X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2Fstranal%2FDmdAnal.lhs;h=84c189e56bb74e2c9d2d85860253eca99f9c7f31;hb=262c142b90c94ca1aa577c950a6ceae1f255e2d6;hp=3fc84773af953823e92b89a5eeaf125dd1612aac;hpb=a4c34367ce3e836f52f0ffb1e379ce81b8d65316;p=ghc-hetmet.git

diff --git a/compiler/stranal/DmdAnal.lhs b/compiler/stranal/DmdAnal.lhs
index 3fc8477..84c189e 100644
--- a/compiler/stranal/DmdAnal.lhs
+++ b/compiler/stranal/DmdAnal.lhs
@@ -43,11 +43,13 @@ import UniqFM		( plusUFM_C, addToUFM_Directly, lookupUFM_Directly,
 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
@@ -262,8 +264,8 @@ 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
@@ -474,7 +476,27 @@ 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.
@@ -971,7 +993,7 @@ 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
@@ -1078,7 +1100,7 @@ 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}