import TyCon ( isProductTyCon, isRecursiveTyCon )
import Id ( Id, idType, idInlineActivation,
isDataConWorkId, isGlobalId, idArity,
- idStrictness, idStrictness_maybe,
+ idStrictness,
setIdStrictness, idDemandInfo, idUnfolding,
- idDemandInfo_maybe,
- setIdDemandInfo
+ idDemandInfo_maybe, setIdDemandInfo
)
import Var ( Var )
import VarEnv
import TysWiredIn ( unboxedPairDataCon )
import TysPrim ( realWorldStatePrimTy )
import UniqFM ( addToUFM_Directly, lookupUFM_Directly,
- minusUFM, ufmToList, filterUFM )
+ minusUFM, filterUFM )
import Type ( isUnLiftedType, coreEqType, splitTyConApp_maybe )
import Coercion ( coercionKind )
import Util ( mapAndUnzip, lengthIs, zipEqual )
import Maybes ( orElse, expectJust )
import Outputable
import Data.List
+import FastString
\end{code}
To think about
is even more important. We don't want the wrapper to rebox an unboxed
argument, and pass an Int to $wfoo!
+
+%************************************************************************
+%* *
+ Demand transformer
+%* *
+%************************************************************************
+
+\begin{code}
+dmdTransform :: SigEnv -- The strictness environment
+ -> Id -- The function
+ -> Demand -- The demand on the function
+ -> DmdType -- The demand type of the function in this context
+ -- Returned DmdEnv includes the demand on
+ -- this function plus demand on its free variables
+
+dmdTransform sigs var dmd
+
+------ DATA CONSTRUCTOR
+ | isDataConWorkId var -- Data constructor
+ = let
+ StrictSig dmd_ty = idStrictness var -- It must have a strictness sig
+ DmdType _ _ con_res = dmd_ty
+ arity = idArity var
+ in
+ if arity == call_depth then -- Saturated, so unleash the demand
+ let
+ -- Important! If we Keep the constructor application, then
+ -- we need the demands the constructor places (always lazy)
+ -- If not, we don't need to. For example:
+ -- f p@(x,y) = (p,y) -- S(AL)
+ -- g a b = f (a,b)
+ -- It's vital that we don't calculate Absent for a!
+ dmd_ds = case res_dmd of
+ Box (Eval ds) -> mapDmds box ds
+ Eval ds -> ds
+ _ -> Poly Top
+
+ -- ds can be empty, when we are just seq'ing the thing
+ -- If so we must make up a suitable bunch of demands
+ arg_ds = case dmd_ds of
+ Poly d -> replicate arity d
+ Prod ds -> ASSERT( ds `lengthIs` arity ) ds
+
+ in
+ mkDmdType emptyDmdEnv arg_ds con_res
+ -- Must remember whether it's a product, hence con_res, not TopRes
+ else
+ topDmdType
+
+------ IMPORTED FUNCTION
+ | isGlobalId var, -- Imported function
+ let StrictSig dmd_ty = idStrictness var
+ = -- pprTrace "strict-sig" (ppr var $$ ppr dmd_ty) $
+ if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
+ dmd_ty
+ else
+ topDmdType
+
+------ LOCAL LET/REC BOUND THING
+ | Just (StrictSig dmd_ty, top_lvl) <- lookupSigEnv sigs var
+ = let
+ fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
+ | otherwise = deferType dmd_ty
+ -- NB: it's important to use deferType, and not just return topDmdType
+ -- Consider let { f x y = p + x } in f 1
+ -- The application isn't saturated, but we must nevertheless propagate
+ -- a lazy demand for p!
+ in
+ if isTopLevel top_lvl then fn_ty -- Don't record top level things
+ else addVarDmd fn_ty var dmd
+
+------ LOCAL NON-LET/REC BOUND THING
+ | otherwise -- Default case
+ = unitVarDmd var dmd
+
+ where
+ (call_depth, res_dmd) = splitCallDmd dmd
+\end{code}
+
%************************************************************************
%* *
\subsection{Bindings}
= loop 1 initial_sigs orig_pairs
where
bndrs = map fst orig_pairs
- initial_sigs = extendSigEnvList sigs [(id, (initialSig id, top_lvl)) | id <- bndrs]
+ initial_sigs = addInitialSigs top_lvl sigs bndrs
loop :: Int
-> SigEnv -- Already contains the current sigs
loop n sigs pairs
| found_fixpoint
= (sigs', lazy_fv, pairs')
- -- Note: use pairs', not pairs. pairs' is the result of
+ -- Note: return pairs', not pairs. pairs' is the result of
-- processing the RHSs with sigs (= sigs'), whereas pairs
-- is the result of processing the RHSs with the *previous*
-- iteration of sigs.
- | n >= 10 = pprTrace "dmdFix loop" (ppr n <+> (vcat
- [ text "Sigs:" <+> ppr [(id,lookup sigs id, lookup sigs' id) | (id,_) <- pairs],
- text "env:" <+> ppr (ufmToList sigs),
- text "binds:" <+> pprCoreBinding (Rec pairs)]))
- (emptySigEnv, lazy_fv, orig_pairs) -- Safe output
- -- The lazy_fv part is really important! orig_pairs has no strictness
- -- info, including nothing about free vars. But if we have
- -- letrec f = ....y..... in ...f...
- -- where 'y' is free in f, we must record that y is mentioned,
- -- otherwise y will get recorded as absent altogether
-
- | otherwise = loop (n+1) sigs' pairs'
+ | n >= 10
+ = pprTrace "dmdFix loop" (ppr n <+> (vcat
+ [ text "Sigs:" <+> ppr [ (id,lookupSigEnv sigs id, lookupSigEnv sigs' id)
+ | (id,_) <- pairs],
+ text "env:" <+> ppr sigs,
+ text "binds:" <+> pprCoreBinding (Rec pairs)]))
+ (emptySigEnv, lazy_fv, orig_pairs) -- Safe output
+ -- The lazy_fv part is really important! orig_pairs has no strictness
+ -- info, including nothing about free vars. But if we have
+ -- letrec f = ....y..... in ...f...
+ -- where 'y' is free in f, we must record that y is mentioned,
+ -- otherwise y will get recorded as absent altogether
+
+ | otherwise
+ = loop (n+1) (setNonVirgin sigs') pairs'
where
found_fixpoint = all (same_sig sigs sigs') bndrs
-- Use the new signature to do the next pair
-- The occurrence analyser has arranged them in a good order
-- so this can significantly reduce the number of iterations needed
- ((sigs',lazy_fv), pairs') = mapAccumL (my_downRhs top_lvl) (sigs, emptyDmdEnv) pairs
+ ((sigs',lazy_fv), pairs') = mapAccumL my_downRhs (sigs, emptyDmdEnv) pairs
- my_downRhs top_lvl (sigs,lazy_fv) (id,rhs)
- = -- pprTrace "downRhs {" (ppr id <+> (ppr old_sig))
- -- (new_sig `seq`
- -- pprTrace "downRhsEnd" (ppr id <+> ppr new_sig <+> char '}' )
- ((sigs', lazy_fv'), pair')
- -- )
+ my_downRhs (sigs,lazy_fv) (id,rhs) = ((sigs', lazy_fv'), pair')
where
(sigs', lazy_fv1, pair') = dmdAnalRhs top_lvl Recursive sigs (id,rhs)
lazy_fv' = plusVarEnv_C both lazy_fv lazy_fv1
- -- old_sig = lookup sigs id
- -- new_sig = lookup sigs' id
same_sig sigs sigs' var = lookup sigs var == lookup sigs' var
- lookup sigs var = case lookupVarEnv sigs var of
+ lookup sigs var = case lookupSigEnv sigs var of
Just (sig,_) -> sig
Nothing -> pprPanic "dmdFix" (ppr var)
- -- Get an initial strictness signature from the Id
- -- itself. That way we make use of earlier iterations
- -- of the fixpoint algorithm. (Cunning plan.)
- -- Note that the cunning plan extends to the DmdEnv too,
- -- since it is part of the strictness signature
-initialSig :: Id -> StrictSig
-initialSig id = idStrictness_maybe id `orElse` botSig
-
dmdAnalRhs :: TopLevelFlag -> RecFlag
-> SigEnv -> (Id, CoreExpr)
-> (SigEnv, DmdEnv, (Id, CoreExpr))
sigs' = extendSigEnv top_lvl sigs id sig_ty
\end{code}
+
%************************************************************************
%* *
\subsection{Strictness signatures and types}
%************************************************************************
\begin{code}
-type SigEnv = VarEnv (StrictSig, TopLevelFlag)
- -- We use the SigEnv to tell us whether to
+data SigEnv
+ = SE { se_env :: VarEnv (StrictSig, TopLevelFlag)
+ , se_virgin :: Bool } -- True on first iteration only
+ -- See Note [Initialising strictness]
+ -- We use the se_env to tell us whether to
-- record info about a variable in the DmdEnv
-- We do so if it's a LocalId, but not top-level
--
-- The DmdEnv gives the demand on the free vars of the function
-- when it is given enough args to satisfy the strictness signature
+instance Outputable SigEnv where
+ ppr (SE { se_env = env, se_virgin = virgin })
+ = ptext (sLit "SE") <+> braces (vcat
+ [ ptext (sLit "se_virgin =") <+> ppr virgin
+ , ptext (sLit "se_env =") <+> ppr env ])
+
emptySigEnv :: SigEnv
-emptySigEnv = emptyVarEnv
+emptySigEnv = SE { se_env = emptyVarEnv, se_virgin = True }
extendSigEnv :: TopLevelFlag -> SigEnv -> Id -> StrictSig -> SigEnv
-extendSigEnv top_lvl env var sig = extendVarEnv env var (sig, top_lvl)
+extendSigEnv top_lvl sigs var sig
+ = sigs { se_env = extendVarEnv (se_env sigs) var (sig, top_lvl) }
+
+lookupSigEnv :: SigEnv -> Id -> Maybe (StrictSig, TopLevelFlag)
+lookupSigEnv sigs id = lookupVarEnv (se_env sigs) id
+
+addInitialSigs :: TopLevelFlag -> SigEnv -> [Id] -> SigEnv
+-- See Note [Initialising strictness]
+addInitialSigs top_lvl sigs@(SE { se_env = env, se_virgin = virgin }) ids
+ = sigs { se_env = extendVarEnvList env [ (id, (init_sig id, top_lvl))
+ | id <- ids ] }
+ where
+ init_sig | virgin = \_ -> botSig
+ | otherwise = idStrictness
-extendSigEnvList :: SigEnv -> [(Id, (StrictSig, TopLevelFlag))] -> SigEnv
-extendSigEnvList = extendVarEnvList
+setNonVirgin :: SigEnv -> SigEnv
+setNonVirgin sigs = sigs { se_virgin = False }
extendSigsWithLam :: SigEnv -> Id -> SigEnv
-- Extend the SigEnv when we meet a lambda binder
extendSigsWithLam sigs id
= case idDemandInfo_maybe id of
- Nothing -> extendVarEnv sigs id (cprSig, NotTopLevel)
+ Nothing -> extendSigEnv NotTopLevel sigs id cprSig
-- Optimistic in the Nothing case;
-- See notes [CPR-AND-STRICTNESS]
- Just (Eval (Prod _)) -> extendVarEnv sigs id (cprSig, NotTopLevel)
+ Just (Eval (Prod _)) -> extendSigEnv NotTopLevel sigs id cprSig
_ -> sigs
+\end{code}
+Note [Initialising strictness]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Our basic plan is to initialise the strictness of each Id in
+a recursive group to "bottom", and find a fixpoint from there.
+However, this group A might be inside an *enclosing* recursive
+group B, in which case we'll do the entire fixpoint shebang on A
+for each iteration of B.
-dmdTransform :: SigEnv -- The strictness environment
- -> Id -- The function
- -> Demand -- The demand on the function
- -> DmdType -- The demand type of the function in this context
- -- Returned DmdEnv includes the demand on
- -- this function plus demand on its free variables
-
-dmdTransform sigs var dmd
-
------- DATA CONSTRUCTOR
- | isDataConWorkId var -- Data constructor
- = let
- StrictSig dmd_ty = idStrictness var -- It must have a strictness sig
- DmdType _ _ con_res = dmd_ty
- arity = idArity var
- in
- if arity == call_depth then -- Saturated, so unleash the demand
- let
- -- Important! If we Keep the constructor application, then
- -- we need the demands the constructor places (always lazy)
- -- If not, we don't need to. For example:
- -- f p@(x,y) = (p,y) -- S(AL)
- -- g a b = f (a,b)
- -- It's vital that we don't calculate Absent for a!
- dmd_ds = case res_dmd of
- Box (Eval ds) -> mapDmds box ds
- Eval ds -> ds
- _ -> Poly Top
-
- -- ds can be empty, when we are just seq'ing the thing
- -- If so we must make up a suitable bunch of demands
- arg_ds = case dmd_ds of
- Poly d -> replicate arity d
- Prod ds -> ASSERT( ds `lengthIs` arity ) ds
-
- in
- mkDmdType emptyDmdEnv arg_ds con_res
- -- Must remember whether it's a product, hence con_res, not TopRes
- else
- topDmdType
-
------- IMPORTED FUNCTION
- | isGlobalId var, -- Imported function
- let StrictSig dmd_ty = idStrictness var
- = if dmdTypeDepth dmd_ty <= call_depth then -- Saturated, so unleash the demand
- dmd_ty
- else
- topDmdType
-
------- LOCAL LET/REC BOUND THING
- | Just (StrictSig dmd_ty, top_lvl) <- lookupVarEnv sigs var
- = let
- fn_ty | dmdTypeDepth dmd_ty <= call_depth = dmd_ty
- | otherwise = deferType dmd_ty
- -- NB: it's important to use deferType, and not just return topDmdType
- -- Consider let { f x y = p + x } in f 1
- -- The application isn't saturated, but we must nevertheless propagate
- -- a lazy demand for p!
- in
- if isTopLevel top_lvl then fn_ty -- Don't record top level things
- else addVarDmd fn_ty var dmd
-
------- LOCAL NON-LET/REC BOUND THING
- | otherwise -- Default case
- = unitVarDmd var dmd
+To speed things up, we initialise each iteration of B from the result
+of the last one, which is neatly recorded in each binder. That way we
+make use of earlier iterations of the fixpoint algorithm. (Cunning
+plan.)
- where
- (call_depth, res_dmd) = splitCallDmd dmd
-\end{code}
+But on the *first* iteration we want to *ignore* the current strictness
+of the Id, and start from "bottom". Nowadays the Id can have a current
+strictness, because interface files record strictness for nested bindings.
+To know when we are in the first iteration, we look at the se_virgin
+field of the SigEnv.
%************************************************************************
%* *
-\subsection{Demands}
+ Demands
%* *
%************************************************************************
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