Define setIdUnfoldingLazily, and use it in Vectorise

Fixes a loop in the compiler, when running the dph tests

compiler/basicTypes/Id.lhs

@@ -76,6 +76,7 @@ module Id (
 	idOccInfo,
 
 	-- ** Writing 'IdInfo' fields
+	setIdUnfoldingLazily,
 	setIdUnfolding,
 	setIdArity,
 	setIdDemandInfo, 
@@ -119,7 +120,8 @@ import Util( count )
 import StaticFlags
 
 -- infixl so you can say (id `set` a `set` b)
-infixl 	1 `setIdUnfolding`,
+infixl 	1 `setIdUnfoldingLazily`,
+	  `setIdUnfolding`,
 	  `setIdArity`,
 	  `setIdOccInfo`,
 	  `setIdDemandInfo`,
@@ -496,6 +498,9 @@ realIdUnfolding :: Id -> Unfolding
 -- Expose the unfolding if there is one, including for loop breakers
 realIdUnfolding id = unfoldingInfo (idInfo id)
 
+setIdUnfoldingLazily :: Id -> Unfolding -> Id
+setIdUnfoldingLazily id unfolding = modifyIdInfo (`setUnfoldingInfoLazily` unfolding) id
+
 setIdUnfolding :: Id -> Unfolding -> Id
 setIdUnfolding id unfolding = modifyIdInfo (`setUnfoldingInfo` unfolding) id
 

compiler/vectorise/Vectorise.hs

@@ -168,7 +168,7 @@ vectTopBinder var inline expr
       vty  <- vectType (idType var)
 
       -- Make the vectorised version of binding's name, and set the unfolding used for inlining.
-      var' <- liftM (`setIdUnfolding` unfolding) 
+      var' <- liftM (`setIdUnfoldingLazily` unfolding) 
            $  cloneId mkVectOcc var vty
 
       -- Add the mapping between the plain and vectorised name to the state.