Fix CodingStyle#Warnings URLs

[ghc-hetmet.git] / compiler / stranal / DmdAnal.lhs

diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs
index 127fa78..a939907 100644 (file)
--- a/compiler/stranal/DmdAnal.lhs
+++ b/compiler/stranal/DmdAnal.lhs
@@ -7,6 +7,13 @@
                        -----------------
 
 \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
@@ -40,13 +47,16 @@ import TysWiredIn   ( unboxedPairDataCon )
 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
@@ -164,16 +174,25 @@ dmdAnal sigs dmd (Lit lit)
 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))
@@ -252,8 +271,8 @@ dmdAnal sigs dmd (Case scrut case_bndr ty [alt@(DataAlt dc,bndrs,rhs)])
        -- 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
@@ -464,7 +483,27 @@ The thunk_cpr_ok stuff [CPR-AND-STRICTNESS]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 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.
@@ -961,7 +1000,7 @@ lub d1@(Eval _) d2           = d2 `lub` d1 -- Bot,Abs,Top,Call,Defer
 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
@@ -1068,7 +1107,7 @@ both d1@(Eval ds1) d2            = d2 `both` d1
 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}