import CoreSyn
import TcIface ( loadImportedRules )
import HscTypes ( HscEnv(..), ModGuts(..), ExternalPackageState(..),
- ModDetails(..), HomeModInfo(..), HomePackageTable, Dependencies( dep_mods ),
+ Dependencies( dep_mods ),
hscEPS, hptRules )
import CSE ( cseProgram )
import Rules ( RuleBase, ruleBaseIds, emptyRuleBase,
extendRuleBaseList, pprRuleBase, ruleCheckProgram )
-import Module ( elemModuleEnv, lookupModuleEnv )
import PprCore ( pprCoreBindings, pprCoreExpr, pprIdRules )
-import OccurAnal ( occurAnalyseBinds, occurAnalyseGlobalExpr )
+import OccurAnal ( occurAnalysePgm, occurAnalyseGlobalExpr )
+import IdInfo ( setNewStrictnessInfo, newStrictnessInfo,
+ setWorkerInfo, workerInfo,
+ setSpecInfo, specInfo )
import CoreUtils ( coreBindsSize )
import Simplify ( simplTopBinds, simplExpr )
import SimplEnv ( SimplEnv, simplBinders, mkSimplEnv, setInScopeSet )
import VarEnv ( mkInScopeSet )
import FloatIn ( floatInwards )
import FloatOut ( floatOutwards )
-import Id ( idIsFrom, idSpecialisation, setIdSpecialisation )
+import Id ( Id, modifyIdInfo, idInfo, idIsFrom, isExportedId, isLocalId,
+ idSpecialisation, setIdSpecialisation )
+import Rules ( addRules )
import VarSet
+import VarEnv
import LiberateCase ( liberateCase )
import SAT ( doStaticArgs )
import Specialise ( specProgram)
import IO ( hPutStr, stderr )
import Outputable
import List ( partition )
-import Maybes ( orElse, fromJust )
+import Maybes ( orElse )
\end{code}
%************************************************************************
| let sz = coreBindsSize (mg_binds guts) in sz == sz
= do {
-- Occurrence analysis
- let { tagged_binds = _scc_ "OccAnal" occurAnalyseBinds (mg_binds guts) } ;
+ let { short_inds = _scc_ "ZapInd" shortOutIndirections (mg_binds guts) ;
+ tagged_binds = _scc_ "OccAnal" occurAnalysePgm short_inds } ;
+
+ dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Short indirections"
+ (pprCoreBindings short_inds);
dumpIfSet_dyn dflags Opt_D_dump_occur_anal "Occurrence analysis"
(pprCoreBindings tagged_binds);
where
(us1, us2) = splitUniqSupply us
\end{code}
+
+
+%************************************************************************
+%* *
+ Top-level occurrence analysis
+ [In here, not OccurAnal, because it uses
+ Rules.lhs, which depends on OccurAnal]
+%* *
+%************************************************************************
+
+In @occAnalPgm@ we do indirection-shorting. That is, if we have this:
+
+ x_local = <expression>
+ ...bindings...
+ x_exported = x_local
+
+where x_exported is exported, and x_local is not, then we replace it with this:
+
+ x_exported = <expression>
+ x_local = x_exported
+ ...bindings...
+
+Without this we never get rid of the x_exported = x_local thing. This
+save a gratuitous jump (from \tr{x_exported} to \tr{x_local}), and
+makes strictness information propagate better. This used to happen in
+the final phase, but it's tidier to do it here.
+
+STRICTNESS: if we have done strictness analysis, we want the strictness info on
+x_local to transfer to x_exported. Hence the copyIdInfo call.
+
+RULES: we want to *add* any RULES for x_local to x_exported.
+
+Note [Rules and indirection-zapping]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Problem: what if x_exported has a RULE that mentions something in ...bindings...?
+Then the things mentioned can be out of scope! Solution
+ a) Make sure that in this pass the usage-info from x_exported is
+ available for ...bindings...
+ b) If there are any such RULES, rec-ify the entire top-level.
+ It'll get sorted out next time round
+
+Messing up the rules
+~~~~~~~~~~~~~~~~~~~~
+The example that went bad on me at one stage was this one:
+
+ iterate :: (a -> a) -> a -> [a]
+ [Exported]
+ iterate = iterateList
+
+ iterateFB c f x = x `c` iterateFB c f (f x)
+ iterateList f x = x : iterateList f (f x)
+ [Not exported]
+
+ {-# RULES
+ "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
+ "iterateFB" iterateFB (:) = iterateList
+ #-}
+
+This got shorted out to:
+
+ iterateList :: (a -> a) -> a -> [a]
+ iterateList = iterate
+
+ iterateFB c f x = x `c` iterateFB c f (f x)
+ iterate f x = x : iterate f (f x)
+
+ {-# RULES
+ "iterate" forall f x. iterate f x = build (\c _n -> iterateFB c f x)
+ "iterateFB" iterateFB (:) = iterate
+ #-}
+
+And now we get an infinite loop in the rule system
+ iterate f x -> build (\cn -> iterateFB c f x)
+ -> iterateFB (:) f x
+ -> iterate f x
+
+Tiresome old solution:
+ don't do shorting out if f has rewrite rules (see shortableIdInfo)
+
+New solution (I think):
+ use rule switching-off pragmas to get rid
+ of iterateList in the first place
+
+
+Other remarks
+~~~~~~~~~~~~~
+If more than one exported thing is equal to a local thing (i.e., the
+local thing really is shared), then we do one only:
+\begin{verbatim}
+ x_local = ....
+ x_exported1 = x_local
+ x_exported2 = x_local
+==>
+ x_exported1 = ....
+
+ x_exported2 = x_exported1
+\end{verbatim}
+
+We rely on prior eta reduction to simplify things like
+\begin{verbatim}
+ x_exported = /\ tyvars -> x_local tyvars
+==>
+ x_exported = x_local
+\end{verbatim}
+Hence,there's a possibility of leaving unchanged something like this:
+\begin{verbatim}
+ x_local = ....
+ x_exported1 = x_local Int
+\end{verbatim}
+By the time we've thrown away the types in STG land this
+could be eliminated. But I don't think it's very common
+and it's dangerous to do this fiddling in STG land
+because we might elminate a binding that's mentioned in the
+unfolding for something.
+
+\begin{code}
+type IndEnv = IdEnv Id -- Maps local_id -> exported_id
+
+shortOutIndirections :: [CoreBind] -> [CoreBind]
+shortOutIndirections binds
+ | isEmptyVarEnv ind_env = binds
+ | no_need_to_flatten = binds'
+ | otherwise = [Rec (flattenBinds binds')] -- See Note [Rules and indirect-zapping]
+ where
+ ind_env = makeIndEnv binds
+ exp_ids = varSetElems ind_env
+ exp_id_set = mkVarSet exp_ids
+ no_need_to_flatten = all (null . rulesRules . idSpecialisation) exp_ids
+ binds' = concatMap zap binds
+
+ zap (NonRec bndr rhs) = [NonRec b r | (b,r) <- zapPair (bndr,rhs)]
+ zap (Rec pairs) = [Rec (concatMap zapPair pairs)]
+
+ zapPair (bndr, rhs)
+ | bndr `elemVarSet` exp_id_set = []
+ | Just exp_id <- lookupVarEnv ind_env bndr = [(transferIdInfo exp_id bndr, rhs),
+ (bndr, Var exp_id)]
+ | otherwise = [(bndr,rhs)]
+
+makeIndEnv :: [CoreBind] -> IndEnv
+makeIndEnv binds
+ = foldr add_bind emptyVarEnv binds
+ where
+ add_bind :: CoreBind -> IndEnv -> IndEnv
+ add_bind (NonRec exported_id rhs) env = add_pair (exported_id, rhs) env
+ add_bind (Rec pairs) env = foldr add_pair env pairs
+
+ add_pair :: (Id,CoreExpr) -> IndEnv -> IndEnv
+ add_pair (exported_id, Var local_id) env
+ | shortMeOut env exported_id local_id = extendVarEnv env local_id exported_id
+ add_pair (exported_id, rhs) env
+ = env
+
+shortMeOut ind_env exported_id local_id
+-- The if-then-else stuff is just so I can get a pprTrace to see
+-- how often I don't get shorting out becuase of IdInfo stuff
+ = if isExportedId exported_id && -- Only if this is exported
+
+ isLocalId local_id && -- Only if this one is defined in this
+ -- module, so that we *can* change its
+ -- binding to be the exported thing!
+
+ not (isExportedId local_id) && -- Only if this one is not itself exported,
+ -- since the transformation will nuke it
+
+ not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
+ then
+ True
+
+{- No longer needed
+ if isEmptyCoreRules (specInfo (idInfo exported_id)) -- Only if no rules
+ then True -- See note on "Messing up rules"
+ else
+#ifdef DEBUG
+ pprTrace "shortMeOut:" (ppr exported_id)
+#endif
+ False
+-}
+ else
+ False
+
+
+-----------------
+transferIdInfo :: Id -> Id -> Id
+transferIdInfo exported_id local_id
+ = modifyIdInfo transfer exported_id
+ where
+ local_info = idInfo local_id
+ transfer exp_info = exp_info `setNewStrictnessInfo` newStrictnessInfo local_info
+ `setWorkerInfo` workerInfo local_info
+ `setSpecInfo` addRules exported_id (specInfo exp_info)
+ (rulesRules (specInfo local_info))
+\end{code}
projects / ghc-hetmet.git / blobdiff