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, 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 ((`elemVarSet` local_ids) . fst) better_rules
214 -- We use (`elemVarSet` local_ids) rather than isLocalId because
215 -- isLocalId isn't true of class methods.
216 -- If we miss any rules for Ids defined here, then we end up
217 -- giving the local decl a new Unique (because the in-scope-set is the
218 -- same as the rule-id set), and now the binding for the class method
219 -- doesn't have the same Unique as the one in the Class and the tc-env
220 -- Example: class Foo a where
222 -- {-# RULES "op" op x = x #-}
224 rule_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) better_rules)
225 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
226 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
227 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hst)
228 rule_base = extendRuleBaseList imp_rule_base orphan_rules
229 final_rule_base = addRuleBaseFVs rule_base (ruleBaseFVs local_rule_base)
230 -- The last step black-lists the free vars of local rules too
232 ; dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
233 (vcat [text "Local rules", pprRuleBase local_rule_base,
235 text "Imported rules", pprRuleBase final_rule_base])
237 ; return (final_rule_base, local_rule_ids, orphan_rules, rule_rhs_fvs)
240 sw_chkr any = SwBool False -- A bit bogus
241 black_list_all v = not (isDataConWrapId v)
242 -- This stops all inlining except the
243 -- wrappers for data constructors
245 add_rules rule_base mds = extendRuleBaseList rule_base (md_rules mds)
247 -- Boringly, we need to gather the in-scope set.
248 local_ids = foldr (unionVarSet . mkVarSet . bindersOf) emptyVarSet binds
251 updateBinders :: IdSet -- Locally defined ids with their Rules attached
252 -> IdSet -- Ids free in the RHS of local rules
254 -> [CoreBind] -> [CoreBind]
255 -- A horrible function
257 -- Update the binders of top-level bindings as follows
258 -- a) Attach the rules for each locally-defined Id to that Id.
259 -- b) Set the no-discard flag if either the Id is exported,
260 -- or it's mentoined in the RHS of a rule
263 -- - It makes the rules easier to look up
264 -- - It means that transformation rules and specialisations for
265 -- locally defined Ids are handled uniformly
266 -- - It keeps alive things that are referred to only from a rule
267 -- (the occurrence analyser knows about rules attached to Ids)
268 -- - It makes sure that, when we apply a rule, the free vars
269 -- of the RHS are more likely to be in scope
272 -- It means that the binding won't be discarded EVEN if the binding
273 -- ends up being trivial (v = w) -- the simplifier would usually just
274 -- substitute w for v throughout, but we don't apply the substitution to
275 -- the rules (maybe we should?), so this substitution would make the rule
278 updateBinders rule_ids rule_rhs_fvs is_exported binds
279 = map update_bndrs binds
281 update_bndrs (NonRec b r) = NonRec (update_bndr b) r
282 update_bndrs (Rec prs) = Rec [(update_bndr b, r) | (b,r) <- prs]
285 | isImplicitId bndr = bndr -- Constructors, selectors; doesn't
286 -- make sense to call setIdNoDiscard
287 -- Also can't have rules
288 | dont_discard bndr = setIdNoDiscard bndr_with_rules
289 | otherwise = bndr_with_rules
291 bndr_with_rules = lookupVarSet rule_ids bndr `orElse` bndr
293 dont_discard bndr = is_exported (idName bndr)
294 || bndr `elemVarSet` rule_rhs_fvs
298 We must do some gentle simplification on the template (but not the RHS)
299 of each rule. The case that forced me to add this was the fold/build rule,
300 which without simplification looked like:
301 fold k z (build (/\a. g a)) ==> ...
302 This doesn't match unless you do eta reduction on the build argument.
305 simplRule rule@(id, BuiltinRule _)
307 simplRule rule@(id, Rule name bndrs args rhs)
308 = simplBinders bndrs $ \ bndrs' ->
309 mapSmpl simplExprGently args `thenSmpl` \ args' ->
310 simplExprGently rhs `thenSmpl` \ rhs' ->
311 returnSmpl (id, Rule name bndrs' args' rhs')
313 -- It's important that simplExprGently does eta reduction.
314 -- For example, in a rule like:
315 -- augment g (build h)
316 -- we do not want to get
317 -- augment (\a. g a) (build h)
318 -- otherwise we don't match when given an argument like
321 -- The simplifier does indeed do eta reduction (it's in
322 -- Simplify.completeLam) but only if -O is on.
326 simplExprGently :: CoreExpr -> SimplM CoreExpr
327 -- Simplifies an expression
328 -- does occurrence analysis, then simplification
329 -- and repeats (twice currently) because one pass
330 -- alone leaves tons of crud.
331 -- Used (a) for user expressions typed in at the interactive prompt
332 -- (b) the LHS and RHS of a RULE
334 = simplExpr (occurAnalyseGlobalExpr expr) `thenSmpl` \ expr1 ->
335 simplExpr (occurAnalyseGlobalExpr expr1)
339 %************************************************************************
341 \subsection{Glomming}
343 %************************************************************************
346 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
347 -- Glom all binds together in one Rec, in case any
348 -- transformations have introduced any new dependencies
350 -- NB: the global invariant is this:
351 -- *** the top level bindings are never cloned, and are always unique ***
353 -- We sort them into dependency order, but applying transformation rules may
354 -- make something at the top refer to something at the bottom:
358 -- RULE: p (q x) = h x
360 -- Applying this rule makes f refer to h,
361 -- although it doesn't appear to in the source program.
362 -- This pass lets us control where it happens.
364 -- NOTICE that this cannot happen for rules whose head is a locally-defined
365 -- function. It only happens for rules whose head is an imported function
366 -- (p in the example above). So, for example, the rule had been
367 -- RULE: f (p x) = h x
368 -- then the rule for f would be attached to f itself (in its IdInfo)
369 -- by prepareLocalRuleBase and h would be regarded by the occurrency
370 -- analyser as free in f.
372 glomBinds dflags binds
373 = do { showPass dflags "GlomBinds" ;
374 let { recd_binds = [Rec (flattenBinds binds)] } ;
376 -- Not much point in printing the result...
377 -- just consumes output bandwidth
381 %************************************************************************
383 \subsection{The driver for the simplifier}
385 %************************************************************************
388 simplifyPgm :: DynFlags
390 -> (SimplifierSwitch -> SwitchResult)
392 -> [CoreBind] -- Input
393 -> IO (SimplCount, [CoreBind]) -- New bindings
395 simplifyPgm dflags rule_base
398 showPass dflags "Simplify";
400 (termination_msg, it_count, counts_out, binds')
401 <- iteration us 1 (zeroSimplCount dflags) binds;
403 dumpIfSet (dopt Opt_D_verbose_core2core dflags
404 && dopt Opt_D_dump_simpl_stats dflags)
405 "Simplifier statistics"
406 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
408 pprSimplCount counts_out]);
410 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
412 return (counts_out, binds')
415 max_iterations = getSimplIntSwitch sw_chkr MaxSimplifierIterations
416 black_list_fn = blackListed rule_lhs_fvs (intSwitchSet sw_chkr SimplInlinePhase)
417 imported_rule_ids = ruleBaseIds rule_base
418 rule_lhs_fvs = ruleBaseFVs rule_base
420 iteration us iteration_no counts binds
421 -- Try and force thunks off the binds; significantly reduces
422 -- space usage, especially with -O. JRS, 000620.
423 | let sz = coreBindsSize binds in sz == sz
425 -- Occurrence analysis
426 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
428 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
429 (pprCoreBindings tagged_binds);
432 -- We do this with a *case* not a *let* because lazy pattern
433 -- matching bit us with bad space leak!
434 -- With a let, we ended up with
439 -- case t of {(_,counts') -> if counts'=0 then ...
440 -- So the conditional didn't force counts', because the
441 -- selection got duplicated. Sigh!
442 case initSmpl dflags sw_chkr us1 imported_rule_ids black_list_fn
443 (simplTopBinds tagged_binds)
444 of { (binds', counts') -> do {
445 -- The imported_rule_ids are used by initSmpl to initialise
446 -- the in-scope set. That way, the simplifier will change any
447 -- occurrences of the imported id to the one in the imported_rule_ids
448 -- set, which are decorated with their rules.
450 let { all_counts = counts `plusSimplCount` counts' } ;
452 -- Stop if nothing happened; don't dump output
453 if isZeroSimplCount counts' then
454 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
457 -- Dump the result of this iteration
458 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations
459 ("Simplifier iteration " ++ show iteration_no
460 ++ " out of " ++ show max_iterations)
461 (pprSimplCount counts') ;
464 ("Simplifier iteration " ++ show iteration_no ++ " result")
465 Opt_D_dump_simpl_iterations
468 -- Stop if we've run out of iterations
469 if iteration_no == max_iterations then
472 if max_iterations > 2 then
473 hPutStr stderr ("NOTE: Simplifier still going after " ++
474 show max_iterations ++
475 " iterations; bailing out.\n")
480 return ("Simplifier baled out", iteration_no, all_counts, binds')
484 else iteration us2 (iteration_no + 1) all_counts binds'
487 (us1, us2) = splitUniqSupply us