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 )
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 dflags pcs hst expr
104 ; showPass dflags "Simplify"
106 ; us <- mkSplitUniqSupply 's'
108 ; let (expr', _counts) = initSmpl dflags sw_chkr us emptyVarSet black_list_all
111 ; dumpIfSet_dyn dflags Opt_D_dump_simpl "Simplfied expression"
117 sw_chkr any = SwBool False -- A bit bogus
118 black_list_all v = True -- Black list everything
121 doCorePasses :: DynFlags
122 -> RuleBase -- the main rule base
123 -> SimplCount -- simplifier stats
124 -> UniqSupply -- uniques
125 -> [CoreBind] -- local binds in (with rules attached)
126 -> [CoreToDo] -- which passes to do
127 -> IO (SimplCount, [CoreBind]) -- stats, binds, local orphan rules
129 doCorePasses dflags rb stats us binds []
130 = return (stats, binds)
132 doCorePasses dflags rb stats us binds (to_do : to_dos)
134 let (us1, us2) = splitUniqSupply us
136 (stats1, binds1) <- doCorePass dflags rb us1 binds to_do
138 doCorePasses dflags rb (stats `plusSimplCount` stats1) us2 binds1 to_dos
140 doCorePass dfs rb us binds (CoreDoSimplify sw_chkr)
141 = _scc_ "Simplify" simplifyPgm dfs rb sw_chkr us binds
142 doCorePass dfs rb us binds CoreCSE
143 = _scc_ "CommonSubExpr" noStats dfs (cseProgram dfs binds)
144 doCorePass dfs rb us binds CoreLiberateCase
145 = _scc_ "LiberateCase" noStats dfs (liberateCase dfs binds)
146 doCorePass dfs rb us binds CoreDoFloatInwards
147 = _scc_ "FloatInwards" noStats dfs (floatInwards dfs binds)
148 doCorePass dfs rb us binds (CoreDoFloatOutwards f)
149 = _scc_ "FloatOutwards" noStats dfs (floatOutwards dfs f us binds)
150 doCorePass dfs rb us binds CoreDoStaticArgs
151 = _scc_ "StaticArgs" noStats dfs (doStaticArgs us binds)
152 doCorePass dfs rb us binds CoreDoStrictness
153 = _scc_ "Stranal" noStats dfs (saBinds dfs binds)
154 doCorePass dfs rb us binds CoreDoWorkerWrapper
155 = _scc_ "WorkWrap" noStats dfs (wwTopBinds dfs us binds)
156 doCorePass dfs rb us binds CoreDoSpecialising
157 = _scc_ "Specialise" noStats dfs (specProgram dfs us binds)
158 doCorePass dfs rb us binds CoreDoCPResult
159 = _scc_ "CPResult" noStats dfs (cprAnalyse dfs binds)
160 doCorePass dfs rb us binds CoreDoPrintCore
161 = _scc_ "PrintCore" noStats dfs (printCore binds)
162 doCorePass dfs rb us binds CoreDoUSPInf
163 = _scc_ "CoreUsageSPInf" noStats dfs (doUsageSPInf dfs us binds)
164 doCorePass dfs rb us binds CoreDoGlomBinds
165 = noStats dfs (glomBinds dfs binds)
166 doCorePass dfs rb us binds CoreDoNothing
167 = noStats dfs (return binds)
169 printCore binds = do dumpIfSet True "Print Core"
170 (pprCoreBindings binds)
173 -- most passes return no stats and don't change rules
174 noStats dfs thing = do { binds <- thing; return (zeroSimplCount dfs, binds) }
179 %************************************************************************
181 \subsection{Dealing with rules}
183 %************************************************************************
185 -- prepareLocalRuleBase takes the CoreBinds and rules defined in this module.
186 -- It attaches those rules that are for local Ids to their binders, and
187 -- returns the remainder attached to Ids in an IdSet. It also returns
188 -- Ids mentioned on LHS of some rule; these should be blacklisted.
190 -- The rule Ids and LHS Ids are black-listed; that is, they aren't inlined
191 -- so that the opportunity to apply the rule isn't lost too soon
194 prepareRules :: DynFlags -> PackageRuleBase -> HomeSymbolTable
197 -> [IdCoreRule] -- Local rules
198 -> IO (RuleBase, -- Full rule base
199 (IdSet,IdSet), -- Local rule Ids, and RHS fvs
200 [IdCoreRule]) -- Orphan rules
202 prepareRules dflags pkg_rule_base hst us binds rules
203 = do { let (better_rules,_) = initSmpl dflags sw_chkr us local_ids black_list_all
204 (mapSmpl simplRule rules)
206 ; dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
207 (vcat (map pprIdCoreRule better_rules))
209 ; let (local_rules, orphan_rules) = partition (isLocalId . fst) better_rules
210 local_rule_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) local_rules)
211 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
212 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
213 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hst)
214 rule_base = extendRuleBaseList imp_rule_base orphan_rules
215 final_rule_base = addRuleBaseFVs rule_base (ruleBaseFVs local_rule_base)
216 -- The last step black-lists the free vars of local rules too
218 ; return (final_rule_base, (local_rule_ids, local_rule_rhs_fvs), orphan_rules)
221 sw_chkr any = SwBool False -- A bit bogus
222 black_list_all v = not (isDataConWrapId v)
223 -- This stops all inlining except the
224 -- wrappers for data constructors
226 add_rules rule_base mds = extendRuleBaseList rule_base (md_rules mds)
228 -- Boringly, we need to gather the in-scope set.
229 -- Typically this thunk won't even be forced, but the test in
230 -- simpVar fails if it isn't right, and it might conceiveably matter
231 local_ids = foldr (unionVarSet . mkVarSet . bindersOf) emptyVarSet binds
234 updateBinders :: (IdSet, -- Locally defined ids with their Rules attached
235 IdSet) -- Ids free in the RHS of local rules
237 -> [CoreBind] -> [CoreBind]
238 -- A horrible function
240 -- Update the binders of top-level bindings as follows
241 -- a) Attach the rules for each locally-defined Id to that Id.
242 -- b) Set the no-discard flag if either the Id is exported,
243 -- or it's mentoined in the RHS of a rule
246 -- - It makes the rules easier to look up
247 -- - It means that transformation rules and specialisations for
248 -- locally defined Ids are handled uniformly
249 -- - It keeps alive things that are referred to only from a rule
250 -- (the occurrence analyser knows about rules attached to Ids)
251 -- - It makes sure that, when we apply a rule, the free vars
252 -- of the RHS are more likely to be in scope
255 -- It means that the binding won't be discarded EVEN if the binding
256 -- ends up being trivial (v = w) -- the simplifier would usually just
257 -- substitute w for v throughout, but we don't apply the substitution to
258 -- the rules (maybe we should?), so this substitution would make the rule
261 updateBinders (rule_ids, rule_rhs_fvs) is_exported binds
262 = map update_bndrs binds
264 update_bndrs (NonRec b r) = NonRec (update_bndr b) r
265 update_bndrs (Rec prs) = Rec [(update_bndr b, r) | (b,r) <- prs]
268 | is_exported (idName bndr)
269 || bndr `elemVarSet` rule_rhs_fvs = setIdNoDiscard bndr'
272 bndr' = lookupVarSet rule_ids bndr `orElse` bndr
276 We must do some gentle simplification on the template (but not the RHS)
277 of each rule. The case that forced me to add this was the fold/build rule,
278 which without simplification looked like:
279 fold k z (build (/\a. g a)) ==> ...
280 This doesn't match unless you do eta reduction on the build argument.
283 simplRule rule@(id, BuiltinRule _)
285 simplRule rule@(id, Rule name bndrs args rhs)
286 = simplBinders bndrs $ \ bndrs' ->
287 mapSmpl simpl_arg args `thenSmpl` \ args' ->
288 simplExpr rhs `thenSmpl` \ rhs' ->
289 returnSmpl (id, Rule name bndrs' args' rhs')
292 -- I've seen rules in which a LHS like
293 -- augment g (build h)
295 -- augment (\a. g a) (build h)
296 -- So it's a help to eta-reduce the args as we simplify them.
297 -- Otherwise we don't match when given an argument like
299 = simplExpr e `thenSmpl` \ e' ->
300 returnSmpl (etaReduce e')
304 %************************************************************************
306 \subsection{Glomming}
308 %************************************************************************
311 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
312 -- Glom all binds together in one Rec, in case any
313 -- transformations have introduced any new dependencies
315 -- NB: the global invariant is this:
316 -- *** the top level bindings are never cloned, and are always unique ***
318 -- We sort them into dependency order, but applying transformation rules may
319 -- make something at the top refer to something at the bottom:
323 -- RULE: p (q x) = h x
325 -- Applying this rule makes f refer to h,
326 -- although it doesn't appear to in the source program.
327 -- This pass lets us control where it happens.
329 -- NOTICE that this cannot happen for rules whose head is a locally-defined
330 -- function. It only happens for rules whose head is an imported function
331 -- (p in the example above). So, for example, the rule had been
332 -- RULE: f (p x) = h x
333 -- then the rule for f would be attached to f itself (in its IdInfo)
334 -- by prepareLocalRuleBase and h would be regarded by the occurrency
335 -- analyser as free in f.
337 glomBinds dflags binds
338 = do { showPass dflags "GlomBinds" ;
339 let { recd_binds = [Rec (flattenBinds binds)] } ;
341 -- Not much point in printing the result...
342 -- just consumes output bandwidth
346 %************************************************************************
348 \subsection{The driver for the simplifier}
350 %************************************************************************
353 simplifyPgm :: DynFlags
355 -> (SimplifierSwitch -> SwitchResult)
357 -> [CoreBind] -- Input
358 -> IO (SimplCount, [CoreBind]) -- New bindings
360 simplifyPgm dflags rule_base
363 showPass dflags "Simplify";
365 (termination_msg, it_count, counts_out, binds')
366 <- iteration us 1 (zeroSimplCount dflags) binds;
368 dumpIfSet (dopt Opt_D_verbose_core2core dflags
369 && dopt Opt_D_dump_simpl_stats dflags)
370 "Simplifier statistics"
371 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
373 pprSimplCount counts_out]);
375 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
377 return (counts_out, binds')
380 max_iterations = getSimplIntSwitch sw_chkr MaxSimplifierIterations
381 black_list_fn = blackListed rule_lhs_fvs (intSwitchSet sw_chkr SimplInlinePhase)
382 imported_rule_ids = ruleBaseIds rule_base
383 rule_lhs_fvs = ruleBaseFVs rule_base
385 iteration us iteration_no counts binds
386 -- Try and force thunks off the binds; significantly reduces
387 -- space usage, especially with -O. JRS, 000620.
388 | let sz = coreBindsSize binds in sz == sz
390 -- Occurrence analysis
391 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
393 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
394 (pprCoreBindings tagged_binds);
397 -- We do this with a *case* not a *let* because lazy pattern
398 -- matching bit us with bad space leak!
399 -- With a let, we ended up with
404 -- case t of {(_,counts') -> if counts'=0 then ...
405 -- So the conditional didn't force counts', because the
406 -- selection got duplicated. Sigh!
407 case initSmpl dflags sw_chkr us1 imported_rule_ids black_list_fn
408 (simplTopBinds tagged_binds)
409 of { (binds', counts') -> do {
410 -- The imported_rule_ids are used by initSmpl to initialise
411 -- the in-scope set. That way, the simplifier will change any
412 -- occurrences of the imported id to the one in the imported_rule_ids
413 -- set, which are decorated with their rules.
415 let { all_counts = counts `plusSimplCount` counts' } ;
417 -- Stop if nothing happened; don't dump output
418 if isZeroSimplCount counts' then
419 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
422 -- Dump the result of this iteration
423 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations
424 ("Simplifier iteration " ++ show iteration_no
425 ++ " out of " ++ show max_iterations)
426 (pprSimplCount counts') ;
428 if dopt Opt_D_dump_simpl_iterations dflags then
430 ("Simplifier iteration " ++ show iteration_no ++ " result")
431 Opt_D_verbose_core2core
436 -- Stop if we've run out of iterations
437 if iteration_no == max_iterations then
440 if max_iterations > 2 then
441 hPutStr stderr ("NOTE: Simplifier still going after " ++
442 show max_iterations ++
443 " iterations; bailing out.\n")
448 return ("Simplifier baled out", iteration_no, all_counts, binds')
452 else iteration us2 (iteration_no + 1) all_counts binds'
455 (us1, us2) = splitUniqSupply us