-- | Commonly useful utilites for manipulating the Core language
module CoreUtils (
-- * Constructing expressions
- mkInlineMe, mkSCC, mkCoerce, mkCoerceI,
+ mkSCC, mkCoerce,
bindNonRec, needsCaseBinding,
mkAltExpr, mkPiType, mkPiTypes,
-- * Properties of expressions
exprType, coreAltType, coreAltsType,
- exprIsDupable, exprIsTrivial, exprIsCheap, exprIsExpandable,
- exprIsHNF,exprOkForSpeculation, exprIsBig,
- exprIsConApp_maybe, exprIsBottom,
- rhsIsStatic,
+ exprIsDupable, exprIsTrivial, exprIsBottom,
+ exprIsCheap, exprIsExpandable, exprIsCheap', CheapAppFun,
+ exprIsHNF, exprOkForSpeculation, exprIsBig, exprIsConLike,
+ rhsIsStatic, isCheapApp, isExpandableApp,
-- * Expression and bindings size
coreBindsSize, exprSize,
+ CoreStats(..), coreBindsStats,
-- * Hashing
hashExpr,
-- * Equality
- cheapEqExpr,
+ cheapEqExpr, eqExpr, eqExprX,
+
+ -- * Eta reduction
+ tryEtaReduce,
-- * Manipulating data constructors and types
applyTypeToArgs, applyTypeToArg,
- dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
+ dataConRepInstPat, dataConRepFSInstPat
) where
#include "HsVersions.h"
import Var
import SrcLoc
import VarEnv
+import VarSet
import Name
-import Module
-#if mingw32_TARGET_OS
-import Packages
-#endif
import Literal
import DataCon
import PrimOp
import Id
import IdInfo
-import NewDemand
import Type
import Coercion
import TyCon
import FastString
import Maybes
import Util
+import Pair
import Data.Word
import Data.Bits
-
-import GHC.Exts -- For `xori`
\end{code}
-- really be said to have a type
exprType (Var var) = idType var
exprType (Lit lit) = literalType lit
+exprType (Coercion co) = coercionType co
exprType (Let _ body) = exprType body
exprType (Case _ _ ty _) = ty
-exprType (Cast _ co) = snd (coercionKind co)
+exprType (Cast _ co) = pSnd (coercionKind co)
exprType (Note _ e) = exprType e
exprType (Lam binder expr) = mkPiType binder (exprType expr)
exprType e@(App _ _)
coreAltType :: CoreAlt -> Type
-- ^ Returns the type of the alternatives right hand side
-coreAltType (_,_,rhs) = exprType rhs
+coreAltType (_,bs,rhs)
+ | any bad_binder bs = expandTypeSynonyms ty
+ | otherwise = ty -- Note [Existential variables and silly type synonyms]
+ where
+ ty = exprType rhs
+ free_tvs = tyVarsOfType ty
+ bad_binder b = isTyVar b && b `elemVarSet` free_tvs
coreAltsType :: [CoreAlt] -> Type
-- ^ Returns the type of the first alternative, which should be the same as for all alternatives
coreAltsType [] = panic "corAltsType"
\end{code}
+Note [Existential variables and silly type synonyms]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ data T = forall a. T (Funny a)
+ type Funny a = Bool
+ f :: T -> Bool
+ f (T x) = x
+
+Now, the type of 'x' is (Funny a), where 'a' is existentially quantified.
+That means that 'exprType' and 'coreAltsType' may give a result that *appears*
+to mention an out-of-scope type variable. See Trac #3409 for a more real-world
+example.
+
+Various possibilities suggest themselves:
+
+ - Ignore the problem, and make Lint not complain about such variables
+
+ - Expand all type synonyms (or at least all those that discard arguments)
+ This is tricky, because at least for top-level things we want to
+ retain the type the user originally specified.
+
+ - Expand synonyms on the fly, when the problem arises. That is what
+ we are doing here. It's not too expensive, I think.
+
\begin{code}
-mkPiType :: Var -> Type -> Type
+mkPiType :: Var -> Type -> Type
-- ^ Makes a @(->)@ type or a forall type, depending
-- on whether it is given a type variable or a term variable.
mkPiTypes :: [Var] -> Type -> Type
go [ty] args
where
go rev_tys (Type ty : args) = go (ty:rev_tys) args
- go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
- where
- op_ty' = applyTysD msg op_ty (reverse rev_tys)
- msg = ptext (sLit "applyTypeToArgs") <+>
- panic_msg e op_ty
+ go rev_tys rest_args = applyTypeToArgs e op_ty' rest_args
+ where
+ op_ty' = applyTysD msg op_ty (reverse rev_tys)
+ msg = ptext (sLit "applyTypeToArgs") <+>
+ panic_msg e op_ty
applyTypeToArgs e op_ty (_ : args)
= case (splitFunTy_maybe op_ty) of
%* *
%************************************************************************
-mkNote removes redundant coercions, and SCCs where possible
-
-\begin{code}
-#ifdef UNUSED
-mkNote :: Note -> CoreExpr -> CoreExpr
-mkNote (SCC cc) expr = mkSCC cc expr
-mkNote InlineMe expr = mkInlineMe expr
-mkNote note expr = Note note expr
-#endif
-\end{code}
-
-Drop trivial InlineMe's. This is somewhat important, because if we have an unfolding
-that looks like (Note InlineMe (Var v)), the InlineMe doesn't go away because it may
-not be *applied* to anything.
-
-We don't use exprIsTrivial here, though, because we sometimes generate worker/wrapper
-bindings like
- fw = ...
- f = inline_me (coerce t fw)
-As usual, the inline_me prevents the worker from getting inlined back into the wrapper.
-We want the split, so that the coerces can cancel at the call site.
-
-However, we can get left with tiresome type applications. Notably, consider
- f = /\ a -> let t = e in (t, w)
-Then lifting the let out of the big lambda gives
- t' = /\a -> e
- f = /\ a -> let t = inline_me (t' a) in (t, w)
-The inline_me is to stop the simplifier inlining t' right back
-into t's RHS. In the next phase we'll substitute for t (since
-its rhs is trivial) and *then* we could get rid of the inline_me.
-But it hardly seems worth it, so I don't bother.
-
-\begin{code}
--- | Wraps the given expression in an inlining hint unless the expression
--- is trivial in some sense, so that doing so would usually hurt us
-mkInlineMe :: CoreExpr -> CoreExpr
-mkInlineMe (Var v) = Var v
-mkInlineMe e = Note InlineMe e
-\end{code}
-
\begin{code}
--- | Wrap the given expression in the coercion, dropping identity coercions and coalescing nested coercions
-mkCoerceI :: CoercionI -> CoreExpr -> CoreExpr
-mkCoerceI IdCo e = e
-mkCoerceI (ACo co) e = mkCoerce co e
-
--- | Wrap the given expression in the coercion safely, coalescing nested coercions
+-- | Wrap the given expression in the coercion safely, dropping
+-- identity coercions and coalescing nested coercions
mkCoerce :: Coercion -> CoreExpr -> CoreExpr
+mkCoerce co e | isReflCo co = e
mkCoerce co (Cast expr co2)
- = ASSERT(let { (from_ty, _to_ty) = coercionKind co;
- (_from_ty2, to_ty2) = coercionKind co2} in
- from_ty `coreEqType` to_ty2 )
- mkCoerce (mkTransCoercion co2 co) expr
+ = ASSERT(let { Pair from_ty _to_ty = coercionKind co;
+ Pair _from_ty2 to_ty2 = coercionKind co2} in
+ from_ty `eqType` to_ty2 )
+ mkCoerce (mkTransCo co2 co) expr
mkCoerce co expr
- = let (from_ty, _to_ty) = coercionKind co in
--- if to_ty `coreEqType` from_ty
+ = let Pair from_ty _to_ty = coercionKind co in
+-- if to_ty `eqType` from_ty
-- then expr
-- else
- ASSERT2(from_ty `coreEqType` (exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ ppr (coercionKindPredTy co))
+ WARN(not (from_ty `eqType` exprType expr), text "Trying to coerce" <+> text "(" <> ppr expr $$ text "::" <+> ppr (exprType expr) <> text ")" $$ ppr co $$ pprEqPred (coercionKind co))
(Cast expr co)
\end{code}
findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
findDefault alts = (alts, Nothing)
+isDefaultAlt :: CoreAlt -> Bool
+isDefaultAlt (DEFAULT, _, _) = True
+isDefaultAlt _ = False
+
+
-- | Find the case alternative corresponding to a particular
-- constructor: panics if no such constructor exists
-findAlt :: AltCon -> [CoreAlt] -> CoreAlt
+findAlt :: AltCon -> [CoreAlt] -> Maybe CoreAlt
+ -- A "Nothing" result *is* legitmiate
+ -- See Note [Unreachable code]
findAlt con alts
= case alts of
- (deflt@(DEFAULT,_,_):alts) -> go alts deflt
- _ -> go alts panic_deflt
+ (deflt@(DEFAULT,_,_):alts) -> go alts (Just deflt)
+ _ -> go alts Nothing
where
- panic_deflt = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
-
- go [] deflt = deflt
+ go [] deflt = deflt
go (alt@(con1,_,_) : alts) deflt
= case con `cmpAltCon` con1 of
LT -> deflt -- Missed it already; the alts are in increasing order
- EQ -> alt
+ EQ -> Just alt
GT -> ASSERT( not (con1 == DEFAULT) ) go alts deflt
-isDefaultAlt :: CoreAlt -> Bool
-isDefaultAlt (DEFAULT, _, _) = True
-isDefaultAlt _ = False
-
---------------------------------
mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
-- ^ Merge alternatives preserving order; alternatives in
trimConArgs (DataAlt dc) args = dropList (dataConUnivTyVars dc) args
\end{code}
+Note [Unreachable code]
+~~~~~~~~~~~~~~~~~~~~~~~
+It is possible (although unusual) for GHC to find a case expression
+that cannot match. For example:
+
+ data Col = Red | Green | Blue
+ x = Red
+ f v = case x of
+ Red -> ...
+ _ -> ...(case x of { Green -> e1; Blue -> e2 })...
+
+Suppose that for some silly reason, x isn't substituted in the case
+expression. (Perhaps there's a NOINLINE on it, or profiling SCC stuff
+gets in the way; cf Trac #3118.) Then the full-lazines pass might produce
+this
+
+ x = Red
+ lvl = case x of { Green -> e1; Blue -> e2 })
+ f v = case x of
+ Red -> ...
+ _ -> ...lvl...
+
+Now if x gets inlined, we won't be able to find a matching alternative
+for 'Red'. That's because 'lvl' is unreachable. So rather than crashing
+we generate (error "Inaccessible alternative").
+
+Similar things can happen (augmented by GADTs) when the Simplifier
+filters down the matching alternatives in Simplify.rebuildCase.
+
%************************************************************************
%* *
-\subsection{Figuring out things about expressions}
+ exprIsTrivial
%* *
%************************************************************************
+Note [exprIsTrivial]
+~~~~~~~~~~~~~~~~~~~~
@exprIsTrivial@ is true of expressions we are unconditionally happy to
duplicate; simple variables and constants, and type
applications. Note that primop Ids aren't considered
trivial unless
+Note [Variable are trivial]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
There used to be a gruesome test for (hasNoBinding v) in the
Var case:
exprIsTrivial (Var v) | hasNoBinding v = idArity v == 0
rare that I plan to allow them to be duplicated and put up with
saturating them.
-SCC notes. We do not treat (_scc_ "foo" x) as trivial, because
- a) it really generates code, (and a heap object when it's
- a function arg) to capture the cost centre
- b) see the note [SCC-and-exprIsTrivial] in Simplify.simplLazyBind
+Note [SCCs are trivial]
+~~~~~~~~~~~~~~~~~~~~~~~
+We used not to treat (_scc_ "foo" x) as trivial, because it really
+generates code, (and a heap object when it's a function arg) to
+capture the cost centre. However, the profiling system discounts the
+allocation costs for such "boxing thunks" whereas the extra costs of
+*not* inlining otherwise-trivial bindings can be high, and are hard to
+discount.
\begin{code}
exprIsTrivial :: CoreExpr -> Bool
-exprIsTrivial (Var _) = True -- See notes above
-exprIsTrivial (Type _) = True
+exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
+exprIsTrivial (Type _) = True
+exprIsTrivial (Coercion _) = True
exprIsTrivial (Lit lit) = litIsTrivial lit
exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
-exprIsTrivial (Note (SCC _) _) = False -- See notes above
-exprIsTrivial (Note _ e) = exprIsTrivial e
+exprIsTrivial (Note _ e) = exprIsTrivial e -- See Note [SCCs are trivial]
exprIsTrivial (Cast e _) = exprIsTrivial e
exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
exprIsTrivial _ = False
\end{code}
+exprIsBottom is a very cheap and cheerful function; it may return
+False for bottoming expressions, but it never costs much to ask.
+See also CoreArity.exprBotStrictness_maybe, but that's a bit more
+expensive.
+\begin{code}
+exprIsBottom :: CoreExpr -> Bool
+exprIsBottom e
+ = go 0 e
+ where
+ go n (Var v) = isBottomingId v && n >= idArity v
+ go n (App e a) | isTypeArg a = go n e
+ | otherwise = go (n+1) e
+ go n (Note _ e) = go n e
+ go n (Cast e _) = go n e
+ go n (Let _ e) = go n e
+ go _ _ = False
+\end{code}
+
+
+%************************************************************************
+%* *
+ exprIsDupable
+%* *
+%************************************************************************
+
+Note [exprIsDupable]
+~~~~~~~~~~~~~~~~~~~~
@exprIsDupable@ is true of expressions that can be duplicated at a modest
cost in code size. This will only happen in different case
branches, so there's no issue about duplicating work.
\begin{code}
exprIsDupable :: CoreExpr -> Bool
-exprIsDupable (Type _) = True
-exprIsDupable (Var _) = True
-exprIsDupable (Lit lit) = litIsDupable lit
-exprIsDupable (Note InlineMe _) = True
-exprIsDupable (Note _ e) = exprIsDupable e
-exprIsDupable (Cast e _) = exprIsDupable e
-exprIsDupable expr
- = go expr 0
+exprIsDupable e
+ = isJust (go dupAppSize e)
where
- go (Var _) _ = True
- go (App f a) n_args = n_args < dupAppSize
- && exprIsDupable a
- && go f (n_args+1)
- go _ _ = False
+ go :: Int -> CoreExpr -> Maybe Int
+ go n (Type {}) = Just n
+ go n (Coercion {}) = Just n
+ go n (Var {}) = decrement n
+ go n (Note _ e) = go n e
+ go n (Cast e _) = go n e
+ go n (App f a) | Just n' <- go n a = go n' f
+ go n (Lit lit) | litIsDupable lit = decrement n
+ go _ _ = Nothing
+
+ decrement :: Int -> Maybe Int
+ decrement 0 = Nothing
+ decrement n = Just (n-1)
dupAppSize :: Int
-dupAppSize = 4 -- Size of application we are prepared to duplicate
+dupAppSize = 8 -- Size of term we are prepared to duplicate
+ -- This is *just* big enough to make test MethSharing
+ -- inline enough join points. Really it should be
+ -- smaller, and could be if we fixed Trac #4960.
\end{code}
+%************************************************************************
+%* *
+ exprIsCheap, exprIsExpandable
+%* *
+%************************************************************************
+
+Note [exprIsCheap] See also Note [Interaction of exprIsCheap and lone variables]
+~~~~~~~~~~~~~~~~~~ in CoreUnfold.lhs
@exprIsCheap@ looks at a Core expression and returns \tr{True} if
it is obviously in weak head normal form, or is cheap to get to WHNF.
[Note that that's not the same as exprIsDupable; an expression might be
Notice that a variable is considered 'cheap': we can push it inside a lambda,
because sharing will make sure it is only evaluated once.
+Note [exprIsCheap and exprIsHNF]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Note that exprIsHNF does not imply exprIsCheap. Eg
+ let x = fac 20 in Just x
+This responds True to exprIsHNF (you can discard a seq), but
+False to exprIsCheap.
+
\begin{code}
-exprIsCheap' :: (Id -> Bool) -> CoreExpr -> Bool
-exprIsCheap' _ (Lit _) = True
-exprIsCheap' _ (Type _) = True
-exprIsCheap' _ (Var _) = True
-exprIsCheap' _ (Note InlineMe _) = True
-exprIsCheap' is_conlike (Note _ e) = exprIsCheap' is_conlike e
-exprIsCheap' is_conlike (Cast e _) = exprIsCheap' is_conlike e
-exprIsCheap' is_conlike (Lam x e) = isRuntimeVar x
- || exprIsCheap' is_conlike e
-exprIsCheap' is_conlike (Case e _ _ alts) = exprIsCheap' is_conlike e &&
- and [exprIsCheap' is_conlike rhs | (_,_,rhs) <- alts]
+exprIsCheap :: CoreExpr -> Bool
+exprIsCheap = exprIsCheap' isCheapApp
+
+exprIsExpandable :: CoreExpr -> Bool
+exprIsExpandable = exprIsCheap' isExpandableApp -- See Note [CONLIKE pragma] in BasicTypes
+
+type CheapAppFun = Id -> Int -> Bool
+exprIsCheap' :: CheapAppFun -> CoreExpr -> Bool
+exprIsCheap' _ (Lit _) = True
+exprIsCheap' _ (Type _) = True
+exprIsCheap' _ (Coercion _) = True
+exprIsCheap' _ (Var _) = True
+exprIsCheap' good_app (Note _ e) = exprIsCheap' good_app e
+exprIsCheap' good_app (Cast e _) = exprIsCheap' good_app e
+exprIsCheap' good_app (Lam x e) = isRuntimeVar x
+ || exprIsCheap' good_app e
+
+exprIsCheap' good_app (Case e _ _ alts) = exprIsCheap' good_app e &&
+ and [exprIsCheap' good_app rhs | (_,_,rhs) <- alts]
-- Experimentally, treat (case x of ...) as cheap
-- (and case __coerce x etc.)
-- This improves arities of overloaded functions where
-- there is only dictionary selection (no construction) involved
-exprIsCheap' is_conlike (Let (NonRec x _) e)
- | isUnLiftedType (idType x) = exprIsCheap' is_conlike e
- | otherwise = False
- -- strict lets always have cheap right hand sides,
- -- and do no allocation.
-exprIsCheap' is_conlike other_expr -- Applications and variables
+exprIsCheap' good_app (Let (NonRec x _) e)
+ | isUnLiftedType (idType x) = exprIsCheap' good_app e
+ | otherwise = False
+ -- Strict lets always have cheap right hand sides,
+ -- and do no allocation, so just look at the body
+ -- Non-strict lets do allocation so we don't treat them as cheap
+ -- See also
+
+exprIsCheap' good_app other_expr -- Applications and variables
= go other_expr []
where
-- Accumulate value arguments, then decide
+ go (Cast e _) val_args = go e val_args
go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
| otherwise = go f val_args
go (Var _) [] = True -- Just a type application of a variable
-- (f t1 t2 t3) counts as WHNF
go (Var f) args
- = case idDetails f of
- RecSelId {} -> go_sel args
- ClassOpId _ -> go_sel args
- PrimOpId op -> go_primop op args
-
- _ | is_conlike f -> go_pap args
- | length args < idArity f -> go_pap args
-
- _ -> isBottomingId f
+ = case idDetails f of
+ RecSelId {} -> go_sel args
+ ClassOpId {} -> go_sel args
+ PrimOpId op -> go_primop op args
+ _ | good_app f (length args) -> go_pap args
+ | isBottomingId f -> True
+ | otherwise -> False
-- Application of a function which
-- always gives bottom; we treat this as cheap
-- because it certainly doesn't need to be shared!
go _ _ = False
--------------
- go_pap args = all exprIsTrivial args
- -- For constructor applications and primops, check that all
- -- the args are trivial. We don't want to treat as cheap, say,
- -- (1:2:3:4:5:[])
- -- We'll put up with one constructor application, but not dozens
-
+ go_pap args = all (exprIsCheap' good_app) args
+ -- Used to be "all exprIsTrivial args" due to concerns about
+ -- duplicating nested constructor applications, but see #4978.
+
--------------
- go_primop op args = primOpIsCheap op && all (exprIsCheap' is_conlike) args
+ go_primop op args = primOpIsCheap op && all (exprIsCheap' good_app) args
-- In principle we should worry about primops
-- that return a type variable, since the result
-- might be applied to something, but I'm not going
-- to bother to check the number of args
--------------
- go_sel [arg] = exprIsCheap' is_conlike arg -- I'm experimenting with making record selection
+ go_sel [arg] = exprIsCheap' good_app arg -- I'm experimenting with making record selection
go_sel _ = False -- look cheap, so we will substitute it inside a
-- lambda. Particularly for dictionary field selection.
-- BUT: Take care with (sel d x)! The (sel d) might be cheap, but
-- there's no guarantee that (sel d x) will be too. Hence (n_val_args == 1)
-exprIsCheap :: CoreExpr -> Bool
-exprIsCheap = exprIsCheap' isDataConWorkId
+isCheapApp :: CheapAppFun
+isCheapApp fn n_val_args
+ = isDataConWorkId fn
+ || n_val_args < idArity fn
-exprIsExpandable :: CoreExpr -> Bool
-exprIsExpandable = exprIsCheap' isConLikeId
+isExpandableApp :: CheapAppFun
+isExpandableApp fn n_val_args
+ = isConLikeId fn
+ || n_val_args < idArity fn
+ || go n_val_args (idType fn)
+ where
+ -- See if all the arguments are PredTys (implicit params or classes)
+ -- If so we'll regard it as expandable; see Note [Expandable overloadings]
+ go 0 _ = True
+ go n_val_args ty
+ | Just (_, ty) <- splitForAllTy_maybe ty = go n_val_args ty
+ | Just (arg, ty) <- splitFunTy_maybe ty
+ , isPredTy arg = go (n_val_args-1) ty
+ | otherwise = False
\end{code}
+Note [Expandable overloadings]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Suppose the user wrote this
+ {-# RULE forall x. foo (negate x) = h x #-}
+ f x = ....(foo (negate x))....
+He'd expect the rule to fire. But since negate is overloaded, we might
+get this:
+ f = \d -> let n = negate d in \x -> ...foo (n x)...
+So we treat the application of a function (negate in this case) to a
+*dictionary* as expandable. In effect, every function is CONLIKE when
+it's applied only to dictionaries.
+
+
+%************************************************************************
+%* *
+ exprOkForSpeculation
+%* *
+%************************************************************************
+
\begin{code}
-- | 'exprOkForSpeculation' returns True of an expression that is:
--
--
-- * Safe /not/ to evaluate even if normal order would do so
--
+-- It is usually called on arguments of unlifted type, but not always
+-- In particular, Simplify.rebuildCase calls it on lifted types
+-- when a 'case' is a plain 'seq'. See the example in
+-- Note [exprOkForSpeculation: case expressions] below
+--
-- Precisely, it returns @True@ iff:
--
-- * The expression guarantees to terminate,
---
-- * soon,
---
-- * without raising an exception,
---
-- * without causing a side effect (e.g. writing a mutable variable)
--
-- Note that if @exprIsHNF e@, then @exprOkForSpecuation e@.
-- We can only do this if the @y + 1@ is ok for speculation: it has no
-- side effects, and can't diverge or raise an exception.
exprOkForSpeculation :: CoreExpr -> Bool
-exprOkForSpeculation (Lit _) = True
-exprOkForSpeculation (Type _) = True
- -- Tick boxes are *not* suitable for speculation
-exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
- && not (isTickBoxOp v)
+exprOkForSpeculation (Lit _) = True
+exprOkForSpeculation (Type _) = True
+exprOkForSpeculation (Coercion _) = True
+
+exprOkForSpeculation (Var v)
+ | isTickBoxOp v = False -- Tick boxes are *not* suitable for speculation
+ | otherwise = isUnLiftedType (idType v) -- c.f. the Var case of exprIsHNF
+ || isDataConWorkId v -- Nullary constructors
+ || idArity v > 0 -- Functions
+ || isEvaldUnfolding (idUnfolding v) -- Let-bound values
+
exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
+
+exprOkForSpeculation (Case e _ _ alts)
+ = exprOkForSpeculation e -- Note [exprOkForSpeculation: case expressions]
+ && all (\(_,_,rhs) -> exprOkForSpeculation rhs) alts
+
exprOkForSpeculation other_expr
= case collectArgs other_expr of
(Var f, args) -> spec_ok (idDetails f) args
-- Often there is a literal divisor, and this
-- can get rid of a thunk in an inner looop
+ | DataToTagOp <- op -- See Note [dataToTag speculation]
+ = True
+
| otherwise
= primOpOkForSpeculation op &&
all exprOkForSpeculation args
-- A bit conservative: we don't really need
-- to care about lazy arguments, but this is easy
+ spec_ok (DFunId _ new_type) _ = not new_type
+ -- DFuns terminate, unless the dict is implemented with a newtype
+ -- in which case they may not
+
spec_ok _ _ = False
-- | True of dyadic operators that can fail only if the second arg is zero!
isDivOp IntRemOp = True
isDivOp WordQuotOp = True
isDivOp WordRemOp = True
-isDivOp IntegerQuotRemOp = True
-isDivOp IntegerDivModOp = True
isDivOp FloatDivOp = True
isDivOp DoubleDivOp = True
isDivOp _ = False
\end{code}
-\begin{code}
--- | True of expressions that are guaranteed to diverge upon execution
-exprIsBottom :: CoreExpr -> Bool
-exprIsBottom e = go 0 e
- where
- -- n is the number of args
- go n (Note _ e) = go n e
- go n (Cast e _) = go n e
- go n (Let _ e) = go n e
- go _ (Case e _ _ _) = go 0 e -- Just check the scrut
- go n (App e _) = go (n+1) e
- go n (Var v) = idAppIsBottom v n
- go _ (Lit _) = False
- go _ (Lam _ _) = False
- go _ (Type _) = False
-
-idAppIsBottom :: Id -> Int -> Bool
-idAppIsBottom id n_val_args = appIsBottom (idNewStrictness id) n_val_args
-\end{code}
+Note [exprOkForSpeculation: case expressions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+It's always sound for exprOkForSpeculation to return False, and we
+don't want it to take too long, so it bales out on complicated-looking
+terms. Notably lets, which can be stacked very deeply; and in any
+case the argument of exprOkForSpeculation is usually in a strict context,
+so any lets will have been floated away.
+
+However, we keep going on case-expressions. An example like this one
+showed up in DPH code (Trac #3717):
+ foo :: Int -> Int
+ foo 0 = 0
+ foo n = (if n < 5 then 1 else 2) `seq` foo (n-1)
+
+If exprOkForSpeculation doesn't look through case expressions, you get this:
+ T.$wfoo =
+ \ (ww :: GHC.Prim.Int#) ->
+ case ww of ds {
+ __DEFAULT -> case (case <# ds 5 of _ {
+ GHC.Types.False -> lvl1;
+ GHC.Types.True -> lvl})
+ of _ { __DEFAULT ->
+ T.$wfoo (GHC.Prim.-# ds_XkE 1) };
+ 0 -> 0
+ }
+
+The inner case is redundant, and should be nuked.
+
+Note [dataToTag speculation]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Is this OK?
+ f x = let v::Int# = dataToTag# x
+ in ...
+We say "yes", even though 'x' may not be evaluated. Reasons
+
+ * dataToTag#'s strictness means that its argument often will be
+ evaluated, but FloatOut makes that temporarily untrue
+ case x of y -> let v = dataToTag# y in ...
+ -->
+ case x of y -> let v = dataToTag# x in ...
+ Note that we look at 'x' instead of 'y' (this is to improve
+ floating in FloatOut). So Lint complains.
+
+ Moreover, it really *might* improve floating to let the
+ v-binding float out
+
+ * CorePrep makes sure dataToTag#'s argument is evaluated, just
+ before code gen. Until then, it's not guaranteed
-\begin{code}
--- | This returns true for expressions that are certainly /already/
+%************************************************************************
+%* *
+ exprIsHNF, exprIsConLike
+%* *
+%************************************************************************
+
+\begin{code}
+-- Note [exprIsHNF] See also Note [exprIsCheap and exprIsHNF]
+-- ~~~~~~~~~~~~~~~~
+-- | exprIsHNF returns true for expressions that are certainly /already/
-- evaluated to /head/ normal form. This is used to decide whether it's ok
-- to change:
--
-- > case x of _ -> e
--
--- into:
+-- into:
--
-- > e
--
-- and to decide whether it's safe to discard a 'seq'.
+--
-- So, it does /not/ treat variables as evaluated, unless they say they are.
-- However, it /does/ treat partial applications and constructor applications
-- as values, even if their arguments are non-trivial, provided the argument
-- > (:) (f x) (map f xs)
-- > map (...redex...)
--
--- Because 'seq' on such things completes immediately.
+-- because 'seq' on such things completes immediately.
--
-- For unlifted argument types, we have to be careful:
--
-- happen: see "CoreSyn#let_app_invariant". This invariant states that arguments of
-- unboxed type must be ok-for-speculation (or trivial).
exprIsHNF :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
-exprIsHNF (Var v) -- NB: There are no value args at this point
- = isDataConWorkId v -- Catches nullary constructors,
+exprIsHNF = exprIsHNFlike isDataConWorkId isEvaldUnfolding
+\end{code}
+
+\begin{code}
+-- | Similar to 'exprIsHNF' but includes CONLIKE functions as well as
+-- data constructors. Conlike arguments are considered interesting by the
+-- inliner.
+exprIsConLike :: CoreExpr -> Bool -- True => lambda, conlike, PAP
+exprIsConLike = exprIsHNFlike isConLikeId isConLikeUnfolding
+
+-- | Returns true for values or value-like expressions. These are lambdas,
+-- constructors / CONLIKE functions (as determined by the function argument)
+-- or PAPs.
+--
+exprIsHNFlike :: (Var -> Bool) -> (Unfolding -> Bool) -> CoreExpr -> Bool
+exprIsHNFlike is_con is_con_unf = is_hnf_like
+ where
+ is_hnf_like (Var v) -- NB: There are no value args at this point
+ = is_con v -- Catches nullary constructors,
-- so that [] and () are values, for example
- || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
- || isEvaldUnfolding (idUnfolding v)
+ || idArity v > 0 -- Catches (e.g.) primops that don't have unfoldings
+ || is_con_unf (idUnfolding v)
-- Check the thing's unfolding; it might be bound to a value
- -- A worry: what if an Id's unfolding is just itself:
- -- then we could get an infinite loop...
-
-exprIsHNF (Lit _) = True
-exprIsHNF (Type _) = True -- Types are honorary Values;
- -- we don't mind copying them
-exprIsHNF (Lam b e) = isRuntimeVar b || exprIsHNF e
-exprIsHNF (Note _ e) = exprIsHNF e
-exprIsHNF (Cast e _) = exprIsHNF e
-exprIsHNF (App e (Type _)) = exprIsHNF e
-exprIsHNF (App e a) = app_is_value e [a]
-exprIsHNF _ = False
-
--- There is at least one value argument
-app_is_value :: CoreExpr -> [CoreArg] -> Bool
-app_is_value (Var fun) args
- = idArity fun > valArgCount args -- Under-applied function
- || isDataConWorkId fun -- or data constructor
-app_is_value (Note _ f) as = app_is_value f as
-app_is_value (Cast f _) as = app_is_value f as
-app_is_value (App f a) as = app_is_value f (a:as)
-app_is_value _ _ = False
+ -- We don't look through loop breakers here, which is a bit conservative
+ -- but otherwise I worry that if an Id's unfolding is just itself,
+ -- we could get an infinite loop
+
+ is_hnf_like (Lit _) = True
+ is_hnf_like (Type _) = True -- Types are honorary Values;
+ -- we don't mind copying them
+ is_hnf_like (Coercion _) = True -- Same for coercions
+ is_hnf_like (Lam b e) = isRuntimeVar b || is_hnf_like e
+ is_hnf_like (Note _ e) = is_hnf_like e
+ is_hnf_like (Cast e _) = is_hnf_like e
+ is_hnf_like (App e (Type _)) = is_hnf_like e
+ is_hnf_like (App e (Coercion _)) = is_hnf_like e
+ is_hnf_like (App e a) = app_is_value e [a]
+ is_hnf_like (Let _ e) = is_hnf_like e -- Lazy let(rec)s don't affect us
+ is_hnf_like _ = False
+
+ -- There is at least one value argument
+ app_is_value :: CoreExpr -> [CoreArg] -> Bool
+ app_is_value (Var fun) args
+ = idArity fun > valArgCount args -- Under-applied function
+ || is_con fun -- or constructor-like
+ app_is_value (Note _ f) as = app_is_value f as
+ app_is_value (Cast f _) as = app_is_value f as
+ app_is_value (App f a) as = app_is_value f (a:as)
+ app_is_value _ _ = False
\end{code}
+
+%************************************************************************
+%* *
+ Instantiating data constructors
+%* *
+%************************************************************************
+
These InstPat functions go here to avoid circularity between DataCon and Id
\begin{code}
-dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
-dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
+dataConRepInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
+dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [Id])
-dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
-dataConRepFSInstPat = dataConInstPat dataConRepArgTys
-dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
- where
- dc_arg_tys dc = map mkPredTy (dataConEqTheta dc) ++ map mkPredTy (dataConDictTheta dc) ++ dataConOrigArgTys dc
- -- Remember to include the existential dictionaries
-
-dataConInstPat :: (DataCon -> [Type]) -- function used to find arg tys
- -> [FastString] -- A long enough list of FSs to use for names
- -> [Unique] -- An equally long list of uniques, at least one for each binder
- -> DataCon
- -> [Type] -- Types to instantiate the universally quantified tyvars
- -> ([TyVar], [CoVar], [Id]) -- Return instantiated variables
+dataConRepInstPat = dataConInstPat (repeat ((fsLit "ipv")))
+dataConRepFSInstPat = dataConInstPat
+
+dataConInstPat :: [FastString] -- A long enough list of FSs to use for names
+ -> [Unique] -- An equally long list of uniques, at least one for each binder
+ -> DataCon
+ -> [Type] -- Types to instantiate the universally quantified tyvars
+ -> ([TyVar], [Id]) -- Return instantiated variables
-- dataConInstPat arg_fun fss us con inst_tys returns a triple
--- (ex_tvs, co_tvs, arg_ids),
+-- (ex_tvs, arg_ids),
--
-- ex_tvs are intended to be used as binders for existential type args
--
--- co_tvs are intended to be used as binders for coercion args and the kinds
--- of these vars have been instantiated by the inst_tys and the ex_tys
--- The co_tvs include both GADT equalities (dcEqSpec) and
--- programmer-specified equalities (dcEqTheta)
---
-- arg_ids are indended to be used as binders for value arguments,
-- and their types have been instantiated with inst_tys and ex_tys
--- The arg_ids include both dicts (dcDictTheta) and
--- programmer-specified arguments (after rep-ing) (deRepArgTys)
+-- The arg_ids include both evidence and
+-- programmer-specified arguments (both after rep-ing)
--
-- Example.
-- The following constructor T1
--
-- dataConInstPat fss us T1 (a1',b') will return
--
--- ([a1'', b''], [c :: (a1', b')~(a1'', b'')], [x :: Int, y :: b''])
+-- ([a1'', b''], [c :: (a1', b')~(a1'', b''), x :: Int, y :: b''])
--
-- where the double-primed variables are created with the FastStrings and
-- Uniques given as fss and us
-dataConInstPat arg_fun fss uniqs con inst_tys
- = (ex_bndrs, co_bndrs, arg_ids)
+dataConInstPat fss uniqs con inst_tys
+ = (ex_bndrs, arg_ids)
where
univ_tvs = dataConUnivTyVars con
ex_tvs = dataConExTyVars con
- arg_tys = arg_fun con
- eq_spec = dataConEqSpec con
- eq_theta = dataConEqTheta con
- eq_preds = eqSpecPreds eq_spec ++ eq_theta
+ arg_tys = dataConRepArgTys con
n_ex = length ex_tvs
- n_co = length eq_preds
-- split the Uniques and FastStrings
- (ex_uniqs, uniqs') = splitAt n_ex uniqs
- (co_uniqs, id_uniqs) = splitAt n_co uniqs'
-
- (ex_fss, fss') = splitAt n_ex fss
- (co_fss, id_fss) = splitAt n_co fss'
+ (ex_uniqs, id_uniqs) = splitAt n_ex uniqs
+ (ex_fss, id_fss) = splitAt n_ex fss
-- Make existential type variables
ex_bndrs = zipWith3 mk_ex_var ex_uniqs ex_fss ex_tvs
-- Make the instantiating substitution
subst = zipOpenTvSubst (univ_tvs ++ ex_tvs) (inst_tys ++ map mkTyVarTy ex_bndrs)
- -- Make new coercion vars, instantiating kind
- co_bndrs = zipWith3 mk_co_var co_uniqs co_fss eq_preds
- mk_co_var uniq fs eq_pred = mkCoVar new_name co_kind
- where
- new_name = mkSysTvName uniq fs
- co_kind = substTy subst (mkPredTy eq_pred)
-
- -- make value vars, instantiating types
- mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
+ -- Make value vars, instantiating types
+ mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (Type.substTy subst ty) noSrcSpan
arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
-
--- | Returns @Just (dc, [x1..xn])@ if the argument expression is
--- a constructor application of the form @dc x1 .. xn@
-exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
-exprIsConApp_maybe (Cast expr co)
- = -- Here we do the KPush reduction rule as described in the FC paper
- case exprIsConApp_maybe expr of {
- Nothing -> Nothing ;
- Just (dc, dc_args) ->
-
- -- The transformation applies iff we have
- -- (C e1 ... en) `cast` co
- -- where co :: (T t1 .. tn) ~ (T s1 ..sn)
- -- That is, with a T at the top of both sides
- -- The left-hand one must be a T, because exprIsConApp returned True
- -- but the right-hand one might not be. (Though it usually will.)
-
- let (from_ty, to_ty) = coercionKind co
- (from_tc, from_tc_arg_tys) = splitTyConApp from_ty
- -- The inner one must be a TyConApp
- in
- case splitTyConApp_maybe to_ty of {
- Nothing -> Nothing ;
- Just (to_tc, to_tc_arg_tys)
- | from_tc /= to_tc -> Nothing
- -- These two Nothing cases are possible; we might see
- -- (C x y) `cast` (g :: T a ~ S [a]),
- -- where S is a type function. In fact, exprIsConApp
- -- will probably not be called in such circumstances,
- -- but there't nothing wrong with it
-
- | otherwise ->
- let
- tc_arity = tyConArity from_tc
-
- (univ_args, rest1) = splitAt tc_arity dc_args
- (ex_args, rest2) = splitAt n_ex_tvs rest1
- (co_args_spec, rest3) = splitAt n_cos_spec rest2
- (co_args_theta, val_args) = splitAt n_cos_theta rest3
-
- arg_tys = dataConRepArgTys dc
- dc_univ_tyvars = dataConUnivTyVars dc
- dc_ex_tyvars = dataConExTyVars dc
- dc_eq_spec = dataConEqSpec dc
- dc_eq_theta = dataConEqTheta dc
- dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
- n_ex_tvs = length dc_ex_tyvars
- n_cos_spec = length dc_eq_spec
- n_cos_theta = length dc_eq_theta
-
- -- Make the "theta" from Fig 3 of the paper
- gammas = decomposeCo tc_arity co
- new_tys = gammas ++ map (\ (Type t) -> t) ex_args
- theta = zipOpenTvSubst dc_tyvars new_tys
-
- -- First we cast the existential coercion arguments
- cast_co_spec (tv, ty) co
- = cast_co_theta (mkEqPred (mkTyVarTy tv, ty)) co
- cast_co_theta eqPred (Type co)
- | (ty1, ty2) <- getEqPredTys eqPred
- = Type $ mkSymCoercion (substTy theta ty1)
- `mkTransCoercion` co
- `mkTransCoercion` (substTy theta ty2)
- new_co_args = zipWith cast_co_spec dc_eq_spec co_args_spec ++
- zipWith cast_co_theta dc_eq_theta co_args_theta
-
- -- ...and now value arguments
- new_val_args = zipWith cast_arg arg_tys val_args
- cast_arg arg_ty arg = mkCoerce (substTy theta arg_ty) arg
-
- in
- ASSERT( length univ_args == tc_arity )
- ASSERT( from_tc == dataConTyCon dc )
- ASSERT( and (zipWith coreEqType [t | Type t <- univ_args] from_tc_arg_tys) )
- ASSERT( all isTypeArg (univ_args ++ ex_args) )
- ASSERT2( equalLength val_args arg_tys, ppr dc $$ ppr dc_tyvars $$ ppr dc_ex_tyvars $$ ppr arg_tys $$ ppr dc_args $$ ppr univ_args $$ ppr ex_args $$ ppr val_args $$ ppr arg_tys )
-
- Just (dc, map Type to_tc_arg_tys ++ ex_args ++ new_co_args ++ new_val_args)
- }}
-
-{-
--- We do not want to tell the world that we have a
--- Cons, to *stop* Case of Known Cons, which removes
--- the TickBox.
-exprIsConApp_maybe (Note (TickBox {}) expr)
- = Nothing
-exprIsConApp_maybe (Note (BinaryTickBox {}) expr)
- = Nothing
--}
-
-exprIsConApp_maybe (Note _ expr)
- = exprIsConApp_maybe expr
- -- We ignore InlineMe notes in case we have
- -- x = __inline_me__ (a,b)
- -- All part of making sure that INLINE pragmas never hurt
- -- Marcin tripped on this one when making dictionaries more inlinable
- --
- -- In fact, we ignore all notes. For example,
- -- case _scc_ "foo" (C a b) of
- -- C a b -> e
- -- should be optimised away, but it will be only if we look
- -- through the SCC note.
-
-exprIsConApp_maybe expr = analyse (collectArgs expr)
- where
- analyse (Var fun, args)
- | Just con <- isDataConWorkId_maybe fun,
- args `lengthAtLeast` dataConRepArity con
- -- Might be > because the arity excludes type args
- = Just (con,args)
-
- -- Look through unfoldings, but only cheap ones, because
- -- we are effectively duplicating the unfolding
- analyse (Var fun, [])
- | let unf = idUnfolding fun,
- isExpandableUnfolding unf
- = exprIsConApp_maybe (unfoldingTemplate unf)
-
- analyse _ = Nothing
\end{code}
-
-
%************************************************************************
%* *
-\subsection{Equality}
+ Equality
%* *
%************************************************************************
cheapEqExpr (Var v1) (Var v2) = v1==v2
cheapEqExpr (Lit lit1) (Lit lit2) = lit1 == lit2
-cheapEqExpr (Type t1) (Type t2) = t1 `coreEqType` t2
+cheapEqExpr (Type t1) (Type t2) = t1 `eqType` t2
+cheapEqExpr (Coercion c1) (Coercion c2) = c1 `coreEqCoercion` c2
cheapEqExpr (App f1 a1) (App f2 a2)
= f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
= e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
cheapEqExpr _ _ = False
+\end{code}
+\begin{code}
exprIsBig :: Expr b -> Bool
-- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
exprIsBig (Lit _) = False
exprIsBig (Var _) = False
-exprIsBig (Type _) = False
+exprIsBig (Type _) = False
+exprIsBig (Coercion _) = False
+exprIsBig (Lam _ e) = exprIsBig e
exprIsBig (App f a) = exprIsBig f || exprIsBig a
exprIsBig (Cast e _) = exprIsBig e -- Hopefully coercions are not too big!
exprIsBig _ = True
\end{code}
+\begin{code}
+eqExpr :: InScopeSet -> CoreExpr -> CoreExpr -> Bool
+-- Compares for equality, modulo alpha
+eqExpr in_scope e1 e2
+ = eqExprX id_unf (mkRnEnv2 in_scope) e1 e2
+ where
+ id_unf _ = noUnfolding -- Don't expand
+\end{code}
+
+\begin{code}
+eqExprX :: IdUnfoldingFun -> RnEnv2 -> CoreExpr -> CoreExpr -> Bool
+-- ^ Compares expressions for equality, modulo alpha.
+-- Does /not/ look through newtypes or predicate types
+-- Used in rule matching, and also CSE
+
+eqExprX id_unfolding_fun env e1 e2
+ = go env e1 e2
+ where
+ go env (Var v1) (Var v2)
+ | rnOccL env v1 == rnOccR env v2
+ = True
+
+ -- The next two rules expand non-local variables
+ -- C.f. Note [Expanding variables] in Rules.lhs
+ -- and Note [Do not expand locally-bound variables] in Rules.lhs
+ go env (Var v1) e2
+ | not (locallyBoundL env v1)
+ , Just e1' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v1))
+ = go (nukeRnEnvL env) e1' e2
+
+ go env e1 (Var v2)
+ | not (locallyBoundR env v2)
+ , Just e2' <- expandUnfolding_maybe (id_unfolding_fun (lookupRnInScope env v2))
+ = go (nukeRnEnvR env) e1 e2'
+
+ go _ (Lit lit1) (Lit lit2) = lit1 == lit2
+ go env (Type t1) (Type t2) = eqTypeX env t1 t2
+ go env (Coercion co1) (Coercion co2) = coreEqCoercion2 env co1 co2
+ go env (Cast e1 co1) (Cast e2 co2) = coreEqCoercion2 env co1 co2 && go env e1 e2
+ go env (App f1 a1) (App f2 a2) = go env f1 f2 && go env a1 a2
+ go env (Note n1 e1) (Note n2 e2) = go_note n1 n2 && go env e1 e2
+
+ go env (Lam b1 e1) (Lam b2 e2)
+ = eqTypeX env (varType b1) (varType b2) -- False for Id/TyVar combination
+ && go (rnBndr2 env b1 b2) e1 e2
+
+ go env (Let (NonRec v1 r1) e1) (Let (NonRec v2 r2) e2)
+ = go env r1 r2 -- No need to check binder types, since RHSs match
+ && go (rnBndr2 env v1 v2) e1 e2
+
+ go env (Let (Rec ps1) e1) (Let (Rec ps2) e2)
+ = all2 (go env') rs1 rs2 && go env' e1 e2
+ where
+ (bs1,rs1) = unzip ps1
+ (bs2,rs2) = unzip ps2
+ env' = rnBndrs2 env bs1 bs2
+
+ go env (Case e1 b1 _ a1) (Case e2 b2 _ a2)
+ = go env e1 e2
+ && eqTypeX env (idType b1) (idType b2)
+ && all2 (go_alt (rnBndr2 env b1 b2)) a1 a2
+
+ go _ _ _ = False
+
+ -----------
+ go_alt env (c1, bs1, e1) (c2, bs2, e2)
+ = c1 == c2 && go (rnBndrs2 env bs1 bs2) e1 e2
+
+ -----------
+ go_note (SCC cc1) (SCC cc2) = cc1 == cc2
+ go_note (CoreNote s1) (CoreNote s2) = s1 == s2
+ go_note _ _ = False
+\end{code}
+
+Auxiliary functions
+
+\begin{code}
+locallyBoundL, locallyBoundR :: RnEnv2 -> Var -> Bool
+locallyBoundL rn_env v = inRnEnvL rn_env v
+locallyBoundR rn_env v = inRnEnvR rn_env v
+\end{code}
%************************************************************************
exprSize :: CoreExpr -> Int
-- ^ A measure of the size of the expressions, strictly greater than 0
-- It also forces the expression pretty drastically as a side effect
+-- Counts *leaves*, not internal nodes. Types and coercions are not counted.
exprSize (Var v) = v `seq` 1
exprSize (Lit lit) = lit `seq` 1
exprSize (App f a) = exprSize f + exprSize a
exprSize (Lam b e) = varSize b + exprSize e
exprSize (Let b e) = bindSize b + exprSize e
exprSize (Case e b t as) = seqType t `seq` exprSize e + varSize b + 1 + foldr ((+) . altSize) 0 as
-exprSize (Cast e co) = (seqType co `seq` 1) + exprSize e
+exprSize (Cast e co) = (seqCo co `seq` 1) + exprSize e
exprSize (Note n e) = noteSize n + exprSize e
-exprSize (Type t) = seqType t `seq` 1
+exprSize (Type t) = seqType t `seq` 1
+exprSize (Coercion co) = seqCo co `seq` 1
noteSize :: Note -> Int
noteSize (SCC cc) = cc `seq` 1
-noteSize InlineMe = 1
noteSize (CoreNote s) = s `seq` 1 -- hdaume: core annotations
varSize :: Var -> Int
altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
\end{code}
+\begin{code}
+data CoreStats = CS { cs_tm, cs_ty, cs_co :: Int }
+
+plusCS :: CoreStats -> CoreStats -> CoreStats
+plusCS (CS { cs_tm = p1, cs_ty = q1, cs_co = r1 })
+ (CS { cs_tm = p2, cs_ty = q2, cs_co = r2 })
+ = CS { cs_tm = p1+p2, cs_ty = q1+q2, cs_co = r1+r2 }
+
+zeroCS, oneTM :: CoreStats
+zeroCS = CS { cs_tm = 0, cs_ty = 0, cs_co = 0 }
+oneTM = zeroCS { cs_tm = 1 }
+
+sumCS :: (a -> CoreStats) -> [a] -> CoreStats
+sumCS f = foldr (plusCS . f) zeroCS
+
+coreBindsStats :: [CoreBind] -> CoreStats
+coreBindsStats = sumCS bindStats
+
+bindStats :: CoreBind -> CoreStats
+bindStats (NonRec v r) = bindingStats v r
+bindStats (Rec prs) = sumCS (\(v,r) -> bindingStats v r) prs
+
+bindingStats :: Var -> CoreExpr -> CoreStats
+bindingStats v r = bndrStats v `plusCS` exprStats r
+
+bndrStats :: Var -> CoreStats
+bndrStats v = oneTM `plusCS` tyStats (varType v)
+
+exprStats :: CoreExpr -> CoreStats
+exprStats (Var {}) = oneTM
+exprStats (Lit {}) = oneTM
+exprStats (Type t) = tyStats t
+exprStats (Coercion c) = coStats c
+exprStats (App f a) = exprStats f `plusCS` exprStats a
+exprStats (Lam b e) = bndrStats b `plusCS` exprStats e
+exprStats (Let b e) = bindStats b `plusCS` exprStats e
+exprStats (Case e b _ as) = exprStats e `plusCS` bndrStats b `plusCS` sumCS altStats as
+exprStats (Cast e co) = coStats co `plusCS` exprStats e
+exprStats (Note _ e) = exprStats e
+
+altStats :: CoreAlt -> CoreStats
+altStats (_, bs, r) = sumCS bndrStats bs `plusCS` exprStats r
+
+tyStats :: Type -> CoreStats
+tyStats ty = zeroCS { cs_ty = typeSize ty }
+
+coStats :: Coercion -> CoreStats
+coStats co = zeroCS { cs_co = coercionSize co }
+\end{code}
%************************************************************************
%* *
hash_expr _ (Type _) = WARN(True, text "hash_expr: type") 1
-- Shouldn't happen. Better to use WARN than trace, because trace
-- prevents the CPR optimisation kicking in for hash_expr.
+hash_expr _ (Coercion _) = WARN(True, text "hash_expr: coercion") 1
fast_hash_expr :: HashEnv -> CoreExpr -> Word32
-fast_hash_expr env (Var v) = hashVar env v
-fast_hash_expr env (Type t) = fast_hash_type env t
-fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
-fast_hash_expr env (Cast e _) = fast_hash_expr env e
-fast_hash_expr env (Note _ e) = fast_hash_expr env e
-fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
-fast_hash_expr _ _ = 1
+fast_hash_expr env (Var v) = hashVar env v
+fast_hash_expr env (Type t) = fast_hash_type env t
+fast_hash_expr env (Coercion co) = fast_hash_co env co
+fast_hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
+fast_hash_expr env (Cast e _) = fast_hash_expr env e
+fast_hash_expr env (Note _ e) = fast_hash_expr env e
+fast_hash_expr env (App _ a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
+fast_hash_expr _ _ = 1
fast_hash_type :: HashEnv -> Type -> Word32
fast_hash_type env ty
in foldr (\t n -> fast_hash_type env t + n) hash_tc tys
| otherwise = 1
+fast_hash_co :: HashEnv -> Coercion -> Word32
+fast_hash_co env co
+ | Just cv <- getCoVar_maybe co = hashVar env cv
+ | Just (tc,cos) <- splitTyConAppCo_maybe co = let hash_tc = fromIntegral (hashName (tyConName tc))
+ in foldr (\c n -> fast_hash_co env c + n) hash_tc cos
+ | otherwise = 1
+
extend_env :: HashEnv -> Var -> (Int, VarEnv Int)
extend_env (n,env) b = (n+1, extendVarEnv env b n)
= fromIntegral (lookupVarEnv env v `orElse` hashName (idName v))
\end{code}
+
+%************************************************************************
+%* *
+ Eta reduction
+%* *
+%************************************************************************
+
+Note [Eta reduction conditions]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+We try for eta reduction here, but *only* if we get all the way to an
+trivial expression. We don't want to remove extra lambdas unless we
+are going to avoid allocating this thing altogether.
+
+There are some particularly delicate points here:
+
+* Eta reduction is not valid in general:
+ \x. bot /= bot
+ This matters, partly for old-fashioned correctness reasons but,
+ worse, getting it wrong can yield a seg fault. Consider
+ f = \x.f x
+ h y = case (case y of { True -> f `seq` True; False -> False }) of
+ True -> ...; False -> ...
+
+ If we (unsoundly) eta-reduce f to get f=f, the strictness analyser
+ says f=bottom, and replaces the (f `seq` True) with just
+ (f `cast` unsafe-co). BUT, as thing stand, 'f' got arity 1, and it
+ *keeps* arity 1 (perhaps also wrongly). So CorePrep eta-expands
+ the definition again, so that it does not termninate after all.
+ Result: seg-fault because the boolean case actually gets a function value.
+ See Trac #1947.
+
+ So it's important to to the right thing.
+
+* Note [Arity care]: we need to be careful if we just look at f's
+ arity. Currently (Dec07), f's arity is visible in its own RHS (see
+ Note [Arity robustness] in SimplEnv) so we must *not* trust the
+ arity when checking that 'f' is a value. Otherwise we will
+ eta-reduce
+ f = \x. f x
+ to
+ f = f
+ Which might change a terminiating program (think (f `seq` e)) to a
+ non-terminating one. So we check for being a loop breaker first.
+
+ However for GlobalIds we can look at the arity; and for primops we
+ must, since they have no unfolding.
+
+* Regardless of whether 'f' is a value, we always want to
+ reduce (/\a -> f a) to f
+ This came up in a RULE: foldr (build (/\a -> g a))
+ did not match foldr (build (/\b -> ...something complex...))
+ The type checker can insert these eta-expanded versions,
+ with both type and dictionary lambdas; hence the slightly
+ ad-hoc isDictId
+
+* Never *reduce* arity. For example
+ f = \xy. g x y
+ Then if h has arity 1 we don't want to eta-reduce because then
+ f's arity would decrease, and that is bad
+
+These delicacies are why we don't use exprIsTrivial and exprIsHNF here.
+Alas.
+
+Note [Eta reduction with casted arguments]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Consider
+ (\(x:t3). f (x |> g)) :: t3 -> t2
+ where
+ f :: t1 -> t2
+ g :: t3 ~ t1
+This should be eta-reduced to
+
+ f |> (sym g -> t2)
+
+So we need to accumulate a coercion, pushing it inward (past
+variable arguments only) thus:
+ f (x |> co_arg) |> co --> (f |> (sym co_arg -> co)) x
+ f (x:t) |> co --> (f |> (t -> co)) x
+ f @ a |> co --> (f |> (forall a.co)) @ a
+ f @ (g:t1~t2) |> co --> (f |> (t1~t2 => co)) @ (g:t1~t2)
+These are the equations for ok_arg.
+
+It's true that we could also hope to eta reduce these:
+ (\xy. (f x |> g) y)
+ (\xy. (f x y) |> g)
+But the simplifier pushes those casts outwards, so we don't
+need to address that here.
+
+\begin{code}
+tryEtaReduce :: [Var] -> CoreExpr -> Maybe CoreExpr
+tryEtaReduce bndrs body
+ = go (reverse bndrs) body (mkReflCo (exprType body))
+ where
+ incoming_arity = count isId bndrs
+
+ go :: [Var] -- Binders, innermost first, types [a3,a2,a1]
+ -> CoreExpr -- Of type tr
+ -> Coercion -- Of type tr ~ ts
+ -> Maybe CoreExpr -- Of type a1 -> a2 -> a3 -> ts
+ -- See Note [Eta reduction with casted arguments]
+ -- for why we have an accumulating coercion
+ go [] fun co
+ | ok_fun fun = Just (mkCoerce co fun)
+
+ go (b : bs) (App fun arg) co
+ | Just co' <- ok_arg b arg co
+ = go bs fun co'
+
+ go _ _ _ = Nothing -- Failure!
+
+ ---------------
+ -- Note [Eta reduction conditions]
+ ok_fun (App fun (Type ty))
+ | not (any (`elemVarSet` tyVarsOfType ty) bndrs)
+ = ok_fun fun
+ ok_fun (Var fun_id)
+ = not (fun_id `elem` bndrs)
+ && (ok_fun_id fun_id || all ok_lam bndrs)
+ ok_fun _fun = False
+
+ ---------------
+ ok_fun_id fun = fun_arity fun >= incoming_arity
+
+ ---------------
+ fun_arity fun -- See Note [Arity care]
+ | isLocalId fun && isLoopBreaker (idOccInfo fun) = 0
+ | otherwise = idArity fun
+
+ ---------------
+ ok_lam v = isTyVar v || isEvVar v
+
+ ---------------
+ ok_arg :: Var -- Of type bndr_t
+ -> CoreExpr -- Of type arg_t
+ -> Coercion -- Of kind (t1~t2)
+ -> Maybe Coercion -- Of type (arg_t -> t1 ~ bndr_t -> t2)
+ -- (and similarly for tyvars, coercion args)
+ -- See Note [Eta reduction with casted arguments]
+ ok_arg bndr (Type ty) co
+ | Just tv <- getTyVar_maybe ty
+ , bndr == tv = Just (mkForAllCo tv co)
+ ok_arg bndr (Var v) co
+ | bndr == v = Just (mkFunCo (mkReflCo (idType bndr)) co)
+ ok_arg bndr (Cast (Var v) co_arg) co
+ | bndr == v = Just (mkFunCo (mkSymCo co_arg) co)
+ -- The simplifier combines multiple casts into one,
+ -- so we can have a simple-minded pattern match here
+ ok_arg _ _ _ = Nothing
+\end{code}
+
+
%************************************************************************
%* *
\subsection{Determining non-updatable right-hand-sides}
-- | This function is called only on *top-level* right-hand sides.
-- Returns @True@ if the RHS can be allocated statically in the output,
-- with no thunks involved at all.
-rhsIsStatic :: PackageId -> CoreExpr -> Bool
+rhsIsStatic :: (Name -> Bool) -> CoreExpr -> Bool
-- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
-- refers to, CAFs; (ii) in CoreToStg to decide whether to put an
-- update flag on it and (iii) in DsExpr to decide how to expand
-- This is a bit like CoreUtils.exprIsHNF, with the following differences:
-- a) scc "foo" (\x -> ...) is updatable (so we catch the right SCC)
--
--- b) (C x xs), where C is a contructors is updatable if the application is
+-- b) (C x xs), where C is a contructor is updatable if the application is
-- dynamic
--
-- c) don't look through unfolding of f in (f x).
-rhsIsStatic _this_pkg rhs = is_static False rhs
+rhsIsStatic _is_dynamic_name rhs = is_static False rhs
where
is_static :: Bool -- True <=> in a constructor argument; must be atomic
-> CoreExpr -> Bool
- is_static False (Lam b e) = isRuntimeVar b || is_static False e
-
- is_static _ (Note (SCC _) _) = False
- is_static in_arg (Note _ e) = is_static in_arg e
- is_static in_arg (Cast e _) = is_static in_arg e
+ is_static False (Lam b e) = isRuntimeVar b || is_static False e
+ is_static in_arg (Note n e) = notSccNote n && is_static in_arg e
+ is_static in_arg (Cast e _) = is_static in_arg e
is_static _ (Lit lit)
= case lit of
where
go (Var f) n_val_args
#if mingw32_TARGET_OS
- | not (isDllName _this_pkg (idName f))
+ | not (_is_dynamic_name (idName f))
#endif
= saturated_data_con f n_val_args
|| (in_arg && n_val_args == 0)
-- x = D# (1.0## /## 2.0##)
-- can't float because /## can fail.
- go (Note (SCC _) _) _ = False
- go (Note _ f) n_val_args = go f n_val_args
- go (Cast e _) n_val_args = go e n_val_args
-
- go _ _ = False
+ go (Note n f) n_val_args = notSccNote n && go f n_val_args
+ go (Cast e _) n_val_args = go e n_val_args
+ go _ _ = False
saturated_data_con f n_val_args
= case isDataConWorkId_maybe f of
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