[project @ 2000-10-16 08:24:18 by simonpj]

[ghc-hetmet.git] / ghc / compiler / basicTypes / IdInfo.lhs

diff --git a/ghc/compiler/basicTypes/IdInfo.lhs b/ghc/compiler/basicTypes/IdInfo.lhs
index 1cf25b1..0db72f1 100644 (file)
--- a/ghc/compiler/basicTypes/IdInfo.lhs
+++ b/ghc/compiler/basicTypes/IdInfo.lhs
@@ -13,7 +13,7 @@ module IdInfo (
        vanillaIdInfo, mkIdInfo, seqIdInfo, megaSeqIdInfo,
 
        -- Zapping
-       zapFragileInfo, zapLamInfo, zapSpecPragInfo, copyIdInfo,
+       zapFragileInfo, zapLamInfo, zapSpecPragInfo, shortableIdInfo, copyIdInfo,
 
        -- Flavour
        IdFlavour(..), flavourInfo, 
@@ -55,10 +55,6 @@ module IdInfo (
        -- Specialisation
        specInfo, setSpecInfo,
 
-       -- Update
-       UpdateInfo, UpdateSpec,
-       mkUpdateInfo, updateInfo, updateInfoMaybe, ppUpdateInfo, setUpdateInfo,
-
        -- CAF info
        CafInfo(..), cafInfo, setCafInfo, ppCafInfo,
 
@@ -86,8 +82,7 @@ import Demand         -- Lots of stuff
 import Outputable      
 import Maybe            ( isJust )
 
-infixl         1 `setUpdateInfo`,
-         `setDemandInfo`,
+infixl         1 `setDemandInfo`,
          `setStrictnessInfo`,
          `setSpecInfo`,
          `setArityInfo`,
@@ -127,7 +122,6 @@ data IdInfo
        strictnessInfo  :: StrictnessInfo,      -- Strictness properties
         workerInfo      :: WorkerInfo,          -- Pointer to Worker Function
        unfoldingInfo   :: Unfolding,           -- Its unfolding
-       updateInfo      :: UpdateInfo,          -- Which args should be updated
        cafInfo         :: CafInfo,
        cprInfo         :: CprInfo,             -- Function always constructs a product result
         lbvarInfo      :: LBVarInfo,           -- Info about a lambda-bound variable
@@ -185,7 +179,6 @@ setUnfoldingInfo  info uf
        -- actually increases residency significantly. 
   = info { unfoldingInfo = uf }
 
-setUpdateInfo    info ud = info { updateInfo = ud }
 setDemandInfo    info dd = info { demandInfo = dd }
 setArityInfo     info ar = info { arityInfo = ar  }
 setCafInfo        info cf = info { cafInfo = cf }
@@ -214,7 +207,6 @@ mkIdInfo flv = IdInfo {
                    workerInfo          = NoWorker,
                    strictnessInfo      = NoStrictnessInfo,
                    unfoldingInfo       = noUnfolding,
-                   updateInfo          = NoUpdateInfo,
                    cafInfo             = MayHaveCafRefs,
                    cprInfo             = NoCPRInfo,
                    lbvarInfo           = NoLBVarInfo,
@@ -402,40 +394,6 @@ wrapperArity (HasWorker _ a) = a
 
 %************************************************************************
 %*                                                                     *
-\subsection[update-IdInfo]{Update-analysis info about an @Id@}
-%*                                                                     *
-%************************************************************************
-
-\begin{code}
-data UpdateInfo
-  = NoUpdateInfo
-  | SomeUpdateInfo UpdateSpec
-  deriving (Eq, Ord)
-      -- we need Eq/Ord to cross-chk update infos in interfaces
-
--- the form in which we pass update-analysis info between modules:
-type UpdateSpec = [Int]
-\end{code}
-
-\begin{code}
-mkUpdateInfo = SomeUpdateInfo
-
-updateInfoMaybe NoUpdateInfo       = Nothing
-updateInfoMaybe (SomeUpdateInfo []) = Nothing
-updateInfoMaybe (SomeUpdateInfo         u) = Just u
-\end{code}
-
-Text instance so that the update annotations can be read in.
-
-\begin{code}
-ppUpdateInfo NoUpdateInfo         = empty
-ppUpdateInfo (SomeUpdateInfo [])   = empty
-ppUpdateInfo (SomeUpdateInfo spec) = (<>) (ptext SLIT("__UA ")) (hcat (map int spec))
-  -- was "__U "; changed to avoid conflict with unfoldings.  KSW 1999-07.
-\end{code}
-
-%************************************************************************
-%*                                                                     *
 \subsection[CAF-IdInfo]{CAF-related information}
 %*                                                                     *
 %************************************************************************
@@ -649,26 +607,60 @@ copyIdInfo is used when shorting out a top-level binding
 where f is exported.  We are going to swizzle it around to
        f = BIG
        f_local = f
-but we must be careful to combine their IdInfos right.
-The fact that things can go wrong here is a bad sign, but I can't see
-how to make it 'patently right', so copyIdInfo is derived (pretty much) by trial and error
 
-Here 'from' is f_local, 'to' is f, and the result is attached to f
+BUT (a) we must be careful about messing up rules
+    (b) we must ensure f's IdInfo ends up right
+
+(a) Messing up the rules
+~~~~~~~~~~~~~~~~~~~~
+The example that went bad on me was this one:
+       
+    iterate :: (a -> a) -> a -> [a]
+    iterate = iterateList
+    
+    iterateFB c f x = x `c` iterateFB c f (f x)
+    iterateList f x =  x : iterateList f (f x)
+    
+    {-# RULES
+    "iterate"  forall f x.     iterate f x = build (\c _n -> iterateFB c f x)
+    "iterateFB"                iterateFB (:) = iterateList
+     #-}
+
+This got shorted out to:
+
+    iterateList :: (a -> a) -> a -> [a]
+    iterateList = iterate
+    
+    iterateFB c f x = x `c` iterateFB c f (f x)
+    iterate f x =  x : iterate f (f x)
+    
+    {-# RULES
+    "iterate"  forall f x.     iterate f x = build (\c _n -> iterateFB c f x)
+    "iterateFB"                iterateFB (:) = iterate
+     #-}
+
+And now we get an infinite loop in the rule system 
+       iterate f x -> build (\cn -> iterateFB c f x
+                   -> iterateFB (:) f x
+                   -> iterate f x
+
+Tiresome solution: don't do shorting out if f has rewrite rules.
+Hence shortableIdInfo.
+
+(b) Keeping the IdInfo right
+~~~~~~~~~~~~~~~~~~~~~~~~
+We want to move strictness/worker info from f_local to f, but keep the rest.
+Hence copyIdInfo.
 
 \begin{code}
-copyIdInfo :: IdInfo   -- From
-          -> IdInfo    -- To
-          -> IdInfo    -- To, updated with stuff from From; except flavour unchanged
-copyIdInfo from to = from { flavourInfo = flavourInfo to,
-                           specInfo = specInfo to,
-                           inlinePragInfo = inlinePragInfo to
+shortableIdInfo :: IdInfo -> Bool
+shortableIdInfo info = isEmptyCoreRules (specInfo info)
+
+copyIdInfo :: IdInfo   -- f_local
+          -> IdInfo    -- f (the exported one)
+          -> IdInfo    -- New info for f
+copyIdInfo f_local f = f { strictnessInfo = strictnessInfo f_local,
+                          workerInfo     = workerInfo     f_local,
+                          cprInfo        = cprInfo        f_local
                          }
-       -- It's important to preserve the inline pragma on 'f'; e.g. consider
-       --      {-# NOINLINE f #-}
-       --      f = local
-       --
-       -- similarly, transformation rules may be attached to f
-       -- and we want to preserve them.  
-       --
-       -- On the other hand, we want the strictness info from f_local.
 \end{code}