%
-% (c) The GRASP/AQUA Project, Glasgow University, 1992-1996
+% (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
%
%************************************************************************
%* *
\begin{code}
module OccurAnal (
- occurAnalyseBinds, occurAnalyseExpr, occurAnalyseGlobalExpr
+ occurAnalyseBinds, occurAnalyseExpr, occurAnalyseGlobalExpr,
+ markBinderInsideLambda, tagBinders,
+ UsageDetails
) where
#include "HsVersions.h"
import BinderInfo
-import CmdLineOpts ( opt_D_dump_occur_anal, SimplifierSwitch(..) )
+import CmdLineOpts ( SimplifierSwitch(..) )
import CoreSyn
-import Digraph ( stronglyConnCompR, SCC(..) )
-import Id ( idWantsToBeINLINEd, addNoInlinePragma, nukeNoInlinePragma,
- omitIfaceSigForId, isSpecPragmaId,
- idType, idUnique, Id,
- emptyIdSet, unionIdSets, mkIdSet,
- elementOfIdSet,
- addOneToIdSet, IdSet,
-
- IdEnv, nullIdEnv, unitIdEnv, combineIdEnvs,
- delOneFromIdEnv, delManyFromIdEnv, isNullIdEnv,
- mapIdEnv, lookupIdEnv, elemIdEnv, addOneToIdEnv
+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 Specialise ( idSpecVars )
-import Name ( isExported, isLocallyDefined )
+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 PprCore
-import Unique ( u2i )
+import Digraph ( stronglyConnCompR, SCC(..) )
+import Unique ( u2i, buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
import UniqFM ( keysUFM )
-import Util ( zipWithEqual )
+import Util ( zipWithEqual, mapAndUnzip, count )
import Outputable
\end{code}
Here's the externally-callable interface:
\begin{code}
-occurAnalyseBinds
- :: [CoreBinding] -- input
- -> (SimplifierSwitch -> Bool)
- -> [SimplifiableCoreBinding] -- output
-
-occurAnalyseBinds binds simplifier_sw_chkr
- | opt_D_dump_occur_anal = pprTrace "OccurAnal:"
- (pprGenericBindings binds')
- binds'
- | otherwise = binds'
- where
- (_, _, binds') = occAnalTop initial_env binds
-
- 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 :: (Id -> Bool) -- Tells if a variable is interesting
-> CoreExpr
-> (IdEnv BinderInfo, -- Occ info for interesting free vars
- SimplifiableCoreExpr)
+ CoreExpr)
occurAnalyseExpr interesting expr
= occAnal initial_env expr
where
- initial_env = OccEnv False {- Do not ignore INLINE Pragma -}
- (\id locals -> interesting id || elementOfIdSet id locals)
- emptyIdSet
+ initial_env = OccEnv interesting emptyVarSet []
-occurAnalyseGlobalExpr :: CoreExpr -> SimplifiableCoreExpr
+occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
occurAnalyseGlobalExpr expr
= -- Top level expr, so no interesting free vars, and
-- discard occurence info returned
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.
+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
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]
- )
+occurAnalyseBinds :: [CoreBind] -> [CoreBind]
-occAnalTop env [] = (emptyDetails, nullIdEnv, [])
-
--- 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
-
-occAnalTop env (NonRec exported_id (Var local_id) : binds)
- | isExported exported_id && -- Only if this is exported
+occurAnalyseBinds binds
+ = binds'
+ where
+ (_, _, 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 (isExported local_id) && -- Only if this one is not itself exported,
+ not (isExportedId 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)]
+ not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
\end{code}
~~~~~~~~
\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, SimplifiableCoreExpr)
-type Details2 = ((Id, BinderInfo), SimplifiableCoreExpr)
+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 -- Not mentioned, so drop dead code
- = (body_usage, [])
-
where
- binder' = nukeNoInlinePragma binder
- (rhs_usage, rhs') = occAnalRhs env binder' rhs
- (final_body_usage, tagged_binder) = tagBinder body_usage binder'
+ (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:
pp_item (_, bndr, _) = ppr bndr
binders = map fst pairs
- new_env = env `addNewCands` binders
+ rhs_env = env `addNewCands` binders
analysed_pairs :: [Details1]
- analysed_pairs = [ (nukeNoInlinePragma bndr, rhs_usage, rhs')
+ analysed_pairs = [ (bndr, rhs_usage, rhs')
| (bndr, rhs) <- pairs,
- let (rhs_usage, rhs') = occAnalRhs new_env bndr rhs
+ let (rhs_usage, rhs') = occAnalRhs rhs_env bndr rhs
]
sccs :: [SCC (Node Details1)]
-- by just extracting the keys from the finite map. Grimy, but fast.
-- Previously we had this:
-- [ bndr | bndr <- bndrs,
- -- maybeToBool (lookupIdEnv rhs_usage bndr)]
+ -- 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]
-- 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
+ | 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
-- 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
+ | 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_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 (bndr, occ_info) ((_, _, rhs'), key, keys) = (((bndr, occ_info), rhs'), key, keys)
+ 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}
@reOrderRec@ is applied to the list of (binder,rhs) pairs for a cyclic
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.
+==============
+[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.]
+
Here's a case that bit me:
letrec
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
-- Common case of simple self-recursion
reOrderRec env (CyclicSCC [bind])
- = [((addNoInlinePragma bndr, occ_info), rhs)]
+ = [(setIdOccInfo tagged_bndr IAmALoopBreaker, rhs)]
where
- (((bndr, occ_info), rhs), _, _) = bind
+ ((tagged_bndr, rhs), _, _) = bind
-reOrderRec env (CyclicSCC binds)
+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))
++
- [((addNoInlinePragma bndr, occ_info), rhs)]
+ [(setIdOccInfo tagged_bndr IAmALoopBreaker, 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)
+ (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
- (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):
+ 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
-
- -- 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
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.
-[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 -> 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)
+ -> (UsageDetails, CoreExpr)
occAnalRhs env id rhs
- | inlineMe env id
- = (mapIdEnv markMany total_usage, rhs')
+ = (final_usage, rhs')
+ where
+ (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
- | otherwise
- = (total_usage, 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.
- 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
+ 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}
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}
+ -- 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
+ 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)
- = (mapIdEnv markDangerousToDup (occAnalArgs env args),
- 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}
+
+\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)
- = (mapIdEnv markInsideSCC usage, Note note body')
- where
- (usage, body') = occAnal env body
+ = case occAnal env body of { (usage, body') ->
+ (mapVarEnv markInsideSCC usage, Note note body')
+ }
occAnal env (Note note body)
- = (usage, Note note body')
- where
- (usage, body') = occAnal env 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)
- = 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)
- = 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')
+ (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
- (scrut_usage, scrut') = occAnal env scrut
- (alts_usage, alts') = occAnalAlts env alts
--}
+ 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 (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, 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
-\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
-
- 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')
+ (final_usage, mkLets new_binds body') }}
where
- (alts_usage, alts') = unzip (map do_alt alts)
- (deflt_usage, deflt') = occAnalDeflt env deflt
+ new_env = env `addNewCands` (bindersOf bind)
- do_alt (lit, rhs)
- = (rhs_usage, (lit, rhs'))
- where
- (rhs_usage, rhs') = occAnal env rhs
-
-occAnalDeflt env NoDefault = (emptyDetails, NoDefault)
-
-occAnalDeflt env (BindDefault binder rhs)
- = (final_usage, BindDefault tagged_binder rhs')
+occAnalArgs env args
+ = case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
+ (foldr combineUsageDetails emptyDetails arg_uds_s, args')}
where
- new_env = env `addNewCand` binder
- (rhs_usage, rhs') = occAnal new_env rhs
- (final_usage, tagged_binder) = tagBinder rhs_usage binder
+ arg_env = zapCtxt env
\end{code}
+Applications are dealt with specially because we want
+the "build hack" to work.
-Atoms
-~~~~~
\begin{code}
-occAnalArgs :: OccEnv -> [CoreArg] -> UsageDetails
-
-occAnalArgs env atoms
- = foldr do_one_atom emptyDetails atoms
+-- 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
- do_one_atom (VarArg v) usage
- | isCandidate env v = addOneOcc usage v (argOccurrence 0)
- | otherwise = usage
- do_one_atom other_arg usage = usage
-
+ 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
+ go n [] = (emptyDetails, []) -- Too few args
-occAnalArg :: OccEnv -> CoreArg -> UsageDetails
+ 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}
-occAnalArg env (VarArg v)
- | isCandidate env v = unitDetails v (argOccurrence 0)
- | otherwise = emptyDetails
-occAnalArg _ _ = emptyDetails
+
+Case alternatives
+~~~~~~~~~~~~~~~~~
+\begin{code}
+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}
%************************************************************************
\begin{code}
-data OccEnv =
- OccEnv
- Bool -- IgnoreINLINEPragma flag
- -- False <=> OK to use INLINEPragma information
- -- True <=> ignore INLINEPragma information
+-- We gather inforamtion for variables that are either
+-- (a) in scope or
+-- (b) interesting
- (Id -> IdSet -> Bool) -- Tells whether an Id occurrence is interesting,
- -- given the set of in-scope variables
+data OccEnv =
+ OccEnv (Id -> Bool) -- Tells whether an Id occurrence is interesting,
+ IdSet -- In-scope Ids
+ CtxtTy -- Tells about linearity
- IdSet -- In-scope Ids
+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 ip ifun cands) ids
- = OccEnv ip ifun (cands `unionIdSets` mkIdSet ids)
+addNewCands (OccEnv ifun cands ctxt) ids
+ = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
addNewCand :: OccEnv -> Id -> OccEnv
-addNewCand (OccEnv ip ifun cands) id
- = OccEnv ip ifun (addOneToIdSet cands id)
+addNewCand (OccEnv ifun cands ctxt) id
+ = OccEnv ifun (extendVarSet cands id) ctxt
-isCandidate :: OccEnv -> Id -> Bool
-isCandidate (OccEnv _ ifun cands) id = ifun id cands
+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.
+
+ -- 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
-inlineMe :: OccEnv -> Id -> Bool
-inlineMe env id
- = {- See comments with simplIdWantsToBeINLINEd in SimplUtils.lhs
- not ignore_inline_prag &&
- -}
- idWantsToBeINLINEd id
+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
+ is_one_shot b = isId b && isOneShotLambda b
+
+ go ctxt [] rev_bndrs = (ctxt, reverse rev_bndrs)
+
+ 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
:: UsageDetails -> UsageDetails -> UsageDetails
combineUsageDetails usage1 usage2
- = combineIdEnvs addBinderInfo usage1 usage2
+ = plusVarEnv_C addBinderInfo usage1 usage2
combineAltsUsageDetails usage1 usage2
- = combineIdEnvs orBinderInfo usage1 usage2
+ = plusVarEnv_C orBinderInfo usage1 usage2
addOneOcc :: UsageDetails -> Id -> BinderInfo -> UsageDetails
addOneOcc usage id info
- = combineIdEnvs addBinderInfo usage (unitIdEnv id info)
+ = plusVarEnv_C addBinderInfo usage (unitVarEnv id info)
-- ToDo: make this more efficient
-emptyDetails = (nullIdEnv :: UsageDetails)
+emptyDetails = (emptyVarEnv :: UsageDetails)
+
+unitDetails id info = (unitVarEnv id info :: UsageDetails)
-unitDetails id info = (unitIdEnv id info :: UsageDetails)
+usedIn :: Id -> UsageDetails -> Bool
+v `usedIn` details = isExportedId v || v `elemVarEnv` details
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 ]
- )
--}
+ [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
- (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 || isSpecPragmaId binder
- = noBinderInfo -- Visible-elsewhere things count as many
- | otherwise
- = case (lookupIdEnv usage binder) of
- Nothing -> deadOccurrence
- Just info -> info
+ 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
+ occ_info = case lookupVarEnv usage bndr of
+ Nothing -> IAmDead
+ Just info -> binderInfoToOccInfo info
-isNeeded env usage binder = not (isDeadOcc (usage_of usage binder))
-\end{code}
+markBinderInsideLambda :: CoreBndr -> CoreBndr
+markBinderInsideLambda bndr
+ | isTyVar bndr
+ = bndr
+ | otherwise
+ = case getIdOccInfo bndr of
+ OneOcc _ once -> bndr `setIdOccInfo` OneOcc insideLam once
+ other -> bndr
+funOccZero = funOccurrence 0
+\end{code}
projects / ghc-hetmet.git / blobdiff