import CoreSyn
import CoreFVs ( idRuleVars )
import CoreUtils ( exprIsTrivial )
-import Id ( isDataConId, isOneShotLambda, setOneShotLambda,
+import Id ( isDataConWorkId, isOneShotLambda, setOneShotLambda,
idOccInfo, setIdOccInfo,
- isExportedId, modifyIdInfo, idInfo,
+ isExportedId, modifyIdInfo, idInfo, idArity,
idSpecialisation, isLocalId,
idType, idUnique, Id
)
-import IdInfo ( OccInfo(..), shortableIdInfo, copyIdInfo )
+import IdInfo ( copyIdInfo )
+import BasicTypes ( OccInfo(..), isOneOcc )
import VarSet
import VarEnv
-import Type ( splitFunTy_maybe, splitForAllTys )
-import Maybes ( maybeToBool, orElse )
+import Type ( isFunTy, dropForAlls )
+import Maybes ( orElse )
import Digraph ( stronglyConnCompR, SCC(..) )
import PrelNames ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
import Unique ( Unique )
import UniqFM ( keysUFM )
import Util ( zipWithEqual, mapAndUnzip )
-import FastTypes
import Outputable
\end{code}
Here's the externally-callable interface:
\begin{code}
-occurAnalyseExpr :: (Id -> Bool) -- Tells if a variable is interesting
- -> CoreExpr
- -> (IdEnv OccInfo, -- Occ info for interesting free vars
- CoreExpr)
-
-occurAnalyseExpr interesting expr
- = occAnal initial_env expr
- where
- initial_env = OccEnv interesting emptyVarSet []
-
occurAnalyseGlobalExpr :: CoreExpr -> CoreExpr
occurAnalyseGlobalExpr expr
= -- Top level expr, so no interesting free vars, and
-- discard occurence info returned
- snd (occurAnalyseExpr (\_ -> False) expr)
+ snd (occAnal (initOccEnv emptyVarSet) expr)
occurAnalyseRule :: CoreRule -> CoreRule
-occurAnalyseRule rule@(BuiltinRule _) = rule
-occurAnalyseRule (Rule str tpl_vars tpl_args rhs)
+occurAnalyseRule rule@(BuiltinRule _ _) = rule
+occurAnalyseRule (Rule str act tpl_vars tpl_args rhs)
-- Add occ info to tpl_vars, rhs
- = Rule str tpl_vars' tpl_args rhs'
+ = Rule str act tpl_vars' tpl_args rhs'
where
- (rhs_uds, rhs') = occurAnalyseExpr isLocalId rhs
+ (rhs_uds, rhs') = occAnal (initOccEnv (mkVarSet tpl_vars)) rhs
(_, tpl_vars') = tagBinders rhs_uds tpl_vars
\end{code}
occurAnalyseBinds binds
= binds'
where
- (_, _, binds') = go initialTopEnv binds
+ (_, _, binds') = go (initOccEnv emptyVarSet) binds
go :: OccEnv -> [CoreBind]
-> (UsageDetails, -- Occurrence info
other -> -- Ho ho! The normal case
(final_usage, ind_env, new_binds ++ binds')
-initialTopEnv = OccEnv isLocalId -- Anything local is interesting
- emptyVarSet
- []
-
-- Deal with any indirections
zapBind ind_env (NonRec bndr rhs)
not (local_id `elemVarEnv` ind_env) -- Only if not already substituted for
then
+ True
+
+{- No longer needed
if shortableIdInfo (idInfo exported_id) -- Only if its IdInfo is 'shortable'
-- (see the defn of IdInfo.shortableIdInfo)
then True
- else pprTrace "shortMeOut:" (ppr exported_id) False
+ else
+#ifdef DEBUG
+ pprTrace "shortMeOut:" (ppr exported_id)
+#endif
+ False
+-}
else
False
\end{code}
where
(final_body_usage, tagged_binder) = tagBinder body_usage binder
- (rhs_usage, rhs') = occAnalRhs env binder rhs
+ (rhs_usage, rhs') = occAnalRhs env tagged_binder rhs
\end{code}
Dropping dead code for recursive bindings is done in a very simple way:
inlineCandidate :: Id -> CoreExpr -> Bool
inlineCandidate id (Note InlineMe _) = True
- inlineCandidate id rhs = case idOccInfo id of
- OneOcc _ _ -> True
- other -> False
+ inlineCandidate id rhs = isOneOcc (idOccInfo id)
-- Real example (the Enum Ordering instance from PrelBase):
-- rec f = \ x -> case d of (p,q,r) -> p x
-- 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
+ not_fun_ty ty = not (isFunTy (dropForAlls ty))
\end{code}
@occAnalRhs@ deals with the question of bindings where the Id is marked
\begin{code}
occAnalRhs :: OccEnv
-> Id -> CoreExpr -- Binder and rhs
+ -- For non-recs the binder is alrady tagged
+ -- with occurrence info
-> (UsageDetails, CoreExpr)
occAnalRhs env id rhs
= (final_usage, rhs')
where
- (rhs_usage, rhs') = occAnal (zapCtxt env) rhs
+ (rhs_usage, rhs') = occAnal ctxt rhs
+ ctxt | certainly_inline id = env
+ | otherwise = rhsCtxt env
+ -- Note that we generally use an rhsCtxt. This tells the occ anal n
+ -- that it's looking at an RHS, which has an effect in occAnalApp
+ --
+ -- But there's a problem. Consider
+ -- x1 = a0 : []
+ -- x2 = a1 : x1
+ -- x3 = a2 : x2
+ -- g = f x3
+ -- First time round, it looks as if x1 and x2 occur as an arg of a
+ -- let-bound constructor ==> give them a many-occurrence.
+ -- But then x3 is inlined (unconditionally as it happens) and
+ -- next time round, x2 will be, and the next time round x1 will be
+ -- Result: multiple simplifier iterations. Sigh.
+ -- Crude solution: use rhsCtxt for things that occur just once...
+
+ certainly_inline id = case idOccInfo id of
+ OneOcc in_lam one_br -> not in_lam && one_br
+ other -> False
-- [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
add v u = addOneOcc u v NoOccInfo -- Give a non-committal binder info
-- (i.e manyOcc) because many copies
-- of the specialised thing can appear
+
\end{code}
Expressions
\begin{code}
occAnal env app@(App fun arg)
- = occAnalApp env (collectArgs app)
+ = occAnalApp env (collectArgs app) False
-- Ignore type variables altogether
-- (a) occurrences inside type lambdas only not marked as InsideLam
-- Then, the simplifier is careful when partially applying lambdas.
occAnal env expr@(Lam _ _)
- = case occAnal (env_body `addNewCands` binders) body of { (body_usage, body') ->
+ = case occAnal env_body 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
(really_final_usage,
mkLams tagged_binders body') }
where
- (binders, body) = collectBinders expr
- (linear, env_body, _) = oneShotGroup env binders
+ (binders, body) = collectBinders expr
+ (linear, env1, _) = oneShotGroup env binders
+ env2 = env1 `addNewCands` binders -- Add in-scope binders
+ env_body = vanillaCtxt env2 -- Body is (no longer) an RhsContext
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') ->
+ = case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts') ->
+ case occAnal (vanillaCtxt env) scrut of { (scrut_usage, scrut') ->
+ -- No need for rhsCtxt
let
alts_usage = foldr1 combineAltsUsageDetails alts_usage_s
alts_usage' = addCaseBndrUsage alts_usage
= case mapAndUnzip (occAnal arg_env) args of { (arg_uds_s, args') ->
(foldr combineUsageDetails emptyDetails arg_uds_s, args')}
where
- arg_env = zapCtxt env
+ arg_env = vanillaCtxt env
\end{code}
Applications are dealt with specially because we want
\begin{code}
-- Hack for build, fold, runST
-occAnalApp env (Var fun, args)
+occAnalApp env (Var fun, args) is_rhs
= case args_stuff of { (args_uds, args') ->
let
- final_uds = fun_uds `combineUsageDetails` args_uds
+ -- We mark the free vars of the argument of a constructor or PAP
+ -- as "many", if it is the RHS of a let(rec).
+ -- 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.
+ --
+ -- This is the *whole point* of the isRhsEnv predicate
+ final_args_uds
+ | isRhsEnv env,
+ isDataConWorkId fun || valArgCount args < idArity fun
+ = mapVarEnv markMany args_uds
+ | otherwise = args_uds
in
- (final_uds, mkApps (Var fun) args') }
+ (fun_uds `combineUsageDetails` final_args_uds, mkApps (Var fun) args') }
where
fun_uniq = idUnique fun
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
-
- | isDataConId fun = case occAnalArgs env args of
- (arg_uds, args') -> (mapVarEnv markMany arg_uds, args')
- -- 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.
-
- | 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') ->
+ | fun_uniq == runSTRepIdKey = appSpecial env 2 [True] args
+ -- (foldr k z xs) may call k many times, but it never
+ -- shares a partial application of k; hence [False,True]
+ -- This means we can optimise
+ -- foldr (\x -> let v = ...x... in \y -> ...v...) z xs
+ -- by floating in the v
+
+ | otherwise = occAnalArgs env args
+
+
+occAnalApp env (fun, args) is_rhs
+ = case occAnal (addAppCtxt env args) fun of { (fun_uds, fun') ->
+ -- The addAppCtxt is a bit cunning. One iteration of the simplifier
+ -- often leaves behind beta redexs like
+ -- (\x y -> e) a1 a2
+ -- Here we would like to mark x,y as one-shot, and treat the whole
+ -- thing much like a let. We do this by pushing some True items
+ -- onto the context stack.
+
+ 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 :: OccEnv
+ -> Int -> CtxtTy -- Argument number, and context to use for it
+ -> [CoreExpr]
+ -> (UsageDetails, [CoreExpr])
appSpecial env n ctxt args
= go n args
where
+ arg_env = vanillaCtxt env
+
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') ->
+ = case occAnal (setCtxt arg_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 occAnal arg_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
~~~~~~~~~~~~~~~~~
+If the case binder occurs at all, the other binders effectively do too.
+For example
+ case e of x { (a,b) -> rhs }
+is rather like
+ let x = (a,b) in rhs
+If e turns out to be (e1,e2) we indeed get something like
+ let a = e1; b = e2; x = (a,b) in rhs
+
\begin{code}
-occAnalAlt env (con, bndrs, rhs)
+occAnalAlt env case_bndr (con, bndrs, rhs)
= case occAnal (env `addNewCands` bndrs) rhs of { (rhs_usage, rhs') ->
let
(final_usage, tagged_bndrs) = tagBinders rhs_usage bndrs
+ final_bndrs | case_bndr `elemVarEnv` final_usage = bndrs
+ | otherwise = tagged_bndrs
+ -- Leave the binders untagged if the case
+ -- binder occurs at all; see note above
in
- (final_usage, (con, tagged_bndrs, rhs')) }
+ (final_usage, (con, final_bndrs, rhs')) }
\end{code}
%************************************************************************
%* *
-\subsection[OccurAnal-types]{Data types}
+\subsection[OccurAnal-types]{OccEnv}
%* *
%************************************************************************
\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
+data OccEnv
+ = OccEnv IdSet -- In-scope Ids; we gather info about these only
+ OccEncl -- Enclosing context information
+ CtxtTy -- Tells about linearity
+
+-- OccEncl is used to control whether to inline into constructor arguments
+-- For example:
+-- x = (p,q) -- Don't inline p or q
+-- y = /\a -> (p a, q a) -- Still don't inline p or q
+-- z = f (p,q) -- Do inline p,q; it may make a rule fire
+-- So OccEncl tells enought about the context to know what to do when
+-- we encounter a contructor application or PAP.
+
+data OccEncl
+ = OccRhs -- RHS of let(rec), albeit perhaps inside a type lambda
+ -- Don't inline into constructor args here
+ | OccVanilla -- Argument of function, body of lambda, scruintee of case etc.
+ -- Do inline into constructor args here
type CtxtTy = [Bool]
-- [] No info
-- be applied many times; but when it is,
-- the CtxtTy inside applies
+initOccEnv :: VarSet -> OccEnv
+initOccEnv vars = OccEnv vars OccRhs []
+
+isRhsEnv (OccEnv _ OccRhs _) = True
+isRhsEnv (OccEnv _ OccVanilla _) = False
+
isCandidate :: OccEnv -> Id -> Bool
-isCandidate (OccEnv ifun cands _) id = id `elemVarSet` cands || ifun id
+isCandidate (OccEnv cands encl _) id = id `elemVarSet` cands
addNewCands :: OccEnv -> [Id] -> OccEnv
-addNewCands (OccEnv ifun cands ctxt) ids
- = OccEnv ifun (cands `unionVarSet` mkVarSet ids) ctxt
+addNewCands (OccEnv cands encl ctxt) ids
+ = OccEnv (extendVarSetList cands ids) encl ctxt
addNewCand :: OccEnv -> Id -> OccEnv
-addNewCand (OccEnv ifun cands ctxt) id
- = OccEnv ifun (extendVarSet cands id) ctxt
+addNewCand (OccEnv cands encl ctxt) id
+ = OccEnv (extendVarSet cands id) encl ctxt
setCtxt :: OccEnv -> CtxtTy -> OccEnv
-setCtxt (OccEnv ifun cands _) ctxt = OccEnv ifun cands ctxt
+setCtxt (OccEnv cands encl _) ctxt = OccEnv cands encl ctxt
oneShotGroup :: OccEnv -> [CoreBndr] -> (Bool, OccEnv, [CoreBndr])
-- True <=> this is a one-shot linear lambda group
-- 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
-oneShotGroup (OccEnv ifun cands ctxt) bndrs
+oneShotGroup (OccEnv cands encl ctxt) bndrs
= case go ctxt bndrs [] of
- (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv ifun cands new_ctxt, new_bndrs)
+ (new_ctxt, new_bndrs) -> (all is_one_shot new_bndrs, OccEnv cands encl new_ctxt, new_bndrs)
where
is_one_shot b = isId b && isOneShotLambda b
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 []
+vanillaCtxt (OccEnv cands _ _) = OccEnv cands OccVanilla []
+rhsCtxt (OccEnv cands _ _) = OccEnv cands OccRhs []
+
+addAppCtxt (OccEnv cands encl ctxt) args
+ = OccEnv cands encl (replicate (valArgCount args) True ++ ctxt)
+\end{code}
+%************************************************************************
+%* *
+\subsection[OccurAnal-types]{OccEnv}
+%* *
+%************************************************************************
+
+\begin{code}
type UsageDetails = IdEnv OccInfo -- A finite map from ids to their usage
combineUsageDetails, combineAltsUsageDetails
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