Inline into tail-called constructor args

Consider
	x = case y of { True -> (p,q); ... }

The occurrence analyser was marking p,q as 'Many', because they args
of a constructor in an RhsCtxt.  But actually they aren't in a RhsCtxt,
and in this case it's better to inline.

diff --git a/compiler/simplCore/OccurAnal.lhs b/compiler/simplCore/OccurAnal.lhs
index 00fdebe..8e19933 100644 (file)
--- a/compiler/simplCore/OccurAnal.lhs
+++ b/compiler/simplCore/OccurAnal.lhs
@@ -502,8 +502,8 @@ occAnal env expr@(Lam _ _)
     is_one_shot b   = isId b && isOneShotBndr b
 
 occAnal env (Case scrut bndr ty alts)
-  = case occ_anal_scrut scrut alts             of { (scrut_usage, scrut') ->
-    case mapAndUnzip (occAnalAlt env bndr) alts of { (alts_usage_s, alts')   -> 
+  = case occ_anal_scrut scrut alts                 of { (scrut_usage, scrut') ->
+    case mapAndUnzip (occAnalAlt alt_env bndr) alts of { (alts_usage_s, alts')   -> 
     let
        alts_usage  = foldr1 combineAltsUsageDetails alts_usage_s
        alts_usage' = addCaseBndrUsage alts_usage
@@ -523,6 +523,10 @@ occAnal env (Case scrut bndr ty alts)
                                Nothing  -> usage
                                Just occ -> extendVarEnv usage bndr (markMany occ)
 
+    alt_env = setVanillaCtxt env
+       -- Consider     x = case v of { True -> (p,q); ... }
+       -- Then it's fine to inline p and q
+
     occ_anal_scrut (Var v) (alt1 : other_alts)
                                | not (null other_alts) || not (isDefaultAlt alt1)
                                = (mkOneOcc env v True, Var v)
@@ -545,7 +549,6 @@ Applications are dealt with specially because we want
 the "build hack" to work.
 
 \begin{code}
--- Hack for build, fold, runST
 occAnalApp env (Var fun, args) is_rhs
   = case args_stuff of { (args_uds, args') ->
     let
@@ -566,6 +569,8 @@ occAnalApp env (Var fun, args) is_rhs
   where
     fun_uniq = idUnique fun
     fun_uds  = mkOneOcc env fun (valArgCount args > 0)
+
+               -- Hack for build, fold, runST
     args_stuff | fun_uniq == buildIdKey    = appSpecial env 2 [True,True]  args
                | fun_uniq == augmentIdKey  = appSpecial env 2 [True,True]  args
                | fun_uniq == foldrIdKey    = appSpecial env 3 [False,True] args
@@ -685,6 +690,10 @@ rhsCtxt     = OccEnv OccRhs     []
 isRhsEnv (OccEnv OccRhs     _) = True
 isRhsEnv (OccEnv OccVanilla _) = False
 
+setVanillaCtxt :: OccEnv -> OccEnv
+setVanillaCtxt (OccEnv OccRhs ctxt_ty) = OccEnv OccVanilla ctxt_ty
+setVanillaCtxt other_env              = other_env
+
 setCtxt :: OccEnv -> CtxtTy -> OccEnv
 setCtxt (OccEnv encl _) ctxt = OccEnv encl ctxt