Don't float an expression wrapped in a cast

There is no point in floating out an expression wrapped in a coercion;
If we do we'll transform
	lvl = e |> co [_$_]
to
	lvl' = e; lvl = lvl' |> co
and then inline lvl.  Better just to float out the payload (e).

diff --git a/compiler/simplCore/SetLevels.lhs b/compiler/simplCore/SetLevels.lhs
index 2c84589..e20bc83 100644 (file)
--- a/compiler/simplCore/SetLevels.lhs
+++ b/compiler/simplCore/SetLevels.lhs
@@ -376,6 +376,13 @@ lvlMFE ::  Bool                    -- True <=> strict context [body of case or let]
 lvlMFE _ _ _ (_, AnnType ty)
   = return (Type ty)
 
+-- No point in floating out an expression wrapped in a coercion;
+-- If we do we'll transform  lvl = e |> co 
+--                      to  lvl' = e; lvl = lvl' |> co
+-- and then inline lvl.  Better just to float out the payload.
+lvlMFE strict_ctxt ctxt_lvl env (_, AnnCast e co)
+  = do { expr' <- lvlMFE strict_ctxt ctxt_lvl env e
+       ; return (Cast expr' co) }
 
 lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
   |  isUnLiftedType ty                 -- Can't let-bind it; see Note [Unlifted MFEs]