Big tidy-up of deriving code

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

diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs
index d13fa3b..fc9104f 100644 (file)
--- a/compiler/simplCore/OccurAnal.lhs
+++ b/compiler/simplCore/OccurAnal.lhs
@@ -23,14 +23,13 @@ import CoreUtils    ( exprIsTrivial, isDefaultAlt )
 import Id              ( isDataConWorkId, isOneShotBndr, setOneShotLambda, 
                          idOccInfo, setIdOccInfo, isLocalId,
                          isExportedId, idArity, idHasRules,
-                         idType, idUnique, Id
+                         idUnique, Id
                        )
 import BasicTypes      ( OccInfo(..), isOneOcc, InterestingCxt )
 
 import VarSet
 import VarEnv
 
-import Type            ( isFunTy, dropForAlls )
 import Maybes          ( orElse )
 import Digraph         ( stronglyConnCompR, SCC(..) )
 import PrelNames       ( buildIdKey, foldrIdKey, runSTRepIdKey, augmentIdKey )
@@ -301,7 +300,7 @@ reOrderCycle bndrs (bind : binds)
                -- where df is the exported dictionary. Then df makes a really
                -- bad choice for loop breaker
          
-       | not_fun_ty (idType bndr) = 3  -- Data types help with cases
+       | is_con_app rhs = 3    -- Data types help with cases
                -- This used to have a lower score than inlineCandidate, but
                -- it's *really* helpful if dictionaries get inlined fast,
                -- so I'm experimenting with giving higher priority to data-typed things
@@ -328,7 +327,16 @@ reOrderCycle bndrs (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 (isFunTy (dropForAlls ty))
+       -- Cheap and cheerful; the simplifer moves casts out of the way
+       -- The lambda case is important to spot x = /\a. C (f a)
+       -- which comes up when C is a dictionary constructor and
+       -- f is a default method.  
+       -- Example: the instance for Show (ST s a) in GHC.ST
+    is_con_app (Var v)    = isDataConWorkId v
+    is_con_app (App f _)  = is_con_app f
+    is_con_app (Lam b e) | isTyVar b = is_con_app e
+    is_con_app (Note _ e) = is_con_app e
+    is_con_app other      = False
 
 makeLoopBreaker :: VarSet              -- Binders of this group
                -> UsageDetails         -- Usage of this rhs (neglecting rules)
@@ -482,7 +490,10 @@ occAnal env (Note note body)
 
 occAnal env (Cast expr co)
   = case occAnal env expr of { (usage, expr') ->
-    (usage, Cast expr' co)
+    (markRhsUds env True usage, Cast expr' co)
+       -- If we see let x = y `cast` co
+       -- then mark y as 'Many' so that we don't
+       -- immediately inline y again. 
     }
 \end{code}
 
@@ -581,23 +592,13 @@ the "build hack" to work.
 occAnalApp env (Var fun, args) is_rhs
   = case args_stuff of { (args_uds, args') ->
     let
-       -- We mark the free vars of the argument of a constructor or PAP 
-       -- as "many", if it is the RHS of a let(rec).
-       -- This means that nothing gets inlined into a constructor argument
-       -- position, which is what we want.  Typically those constructor
-       -- arguments are just variables, or trivial expressions.
-       --
-       -- This is the *whole point* of the isRhsEnv predicate
-        final_args_uds
-               | isRhsEnv env,
-                 isDataConWorkId fun || valArgCount args < idArity fun
-               = mapVarEnv markMany args_uds
-               | otherwise = args_uds
+        final_args_uds = markRhsUds env is_pap args_uds
     in
     (fun_uds +++ final_args_uds, mkApps (Var fun) args') }
   where
     fun_uniq = idUnique fun
     fun_uds  = mkOneOcc env fun (valArgCount args > 0)
+    is_pap = isDataConWorkId fun || valArgCount args < idArity fun
 
                -- Hack for build, fold, runST
     args_stuff | fun_uniq == buildIdKey    = appSpecial env 2 [True,True]  args
@@ -628,6 +629,23 @@ occAnalApp env (fun, args) is_rhs
     in
     (final_uds, mkApps fun' args') }}
     
+
+markRhsUds :: OccEnv           -- Check if this is a RhsEnv
+          -> Bool              -- and this is true
+          -> UsageDetails      -- The do markMany on this
+          -> UsageDetails
+-- We mark the free vars of the argument of a constructor or PAP 
+-- as "many", if it is the RHS of a let(rec).
+-- This means that nothing gets inlined into a constructor argument
+-- position, which is what we want.  Typically those constructor
+-- arguments are just variables, or trivial expressions.
+--
+-- This is the *whole point* of the isRhsEnv predicate
+markRhsUds env is_pap arg_uds
+  | isRhsEnv env && is_pap = mapVarEnv markMany arg_uds
+  | otherwise             = arg_uds
+
+
 appSpecial :: OccEnv 
           -> Int -> CtxtTy     -- Argument number, and context to use for it
           -> [CoreExpr]