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, pprRuleBase )
24 import Module ( moduleEnvElts )
26 import PprCore ( pprCoreBindings, pprCoreExpr )
27 import OccurAnal ( occurAnalyseBinds, occurAnalyseGlobalExpr )
28 import CoreUtils ( 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, isImplicitId )
37 import LiberateCase ( liberateCase )
38 import SAT ( doStaticArgs )
39 import Specialise ( specProgram)
40 import SpecConstr ( specConstrProgram)
41 import UsageSPInf ( doUsageSPInf )
42 import StrictAnal ( saBinds )
43 import WorkWrap ( wwTopBinds )
44 import CprAnalyse ( cprAnalyse )
46 import UniqSupply ( UniqSupply, mkSplitUniqSupply, splitUniqSupply )
47 import IO ( hPutStr, stderr )
50 import Maybes ( orElse )
51 import List ( partition )
54 %************************************************************************
56 \subsection{The driver for the simplifier}
58 %************************************************************************
61 core2core :: DynFlags -- includes spec of what core-to-core passes to do
62 -> PersistentCompilerState
68 core2core dflags pcs hst is_exported
69 mod_details@(ModDetails { md_binds = binds_in, md_rules = rules_in })
71 let core_todos = dopt_CoreToDo dflags
72 let pkg_rule_base = pcs_rules pcs -- Rule-base accumulated from imported packages
75 us <- mkSplitUniqSupply 's'
76 let (cp_us, ru_us) = splitUniqSupply us
78 -- COMPUTE THE RULE BASE TO USE
79 (rule_base, local_rule_ids, orphan_rules, rule_rhs_fvs)
80 <- prepareRules dflags pkg_rule_base hst ru_us binds_in rules_in
82 -- PREPARE THE BINDINGS
83 let binds1 = updateBinders local_rule_ids rule_rhs_fvs is_exported binds_in
86 (stats, processed_binds)
87 <- doCorePasses dflags rule_base (zeroSimplCount dflags) cp_us binds1 core_todos
89 dumpIfSet_dyn dflags Opt_D_dump_simpl_stats
90 "Grand total simplifier statistics"
94 -- We only return local orphan rules, i.e., local rules not attached to an Id
95 -- The bindings cotain more rules, embedded in the Ids
96 return (mod_details { md_binds = processed_binds, md_rules = orphan_rules})
99 simplifyExpr :: DynFlags -- includes spec of what core-to-core passes to do
100 -> PersistentCompilerState
104 -- simplifyExpr is called by the driver to simplify an
105 -- expression typed in at the interactive prompt
106 simplifyExpr dflags pcs hst expr
108 ; showPass dflags "Simplify"
110 ; us <- mkSplitUniqSupply 's'
112 ; let (expr', _counts) = initSmpl dflags sw_chkr us emptyVarSet black_list_nothing
113 (simplExprGently expr)
115 ; dumpIfSet_dyn dflags Opt_D_dump_simpl "Simplified expression"
121 sw_chkr any = SwBool False -- A bit bogus
122 black_list_nothing v = False -- Black list nothing
125 doCorePasses :: DynFlags
126 -> RuleBase -- the main rule base
127 -> SimplCount -- simplifier stats
128 -> UniqSupply -- uniques
129 -> [CoreBind] -- local binds in (with rules attached)
130 -> [CoreToDo] -- which passes to do
131 -> IO (SimplCount, [CoreBind]) -- stats, binds, local orphan rules
133 doCorePasses dflags rb stats us binds []
134 = return (stats, binds)
136 doCorePasses dflags rb stats us binds (to_do : to_dos)
138 let (us1, us2) = splitUniqSupply us
140 (stats1, binds1) <- doCorePass dflags rb us1 binds to_do
142 doCorePasses dflags rb (stats `plusSimplCount` stats1) us2 binds1 to_dos
144 doCorePass dfs rb us binds (CoreDoSimplify sw_chkr)
145 = _scc_ "Simplify" simplifyPgm dfs rb sw_chkr us binds
146 doCorePass dfs rb us binds CoreCSE
147 = _scc_ "CommonSubExpr" noStats dfs (cseProgram dfs binds)
148 doCorePass dfs rb us binds CoreLiberateCase
149 = _scc_ "LiberateCase" noStats dfs (liberateCase dfs binds)
150 doCorePass dfs rb us binds CoreDoFloatInwards
151 = _scc_ "FloatInwards" noStats dfs (floatInwards dfs binds)
152 doCorePass dfs rb us binds (CoreDoFloatOutwards f)
153 = _scc_ "FloatOutwards" noStats dfs (floatOutwards dfs f us binds)
154 doCorePass dfs rb us binds CoreDoStaticArgs
155 = _scc_ "StaticArgs" noStats dfs (doStaticArgs us binds)
156 doCorePass dfs rb us binds CoreDoStrictness
157 = _scc_ "Stranal" noStats dfs (saBinds dfs binds)
158 doCorePass dfs rb us binds CoreDoWorkerWrapper
159 = _scc_ "WorkWrap" noStats dfs (wwTopBinds dfs us binds)
160 doCorePass dfs rb us binds CoreDoSpecialising
161 = _scc_ "Specialise" noStats dfs (specProgram dfs us binds)
162 doCorePass dfs rb us binds CoreDoSpecConstr
163 = _scc_ "SpecConstr" noStats dfs (specConstrProgram dfs us binds)
164 doCorePass dfs rb us binds CoreDoCPResult
165 = _scc_ "CPResult" noStats dfs (cprAnalyse dfs binds)
166 doCorePass dfs rb us binds CoreDoPrintCore
167 = _scc_ "PrintCore" noStats dfs (printCore binds)
168 doCorePass dfs rb us binds CoreDoUSPInf
169 = _scc_ "CoreUsageSPInf" noStats dfs (doUsageSPInf dfs us binds)
170 doCorePass dfs rb us binds CoreDoGlomBinds
171 = noStats dfs (glomBinds dfs binds)
172 doCorePass dfs rb us binds CoreDoNothing
173 = noStats dfs (return binds)
175 printCore binds = do dumpIfSet True "Print Core"
176 (pprCoreBindings binds)
179 -- most passes return no stats and don't change rules
180 noStats dfs thing = do { binds <- thing; return (zeroSimplCount dfs, binds) }
185 %************************************************************************
187 \subsection{Dealing with rules}
189 %************************************************************************
191 -- prepareLocalRuleBase takes the CoreBinds and rules defined in this module.
192 -- It attaches those rules that are for local Ids to their binders, and
193 -- returns the remainder attached to Ids in an IdSet. It also returns
194 -- Ids mentioned on LHS of some rule; these should be blacklisted.
196 -- The rule Ids and LHS Ids are black-listed; that is, they aren't inlined
197 -- so that the opportunity to apply the rule isn't lost too soon
200 prepareRules :: DynFlags -> PackageRuleBase -> HomeSymbolTable
203 -> [IdCoreRule] -- Local rules
204 -> IO (RuleBase, -- Full rule base
205 IdSet, -- Local rule Ids
206 [IdCoreRule], -- Orphan rules
207 IdSet) -- RHS free vars of all rules
209 prepareRules dflags pkg_rule_base hst us binds local_rules
210 = do { let (better_rules,_) = initSmpl dflags sw_chkr us local_ids black_list_all
211 (mapSmpl simplRule local_rules)
213 ; let (local_rules, orphan_rules) = partition (isLocalId . fst) better_rules
214 rule_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) better_rules)
215 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
216 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
217 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hst)
218 rule_base = extendRuleBaseList imp_rule_base orphan_rules
219 final_rule_base = addRuleBaseFVs rule_base (ruleBaseFVs local_rule_base)
220 -- The last step black-lists the free vars of local rules too
222 ; dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
223 (vcat [text "Local rules", pprRuleBase local_rule_base,
225 text "Imported rules", pprRuleBase final_rule_base])
227 ; return (final_rule_base, local_rule_ids, orphan_rules, rule_rhs_fvs)
230 sw_chkr any = SwBool False -- A bit bogus
231 black_list_all v = not (isDataConWrapId v)
232 -- This stops all inlining except the
233 -- wrappers for data constructors
235 add_rules rule_base mds = extendRuleBaseList rule_base (md_rules mds)
237 -- Boringly, we need to gather the in-scope set.
238 -- Typically this thunk won't even be forced, but the test in
239 -- simpVar fails if it isn't right, and it might conceiveably matter
240 local_ids = foldr (unionVarSet . mkVarSet . bindersOf) emptyVarSet binds
243 updateBinders :: IdSet -- Locally defined ids with their Rules attached
244 -> IdSet -- Ids free in the RHS of local rules
246 -> [CoreBind] -> [CoreBind]
247 -- A horrible function
249 -- Update the binders of top-level bindings as follows
250 -- a) Attach the rules for each locally-defined Id to that Id.
251 -- b) Set the no-discard flag if either the Id is exported,
252 -- or it's mentoined in the RHS of a rule
255 -- - It makes the rules easier to look up
256 -- - It means that transformation rules and specialisations for
257 -- locally defined Ids are handled uniformly
258 -- - It keeps alive things that are referred to only from a rule
259 -- (the occurrence analyser knows about rules attached to Ids)
260 -- - It makes sure that, when we apply a rule, the free vars
261 -- of the RHS are more likely to be in scope
264 -- It means that the binding won't be discarded EVEN if the binding
265 -- ends up being trivial (v = w) -- the simplifier would usually just
266 -- substitute w for v throughout, but we don't apply the substitution to
267 -- the rules (maybe we should?), so this substitution would make the rule
270 updateBinders rule_ids rule_rhs_fvs is_exported binds
271 = map update_bndrs binds
273 update_bndrs (NonRec b r) = NonRec (update_bndr b) r
274 update_bndrs (Rec prs) = Rec [(update_bndr b, r) | (b,r) <- prs]
277 | isImplicitId bndr = bndr -- Constructors, selectors; doesn't
278 -- make sense to call setIdNoDiscard
279 -- Also can't have rules
280 | dont_discard bndr = setIdNoDiscard bndr_with_rules
281 | otherwise = bndr_with_rules
283 bndr_with_rules = lookupVarSet rule_ids bndr `orElse` bndr
285 dont_discard bndr = is_exported (idName bndr)
286 || bndr `elemVarSet` rule_rhs_fvs
290 We must do some gentle simplification on the template (but not the RHS)
291 of each rule. The case that forced me to add this was the fold/build rule,
292 which without simplification looked like:
293 fold k z (build (/\a. g a)) ==> ...
294 This doesn't match unless you do eta reduction on the build argument.
297 simplRule rule@(id, BuiltinRule _)
299 simplRule rule@(id, Rule name bndrs args rhs)
300 = simplBinders bndrs $ \ bndrs' ->
301 mapSmpl simplExprGently args `thenSmpl` \ args' ->
302 simplExprGently rhs `thenSmpl` \ rhs' ->
303 returnSmpl (id, Rule name bndrs' args' rhs')
305 -- It's important that simplExprGently does eta reduction.
306 -- For example, in a rule like:
307 -- augment g (build h)
308 -- we do not want to get
309 -- augment (\a. g a) (build h)
310 -- otherwise we don't match when given an argument like
313 -- The simplifier does indeed do eta reduction (it's in
314 -- Simplify.completeLam) but only if -O is on.
318 simplExprGently :: CoreExpr -> SimplM CoreExpr
319 -- Simplifies an expression
320 -- does occurrence analysis, then simplification
321 -- and repeats (twice currently) because one pass
322 -- alone leaves tons of crud.
323 -- Used (a) for user expressions typed in at the interactive prompt
324 -- (b) the LHS and RHS of a RULE
326 = simplExpr (occurAnalyseGlobalExpr expr) `thenSmpl` \ expr1 ->
327 simplExpr (occurAnalyseGlobalExpr expr1)
331 %************************************************************************
333 \subsection{Glomming}
335 %************************************************************************
338 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
339 -- Glom all binds together in one Rec, in case any
340 -- transformations have introduced any new dependencies
342 -- NB: the global invariant is this:
343 -- *** the top level bindings are never cloned, and are always unique ***
345 -- We sort them into dependency order, but applying transformation rules may
346 -- make something at the top refer to something at the bottom:
350 -- RULE: p (q x) = h x
352 -- Applying this rule makes f refer to h,
353 -- although it doesn't appear to in the source program.
354 -- This pass lets us control where it happens.
356 -- NOTICE that this cannot happen for rules whose head is a locally-defined
357 -- function. It only happens for rules whose head is an imported function
358 -- (p in the example above). So, for example, the rule had been
359 -- RULE: f (p x) = h x
360 -- then the rule for f would be attached to f itself (in its IdInfo)
361 -- by prepareLocalRuleBase and h would be regarded by the occurrency
362 -- analyser as free in f.
364 glomBinds dflags binds
365 = do { showPass dflags "GlomBinds" ;
366 let { recd_binds = [Rec (flattenBinds binds)] } ;
368 -- Not much point in printing the result...
369 -- just consumes output bandwidth
373 %************************************************************************
375 \subsection{The driver for the simplifier}
377 %************************************************************************
380 simplifyPgm :: DynFlags
382 -> (SimplifierSwitch -> SwitchResult)
384 -> [CoreBind] -- Input
385 -> IO (SimplCount, [CoreBind]) -- New bindings
387 simplifyPgm dflags rule_base
390 showPass dflags "Simplify";
392 (termination_msg, it_count, counts_out, binds')
393 <- iteration us 1 (zeroSimplCount dflags) binds;
395 dumpIfSet (dopt Opt_D_verbose_core2core dflags
396 && dopt Opt_D_dump_simpl_stats dflags)
397 "Simplifier statistics"
398 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
400 pprSimplCount counts_out]);
402 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
404 return (counts_out, binds')
407 max_iterations = getSimplIntSwitch sw_chkr MaxSimplifierIterations
408 black_list_fn = blackListed rule_lhs_fvs (intSwitchSet sw_chkr SimplInlinePhase)
409 imported_rule_ids = ruleBaseIds rule_base
410 rule_lhs_fvs = ruleBaseFVs rule_base
412 iteration us iteration_no counts binds
413 -- Try and force thunks off the binds; significantly reduces
414 -- space usage, especially with -O. JRS, 000620.
415 | let sz = coreBindsSize binds in sz == sz
417 -- Occurrence analysis
418 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
420 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
421 (pprCoreBindings tagged_binds);
424 -- We do this with a *case* not a *let* because lazy pattern
425 -- matching bit us with bad space leak!
426 -- With a let, we ended up with
431 -- case t of {(_,counts') -> if counts'=0 then ...
432 -- So the conditional didn't force counts', because the
433 -- selection got duplicated. Sigh!
434 case initSmpl dflags sw_chkr us1 imported_rule_ids black_list_fn
435 (simplTopBinds tagged_binds)
436 of { (binds', counts') -> do {
437 -- The imported_rule_ids are used by initSmpl to initialise
438 -- the in-scope set. That way, the simplifier will change any
439 -- occurrences of the imported id to the one in the imported_rule_ids
440 -- set, which are decorated with their rules.
442 let { all_counts = counts `plusSimplCount` counts' } ;
444 -- Stop if nothing happened; don't dump output
445 if isZeroSimplCount counts' then
446 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
449 -- Dump the result of this iteration
450 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations
451 ("Simplifier iteration " ++ show iteration_no
452 ++ " out of " ++ show max_iterations)
453 (pprSimplCount counts') ;
456 ("Simplifier iteration " ++ show iteration_no ++ " result")
457 Opt_D_dump_simpl_iterations
460 -- Stop if we've run out of iterations
461 if iteration_no == max_iterations then
464 if max_iterations > 2 then
465 hPutStr stderr ("NOTE: Simplifier still going after " ++
466 show max_iterations ++
467 " iterations; bailing out.\n")
472 return ("Simplifier baled out", iteration_no, all_counts, binds')
476 else iteration us2 (iteration_no + 1) all_counts binds'
479 (us1, us2) = splitUniqSupply us