More SpecConstr tuning

For some reason, SpecConstr wasn't taking account of let-bound constructors:
	let v = Just 4
	in ...(f v)...

Now it does.  An easy fix fortunately.

diff --git a/compiler/specialise/SpecConstr.lhs b/compiler/specialise/SpecConstr.lhs
index e6908ec..9570c24 100644 (file)
--- a/compiler/specialise/SpecConstr.lhs
+++ b/compiler/specialise/SpecConstr.lhs
@@ -22,7 +22,7 @@ import DataCon                ( dataConRepArity, isVanillaDataCon )
 import Type            ( tyConAppArgs, tyVarsOfTypes )
 import Unify           ( coreRefineTys )
 import Id              ( Id, idName, idType, isDataConWorkId_maybe, 
-                         mkUserLocal, mkSysLocal )
+                         mkUserLocal, mkSysLocal, idUnfolding )
 import Var             ( Var )
 import VarEnv
 import VarSet
@@ -638,10 +638,20 @@ argsToPats env us args = mapAccumL (argToPat env) us args
 \begin{code}
 is_con_app_maybe :: ConstrEnv -> CoreExpr -> Maybe ConValue
 is_con_app_maybe env (Var v)
-  = lookupVarEnv env v
-       -- You might think we could look in the idUnfolding here
-       -- but that doesn't take account of which branch of a 
-       -- case we are in, which is the whole point
+  = case lookupVarEnv env v of
+       Just stuff -> Just stuff
+               -- You might think we could look in the idUnfolding here
+               -- but that doesn't take account of which branch of a 
+               -- case we are in, which is the whole point
+
+       Nothing | isCheapUnfolding unf
+               -> is_con_app_maybe env (unfoldingTemplate unf)
+               where
+                 unf = idUnfolding v
+               -- However we do want to consult the unfolding as well,
+               -- for let-bound constructors!
+
+       other  -> Nothing
 
 is_con_app_maybe env (Lit lit)
   = Just (CV (LitAlt lit) [])