382 -- NB: the global invariant is this:
383 -- *** the top level bindings are never cloned, and are always unique ***
385 -- We sort them into dependency order, but applying transformation rules may
386 -- make something at the top refer to something at the bottom:
390 -- RULE: p (q x) = h x
392 -- Applying this rule makes f refer to h,
393 -- although it doesn't appear to in the source program.
394 -- This pass lets us control where it happens.
396 -- NOTICE that this cannot happen for rules whose head is a locally-defined
397 -- function. It only happens for rules whose head is an imported function
398 -- (p in the example above). So, for example, the rule had been
399 -- RULE: f (p x) = h x
400 -- then the rule for f would be attached to f itself (in its IdInfo)
401 -- by prepareLocalRuleBase and h would be regarded by the occurrency
402 -- analyser as free in f.
404 glomBinds dflags binds
405 = do { showPass dflags "GlomBinds" ;
406 let { recd_binds = [Rec (flattenBinds binds)] } ;
408 -- Not much point in printing the result...
409 -- just consumes output bandwidth
413 %************************************************************************
415 \subsection{The driver for the simplifier}
417 %************************************************************************
420 simplifyPgm :: DynFlags
423 -> [SimplifierSwitch]
425 -> [CoreBind] -- Input
426 -> IO (SimplCount, [CoreBind]) -- New bindings
428 simplifyPgm dflags rule_base
429 mode switches us binds
431 showPass dflags "Simplify";
433 (termination_msg, it_count, counts_out, binds')
434 <- iteration us 1 (zeroSimplCount dflags) binds;
436 dumpIfSet (dopt Opt_D_verbose_core2core dflags
437 && dopt Opt_D_dump_simpl_stats dflags)
438 "Simplifier statistics"
439 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
441 pprSimplCount counts_out]);
443 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
445 return (counts_out, binds')
448 phase_info = case mode of
449 SimplGently -> "gentle"
450 SimplPhase n -> show n
452 imported_rule_ids = ruleBaseIds rule_base
453 simpl_env = emptySimplEnv mode switches imported_rule_ids
454 sw_chkr = getSwitchChecker simpl_env
455 max_iterations = intSwitchSet sw_chkr MaxSimplifierIterations `orElse` 2
457 iteration us iteration_no counts binds
458 -- iteration_no is the number of the iteration we are
459 -- about to begin, with '1' for the first
460 | iteration_no > max_iterations -- Stop if we've run out of iterations
463 if max_iterations > 2 then
464 hPutStr stderr ("NOTE: Simplifier still going after " ++
465 show max_iterations ++
466 " iterations; bailing out.\n")
470 -- Subtract 1 from iteration_no to get the
471 -- number of iterations we actually completed
472 return ("Simplifier baled out", iteration_no - 1, counts, binds)
475 -- Try and force thunks off the binds; significantly reduces
476 -- space usage, especially with -O. JRS, 000620.
477 | let sz = coreBindsSize binds in sz == sz
479 -- Occurrence analysis
480 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
482 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
483 (pprCoreBindings tagged_binds);
486 -- We do this with a *case* not a *let* because lazy pattern
487 -- matching bit us with bad space leak!
488 -- With a let, we ended up with
493 -- case t of {(_,counts') -> if counts'=0 then ... }
494 -- So the conditional didn't force counts', because the
495 -- selection got duplicated. Sigh!
496 case initSmpl dflags us1 (simplTopBinds simpl_env tagged_binds) of {
497 (binds', counts') -> do {
498 -- The imported_rule_ids are used by initSmpl to initialise
499 -- the in-scope set. That way, the simplifier will change any
500 -- occurrences of the imported id to the one in the imported_rule_ids
501 -- set, which are decorated with their rules.
503 let { all_counts = counts `plusSimplCount` counts' ;
504 herald = "Simplifier phase " ++ phase_info ++
505 ", iteration " ++ show iteration_no ++
506 " out of " ++ show max_iterations
509 -- Stop if nothing happened; don't dump output
510 if isZeroSimplCount counts' then
511 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
514 -- Dump the result of this iteration
515 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations herald
516 (pprSimplCount counts') ;
518 endPass dflags herald Opt_D_dump_simpl_iterations binds' ;
521 iteration us2 (iteration_no + 1) all_counts binds'
524 (us1, us2) = splitUniqSupply us