[project @ 2002-09-10 11:38:11 by simonpj]

Remove redundant debug printing

diff --git a/ghc/compiler/stranal/DmdAnal.lhs b/ghc/compiler/stranal/DmdAnal.lhs
index c42099d..527004a 100644 (file)
--- a/ghc/compiler/stranal/DmdAnal.lhs
+++ b/ghc/compiler/stranal/DmdAnal.lhs
@@ -270,18 +270,18 @@ dmdAnal sigs dmd (Let (NonRec id rhs) body)
        (body_ty1, id2)               = annotateBndr body_ty id1
        body_ty2                      = addLazyFVs body_ty1 lazy_fv
     in
-#ifdef DEBUG
-       -- If the actual demand is better than the vanilla
-       -- demand, we might do better to re-analyse with the
-       -- stronger demand.
-    (let vanilla_dmd = vanillaCall (idArity id)
-        actual_dmd  = idNewDemandInfo id2
-     in
-     if actual_dmd `betterDemand` vanilla_dmd && actual_dmd /= vanilla_dmd then
-       pprTrace "dmdLet: better demand" (ppr id <+> vcat [text "vanilla" <+> ppr vanilla_dmd,
-                                                          text "actual" <+> ppr actual_dmd])
-     else \x -> x)
-#endif
+       -- If the actual demand is better than the vanilla call
+       -- demand, you might think that we might do better to re-analyse 
+       -- the RHS with the stronger demand.
+       -- But (a) That seldom happens, because it means that *every* path in 
+       --         the body of the let has to use that stronger demand
+       -- (b) It often happens temporarily in when fixpointing, because
+       --     the recursive function at first seems to place a massive demand.
+       --     But we don't want to go to extra work when the function will
+       --     probably iterate to something less demanding.  
+       -- In practice, all the times the actual demand on id2 is more than
+       -- the vanilla call demand seem to be due to (b).  So we don't
+       -- bother to re-analyse the RHS.
     (body_ty2, Let (NonRec id2 rhs') body')    
 
 dmdAnal sigs dmd (Let (Rec pairs) body)