Utility functions on @Core@ syntax
\begin{code}
+{-# OPTIONS -fno-warn-incomplete-patterns #-}
+-- The above warning supression flag is a temporary kludge.
+-- While working on this module you are encouraged to remove it and fix
+-- any warnings in the module. See
+-- http://hackage.haskell.org/trac/ghc/wiki/Commentary/CodingStyle#Warnings
+-- for details
+
+-- | Commonly useful utilites for manipulating the Core language
module CoreUtils (
- -- Construction
- mkInlineMe, mkSCC, mkCoerce,
+ -- * Constructing expressions
+ mkSCC, mkCoerce, mkCoerceI,
bindNonRec, needsCaseBinding,
- mkIfThenElse, mkAltExpr, mkPiType, mkPiTypes,
+ mkAltExpr, mkPiType, mkPiTypes,
- -- Taking expressions apart
+ -- * Taking expressions apart
findDefault, findAlt, isDefaultAlt, mergeAlts, trimConArgs,
- -- Properties of expressions
- exprType, coreAltType,
- exprIsDupable, exprIsTrivial, exprIsCheap,
+ -- * Properties of expressions
+ exprType, coreAltType, coreAltsType,
+ exprIsDupable, exprIsTrivial, exprIsCheap, exprIsExpandable,
exprIsHNF,exprOkForSpeculation, exprIsBig,
- exprIsConApp_maybe, exprIsBottom,
rhsIsStatic,
- -- Arity and eta expansion
- manifestArity, exprArity,
- exprEtaExpandArity, etaExpand,
+ -- * Expression and bindings size
+ coreBindsSize, exprSize,
- -- Size
- coreBindsSize,
-
- -- Hashing
+ -- * Hashing
hashExpr,
- -- Equality
- cheapEqExpr, tcEqExpr, tcEqExprX, applyTypeToArgs, applyTypeToArg,
+ -- * Equality
+ cheapEqExpr,
+ -- * Manipulating data constructors and types
+ applyTypeToArgs, applyTypeToArg,
dataConOrigInstPat, dataConRepInstPat, dataConRepFSInstPat
) where
#include "HsVersions.h"
import CoreSyn
-import CoreFVs
import PprCore
import Var
import SrcLoc
-import VarSet
import VarEnv
+import VarSet
import Name
+import Module
#if mingw32_TARGET_OS
import Packages
#endif
import PrimOp
import Id
import IdInfo
-import NewDemand
import Type
import Coercion
import TyCon
-import TysWiredIn
import CostCentre
-import BasicTypes
-import PackageConfig
import Unique
import Outputable
-import DynFlags
import TysPrim
import FastString
import Maybes
import Util
import Data.Word
import Data.Bits
-
-import GHC.Exts -- For `xori`
\end{code}
\begin{code}
exprType :: CoreExpr -> Type
-
+-- ^ Recover the type of a well-typed Core expression. Fails when
+-- applied to the actual 'CoreSyn.Type' expression as it cannot
+-- really be said to have a type
exprType (Var var) = idType var
exprType (Lit lit) = literalType lit
exprType (Let _ body) = exprType body
-exprType (Case _ _ ty alts) = ty
-exprType (Cast e co) = snd (coercionKind co)
-exprType (Note other_note e) = exprType e
+exprType (Case _ _ ty _) = ty
+exprType (Cast _ co) = snd (coercionKind co)
+exprType (Note _ e) = exprType e
exprType (Lam binder expr) = mkPiType binder (exprType expr)
exprType e@(App _ _)
= case collectArgs e of
exprType other = pprTrace "exprType" (pprCoreExpr other) alphaTy
coreAltType :: CoreAlt -> Type
-coreAltType (_,_,rhs) = exprType rhs
+-- ^ Returns the type of the alternatives right hand side
+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 (alt:_) = coreAltType alt
+coreAltsType [] = panic "corAltsType"
\end{code}
-@mkPiType@ makes a (->) type or a forall type, depending on whether
-it is given a type variable or a term variable. We cleverly use the
-lbvarinfo field to figure out the right annotation for the arrove in
-case of a term variable.
+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
-\begin{code}
-mkPiType :: Var -> Type -> Type -- The more polymorphic version
-mkPiTypes :: [Var] -> Type -> Type -- doesn't work...
+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.
-mkPiTypes vs ty = foldr mkPiType ty vs
+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
+-- ^ Makes a @(->)@ type or a forall type, depending
+-- on whether it is given a type variable or a term variable.
+mkPiTypes :: [Var] -> Type -> Type
+-- ^ 'mkPiType' for multiple type or value arguments
mkPiType v ty
| isId v = mkFunTy (idType v) ty
| otherwise = mkForAllTy v ty
+
+mkPiTypes vs ty = foldr mkPiType ty vs
\end{code}
\begin{code}
applyTypeToArg :: Type -> CoreExpr -> Type
+-- ^ Determines the type resulting from applying an expression to a function with the given type
applyTypeToArg fun_ty (Type arg_ty) = applyTy fun_ty arg_ty
-applyTypeToArg fun_ty other_arg = funResultTy fun_ty
+applyTypeToArg fun_ty _ = funResultTy fun_ty
applyTypeToArgs :: CoreExpr -> Type -> [CoreExpr] -> Type
--- A more efficient version of applyTypeToArg
--- when we have several args
--- The first argument is just for debugging
-applyTypeToArgs e op_ty [] = op_ty
+-- ^ A more efficient version of 'applyTypeToArg' when we have several arguments.
+-- The first argument is just for debugging, and gives some context
+applyTypeToArgs _ op_ty [] = op_ty
applyTypeToArgs e op_ty (Type ty : args)
= -- Accumulate type arguments so we can instantiate all at once
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' = applyTys op_ty (reverse rev_tys)
+ op_ty' = applyTysD msg op_ty (reverse rev_tys)
+ msg = ptext (sLit "applyTypeToArgs") <+>
+ panic_msg e op_ty
-applyTypeToArgs e op_ty (other_arg : args)
+applyTypeToArgs e op_ty (_ : args)
= case (splitFunTy_maybe op_ty) of
Just (_, res_ty) -> applyTypeToArgs e res_ty args
- Nothing -> pprPanic "applyTypeToArgs" (pprCoreExpr e $$ ppr op_ty)
-\end{code}
-
+ Nothing -> pprPanic "applyTypeToArgs" (panic_msg e op_ty)
+panic_msg :: CoreExpr -> Type -> SDoc
+panic_msg e op_ty = pprCoreExpr e $$ ppr op_ty
+\end{code}
%************************************************************************
%* *
%* *
%************************************************************************
-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}
-mkInlineMe (Var v) = Var v
-mkInlineMe e = Note InlineMe e
-\end{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
-\begin{code}
+-- | Wrap the given expression in the coercion safely, coalescing nested coercions
mkCoerce :: Coercion -> CoreExpr -> CoreExpr
mkCoerce co (Cast expr co2)
= ASSERT(let { (from_ty, _to_ty) = coercionKind co;
mkCoerce (mkTransCoercion co2 co) expr
mkCoerce co expr
- = let (from_ty, to_ty) = coercionKind co in
+ = let (from_ty, _to_ty) = coercionKind co in
-- if to_ty `coreEqType` from_ty
-- then expr
-- else
\end{code}
\begin{code}
+-- | Wraps the given expression in the cost centre unless
+-- in a way that maximises their utility to the user
mkSCC :: CostCentre -> Expr b -> Expr b
-- Note: Nested SCC's *are* preserved for the benefit of
-- cost centre stack profiling
-mkSCC cc (Lit lit) = Lit lit
+mkSCC _ (Lit lit) = Lit lit
mkSCC cc (Lam x e) = Lam x (mkSCC cc e) -- Move _scc_ inside lambda
mkSCC cc (Note (SCC cc') e) = Note (SCC cc) (Note (SCC cc') e)
mkSCC cc (Note n e) = Note n (mkSCC cc e) -- Move _scc_ inside notes
\begin{code}
bindNonRec :: Id -> CoreExpr -> CoreExpr -> CoreExpr
--- (bindNonRec x r b) produces either
--- let x = r in b
--- or
--- case r of x { _DEFAULT_ -> b }
+-- ^ @bindNonRec x r b@ produces either:
+--
+-- > let x = r in b
--
--- depending on whether x is unlifted or not
+-- or:
+--
+-- > case r of x { _DEFAULT_ -> b }
+--
+-- depending on whether we have to use a @case@ or @let@
+-- binding for the expression (see 'needsCaseBinding').
-- It's used by the desugarer to avoid building bindings
--- that give Core Lint a heart attack. Actually the simplifier
--- deals with them perfectly well.
-
+-- that give Core Lint a heart attack, although actually
+-- the simplifier deals with them perfectly well. See
+-- also 'MkCore.mkCoreLet'
bindNonRec bndr rhs body
- | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT,[],body)]
+ | needsCaseBinding (idType bndr) rhs = Case rhs bndr (exprType body) [(DEFAULT, [], body)]
| otherwise = Let (NonRec bndr rhs) body
+-- | Tests whether we have to use a @case@ rather than @let@ binding for this expression
+-- as per the invariants of 'CoreExpr': see "CoreSyn#let_app_invariant"
+needsCaseBinding :: Type -> CoreExpr -> Bool
needsCaseBinding ty rhs = isUnLiftedType ty && not (exprOkForSpeculation rhs)
-- Make a case expression instead of a let
-- These can arise either from the desugarer,
\end{code}
\begin{code}
-mkAltExpr :: AltCon -> [CoreBndr] -> [Type] -> CoreExpr
- -- This guy constructs the value that the scrutinee must have
- -- when you are in one particular branch of a case
+mkAltExpr :: AltCon -- ^ Case alternative constructor
+ -> [CoreBndr] -- ^ Things bound by the pattern match
+ -> [Type] -- ^ The type arguments to the case alternative
+ -> CoreExpr
+-- ^ This guy constructs the value that the scrutinee must have
+-- given that you are in one particular branch of a case
mkAltExpr (DataAlt con) args inst_tys
= mkConApp con (map Type inst_tys ++ varsToCoreExprs args)
mkAltExpr (LitAlt lit) [] []
= Lit lit
mkAltExpr (LitAlt _) _ _ = panic "mkAltExpr LitAlt"
mkAltExpr DEFAULT _ _ = panic "mkAltExpr DEFAULT"
-
-mkIfThenElse :: CoreExpr -> CoreExpr -> CoreExpr -> CoreExpr
-mkIfThenElse guard then_expr else_expr
--- Not going to be refining, so okay to take the type of the "then" clause
- = Case guard (mkWildId boolTy) (exprType then_expr)
- [ (DataAlt falseDataCon, [], else_expr), -- Increasing order of tag!
- (DataAlt trueDataCon, [], then_expr) ]
\end{code}
This makes it easy to find, though it makes matching marginally harder.
\begin{code}
+-- | Extract the default case alternative
findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null args ) (alts, Just rhs)
findDefault alts = (alts, Nothing)
-findAlt :: AltCon -> [CoreAlt] -> CoreAlt
+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] -> Maybe CoreAlt
+ -- A "Nothing" result *is* legitmiate
+ -- See Note [Unreachable code]
findAlt con alts
= case alts of
- (deflt@(DEFAULT,_,_):alts) -> go alts deflt
- other -> 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 other = False
-
---------------------------------
mergeAlts :: [CoreAlt] -> [CoreAlt] -> [CoreAlt]
--- Merge preserving order; alternatives in the first arg
--- shadow ones in the second
+-- ^ Merge alternatives preserving order; alternatives in
+-- the first argument shadow ones in the second
mergeAlts [] as2 = as2
mergeAlts as1 [] = as1
mergeAlts (a1:as1) (a2:as2)
---------------------------------
trimConArgs :: AltCon -> [CoreArg] -> [CoreArg]
--- Given case (C a b x y) of
--- C b x y -> ...
--- we want to drop the leading type argument of the scrutinee
+-- ^ Given:
+--
+-- > case (C a b x y) of
+-- > C b x y -> ...
+--
+-- We want to drop the leading type argument of the scrutinee
-- leaving the arguments to match agains the pattern
trimConArgs DEFAULT args = ASSERT( null args ) []
-trimConArgs (LitAlt lit) args = ASSERT( null args ) []
+trimConArgs (LitAlt _) args = ASSERT( null args ) []
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}
+ Figuring out things about expressions
%* *
%************************************************************************
applications. Note that primop Ids aren't considered
trivial unless
-@exprIsBottom@ is true of expressions that are guaranteed to diverge
-
-
+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
-The idea here is that a constructor worker, like $wJust, is
-really short for (\x -> $wJust x), becuase $wJust has no binding.
+The idea here is that a constructor worker, like \$wJust, is
+really short for (\x -> \$wJust x), becuase \$wJust has no binding.
So it should be treated like a lambda. Ditto unsaturated primops.
But now constructor workers are not "have-no-binding" Ids. And
completely un-applied primops and foreign-call Ids are sufficiently
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 (Var v) = True -- See notes above
-exprIsTrivial (Type _) = True
-exprIsTrivial (Lit lit) = litIsTrivial lit
-exprIsTrivial (App e arg) = not (isRuntimeArg arg) && exprIsTrivial e
-exprIsTrivial (Note (SCC _) e) = False -- See notes above
-exprIsTrivial (Note _ e) = exprIsTrivial e
-exprIsTrivial (Cast e co) = exprIsTrivial e
-exprIsTrivial (Lam b body) = not (isRuntimeVar b) && exprIsTrivial body
-exprIsTrivial other = False
+exprIsTrivial :: CoreExpr -> Bool
+exprIsTrivial (Var _) = True -- See Note [Variables are trivial]
+exprIsTrivial (Type _) = True
+exprIsTrivial (Lit lit) = litIsTrivial lit
+exprIsTrivial (App e arg) = not (isRuntimeArg arg) && 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}
\begin{code}
-exprIsDupable (Type _) = True
-exprIsDupable (Var v) = True
-exprIsDupable (Lit lit) = litIsDupable lit
-exprIsDupable (Note InlineMe e) = True
-exprIsDupable (Note _ e) = exprIsDupable e
-exprIsDupable (Cast e co) = exprIsDupable e
-exprIsDupable expr
+exprIsDupable :: CoreExpr -> Bool
+exprIsDupable (Type _) = True
+exprIsDupable (Var _) = True
+exprIsDupable (Lit lit) = litIsDupable lit
+exprIsDupable (Note _ e) = exprIsDupable e
+exprIsDupable (Cast e _) = exprIsDupable e
+exprIsDupable expr
= go expr 0
where
- go (Var v) n_args = True
+ go (Var _) _ = True
go (App f a) n_args = n_args < dupAppSize
&& exprIsDupable a
&& go f (n_args+1)
- go other n_args = False
+ go _ _ = False
dupAppSize :: Int
dupAppSize = 4 -- Size of application we are prepared to duplicate
because sharing will make sure it is only evaluated once.
\begin{code}
-exprIsCheap :: CoreExpr -> Bool
-exprIsCheap (Lit lit) = True
-exprIsCheap (Type _) = True
-exprIsCheap (Var _) = True
-exprIsCheap (Note InlineMe e) = True
-exprIsCheap (Note _ e) = exprIsCheap e
-exprIsCheap (Cast e co) = exprIsCheap e
-exprIsCheap (Lam x e) = isRuntimeVar x || exprIsCheap e
-exprIsCheap (Case e _ _ alts) = exprIsCheap e &&
- and [exprIsCheap rhs | (_,_,rhs) <- alts]
+exprIsCheap' :: (Id -> Bool) -> CoreExpr -> Bool
+exprIsCheap' _ (Lit _) = True
+exprIsCheap' _ (Type _) = True
+exprIsCheap' _ (Var _) = 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]
-- 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 (Let (NonRec x _) e)
- | isUnLiftedType (idType x) = exprIsCheap e
+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 other_expr -- Applications and variables
+exprIsCheap' is_conlike other_expr -- Applications and variables
= go other_expr []
where
-- Accumulate value arguments, then decide
go (App f a) val_args | isRuntimeArg a = go f (a:val_args)
| otherwise = go f val_args
- go (Var f) [] = True -- Just a type application of a variable
+ go (Var _) [] = True -- Just a type application of a variable
-- (f t1 t2 t3) counts as WHNF
go (Var f) args
- = case globalIdDetails f of
- RecordSelId {} -> go_sel args
- ClassOpId _ -> go_sel args
- PrimOpId op -> go_primop op args
+ = case idDetails f of
+ RecSelId {} -> go_sel args
+ ClassOpId {} -> go_sel args
+ PrimOpId op -> go_primop op args
- DataConWorkId _ -> go_pap args
- other | length args < idArity f -> go_pap args
+ _ | is_conlike f -> go_pap args
+ | length args < idArity f -> go_pap args
- other -> isBottomingId f
+ _ -> isBottomingId f
-- Application of a function which
-- always gives bottom; we treat this as cheap
-- because it certainly doesn't need to be shared!
- go other args = False
+ go _ _ = False
--------------
go_pap args = all exprIsTrivial args
-- We'll put up with one constructor application, but not dozens
--------------
- go_primop op args = primOpIsCheap op && all exprIsCheap args
+ go_primop op args = primOpIsCheap op && all (exprIsCheap' is_conlike) 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 arg -- I'm experimenting with making record selection
- go_sel other = False -- look cheap, so we will substitute it inside a
+ go_sel [arg] = exprIsCheap' is_conlike 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)
-\end{code}
-
-exprOkForSpeculation returns True of an expression that it is
-
- * safe to evaluate even if normal order eval might not
- evaluate the expression at all, or
-
- * safe *not* to evaluate even if normal order would do so
-
-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)
-
-NB: if exprIsHNF e, then exprOkForSpecuation e
-
-E.G.
- let x = case y# +# 1# of { r# -> I# r# }
- in E
-==>
- case y# +# 1# of { r# ->
- let x = I# r#
- in E
- }
+exprIsCheap :: CoreExpr -> Bool
+exprIsCheap = exprIsCheap' isDataConWorkId
-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.
+exprIsExpandable :: CoreExpr -> Bool
+exprIsExpandable = exprIsCheap' isConLikeId -- See Note [CONLIKE pragma] in BasicTypes
+\end{code}
\begin{code}
+-- | 'exprOkForSpeculation' returns True of an expression that is:
+--
+-- * Safe to evaluate even if normal order eval might not
+-- evaluate the expression at all, or
+--
+-- * Safe /not/ to evaluate even if normal order would do so
+--
+-- 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@.
+-- As an example of the considerations in this test, consider:
+--
+-- > let x = case y# +# 1# of { r# -> I# r# }
+-- > in E
+--
+-- being translated to:
+--
+-- > case y# +# 1# of { r# ->
+-- > let x = I# r#
+-- > in 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
exprOkForSpeculation (Var v) = isUnLiftedType (idType v)
&& not (isTickBoxOp v)
exprOkForSpeculation (Note _ e) = exprOkForSpeculation e
-exprOkForSpeculation (Cast e co) = exprOkForSpeculation e
+exprOkForSpeculation (Cast e _) = exprOkForSpeculation e
exprOkForSpeculation other_expr
= case collectArgs other_expr of
- (Var f, args) -> spec_ok (globalIdDetails f) args
- other -> False
+ (Var f, args) -> spec_ok (idDetails f) args
+ _ -> False
where
- spec_ok (DataConWorkId _) args
+ spec_ok (DataConWorkId _) _
= True -- The strictness of the constructor has already
-- been expressed by its "wrapper", so we don't need
-- to take the arguments into account
-- A bit conservative: we don't really need
-- to care about lazy arguments, but this is easy
- spec_ok other args = False
+ 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 :: PrimOp -> Bool
--- True of dyadic operators that can fail
--- only if the second arg is zero
-- This function probably belongs in PrimOp, or even in
-- an automagically generated file.. but it's such a
-- special case I thought I'd leave it here for now.
isDivOp IntRemOp = True
isDivOp WordQuotOp = True
isDivOp WordRemOp = True
-isDivOp IntegerQuotRemOp = True
-isDivOp IntegerDivModOp = True
isDivOp FloatDivOp = True
isDivOp DoubleDivOp = True
-isDivOp other = False
+isDivOp _ = False
\end{code}
-
\begin{code}
+{- Never used -- omitting
+-- | True of expressions that are guaranteed to diverge upon execution
exprIsBottom :: CoreExpr -> Bool -- True => definitely bottom
exprIsBottom e = go 0 e
- where
- -- n is the number of args
- go n (Note _ e) = go n e
- go n (Cast e co) = go n e
- go n (Let _ e) = go n e
- go n (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 n (Lit _) = False
- go n (Lam _ _) = False
- go n (Type _) = False
+ 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}
-@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 ===> 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.
-
-But it *does* treat partial applications and constructor applications
-as values, even if their arguments are non-trivial, provided the argument
-type is lifted;
- e.g. (:) (f x) (map f xs) is a value
- map (...redex...) is a value
-Because `seq` on such things completes immediately
-
-For unlifted argument types, we have to be careful:
- C (f x :: Int#)
-Suppose (f x) diverges; then C (f x) is not a value. However this can't
-happen: see CoreSyn Note [CoreSyn let/app invariant]. Args of unboxed
-type must be ok-for-speculation (or trivial).
-
\begin{code}
+
+-- | This 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:
+--
+-- > 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
+-- type is lifted. For example, both of these are values:
+--
+-- > (:) (f x) (map f xs)
+-- > map (...redex...)
+--
+-- Because 'seq' on such things completes immediately.
+--
+-- For unlifted argument types, we have to be careful:
+--
+-- > C (f x :: Int#)
+--
+-- Suppose @f x@ diverges; then @C (f x)@ is not a value. However this can't
+-- 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,
-- A worry: what if an Id's unfolding is just itself:
-- then we could get an infinite loop...
-exprIsHNF (Lit l) = True
-exprIsHNF (Type ty) = 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 co) = exprIsHNF e
+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 other = False
+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 n f) as = app_is_value f as
+ = 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 other as = False
+app_is_value _ _ = False
\end{code}
+These InstPat functions go here to avoid circularity between DataCon and Id
+
\begin{code}
--- These InstPat functions go here to avoid circularity between DataCon and Id
-dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat (FSLIT("ipv")))
+dataConRepInstPat, dataConOrigInstPat :: [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
+dataConRepFSInstPat :: [FastString] -> [Unique] -> DataCon -> [Type] -> ([TyVar], [CoVar], [Id])
+
+dataConRepInstPat = dataConInstPat dataConRepArgTys (repeat ((fsLit "ipv")))
dataConRepFSInstPat = dataConInstPat dataConRepArgTys
-dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat (FSLIT("ipv")))
+dataConOrigInstPat = dataConInstPat dc_arg_tys (repeat ((fsLit "ipv")))
where
- dc_arg_tys dc = map mkPredTy (dataConTheta dc) ++ dataConOrigArgTys dc
+ 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
--
-- 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, including
--- dicts, and their types have been instantiated with inst_tys and ex_tys
+-- 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)
--
-- Example.
-- The following constructor T1
-- ...
--
-- has representation type
--- forall a. forall a1. forall b. (a :=: (a1,b)) =>
+-- forall a. forall a1. forall b. (a ~ (a1,b)) =>
-- Int -> b -> T a
--
-- 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, id_bndrs)
+ = (ex_bndrs, co_bndrs, arg_ids)
where
univ_tvs = dataConUnivTyVars con
ex_tvs = dataConExTyVars con
arg_tys = arg_fun con
eq_spec = dataConEqSpec con
- eq_preds = eqSpecPreds eq_spec
+ eq_theta = dataConEqTheta con
+ eq_preds = eqSpecPreds eq_spec ++ eq_theta
n_ex = length ex_tvs
- n_co = length eq_spec
+ n_co = length eq_preds
-- split the Uniques and FastStrings
(ex_uniqs, uniqs') = splitAt n_ex uniqs
-- make value vars, instantiating types
mk_id_var uniq fs ty = mkUserLocal (mkVarOccFS fs) uniq (substTy subst ty) noSrcSpan
- id_bndrs = zipWith3 mk_id_var id_uniqs id_fss arg_tys
-
-exprIsConApp_maybe :: CoreExpr -> Maybe (DataCon, [CoreExpr])
--- Returns (Just (dc, [x1..xn])) if the argument expression is
--- a constructor application of the form (dc x1 .. xn)
-exprIsConApp_maybe (Cast expr co)
- = -- Here we do the PushC 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, val_args) = splitAt n_cos rest2
-
- arg_tys = dataConRepArgTys dc
- dc_univ_tyvars = dataConUnivTyVars dc
- dc_ex_tyvars = dataConExTyVars dc
- dc_eq_spec = dataConEqSpec dc
- dc_tyvars = dc_univ_tyvars ++ dc_ex_tyvars
- n_ex_tvs = length dc_ex_tyvars
- n_cos = length dc_eq_spec
-
- -- 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 (tv,ty) (Type co) = Type $ mkSymCoercion (substTyVar theta tv)
- `mkTransCoercion` co
- `mkTransCoercion` (substTy theta ty)
- new_co_args = zipWith cast_co dc_eq_spec co_args
-
- -- ...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
--}
+ arg_ids = zipWith3 mk_id_var id_uniqs id_fss arg_tys
-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,
- isCheapUnfolding unf
- = exprIsConApp_maybe (unfoldingTemplate unf)
-
- analyse other = Nothing
\end{code}
-
-
%************************************************************************
%* *
-\subsection{Eta reduction and expansion}
+ Equality
%* *
%************************************************************************
\begin{code}
-exprEtaExpandArity :: DynFlags -> CoreExpr -> Arity
-{- The Arity returned is the number of value args the
- thing can be applied to without doing much work
-
-exprEtaExpandArity is used when eta expanding
- e ==> \xy -> e x y
-
-It returns 1 (or more) to:
- case x of p -> \s -> ...
-because for I/O ish things we really want to get that \s to the top.
-We are prepared to evaluate x each time round the loop in order to get that
-
-It's all a bit more subtle than it looks:
-
-1. One-shot lambdas
-
-Consider one-shot lambdas
- let x = expensive in \y z -> E
-We want this to have arity 2 if the \y-abstraction is a 1-shot lambda
-Hence the ArityType returned by arityType
-
-2. The state-transformer hack
-
-The one-shot lambda special cause is particularly important/useful for
-IO state transformers, where we often get
- let x = E in \ s -> ...
-
-and the \s is a real-world state token abstraction. Such abstractions
-are almost invariably 1-shot, so we want to pull the \s out, past the
-let x=E, even if E is expensive. So we treat state-token lambdas as
-one-shot even if they aren't really. The hack is in Id.isOneShotBndr.
-
-3. Dealing with bottom
-
-Consider also
- f = \x -> error "foo"
-Here, arity 1 is fine. But if it is
- f = \x -> case x of
- True -> error "foo"
- False -> \y -> x+y
-then we want to get arity 2. Tecnically, this isn't quite right, because
- (f True) `seq` 1
-should diverge, but it'll converge if we eta-expand f. Nevertheless, we
-do so; it improves some programs significantly, and increasing convergence
-isn't a bad thing. Hence the ABot/ATop in ArityType.
-
-Actually, the situation is worse. Consider
- f = \x -> case x of
- True -> \y -> x+y
- False -> \y -> x-y
-Can we eta-expand here? At first the answer looks like "yes of course", but
-consider
- (f bot) `seq` 1
-This should diverge! But if we eta-expand, it won't. Again, we ignore this
-"problem", because being scrupulous would lose an important transformation for
-many programs.
-
-
-4. Newtypes
-
-Non-recursive newtypes are transparent, and should not get in the way.
-We do (currently) eta-expand recursive newtypes too. So if we have, say
-
- newtype T = MkT ([T] -> Int)
-
-Suppose we have
- e = coerce T f
-where f has arity 1. Then: etaExpandArity e = 1;
-that is, etaExpandArity looks through the coerce.
-
-When we eta-expand e to arity 1: eta_expand 1 e T
-we want to get: coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
-
-HOWEVER, note that if you use coerce bogusly you can ge
- coerce Int negate
-And since negate has arity 2, you might try to eta expand. But you can't
-decopose Int to a function type. Hence the final case in eta_expand.
--}
-
-
-exprEtaExpandArity dflags e = arityDepth (arityType dflags e)
-
--- A limited sort of function type
-data ArityType = AFun Bool ArityType -- True <=> one-shot
- | ATop -- Know nothing
- | ABot -- Diverges
-
-arityDepth :: ArityType -> Arity
-arityDepth (AFun _ ty) = 1 + arityDepth ty
-arityDepth ty = 0
-
-andArityType ABot at2 = at2
-andArityType ATop at2 = ATop
-andArityType (AFun t1 at1) (AFun t2 at2) = AFun (t1 && t2) (andArityType at1 at2)
-andArityType at1 at2 = andArityType at2 at1
-
-arityType :: DynFlags -> CoreExpr -> ArityType
- -- (go1 e) = [b1,..,bn]
- -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
- -- where bi is True <=> the lambda is one-shot
-
-arityType dflags (Note n e) = arityType dflags e
--- Not needed any more: etaExpand is cleverer
--- | ok_note n = arityType dflags e
--- | otherwise = ATop
-
-arityType dflags (Cast e co) = arityType dflags e
-
-arityType dflags (Var v)
- = mk (idArity v) (arg_tys (idType v))
- where
- mk :: Arity -> [Type] -> ArityType
- -- The argument types are only to steer the "state hack"
- -- Consider case x of
- -- True -> foo
- -- False -> \(s:RealWorld) -> e
- -- where foo has arity 1. Then we want the state hack to
- -- apply to foo too, so we can eta expand the case.
- mk 0 tys | isBottomingId v = ABot
- | (ty:tys) <- tys, isStateHackType ty = AFun True ATop
- | otherwise = ATop
- mk n (ty:tys) = AFun (isStateHackType ty) (mk (n-1) tys)
- mk n [] = AFun False (mk (n-1) [])
-
- arg_tys :: Type -> [Type] -- Ignore for-alls
- arg_tys ty
- | Just (_, ty') <- splitForAllTy_maybe ty = arg_tys ty'
- | Just (arg,res) <- splitFunTy_maybe ty = arg : arg_tys res
- | otherwise = []
-
- -- Lambdas; increase arity
-arityType dflags (Lam x e)
- | isId x = AFun (isOneShotBndr x) (arityType dflags e)
- | otherwise = arityType dflags e
-
- -- Applications; decrease arity
-arityType dflags (App f (Type _)) = arityType dflags f
-arityType dflags (App f a) = case arityType dflags f of
- AFun one_shot xs | exprIsCheap a -> xs
- other -> ATop
-
- -- Case/Let; keep arity if either the expression is cheap
- -- or it's a 1-shot lambda
- -- The former is not really right for Haskell
- -- f x = case x of { (a,b) -> \y. e }
- -- ===>
- -- f x y = case x of { (a,b) -> e }
- -- The difference is observable using 'seq'
-arityType dflags (Case scrut _ _ alts)
- = case foldr1 andArityType [arityType dflags rhs | (_,_,rhs) <- alts] of
- xs | exprIsCheap scrut -> xs
- xs@(AFun one_shot _) | one_shot -> AFun True ATop
- other -> ATop
-
-arityType dflags (Let b e)
- = case arityType dflags e of
- xs | cheap_bind b -> xs
- xs@(AFun one_shot _) | one_shot -> AFun True ATop
- other -> ATop
- where
- cheap_bind (NonRec b e) = is_cheap (b,e)
- cheap_bind (Rec prs) = all is_cheap prs
- is_cheap (b,e) = (dopt Opt_DictsCheap dflags && isDictId b)
- || exprIsCheap e
- -- If the experimental -fdicts-cheap flag is on, we eta-expand through
- -- dictionary bindings. This improves arities. Thereby, it also
- -- means that full laziness is less prone to floating out the
- -- application of a function to its dictionary arguments, which
- -- can thereby lose opportunities for fusion. Example:
- -- foo :: Ord a => a -> ...
- -- foo = /\a \(d:Ord a). let d' = ...d... in \(x:a). ....
- -- -- So foo has arity 1
- --
- -- f = \x. foo dInt $ bar x
- --
- -- The (foo DInt) is floated out, and makes ineffective a RULE
- -- foo (bar x) = ...
- --
- -- One could go further and make exprIsCheap reply True to any
- -- dictionary-typed expression, but that's more work.
-
-arityType dflags other = ATop
-
-{- NOT NEEDED ANY MORE: etaExpand is cleverer
-ok_note InlineMe = False
-ok_note other = True
- -- Notice that we do not look through __inline_me__
- -- This may seem surprising, but consider
- -- f = _inline_me (\x -> e)
- -- We DO NOT want to eta expand this to
- -- f = \x -> (_inline_me (\x -> e)) x
- -- because the _inline_me gets dropped now it is applied,
- -- giving just
- -- f = \x -> e
- -- A Bad Idea
--}
-\end{code}
-
-
-\begin{code}
-etaExpand :: Arity -- Result should have this number of value args
- -> [Unique]
- -> CoreExpr -> Type -- Expression and its type
- -> CoreExpr
--- (etaExpand n us e ty) returns an expression with
--- the same meaning as 'e', but with arity 'n'.
---
--- Given e' = etaExpand n us e ty
--- We should have
--- ty = exprType e = exprType e'
+-- | A cheap equality test which bales out fast!
+-- If it returns @True@ the arguments are definitely equal,
+-- otherwise, they may or may not be equal.
--
--- Note that SCCs are not treated specially. If we have
--- etaExpand 2 (\x -> scc "foo" e)
--- = (\xy -> (scc "foo" e) y)
--- So the costs of evaluating 'e' (not 'e y') are attributed to "foo"
-
-etaExpand n us expr ty
- | manifestArity expr >= n = expr -- The no-op case
- | otherwise
- = eta_expand n us expr ty
- where
-
--- manifestArity sees how many leading value lambdas there are
-manifestArity :: CoreExpr -> Arity
-manifestArity (Lam v e) | isId v = 1 + manifestArity e
- | otherwise = manifestArity e
-manifestArity (Note _ e) = manifestArity e
-manifestArity (Cast e _) = manifestArity e
-manifestArity e = 0
-
--- etaExpand deals with for-alls. For example:
--- etaExpand 1 E
--- where E :: forall a. a -> a
--- would return
--- (/\b. \y::a -> E b y)
---
--- It deals with coerces too, though they are now rare
--- so perhaps the extra code isn't worth it
-
-eta_expand n us expr ty
- | n == 0 &&
- -- The ILX code generator requires eta expansion for type arguments
- -- too, but alas the 'n' doesn't tell us how many of them there
- -- may be. So we eagerly eta expand any big lambdas, and just
- -- cross our fingers about possible loss of sharing in the ILX case.
- -- The Right Thing is probably to make 'arity' include
- -- type variables throughout the compiler. (ToDo.)
- not (isForAllTy ty)
- -- Saturated, so nothing to do
- = expr
-
- -- Short cut for the case where there already
- -- is a lambda; no point in gratuitously adding more
-eta_expand n us (Lam v body) ty
- | isTyVar v
- = Lam v (eta_expand n us body (applyTy ty (mkTyVarTy v)))
-
- | otherwise
- = Lam v (eta_expand (n-1) us body (funResultTy ty))
-
--- We used to have a special case that stepped inside Coerces here,
--- thus: eta_expand n us (Note note@(Coerce _ ty) e) _
--- = Note note (eta_expand n us e ty)
--- BUT this led to an infinite loop
--- Example: newtype T = MkT (Int -> Int)
--- eta_expand 1 (coerce (Int->Int) e)
--- --> coerce (Int->Int) (eta_expand 1 T e)
--- by the bogus eqn
--- --> coerce (Int->Int) (coerce T
--- (\x::Int -> eta_expand 1 (coerce (Int->Int) e)))
--- by the splitNewType_maybe case below
--- and round we go
-
-eta_expand n us expr ty
- = ASSERT2 (exprType expr `coreEqType` ty, ppr (exprType expr) $$ ppr ty)
- case splitForAllTy_maybe ty of {
- Just (tv,ty') ->
-
- Lam lam_tv (eta_expand n us2 (App expr (Type (mkTyVarTy lam_tv))) (substTyWith [tv] [mkTyVarTy lam_tv] ty'))
- where
- lam_tv = setVarName tv (mkSysTvName uniq FSLIT("etaT"))
- -- Using tv as a base retains its tyvar/covar-ness
- (uniq:us2) = us
- ; Nothing ->
-
- case splitFunTy_maybe ty of {
- Just (arg_ty, res_ty) -> Lam arg1 (eta_expand (n-1) us2 (App expr (Var arg1)) res_ty)
- where
- arg1 = mkSysLocal FSLIT("eta") uniq arg_ty
- (uniq:us2) = us
-
- ; Nothing ->
-
- -- Given this:
- -- newtype T = MkT ([T] -> Int)
- -- Consider eta-expanding this
- -- eta_expand 1 e T
- -- We want to get
- -- coerce T (\x::[T] -> (coerce ([T]->Int) e) x)
-
- case splitNewTypeRepCo_maybe ty of {
- Just(ty1,co) ->
- mkCoerce (mkSymCoercion co) (eta_expand n us (mkCoerce co expr) ty1) ;
- Nothing ->
-
- -- We have an expression of arity > 0, but its type isn't a function
- -- This *can* legitmately happen: e.g. coerce Int (\x. x)
- -- Essentially the programmer is playing fast and loose with types
- -- (Happy does this a lot). So we simply decline to eta-expand.
- expr
- }}}
-\end{code}
-
-exprArity is a cheap-and-cheerful version of exprEtaExpandArity.
-It tells how many things the expression can be applied to before doing
-any work. It doesn't look inside cases, lets, etc. The idea is that
-exprEtaExpandArity will do the hard work, leaving something that's easy
-for exprArity to grapple with. In particular, Simplify uses exprArity to
-compute the ArityInfo for the Id.
-
-Originally I thought that it was enough just to look for top-level lambdas, but
-it isn't. I've seen this
-
- foo = PrelBase.timesInt
-
-We want foo to get arity 2 even though the eta-expander will leave it
-unchanged, in the expectation that it'll be inlined. But occasionally it
-isn't, because foo is blacklisted (used in a rule).
-
-Similarly, see the ok_note check in exprEtaExpandArity. So
- f = __inline_me (\x -> e)
-won't be eta-expanded.
-
-And in any case it seems more robust to have exprArity be a bit more intelligent.
-But note that (\x y z -> f x y z)
-should have arity 3, regardless of f's arity.
-
-\begin{code}
-exprArity :: CoreExpr -> Arity
-exprArity e = go e
- where
- go (Var v) = idArity v
- go (Lam x e) | isId x = go e + 1
- | otherwise = go e
- go (Note n e) = go e
- go (Cast e _) = go e
- go (App e (Type t)) = go e
- go (App f a) | exprIsCheap a = (go f - 1) `max` 0
- -- NB: exprIsCheap a!
- -- f (fac x) does not have arity 2,
- -- even if f has arity 3!
- -- NB: `max 0`! (\x y -> f x) has arity 2, even if f is
- -- unknown, hence arity 0
- go _ = 0
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Equality}
-%* *
-%************************************************************************
-
-@cheapEqExpr@ is a cheap equality test which bales out fast!
- True => definitely equal
- False => may or may not be equal
-
-\begin{code}
+-- See also 'exprIsBig'
cheapEqExpr :: Expr b -> Expr b -> Bool
cheapEqExpr (Var v1) (Var v2) = v1==v2
cheapEqExpr (App f1 a1) (App f2 a2)
= f1 `cheapEqExpr` f2 && a1 `cheapEqExpr` a2
+cheapEqExpr (Cast e1 t1) (Cast e2 t2)
+ = e1 `cheapEqExpr` e2 && t1 `coreEqCoercion` t2
+
cheapEqExpr _ _ = False
exprIsBig :: Expr b -> Bool
--- Returns True of expressions that are too big to be compared by cheapEqExpr
+-- ^ Returns @True@ of expressions that are too big to be compared by 'cheapEqExpr'
exprIsBig (Lit _) = False
-exprIsBig (Var v) = False
-exprIsBig (Type t) = False
+exprIsBig (Var _) = False
+exprIsBig (Type _) = 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 other = True
+exprIsBig _ = True
\end{code}
-\begin{code}
-tcEqExpr :: CoreExpr -> CoreExpr -> Bool
--- Used in rule matching, so does *not* look through
--- newtypes, predicate types; hence tcEqExpr
-
-tcEqExpr e1 e2 = tcEqExprX rn_env e1 e2
- where
- rn_env = mkRnEnv2 (mkInScopeSet (exprFreeVars e1 `unionVarSet` exprFreeVars e2))
-
-tcEqExprX :: RnEnv2 -> CoreExpr -> CoreExpr -> Bool
-tcEqExprX env (Var v1) (Var v2) = rnOccL env v1 == rnOccR env v2
-tcEqExprX env (Lit lit1) (Lit lit2) = lit1 == lit2
-tcEqExprX env (App f1 a1) (App f2 a2) = tcEqExprX env f1 f2 && tcEqExprX env a1 a2
-tcEqExprX env (Lam v1 e1) (Lam v2 e2) = tcEqExprX (rnBndr2 env v1 v2) e1 e2
-tcEqExprX env (Let (NonRec v1 r1) e1)
- (Let (NonRec v2 r2) e2) = tcEqExprX env r1 r2
- && tcEqExprX (rnBndr2 env v1 v2) e1 e2
-tcEqExprX env (Let (Rec ps1) e1)
- (Let (Rec ps2) e2) = equalLength ps1 ps2
- && and (zipWith eq_rhs ps1 ps2)
- && tcEqExprX env' e1 e2
- where
- env' = foldl2 rn_bndr2 env ps2 ps2
- rn_bndr2 env (b1,_) (b2,_) = rnBndr2 env b1 b2
- eq_rhs (_,r1) (_,r2) = tcEqExprX env' r1 r2
-tcEqExprX env (Case e1 v1 t1 a1)
- (Case e2 v2 t2 a2) = tcEqExprX env e1 e2
- && tcEqTypeX env t1 t2
- && equalLength a1 a2
- && and (zipWith (eq_alt env') a1 a2)
- where
- env' = rnBndr2 env v1 v2
-
-tcEqExprX env (Note n1 e1) (Note n2 e2) = eq_note env n1 n2 && tcEqExprX env e1 e2
-tcEqExprX env (Cast e1 co1) (Cast e2 co2) = tcEqTypeX env co1 co2 && tcEqExprX env e1 e2
-tcEqExprX env (Type t1) (Type t2) = tcEqTypeX env t1 t2
-tcEqExprX env e1 e2 = False
-
-eq_alt env (c1,vs1,r1) (c2,vs2,r2) = c1==c2 && tcEqExprX (rnBndrs2 env vs1 vs2) r1 r2
-
-eq_note env (SCC cc1) (SCC cc2) = cc1 == cc2
-eq_note env (CoreNote s1) (CoreNote s2) = s1 == s2
-eq_note env other1 other2 = False
-\end{code}
-
%************************************************************************
%* *
coreBindsSize bs = foldr ((+) . bindSize) 0 bs
exprSize :: CoreExpr -> Int
- -- A measure of the size of the expressions
- -- It also forces the expression pretty drastically as a side effect
+-- ^ A measure of the size of the expressions, strictly greater than 0
+-- It also forces the expression pretty drastically as a side effect
exprSize (Var v) = v `seq` 1
exprSize (Lit lit) = lit `seq` 1
exprSize (App f a) = exprSize f + exprSize a
exprSize (Note n e) = noteSize n + exprSize e
exprSize (Type t) = seqType t `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
megaSeqIdInfo (idInfo b) `seq`
1
-varsSize = foldr ((+) . varSize) 0
+varsSize :: [Var] -> Int
+varsSize = sum . map varSize
+bindSize :: CoreBind -> Int
bindSize (NonRec b e) = varSize b + exprSize e
bindSize (Rec prs) = foldr ((+) . pairSize) 0 prs
+pairSize :: (Var, CoreExpr) -> Int
pairSize (b,e) = varSize b + exprSize e
+altSize :: CoreAlt -> Int
altSize (c,bs,e) = c `seq` varsSize bs + exprSize e
\end{code}
\begin{code}
hashExpr :: CoreExpr -> Int
--- Two expressions that hash to the same Int may be equal (but may not be)
--- Two expressions that hash to the different Ints are definitely unequal
---
--- But "unequal" here means "not identical"; two alpha-equivalent
--- expressions may hash to the different Ints
+-- ^ Two expressions that hash to the same @Int@ may be equal (but may not be)
+-- Two expressions that hash to the different Ints are definitely unequal.
--
--- The emphasis is on a crude, fast hash, rather than on high precision
+-- The emphasis is on a crude, fast hash, rather than on high precision.
+--
+-- But unequal here means \"not identical\"; two alpha-equivalent
+-- expressions may hash to the different Ints.
--
--- We must be careful that \x.x and \y.y map to the same hash code,
--- (at least if we want the above invariant to be true)
+-- We must be careful that @\\x.x@ and @\\y.y@ map to the same hash code,
+-- (at least if we want the above invariant to be true).
hashExpr e = fromIntegral (hash_expr (1,emptyVarEnv) e .&. 0x7fffffff)
-- UniqFM doesn't like negative Ints
-type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
+type HashEnv = (Int, VarEnv Int) -- Hash code for bound variables
hash_expr :: HashEnv -> CoreExpr -> Word32
-- Word32, because we're expecting overflows here, and overflowing
-- signed types just isn't cool. In C it's even undefined.
hash_expr env (Note _ e) = hash_expr env e
-hash_expr env (Cast e co) = hash_expr env e
+hash_expr env (Cast e _) = hash_expr env e
hash_expr env (Var v) = hashVar env v
-hash_expr env (Lit lit) = fromIntegral (hashLiteral lit)
+hash_expr _ (Lit lit) = fromIntegral (hashLiteral lit)
hash_expr env (App f e) = hash_expr env f * fast_hash_expr env e
hash_expr env (Let (NonRec b r) e) = hash_expr (extend_env env b) e * fast_hash_expr env r
-hash_expr env (Let (Rec ((b,r):_)) e) = hash_expr (extend_env env b) e
+hash_expr env (Let (Rec ((b,_):_)) e) = hash_expr (extend_env env b) e
hash_expr env (Case e _ _ _) = hash_expr env e
hash_expr env (Lam b e) = hash_expr (extend_env env b) e
-hash_expr env (Type t) = WARN(True, text "hash_expr: type") 1
+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.
+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 env (Lit lit) = fromIntegral (hashLiteral lit)
-fast_hash_expr env (Cast e co) = fast_hash_expr env e
-fast_hash_expr env (Note n e) = fast_hash_expr env e
-fast_hash_expr env (App f a) = fast_hash_expr env a -- A bit idiosyncratic ('a' not 'f')!
-fast_hash_expr env other = 1
+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
labels in other DLLs).
If this happens we simply make the RHS into an updatable thunk,
-and 'exectute' it rather than allocating it statically.
+and 'execute' it rather than allocating it statically.
\begin{code}
+-- | 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
--- This function is called only on *top-level* right-hand sides
--- Returns True if the RHS can be allocated statically, with
--- no thunks involved at all.
---
-- It's called (i) in TidyPgm.hasCafRefs to decide if the rhs is, or
--- refers to, CAFs; and (ii) in CoreToStg to decide whether to put an
--- update flag on it.
+-- 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
+-- list literals
--
-- The basic idea is that rhsIsStatic returns True only if the RHS is
-- (a) a value lambda
-- 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).
---
--- When opt_RuntimeTypes is on, we keep type lambdas and treat
--- them as making the RHS re-entrant (non-updatable).
-rhsIsStatic this_pkg rhs = is_static False rhs
+rhsIsStatic _this_pkg 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 in_arg (Note (SCC _) e) = False
+ is_static _ (Note (SCC _) _) = False
is_static in_arg (Note _ e) = is_static in_arg e
- is_static in_arg (Cast e co) = is_static in_arg e
+ is_static in_arg (Cast e _) = is_static in_arg e
- is_static in_arg (Lit lit)
+ is_static _ (Lit lit)
= case lit of
- MachLabel _ _ -> False
- other -> True
+ MachLabel _ _ _ -> False
+ _ -> True
-- A MachLabel (foreign import "&foo") in an argument
-- prevents a constructor application from being static. The
-- reason is that it might give rise to unresolvable symbols
where
go (Var f) n_val_args
#if mingw32_TARGET_OS
- | not (isDllName this_pkg (idName f))
+ | not (isDllName _this_pkg (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 _) f) n_val_args = False
- go (Note _ f) n_val_args = go f n_val_args
- go (Cast e co) n_val_args = go e n_val_args
+ 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 other n_val_args = False
+ go _ _ = False
saturated_data_con f n_val_args
= case isDataConWorkId_maybe f of
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