[project @ 2002-12-11 15:36:20 by simonmar]

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

diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs
index 527004a..e02bf5e 100644 (file)
--- a/ghc/compiler/stranal/DmdAnal.lhs
+++ b/ghc/compiler/stranal/DmdAnal.lhs
@@ -23,12 +23,12 @@ import TyCon                ( isProductTyCon, isRecursiveTyCon )
 import Id              ( Id, idType, idInlinePragma,
                          isDataConId, isGlobalId, idArity,
 #ifdef OLD_STRICTNESS
-                         idDemandInfo,  idStrictness, idCprInfo,
+                         idDemandInfo,  idStrictness, idCprInfo, idName,
 #endif
                          idNewStrictness, idNewStrictness_maybe,
                          setIdNewStrictness, idNewDemandInfo,
                          idNewDemandInfo_maybe,
-                         setIdNewDemandInfo, idName 
+                         setIdNewDemandInfo
                        )
 #ifdef OLD_STRICTNESS
 import IdInfo          ( newStrictnessFromOld, newDemand )
@@ -487,11 +487,10 @@ We can't start with 'not-demanded' because then consider
 
 In the first iteration we'd have no demand info for x, so assume
 not-demanded; then we'd get TopRes for f's CPR info.  Next iteration
-we'd see that t was demanded, and so give it the CPR property, but
-by now f has TopRes, so it will stay TopRes.  
-ever_in
-Instead, with the Nothing setting the first time round, we say
-'yes t is demanded' the first time.  
+we'd see that t was demanded, and so give it the CPR property, but by
+now f has TopRes, so it will stay TopRes.  Instead, with the Nothing
+setting the first time round, we say 'yes t is demanded' the first
+time.
 
 However, this does mean that for non-recursive bindings we must
 iterate twice to be sure of not getting over-optimistic CPR info,
@@ -729,10 +728,15 @@ extendSigEnvList = extendVarEnvList
 
 extendSigsWithLam :: SigEnv -> Id -> SigEnv
 -- Extend the SigEnv when we meet a lambda binder
---  If the binder is marked demanded with a product demand, then give it a CPR 
+-- If the binder is marked demanded with a product demand, then give it a CPR 
 -- signature, because in the likely event that this is a lambda on a fn defn 
 -- [we only use this when the lambda is being consumed with a call demand],
--- it'll be w/w'd and so it will be CPR-ish.
+-- it'll be w/w'd and so it will be CPR-ish.  E.g.
+--     f = \x::(Int,Int).  if ...strict in x... then
+--                             x
+--                         else
+--                             (a,b)
+-- We want f to have the CPR property because x does, by the time f has been w/w'd
 --
 --     NOTE: see notes [CPR-AND-STRICTNESS]
 --
@@ -853,7 +857,7 @@ argDemand (Defer d) = lazyDmd
 argDemand (Eval ds) = Eval (mapDmds argDemand ds)
 argDemand (Box Bot) = evalDmd
 argDemand (Box d)   = box (argDemand d)
-argDemand Bot      = Abs       -- Don't pass args that are consumed by bottom/err
+argDemand Bot      = Abs       -- Don't pass args that are consumed (only) by bottom
 argDemand d        = d
 \end{code}