-----------------
\begin{code}
+{-# OPTIONS -w #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
module DmdAnal ( dmdAnalPgm, dmdAnalTopRhs,
both {- needed by WwLib -}
) where
import TysPrim ( realWorldStatePrimTy )
import UniqFM ( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
keysUFM, minusUFM, ufmToList, filterUFM )
-import Type ( isUnLiftedType, coreEqType )
+import Type ( isUnLiftedType, coreEqType, splitTyConApp_maybe )
+import Coercion ( coercionKind )
import CoreLint ( showPass, endPass )
-import Util ( mapAndUnzip, mapAccumL, mapAccumR, lengthIs )
+import Util ( mapAndUnzip, lengthIs )
import BasicTypes ( Arity, TopLevelFlag(..), isTopLevel, isNeverActive,
RecFlag(..), isRec )
import Maybes ( orElse, expectJust )
import Outputable
+
+import Data.List
\end{code}
To think about
dmdAnalPgm :: DynFlags -> [CoreBind] -> IO [CoreBind]
dmdAnalPgm dflags binds
= do {
- showPass dflags "Demand analysis" ;
let { binds_plus_dmds = do_prog binds } ;
-
- endPass dflags "Demand analysis"
- Opt_D_dump_stranal binds_plus_dmds ;
#ifdef OLD_STRICTNESS
-- Only if OLD_STRICTNESS is on, because only then is the old
-- strictness analyser run
dmdAnal sigs dmd (Var var)
= (dmdTransform sigs var dmd, Var var)
+dmdAnal sigs dmd (Cast e co)
+ = (dmd_ty, Cast e' co)
+ where
+ (dmd_ty, e') = dmdAnal sigs dmd' e
+ to_co = snd (coercionKind co)
+ dmd'
+ | Just (tc, args) <- splitTyConApp_maybe to_co
+ , isRecursiveTyCon tc = evalDmd
+ | otherwise = dmd
+ -- This coerce usually arises from a recursive
+ -- newtype, and we don't want to look inside them
+ -- for exactly the same reason that we don't look
+ -- inside recursive products -- we might not reach
+ -- a fixpoint. So revert to a vanilla Eval demand
+
dmdAnal sigs dmd (Note n e)
= (dmd_ty, Note n e')
where
- (dmd_ty, e') = dmdAnal sigs dmd' e
- dmd' = case n of
- Coerce _ _ -> evalDmd -- This coerce usually arises from a recursive
- other -> dmd -- newtype, and we don't want to look inside them
- -- for exactly the same reason that we don't look
- -- inside recursive products -- we might not reach
- -- a fixpoint. So revert to a vanilla Eval demand
+ (dmd_ty, e') = dmdAnal sigs dmd e
dmdAnal sigs dmd (App fun (Type ty))
= (fun_ty, App fun' (Type ty))
-- The insight is, of course, that a demand on y is a demand on the
-- scrutinee, so we need to `both` it with the scrut demand
- scrut_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b])
- `both`
+ alt_dmd = Eval (Prod [idNewDemandInfo b | b <- bndrs', isId b])
+ scrut_dmd = alt_dmd `both`
idNewDemandInfo case_bndr'
(scrut_ty, scrut') = dmdAnal sigs scrut_dmd scrut
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If the rhs is a thunk, we usually forget the CPR info, because
it is presumably shared (else it would have been inlined, and
-so we'd lose sharing if w/w'd it into a function.
+so we'd lose sharing if w/w'd it into a function). E.g.
+
+ let r = case expensive of
+ (a,b) -> (b,a)
+ in ...
+
+If we marked r as having the CPR property, then we'd w/w into
+
+ let $wr = \() -> case expensive of
+ (a,b) -> (# b, a #)
+ r = case $wr () of
+ (# b,a #) -> (b,a)
+ in ...
+
+But now r is a thunk, which won't be inlined, so we are no further ahead.
+But consider
+
+ f x = let r = case expensive of (a,b) -> (b,a)
+ in if foo r then r else (x,x)
+
+Does f have the CPR property? Well, no.
However, if the strictness analyser has figured out (in a previous
iteration) that it's strict, then we DON'T need to forget the CPR info.
by dmdAnalTopBind.
+Note [NOINLINE and strictness]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+The strictness analyser used to have a HACK which ensured that NOINLNE
+things were not strictness-analysed. The reason was unsafePerformIO.
+Left to itself, the strictness analyser would discover this strictness
+for unsafePerformIO:
+ unsafePerformIO: C(U(AV))
+But then consider this sub-expression
+ unsafePerformIO (\s -> let r = f x in
+ case writeIORef v r s of (# s1, _ #) ->
+ (# s1, r #)
+The strictness analyser will now find that r is sure to be eval'd,
+and may then hoist it out. This makes tests/lib/should_run/memo002
+deadlock.
+
+Solving this by making all NOINLINE things have no strictness info is overkill.
+In particular, it's overkill for runST, which is perfectly respectable.
+Consider
+ f x = runST (return x)
+This should be strict in x.
+
+So the new plan is to define unsafePerformIO using the 'lazy' combinator:
+
+ unsafePerformIO (IO m) = lazy (case m realWorld# of (# _, r #) -> r)
+
+Remember, 'lazy' is a wired-in identity-function Id, of type a->a, which is
+magically NON-STRICT, and is inlined after strictness analysis. So
+unsafePerformIO will look non-strict, and that's what we want.
+
+Now we don't need the hack in the strictness analyser. HOWEVER, this
+decision does mean that even a NOINLINE function is not entirely
+opaque: some aspect of its implementation leaks out, notably its
+strictness. For example, if you have a function implemented by an
+error stub, but which has RULES, you may want it not to be eliminated
+in favour of error!
+
+
\begin{code}
mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res)
= (lazy_fv, mkStrictSig dmd_ty)
+ -- Re unused never_inline, see Note [NOINLINE and strictness]
where
dmd_ty = DmdType strict_fv final_dmds res'
%************************************************************************
\begin{code}
-splitDmdTy :: DmdType -> (Demand, DmdType)
--- Split off one function argument
--- We already have a suitable demand on all
--- free vars, so no need to add more!
-splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
-splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty)
-\end{code}
-
-\begin{code}
unitVarDmd var dmd = DmdType (unitVarEnv var dmd) [] TopRes
addVarDmd top_lvl dmd_ty@(DmdType fv ds res) var dmd
annotateBndrs = mapAccumR annotateBndr
+annotateLamIdBndr :: DmdType -- Demand type of body
+ -> Id -- Lambda binder
+ -> (DmdType, -- Demand type of lambda
+ Id) -- and binder annotated with demand
+
annotateLamIdBndr dmd_ty@(DmdType fv ds res) id
-- For lambdas we add the demand to the argument demands
-- Only called for Ids
%************************************************************************
\begin{code}
+splitDmdTy :: DmdType -> (Demand, DmdType)
+-- Split off one function argument
+-- We already have a suitable demand on all
+-- free vars, so no need to add more!
+splitDmdTy (DmdType fv (dmd:dmds) res_ty) = (dmd, DmdType fv dmds res_ty)
+splitDmdTy ty@(DmdType fv [] res_ty) = (resTypeArgDmd res_ty, ty)
+
splitCallDmd :: Demand -> (Int, Demand)
splitCallDmd (Call d) = case splitCallDmd d of
(n, r) -> (n+1, r)
-- Notice that we throw away info about both arguments and results
-- For example, f = let ... in \x -> x
-- We don't want to get a stricness type V->T for f.
- -- Peter??
deferEnv :: DmdEnv -> DmdEnv
deferEnv fv = mapVarEnv defer fv
lub (Box d1) (Box d2) = box (d1 `lub` d2)
lub d1@(Box _) d2 = d2 `lub` d1
-lubs = zipWithDmds lub
+lubs ds1 ds2 = zipWithDmds lub ds1 ds2
---------------------
-- box is the smart constructor for Box
both (Defer ds1) (Defer ds2) = deferEval (ds1 `boths` ds2)
both d1@(Defer ds1) d2 = d2 `both` d1
-boths = zipWithDmds both
+boths ds1 ds2 = zipWithDmds both ds1 ds2
\end{code}
projects / ghc-hetmet.git / blobdiff