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(..), SimplifierMode(..),
12 DynFlags, DynFlag(..), dopt, dopt_CoreToDo
15 import CoreFVs ( ruleRhsFreeVars )
16 import HscTypes ( PersistentCompilerState(..),
17 PackageRuleBase, HomeSymbolTable, IsExported, ModDetails(..)
19 import CSE ( cseProgram )
20 import Rules ( RuleBase, emptyRuleBase, ruleBaseFVs, ruleBaseIds,
21 extendRuleBaseList, addRuleBaseFVs, pprRuleBase,
23 import Module ( moduleEnvElts )
24 import PprCore ( pprCoreBindings, pprCoreExpr )
25 import OccurAnal ( occurAnalyseBinds, occurAnalyseGlobalExpr )
26 import CoreUtils ( coreBindsSize )
27 import Simplify ( simplTopBinds, simplExpr )
28 import SimplUtils ( simplBinders )
30 import ErrUtils ( dumpIfSet, dumpIfSet_dyn, showPass )
31 import CoreLint ( endPass )
32 import FloatIn ( floatInwards )
33 import FloatOut ( floatOutwards )
34 import Id ( idName, setIdLocalExported )
36 import LiberateCase ( liberateCase )
37 import SAT ( doStaticArgs )
38 import Specialise ( specProgram)
39 import SpecConstr ( specConstrProgram)
40 import UsageSPInf ( doUsageSPInf )
41 import StrictAnal ( saBinds )
42 import DmdAnal ( dmdAnalPgm )
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 env = emptySimplEnv (SimplPhase 0) [] emptyVarSet
113 (expr', _counts) = initSmpl dflags us (simplExprGently env expr)
115 ; dumpIfSet_dyn dflags Opt_D_dump_simpl "Simplified expression"
122 doCorePasses :: DynFlags
123 -> RuleBase -- the main rule base
124 -> SimplCount -- simplifier stats
125 -> UniqSupply -- uniques
126 -> [CoreBind] -- local binds in (with rules attached)
127 -> [CoreToDo] -- which passes to do
128 -> IO (SimplCount, [CoreBind]) -- stats, binds, local orphan rules
130 doCorePasses dflags rb stats us binds []
131 = return (stats, binds)
133 doCorePasses dflags rb stats us binds (to_do : to_dos)
135 let (us1, us2) = splitUniqSupply us
137 (stats1, binds1) <- doCorePass dflags rb us1 binds to_do
139 doCorePasses dflags rb (stats `plusSimplCount` stats1) us2 binds1 to_dos
141 doCorePass dfs rb us binds (CoreDoSimplify mode switches)
142 = _scc_ "Simplify" simplifyPgm dfs rb mode switches us binds
143 doCorePass dfs rb us binds CoreCSE
144 = _scc_ "CommonSubExpr" noStats dfs (cseProgram dfs binds)
145 doCorePass dfs rb us binds CoreLiberateCase
146 = _scc_ "LiberateCase" noStats dfs (liberateCase dfs binds)
147 doCorePass dfs rb us binds CoreDoFloatInwards
148 = _scc_ "FloatInwards" noStats dfs (floatInwards dfs binds)
149 doCorePass dfs rb us binds (CoreDoFloatOutwards f)
150 = _scc_ "FloatOutwards" noStats dfs (floatOutwards dfs f us binds)
151 doCorePass dfs rb us binds CoreDoStaticArgs
152 = _scc_ "StaticArgs" noStats dfs (doStaticArgs us binds)
153 doCorePass dfs rb us binds CoreDoStrictness
154 = _scc_ "Stranal" noStats dfs (do { binds1 <- saBinds dfs binds ;
155 dmdAnalPgm dfs binds1 })
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 CoreDoSpecConstr
161 = _scc_ "SpecConstr" noStats dfs (specConstrProgram dfs us binds)
162 doCorePass dfs rb us binds CoreDoCPResult
163 = _scc_ "CPResult" noStats dfs (cprAnalyse dfs binds)
164 doCorePass dfs rb us binds CoreDoPrintCore
165 = _scc_ "PrintCore" noStats dfs (printCore binds)
166 doCorePass dfs rb us binds CoreDoUSPInf
167 = _scc_ "CoreUsageSPInf" noStats dfs (doUsageSPInf dfs us binds)
168 doCorePass dfs rb us binds CoreDoGlomBinds
169 = noStats dfs (glomBinds dfs binds)
170 doCorePass dfs rb us binds (CoreDoRuleCheck phase pat)
171 = noStats dfs (ruleCheck dfs phase pat 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 ruleCheck dflags phase pat binds = do showPass dflags "RuleCheck"
180 printDump (ruleCheckProgram phase pat binds)
183 -- most passes return no stats and don't change rules
184 noStats dfs thing = do { binds <- thing; return (zeroSimplCount dfs, binds) }
190 %************************************************************************
192 \subsection{Dealing with rules}
194 %************************************************************************
196 -- prepareLocalRuleBase takes the CoreBinds and rules defined in this module.
197 -- It attaches those rules that are for local Ids to their binders, and
198 -- returns the remainder attached to Ids in an IdSet. It also returns
199 -- Ids mentioned on LHS of some rule; these should be blacklisted.
201 -- The rule Ids and LHS Ids are black-listed; that is, they aren't inlined
202 -- so that the opportunity to apply the rule isn't lost too soon
205 prepareRules :: DynFlags -> PackageRuleBase -> HomeSymbolTable
208 -> [IdCoreRule] -- Local rules
209 -> IO (RuleBase, -- Full rule base
210 IdSet, -- Local rule Ids
211 [IdCoreRule], -- Orphan rules
212 IdSet) -- RHS free vars of all rules
214 prepareRules dflags pkg_rule_base hst us binds local_rules
215 = do { let env = emptySimplEnv SimplGently [] local_ids
216 (better_rules,_) = initSmpl dflags us (mapSmpl (simplRule env) local_rules)
218 ; let (local_rules, orphan_rules) = partition ((`elemVarSet` local_ids) . fst) better_rules
219 -- We use (`elemVarSet` local_ids) rather than isLocalId because
220 -- isLocalId isn't true of class methods.
221 -- If we miss any rules for Ids defined here, then we end up
222 -- giving the local decl a new Unique (because the in-scope-set is the
223 -- same as the rule-id set), and now the binding for the class method
224 -- doesn't have the same Unique as the one in the Class and the tc-env
225 -- Example: class Foo a where
227 -- {-# RULES "op" op x = x #-}
229 rule_rhs_fvs = unionVarSets (map (ruleRhsFreeVars . snd) better_rules)
230 local_rule_base = extendRuleBaseList emptyRuleBase local_rules
231 local_rule_ids = ruleBaseIds local_rule_base -- Local Ids with rules attached
232 imp_rule_base = foldl add_rules pkg_rule_base (moduleEnvElts hst)
233 rule_base = extendRuleBaseList imp_rule_base orphan_rules
234 final_rule_base = addRuleBaseFVs rule_base (ruleBaseFVs local_rule_base)
235 -- The last step black-lists the free vars of local rules too
237 ; dumpIfSet_dyn dflags Opt_D_dump_rules "Transformation rules"
238 (vcat [text "Local rules", pprRuleBase local_rule_base,
240 text "Imported rules", pprRuleBase final_rule_base])
242 ; return (final_rule_base, local_rule_ids, orphan_rules, rule_rhs_fvs)
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 | dont_discard bndr = setIdLocalExported bndr_with_rules
286 | otherwise = bndr_with_rules
288 bndr_with_rules = lookupVarSet rule_ids bndr `orElse` bndr
290 dont_discard bndr = is_exported (idName bndr)
291 || bndr `elemVarSet` rule_rhs_fvs
295 We must do some gentle simplification on the template (but not the RHS)
296 of each rule. The case that forced me to add this was the fold/build rule,
297 which without simplification looked like:
298 fold k z (build (/\a. g a)) ==> ...
299 This doesn't match unless you do eta reduction on the build argument.
302 simplRule env rule@(id, BuiltinRule _ _)
304 simplRule env rule@(id, Rule act name bndrs args rhs)
305 = simplBinders env bndrs `thenSmpl` \ (env, bndrs') ->
306 mapSmpl (simplExprGently env) args `thenSmpl` \ args' ->
307 simplExprGently env rhs `thenSmpl` \ rhs' ->
308 returnSmpl (id, Rule act name bndrs' args' rhs')
310 -- It's important that simplExprGently does eta reduction.
311 -- For example, in a rule like:
312 -- augment g (build h)
313 -- we do not want to get
314 -- augment (\a. g a) (build h)
315 -- otherwise we don't match when given an argument like
318 -- The simplifier does indeed do eta reduction (it's in
319 -- Simplify.completeLam) but only if -O is on.
323 simplExprGently :: SimplEnv -> CoreExpr -> SimplM CoreExpr
324 -- Simplifies an expression
325 -- does occurrence analysis, then simplification
326 -- and repeats (twice currently) because one pass
327 -- alone leaves tons of crud.
328 -- Used (a) for user expressions typed in at the interactive prompt
329 -- (b) the LHS and RHS of a RULE
330 simplExprGently env expr
331 = simplExpr env (occurAnalyseGlobalExpr expr) `thenSmpl` \ expr1 ->
332 simplExpr env (occurAnalyseGlobalExpr expr1)
336 %************************************************************************
338 \subsection{Glomming}
340 %************************************************************************
343 glomBinds :: DynFlags -> [CoreBind] -> IO [CoreBind]
344 -- Glom all binds together in one Rec, in case any
345 -- transformations have introduced any new dependencies
347 -- NB: the global invariant is this:
348 -- *** the top level bindings are never cloned, and are always unique ***
350 -- We sort them into dependency order, but applying transformation rules may
351 -- make something at the top refer to something at the bottom:
355 -- RULE: p (q x) = h x
357 -- Applying this rule makes f refer to h,
358 -- although it doesn't appear to in the source program.
359 -- This pass lets us control where it happens.
361 -- NOTICE that this cannot happen for rules whose head is a locally-defined
362 -- function. It only happens for rules whose head is an imported function
363 -- (p in the example above). So, for example, the rule had been
364 -- RULE: f (p x) = h x
365 -- then the rule for f would be attached to f itself (in its IdInfo)
366 -- by prepareLocalRuleBase and h would be regarded by the occurrency
367 -- analyser as free in f.
369 glomBinds dflags binds
370 = do { showPass dflags "GlomBinds" ;
371 let { recd_binds = [Rec (flattenBinds binds)] } ;
373 -- Not much point in printing the result...
374 -- just consumes output bandwidth
378 %************************************************************************
380 \subsection{The driver for the simplifier}
382 %************************************************************************
385 simplifyPgm :: DynFlags
388 -> [SimplifierSwitch]
390 -> [CoreBind] -- Input
391 -> IO (SimplCount, [CoreBind]) -- New bindings
393 simplifyPgm dflags rule_base
394 mode switches us binds
396 showPass dflags "Simplify";
398 (termination_msg, it_count, counts_out, binds')
399 <- iteration us 1 (zeroSimplCount dflags) binds;
401 dumpIfSet (dopt Opt_D_verbose_core2core dflags
402 && dopt Opt_D_dump_simpl_stats dflags)
403 "Simplifier statistics"
404 (vcat [text termination_msg <+> text "after" <+> ppr it_count <+> text "iterations",
406 pprSimplCount counts_out]);
408 endPass dflags "Simplify" Opt_D_verbose_core2core binds';
410 return (counts_out, binds')
413 phase_info = case mode of
414 SimplGently -> "gentle"
415 SimplPhase n -> show n
417 imported_rule_ids = ruleBaseIds rule_base
418 simpl_env = emptySimplEnv mode switches imported_rule_ids
419 sw_chkr = getSwitchChecker simpl_env
420 max_iterations = intSwitchSet sw_chkr MaxSimplifierIterations `orElse` 2
422 iteration us iteration_no counts binds
423 -- Try and force thunks off the binds; significantly reduces
424 -- space usage, especially with -O. JRS, 000620.
425 | let sz = coreBindsSize binds in sz == sz
427 -- Occurrence analysis
428 let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds binds } ;
430 dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
431 (pprCoreBindings tagged_binds);
434 -- We do this with a *case* not a *let* because lazy pattern
435 -- matching bit us with bad space leak!
436 -- With a let, we ended up with
441 -- case t of {(_,counts') -> if counts'=0 then ...
442 -- So the conditional didn't force counts', because the
443 -- selection got duplicated. Sigh!
444 case initSmpl dflags us1 (simplTopBinds simpl_env tagged_binds) of {
445 (binds', counts') -> do {
446 -- The imported_rule_ids are used by initSmpl to initialise
447 -- the in-scope set. That way, the simplifier will change any
448 -- occurrences of the imported id to the one in the imported_rule_ids
449 -- set, which are decorated with their rules.
451 let { all_counts = counts `plusSimplCount` counts' ;
452 herald = "Simplifier phase " ++ phase_info ++
453 ", iteration " ++ show iteration_no ++
454 " out of " ++ show max_iterations
457 -- Stop if nothing happened; don't dump output
458 if isZeroSimplCount counts' then
459 return ("Simplifier reached fixed point", iteration_no, all_counts, binds')
462 -- Dump the result of this iteration
463 dumpIfSet_dyn dflags Opt_D_dump_simpl_iterations herald
464 (pprSimplCount counts') ;
466 endPass dflags herald Opt_D_dump_simpl_iterations binds' ;
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