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
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.
\begin{code}
mk_sig_ty never_inline thunk_cpr_ok rhs (DmdType fv dmds res)
- | never_inline && not (isBotRes res)
- -- HACK ALERT
- -- Don't strictness-analyse NOINLINE things. Why not? Because
- -- the NOINLINE says "don't expose any of the inner workings at the call
- -- site" and the strictness is certainly an inner working.
- --
- -- More concretely, the demand analyser discovers the following strictness
- -- for unsafePerformIO: C(U(AV))
- -- But then consider
- -- unsafePerformIO (\s -> let r = f x in
- -- case writeIORef v r s of (# s1, _ #) ->
- -- (# s1, r #)
- -- The strictness analyser will find that the binding for r is strict,
- -- (becuase of uPIO's strictness sig), and so it'll evaluate it before
- -- doing the writeIORef. This actually makes tests/lib/should_run/memo002
- -- get a deadlock!
- --
- -- Solution: don't expose the strictness of unsafePerformIO.
- --
- -- But we do want to expose the strictness of error functions,
- -- which are also often marked NOINLINE
- -- {-# NOINLINE foo #-}
- -- foo x = error ("wubble buggle" ++ x)
- -- So (hack, hack) we only drop the strictness for non-bottom things
- -- This is all very unsatisfactory.
- = (deferEnv fv, topSig)
-
- | otherwise
= (lazy_fv, mkStrictSig dmd_ty)
where
dmd_ty = DmdType strict_fv final_dmds res'
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}