bindNonRec, mkIfThenElse, mkAltExpr,
mkPiType,
+ -- Taking expressions apart
+ findDefault, findAlt,
+
-- Properties of expressions
exprType, coreAltsType,
exprIsBottom, exprIsDupable, exprIsTrivial, exprIsCheap,
import VarSet
import VarEnv
import Name ( hashName )
-import Literal ( hashLiteral, literalType, litSize, litIsDupable )
+import Literal ( hashLiteral, literalType, litIsDupable )
import DataCon ( DataCon, dataConRepArity )
import PrimOp ( primOpOkForSpeculation, primOpIsCheap,
primOpIsDupable )
-import Id ( Id, idType, idFlavour, idStrictness, idLBVarInfo,
- mkWildId, idArity, idName, idUnfolding, idInfo,
- isDataConId_maybe, isPrimOpId_maybe, mkSysLocal
+import Id ( Id, idType, globalIdDetails, idStrictness, idLBVarInfo,
+ mkWildId, idArity, idName, idUnfolding, idInfo, isOneShotLambda,
+ isDataConId_maybe, isPrimOpId_maybe, mkSysLocal, hasNoBinding
)
import IdInfo ( LBVarInfo(..),
- IdFlavour(..),
+ GlobalIdDetails(..),
megaSeqIdInfo )
import Demand ( appIsBottom )
import Type ( Type, mkFunTy, mkForAllTy, splitFunTy_maybe,
(DataAlt falseDataCon, [], else_expr) ]
\end{code}
+
+%************************************************************************
+%* *
+\subsection{Taking expressions apart}
+%* *
+%************************************************************************
+
+
+\begin{code}
+findDefault :: [CoreAlt] -> ([CoreAlt], Maybe CoreExpr)
+findDefault [] = ([], Nothing)
+findDefault ((DEFAULT,args,rhs) : alts) = ASSERT( null alts && null args )
+ ([], Just rhs)
+findDefault (alt : alts) = case findDefault alts of
+ (alts', deflt) -> (alt : alts', deflt)
+
+findAlt :: AltCon -> [CoreAlt] -> CoreAlt
+findAlt con alts
+ = go alts
+ where
+ go [] = pprPanic "Missing alternative" (ppr con $$ vcat (map ppr alts))
+ go (alt : alts) | matches alt = alt
+ | otherwise = go alts
+
+ matches (DEFAULT, _, _) = True
+ matches (con1, _, _) = con == con1
+\end{code}
+
+
%************************************************************************
%* *
\subsection{Figuring out things about expressions}
\begin{code}
exprIsTrivial (Var v)
- | Just op <- isPrimOpId_maybe v = primOpIsDupable op
+ | hasNoBinding v = idArity v == 0
+ -- WAS: | Just op <- isPrimOpId_maybe v = primOpIsDupable op
+ -- 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.
+ -- This came up when dealing with eta expansion/reduction for
+ -- x = $wJust
+ -- Here we want to eta-expand. This looks like an optimisation,
+ -- but it's important (albeit tiresome) that CoreSat doesn't increase
+ -- anything's arity
| otherwise = True
exprIsTrivial (Type _) = True
exprIsTrivial (Lit lit) = True
exprIsAtom (Var v) = True -- primOpIsDupable?
exprIsAtom (Lit lit) = True
exprIsAtom (Type ty) = True
+exprIsAtom (Note (SCC _) e) = False
exprIsAtom (Note _ e) = exprIsAtom e
exprIsAtom other = False
\end{code}
\begin{code}
-exprIsDupable (Type _) = True
-exprIsDupable (Var v) = True
-exprIsDupable (Lit lit) = litIsDupable lit
-exprIsDupable (Note _ e) = exprIsDupable e
+exprIsDupable (Type _) = True
+exprIsDupable (Var v) = True
+exprIsDupable (Lit lit) = litIsDupable lit
+exprIsDupable (Note InlineMe e) = True
+exprIsDupable (Note _ e) = exprIsDupable e
exprIsDupable expr
= go expr 0
where
exprIsCheap (Lit lit) = True
exprIsCheap (Type _) = True
exprIsCheap (Var _) = True
+exprIsCheap (Note InlineMe e) = True
exprIsCheap (Note _ e) = exprIsCheap e
exprIsCheap (Lam x e) = if isId x then True else exprIsCheap e
exprIsCheap (Case e _ alts) = exprIsCheap e &&
| n_val_args == 0 = True -- Just a type application of
-- a variable (f t1 t2 t3)
-- counts as WHNF
- | otherwise = case idFlavour id of
+ | otherwise = case globalIdDetails id of
DataConId _ -> True
RecordSelId _ -> True -- I'm experimenting with making record selection
-- look cheap, so we will substitute it inside a
= go other_expr 0 True
where
go (Var f) n_args args_ok
- = case idFlavour f of
+ = case globalIdDetails f of
DataConId _ -> True -- The strictness of the constructor has already
-- been expressed by its "wrapper", so we don't need
-- to take the arguments into account
and to decide whether it's safe to discard a `seq`
-So, it does *not* treat variables as evaluated, unless they say they are
+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;
+ e.g. (:) (f x) (map f xs) is a value
+ map (...redex...) is a value
+Because `seq` on such things completes immediately
+
+A possible worry: constructors with unboxed args:
+ C (f x :: Int#)
+Suppose (f x) diverges; then C (f x) is not a value. True, but
+this form is illegal (see the invariants in CoreSyn). Args of unboxed
+type must be ok-for-speculation (or trivial).
\begin{code}
exprIsValue :: CoreExpr -> Bool -- True => Value-lambda, constructor, PAP
idAppIsValue :: Id -> Int -> Bool
idAppIsValue id n_val_args
- = case idFlavour id of
+ = case globalIdDetails id of
DataConId _ -> True
PrimOpId _ -> n_val_args < idArity id
other | n_val_args == 0 -> isEvaldUnfolding (idUnfolding id)
= analyse (collectArgs expr)
where
analyse (Var fun, args)
- | maybeToBool maybe_con_app = maybe_con_app
- where
- maybe_con_app = case isDataConId_maybe fun of
- Just con | length args >= dataConRepArity con
- -- Might be > because the arity excludes type args
- -> Just (con, args)
- other -> Nothing
+ | Just con <- isDataConId_maybe fun,
+ length args >= 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, [])
- = case maybeUnfoldingTemplate (idUnfolding fun) of
- Nothing -> Nothing
- Just unf -> exprIsConApp_maybe unf
+ | let unf = idUnfolding fun,
+ isCheapUnfolding unf
+ = exprIsConApp_maybe (unfoldingTemplate unf)
analyse other = Nothing
\end{code}
-- 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
--- Hence "generous" arity
+--
+-- Consider 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 extra Bool returned by go1
+-- NB: this 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.
+-- The hack is in Id.isOneShotLambda
exprEtaExpandArity e
= go 0 e
where
+ go :: Int -> CoreExpr -> (Int,Bool)
go ar (Lam x e) | isId x = go (ar+1) e
| otherwise = go ar e
go ar (Note n e) | ok_note n = go ar e
go ar other = (ar + ar', ar' == 0)
where
- ar' = go1 other `max` 0
-
- go1 (Var v) = idArity v
- go1 (Lam x e) | isId x = go1 e + 1
- | otherwise = go1 e
- go1 (Note n e) | ok_note n = go1 e
- go1 (App f (Type _)) = go1 f
- go1 (App f a) | exprIsCheap a = go1 f - 1
- go1 (Case scrut _ alts)
- | exprIsCheap scrut = min_zero [go1 rhs | (_,_,rhs) <- alts]
- go1 (Let b e)
- | all exprIsCheap (rhssOfBind b) = go1 e
-
- go1 other = 0
+ ar' = length (go1 other)
+
+ go1 :: CoreExpr -> [Bool]
+ -- (go1 e) = [b1,..,bn]
+ -- means expression can be rewritten \x_b1 -> ... \x_bn -> body
+ -- where bi is True <=> the lambda is one-shot
+
+ go1 (Note n e) | ok_note n = go1 e
+ go1 (Var v) = replicate (idArity v) False -- When the type of the Id
+ -- encodes one-shot-ness, use
+ -- th iinfo here
+
+ -- Lambdas; increase arity
+ go1 (Lam x e) | isId x = isOneShotLambda x : go1 e
+ | otherwise = go1 e
+
+ -- Applications; decrease arity
+ go1 (App f (Type _)) = go1 f
+ go1 (App f a) = case go1 f of
+ (one_shot : xs) | one_shot || exprIsCheap a -> xs
+ other -> []
+
+ -- Case/Let; keep arity if either the expression is cheap
+ -- or it's a 1-shot lambda
+ go1 (Case scrut _ alts) = case foldr1 (zipWith (&&)) [go1 rhs | (_,_,rhs) <- alts] of
+ xs@(one_shot : _) | one_shot || exprIsCheap scrut -> xs
+ other -> []
+ go1 (Let b e) = case go1 e of
+ xs@(one_shot : _) | one_shot || all exprIsCheap (rhssOfBind b) -> xs
+ other -> []
+
+ go1 other = []
ok_note (Coerce _ _) = True
ok_note InlineCall = True
projects / ghc-hetmet.git / blobdiff