IMP_Ubiq(){-uitous-}
IMPORT_DELOOPER(IdLoop) -- paranoia
+IMPORT_1_3(List(partition))
import BinderInfo
import CmdLineOpts ( opt_D_dump_occur_anal, SimplifierSwitch(..) )
import CoreSyn
-import Digraph ( stronglyConnComp )
-import Id ( idWantsToBeINLINEd, isConstMethodId,
+import Digraph ( stronglyConnComp, stronglyConnCompR, SCC(..) )
+import Id ( idWantsToBeINLINEd, addNoInlinePragma, nukeNoInlinePragma,
+ idType, idUnique,
+ isConstMethodId,
emptyIdSet, unionIdSets, mkIdSet,
unitIdSet, elementOfIdSet,
addOneToIdSet, SYN_IE(IdSet),
mapIdEnv, lookupIdEnv, SYN_IE(IdEnv),
GenId{-instance Eq-}
)
-import Name ( isExported )
+import Name ( isExported, isLocallyDefined )
+import Type ( getFunTy_maybe, splitForAllTy )
import Maybes ( maybeToBool )
import Outputable ( Outputable(..){-instance * (,) -} )
import PprCore
import PprStyle ( PprStyle(..) )
import PprType ( GenType{-instance Outputable-}, GenTyVar{-ditto-} )
-import Pretty ( ppAboves )
+import Pretty ( Doc, vcat, ptext, nest, punctuate, comma, hcat, text )
import TyVar ( GenTyVar{-instance Eq-} )
-import Unique ( Unique{-instance Eq-} )
-import Util ( assoc, zipEqual, pprTrace, panic )
+import Unique ( Unique{-instance Eq-}, u2i )
+import UniqFM ( keysUFM )
+import Util ( assoc, zipEqual, zipWithEqual, Ord3(..)
+ , pprTrace, panic
+#ifdef DEBUG
+ , assertPanic
+#endif
+ )
isSpecPragmaId_maybe x = Nothing -- ToDo:!trace "OccurAnal.isSpecPragmaId_maybe"
\end{code}
-- are top-level. A use of a "conjurable"
-- Id may appear out of thin air -- e.g.,
-- specialiser conjuring up refs to const methods.
- Bool -- IgnoreINLINEPragma flag
+ Bool -- IgnoreINLINEPragma flag
-- False <=> OK to use INLINEPragma information
-- True <=> ignore INLINEPragma information
- IdSet -- Candidates
+
+ (Id -> IdSet -> Bool) -- Tells whether an Id occurrence is interesting,
+ -- given the set of in-scope variables
+
+ IdSet -- In-scope Ids
+
addNewCands :: OccEnv -> [Id] -> OccEnv
-addNewCands (OccEnv kd ks kc ip cands) ids
- = OccEnv kd ks kc ip (cands `unionIdSets` mkIdSet ids)
+addNewCands (OccEnv kd ks kc ip ifun cands) ids
+ = OccEnv kd ks kc ip ifun (cands `unionIdSets` mkIdSet ids)
addNewCand :: OccEnv -> Id -> OccEnv
-addNewCand (OccEnv ks kd kc ip cands) id
- = OccEnv kd ks kc ip (addOneToIdSet cands id)
+addNewCand (OccEnv ks kd kc ip ifun cands) id
+ = OccEnv kd ks kc ip ifun (addOneToIdSet cands id)
isCandidate :: OccEnv -> Id -> Bool
-isCandidate (OccEnv _ _ _ _ cands) id = id `elementOfIdSet` cands
+isCandidate (OccEnv _ _ _ _ ifun cands) id = ifun id cands
-ignoreINLINEPragma :: OccEnv -> Bool
-ignoreINLINEPragma (OccEnv _ _ _ ip _) = ip
+inlineMe :: OccEnv -> Id -> Bool
+inlineMe env id
+ = {- See comments with simplIdWantsToBeINLINEd in SimplUtils.lhs
+ not ignore_inline_prag &&
+ -}
+ idWantsToBeINLINEd id
keepUnusedBinding :: OccEnv -> Id -> Bool
-keepUnusedBinding (OccEnv keep_dead keep_spec keep_conjurable _ _) binder
+keepUnusedBinding (OccEnv keep_dead keep_spec keep_conjurable _ _ _) binder
= keep_dead || (keep_spec && maybeToBool (isSpecPragmaId_maybe binder))
keepBecauseConjurable :: OccEnv -> Id -> Bool
-keepBecauseConjurable (OccEnv _ _ keep_conjurable _ _) binder
+keepBecauseConjurable (OccEnv _ _ keep_conjurable _ _ _) binder
= keep_conjurable && isConstMethodId binder
type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
occurAnalyseBinds binds simplifier_sw_chkr
| opt_D_dump_occur_anal = pprTrace "OccurAnal:"
- (ppAboves (map (ppr PprDebug) binds'))
+ (vcat (map ppr_bind binds'))
binds'
| otherwise = binds'
where
(simplifier_sw_chkr KeepSpecPragmaIds)
(not (simplifier_sw_chkr SimplMayDeleteConjurableIds))
(simplifier_sw_chkr IgnoreINLINEPragma)
- emptyIdSet
+ (\id in_scope -> isLocallyDefined id) -- Anything local is interesting
+ emptyIdSet -- Not actually used
doo env [] = (emptyDetails, [])
doo env (bind:binds)
new_env = env `addNewCands` (bindersOf bind)
(binds_usage, the_rest) = doo new_env binds
(final_usage, new_binds) = occAnalBind env bind binds_usage
+
+ -- This really ought to be done properly by PprCore, but
+ -- it isn't. pprCoreBinding only works on Id binders, and
+ -- the general case is complicated by the fact that it has to work
+ -- for interface files too. Sigh
+
+ppr_bind bind@(NonRec binder expr)
+ = ppr PprDebug bind
+
+ppr_bind bind@(Rec binds)
+ = vcat [ptext SLIT("Rec {"),
+ nest 2 (ppr PprDebug bind),
+ ptext SLIT("end Rec }")]
\end{code}
\begin{code}
-occurAnalyseExpr :: IdSet -- Set of interesting free vars
+occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
-> CoreExpr
-> (IdEnv BinderInfo, -- Occ info for interesting free vars
SimplifiableCoreExpr)
-occurAnalyseExpr candidates expr
+occurAnalyseExpr interesting expr
= occAnal initial_env expr
where
initial_env = OccEnv False {- Drop unused bindings -}
False {- Drop SpecPragmaId bindings -}
True {- Keep conjurable Ids -}
False {- Do not ignore INLINE Pragma -}
- candidates
+ (\id locals -> interesting id || elementOfIdSet id locals)
+ emptyIdSet
occurAnalyseGlobalExpr :: CoreExpr -> SimplifiableCoreExpr
occurAnalyseGlobalExpr expr
= -- Top level expr, so no interesting free vars, and
-- discard occurence info returned
- snd (occurAnalyseExpr emptyIdSet expr)
+ snd (occurAnalyseExpr (\_ -> False) expr)
\end{code}
%************************************************************************
~~~~~~~~
\begin{code}
+type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
+ -- which is gotten from the Id.
+type Details1 = (Id, (UsageDetails, SimplifiableCoreExpr))
+type Details2 = ((Id, BinderInfo), SimplifiableCoreExpr)
+
+
occAnalBind :: OccEnv
-> CoreBinding
-> UsageDetails -- Usage details of scope
= (final_body_usage `combineUsageDetails` rhs_usage,
[NonRec tagged_binder rhs'])
- | otherwise
+ | otherwise -- Not mentioned, so drop dead code
= (body_usage, [])
where
- (rhs_usage, rhs') = occAnalRhs env binder rhs
- (final_body_usage, tagged_binder) = tagBinder body_usage binder
+ binder' = nukeNoInlinePragma binder
+ (rhs_usage, rhs') = occAnalRhs env binder' rhs
+ (final_body_usage, tagged_binder) = tagBinder body_usage binder'
\end{code}
Dropping dead code for recursive bindings is done in a very simple way:
\begin{code}
occAnalBind env (Rec pairs) body_usage
- = foldr do_final_bind (body_usage, []) sccs
+ = foldr (_scc_ "occAnalBind.dofinal" do_final_bind) (body_usage, []) sccs
where
+ pp_scc (CyclicSCC cycle) = hcat [text "Cyclic ", hcat (punctuate comma (map pp_item cycle))]
+ pp_scc (AcyclicSCC item) = hcat [text "Acyclic ", pp_item item]
+ pp_item (_, bndr, _) = ppr PprDebug bndr
- (binders, rhss) = unzip pairs
- new_env = env `addNewCands` binders
+ binders = map fst pairs
+ new_env = env `addNewCands` binders
- analysed_pairs :: [(Id, (UsageDetails, SimplifiableCoreExpr))]
- analysed_pairs = [(id, occAnalRhs new_env id rhs) | (id,rhs) <- pairs]
+ analysed_pairs :: [Details1]
+ analysed_pairs = [(nukeNoInlinePragma bndr, occAnalRhs new_env bndr rhs) | (bndr,rhs) <- pairs]
- lookup :: Id -> (UsageDetails, SimplifiableCoreExpr)
- lookup id = assoc "occAnalBind:lookup" analysed_pairs id
+ sccs :: [SCC (Node Details1)]
+ sccs = _scc_ "occAnalBind.scc" stronglyConnCompR edges
---- stuff for dependency analysis of binds -------------------------------
-
- edges :: [(Id,Id)] -- (a,b) means a mentions b
- edges = concat [ edges_from binder rhs_usage
- | (binder, (rhs_usage, _)) <- analysed_pairs]
-
- edges_from :: Id -> UsageDetails -> [(Id,Id)]
- edges_from id its_rhs_usage
- = [(id,mentioned) | mentioned <- binders,
- maybeToBool (lookupIdEnv its_rhs_usage mentioned)
- ]
-
- sccs :: [[Id]]
- sccs = case binders of
- [_] -> [binders] -- Singleton; no need to analyse
- other -> stronglyConnComp (==) edges binders
+ edges :: [Node Details1]
+ edges = _scc_ "occAnalBind.assoc"
+ [ (pair, IBOX(u2i (idUnique id)), edges_from rhs_usage)
+ | pair@(id, (rhs_usage, rhs)) <- analysed_pairs
+ ]
+
+ -- (a -> b) means a mentions b
+ -- Given the usage details (a UFM that gives occ info for each free var of
+ -- the RHS) we can get the list of free vars -- or rather their Int keys --
+ -- by just extracting the keys from the finite map. Grimy, but fast.
+ -- Previously we had this:
+ -- [ bndr | bndr <- bndrs,
+ -- maybeToBool (lookupIdEnv rhs_usage bndr)]
+ -- which has n**2 cost, and this meant that edges_from alone
+ -- consumed 10% of total runtime!
+ edges_from :: UsageDetails -> [Int]
+ edges_from rhs_usage = _scc_ "occAnalBind.edges_from"
+ keysUFM rhs_usage
---- stuff to "re-constitute" bindings from dependency-analysis info ------
- do_final_bind sCC@[binder] (body_usage, binds_so_far)
- | isNeeded env body_usage binder
- = (combined_usage, new_bind:binds_so_far)
-
- | otherwise -- Dead
- = (body_usage, binds_so_far)
+ -- Non-recursive SCC
+ do_final_bind (AcyclicSCC ((bndr, (rhs_usage, rhs')), _, _)) (body_usage, binds_so_far)
+ | isNeeded env body_usage bndr
+ = (combined_usage, new_bind : binds_so_far)
+ | otherwise
+ = (body_usage, binds_so_far) -- Dead code
where
- total_usage = combineUsageDetails body_usage rhs_usage
- (rhs_usage, rhs') = lookup binder
- (combined_usage, tagged_binder) = tagBinder total_usage binder
-
- new_bind
- | mentions_itself binder rhs_usage = Rec [(tagged_binder,rhs')]
- | otherwise = NonRec tagged_binder rhs'
- where
- mentions_itself binder usage
- = maybeToBool (lookupIdEnv usage binder)
-
- do_final_bind sCC (body_usage, binds_so_far)
- | any (isNeeded env body_usage) sCC
- = (combined_usage, new_bind:binds_so_far)
-
- | otherwise -- Dead
- = (body_usage, binds_so_far)
+ total_usage = combineUsageDetails body_usage rhs_usage
+ (combined_usage, tagged_bndr) = tagBinder total_usage bndr
+ new_bind = NonRec tagged_bndr rhs'
+
+ -- Recursive SCC
+ do_final_bind (CyclicSCC cycle) (body_usage, binds_so_far)
+ | any (isNeeded env body_usage) bndrs
+ = (combined_usage, final_bind:binds_so_far)
+ | otherwise
+ = (body_usage, binds_so_far) -- Dead code
where
- (rhs_usages, rhss') = unzip (map lookup sCC)
+ pairs = [pair | (pair, _, _) <- cycle]
+ bndrs = [bndr | (bndr, _) <- pairs]
+ rhs_usages = [rhs_usage | (_, (rhs_usage, _)) <- pairs]
total_usage = foldr combineUsageDetails body_usage rhs_usages
- (combined_usage, tagged_binders) = tagBinders total_usage sCC
+ (combined_usage, tagged_binders) = tagBinders total_usage bndrs
+ final_bind = Rec (reOrderRec env new_cycle)
+
+ new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_binders cycle)
+ mk_new_bind tagged_bndr ((_, (_, rhs')), key, keys) = ((tagged_bndr, rhs'), key, keys)
+\end{code}
- new_bind = Rec (zipEqual "occAnalBind" tagged_binders rhss')
+@reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
+strongly connected component (there's guaranteed to be a cycle). It returns the
+same pairs, but
+ a) in a better order,
+ b) with some of the Ids having a IMustNotBeINLINEd pragma
+
+The "no-inline" Ids are sufficient to break all cycles in the SCC. This means
+that the simplifier can guarantee not to loop provided it never records an inlining
+for these no-inline guys.
+
+Furthermore, the order of the binds is such that if we neglect dependencies
+on the no-inline Ids then the binds are topologically sorted. This means
+that the simplifier will generally do a good job if it works from top bottom,
+recording inlinings for any Ids which aren't marked as "no-inline" as it goes.
+
+Here's a case that bit me:
+
+ letrec
+ a = b
+ b = \x. BIG
+ in
+ ...a...a...a....
+
+Re-ordering doesn't change the order of bindings, but there was no loop-breaker.
+(The first binding was a var-rhs; the second was a one-occ.) So the simplifier looped.
+My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
+Perhaps something cleverer would suffice.
+
+\begin{code}
+reOrderRec
+ :: OccEnv
+ -> SCC (Node Details2)
+ -> [Details2]
+ -- Sorted into a plausible order. Enough of the Ids have
+ -- dontINLINE pragmas that there are no loops left.
+
+ -- Non-recursive case
+reOrderRec env (AcyclicSCC (pair, _, _)) = [pair]
+
+ -- Common case of simple self-recursion
+reOrderRec env (CyclicSCC [bind])
+ = [((addNoInlinePragma bndr, occ_info), rhs)]
+ where
+ (((bndr,occ_info), rhs), _, _) = bind
+
+reOrderRec env (CyclicSCC binds)
+ = -- Choose a loop breaker, mark it no-inline,
+ -- do SCC analysis on the rest, and recursively sort them out
+ concat (map (reOrderRec env) (stronglyConnCompR unchosen))
+ ++
+ [((addNoInlinePragma bndr, occ_info), rhs)]
+
+ where
+ (chosen_pair, unchosen) = choose_loop_breaker binds
+ ((bndr,occ_info), rhs) = chosen_pair
+
+ -- Choosing the loop breaker; heursitic
+ choose_loop_breaker (bind@(pair, _, _) : rest)
+ | not (null rest) &&
+ bad_choice pair
+ = (chosen, bind : unchosen) -- Don't pick it
+ | otherwise -- Pick it
+ = (pair,rest)
+ where
+ (chosen, unchosen) = choose_loop_breaker rest
+
+ bad_choice ((bndr, occ_info), rhs)
+ = var_rhs rhs -- Dont pick var RHS
+ || inlineMe env bndr -- Dont pick INLINE thing
+ || one_occ occ_info -- Dont pick single-occ thing
+ || not_fun_ty (idType bndr) -- Dont pick data-ty thing
+
+ not_fun_ty ty = not (maybeToBool (getFunTy_maybe rho_ty))
+ where
+ (_, rho_ty) = splitForAllTy ty
+
+ -- A variable RHS
+ var_rhs (Var v) = True
+ var_rhs other_rhs = False
+
+ -- One textual occurrence, whether inside lambda or whatever
+ -- We stick to just FunOccs because if we're not going to be able
+ -- to inline the thing on this round it might be better to pick
+ -- this one as the loop breaker. Real example (the Enum Ordering instance
+ -- from PrelBase):
+ -- rec f = \ x -> case d of (p,q,r) -> p x
+ -- g = \ x -> case d of (p,q,r) -> q x
+ -- d = (v, f, g)
+ --
+ -- Here, f and g occur just once; but we can't inline them into d.
+ -- On the other hand we *could* simplify those case expressions if
+ -- we didn't stupidly choose d as the loop breaker.
+
+ one_occ (OneOcc fun_or_arg _ _ _ _) = isFun fun_or_arg
+ one_occ other_bind = False
\end{code}
@occAnalRhs@ deals with the question of bindings where the Id is marked
we'll catch it next time round. At worst this costs an extra simplifier pass.
ToDo: try using the occurrence info for the inline'd binder.
+[March 97] We do the same for atomic RHSs. Reason: see notes with reOrderRec.
+
\begin{code}
occAnalRhs :: OccEnv
- -> Id -- Binder
- -> CoreExpr -- Rhs
+ -> Id -> CoreExpr -- Binder and rhs
-> (UsageDetails, SimplifiableCoreExpr)
+occAnalRhs env id (Var v)
+ | isCandidate env v
+ = (unitIdEnv v (markMany (funOccurrence 0)), Var v)
+
+ | otherwise
+ = (emptyDetails, Var v)
+
occAnalRhs env id rhs
- | idWantsToBeINLINEd id && not (ignoreINLINEPragma env)
+ | inlineMe env id
= (mapIdEnv markMany rhs_usage, rhs')
| otherwise
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