%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
%************************************************************************
%* *
core expression with (hopefully) improved usage information.
\begin{code}
-#include "HsVersions.h"
-
module OccurAnal (
- occurAnalyseBinds, occurAnalyseExpr, occurAnalyseGlobalExpr
+ occurAnalyseBinds, occurAnalyseExpr, occurAnalyseGlobalExpr,
+ markBinderInsideLambda, tagBinders,
+ UsageDetails
) where
-IMP_Ubiq(){-uitous-}
-IMPORT_DELOOPER(IdLoop) -- paranoia
+#include "HsVersions.h"
import BinderInfo
-import CmdLineOpts ( opt_D_dump_occur_anal, SimplifierSwitch(..) )
+import CmdLineOpts ( SimplifierSwitch(..) )
import CoreSyn
-import Digraph ( stronglyConnComp )
-import Id ( idWantsToBeINLINEd, isConstMethodId,
- emptyIdSet, unionIdSets, mkIdSet,
- unitIdSet, elementOfIdSet,
- addOneToIdSet, SYN_IE(IdSet),
- nullIdEnv, unitIdEnv, combineIdEnvs,
- delOneFromIdEnv, delManyFromIdEnv,
- mapIdEnv, lookupIdEnv, SYN_IE(IdEnv),
- GenId{-instance Eq-}
+import CoreFVs ( idRuleVars )
+import CoreUtils ( exprIsTrivial )
+import Const ( Con(..), Literal(..) )
+import Id ( isSpecPragmaId, isOneShotLambda, setOneShotLambda,
+ getIdOccInfo, setIdOccInfo,
+ isExportedId, modifyIdInfo, idInfo,
+ getIdSpecialisation,
+ idType, idUnique, Id
)
-import Name ( isExported )
+import IdInfo ( OccInfo(..), insideLam, copyIdInfo )
+
+import VarSet
+import VarEnv
+
+import ThinAir ( noRepStrIds, noRepIntegerIds )
+import Name ( isLocallyDefined )
+import Type ( splitFunTy_maybe, splitForAllTys )
import Maybes ( maybeToBool )
-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, zipEqual, pprTrace, panic )
-
-isSpecPragmaId_maybe x = Nothing -- ToDo:!trace "OccurAnal.isSpecPragmaId_maybe"
+import Digraph ( stronglyConnCompR, SCC(..) )
+import Unique ( u2i, buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
+import UniqFM ( keysUFM )
+import Util ( zipWithEqual, mapAndUnzip, count )
+import Outputable
\end{code}
%************************************************************************
%* *
-\subsection[OccurAnal-types]{Data types}
+\subsection[OccurAnal-main]{Counting occurrences: main function}
%* *
%************************************************************************
-\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 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
- = (usage `delManyFromIdEnv` binders,
- [ (binder, usage_of usage binder) | binder <- binders ]
- )
+Here's the externally-callable interface:
-tagBinder :: UsageDetails -- Of scope
- -> Id -- Binders
- -> (UsageDetails, -- Details with binders removed
- (Id,BinderInfo)) -- Tagged binders
+\begin{code}
+occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
+ -> CoreExpr
+ -> (IdEnv BinderInfo, -- Occ info for interesting free vars
+ CoreExpr)
-tagBinder usage binder
- = (usage `delOneFromIdEnv` binder,
- (binder, usage_of usage binder)
- )
+occurAnalyseExpr interesting expr
+ = occAnal initial_env expr
+ where
+ initial_env = OccEnv interesting emptyVarSet []
-usage_of usage binder
- | isExported binder = ManyOcc 0 -- Visible-elsewhere 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
+occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
+occurAnalyseGlobalExpr expr
+ = -- Top level expr, so no interesting free vars, and
+ -- discard occurence info returned
+ snd (occurAnalyseExpr (\_ -> False) expr)
\end{code}
%************************************************************************
%* *
-\subsection[OccurAnal-main]{Counting occurrences: main function}
+\subsection{Top level stuff}
%* *
%************************************************************************
-Here's the externally-callable interface:
+In @occAnalTop@ we do indirection-shorting. That is, if we have this:
-\begin{code}
-occurAnalyseBinds
- :: [CoreBinding] -- input
- -> (SimplifierSwitch -> Bool)
- -> [SimplifiableCoreBinding] -- output
-
-occurAnalyseBinds binds simplifier_sw_chkr
- | opt_D_dump_occur_anal = pprTrace "OccurAnal:"
- (ppAboves (map (ppr PprDebug) binds'))
- binds'
- | otherwise = binds'
- where
- (_, binds') = doo initial_env binds
+ loc = <expression>
+ ...
+ exp = loc
- initial_env = OccEnv (simplifier_sw_chkr KeepUnusedBindings)
- (simplifier_sw_chkr KeepSpecPragmaIds)
- (not (simplifier_sw_chkr SimplMayDeleteConjurableIds))
- (simplifier_sw_chkr IgnoreINLINEPragma)
- emptyIdSet
+where exp is exported, and loc is not, then we replace it with this:
- doo env [] = (emptyDetails, [])
- doo env (bind:binds)
- = (final_usage, new_binds ++ the_rest)
- where
- new_env = env `addNewCands` (bindersOf bind)
- (binds_usage, the_rest) = doo new_env binds
- (final_usage, new_binds) = occAnalBind env bind binds_usage
-\end{code}
+ 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 it's 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}
-occurAnalyseExpr :: IdSet -- Set of interesting free vars
- -> CoreExpr
- -> (IdEnv BinderInfo, -- Occ info for interesting free vars
- SimplifiableCoreExpr)
+occurAnalyseBinds :: [CoreBind] -> [CoreBind]
-occurAnalyseExpr candidates expr
- = occAnal initial_env expr
+occurAnalyseBinds binds
+ = binds'
where
- initial_env = OccEnv False {- Drop unused bindings -}
- False {- Drop SpecPragmaId bindings -}
- True {- Keep conjurable Ids -}
- False {- Do not ignore INLINE Pragma -}
- candidates
-
-occurAnalyseGlobalExpr :: CoreExpr -> SimplifiableCoreExpr
-occurAnalyseGlobalExpr expr
- = -- Top level expr, so no interesting free vars, and
- -- discard occurence info returned
- snd (occurAnalyseExpr emptyIdSet expr)
+ (_, _, binds') = go initialTopEnv binds
+
+ go :: OccEnv -> [CoreBind]
+ -> (UsageDetails, -- Occurrence info
+ IdEnv Id, -- Indirection elimination info
+ [CoreBind])
+
+ go env [] = (emptyDetails, emptyVarEnv, [])
+
+ go env (bind : binds)
+ = let
+ new_env = env `addNewCands` (bindersOf bind)
+ (scope_usage, ind_env, binds') = go new_env binds
+ (final_usage, new_binds) = occAnalBind env (zapBind ind_env bind) scope_usage
+ -- NB: I zap before occur-analysing, so
+ -- I don't need to worry about getting the
+ -- occ info on the new bindings right.
+ in
+ case bind of
+ NonRec exported_id (Var local_id)
+ | shortMeOut ind_env exported_id local_id
+ -- Special case for eliminating indirections
+ -- Note: it's a shortcoming that this only works for
+ -- non-recursive bindings. Elminating indirections
+ -- makes perfect sense for recursive bindings too, but
+ -- it's more complicated to implement, so I haven't done so
+ -> (scope_usage, ind_env', binds')
+ where
+ ind_env' = extendVarEnv ind_env local_id exported_id
+
+ other -> -- Ho ho! The normal case
+ (final_usage, ind_env, new_binds ++ binds')
+
+initialTopEnv = OccEnv isLocallyDefined -- Anything local is interesting
+ emptyVarSet
+ []
+
+
+-- Deal with any indirections
+zapBind ind_env (NonRec bndr rhs)
+ | bndr `elemVarEnv` ind_env = Rec (zap ind_env (bndr,rhs))
+ -- The Rec isn't strictly necessary, but it's convenient
+zapBind ind_env (Rec pairs)
+ | or [id `elemVarEnv` ind_env | (id,_) <- pairs] = Rec (concat (map (zap ind_env) pairs))
+
+zapBind ind_env bind = bind
+
+zap ind_env pair@(bndr,rhs)
+ = case lookupVarEnv ind_env bndr of
+ Nothing -> [pair]
+ Just exported_id -> [(bndr, Var exported_id),
+ (exported_id_w_info, rhs)]
+ where
+ exported_id_w_info = modifyIdInfo (copyIdInfo (idInfo bndr)) exported_id
+ -- See notes with copyIdInfo about propagating IdInfo from
+ -- one to t'other
+
+shortMeOut ind_env exported_id local_id
+ = isExportedId 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 (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
\end{code}
+
%************************************************************************
%* *
\subsection[OccurAnal-main]{Counting occurrences: main function}
~~~~~~~~
\begin{code}
+type IdWithOccInfo = Id -- An Id with fresh PragmaInfo attached
+
+type Node details = (details, Int, [Int]) -- The Ints are gotten from the Unique,
+ -- which is gotten from the Id.
+type Details1 = (Id, UsageDetails, CoreExpr)
+type Details2 = (IdWithOccInfo, CoreExpr)
+
+
occAnalBind :: OccEnv
- -> CoreBinding
+ -> CoreBind
-> UsageDetails -- Usage details of scope
-> (UsageDetails, -- Of the whole let(rec)
- [SimplifiableCoreBinding])
+ [CoreBind])
occAnalBind env (NonRec binder rhs) body_usage
- | isNeeded env body_usage binder -- It's mentioned in body
+ | not (binder `usedIn` body_usage) -- It's not mentioned
+ = (body_usage, [])
+
+ | otherwise -- It's mentioned in the body
= (final_body_usage `combineUsageDetails` rhs_usage,
[NonRec tagged_binder rhs'])
- | otherwise
- = (body_usage, [])
-
where
- (rhs_usage, rhs') = occAnalRhs env binder rhs
(final_body_usage, tagged_binder) = tagBinder body_usage binder
+ (rhs_usage, rhs') = occAnalRhs env binder rhs
\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
+ rhs_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 = [ (bndr, rhs_usage, rhs')
+ | (bndr, rhs) <- pairs,
+ let (rhs_usage, rhs') = occAnalRhs rhs_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 :: [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 (lookupVarEnv 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
- edges :: [(Id,Id)] -- (a,b) means a mentions b
- edges = concat [ edges_from binder rhs_usage
- | (binder, (rhs_usage, _)) <- analysed_pairs]
+ ---- stuff to "re-constitute" bindings from dependency-analysis info ------
- edges_from :: Id -> UsageDetails -> [(Id,Id)]
- edges_from id its_rhs_usage
- = [(id,mentioned) | mentioned <- binders,
- maybeToBool (lookupIdEnv its_rhs_usage mentioned)
- ]
+ -- Non-recursive SCC
+ do_final_bind (AcyclicSCC ((bndr, rhs_usage, rhs'), _, _)) (body_usage, binds_so_far)
+ | not (bndr `usedIn` body_usage)
+ = (body_usage, binds_so_far) -- Dead code
+ | otherwise
+ = (combined_usage, new_bind : binds_so_far)
+ where
+ 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)
+ | not (any (`usedIn` body_usage) bndrs) -- NB: look at body_usage, not total_usage
+ = (body_usage, binds_so_far) -- Dead code
+ | otherwise
+ = (combined_usage, final_bind:binds_so_far)
+ where
+ 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_bndrs) = tagBinders total_usage bndrs
+ final_bind = Rec (reOrderRec env new_cycle)
+
+ new_cycle = CyclicSCC (zipWithEqual "occAnalBind" mk_new_bind tagged_bndrs cycle)
+ mk_new_bind tagged_bndr ((_, _, rhs'), key, keys) = ((tagged_bndr, rhs'), key, keys)
+\end{code}
- sccs :: [[Id]]
- sccs = case binders of
- [_] -> [binders] -- Singleton; no need to analyse
- other -> stronglyConnComp (==) edges binders
+@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
- ---- stuff to "re-constitute" bindings from dependency-analysis info ------
+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.
- do_final_bind sCC@[binder] (body_usage, binds_so_far)
- | isNeeded env body_usage binder
- = (combined_usage, new_bind:binds_so_far)
+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.
- | otherwise -- Dead
- = (body_usage, binds_so_far)
- 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)
- where
- (rhs_usages, rhss') = unzip (map lookup sCC)
- total_usage = foldr combineUsageDetails body_usage rhs_usages
- (combined_usage, tagged_binders) = tagBinders total_usage sCC
+==============
+[June 98: I don't understand the following paragraphs, and I've
+ changed the a=b case again so that it isn't a special case any more.]
- new_bind = Rec (zipEqual "occAnalBind" tagged_binders rhss')
+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])
+ = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
+ where
+ ((tagged_bndr, rhs), _, _) = bind
+
+reOrderRec env (CyclicSCC (bind : 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))
+ ++
+ [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
+
+ where
+ (chosen_pair, unchosen) = choose_loop_breaker bind (score bind) [] binds
+ (tagged_bndr, rhs) = chosen_pair
+
+ -- This loop looks for the bind with the lowest score
+ -- to pick as the loop breaker. The rest accumulate in
+ choose_loop_breaker (details,_,_) loop_sc acc []
+ = (details, acc) -- Done
+
+ choose_loop_breaker loop_bind loop_sc acc (bind : binds)
+ | sc < loop_sc -- Lower score so pick this new one
+ = choose_loop_breaker bind sc (loop_bind : acc) binds
+
+ | otherwise -- No lower so don't pick it
+ = choose_loop_breaker loop_bind loop_sc (bind : acc) binds
+ where
+ sc = score bind
+
+ score :: Node Details2 -> Int -- Higher score => less likely to be picked as loop breaker
+ score ((bndr, rhs), _, _)
+ | exprIsTrivial rhs &&
+ not (isExportedId bndr) = 3 -- Practically certain to be inlined
+ | inlineCandidate bndr rhs = 3 -- Likely to be inlined
+ | not_fun_ty (idType bndr) = 2 -- Data types help with cases
+ | not (isEmptyCoreRules (getIdSpecialisation bndr)) = 1
+ -- Avoid things with specialisations; we'd like
+ -- to take advantage of them in the subsequent bindings
+ | otherwise = 0
+
+ inlineCandidate :: Id -> CoreExpr -> Bool
+ inlineCandidate id (Note InlineMe _) = True
+ inlineCandidate id rhs = case getIdOccInfo id of
+ OneOcc _ _ -> True
+ other -> False
+
+ -- 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.
+ -- But we won't because constructor args are marked "Many".
+
+ not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
+ where
+ (_, rho_ty) = splitForAllTys ty
\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.
+[June 98, SLPJ] I've undone this change; I don't understand it. See notes with reOrderRec.
+
+
\begin{code}
occAnalRhs :: OccEnv
- -> Id -- Binder
- -> CoreExpr -- Rhs
- -> (UsageDetails, SimplifiableCoreExpr)
+ -> Id -> CoreExpr -- Binder and rhs
+ -> (UsageDetails, CoreExpr)
occAnalRhs env id rhs
- | idWantsToBeINLINEd id && not (ignoreINLINEPragma env)
- = (mapIdEnv markMany rhs_usage, rhs')
-
- | otherwise
- = (rhs_usage, rhs')
-
+ = (final_usage, rhs')
where
- (rhs_usage, rhs') = occAnal env rhs
+ (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
+
+ -- [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.
+
+ final_usage = foldVarSet add rhs_usage (idRuleVars 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
occAnal :: OccEnv
-> CoreExpr
-> (UsageDetails, -- Gives info only about the "interesting" Ids
- SimplifiableCoreExpr)
+ CoreExpr)
-occAnal env (Var v)
- | isCandidate env v
- = (unitIdEnv v (funOccurrence 0), Var v)
+occAnal env (Type t) = (emptyDetails, Type t)
- | otherwise
- = (emptyDetails, Var v)
+occAnal env (Var v)
+ = (var_uds, Var v)
+ where
+ var_uds | isCandidate env v = unitVarEnv v funOccZero
+ | otherwise = emptyDetails
+
+ -- At one stage, I gathered the idRuleVars for v here too,
+ -- which in a way is the right thing to do.
+ -- But that went wrong right after specialisation, when
+ -- the *occurrences* of the overloaded function didn't have any
+ -- rules in them, so the *specialised* versions looked as if they
+ -- weren't used at all.
-occAnal env (Lit lit) = (emptyDetails, Lit lit)
-occAnal env (Prim op args) = (occAnalArgs env args, Prim op args)
\end{code}
We regard variables that occur as constructor arguments as "dangerousToDup":
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')
+ -- For NoRep literals we have to report an occurrence of
+ -- the things which tidyCore will later add, so that when
+ -- we are compiling the very module in which those thin-air Ids
+ -- are defined we have them in scope!
+occAnal env expr@(Con (Literal lit) args)
+ = ASSERT( null args )
+ (mk_lit_uds lit, expr)
where
- (usage, body') = occAnal env body
+ mk_lit_uds (NoRepStr _ _) = try noRepStrIds
+ mk_lit_uds (NoRepInteger _ _) = try noRepIntegerIds
+ mk_lit_uds lit = emptyDetails
+
+ try vs = foldr add emptyDetails vs
+ add v uds | isCandidate env v = extendVarEnv uds v funOccZero
+ | otherwise = uds
+
+occAnal env (Con con args)
+ = case occAnalArgs env args of { (arg_uds, args') ->
+ let
+ -- We mark the free vars of the argument of a constructor as "many"
+ -- This means that nothing gets inlined into a constructor argument
+ -- position, which is what we want. Typically those constructor
+ -- arguments are just variables, or trivial expressions.
+ final_arg_uds = case con of
+ DataCon _ -> mapVarEnv markMany arg_uds
+ other -> arg_uds
+ in
+ (final_arg_uds, Con con args')
+ }
+\end{code}
-occAnal env (Coerce c ty body)
- = (usage, Coerce c ty body')
- where
- (usage, body') = occAnal env body
+\begin{code}
+occAnal env (Note InlineMe body)
+ = case occAnal env body of { (usage, body') ->
+ (mapVarEnv markMany usage, Note InlineMe body')
+ }
+
+occAnal env (Note note@(SCC cc) body)
+ = case occAnal env body of { (usage, body') ->
+ (mapVarEnv markInsideSCC usage, Note note body')
+ }
+
+occAnal env (Note note body)
+ = case occAnal env body of { (usage, body') ->
+ (usage, Note note body')
+ }
+\end{code}
-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
+\begin{code}
+occAnal env app@(App fun arg)
+ = occAnalApp env (collectArgs app)
+
+-- Ignore type variables altogether
+-- (a) occurrences inside type lambdas only not marked as InsideLam
+-- (b) type variables not in environment
+
+occAnal env expr@(Lam x body) | isTyVar x
+ = case occAnal env body of { (body_usage, body') ->
+ (body_usage, Lam x 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,
- foldr ( \v b -> Lam (ValBinder v) b) body' tagged_binders)
+-- So instead, we just mark each binder with its occurrence
+-- info in the *body* of the multiple lambda.
+-- Then, the simplifier is careful when partially applying lambdas.
+
+occAnal env expr@(Lam _ _)
+ = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
+ let
+ (final_usage, tagged_binders) = tagBinders body_usage binders
+ -- URGH! Sept 99: we don't seem to be able to use binders' here, because
+ -- we get linear-typed things in the resulting program that we can't handle yet.
+ -- (e.g. PrelShow) TODO
+
+ really_final_usage = if linear then
+ final_usage
+ else
+ mapVarEnv markInsideLam final_usage
+ in
+ (really_final_usage,
+ mkLams tagged_binders body') }
where
- (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')
+ (binders, body) = collectBinders expr
+ (linear, env_body, binders') = oneShotGroup env binders
+
+occAnal env (Case scrut bndr alts)
+ = case mapAndUnzip (occAnalAlt alt_env) alts of { (alts_usage_s, alts') ->
+ case occAnal (zapCtxt env) scrut of { (scrut_usage, scrut') ->
+ let
+ alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
+ alts_usage' = addCaseBndrUsage alts_usage
+ (alts_usage1, tagged_bndr) = tagBinder alts_usage' bndr
+ total_usage = scrut_usage `combineUsageDetails` alts_usage1
+ in
+ total_usage `seq` (total_usage, Case scrut' tagged_bndr alts') }}
where
- (body_usage, body') = occAnal env body
+ alt_env = env `addNewCand` bndr
+
+ -- The case binder gets a usage of either "many" or "dead", never "one".
+ -- Reason: we like to inline single occurrences, to eliminate a binding,
+ -- but inlining a case binder *doesn't* eliminate a binding.
+ -- We *don't* want to transform
+ -- case x of w { (p,q) -> f w }
+ -- into
+ -- case x of w { (p,q) -> f (p,q) }
+ addCaseBndrUsage usage = case lookupVarEnv usage bndr of
+ Nothing -> usage
+ Just occ -> extendVarEnv usage bndr (markMany occ)
-occAnal env (Lam (UsageBinder _) _) = panic "OccurAnal.occAnal Lam UsageBinder"
+occAnal env (Let bind body)
+ = case occAnal new_env body of { (body_usage, body') ->
+ case occAnalBind env bind body_usage of { (final_usage, new_binds) ->
+ (final_usage, mkLets new_binds body') }}
+ where
+ new_env = env `addNewCands` (bindersOf bind)
-occAnal env (Case scrut alts)
- = (scrut_usage `combineUsageDetails` alts_usage,
- Case scrut' alts')
+occAnalArgs env args
+ = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
+ (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
where
- (scrut_usage, scrut') = occAnal env scrut
- (alts_usage, alts') = occAnalAlts env alts
+ arg_env = zapCtxt env
+\end{code}
-occAnal env (Let bind body)
- = (final_usage, foldr Let body' new_binds) -- mkCoLet* wants Core... (sigh)
+Applications are dealt with specially because we want
+the "build hack" to work.
+
+\begin{code}
+-- Hack for build, fold, runST
+occAnalApp env (Var fun, args)
+ = case args_stuff of { (args_uds, args') ->
+ let
+ final_uds = fun_uds `combineUsageDetails` args_uds
+ in
+ (final_uds, mkApps (Var fun) args') }
+ where
+ fun_uniq = idUnique fun
+
+ fun_uds | isCandidate env fun = unitVarEnv fun funOccZero
+ | otherwise = emptyDetails
+
+ args_stuff | fun_uniq == buildIdKey = appSpecial env 2 [True,True] args
+ | fun_uniq == augmentIdKey = appSpecial env 2 [True,True] args
+ | fun_uniq == foldrIdKey = appSpecial env 3 [False,True] args
+ | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
+ | otherwise = occAnalArgs env args
+
+occAnalApp env (fun, args)
+ = case occAnal (zapCtxt env) fun of { (fun_uds, fun') ->
+ case occAnalArgs env args of { (args_uds, args') ->
+ let
+ final_uds = fun_uds `combineUsageDetails` args_uds
+ in
+ (final_uds, mkApps fun' args') }}
+
+appSpecial :: OccEnv -> Int -> CtxtTy -> [CoreExpr] -> (UsageDetails, [CoreExpr])
+appSpecial env n ctxt args
+ = go n args
where
- new_env = env `addNewCands` (bindersOf bind)
- (body_usage, body') = occAnal new_env body
- (final_usage, new_binds) = occAnalBind env bind body_usage
+ go n [] = (emptyDetails, []) -- Too few args
+
+ go 1 (arg:args) -- The magic arg
+ = case occAnal (setCtxt env ctxt) arg of { (arg_uds, arg') ->
+ case occAnalArgs env args of { (args_uds, args') ->
+ (combineUsageDetails arg_uds args_uds, arg':args') }}
+
+ go n (arg:args)
+ = case occAnal env arg of { (arg_uds, arg') ->
+ case go (n-1) args of { (args_uds, args') ->
+ (combineUsageDetails arg_uds args_uds, arg':args') }}
\end{code}
+
Case alternatives
~~~~~~~~~~~~~~~~~
\begin{code}
-occAnalAlts env (AlgAlts alts deflt)
- = (foldr combineAltsUsageDetails deflt_usage alts_usage,
- -- Note: combine*Alts*UsageDetails...
- AlgAlts alts' deflt')
- where
- (alts_usage, alts') = unzip (map do_alt alts)
- (deflt_usage, deflt') = occAnalDeflt env deflt
+occAnalAlt env (con, bndrs, rhs)
+ = case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
+ let
+ (final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
+ in
+ (final_usage, (con, tagged_bndrs, rhs')) }
+\end{code}
- do_alt (con, args, rhs)
- = (final_usage, (con, tagged_args, rhs'))
- where
- new_env = env `addNewCands` args
- (rhs_usage, rhs') = occAnal new_env rhs
- (final_usage, tagged_args) = tagBinders rhs_usage args
-
-occAnalAlts env (PrimAlts alts deflt)
- = (foldr combineAltsUsageDetails deflt_usage alts_usage,
- -- Note: combine*Alts*UsageDetails...
- PrimAlts alts' deflt')
- where
- (alts_usage, alts') = unzip (map do_alt alts)
- (deflt_usage, deflt') = occAnalDeflt env deflt
- do_alt (lit, rhs)
- = (rhs_usage, (lit, rhs'))
- where
- (rhs_usage, rhs') = occAnal env rhs
+%************************************************************************
+%* *
+\subsection[OccurAnal-types]{Data types}
+%* *
+%************************************************************************
+
+\begin{code}
+-- We gather inforamtion for variables that are either
+-- (a) in scope or
+-- (b) interesting
+
+data OccEnv =
+ OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
+ IdSet -- In-scope Ids
+ CtxtTy -- Tells about linearity
+
+type CtxtTy = [Bool]
+ -- [] No info
+ --
+ -- True:ctxt Analysing a function-valued expression that will be
+ -- applied just once
+ --
+ -- False:ctxt Analysing a function-valued expression that may
+ -- be applied many times; but when it is,
+ -- the CtxtTy inside applies
+
+isCandidate :: OccEnv -> Id -> Bool
+isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
+
+addNewCands :: OccEnv -> [Id] -> OccEnv
+addNewCands (OccEnv ifun cands ctxt) ids
+ = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
+
+addNewCand :: OccEnv -> Id -> OccEnv
+addNewCand (OccEnv ifun cands ctxt) id
+ = OccEnv ifun (extendVarSet cands id) ctxt
+
+setCtxt :: OccEnv -> CtxtTy -> OccEnv
+setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
+
+oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
+ -- True <=> this is a one-shot linear lambda group
+ -- The [CoreBndr] are the binders.
-occAnalDeflt env NoDefault = (emptyDetails, NoDefault)
+ -- The result binders have one-shot-ness set that they might not have had originally.
+ -- This happens in (build (\cn -> e)). Here the occurrence analyser
+ -- linearity context knows that c,n are one-shot, and it records that fact in
+ -- the binder. This is useful to guide subsequent float-in/float-out tranformations
-occAnalDeflt env (BindDefault binder rhs)
- = (final_usage, BindDefault tagged_binder rhs')
+oneShotGroup (OccEnv ifun cands ctxt) bndrs
+ = case go ctxt bndrs [] of
+ (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
where
- new_env = env `addNewCand` binder
- (rhs_usage, rhs') = occAnal new_env rhs
- (final_usage, tagged_binder) = tagBinder rhs_usage binder
-\end{code}
+ is_one_shot b = isId b && isOneShotLambda b
+ go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
-Atoms
-~~~~~
-\begin{code}
-occAnalArgs :: OccEnv -> [CoreArg] -> UsageDetails
+ go (lin_ctxt:ctxt) (bndr:bndrs) rev_bndrs
+ | isId bndr = go ctxt bndrs (bndr':rev_bndrs)
+ where
+ bndr' | lin_ctxt = setOneShotLambda bndr
+ | otherwise = bndr
+
+ go ctxt (bndr:bndrs) rev_bndrs = go ctxt bndrs (bndr:rev_bndrs)
+
+
+zapCtxt env@(OccEnv ifun cands []) = env
+zapCtxt (OccEnv ifun cands _ ) = OccEnv ifun cands []
+
+type UsageDetails = IdEnv BinderInfo -- A finite map from ids to their usage
+
+combineUsageDetails, combineAltsUsageDetails
+ :: UsageDetails -> UsageDetails -> UsageDetails
+
+combineUsageDetails usage1 usage2
+ = plusVarEnv_C addBinderInfo usage1 usage2
+
+combineAltsUsageDetails usage1 usage2
+ = plusVarEnv_C orBinderInfo usage1 usage2
+
+addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
+addOneOcc usage id info
+ = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
+ -- ToDo: make this more efficient
+
+emptyDetails = (emptyVarEnv :: UsageDetails)
+
+unitDetails id info = (unitVarEnv id info :: UsageDetails)
+
+usedIn :: Id -> UsageDetails -> Bool
+v `usedIn` details = isExportedId v || v `elemVarEnv` details
-occAnalArgs env atoms
- = foldr do_one_atom emptyDetails atoms
+tagBinders :: UsageDetails -- Of scope
+ -> [Id] -- Binders
+ -> (UsageDetails, -- Details with binders removed
+ [IdWithOccInfo]) -- Tagged binders
+
+tagBinders usage binders
+ = let
+ usage' = usage `delVarEnvList` binders
+ uss = map (setBinderOcc usage) binders
+ in
+ usage' `seq` (usage', uss)
+
+tagBinder :: UsageDetails -- Of scope
+ -> Id -- Binders
+ -> (UsageDetails, -- Details with binders removed
+ IdWithOccInfo) -- Tagged binders
+
+tagBinder usage binder
+ = let
+ usage' = usage `delVarEnv` binder
+ binder' = setBinderOcc usage binder
+ in
+ usage' `seq` (usage', binder')
+
+
+setBinderOcc :: UsageDetails -> CoreBndr -> CoreBndr
+setBinderOcc usage bndr
+ | isTyVar bndr = bndr
+ | isExportedId bndr
+ = -- Don't use local usage info for visible-elsewhere things
+ -- BUT *do* erase any IAmALoopBreaker annotation, because we're
+ -- about to re-generate it and it shouldn't be "sticky"
+ case getIdOccInfo bndr of
+ NoOccInfo -> bndr
+ other -> setIdOccInfo bndr NoOccInfo
+
+ | otherwise = setIdOccInfo bndr occ_info
where
- do_one_atom (VarArg v) usage
- | isCandidate env v = addOneOcc usage v (argOccurrence 0)
- | otherwise = usage
- do_one_atom other_arg usage = usage
+ occ_info = case lookupVarEnv usage bndr of
+ Nothing -> IAmDead
+ Just info -> binderInfoToOccInfo info
+markBinderInsideLambda :: CoreBndr -> CoreBndr
+markBinderInsideLambda bndr
+ | isTyVar bndr
+ = bndr
-occAnalArg :: OccEnv -> CoreArg -> UsageDetails
+ | otherwise
+ = case getIdOccInfo bndr of
+ OneOcc _ once -> bndr `setIdOccInfo` OneOcc insideLam once
+ other -> bndr
-occAnalArg env (VarArg v)
- | isCandidate env v = unitDetails v (argOccurrence 0)
- | otherwise = emptyDetails
-occAnalArg _ _ = emptyDetails
+funOccZero = funOccurrence 0
\end{code}
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