Remove unused imports

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

diff --git a/compiler/simplCore/SetLevels.lhs b/compiler/simplCore/SetLevels.lhs
index 4b4a349..0797ad7 100644 (file)
--- a/compiler/simplCore/SetLevels.lhs
+++ b/compiler/simplCore/SetLevels.lhs
@@ -60,7 +60,7 @@ import CoreUtils      ( exprType, exprIsTrivial, mkPiTypes )
 import CoreFVs         -- all of it
 import CoreSubst       ( Subst, emptySubst, extendInScope, extendIdSubst,
                          cloneIdBndr, cloneRecIdBndrs )
-import Id              ( Id, idType, mkSysLocal, isOneShotLambda,
+import Id              ( idType, mkSysLocal, isOneShotLambda,
                          zapDemandIdInfo, transferPolyIdInfo,
                          idSpecialisation, idWorkerInfo, setIdInfo
                        )
@@ -358,13 +358,22 @@ lvlExpr ctxt_lvl env (_, AnnCase expr case_bndr ty alts) = do
 @lvlMFE@ is just like @lvlExpr@, except that it might let-bind
 the expression, so that it can itself be floated.
 
-[NOTE: unlifted MFEs]
+Note [Unlifted MFEs]
+~~~~~~~~~~~~~~~~~~~~~
 We don't float unlifted MFEs, which potentially loses big opportunites.
 For example:
        \x -> f (h y)
 where h :: Int -> Int# is expensive. We'd like to float the (h y) outside
 the \x, but we don't because it's unboxed.  Possible solution: box it.
 
+Note [Case MFEs]
+~~~~~~~~~~~~~~~~
+We don't float a case expression as an MFE from a strict context.  Why not?
+Because in doing so we share a tiny bit of computation (the switch) but
+in exchange we build a thunk, which is bad.  This case reduces allocation 
+by 7% in spectral/puzzle (a rather strange benchmark) and 1.2% in real/fem.
+Doesn't change any other allocation at all.
+
 \begin{code}
 lvlMFE ::  Bool                        -- True <=> strict context [body of case or let]
        -> Level                -- Level of innermost enclosing lambda/tylam
@@ -375,9 +384,20 @@ 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) }
+
+-- Note [Case MFEs]
+lvlMFE True ctxt_lvl env e@(_, AnnCase {})
+  = lvlExpr ctxt_lvl env e     -- Don't share cases
 
 lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
-  |  isUnLiftedType ty                 -- Can't let-bind it; see [NOTE: unlifted MFEs]
+  |  isUnLiftedType ty                 -- Can't let-bind it; see Note [Unlifted MFEs]
   || isInlineCtxt ctxt_lvl             -- Don't float out of an __inline__ context
   || exprIsTrivial expr                        -- Never float if it's trivial
   || not good_destination
@@ -481,7 +501,9 @@ lvlBind :: TopLevelFlag             -- Used solely to decide whether to clone
        -> LvlM (LevelledBind, LevelEnv)
 
 lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
-  | isInlineCtxt ctxt_lvl              -- Don't do anything inside InlineMe
+  |  isTyVar bndr              -- Don't do anything for TyVar binders
+                               --   (simplifier gets rid of them pronto)
+  || isInlineCtxt ctxt_lvl     -- Don't do anything inside InlineMe
   = do rhs' <- lvlExpr ctxt_lvl env rhs
        return (NonRec (TB bndr ctxt_lvl) rhs', env)
 
@@ -595,7 +617,7 @@ lvlLamBndrs lvl bndrs
        [] bndrs
   where
     go old_lvl bumped_major rev_lvld_bndrs (bndr:bndrs)
-       | isId bndr &&                  -- Go to the next major level if this is a value binder,
+       | isId bndr &&                  -- Go to the next major level if this is a value binder,
          not bumped_major &&           -- and we havn't already gone to the next level (one jump per group)
          not (isOneShotLambda bndr)    -- and it isn't a one-shot lambda
        = go new_lvl True (TB bndr new_lvl : rev_lvld_bndrs) bndrs
@@ -681,10 +703,10 @@ initialEnv :: FloatOutSwitches -> LevelEnv
 initialEnv float_lams = (float_lams, emptyVarEnv, emptySubst, emptyVarEnv)
 
 floatLams :: LevelEnv -> Bool
-floatLams (FloatOutSw float_lams _, _, _, _) = float_lams
+floatLams (fos, _, _, _) = floatOutLambdas fos
 
 floatConsts :: LevelEnv -> Bool
-floatConsts (FloatOutSw _ float_consts, _, _, _) = float_consts
+floatConsts (fos, _, _, _) = floatOutConstants fos
 
 extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv
 -- Used when *not* cloning
@@ -841,7 +863,7 @@ newPolyBndrs dest_lvl env abs_vars bndrs = do
     let new_bndrs = zipWith mk_poly_bndr bndrs uniqs
     return (extendPolyLvlEnv dest_lvl env abs_vars (bndrs `zip` new_bndrs), new_bndrs)
   where
-    mk_poly_bndr bndr uniq = transferPolyIdInfo bndr $         -- Note [transferPolyIdInfo] in Id.lhs
+    mk_poly_bndr bndr uniq = transferPolyIdInfo bndr abs_vars $        -- Note [transferPolyIdInfo] in Id.lhs
                             mkSysLocal (mkFastString str) uniq poly_ty
                           where
                             str     = "poly_" ++ occNameString (getOccName bndr)