module SimplUtils (
simplBinder, simplBinders, simplIds,
transformRhs,
- etaCoreExpr,
mkCase, findAlt, findDefault,
- mkCoerce
+
+ -- The continuation type
+ SimplCont(..), DupFlag(..), contIsDupable, contResultType,
+ pushArgs, discardCont, countValArgs, countArgs,
+ analyseCont, discardInline
+
) where
#include "HsVersions.h"
import BinderInfo
import CmdLineOpts ( opt_SimplDoLambdaEtaExpansion, opt_SimplCaseMerge )
import CoreSyn
+import CoreUnfold ( isValueUnfolding )
import CoreFVs ( exprFreeVars )
-import CoreUtils ( exprIsTrivial, cheapEqExpr, coreExprType, exprIsCheap, exprGenerousArity )
-import Subst ( substBndrs, substBndr, substIds )
-import Id ( Id, idType, getIdArity, isId, idName,
- getInlinePragma, setInlinePragma,
- getIdDemandInfo, mkId
+import CoreUtils ( exprIsTrivial, cheapEqExpr, exprType, exprIsCheap, exprEtaExpandArity )
+import Subst ( InScopeSet, mkSubst, substBndrs, substBndr, substIds, lookupIdSubst )
+import Id ( Id, idType, isId, idName,
+ idOccInfo, idUnfolding,
+ idDemandInfo, mkId, idInfo
)
-import IdInfo ( arityLowerBound, InlinePragInfo(..), setInlinePragInfo, vanillaIdInfo )
+import IdInfo ( arityLowerBound, setOccInfo, vanillaIdInfo )
import Maybes ( maybeToBool, catMaybes )
-import Const ( Con(..) )
import Name ( isLocalName, setNameUnique )
import SimplMonad
-import Type ( Type, tyVarsOfType, tyVarsOfTypes, mkForAllTys,
- splitTyConApp_maybe, mkTyVarTys, applyTys, splitFunTys, mkFunTys
+import Type ( Type, tyVarsOfType, tyVarsOfTypes, mkForAllTys, seqType,
+ splitTyConApp_maybe, splitAlgTyConApp_maybe, mkTyVarTys, applyTys, splitFunTys, mkFunTys
)
+import DataCon ( dataConRepArity )
import TysPrim ( statePrimTyCon )
import Var ( setVarUnique )
import VarSet
+import VarEnv ( SubstEnv, SubstResult(..) )
import UniqSupply ( splitUniqSupply, uniqFromSupply )
import Util ( zipWithEqual, mapAccumL )
import Outputable
%************************************************************************
%* *
+\subsection{The continuation data type}
+%* *
+%************************************************************************
+
+\begin{code}
+data SimplCont -- Strict contexts
+ = Stop OutType -- Type of the result
+
+ | CoerceIt OutType -- The To-type, simplified
+ SimplCont
+
+ | InlinePlease -- This continuation makes a function very
+ SimplCont -- keen to inline itelf
+
+ | ApplyTo DupFlag
+ InExpr SubstEnv -- The argument, as yet unsimplified,
+ SimplCont -- and its subst-env
+
+ | Select DupFlag
+ InId [InAlt] SubstEnv -- The case binder, alts, and subst-env
+ SimplCont
+
+ | ArgOf DupFlag -- An arbitrary strict context: the argument
+ -- of a strict function, or a primitive-arg fn
+ -- or a PrimOp
+ OutType -- The type of the expression being sought by the context
+ -- f (error "foo") ==> coerce t (error "foo")
+ -- when f is strict
+ -- We need to know the type t, to which to coerce.
+ (OutExpr -> SimplM OutExprStuff) -- What to do with the result
+
+instance Outputable SimplCont where
+ ppr (Stop _) = ptext SLIT("Stop")
+ ppr (ApplyTo dup arg se cont) = (ptext SLIT("ApplyTo") <+> ppr dup <+> ppr arg) $$ ppr cont
+ ppr (ArgOf dup _ _) = ptext SLIT("ArgOf...") <+> ppr dup
+ ppr (Select dup bndr alts se cont) = (ptext SLIT("Select") <+> ppr dup <+> ppr bndr) $$
+ (nest 4 (ppr alts)) $$ ppr cont
+ ppr (CoerceIt ty cont) = (ptext SLIT("CoerceIt") <+> ppr ty) $$ ppr cont
+ ppr (InlinePlease cont) = ptext SLIT("InlinePlease") $$ ppr cont
+
+data DupFlag = OkToDup | NoDup
+
+instance Outputable DupFlag where
+ ppr OkToDup = ptext SLIT("ok")
+ ppr NoDup = ptext SLIT("nodup")
+
+contIsDupable :: SimplCont -> Bool
+contIsDupable (Stop _) = True
+contIsDupable (ApplyTo OkToDup _ _ _) = True
+contIsDupable (ArgOf OkToDup _ _) = True
+contIsDupable (Select OkToDup _ _ _ _) = True
+contIsDupable (CoerceIt _ cont) = contIsDupable cont
+contIsDupable (InlinePlease cont) = contIsDupable cont
+contIsDupable other = False
+
+pushArgs :: SubstEnv -> [InExpr] -> SimplCont -> SimplCont
+pushArgs se [] cont = cont
+pushArgs se (arg:args) cont = ApplyTo NoDup arg se (pushArgs se args cont)
+
+discardCont :: SimplCont -- A continuation, expecting
+ -> SimplCont -- Replace the continuation with a suitable coerce
+discardCont (Stop to_ty) = Stop to_ty
+discardCont cont = CoerceIt to_ty (Stop to_ty)
+ where
+ to_ty = contResultType cont
+
+contResultType :: SimplCont -> OutType
+contResultType (Stop to_ty) = to_ty
+contResultType (ArgOf _ to_ty _) = to_ty
+contResultType (ApplyTo _ _ _ cont) = contResultType cont
+contResultType (CoerceIt _ cont) = contResultType cont
+contResultType (InlinePlease cont) = contResultType cont
+contResultType (Select _ _ _ _ cont) = contResultType cont
+
+countValArgs :: SimplCont -> Int
+countValArgs (ApplyTo _ (Type ty) se cont) = countValArgs cont
+countValArgs (ApplyTo _ val_arg se cont) = 1 + countValArgs cont
+countValArgs other = 0
+
+countArgs :: SimplCont -> Int
+countArgs (ApplyTo _ arg se cont) = 1 + countArgs cont
+countArgs other = 0
+\end{code}
+
+
+Comment about analyseCont
+~~~~~~~~~~~~~~~~~~~~~~~~~
+We want to avoid inlining an expression where there can't possibly be
+any gain, such as in an argument position. Hence, if the continuation
+is interesting (eg. a case scrutinee, application etc.) then we
+inline, otherwise we don't.
+
+Previously some_benefit used to return True only if the variable was
+applied to some value arguments. This didn't work:
+
+ let x = _coerce_ (T Int) Int (I# 3) in
+ case _coerce_ Int (T Int) x of
+ I# y -> ....
+
+we want to inline x, but can't see that it's a constructor in a case
+scrutinee position, and some_benefit is False.
+
+Another example:
+
+dMonadST = _/\_ t -> :Monad (g1 _@_ t, g2 _@_ t, g3 _@_ t)
+
+.... case dMonadST _@_ x0 of (a,b,c) -> ....
+
+we'd really like to inline dMonadST here, but we *don't* want to
+inline if the case expression is just
+
+ case x of y { DEFAULT -> ... }
+
+since we can just eliminate this case instead (x is in WHNF). Similar
+applies when x is bound to a lambda expression. Hence
+contIsInteresting looks for case expressions with just a single
+default case.
+
+\begin{code}
+analyseCont :: InScopeSet -> SimplCont
+ -> ([Bool], -- Arg-info flags; one for each value argument
+ Bool, -- Context of the result of the call is interesting
+ Bool) -- There was an InlinePlease
+
+analyseCont in_scope cont
+ = case cont of
+ -- The "lone-variable" case is important. I spent ages
+ -- messing about with unsatisfactory varaints, but this is nice.
+ -- The idea is that if a variable appear all alone
+ -- as an arg of lazy fn, or rhs Stop
+ -- as scrutinee of a case Select
+ -- as arg of a strict fn ArgOf
+ -- then we should not inline it (unless there is some other reason,
+ -- e.g. is is the sole occurrence).
+ -- Why not? At least in the case-scrutinee situation, turning
+ -- case x of y -> ...
+ -- into
+ -- let y = (a,b) in ...
+ -- is bad if the binding for x will remain.
+ --
+ -- Another example: I discovered that strings
+ -- were getting inlined straight back into applications of 'error'
+ -- because the latter is strict.
+ -- s = "foo"
+ -- f = \x -> ...(error s)...
+
+ -- Fundamentally such contexts should not ecourage inlining becuase
+ -- the context can ``see'' the unfolding of the variable (e.g. case or a RULE)
+ -- so there's no gain.
+ --
+ -- However, even a type application isn't a lone variable. Consider
+ -- case $fMonadST @ RealWorld of { :DMonad a b c -> c }
+ -- We had better inline that sucker! The case won't see through it.
+
+ (Stop _) -> boring_result -- Don't inline a lone variable
+ (Select _ _ _ _ _) -> boring_result -- Ditto
+ (ArgOf _ _ _) -> boring_result -- Ditto
+ (ApplyTo _ (Type _) _ cont) -> analyse_ty_app cont
+ other -> analyse_app cont
+ where
+ boring_result = ([], False, False)
+
+ -- For now, I'm treating not treating a variable applied to types as
+ -- "lone". The motivating example was
+ -- f = /\a. \x. BIG
+ -- g = /\a. \y. h (f a)
+ -- There's no advantage in inlining f here, and perhaps
+ -- a significant disadvantage.
+ analyse_ty_app (Stop _) = boring_result
+ analyse_ty_app (ArgOf _ _ _) = boring_result
+ analyse_ty_app (Select _ _ _ _ _) = ([], True, False) -- See the $fMonadST example above
+ analyse_ty_app (ApplyTo _ (Type _) _ cont) = analyse_ty_app cont
+ analyse_ty_app cont = analyse_app cont
+
+ analyse_app (InlinePlease cont)
+ = case analyse_app cont of
+ (infos, icont, inline) -> (infos, icont, True)
+
+ analyse_app (ApplyTo _ arg subst cont)
+ | isValArg arg = case analyse_app cont of
+ (infos, icont, inline) -> (analyse_arg subst arg : infos, icont, inline)
+ | otherwise = analyse_app cont
+
+ analyse_app cont = ([], interesting_call_context cont, False)
+
+ -- An argument is interesting if it has *some* structure
+ -- We are here trying to avoid unfolding a function that
+ -- is applied only to variables that have no unfolding
+ -- (i.e. they are probably lambda bound): f x y z
+ -- There is little point in inlining f here.
+ analyse_arg :: SubstEnv -> InExpr -> Bool
+ analyse_arg subst (Var v) = case lookupIdSubst (mkSubst in_scope subst) v of
+ DoneId v' _ -> isValueUnfolding (idUnfolding v')
+ other -> False
+ analyse_arg subst (Type _) = False
+ analyse_arg subst (App fn (Type _)) = analyse_arg subst fn
+ analyse_arg subst (Note _ a) = analyse_arg subst a
+ analyse_arg subst other = True
+
+ interesting_call_context (Stop ty) = canUpdateInPlace ty
+ interesting_call_context (InlinePlease _) = True
+ interesting_call_context (Select _ _ _ _ _) = True
+ interesting_call_context (CoerceIt _ cont) = interesting_call_context cont
+ interesting_call_context (ApplyTo _ (Type _) _ cont) = interesting_call_context cont
+ interesting_call_context (ApplyTo _ _ _ _) = True
+ interesting_call_context (ArgOf _ _ _) = True
+ -- If this call is the arg of a strict function, the context
+ -- is a bit interesting. If we inline here, we may get useful
+ -- evaluation information to avoid repeated evals: e.g.
+ -- x + (y * z)
+ -- Here the contIsInteresting makes the '*' keener to inline,
+ -- which in turn exposes a constructor which makes the '+' inline.
+ -- Assuming that +,* aren't small enough to inline regardless.
+ --
+ -- It's also very important to inline in a strict context for things
+ -- like
+ -- foldr k z (f x)
+ -- Here, the context of (f x) is strict, and if f's unfolding is
+ -- a build it's *great* to inline it here. So we must ensure that
+ -- the context for (f x) is not totally uninteresting.
+
+
+discardInline :: SimplCont -> SimplCont
+discardInline (InlinePlease cont) = cont
+discardInline (ApplyTo d e s cont) = ApplyTo d e s (discardInline cont)
+discardInline cont = cont
+
+-- Consider let x = <wurble> in ...
+-- If <wurble> returns an explicit constructor, we might be able
+-- to do update in place. So we treat even a thunk RHS context
+-- as interesting if update in place is possible. We approximate
+-- this by seeing if the type has a single constructor with a
+-- small arity. But arity zero isn't good -- we share the single copy
+-- for that case, so no point in sharing.
+
+canUpdateInPlace ty = case splitAlgTyConApp_maybe ty of
+ Just (_, _, [dc]) -> arity == 1 || arity == 2
+ where
+ arity = dataConRepArity dc
+ other -> False
+\end{code}
+
+
+
+%************************************************************************
+%* *
\section{Dealing with a single binder}
%* *
%************************************************************************
let
(subst', bndrs') = substBndrs subst bndrs
in
- setSubst subst' $
- thing_inside bndrs'
+ seqBndrs bndrs' `seq`
+ setSubst subst' (thing_inside bndrs')
simplBinder :: InBinder -> (OutBinder -> SimplM a) -> SimplM a
simplBinder bndr thing_inside
let
(subst', bndr') = substBndr subst bndr
in
- setSubst subst' $
- thing_inside bndr'
+ seqBndr bndr' `seq`
+ setSubst subst' (thing_inside bndr')
-- Same semantics as simplBinders, but a little less
let
(subst', bndrs') = substIds subst ids
in
- setSubst subst' $
- thing_inside bndrs'
+ seqBndrs bndrs' `seq`
+ setSubst subst' (thing_inside bndrs')
+
+seqBndrs [] = ()
+seqBndrs (b:bs) = seqBndr b `seq` seqBndrs bs
+
+seqBndr b | isTyVar b = b `seq` ()
+ | otherwise = seqType (idType b) `seq`
+ idInfo b `seq`
+ ()
\end{code}
poly_name = setNameUnique (idName var) uniq -- Keep same name
poly_ty = mkForAllTys tyvars_here (idType var) -- But new type of course
- -- It's crucial to copy the inline-prag of the original var, because
+ -- It's crucial to copy the occInfo of the original var, because
-- we're looking at occurrence-analysed but as yet unsimplified code!
-- In particular, we mustn't lose the loop breakers.
--
-- where x* has an INLINE prag on it. Now, once x* is inlined,
-- the occurrences of x' will be just the occurrences originaly
-- pinned on x.
- poly_info = vanillaIdInfo `setInlinePragInfo` getInlinePragma var
+ poly_info = vanillaIdInfo `setOccInfo` idOccInfo var
poly_id = mkId poly_name poly_ty poly_info
in
returnSmpl (poly_id, mkTyApps (Var poly_id) (mkTyVarTys tyvars_here))
- mk_silly_bind var rhs = NonRec (setInlinePragma var IMustBeINLINEd) rhs
- -- The addInlinePragma is really important! If we don't say
+ mk_silly_bind var rhs = NonRec var rhs
+ -- The Inline note is really important! If we don't say
-- INLINE on these silly little bindings then look what happens!
-- Suppose we start with:
--
-- * but then it gets inlined into the rhs of g*
-- * then the binding for g* is floated out of the /\b
-- * so we're back to square one
- -- The silly binding for g* must be IMustBeINLINEs, so that
+ -- The silly binding for g* must be INLINEd, so that
-- we simply substitute for g* throughout.
\end{code}
(x_bndrs, body) = collectValBinders rhs
(fun, args) = collectArgs body
trivial_args = map exprIsTrivial args
- fun_arity = exprGenerousArity fun
+ fun_arity = exprEtaExpandArity fun
bind_z_arg (arg, trivial_arg)
| trivial_arg = returnSmpl (Nothing, arg)
- | otherwise = newId (coreExprType arg) $ \ z ->
+ | otherwise = newId (exprType arg) $ \ z ->
returnSmpl (Just (NonRec z arg), Var z)
- -- Note: I used to try to avoid the coreExprType call by using
+ -- Note: I used to try to avoid the exprType call by using
-- the type of the binder. But this type doesn't necessarily
-- belong to the same substitution environment as this rhs;
-- and we are going to make extra term binders (y_bndrs) from the type
-- which will be processed with the rhs substitution environment.
-- This only went wrong in a mind bendingly complicated case.
- (potential_extra_arg_tys, inner_ty) = splitFunTys (coreExprType body)
+ (potential_extra_arg_tys, inner_ty) = splitFunTys (exprType body)
y_tys :: [InType]
y_tys = take no_extras_wanted potential_extra_arg_tys
-- See if the body could obviously do with more args
(fun_arity - valArgCount args)
--- This case is now deal with by exprGenerousArity
+-- This case is now deal with by exprEtaExpandArity
-- Finally, see if it's a state transformer, and xs is non-null
-- (so it's also a function not a thunk) in which
-- case we eta-expand on principle! This can waste work,
%************************************************************************
%* *
-\subsection{Eta reduction}
-%* *
-%************************************************************************
-
-@etaCoreExpr@ trys an eta reduction at the top level of a Core Expr.
-
-e.g. \ x y -> f x y ===> f
-
-It is used
--- OLD
--- a) Before constructing an Unfolding, to
--- try to make the unfolding smaller;
- b) In tidyCoreExpr, which is done just before converting to STG.
-
-But we only do this if
- i) It gets rid of a whole lambda, not part.
- The idea is that lambdas are often quite helpful: they indicate
- head normal forms, so we don't want to chuck them away lightly.
-
--- OLD: in core2stg we want to do this even if the result isn't trivial
--- ii) It exposes a simple variable or a type application; in short
--- it exposes a "trivial" expression. (exprIsTrivial)
-
-\begin{code}
-etaCoreExpr :: CoreExpr -> CoreExpr
- -- ToDo: we should really check that we don't turn a non-bottom
- -- lambda into a bottom variable. Sigh
-
-etaCoreExpr expr@(Lam bndr body)
- = check (reverse binders) body
- where
- (binders, body) = collectBinders expr
-
- check [] body
- | not (any (`elemVarSet` body_fvs) binders)
- = body -- Success!
- where
- body_fvs = exprFreeVars body
-
- check (b : bs) (App fun arg)
- | (varToCoreExpr b `cheapEqExpr` arg)
- = check bs fun
-
- check _ _ = expr -- Bale out
-
-etaCoreExpr expr = expr -- The common case
-\end{code}
-
-
-%************************************************************************
-%* *
\subsection{Case absorption and identity-case elimination}
%* *
%************************************************************************
= tick (CaseIdentity case_bndr) `thenSmpl_`
returnSmpl scrut
where
- identity_alt (DEFAULT, [], Var v) = v == case_bndr
- identity_alt (con, args, Con con' args') = con == con' &&
- and (zipWithEqual "mkCase"
- cheapEqExpr
- (map Type arg_tys ++ map varToCoreExpr args)
- args')
- identity_alt other = False
+ identity_alt (DEFAULT, [], Var v) = v == case_bndr
+ identity_alt (DataAlt con, args, rhs) = cheapEqExpr rhs
+ (mkConApp con (map Type arg_tys ++ map varToCoreExpr args))
+ identity_alt other = False
arg_tys = case splitTyConApp_maybe (idType case_bndr) of
Just (tycon, arg_tys) -> arg_tys
findDefault (alt : alts) = case findDefault alts of
(alts', deflt) -> (alt : alts', deflt)
-findAlt :: Con -> [CoreAlt] -> CoreAlt
+findAlt :: AltCon -> [CoreAlt] -> CoreAlt
findAlt con alts
= go alts
where
matches (DEFAULT, _, _) = True
matches (con1, _, _) = con == con1
-
-
-mkCoerce to_ty (Note (Coerce _ from_ty) expr)
- | to_ty == from_ty = expr
- | otherwise = Note (Coerce to_ty from_ty) expr
-mkCoerce to_ty expr
- = Note (Coerce to_ty (coreExprType expr)) expr
\end{code}
projects / ghc-hetmet.git / blobdiff