core expression with (hopefully) improved usage information.
\begin{code}
-#include "HsVersions.h"
-
module OccurAnal (
occurAnalyseBinds, occurAnalyseExpr, occurAnalyseGlobalExpr
) where
-import Ubiq{-uitous-}
+#include "HsVersions.h"
import BinderInfo
import CmdLineOpts ( opt_D_dump_occur_anal, SimplifierSwitch(..) )
import CoreSyn
-import Digraph ( stronglyConnComp )
-import Id ( idWantsToBeINLINEd, isConstMethodId,
+import Digraph ( stronglyConnCompR, SCC(..) )
+import Id ( idWantsToBeINLINEd, addNoInlinePragma, nukeNoInlinePragma,
+ omitIfaceSigForId,
+ idType, idUnique, Id,
emptyIdSet, unionIdSets, mkIdSet,
- unitIdSet, elementOfIdSet,
- addOneToIdSet, IdSet(..),
- nullIdEnv, unitIdEnv, combineIdEnvs,
- delOneFromIdEnv, delManyFromIdEnv,
- mapIdEnv, lookupIdEnv, IdEnv(..),
- GenId{-instance Eq-}
+ elementOfIdSet,
+ addOneToIdSet, IdSet,
+
+ IdEnv, nullIdEnv, unitIdEnv, combineIdEnvs,
+ delOneFromIdEnv, delManyFromIdEnv, isNullIdEnv,
+ mapIdEnv, lookupIdEnv, elemIdEnv, addOneToIdEnv
)
+import Specialise ( idSpecVars )
+import Name ( isExported, isLocallyDefined )
+import Type ( splitFunTy_maybe, splitForAllTys )
import Maybes ( maybeToBool )
-import Name ( isExported )
-import Outputable ( Outputable(..){-instance * (,) -} )
import PprCore
-import PprStyle ( PprStyle(..) )
-import PprType ( GenType{-instance Outputable-}, GenTyVar{-ditto-} )
-import Pretty ( ppAboves )
-import TyVar ( GenTyVar{-instance Eq-} )
-import Unique ( Unique{-instance Eq-} )
-import Util ( assoc, pprTrace, panic )
-
-isSpecPragmaId_maybe = panic "OccurAnal.isSpecPragmaId_maybe (ToDo)"
-\end{code}
-
-
-%************************************************************************
-%* *
-\subsection[OccurAnal-types]{Data types}
-%* *
-%************************************************************************
-
-\begin{code}
-data OccEnv =
- OccEnv
- Bool -- Keep-unused-bindings flag
- -- False <=> OK to chuck away binding
- -- and ignore occurrences within it
- Bool -- Keep-spec-pragma-ids flag
- -- False <=> OK to chuck away spec pragma bindings
- -- and ignore occurrences within it
- Bool -- Keep-conjurable flag
- -- False <=> OK to throw away *dead*
- -- "conjurable" Ids; at the moment, that
- -- *only* means constant methods, which
- -- 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
- -- False <=> OK to use INLINEPragma information
- -- True <=> ignore INLINEPragma information
- IdSet -- Candidates
-
-addNewCands :: OccEnv -> [Id] -> OccEnv
-addNewCands (OccEnv kd ks kc ip cands) ids
- = OccEnv kd ks kc ip (cands `unionIdSets` mkIdSet ids)
-
-addNewCand :: OccEnv -> Id -> OccEnv
-addNewCand (OccEnv ks kd kc ip cands) id
- = OccEnv kd ks kc ip (addOneToIdSet cands id)
-
-isCandidate :: OccEnv -> Id -> Bool
-isCandidate (OccEnv _ _ _ _ cands) id = id `elementOfIdSet` cands
-
-ignoreINLINEPragma :: OccEnv -> Bool
-ignoreINLINEPragma (OccEnv _ _ _ ip _) = ip
-
-keepUnusedBinding :: OccEnv -> Id -> Bool
-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
- = keep_conjurable && isConstMethodId binder
-
-type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
-
-combineUsageDetails, combineAltsUsageDetails
- :: UsageDetails -> UsageDetails -> UsageDetails
-
-combineUsageDetails usage1 usage2
- = combineIdEnvs combineBinderInfo usage1 usage2
-
-combineAltsUsageDetails usage1 usage2
- = combineIdEnvs combineAltsBinderInfo usage1 usage2
-
-addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
-addOneOcc usage id info
- = combineIdEnvs combineBinderInfo usage (unitIdEnv id info)
- -- ToDo: make this more efficient
-
-emptyDetails = (nullIdEnv :: UsageDetails)
-
-unitDetails id info = (unitIdEnv id info :: UsageDetails)
-
-tagBinders :: UsageDetails -- Of scope
- -> [Id] -- Binders
- -> (UsageDetails, -- Details with binders removed
- [(Id,BinderInfo)]) -- Tagged binders
-
-tagBinders usage binders
- = (usage `delManyFromIdEnv` binders,
- [ (binder, usage_of usage binder) | binder <- binders ]
- )
-
-tagBinder :: UsageDetails -- Of scope
- -> Id -- Binders
- -> (UsageDetails, -- Details with binders removed
- (Id,BinderInfo)) -- Tagged binders
-
-tagBinder usage binder
- = (usage `delOneFromIdEnv` binder,
- (binder, usage_of usage binder)
- )
-
-usage_of usage binder
- | isExported binder = ManyOcc 0 -- Exported things count as many
- | otherwise
- = case (lookupIdEnv usage binder) of
- Nothing -> DeadCode
- Just info -> info
-
-isNeeded env usage binder
- = case (usage_of usage binder) of
- DeadCode -> keepUnusedBinding env binder -- Maybe keep it anyway
- other -> True
+import Unique ( u2i )
+import UniqFM ( keysUFM )
+import Util ( zipWithEqual )
+import Outputable
\end{code}
occurAnalyseBinds binds simplifier_sw_chkr
| opt_D_dump_occur_anal = pprTrace "OccurAnal:"
- (ppAboves (map (ppr PprDebug) binds'))
+ (pprGenericBindings binds')
binds'
| otherwise = binds'
where
- (_, binds') = do initial_env binds
+ (_, _, binds') = occAnalTop initial_env binds
- initial_env = OccEnv (simplifier_sw_chkr KeepUnusedBindings)
- (simplifier_sw_chkr KeepSpecPragmaIds)
- (not (simplifier_sw_chkr SimplMayDeleteConjurableIds))
- (simplifier_sw_chkr IgnoreINLINEPragma)
- emptyIdSet
-
- do env [] = (emptyDetails, [])
- do env (bind:binds)
- = (final_usage, new_binds ++ the_rest)
- where
- new_env = env `addNewCands` (bindersOf bind)
- (binds_usage, the_rest) = do new_env binds
- (final_usage, new_binds) = occAnalBind env bind binds_usage
+ initial_env = OccEnv (simplifier_sw_chkr IgnoreINLINEPragma)
+ (\id in_scope -> isLocallyDefined id) -- Anything local is interesting
+ emptyIdSet -- Not actually used
\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
+ initial_env = OccEnv False {- Do not ignore INLINE Pragma -}
+ (\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
- expr' where (_, expr') = occurAnalyseExpr emptyIdSet expr
+ snd (occurAnalyseExpr (\_ -> False) expr)
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Top level stuff}
+%* *
+%************************************************************************
+
+In @occAnalTop@ we do indirection-shorting. That is, if we have this:
+
+ loc = <expression>
+ ...
+ exp = loc
+
+where exp is exported, and loc is not, then we replace it with this:
+
+ loc = exp
+ exp = <expression>
+ ...
+
+Without this we never get rid of the exp = loc 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 its tidier to do it here.
+
+
+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}
+occAnalTop :: OccEnv -- What's in scope
+ -> [CoreBinding]
+ -> (IdEnv BinderInfo, -- Occurrence info
+ IdEnv Id, -- Indirection elimination info
+ [SimplifiableCoreBinding]
+ )
+
+occAnalTop env [] = (emptyDetails, nullIdEnv, [])
+
+-- Special case for eliminating indirections
+occAnalTop env (NonRec exported_id (Var local_id) : binds)
+ | isExported exported_id && -- Only if this is exported
+
+ isLocallyDefined local_id && -- Only if this one is defined in this
+ -- module, so that we *can* change its
+ -- binding to be the exported thing!
+
+ not (isExported local_id) && -- Only if this one is not itself exported,
+ -- since the transformation will nuke it
+
+ not (omitIfaceSigForId local_id) && -- Don't do the transformation if rhs_id is
+ -- something like a constructor, whose
+ -- definition is implicitly exported and
+ -- which must not vanish.
+ -- To illustrate the preceding check consider
+ -- data T = MkT Int
+ -- mkT = MkT
+ -- f x = MkT (x+1)
+ -- Here, we'll make a local, non-exported, defn for MkT, and without the
+ -- above condition we'll transform it to:
+ -- mkT = \x. MkT [x]
+ -- f = \y. mkT (y+1)
+ -- This is bad because mkT will get the IdDetails of MkT, and won't
+ -- be exported. Also the code generator won't make a definition for
+ -- the MkT constructor.
+ -- Slightly gruesome, this.
+
+
+ not (maybeToBool (lookupIdEnv ind_env local_id))
+ -- Only if not already substituted for
+
+ = -- Aha! An indirection; let's eliminate it!
+ (scope_usage, ind_env', binds')
+ where
+ (scope_usage, ind_env, binds') = occAnalTop env binds
+ ind_env' = addOneToIdEnv ind_env local_id exported_id
+
+-- The normal case
+occAnalTop env (bind : binds)
+ = (final_usage, ind_env, new_binds ++ binds')
+ where
+ new_env = env `addNewCands` (bindersOf bind)
+ (scope_usage, ind_env, binds') = occAnalTop new_env binds
+ (final_usage, new_binds) = occAnalBind env (zap_bind bind) scope_usage
+
+ -- Deal with any indirections
+ zap_bind (NonRec bndr rhs)
+ | bndr `elemIdEnv` ind_env = Rec (zap (bndr,rhs))
+ -- The Rec isn't strictly necessary, but it's convenient
+ zap_bind (Rec pairs)
+ | or [id `elemIdEnv` ind_env | (id,_) <- pairs] = Rec (concat (map zap pairs))
+
+ zap_bind bind = bind
+
+ zap pair@(bndr,rhs) = case lookupIdEnv ind_env bndr of
+ Nothing -> [pair]
+ Just exported_id -> [(bndr, Var exported_id),
+ (exported_id, rhs)]
\end{code}
+
%************************************************************************
%* *
\subsection[OccurAnal-main]{Counting occurrences: main function}
~~~~~~~~
\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_item (_, bndr, _) = ppr 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, rhs_usage, rhs')
+ | (bndr, rhs) <- pairs,
+ let (rhs_usage, rhs') = occAnalRhs new_env bndr rhs
+ ]
- 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"
+ [ (details, IBOX(u2i (idUnique id)), edges_from rhs_usage)
+ | details@(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)
+ details = [details | (details, _, _) <- cycle]
+ bndrs = [bndr | (bndr, _, _) <- details]
+ rhs_usages = [rhs_usage | (_, rhs_usage, _) <- details]
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_bind = Rec (tagged_binders `zip` rhss')
+ new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_binders cycle)
+ mk_new_bind (bndr, occ_info) ((_, _, rhs'), key, keys) = (((bndr, occ_info), rhs'), key, keys)
+\end{code}
+
+@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.
+
+My solution was to make a=b bindings record b as Many, rather like INLINE bindings.
+Perhaps something cleverer would suffice.
+
+You might think that you can prevent non-termination simply by making
+sure that we simplify a recursive binding's RHS in an environment that
+simply clones the recursive Id. But no. Consider
+
+ letrec f = \x -> let z = f x' in ...
+
+ in
+ let n = f y
+ in
+ case n of { ... }
+
+We bind n to its *simplified* RHS, we then *re-simplify* it when
+we inline n. Then we may well inline f; and then the same thing
+happens with z!
+
+I don't think it's possible to prevent non-termination by environment
+manipulation in this way. Apart from anything else, successive
+iterations of the simplifier may unroll recursive loops in cases like
+that above. The idea of beaking every recursive loop with an
+IMustNotBeINLINEd pragma is much much better.
+
+
+\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 (bind, _, _)) = [bind]
+
+ -- 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@(details, _, _) : rest)
+ | not (null rest) &&
+ bad_choice details
+ = (chosen, bind : unchosen) -- Don't pick it
+ | otherwise -- Pick it
+ = (details,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
+ || isOneFunOcc occ_info -- Dont pick single-occ thing
+ || not_fun_ty (idType bndr) -- Dont pick data-ty thing
+
+ -- isOneFunOcc looks for 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.
+
+ not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
+ where
+ (_, rho_ty) = splitForAllTys ty
+
+ -- A variable RHS
+ var_rhs (Var v) = True
+ var_rhs other_rhs = 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.
+
+[March 98] A new wrinkle is that if the binder has specialisations inside
+it then we count the specialised Ids as "extra rhs's". That way
+the "parent" keeps the specialised "children" alive. If the parent
+dies (because it isn't referenced any more), then the children will
+die too unless they are already referenced directly.
+
\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)
- = (mapIdEnv markMany rhs_usage, rhs')
+ | inlineMe env id
+ = (mapIdEnv markMany total_usage, rhs')
| otherwise
- = (rhs_usage, rhs')
+ = (total_usage, rhs')
where
(rhs_usage, rhs') = occAnal env rhs
+ total_usage = foldr add rhs_usage (idSpecVars id)
+ add v u = addOneOcc u v noBinderInfo -- Give a non-committal binder info
+ -- (i.e manyOcc) because many copies
+ -- of the specialised thing can appear
\end{code}
Expressions
= (emptyDetails, Var v)
occAnal env (Lit lit) = (emptyDetails, Lit lit)
-occAnal env (Con con args) = (occAnalArgs env args, Con con args)
occAnal env (Prim op args) = (occAnalArgs env args, Prim op args)
+\end{code}
+
+We regard variables that occur as constructor arguments as "dangerousToDup":
+
+\begin{verbatim}
+module A where
+f x = let y = expensive x in
+ let z = (True,y) in
+ (case z of {(p,q)->q}, case z of {(p,q)->q})
+\end{verbatim}
+
+We feel free to duplicate the WHNF (True,y), but that means
+that y may be duplicated thereby.
+
+If we aren't careful we duplicate the (expensive x) call!
+Constructors are rather like lambdas in this way.
+
+\begin{code}
+occAnal env (Con con args) = (mapIdEnv markDangerousToDup (occAnalArgs env args),
+ Con con args)
occAnal env (SCC cc body)
= (mapIdEnv markInsideSCC usage, SCC cc body')
where
(usage, body') = occAnal env body
+occAnal env (Coerce c ty body)
+ = (usage, Coerce c ty body')
+ where
+ (usage, body') = occAnal env body
+
occAnal env (App fun arg)
= (fun_usage `combineUsageDetails` arg_usage, App fun' arg)
where
(fun_usage, fun') = occAnal env fun
arg_usage = occAnalArg env arg
-occAnal env (Lam (ValBinder binder) body)
+-- For value lambdas we do a special hack. Consider
+-- (\x. \y. ...x...)
+-- If we did nothing, x is used inside the \y, so would be marked
+-- as dangerous to dup. But in the common case where the abstraction
+-- is applied to two arguments this is over-pessimistic.
+-- So instead we don't take account of the \y when dealing with x's usage;
+-- instead, the simplifier is careful when partially applying lambdas
+
+occAnal env expr@(Lam (ValBinder binder) body)
= (mapIdEnv markDangerousToDup final_usage,
- Lam (ValBinder tagged_binder) body')
+ foldr ( \v b -> Lam (ValBinder v) b) body' tagged_binders)
where
- (body_usage, body') = occAnal (env `addNewCand` binder) body
- (final_usage, tagged_binder) = tagBinder body_usage binder
+ (binders,body) = collectValBinders expr
+ (body_usage, body') = occAnal (env `addNewCands` binders) body
+ (final_usage, tagged_binders) = tagBinders body_usage binders
-- ANDY: WE MUST THINK ABOUT THIS! (ToDo)
occAnal env (Lam (TyBinder tyvar) body)
- = (mapIdEnv markDangerousToDup body_usage,
- Lam (TyBinder tyvar) body')
- where
- (body_usage, body') = occAnal env body
-
-occAnal env (Lam (UsageBinder _) _) = panic "OccurAnal.occAnal Lam UsageBinder"
+ = case occAnal env body of { (body_usage, body') ->
+ (mapIdEnv markDangerousToDup body_usage,
+ Lam (TyBinder tyvar) body') }
+-- where
+-- (body_usage, body') = occAnal env body
occAnal env (Case scrut alts)
- = (scrut_usage `combineUsageDetails` alts_usage,
- Case scrut' alts')
+ = case occAnalAlts env alts of { (alts_usage, alts') ->
+ case occAnal env scrut of { (scrut_usage, scrut') ->
+ let
+ det = scrut_usage `combineUsageDetails` alts_usage
+ in
+ if isNullIdEnv det then
+ (det, Case scrut' alts')
+ else
+ (det, Case scrut' alts') }}
+{-
+ (scrut_usage `combineUsageDetails` alts_usage,
+ Case scrut' alts')
where
(scrut_usage, scrut') = occAnal env scrut
(alts_usage, alts') = occAnalAlts env alts
+-}
occAnal env (Let bind body)
- = (final_usage, foldr Let body' new_binds) -- mkCoLet* wants Core... (sigh)
+ = case occAnal new_env body of { (body_usage, body') ->
+ case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
+ (final_usage, foldr Let body' new_binds) }} -- mkCoLet* wants Core... (sigh)
where
new_env = env `addNewCands` (bindersOf bind)
- (body_usage, body') = occAnal new_env body
- (final_usage, new_binds) = occAnalBind env bind body_usage
+-- (body_usage, body') = occAnal new_env body
+-- (final_usage, new_binds) = occAnalBind env bind body_usage
\end{code}
Case alternatives
| otherwise = emptyDetails
occAnalArg _ _ = emptyDetails
\end{code}
+
+
+%************************************************************************
+%* *
+\subsection[OccurAnal-types]{Data types}
+%* *
+%************************************************************************
+
+\begin{code}
+data OccEnv =
+ OccEnv
+ Bool -- IgnoreINLINEPragma flag
+ -- False <=> OK to use INLINEPragma information
+ -- True <=> ignore INLINEPragma information
+
+ (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 ip ifun cands) ids
+ = OccEnv ip ifun (cands `unionIdSets` mkIdSet ids)
+
+addNewCand :: OccEnv -> Id -> OccEnv
+addNewCand (OccEnv ip ifun cands) id
+ = OccEnv ip ifun (addOneToIdSet cands id)
+
+isCandidate :: OccEnv -> Id -> Bool
+isCandidate (OccEnv _ ifun cands) id = ifun id cands
+
+inlineMe :: OccEnv -> Id -> Bool
+inlineMe env id
+ = {- See comments with simplIdWantsToBeINLINEd in SimplUtils.lhs
+ not ignore_inline_prag &&
+ -}
+ idWantsToBeINLINEd id
+
+
+type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
+
+combineUsageDetails, combineAltsUsageDetails
+ :: UsageDetails -> UsageDetails -> UsageDetails
+
+combineUsageDetails usage1 usage2
+ = combineIdEnvs addBinderInfo usage1 usage2
+
+combineAltsUsageDetails usage1 usage2
+ = combineIdEnvs orBinderInfo usage1 usage2
+
+addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
+addOneOcc usage id info
+ = combineIdEnvs addBinderInfo usage (unitIdEnv id info)
+ -- ToDo: make this more efficient
+
+emptyDetails = (nullIdEnv :: UsageDetails)
+
+unitDetails id info = (unitIdEnv id info :: UsageDetails)
+
+tagBinders :: UsageDetails -- Of scope
+ -> [Id] -- Binders
+ -> (UsageDetails, -- Details with binders removed
+ [(Id,BinderInfo)]) -- Tagged binders
+
+tagBinders usage binders =
+ let
+ usage' = usage `delManyFromIdEnv` binders
+ uss = [ (binder, usage_of usage binder) | binder <- binders ]
+ in
+ if isNullIdEnv usage' then
+ (usage', uss)
+ else
+ (usage', uss)
+{-
+ = (usage `delManyFromIdEnv` binders,
+ [ (binder, usage_of usage binder) | binder <- binders ]
+ )
+-}
+tagBinder :: UsageDetails -- Of scope
+ -> Id -- Binders
+ -> (UsageDetails, -- Details with binders removed
+ (Id,BinderInfo)) -- Tagged binders
+
+tagBinder usage binder =
+ let
+ usage' = usage `delOneFromIdEnv` binder
+ us = usage_of usage binder
+ cont =
+ if isNullIdEnv usage' then -- Bogus test to force evaluation.
+ (usage', (binder, us))
+ else
+ (usage', (binder, us))
+ in
+ if isDeadOcc us then -- Ditto
+ cont
+ else
+ cont
+
+
+usage_of usage binder
+ | isExported binder
+ = noBinderInfo -- Visible-elsewhere things count as many
+ | otherwise
+ = case (lookupIdEnv usage binder) of
+ Nothing -> deadOccurrence
+ Just info -> info
+
+isNeeded env usage binder = not (isDeadOcc (usage_of usage binder))
+\end{code}
+
+
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