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

[ghc-hetmet.git] / ghc / compiler / simplCore / OccurAnal.lhs

diff --git a/ghc/compiler/simplCore/OccurAnal.lhs b/ghc/compiler/simplCore/OccurAnal.lhs
index 3ac0dcc..02fe904 100644 (file)
--- a/ghc/compiler/simplCore/OccurAnal.lhs
+++ b/ghc/compiler/simplCore/OccurAnal.lhs
@@ -26,13 +26,14 @@ import Id           ( isDataConId, isOneShotLambda, setOneShotLambda,
                          idSpecialisation, isLocalId,
                          idType, idUnique, Id
                        )
-import IdInfo          ( OccInfo(..), shortableIdInfo, copyIdInfo )
+import IdInfo          ( copyIdInfo )
+import BasicTypes      ( OccInfo(..), isOneOcc )
 
 import VarSet
 import VarEnv
 
-import Type            ( splitFunTy_maybe, splitForAllTys )
-import Maybes          ( maybeToBool, orElse )
+import Type            ( isFunTy, dropForAlls )
+import Maybes          ( orElse )
 import Digraph         ( stronglyConnCompR, SCC(..) )
 import PrelNames       ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
 import Unique          ( Unique )
@@ -194,6 +195,9 @@ shortMeOut ind_env exported_id local_id
    
        not (local_id `elemVarEnv` ind_env)     -- Only if not already substituted for
     then
+       True
+
+{- No longer needed
        if shortableIdInfo (idInfo exported_id)         -- Only if its IdInfo is 'shortable'
                                                        -- (see the defn of IdInfo.shortableIdInfo)
        then True
@@ -202,6 +206,7 @@ shortMeOut ind_env exported_id local_id
           pprTrace "shortMeOut:" (ppr exported_id)
 #endif
                                                 False
+-}
     else
        False
 \end{code}
@@ -241,7 +246,7 @@ occAnalBind env (NonRec binder rhs) body_usage
 
   where
     (final_body_usage, tagged_binder) = tagBinder body_usage binder
-    (rhs_usage, rhs')                = occAnalRhs env binder rhs
+    (rhs_usage, rhs')                = occAnalRhs env tagged_binder rhs
 \end{code}
 
 Dropping dead code for recursive bindings is done in a very simple way:
@@ -468,9 +473,7 @@ reOrderRec env (CyclicSCC (bind : binds))
 
     inlineCandidate :: Id -> CoreExpr -> Bool
     inlineCandidate id (Note InlineMe _) = True
-    inlineCandidate id rhs              = case idOccInfo id of
-                                               OneOcc _ _ -> True
-                                               other      -> False
+    inlineCandidate id rhs              = isOneOcc (idOccInfo id)
 
        -- Real example (the Enum Ordering instance from PrelBase):
        --      rec     f = \ x -> case d of (p,q,r) -> p x
@@ -482,9 +485,7 @@ reOrderRec env (CyclicSCC (bind : binds))
        -- we didn't stupidly choose d as the loop breaker.
        -- But we won't because constructor args are marked "Many".
 
-    not_fun_ty ty = not (maybeToBool (splitFunTy_maybe rho_ty))
-                 where
-                   (_, rho_ty) = splitForAllTys ty
+    not_fun_ty ty = not (isFunTy (dropForAlls ty))
 \end{code}
 
 @occAnalRhs@ deals with the question of bindings where the Id is marked
@@ -501,12 +502,34 @@ ToDo: try using the occurrence info for the inline'd binder.
 \begin{code}
 occAnalRhs :: OccEnv
           -> Id -> CoreExpr    -- Binder and rhs
+                               -- For non-recs the binder is alrady tagged
+                               -- with occurrence info
           -> (UsageDetails, CoreExpr)
 
 occAnalRhs env id rhs
   = (final_usage, rhs')
   where
-    (rhs_usage, rhs') = occAnal (rhsCtxt env) rhs
+    (rhs_usage, rhs') = occAnal ctxt rhs
+    ctxt | certainly_inline id = env
+        | otherwise           = rhsCtxt env
+       -- Note that we generally use an rhsCtxt.  This tells the occ anal n
+       -- that it's looking at an RHS, which has an effect in occAnalApp
+       --
+       -- But there's a problem.  Consider
+       --      x1 = a0 : []
+       --      x2 = a1 : x1
+       --      x3 = a2 : x2
+       --      g  = f x3
+       -- First time round, it looks as if x1 and x2 occur as an arg of a 
+       -- let-bound constructor ==> give them a many-occurrence.
+       -- But then x3 is inlined (unconditionally as it happens) and
+       -- next time round, x2 will be, and the next time round x1 will be
+       -- Result: multiple simplifier iterations.  Sigh.  
+       -- Crude solution: use rhsCtxt for things that occur just once...
+
+    certainly_inline id = case idOccInfo id of
+                           OneOcc in_lam one_br -> not in_lam && one_br
+                           other                -> False
 
        -- [March 98] A new wrinkle is that if the binder has specialisations inside
        -- it then we count the specialised Ids as "extra rhs's".  That way
@@ -518,6 +541,7 @@ occAnalRhs env id rhs
     add v u = addOneOcc u v NoOccInfo          -- Give a non-committal binder info
                                                -- (i.e manyOcc) because many copies
                                                -- of the specialised thing can appear
+
 \end{code}
 
 Expressions
@@ -622,7 +646,7 @@ occAnal env expr@(Lam _ _)
     (binders, body)   = collectBinders expr
     (linear, env1, _) = oneShotGroup env binders
     env2             = env1 `addNewCands` binders      -- Add in-scope binders
-    env_body         = vanillaCtxt env2                        -- Body is (no longer) an RhsContext
+    env_body         = vanillaCtxt env2                -- Body is (no longer) an RhsContext
 
 occAnal env (Case scrut bndr alts)
   = case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts')   ->