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 SwitchResult(..), intSwitchSet,
13 DynFlags, DynFlag(..), dopt, dopt_CoreToDo
15 import CoreLint ( showPass, endPass )
17 import CoreFVs ( ruleRhsFreeVars )
18 import HscTypes ( PersistentCompilerState(..),
19 PackageRuleBase, HomeSymbolTable, IsExported, ModDetails(..)
21 import CSE ( cseProgram )
22 import Rules ( RuleBase, emptyRuleBase, ruleBaseFVs, ruleBaseIds,
23 extendRuleBaseList, addRuleBaseFVs )
24 import Module ( moduleEnvElts )
26 import PprCore ( pprCoreBindings, pprIdCoreRule, pprCoreExpr )
27 import OccurAnal ( occurAnalyseBinds, occurAnalyseGlobalExpr )
28 import CoreUtils ( etaReduce, coreBindsSize )
29 import Simplify ( simplTopBinds, simplExpr )
30 import SimplUtils ( simplBinders )
32 import ErrUtils ( dumpIfSet, dumpIfSet_dyn )
33 import FloatIn ( floatInwards )
34 import FloatOut ( floatOutwards )
35 import Id ( idName, isDataConWrapId, setIdNoDiscard, isLocalId )
37 import LiberateCase ( liberateCase )
38 import SAT ( doStaticArgs )
39 import Specialise ( specProgram)
40 import UsageSPInf ( doUsageSPInf )
41 import StrictAnal ( saBinds )
42 import WorkWrap ( wwTopBinds )
43 import CprAnalyse ( cprAnalyse )
45 import UniqSupply ( UniqSupply, mkSplitUniqSupply, splitUniqSupply )
46 import IO ( hPutStr, stderr )
49 import Maybes ( orElse )
50 import List ( partition )
53 %************************************************************************
55 \subsection{The driver for the simplifier}
57 %************************************************************************
60 core2core :: DynFlags -- includes spec of what core-to-core passes to do
61 -> PersistentCompilerState
64 -> [CoreBind] -- Binds in
65 -> [IdCoreRule] -- Rules in
66 -> IO ([CoreBind], [IdCoreRule]) -- binds, local orphan rules out
68 core2core dflags pcs hst is_exported binds rules
70 let core_todos = dopt_CoreToDo dflags
71 let pkg_rule_base = pcs_rules pcs -- Rule-base accumulated from imported packages
73 us <- mkSplitUniqSupply 's'
74 let (cp_us, ru_us) = splitUniqSupply us
76 -- COMPUTE THE RULE BASE TO USE
77 (rule_base, local_rule_stuff, orphan_rules)
78 <- prepareRules dflags pkg_rule_base hst ru_us binds rules
80 -- PREPARE THE BINDINGS
81 let binds1 = updateBinders local_rule_stuff is_exported binds
84 (stats, processed_binds)
85 <- doCorePasses dflags rule_base (zeroSimplCount dflags) cp_us binds1 core_todos
87 dumpIfSet_dyn dflags Opt_D_dump_simpl_stats
88 "Grand total simplifier statistics"
92 -- We only return local orphan rules, i.e., local rules not attached to an Id
93 -- The bindings cotain more rules, embedded in the Ids
94 return (processed_binds, orphan_rules)
97 simplifyExpr :: DynFlags -- includes spec of what core-to-core passes to do
98 -> PersistentCompilerState
102 -- simplifyExpr is called by the driver to simplify an
103 -- expression typed in at the interactive prompt
104 simplifyExpr dflags pcs hst expr
106 ; showPass dflags "Simplify"
108 ; us <- mkSplitUniqSupply 's'
110 ; let (expr', _counts) = initSmpl dflags sw_chkr us emptyVarSet black_list_all
111 (simplExprGently expr)
113 ; dumpIfSet_dyn dflags Opt_D_dump_simpl "Simplified expression"
119 sw_chkr any = SwBool False -- A bit bogus
120 black_list_all v = True -- Black list everything
123 doCorePasses :: DynFlags
124 -> RuleBase -- the main rule base
125 -> SimplCount -- simplifier stats
126 -> UniqSupply -- uniques
127 -> [CoreBind] -- local binds in (with rules attached)
128 -> [CoreToDo] -- which passes to do
129 -> IO (SimplCount, [CoreBind]) -- stats, binds, local orphan rules
131 doCorePasses dflags rb stats us binds []
132 = return (stats, binds)
134 doCorePasses dflags rb stats us binds (to_do : to_dos)
136 let (us1, us2) = splitUniqSupply us
138 (stats1, binds1) <- doCorePass dflags rb us1 binds to_do
140 doCorePasses dflags rb (stats `plusSimplCount` stats1) us2 binds1 to_dos
142 doCorePass dfs rb us binds (CoreDoSimplify sw_chkr)
143 = _scc_ "Simplify" simplifyPgm dfs rb sw_chkr us binds
144 doCorePass dfs rb us binds CoreCSE
145 = _scc_ "CommonSubExpr" noStats dfs (cseProgram dfs binds)
146 doCorePass dfs rb us binds CoreLiberateCase
147 = _scc_ "LiberateCase" noStats dfs (liberateCase dfs binds)
148 doCorePass dfs rb us binds CoreDoFloatInwards
149 = _scc_ "FloatInwards" noStats dfs (floatInwards dfs binds)
150 doCorePass dfs rb us binds (CoreDoFloatOutwards f)
151 = _scc_ "FloatOutwards" noStats dfs (floatOutwards dfs f us binds)
152 doCorePass dfs rb us binds CoreDoStaticArgs
153 = _scc_ "StaticArgs" noStats dfs (doStaticArgs us binds)
154 doCorePass dfs rb us binds CoreDoStrictness
155 = _scc_ "Stranal" noStats dfs (saBinds dfs binds)
156 doCorePass dfs rb us binds CoreDoWorkerWrapper
157 = _scc_ "WorkWrap" noStats dfs (wwTopBinds dfs us binds)
158 doCorePass dfs rb us binds CoreDoSpecialising
159 = _scc_ "Specialise" noStats dfs (specProgram dfs us binds)
160 doCorePass dfs rb us binds CoreDoCPResult
161 = _scc_ "CPResult" noStats dfs (cprAnalyse dfs binds)
162 doCorePass dfs rb us binds CoreDoPrintCore
163 = _scc_ "PrintCore" noStats dfs (printCore binds)
164 doCorePass dfs rb us binds CoreDoUSPInf
165 = _scc_ "CoreUsageSPInf" noStats dfs (doUsageSPInf dfs us binds)
166 doCorePass dfs rb us binds CoreDoGlomBinds
167 = noStats dfs (glomBinds dfs binds)
168 doCorePass dfs rb us binds CoreDoNothing
169 = noStats dfs (return binds)
171 printCore binds = do dumpIfSet True "Print Core"
172 (pprCoreBindings binds)
175 -- most passes return no stats and don't change rules
176 noStats dfs thing = do { binds <- thing; return (zeroSimplCount dfs, binds) }
181 %************************************************************************
183 \subsection{Dealing with rules}
185 %************************************************************************
187 -- prepareLocalRuleBase takes the CoreBinds and rules defined in this module.
188 -- It attaches those rules that are for local Ids to their binders, and
189 -- returns the remainder attached to Ids in an IdSet. It also returns
190 -- Ids mentioned on LHS of some rule; these should be blacklisted.
192 -- The rule Ids and LHS Ids are black-listed; that is, they aren't inlined
193 -- so that the opportunity to apply the rule isn't lost too soon
196 prepareRules :: DynFlags -> PackageRuleBase -> HomeSymbolTable
199 -> [IdCoreRule] -- Local rules
200 -> IO (RuleBase, -- Full rule base
201 (IdSet,IdSet), -- Local rule Ids, and RHS fvs
202 [IdCoreRule]) -- Orphan rules
204 prepareRules dflags pkg_rule_base hst us binds rules
205 = do { let (better_rules,_) = initSmpl dflags sw_chkr us local_ids black_list_all
206 (mapSmpl simplRule rules)
208 ; dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
209 (vcat (map pprIdCoreRule better_rules))
211 ; let (local_rules, orphan_rules) = partition (isLocalId . fst) better_rules
212 local_rule_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) local_rules)
213 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
214 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
215 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hst)
216 rule_base = extendRuleBaseList imp_rule_base orphan_rules
217 final_rule_base = addRuleBaseFVs rule_base (ruleBaseFVs local_rule_base)
218 -- The last step black-lists the free vars of local rules too
220 ; return (final_rule_base, (local_rule_ids, local_rule_rhs_fvs), orphan_rules)
223 sw_chkr any = SwBool False -- A bit bogus
224 black_list_all v = not (isDataConWrapId v)
225 -- This stops all inlining except the
226 -- wrappers for data constructors
228 add_rules rule_base mds = extendRuleBaseList rule_base (md_rules mds)
230 -- Boringly, we need to gather the in-scope set.
231 -- Typically this thunk won't even be forced, but the test in
232 -- simpVar fails if it isn't right, and it might conceiveably matter
233 local_ids = foldr (unionVarSet . mkVarSet . bindersOf) emptyVarSet binds
236 updateBinders :: (IdSet, -- Locally defined ids with their Rules attached
237 IdSet) -- Ids free in the RHS of local rules
239 -> [CoreBind] -> [CoreBind]
240 -- A horrible function
242 -- Update the binders of top-level bindings as follows
243 -- a) Attach the rules for each locally-defined Id to that Id.
244 -- b) Set the no-discard flag if either the Id is exported,
245 -- or it's mentoined in the RHS of a rule
248 -- - It makes the rules easier to look up
249 -- - It means that transformation rules and specialisations for
250 -- locally defined Ids are handled uniformly
251 -- - It keeps alive things that are referred to only from a rule
252 -- (the occurrence analyser knows about rules attached to Ids)
253 -- - It makes sure that, when we apply a rule, the free vars
254 -- of the RHS are more likely to be in scope
257 -- It means that the binding won't be discarded EVEN if the binding
258 -- ends up being trivial (v = w) -- the simplifier would usually just
259 -- substitute w for v throughout, but we don't apply the substitution to
260 -- the rules (maybe we should?), so this substitution would make the rule
263 updateBinders (rule_ids, rule_rhs_fvs) is_exported binds
264 = map update_bndrs binds
266 update_bndrs (NonRec b r) = NonRec (update_bndr b) r
267 update_bndrs (Rec prs) = Rec [(update_bndr b, r) | (b,r) <- prs]
270 | is_exported (idName bndr)
271 || bndr `elemVarSet` rule_rhs_fvs = setIdNoDiscard bndr'
274 bndr' = lookupVarSet rule_ids bndr `orElse` bndr
278 We must do some gentle simplification on the template (but not the RHS)
279 of each rule. The case that forced me to add this was the fold/build rule,
280 which without simplification looked like:
281 fold k z (build (/\a. g a)) ==> ...
282 This doesn't match unless you do eta reduction on the build argument.
285 simplRule rule@(id, BuiltinRule _)
287 simplRule rule@(id, Rule name bndrs args rhs)
288 = simplBinders bndrs $ \ bndrs' ->
289 mapSmpl simplExprGently args `thenSmpl` \ args' ->
290 simplExprGently rhs `thenSmpl` \ rhs' ->
291 returnSmpl (id, Rule name bndrs' args' rhs')
293 -- It's important that simplExprGently does eta reduction.
294 -- For example, in a rule like:
295 -- augment g (build h)
296 -- we do not want to get
297 -- augment (\a. g a) (build h)
298 -- otherwise we don't match when given an argument like
301 -- The simplifier does indeed do eta reduction (it's in
302 -- Simplify.completeLam) but only if -O is on.
306 simplExprGently :: CoreExpr -> SimplM CoreExpr
307 -- Simplifies an expression
308 -- does occurrence analysis, then simplification
309 -- and repeats (twice currently) because one pass
310 -- alone leaves tons of crud.
311 -- Used (a) for user expressions typed in at the interactive prompt
312 -- (b) the LHS and RHS of a RULE
314 = simplExpr (occurAnalyseGlobalExpr expr) `thenSmpl` \ expr1 ->
315 simplExpr (occurAnalyseGlobalExpr expr1)
319 %************************************************************************
321 \subsection{Glomming}
323 %************************************************************************
326 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
327 -- Glom all binds together in one Rec, in case any
328 -- transformations have introduced any new dependencies
330 -- NB: the global invariant is this:
331 -- *** the top level bindings are never cloned, and are always unique ***
333 -- We sort them into dependency order, but applying transformation rules may
334 -- make something at the top refer to something at the bottom:
338 -- RULE: p (q x) = h x
340 -- Applying this rule makes f refer to h,
341 -- although it doesn't appear to in the source program.
342 -- This pass lets us control where it happens.
344 -- NOTICE that this cannot happen for rules whose head is a locally-defined
345 -- function. It only happens for rules whose head is an imported function
346 -- (p in the example above). So, for example, the rule had been
347 -- RULE: f (p x) = h x
348 -- then the rule for f would be attached to f itself (in its IdInfo)
349 -- by prepareLocalRuleBase and h would be regarded by the occurrency
350 -- analyser as free in f.
352 glomBinds dflags binds
353 = do { showPass dflags "GlomBinds" ;
354 let { recd_binds = [Rec (flattenBinds binds)] } ;
356 -- Not much point in printing the result...
357 -- just consumes output bandwidth
361 %************************************************************************
363 \subsection{The driver for the simplifier}
365 %************************************************************************
368 simplifyPgm :: DynFlags
370 -> (SimplifierSwitch -> SwitchResult)
372 -> [CoreBind] -- Input
373 -> IO (SimplCount, [CoreBind]) -- New bindings
375 simplifyPgm dflags rule_base
378 showPass dflags "Simplify";
380 (termination_msg, it_count, counts_out, binds')
381 <- iteration us 1 (zeroSimplCount dflags) binds;
383 dumpIfSet (dopt Opt_D_verbose_core2core dflags
384 && dopt Opt_D_dump_simpl_stats dflags)
385 "Simplifier statistics"
386 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
388 pprSimplCount counts_out]);
390 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
392 return (counts_out, binds')
395 max_iterations = getSimplIntSwitch sw_chkr MaxSimplifierIterations
396 black_list_fn = blackListed rule_lhs_fvs (intSwitchSet sw_chkr SimplInlinePhase)
397 imported_rule_ids = ruleBaseIds rule_base
398 rule_lhs_fvs = ruleBaseFVs rule_base
400 iteration us iteration_no counts binds
401 -- Try and force thunks off the binds; significantly reduces
402 -- space usage, especially with -O. JRS, 000620.
403 | let sz = coreBindsSize binds in sz == sz
405 -- Occurrence analysis
406 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
408 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
409 (pprCoreBindings tagged_binds);
412 -- We do this with a *case* not a *let* because lazy pattern
413 -- matching bit us with bad space leak!
414 -- With a let, we ended up with
419 -- case t of {(_,counts') -> if counts'=0 then ...
420 -- So the conditional didn't force counts', because the
421 -- selection got duplicated. Sigh!
422 case initSmpl dflags sw_chkr us1 imported_rule_ids black_list_fn
423 (simplTopBinds tagged_binds)
424 of { (binds', counts') -> do {
425 -- The imported_rule_ids are used by initSmpl to initialise
426 -- the in-scope set. That way, the simplifier will change any
427 -- occurrences of the imported id to the one in the imported_rule_ids
428 -- set, which are decorated with their rules.
430 let { all_counts = counts `plusSimplCount` counts' } ;
432 -- Stop if nothing happened; don't dump output
433 if isZeroSimplCount counts' then
434 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
437 -- Dump the result of this iteration
438 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations
439 ("Simplifier iteration " ++ show iteration_no
440 ++ " out of " ++ show max_iterations)
441 (pprSimplCount counts') ;
444 ("Simplifier iteration " ++ show iteration_no ++ " result")
445 Opt_D_dump_simpl_iterations
448 -- Stop if we've run out of iterations
449 if iteration_no == max_iterations then
452 if max_iterations > 2 then
453 hPutStr stderr ("NOTE: Simplifier still going after " ++
454 show max_iterations ++
455 " iterations; bailing out.\n")
460 return ("Simplifier baled out", iteration_no, all_counts, binds')
464 else iteration us2 (iteration_no + 1) all_counts binds'
467 (us1, us2) = splitUniqSupply us