-----------------
\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 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
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