#include "HsVersions.h"
import CoreSyn
-
-import DynFlags ( FloatOutSwitches(..) )
-import CoreUtils ( exprType, exprIsTrivial, mkPiTypes )
+import CoreMonad ( FloatOutSwitches(..) )
+import CoreUtils ( exprType, mkPiTypes )
import CoreArity ( exprBotStrictness_maybe )
import CoreFVs -- all of it
import CoreSubst ( Subst, emptySubst, extendInScope, extendInScopeList,
extendIdSubst, cloneIdBndr, cloneRecIdBndrs )
-import Id ( idType, mkSysLocal, isOneShotLambda,
- zapDemandIdInfo, transferPolyIdInfo,
- idSpecialisation, idUnfolding, setIdInfo,
- setIdNewStrictness, setIdArity
- )
+import Id
import IdInfo
import Var
import VarSet
import VarEnv
-import Name ( getOccName )
+import Demand ( StrictSig, increaseStrictSigArity )
+import Name ( getOccName, mkSystemVarName )
import OccName ( occNameString )
import Type ( isUnLiftedType, Type )
-import BasicTypes ( TopLevelFlag(..) )
+import BasicTypes ( TopLevelFlag(..), Arity )
import UniqSupply
import Util ( sortLe, isSingleton, count )
import Outputable
lvlExpr _ env (_, AnnVar v) = return (lookupVar env v)
lvlExpr _ _ (_, AnnLit lit) = return (Lit lit)
-lvlExpr ctxt_lvl env (_, AnnApp fun arg) = do
- fun' <- lvl_fun fun
- arg' <- lvlMFE False ctxt_lvl env arg
- return (App fun' arg')
- where
--- gaw 2004
- lvl_fun (_, AnnCase _ _ _ _) = lvlMFE True ctxt_lvl env fun
- lvl_fun _ = lvlExpr ctxt_lvl env fun
- -- We don't do MFE on partial applications generally,
- -- but we do if the function is big and hairy, like a case
+lvlExpr ctxt_lvl env expr@(_, AnnApp _ _) = do
+ let
+ (fun, args) = collectAnnArgs expr
+ --
+ case fun of
+ -- float out partial applications. This is very beneficial
+ -- in some cases (-7% runtime -4% alloc over nofib -O2).
+ -- In order to float a PAP, there must be a function at the
+ -- head of the application, and the application must be
+ -- over-saturated with respect to the function's arity.
+ (_, AnnVar f) | floatPAPs env &&
+ arity > 0 && arity < n_val_args ->
+ do
+ let (lapp, rargs) = left (n_val_args - arity) expr []
+ rargs' <- mapM (lvlMFE False ctxt_lvl env) rargs
+ lapp' <- lvlMFE False ctxt_lvl env lapp
+ return (foldl App lapp' rargs')
+ where
+ n_val_args = count (isValArg . deAnnotate) args
+ arity = idArity f
+
+ -- separate out the PAP that we are floating from the extra
+ -- arguments, by traversing the spine until we have collected
+ -- (n_val_args - arity) value arguments.
+ left 0 e rargs = (e, rargs)
+ left n (_, AnnApp f a) rargs
+ | isValArg (deAnnotate a) = left (n-1) f (a:rargs)
+ | otherwise = left n f (a:rargs)
+ left _ _ _ = panic "SetLevels.lvlExpr.left"
+
+ -- No PAPs that we can float: just carry on with the
+ -- arguments and the function.
+ _otherwise -> do
+ args' <- mapM (lvlMFE False ctxt_lvl env) args
+ fun' <- lvlExpr ctxt_lvl env fun
+ return (foldl App fun' args')
lvlExpr ctxt_lvl env (_, AnnNote note expr) = do
expr' <- lvlExpr ctxt_lvl env expr
we'd like to float the call to error, to get
lvl = error "urk"
f = \x. g lvl
-But, it's very helpful for lvl to get a strictness signature, so that,
-for example, its unfolding is not exposed in interface files (unnecessary).
-But this float-out might occur after strictness analysis. So we use the
-cheap-and-cheerful exprBotStrictness_maybe function.
+Furthermore, we want to float a bottoming expression even if it has free
+variables:
+ f = \x. g (let v = h x in error ("urk" ++ v))
+Then we'd like to abstact over 'x' can float the whole arg of g:
+ lvl = \x. let v = h x in error ("urk" ++ v)
+ f = \x. g (lvl x)
+See Maessen's paper 1999 "Bottom extraction: factoring error handling out
+of functional programs" (unpublished I think).
+
+When we do this, we set the strictness and arity of the new bottoming
+Id, so that it's properly exposed as such in the interface file, even if
+this is all happening after strictness analysis.
+
+Note [Bottoming floats: eta expansion] c.f Note [Bottoming floats]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Tiresomely, though, the simplifier has an invariant that the manifest
+arity of the RHS should be the same as the arity; but we can't call
+etaExpand during SetLevels because it works over a decorated form of
+CoreExpr. So we do the eta expansion later, in FloatOut.
Note [Case MFEs]
~~~~~~~~~~~~~~~~
lvlMFE strict_ctxt ctxt_lvl env ann_expr@(fvs, _)
| isUnLiftedType ty -- Can't let-bind it; see Note [Unlifted MFEs]
- || exprIsTrivial expr -- Never float if it's trivial
+ || notWorthFloating ann_expr abs_vars
|| not good_destination
= -- Don't float it out
lvlExpr ctxt_lvl env ann_expr
| otherwise -- Float it out!
= do expr' <- lvlFloatRhs abs_vars dest_lvl env ann_expr
- var <- newLvlVar "lvl" abs_vars ty
- -- Note [Bottoming floats]
- let var_w_str = case exprBotStrictness_maybe expr of
- Just (arity,str) -> var `setIdArity` arity
- `setIdNewStrictness` str
- Nothing -> var
- return (Let (NonRec (TB var_w_str dest_lvl) expr')
- (mkVarApps (Var var_w_str) abs_vars))
+ var <- newLvlVar abs_vars ty mb_bot
+ return (Let (NonRec (TB var dest_lvl) expr')
+ (mkVarApps (Var var) abs_vars))
where
expr = deAnnotate ann_expr
ty = exprType expr
- dest_lvl = destLevel env fvs (isFunction ann_expr)
+ mb_bot = exprBotStrictness_maybe expr
+ dest_lvl = destLevel env fvs (isFunction ann_expr) mb_bot
abs_vars = abstractVars dest_lvl env fvs
-- A decision to float entails let-binding this thing, and we only do
-- concat = /\ a -> lvl a
-- lvl = /\ a -> foldr ..a.. (++) []
-- which is pretty stupid. Hence the strict_ctxt test
+
+annotateBotStr :: Id -> Maybe (Arity, StrictSig) -> Id
+annotateBotStr id Nothing = id
+annotateBotStr id (Just (arity,sig)) = id `setIdArity` arity
+ `setIdStrictness` sig
+
+notWorthFloating :: CoreExprWithFVs -> [Var] -> Bool
+-- Returns True if the expression would be replaced by
+-- something bigger than it is now. For example:
+-- abs_vars = tvars only: return True if e is trivial,
+-- but False for anything bigger
+-- abs_vars = [x] (an Id): return True for trivial, or an application (f x)
+-- but False for (f x x)
+--
+-- One big goal is that floating should be idempotent. Eg if
+-- we replace e with (lvl79 x y) and then run FloatOut again, don't want
+-- to replace (lvl79 x y) with (lvl83 x y)!
+
+notWorthFloating e abs_vars
+ = go e (count isId abs_vars)
+ where
+ go (_, AnnVar {}) n = n >= 0
+ go (_, AnnLit {}) n = n >= 0
+ go (_, AnnCast e _) n = go e n
+ go (_, AnnApp e arg) n
+ | (_, AnnType {}) <- arg = go e n
+ | n==0 = False
+ | is_triv arg = go e (n-1)
+ | otherwise = False
+ go _ _ = False
+
+ is_triv (_, AnnLit {}) = True -- Treat all literals as trivial
+ is_triv (_, AnnVar {}) = True -- (ie not worth floating)
+ is_triv (_, AnnCast e _) = is_triv e
+ is_triv (_, AnnApp e (_, AnnType {})) = is_triv e
+ is_triv _ = False
\end{code}
Note [Escaping a value lambda]
-> LvlM (LevelledBind, LevelEnv)
lvlBind top_lvl ctxt_lvl env (AnnNonRec bndr rhs@(rhs_fvs,_))
- | isTyVar bndr -- Don't do anything for TyVar binders
+ | isTyCoVar bndr -- Don't do anything for TyVar binders
-- (simplifier gets rid of them pronto)
= do rhs' <- lvlExpr ctxt_lvl env rhs
return (NonRec (TB bndr ctxt_lvl) rhs', env)
| otherwise
= do -- Yes, type abstraction; create a new binder, extend substitution, etc
rhs' <- lvlFloatRhs abs_vars dest_lvl env rhs
- (env', [bndr']) <- newPolyBndrs dest_lvl env abs_vars [bndr]
+ (env', [bndr']) <- newPolyBndrs dest_lvl env abs_vars [bndr_w_str]
return (NonRec (TB bndr' dest_lvl) rhs', env')
where
- bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
- abs_vars = abstractVars dest_lvl env bind_fvs
- dest_lvl = destLevel env bind_fvs (isFunction rhs)
+ bind_fvs = rhs_fvs `unionVarSet` idFreeVars bndr
+ abs_vars = abstractVars dest_lvl env bind_fvs
+ dest_lvl = destLevel env bind_fvs (isFunction rhs) mb_bot
+ mb_bot = exprBotStrictness_maybe (deAnnotate rhs)
+ bndr_w_str = annotateBotStr bndr mb_bot
\end{code}
`minusVarSet`
mkVarSet bndrs
- dest_lvl = destLevel env bind_fvs (all isFunction rhss)
+ dest_lvl = destLevel env bind_fvs (all isFunction rhss) Nothing
abs_vars = abstractVars dest_lvl env bind_fvs
----------------------------------------------------
--- Three help functons for the type-abstraction case
+-- Three help functions for the type-abstraction case
lvlFloatRhs :: [CoreBndr] -> Level -> LevelEnv -> CoreExprWithFVs
-> UniqSM (Expr (TaggedBndr Level))
\begin{code}
-- Destintion level is the max Id level of the expression
-- (We'll abstract the type variables, if any.)
-destLevel :: LevelEnv -> VarSet -> Bool -> Level
-destLevel env fvs is_function
+destLevel :: LevelEnv -> VarSet -> Bool -> Maybe (Arity, StrictSig) -> Level
+destLevel env fvs is_function mb_bot
+ | Just {} <- mb_bot = tOP_LEVEL -- Send bottoming bindings to the top
+ -- regardless; see Note [Bottoming floats]
| floatLams env
- && is_function = tOP_LEVEL -- Send functions to top level; see
+ && is_function = tOP_LEVEL -- Send functions to top level; see
-- the comments with isFunction
- | otherwise = maxIdLevel env fvs
+ | otherwise = maxIdLevel env fvs
isFunction :: CoreExprWithFVs -> Bool
-- The idea here is that we want to float *functions* to
floatConsts :: LevelEnv -> Bool
floatConsts (fos, _, _, _) = floatOutConstants fos
+floatPAPs :: LevelEnv -> Bool
+floatPAPs (fos, _, _, _) = floatOutPartialApplications fos
+
extendLvlEnv :: LevelEnv -> [TaggedBndr Level] -> LevelEnv
-- Used when *not* cloning
extendLvlEnv (float_lams, lvl_env, subst, id_env) prs
(False, True) -> False
_ -> v1 <= v2 -- Same family
- is_tv v = isTyVar v && not (isCoVar v)
+ is_tv v = isTyCoVar v && not (isCoVar v)
uniq :: [Var] -> [Var]
-- Remove adjacent duplicates; the sort will have brought them together
-- We are going to lambda-abstract, so nuke any IdInfo,
-- and add the tyvars of the Id (if necessary)
- zap v | isId v = WARN( isInlineRule (idUnfolding v) ||
+ zap v | isId v = WARN( isStableUnfolding (idUnfolding v) ||
not (isEmptySpecInfo (idSpecialisation v)),
text "absVarsOf: discarding info on" <+> ppr v )
setIdInfo v vanillaIdInfo
str = "poly_" ++ occNameString (getOccName bndr)
poly_ty = mkPiTypes abs_vars (idType bndr)
-newLvlVar :: String
- -> [CoreBndr] -> Type -- Abstract wrt these bndrs
+newLvlVar :: [CoreBndr] -> Type -- Abstract wrt these bndrs
+ -> Maybe (Arity, StrictSig) -- Note [Bottoming floats]
-> LvlM Id
-newLvlVar str vars body_ty = do
- uniq <- getUniqueM
- return (mkSysLocal (mkFastString str) uniq (mkPiTypes vars body_ty))
+newLvlVar vars body_ty mb_bot
+ = do { uniq <- getUniqueM
+ ; return (mkLocalIdWithInfo (mk_name uniq) (mkPiTypes vars body_ty) info) }
+ where
+ mk_name uniq = mkSystemVarName uniq (mkFastString "lvl")
+ arity = count isId vars
+ info = case mb_bot of
+ Nothing -> vanillaIdInfo
+ Just (bot_arity, sig) -> vanillaIdInfo
+ `setArityInfo` (arity + bot_arity)
+ `setStrictnessInfo` Just (increaseStrictSigArity arity sig)
-- The deeply tiresome thing is that we have to apply the substitution
-- to the rules inside each Id. Grr. But it matters.