-
+%
% (c) The AQUA Project, Glasgow University, 1993-1998
%
\section[Simplify]{The main module of the simplifier}
#include "HsVersions.h"
-import CmdLineOpts ( intSwitchSet,
- opt_SccProfilingOn, opt_PprStyle_Debug, opt_SimplDoEtaReduction,
- opt_SimplNoPreInlining, opt_DictsStrict, opt_SimplPedanticBottoms,
+import DynFlags ( dopt, DynFlag(Opt_D_dump_inlinings),
SimplifierSwitch(..)
)
import SimplMonad
-import SimplUtils ( mkCase, transformRhs, findAlt,
- simplBinder, simplBinders, simplIds, findDefault, mkCoerce
+import SimplEnv
+import SimplUtils ( mkCase, mkLam, prepareAlts,
+ SimplCont(..), DupFlag(..), LetRhsFlag(..),
+ mkRhsStop, mkBoringStop, pushContArgs,
+ contResultType, countArgs, contIsDupable, contIsRhsOrArg,
+ getContArgs, interestingCallContext, interestingArg, isStrictType,
+ preInlineUnconditionally, postInlineUnconditionally,
+ inlineMode, activeInline, activeRule
)
-import Var ( TyVar, mkSysTyVar, tyVarKind, maybeModifyIdInfo )
-import VarEnv
-import VarSet
-import Id ( Id, idType, idInfo, idUnique,
- getIdUnfolding, setIdUnfolding, isExportedId,
- getIdSpecialisation, setIdSpecialisation,
- getIdDemandInfo, setIdDemandInfo,
- getIdArity, setIdArity, setIdInfo,
- getIdStrictness,
- setInlinePragma, getInlinePragma, idMustBeINLINEd,
- setOneShotLambda, maybeModifyIdInfo
+import Id ( Id, idType, idInfo, idArity, isDataConWorkId,
+ setIdUnfolding, isDeadBinder,
+ idNewDemandInfo, setIdInfo,
+ setIdOccInfo, zapLamIdInfo, setOneShotLambda
)
-import IdInfo ( InlinePragInfo(..), OccInfo(..), StrictnessInfo(..),
- ArityInfo(..), atLeastArity, arityLowerBound, unknownArity, zapFragileIdInfo,
- specInfo, inlinePragInfo, zapLamIdInfo, setArityInfo, setInlinePragInfo, setUnfoldingInfo
+import MkId ( eRROR_ID )
+import Literal ( mkStringLit )
+import IdInfo ( OccInfo(..), isLoopBreaker,
+ setArityInfo, zapDemandInfo,
+ setUnfoldingInfo,
+ occInfo
)
-import Demand ( Demand, isStrict, wwLazy )
-import Const ( isWHNFCon, conOkForAlt )
-import ConFold ( tryPrimOp )
-import PrimOp ( PrimOp, primOpStrictness, primOpType )
-import DataCon ( DataCon, dataConNumInstArgs, dataConRepStrictness, dataConSig, dataConArgTys )
-import Const ( Con(..) )
-import Name ( isLocallyDefined )
+import NewDemand ( isStrictDmd )
+import Unify ( coreRefineTys )
+import DataCon ( dataConTyCon, dataConRepStrictness, isVanillaDataCon )
+import TyCon ( tyConArity )
import CoreSyn
-import CoreFVs ( exprFreeVars )
-import CoreUnfold ( Unfolding, mkOtherCon, mkUnfolding, otherCons,
- callSiteInline, hasSomeUnfolding
- )
-import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsCheap, exprIsTrivial,
- coreExprType, coreAltsType, exprArity, exprIsValue,
- exprOkForSpeculation
+import PprCore ( pprParendExpr, pprCoreExpr )
+import CoreUnfold ( mkUnfolding, callSiteInline )
+import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding,
+ exprIsConApp_maybe, mkPiTypes, findAlt,
+ exprType, exprIsHNF,
+ exprOkForSpeculation, exprArity,
+ mkCoerce, mkCoerce2, mkSCC, mkInlineMe, applyTypeToArg
)
import Rules ( lookupRule )
-import CostCentre ( isSubsumedCCS, currentCCS, isEmptyCC )
-import Type ( Type, mkTyVarTy, mkTyVarTys, isUnLiftedType, seqType,
- mkFunTy, splitFunTys, splitTyConApp_maybe, splitFunTy_maybe,
- funResultTy, isDictTy, isDataType, applyTy, applyTys, mkFunTys
- )
-import Subst ( Subst, mkSubst, emptySubst, substExpr, substTy,
- substEnv, lookupInScope, lookupSubst, substIdInfo
+import BasicTypes ( isMarkedStrict )
+import CostCentre ( currentCCS )
+import Type ( TvSubstEnv, isUnLiftedType, seqType, tyConAppArgs, funArgTy,
+ splitFunTy_maybe, splitFunTy, coreEqType
)
-import TyCon ( isDataTyCon, tyConDataCons, tyConClass_maybe, tyConArity, isDataTyCon )
+import VarEnv ( elemVarEnv, emptyVarEnv )
import TysPrim ( realWorldStatePrimTy )
import PrelInfo ( realWorldPrimId )
-import BasicTypes ( TopLevelFlag(..), isTopLevel )
-import Maybes ( maybeToBool )
-import Util ( zipWithEqual, stretchZipEqual, lengthExceeds )
-import PprCore
+import BasicTypes ( TopLevelFlag(..), isTopLevel,
+ RecFlag(..), isNonRec
+ )
+import StaticFlags ( opt_PprStyle_Debug )
+import OrdList
+import Maybes ( orElse )
import Outputable
+import Util ( notNull )
\end{code}
-The guts of the simplifier is in this module, but the driver
-loop for the simplifier is in SimplCore.lhs.
+The guts of the simplifier is in this module, but the driver loop for
+the simplifier is in SimplCore.lhs.
+
+
+-----------------------------------------
+ *** IMPORTANT NOTE ***
+-----------------------------------------
+The simplifier used to guarantee that the output had no shadowing, but
+it does not do so any more. (Actually, it never did!) The reason is
+documented with simplifyArgs.
+
+
+-----------------------------------------
+ *** IMPORTANT NOTE ***
+-----------------------------------------
+Many parts of the simplifier return a bunch of "floats" as well as an
+expression. This is wrapped as a datatype SimplUtils.FloatsWith.
+
+All "floats" are let-binds, not case-binds, but some non-rec lets may
+be unlifted (with RHS ok-for-speculation).
+
+
+
+-----------------------------------------
+ ORGANISATION OF FUNCTIONS
+-----------------------------------------
+simplTopBinds
+ - simplify all top-level binders
+ - for NonRec, call simplRecOrTopPair
+ - for Rec, call simplRecBind
+
+
+ ------------------------------
+simplExpr (applied lambda) ==> simplNonRecBind
+simplExpr (Let (NonRec ...) ..) ==> simplNonRecBind
+simplExpr (Let (Rec ...) ..) ==> simplify binders; simplRecBind
+
+ ------------------------------
+simplRecBind [binders already simplfied]
+ - use simplRecOrTopPair on each pair in turn
+
+simplRecOrTopPair [binder already simplified]
+ Used for: recursive bindings (top level and nested)
+ top-level non-recursive bindings
+ Returns:
+ - check for PreInlineUnconditionally
+ - simplLazyBind
+
+simplNonRecBind
+ Used for: non-top-level non-recursive bindings
+ beta reductions (which amount to the same thing)
+ Because it can deal with strict arts, it takes a
+ "thing-inside" and returns an expression
+
+ - check for PreInlineUnconditionally
+ - simplify binder, including its IdInfo
+ - if strict binding
+ simplStrictArg
+ mkAtomicArgs
+ completeNonRecX
+ else
+ simplLazyBind
+ addFloats
+
+simplNonRecX: [given a *simplified* RHS, but an *unsimplified* binder]
+ Used for: binding case-binder and constr args in a known-constructor case
+ - check for PreInLineUnconditionally
+ - simplify binder
+ - completeNonRecX
+
+ ------------------------------
+simplLazyBind: [binder already simplified, RHS not]
+ Used for: recursive bindings (top level and nested)
+ top-level non-recursive bindings
+ non-top-level, but *lazy* non-recursive bindings
+ [must not be strict or unboxed]
+ Returns floats + an augmented environment, not an expression
+ - substituteIdInfo and add result to in-scope
+ [so that rules are available in rec rhs]
+ - simplify rhs
+ - mkAtomicArgs
+ - float if exposes constructor or PAP
+ - completeLazyBind
+
+
+completeNonRecX: [binder and rhs both simplified]
+ - if the the thing needs case binding (unlifted and not ok-for-spec)
+ build a Case
+ else
+ completeLazyBind
+ addFloats
+
+completeLazyBind: [given a simplified RHS]
+ [used for both rec and non-rec bindings, top level and not]
+ - try PostInlineUnconditionally
+ - add unfolding [this is the only place we add an unfolding]
+ - add arity
+
+
+
+Right hand sides and arguments
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+In many ways we want to treat
+ (a) the right hand side of a let(rec), and
+ (b) a function argument
+in the same way. But not always! In particular, we would
+like to leave these arguments exactly as they are, so they
+will match a RULE more easily.
+
+ f (g x, h x)
+ g (+ x)
+
+It's harder to make the rule match if we ANF-ise the constructor,
+or eta-expand the PAP:
+
+ f (let { a = g x; b = h x } in (a,b))
+ g (\y. + x y)
+
+On the other hand if we see the let-defns
+
+ p = (g x, h x)
+ q = + x
+
+then we *do* want to ANF-ise and eta-expand, so that p and q
+can be safely inlined.
+
+Even floating lets out is a bit dubious. For let RHS's we float lets
+out if that exposes a value, so that the value can be inlined more vigorously.
+For example
+
+ r = let x = e in (x,x)
+
+Here, if we float the let out we'll expose a nice constructor. We did experiments
+that showed this to be a generally good thing. But it was a bad thing to float
+lets out unconditionally, because that meant they got allocated more often.
+
+For function arguments, there's less reason to expose a constructor (it won't
+get inlined). Just possibly it might make a rule match, but I'm pretty skeptical.
+So for the moment we don't float lets out of function arguments either.
+
+
+Eta expansion
+~~~~~~~~~~~~~~
+For eta expansion, we want to catch things like
+
+ case e of (a,b) -> \x -> case a of (p,q) -> \y -> r
+
+If the \x was on the RHS of a let, we'd eta expand to bring the two
+lambdas together. And in general that's a good thing to do. Perhaps
+we should eta expand wherever we find a (value) lambda? Then the eta
+expansion at a let RHS can concentrate solely on the PAP case.
%************************************************************************
%************************************************************************
\begin{code}
-simplTopBinds :: [InBind] -> SimplM [OutBind]
+simplTopBinds :: SimplEnv -> [InBind] -> SimplM [OutBind]
-simplTopBinds binds
+simplTopBinds env binds
= -- Put all the top-level binders into scope at the start
-- so that if a transformation rule has unexpectedly brought
-- anything into scope, then we don't get a complaint about that.
-- It's rather as if the top-level binders were imported.
- extendInScopes top_binders $
- simpl_binds binds `thenSmpl` \ (binds', _) ->
- freeTick SimplifierDone `thenSmpl_`
- returnSmpl binds'
+ simplLetBndrs env (bindersOfBinds binds) `thenSmpl` \ (env, bndrs') ->
+ simpl_binds env binds bndrs' `thenSmpl` \ (floats, _) ->
+ freeTick SimplifierDone `thenSmpl_`
+ returnSmpl (floatBinds floats)
where
- top_binders = bindersOfBinds binds
+ -- We need to track the zapped top-level binders, because
+ -- they should have their fragile IdInfo zapped (notably occurrence info)
+ -- That's why we run down binds and bndrs' simultaneously.
+ simpl_binds :: SimplEnv -> [InBind] -> [OutId] -> SimplM (FloatsWith ())
+ simpl_binds env [] bs = ASSERT( null bs ) returnSmpl (emptyFloats env, ())
+ simpl_binds env (bind:binds) bs = simpl_bind env bind bs `thenSmpl` \ (floats,env) ->
+ addFloats env floats $ \env ->
+ simpl_binds env binds (drop_bs bind bs)
+
+ drop_bs (NonRec _ _) (_ : bs) = bs
+ drop_bs (Rec prs) bs = drop (length prs) bs
+
+ simpl_bind env bind bs
+ = getDOptsSmpl `thenSmpl` \ dflags ->
+ if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "SimplBind" (ppr (bindersOf bind)) $ simpl_bind1 env bind bs
+ else
+ simpl_bind1 env bind bs
+
+ simpl_bind1 env (NonRec b r) (b':_) = simplRecOrTopPair env TopLevel b b' r
+ simpl_bind1 env (Rec pairs) bs' = simplRecBind env TopLevel pairs bs'
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{simplNonRec}
+%* *
+%************************************************************************
+
+simplNonRecBind is used for
+ * non-top-level non-recursive lets in expressions
+ * beta reduction
- simpl_binds [] = returnSmpl ([], panic "simplTopBinds corner")
- simpl_binds (NonRec bndr rhs : binds) = simplLazyBind TopLevel bndr (zap bndr) rhs (simpl_binds binds)
- simpl_binds (Rec pairs : binds) = simplRecBind TopLevel pairs (map (zap . fst) pairs) (simpl_binds binds)
+It takes
+ * An unsimplified (binder, rhs) pair
+ * The env for the RHS. It may not be the same as the
+ current env because the bind might occur via (\x.E) arg
- zap id = maybeModifyIdInfo zapFragileIdInfo id
--- TEMP
+It uses the CPS form because the binding might be strict, in which
+case we might discard the continuation:
+ let x* = error "foo" in (...x...)
+It needs to turn unlifted bindings into a @case@. They can arise
+from, say: (\x -> e) (4# + 3#)
+
+\begin{code}
+simplNonRecBind :: SimplEnv
+ -> InId -- Binder
+ -> InExpr -> SimplEnv -- Arg, with its subst-env
+ -> OutType -- Type of thing computed by the context
+ -> (SimplEnv -> SimplM FloatsWithExpr) -- The body
+ -> SimplM FloatsWithExpr
+#ifdef DEBUG
+simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
+ | isTyVar bndr
+ = pprPanic "simplNonRecBind" (ppr bndr <+> ppr rhs)
+#endif
+
+simplNonRecBind env bndr rhs rhs_se cont_ty thing_inside
+ = simplNonRecBind' env bndr rhs rhs_se cont_ty thing_inside
+
+simplNonRecBind' env bndr rhs rhs_se cont_ty thing_inside
+ | preInlineUnconditionally env NotTopLevel bndr rhs
+ = tick (PreInlineUnconditionally bndr) `thenSmpl_`
+ thing_inside (extendIdSubst env bndr (mkContEx rhs_se rhs))
+
+ | isStrictDmd (idNewDemandInfo bndr) || isStrictType bndr_ty -- A strict let
+ = -- Don't use simplBinder because that doesn't keep
+ -- fragile occurrence info in the substitution
+ simplLetBndr env bndr `thenSmpl` \ (env, bndr1) ->
+ simplStrictArg AnRhs env rhs rhs_se (idType bndr1) cont_ty $ \ env1 rhs1 ->
+
+ -- Now complete the binding and simplify the body
+ let
+ -- simplLetBndr doesn't deal with the IdInfo, so we must
+ -- do so here (c.f. simplLazyBind)
+ bndr2 = bndr1 `setIdInfo` simplIdInfo env (idInfo bndr)
+ env2 = modifyInScope env1 bndr2 bndr2
+ in
+ if needsCaseBinding bndr_ty rhs1
+ then
+ thing_inside env2 `thenSmpl` \ (floats, body) ->
+ returnSmpl (emptyFloats env2, Case rhs1 bndr2 (exprType body)
+ [(DEFAULT, [], wrapFloats floats body)])
+ else
+ completeNonRecX env2 True {- strict -} bndr bndr2 rhs1 thing_inside
+
+ | otherwise -- Normal, lazy case
+ = -- Don't use simplBinder because that doesn't keep
+ -- fragile occurrence info in the substitution
+ simplLetBndr env bndr `thenSmpl` \ (env, bndr') ->
+ simplLazyBind env NotTopLevel NonRecursive
+ bndr bndr' rhs rhs_se `thenSmpl` \ (floats, env) ->
+ addFloats env floats thing_inside
-simplRecBind :: TopLevelFlag -> [(InId, InExpr)] -> [OutId]
- -> SimplM (OutStuff a) -> SimplM (OutStuff a)
-simplRecBind top_lvl pairs bndrs' thing_inside
- = go pairs bndrs' `thenSmpl` \ (binds', stuff) ->
- returnSmpl (addBind (Rec (flattenBinds binds')) stuff)
where
- go [] _ = thing_inside `thenSmpl` \ stuff ->
- returnSmpl ([], stuff)
-
- go ((bndr, rhs) : pairs) (bndr' : bndrs')
- = simplLazyBind top_lvl bndr bndr' rhs (go pairs bndrs')
- -- Don't float unboxed bindings out,
- -- because we can't "rec" them
+ bndr_ty = idType bndr
+\end{code}
+
+A specialised variant of simplNonRec used when the RHS is already simplified, notably
+in knownCon. It uses case-binding where necessary.
+
+\begin{code}
+simplNonRecX :: SimplEnv
+ -> InId -- Old binder
+ -> OutExpr -- Simplified RHS
+ -> (SimplEnv -> SimplM FloatsWithExpr)
+ -> SimplM FloatsWithExpr
+
+simplNonRecX env bndr new_rhs thing_inside
+ | needsCaseBinding (idType bndr) new_rhs
+ -- Make this test *before* the preInlineUnconditionally
+ -- Consider case I# (quotInt# x y) of
+ -- I# v -> let w = J# v in ...
+ -- If we gaily inline (quotInt# x y) for v, we end up building an
+ -- extra thunk:
+ -- let w = J# (quotInt# x y) in ...
+ -- because quotInt# can fail.
+ = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
+ thing_inside env `thenSmpl` \ (floats, body) ->
+ let body' = wrapFloats floats body in
+ returnSmpl (emptyFloats env, Case new_rhs bndr' (exprType body') [(DEFAULT, [], body')])
+
+ | preInlineUnconditionally env NotTopLevel bndr new_rhs
+ -- This happens; for example, the case_bndr during case of
+ -- known constructor: case (a,b) of x { (p,q) -> ... }
+ -- Here x isn't mentioned in the RHS, so we don't want to
+ -- create the (dead) let-binding let x = (a,b) in ...
+ --
+ -- Similarly, single occurrences can be inlined vigourously
+ -- e.g. case (f x, g y) of (a,b) -> ....
+ -- If a,b occur once we can avoid constructing the let binding for them.
+ = thing_inside (extendIdSubst env bndr (DoneEx new_rhs))
+
+ | otherwise
+ = simplBinder env bndr `thenSmpl` \ (env, bndr') ->
+ completeNonRecX env False {- Non-strict; pessimistic -}
+ bndr bndr' new_rhs thing_inside
+
+completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside
+ = mkAtomicArgs is_strict
+ True {- OK to float unlifted -}
+ new_rhs `thenSmpl` \ (aux_binds, rhs2) ->
+
+ -- Make the arguments atomic if necessary,
+ -- adding suitable bindings
+ addAtomicBindsE env (fromOL aux_binds) $ \ env ->
+ completeLazyBind env NotTopLevel
+ old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) ->
+ addFloats env floats thing_inside
\end{code}
%************************************************************************
%* *
-\subsection[Simplify-simplExpr]{The main function: simplExpr}
+\subsection{Lazy bindings}
%* *
%************************************************************************
+simplRecBind is used for
+ * recursive bindings only
+
\begin{code}
-addBind :: CoreBind -> OutStuff a -> OutStuff a
-addBind bind (binds, res) = (bind:binds, res)
+simplRecBind :: SimplEnv -> TopLevelFlag
+ -> [(InId, InExpr)] -> [OutId]
+ -> SimplM (FloatsWith SimplEnv)
+simplRecBind env top_lvl pairs bndrs'
+ = go env pairs bndrs' `thenSmpl` \ (floats, env) ->
+ returnSmpl (flattenFloats floats, env)
+ where
+ go env [] _ = returnSmpl (emptyFloats env, env)
+
+ go env ((bndr, rhs) : pairs) (bndr' : bndrs')
+ = simplRecOrTopPair env top_lvl bndr bndr' rhs `thenSmpl` \ (floats, env) ->
+ addFloats env floats (\env -> go env pairs bndrs')
+\end{code}
+
-addBinds :: [CoreBind] -> OutStuff a -> OutStuff a
-addBinds [] stuff = stuff
-addBinds binds1 (binds2, res) = (binds1++binds2, res)
+simplRecOrTopPair is used for
+ * recursive bindings (whether top level or not)
+ * top-level non-recursive bindings
+
+It assumes the binder has already been simplified, but not its IdInfo.
+
+\begin{code}
+simplRecOrTopPair :: SimplEnv
+ -> TopLevelFlag
+ -> InId -> OutId -- Binder, both pre-and post simpl
+ -> InExpr -- The RHS and its environment
+ -> SimplM (FloatsWith SimplEnv)
+
+simplRecOrTopPair env top_lvl bndr bndr' rhs
+ | preInlineUnconditionally env top_lvl bndr rhs -- Check for unconditional inline
+ = tick (PreInlineUnconditionally bndr) `thenSmpl_`
+ returnSmpl (emptyFloats env, extendIdSubst env bndr (mkContEx env rhs))
+
+ | otherwise
+ = simplLazyBind env top_lvl Recursive bndr bndr' rhs env
+ -- May not actually be recursive, but it doesn't matter
\end{code}
+
+simplLazyBind is used for
+ * recursive bindings (whether top level or not)
+ * top-level non-recursive bindings
+ * non-top-level *lazy* non-recursive bindings
+
+[Thus it deals with the lazy cases from simplNonRecBind, and all cases
+from SimplRecOrTopBind]
+
+Nota bene:
+ 1. It assumes that the binder is *already* simplified,
+ and is in scope, but not its IdInfo
+
+ 2. It assumes that the binder type is lifted.
+
+ 3. It does not check for pre-inline-unconditionallly;
+ that should have been done already.
+
+\begin{code}
+simplLazyBind :: SimplEnv
+ -> TopLevelFlag -> RecFlag
+ -> InId -> OutId -- Binder, both pre-and post simpl
+ -> InExpr -> SimplEnv -- The RHS and its environment
+ -> SimplM (FloatsWith SimplEnv)
+
+simplLazyBind env top_lvl is_rec bndr bndr1 rhs rhs_se
+ = let -- Transfer the IdInfo of the original binder to the new binder
+ -- This is crucial: we must preserve
+ -- strictness
+ -- rules
+ -- worker info
+ -- etc. To do this we must apply the current substitution,
+ -- which incorporates earlier substitutions in this very letrec group.
+ --
+ -- NB 1. We do this *before* processing the RHS of the binder, so that
+ -- its substituted rules are visible in its own RHS.
+ -- This is important. Manuel found cases where he really, really
+ -- wanted a RULE for a recursive function to apply in that function's
+ -- own right-hand side.
+ --
+ -- NB 2: We do not transfer the arity (see Subst.substIdInfo)
+ -- The arity of an Id should not be visible
+ -- in its own RHS, else we eta-reduce
+ -- f = \x -> f x
+ -- to
+ -- f = f
+ -- which isn't sound. And it makes the arity in f's IdInfo greater than
+ -- the manifest arity, which isn't good.
+ -- The arity will get added later.
+ --
+ -- NB 3: It's important that we *do* transer the loop-breaker OccInfo,
+ -- because that's what stops the Id getting inlined infinitely, in the body
+ -- of the letrec.
+
+ -- NB 4: does no harm for non-recursive bindings
+
+ bndr2 = bndr1 `setIdInfo` simplIdInfo env (idInfo bndr)
+ env1 = modifyInScope env bndr2 bndr2
+ rhs_env = setInScope rhs_se env1
+ is_top_level = isTopLevel top_lvl
+ ok_float_unlifted = not is_top_level && isNonRec is_rec
+ rhs_cont = mkRhsStop (idType bndr1)
+ in
+ -- Simplify the RHS; note the mkRhsStop, which tells
+ -- the simplifier that this is the RHS of a let.
+ simplExprF rhs_env rhs rhs_cont `thenSmpl` \ (floats, rhs1) ->
+
+ -- If any of the floats can't be floated, give up now
+ -- (The allLifted predicate says True for empty floats.)
+ if (not ok_float_unlifted && not (allLifted floats)) then
+ completeLazyBind env1 top_lvl bndr bndr2
+ (wrapFloats floats rhs1)
+ else
+
+ -- ANF-ise a constructor or PAP rhs
+ mkAtomicArgs False {- Not strict -}
+ ok_float_unlifted rhs1 `thenSmpl` \ (aux_binds, rhs2) ->
+
+ -- If the result is a PAP, float the floats out, else wrap them
+ -- By this time it's already been ANF-ised (if necessary)
+ if isEmptyFloats floats && isNilOL aux_binds then -- Shortcut a common case
+ completeLazyBind env1 top_lvl bndr bndr2 rhs2
+
+ else if is_top_level || exprIsTrivial rhs2 || exprIsHNF rhs2 then
+ -- WARNING: long dodgy argument coming up
+ -- WANTED: a better way to do this
+ --
+ -- We can't use "exprIsCheap" instead of exprIsHNF,
+ -- because that causes a strictness bug.
+ -- x = let y* = E in case (scc y) of { T -> F; F -> T}
+ -- The case expression is 'cheap', but it's wrong to transform to
+ -- y* = E; x = case (scc y) of {...}
+ -- Either we must be careful not to float demanded non-values, or
+ -- we must use exprIsHNF for the test, which ensures that the
+ -- thing is non-strict. So exprIsHNF => bindings are non-strict
+ -- I think. The WARN below tests for this.
+ --
+ -- We use exprIsTrivial here because we want to reveal lone variables.
+ -- E.g. let { x = letrec { y = E } in y } in ...
+ -- Here we definitely want to float the y=E defn.
+ -- exprIsHNF definitely isn't right for that.
+ --
+ -- Again, the floated binding can't be strict; if it's recursive it'll
+ -- be non-strict; if it's non-recursive it'd be inlined.
+ --
+ -- Note [SCC-and-exprIsTrivial]
+ -- If we have
+ -- y = let { x* = E } in scc "foo" x
+ -- then we do *not* want to float out the x binding, because
+ -- it's strict! Fortunately, exprIsTrivial replies False to
+ -- (scc "foo" x).
+
+ -- There's a subtlety here. There may be a binding (x* = e) in the
+ -- floats, where the '*' means 'will be demanded'. So is it safe
+ -- to float it out? Answer no, but it won't matter because
+ -- we only float if (a) arg' is a WHNF, or (b) it's going to top level
+ -- and so there can't be any 'will be demanded' bindings in the floats.
+ -- Hence the warning
+ ASSERT2( is_top_level || not (any demanded_float (floatBinds floats)),
+ ppr (filter demanded_float (floatBinds floats)) )
+
+ tick LetFloatFromLet `thenSmpl_` (
+ addFloats env1 floats $ \ env2 ->
+ addAtomicBinds env2 (fromOL aux_binds) $ \ env3 ->
+ completeLazyBind env3 top_lvl bndr bndr2 rhs2)
+
+ else
+ completeLazyBind env1 top_lvl bndr bndr2 (wrapFloats floats rhs1)
+
+#ifdef DEBUG
+demanded_float (NonRec b r) = isStrictDmd (idNewDemandInfo b) && not (isUnLiftedType (idType b))
+ -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
+demanded_float (Rec _) = False
+#endif
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Completing a lazy binding}
+%* *
+%************************************************************************
+
+completeLazyBind
+ * deals only with Ids, not TyVars
+ * takes an already-simplified binder and RHS
+ * is used for both recursive and non-recursive bindings
+ * is used for both top-level and non-top-level bindings
+
+It does the following:
+ - tries discarding a dead binding
+ - tries PostInlineUnconditionally
+ - add unfolding [this is the only place we add an unfolding]
+ - add arity
+
+It does *not* attempt to do let-to-case. Why? Because it is used for
+ - top-level bindings (when let-to-case is impossible)
+ - many situations where the "rhs" is known to be a WHNF
+ (so let-to-case is inappropriate).
+
+\begin{code}
+completeLazyBind :: SimplEnv
+ -> TopLevelFlag -- Flag stuck into unfolding
+ -> InId -- Old binder
+ -> OutId -- New binder
+ -> OutExpr -- Simplified RHS
+ -> SimplM (FloatsWith SimplEnv)
+-- We return a new SimplEnv, because completeLazyBind may choose to do its work
+-- by extending the substitution (e.g. let x = y in ...)
+-- The new binding (if any) is returned as part of the floats.
+-- NB: the returned SimplEnv has the right SubstEnv, but you should
+-- (as usual) use the in-scope-env from the floats
+
+completeLazyBind env top_lvl old_bndr new_bndr new_rhs
+ | postInlineUnconditionally env top_lvl new_bndr occ_info new_rhs unfolding
+ = -- Drop the binding
+ tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
+ returnSmpl (emptyFloats env, extendIdSubst env old_bndr (DoneEx new_rhs))
+ -- Use the substitution to make quite, quite sure that the substitution
+ -- will happen, since we are going to discard the binding
+
+ | otherwise
+ = let
+ -- Add arity info
+ new_bndr_info = idInfo new_bndr `setArityInfo` exprArity new_rhs
+
+ -- Add the unfolding *only* for non-loop-breakers
+ -- Making loop breakers not have an unfolding at all
+ -- means that we can avoid tests in exprIsConApp, for example.
+ -- This is important: if exprIsConApp says 'yes' for a recursive
+ -- thing, then we can get into an infinite loop
+
+ -- If the unfolding is a value, the demand info may
+ -- go pear-shaped, so we nuke it. Example:
+ -- let x = (a,b) in
+ -- case x of (p,q) -> h p q x
+ -- Here x is certainly demanded. But after we've nuked
+ -- the case, we'll get just
+ -- let x = (a,b) in h a b x
+ -- and now x is not demanded (I'm assuming h is lazy)
+ -- This really happens. Similarly
+ -- let f = \x -> e in ...f..f...
+ -- After inling f at some of its call sites the original binding may
+ -- (for example) be no longer strictly demanded.
+ -- The solution here is a bit ad hoc...
+ info_w_unf = new_bndr_info `setUnfoldingInfo` unfolding
+ final_info | loop_breaker = new_bndr_info
+ | isEvaldUnfolding unfolding = zapDemandInfo info_w_unf `orElse` info_w_unf
+ | otherwise = info_w_unf
+
+ final_id = new_bndr `setIdInfo` final_info
+ in
+ -- These seqs forces the Id, and hence its IdInfo,
+ -- and hence any inner substitutions
+ final_id `seq`
+ returnSmpl (unitFloat env final_id new_rhs, env)
+
+ where
+ unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs
+ loop_breaker = isLoopBreaker occ_info
+ old_info = idInfo old_bndr
+ occ_info = occInfo old_info
+\end{code}
+
+
+
+%************************************************************************
+%* *
+\subsection[Simplify-simplExpr]{The main function: simplExpr}
+%* *
+%************************************************************************
+
The reason for this OutExprStuff stuff is that we want to float *after*
simplifying a RHS, not before. If we do so naively we get quadratic
behaviour as things float out.
\begin{code}
-simplExpr :: CoreExpr -> SimplM CoreExpr
-simplExpr expr = getSubst `thenSmpl` \ subst ->
- simplExprC expr (Stop (substTy subst (coreExprType expr)))
- -- The type in the Stop continuation is usually not used
+simplExpr :: SimplEnv -> CoreExpr -> SimplM CoreExpr
+simplExpr env expr = simplExprC env expr (mkBoringStop expr_ty')
+ where
+ expr_ty' = substTy env (exprType expr)
+ -- The type in the Stop continuation, expr_ty', is usually not used
-- It's only needed when discarding continuations after finding
-- a function that returns bottom.
-- Hence the lazy substitution
-simplExprC :: CoreExpr -> SimplCont -> SimplM CoreExpr
- -- Simplify an expression, given a continuation
-simplExprC expr cont = simplExprF expr cont `thenSmpl` \ (floats, (_, body)) ->
- returnSmpl (mkLets floats body)
+simplExprC :: SimplEnv -> CoreExpr -> SimplCont -> SimplM CoreExpr
+ -- Simplify an expression, given a continuation
+simplExprC env expr cont
+ = simplExprF env expr cont `thenSmpl` \ (floats, expr) ->
+ returnSmpl (wrapFloats floats expr)
-simplExprF :: InExpr -> SimplCont -> SimplM OutExprStuff
+simplExprF :: SimplEnv -> InExpr -> SimplCont -> SimplM FloatsWithExpr
-- Simplify an expression, returning floated binds
-simplExprF (Var v) cont
- = simplVar v cont
+simplExprF env (Var v) cont = simplVar env v cont
+simplExprF env (Lit lit) cont = rebuild env (Lit lit) cont
+simplExprF env expr@(Lam _ _) cont = simplLam env expr cont
+simplExprF env (Note note expr) cont = simplNote env note expr cont
+simplExprF env (App fun arg) cont = simplExprF env fun (ApplyTo NoDup arg env cont)
-simplExprF expr@(Con (PrimOp op) args) cont
- = getSubstEnv `thenSmpl` \ se ->
- prepareArgs (ppr op)
- (primOpType op)
- (primOpStrictness op)
- (pushArgs se args cont) $ \ args1 cont1 ->
+simplExprF env (Type ty) cont
+ = ASSERT( contIsRhsOrArg cont )
+ simplType env ty `thenSmpl` \ ty' ->
+ rebuild env (Type ty') cont
- let
- -- Boring... we may have too many arguments now, so we push them back
- n_args = length args
- args2 = ASSERT( length args1 >= n_args )
- take n_args args1
- cont2 = pushArgs emptySubstEnv (drop n_args args1) cont1
- in
- -- Try the prim op simplification
- -- It's really worth trying simplExpr again if it succeeds,
- -- because you can find
- -- case (eqChar# x 'a') of ...
- -- ==>
- -- case (case x of 'a' -> True; other -> False) of ...
- case tryPrimOp op args2 of
- Just e' -> zapSubstEnv (simplExprF e' cont2)
- Nothing -> rebuild (Con (PrimOp op) args2) cont2
-
-simplExprF (Con con@(DataCon _) args) cont
- = simplConArgs args ( \ args' ->
- rebuild (Con con args') cont)
-
-simplExprF expr@(Con con@(Literal _) args) cont
- = ASSERT( null args )
- rebuild expr cont
-
-simplExprF (App fun arg) cont
- = getSubstEnv `thenSmpl` \ se ->
- simplExprF fun (ApplyTo NoDup arg se cont)
-
-simplExprF (Case scrut bndr alts) cont
- = getSubstEnv `thenSmpl` \ se ->
- simplExprF scrut (Select NoDup bndr alts se cont)
-
-
-simplExprF (Let (Rec pairs) body) cont
- = simplIds (map fst pairs) $ \ bndrs' ->
- -- NB: bndrs' don't have unfoldings or spec-envs
- -- We add them as we go down, using simplPrags
-
- simplRecBind NotTopLevel pairs bndrs' (simplExprF body cont)
-
-simplExprF expr@(Lam _ _) cont = simplLam expr cont
-
-simplExprF (Type ty) cont
- = ASSERT( case cont of { Stop _ -> True; ArgOf _ _ _ -> True; other -> False } )
- simplType ty `thenSmpl` \ ty' ->
- rebuild (Type ty') cont
-
-simplExprF (Note (Coerce to from) e) cont
- | to == from = simplExprF e cont
- | otherwise = simplType to `thenSmpl` \ to' ->
- simplExprF e (CoerceIt to' cont)
-
--- hack: we only distinguish subsumed cost centre stacks for the purposes of
--- inlining. All other CCCSs are mapped to currentCCS.
-simplExprF (Note (SCC cc) e) cont
- = setEnclosingCC currentCCS $
- simplExpr e `thenSmpl` \ e ->
- rebuild (mkNote (SCC cc) e) cont
-
-simplExprF (Note InlineCall e) cont
- = simplExprF e (InlinePlease cont)
-
--- Comments about the InlineMe case
--- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
--- Don't inline in the RHS of something that has an
--- inline pragma. But be careful that the InScopeEnv that
--- we return does still have inlinings on!
---
--- It really is important to switch off inlinings. This function
--- may be inlinined in other modules, so we don't want to remove
--- (by inlining) calls to functions that have specialisations, or
--- that may have transformation rules in an importing scope.
--- E.g. {-# INLINE f #-}
--- f x = ...g...
--- and suppose that g is strict *and* has specialisations.
--- If we inline g's wrapper, we deny f the chance of getting
--- the specialised version of g when f is inlined at some call site
--- (perhaps in some other module).
-
-simplExprF (Note InlineMe e) cont
- = case cont of
- Stop _ -> -- Totally boring continuation
- -- Don't inline inside an INLINE expression
- switchOffInlining (simplExpr e) `thenSmpl` \ e' ->
- rebuild (mkNote InlineMe e') cont
-
- other -> -- Dissolve the InlineMe note if there's
- -- an interesting context of any kind to combine with
- -- (even a type application -- anything except Stop)
- simplExprF e cont
-
--- A non-recursive let is dealt with by simplBeta
-simplExprF (Let (NonRec bndr rhs) body) cont
- = getSubstEnv `thenSmpl` \ se ->
- simplBeta bndr rhs se (contResultType cont) $
- simplExprF body cont
-\end{code}
+simplExprF env (Case scrut bndr case_ty alts) cont
+ | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
+ = -- Simplify the scrutinee with a Select continuation
+ simplExprF env scrut (Select NoDup bndr alts env cont)
+
+ | otherwise
+ = -- If case-of-case is off, simply simplify the case expression
+ -- in a vanilla Stop context, and rebuild the result around it
+ simplExprC env scrut case_cont `thenSmpl` \ case_expr' ->
+ rebuild env case_expr' cont
+ where
+ case_cont = Select NoDup bndr alts env (mkBoringStop case_ty')
+ case_ty' = substTy env case_ty -- c.f. defn of simplExpr
+
+simplExprF env (Let (Rec pairs) body) cont
+ = simplLetBndrs env (map fst pairs) `thenSmpl` \ (env, bndrs') ->
+ -- NB: bndrs' don't have unfoldings or rules
+ -- We add them as we go down
+
+ simplRecBind env NotTopLevel pairs bndrs' `thenSmpl` \ (floats, env) ->
+ addFloats env floats $ \ env ->
+ simplExprF env body cont
+
+-- A non-recursive let is dealt with by simplNonRecBind
+simplExprF env (Let (NonRec bndr rhs) body) cont
+ = simplNonRecBind env bndr rhs env (contResultType cont) $ \ env ->
+ simplExprF env body cont
---------------------------------
+simplType :: SimplEnv -> InType -> SimplM OutType
+ -- Kept monadic just so we can do the seqType
+simplType env ty
+ = seqType new_ty `seq` returnSmpl new_ty
+ where
+ new_ty = substTy env ty
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Lambdas}
+%* *
+%************************************************************************
\begin{code}
-simplLam fun cont
- = go fun cont
+simplLam env fun cont
+ = go env fun cont
where
- zap_it = mkLamBndrZapper fun (countArgs cont)
+ zap_it = mkLamBndrZapper fun (countArgs cont)
cont_ty = contResultType cont
-- Type-beta reduction
- go (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
+ go env (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont)
= ASSERT( isTyVar bndr )
- tick (BetaReduction bndr) `thenSmpl_`
- getInScope `thenSmpl` \ in_scope ->
- let
- ty' = substTy (mkSubst in_scope arg_se) ty_arg
- in
- seqType ty' `seq`
- extendSubst bndr (DoneTy ty')
- (go body body_cont)
+ tick (BetaReduction bndr) `thenSmpl_`
+ simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' ->
+ go (extendTvSubst env bndr ty_arg') body body_cont
-- Ordinary beta reduction
- go (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
- = tick (BetaReduction bndr) `thenSmpl_`
- simplBeta zapped_bndr arg arg_se cont_ty
- (go body body_cont)
+ go env (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont)
+ = tick (BetaReduction bndr) `thenSmpl_`
+ simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env ->
+ go env body body_cont
+
+ -- Not enough args, so there are real lambdas left to put in the result
+ go env lam@(Lam _ _) cont
+ = simplLamBndrs env bndrs `thenSmpl` \ (env, bndrs') ->
+ simplExpr env body `thenSmpl` \ body' ->
+ mkLam env bndrs' body' cont `thenSmpl` \ (floats, new_lam) ->
+ addFloats env floats $ \ env ->
+ rebuild env new_lam cont
where
- zapped_bndr = zap_it bndr
-
- -- Not enough args
- go lam@(Lam _ _) cont = completeLam [] lam cont
+ (bndrs,body) = collectBinders lam
-- Exactly enough args
- go expr cont = simplExprF expr cont
-
-
--- completeLam deals with the case where a lambda doesn't have an ApplyTo
--- continuation. Try for eta reduction, but *only* if we get all
--- the way to an exprIsTrivial expression.
--- 'acc' holds the simplified binders, in reverse order
-
-completeLam acc (Lam bndr body) cont
- = simplBinder bndr $ \ bndr' ->
- completeLam (bndr':acc) body cont
-
-completeLam acc body cont
- = simplExpr body `thenSmpl` \ body' ->
-
- case (opt_SimplDoEtaReduction, check_eta acc body') of
- (True, Just body'') -- Eta reduce!
- -> tick (EtaReduction (head acc)) `thenSmpl_`
- rebuild body'' cont
-
- other -> -- No eta reduction
- rebuild (foldl (flip Lam) body' acc) cont
- -- Remember, acc is the reversed binders
- where
- -- NB: the binders are reversed
- check_eta (b : bs) (App fun arg)
- | (varToCoreExpr b `cheapEqExpr` arg)
- = check_eta bs fun
-
- check_eta [] body
- | exprIsTrivial body && -- ONLY if the body is trivial
- not (any (`elemVarSet` body_fvs) acc)
- = Just body -- Success!
- where
- body_fvs = exprFreeVars body
-
- check_eta _ _ = Nothing -- Bale out
+ go env expr cont = simplExprF env expr cont
mkLamBndrZapper :: CoreExpr -- Function
- -> Int -- Number of args
+ -> Int -- Number of args supplied, *including* type args
-> Id -> Id -- Use this to zap the binders
mkLamBndrZapper fun n_args
| n_args >= n_params fun = \b -> b -- Enough args
- | otherwise = \b -> maybeModifyIdInfo zapLamIdInfo b
+ | otherwise = \b -> zapLamIdInfo b
where
- n_params (Lam b e) | isId b = 1 + n_params e
- | otherwise = n_params e
- n_params other = 0::Int
+ -- NB: we count all the args incl type args
+ -- so we must count all the binders (incl type lambdas)
+ n_params (Note _ e) = n_params e
+ n_params (Lam b e) = 1 + n_params e
+ n_params other = 0::Int
\end{code}
----------------------------------
-simplConArgs makes sure that the arguments all end up being atomic.
-That means it may generate some Lets, hence the strange type
-
-\begin{code}
-simplConArgs :: [InArg] -> ([OutArg] -> SimplM OutExprStuff) -> SimplM OutExprStuff
-simplConArgs [] thing_inside
- = thing_inside []
-
-simplConArgs (arg:args) thing_inside
- = switchOffInlining (simplExpr arg) `thenSmpl` \ arg' ->
- -- Simplify the RHS with inlining switched off, so that
- -- only absolutely essential things will happen.
-
- simplConArgs args $ \ args' ->
-
- -- If the argument ain't trivial, then let-bind it
- if exprIsTrivial arg' then
- thing_inside (arg' : args')
- else
- newId (coreExprType arg') $ \ arg_id ->
- thing_inside (Var arg_id : args') `thenSmpl` \ res ->
- returnSmpl (addBind (NonRec arg_id arg') res)
-\end{code}
-
+%************************************************************************
+%* *
+\subsection{Notes}
+%* *
+%************************************************************************
----------------------------------
\begin{code}
-simplType :: InType -> SimplM OutType
-simplType ty
- = getSubst `thenSmpl` \ subst ->
- let
- new_ty = substTy subst ty
+simplNote env (Coerce to from) body cont
+ = let
+ addCoerce s1 k1 cont -- Drop redundant coerces. This can happen if a polymoprhic
+ -- (coerce a b e) is instantiated with a=ty1 b=ty2 and the
+ -- two are the same. This happens a lot in Happy-generated parsers
+ | s1 `coreEqType` k1 = cont
+
+ addCoerce s1 k1 (CoerceIt t1 cont)
+ -- coerce T1 S1 (coerce S1 K1 e)
+ -- ==>
+ -- e, if T1=K1
+ -- coerce T1 K1 e, otherwise
+ --
+ -- For example, in the initial form of a worker
+ -- we may find (coerce T (coerce S (\x.e))) y
+ -- and we'd like it to simplify to e[y/x] in one round
+ -- of simplification
+ | t1 `coreEqType` k1 = cont -- The coerces cancel out
+ | otherwise = CoerceIt t1 cont -- They don't cancel, but
+ -- the inner one is redundant
+
+ addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont)
+ | not (isTypeArg arg), -- This whole case only works for value args
+ -- Could upgrade to have equiv thing for type apps too
+ Just (s1, s2) <- splitFunTy_maybe s1s2
+ -- (coerce (T1->T2) (S1->S2) F) E
+ -- ===>
+ -- coerce T2 S2 (F (coerce S1 T1 E))
+ --
+ -- t1t2 must be a function type, T1->T2, because it's applied to something
+ -- but s1s2 might conceivably not be
+ --
+ -- When we build the ApplyTo we can't mix the out-types
+ -- with the InExpr in the argument, so we simply substitute
+ -- to make it all consistent. It's a bit messy.
+ -- But it isn't a common case.
+ = let
+ (t1,t2) = splitFunTy t1t2
+ new_arg = mkCoerce2 s1 t1 (substExpr arg_env arg)
+ arg_env = setInScope arg_se env
+ in
+ ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont)
+
+ addCoerce to' _ cont = CoerceIt to' cont
in
- seqType new_ty `seq`
- returnSmpl new_ty
+ simplType env to `thenSmpl` \ to' ->
+ simplType env from `thenSmpl` \ from' ->
+ simplExprF env body (addCoerce to' from' cont)
+
+
+-- Hack: we only distinguish subsumed cost centre stacks for the purposes of
+-- inlining. All other CCCSs are mapped to currentCCS.
+simplNote env (SCC cc) e cont
+ = simplExpr (setEnclosingCC env currentCCS) e `thenSmpl` \ e' ->
+ rebuild env (mkSCC cc e') cont
+
+simplNote env InlineCall e cont
+ = simplExprF env e (InlinePlease cont)
+
+-- See notes with SimplMonad.inlineMode
+simplNote env InlineMe e cont
+ | contIsRhsOrArg cont -- Totally boring continuation; see notes above
+ = -- Don't inline inside an INLINE expression
+ simplExpr (setMode inlineMode env ) e `thenSmpl` \ e' ->
+ rebuild env (mkInlineMe e') cont
+
+ | otherwise -- Dissolve the InlineMe note if there's
+ -- an interesting context of any kind to combine with
+ -- (even a type application -- anything except Stop)
+ = simplExprF env e cont
+
+simplNote env (CoreNote s) e cont
+ = simplExpr env e `thenSmpl` \ e' ->
+ rebuild env (Note (CoreNote s) e') cont
\end{code}
%************************************************************************
%* *
-\subsection{Binding}
+\subsection{Dealing with calls}
%* *
%************************************************************************
-@simplBeta@ is used for non-recursive lets in expressions,
-as well as true beta reduction.
-
-Very similar to @simplLazyBind@, but not quite the same.
-
\begin{code}
-simplBeta :: InId -- Binder
- -> InExpr -> SubstEnv -- Arg, with its subst-env
- -> OutType -- Type of thing computed by the context
- -> SimplM OutExprStuff -- The body
- -> SimplM OutExprStuff
-#ifdef DEBUG
-simplBeta bndr rhs rhs_se cont_ty thing_inside
- | isTyVar bndr
- = pprPanic "simplBeta" (ppr bndr <+> ppr rhs)
-#endif
-
-simplBeta bndr rhs rhs_se cont_ty thing_inside
- | preInlineUnconditionally bndr && not opt_SimplNoPreInlining
- = tick (PreInlineUnconditionally bndr) `thenSmpl_`
- extendSubst bndr (ContEx rhs_se rhs) thing_inside
-
- | otherwise
- = -- Simplify the RHS
- simplBinder bndr $ \ bndr' ->
- simplArg (idType bndr') (getIdDemandInfo bndr)
- rhs rhs_se cont_ty $ \ rhs' ->
+simplVar env var cont
+ = case substId env var of
+ DoneEx e -> simplExprF (zapSubstEnv env) e cont
+ ContEx tvs ids e -> simplExprF (setSubstEnv env tvs ids) e cont
+ DoneId var1 occ -> completeCall (zapSubstEnv env) var1 occ cont
+ -- Note [zapSubstEnv]
+ -- The template is already simplified, so don't re-substitute.
+ -- This is VITAL. Consider
+ -- let x = e in
+ -- let y = \z -> ...x... in
+ -- \ x -> ...y...
+ -- We'll clone the inner \x, adding x->x' in the id_subst
+ -- Then when we inline y, we must *not* replace x by x' in
+ -- the inlined copy!!
- -- Now complete the binding and simplify the body
- completeBeta bndr bndr' rhs' thing_inside
+---------------------------------------------------------
+-- Dealing with a call site
-completeBeta bndr bndr' rhs' thing_inside
- | isUnLiftedType (idType bndr') && not (exprOkForSpeculation rhs')
- -- Make a case expression instead of a let
- -- These can arise either from the desugarer,
- -- or from beta reductions: (\x.e) (x +# y)
- = getInScope `thenSmpl` \ in_scope ->
- thing_inside `thenSmpl` \ (floats, (_, body)) ->
- returnSmpl ([], (in_scope, Case rhs' bndr' [(DEFAULT, [], mkLets floats body)]))
+completeCall env var occ_info cont
+ = -- Simplify the arguments
+ getDOptsSmpl `thenSmpl` \ dflags ->
+ let
+ chkr = getSwitchChecker env
+ (args, call_cont, inline_call) = getContArgs chkr var cont
+ fn_ty = idType var
+ in
+ simplifyArgs env fn_ty args (contResultType call_cont) $ \ env args ->
- | otherwise
- = completeBinding bndr bndr' False rhs' thing_inside
-\end{code}
+ -- Next, look for rules or specialisations that match
+ --
+ -- It's important to simplify the args first, because the rule-matcher
+ -- doesn't do substitution as it goes. We don't want to use subst_args
+ -- (defined in the 'where') because that throws away useful occurrence info,
+ -- and perhaps-very-important specialisations.
+ --
+ -- Some functions have specialisations *and* are strict; in this case,
+ -- we don't want to inline the wrapper of the non-specialised thing; better
+ -- to call the specialised thing instead.
+ -- We used to use the black-listing mechanism to ensure that inlining of
+ -- the wrapper didn't occur for things that have specialisations till a
+ -- later phase, so but now we just try RULES first
+ --
+ -- You might think that we shouldn't apply rules for a loop breaker:
+ -- doing so might give rise to an infinite loop, because a RULE is
+ -- rather like an extra equation for the function:
+ -- RULE: f (g x) y = x+y
+ -- Eqn: f a y = a-y
+ --
+ -- But it's too drastic to disable rules for loop breakers.
+ -- Even the foldr/build rule would be disabled, because foldr
+ -- is recursive, and hence a loop breaker:
+ -- foldr k z (build g) = g k z
+ -- So it's up to the programmer: rules can cause divergence
+ let
+ in_scope = getInScope env
+ rules = getRules env
+ maybe_rule = case activeRule env of
+ Nothing -> Nothing -- No rules apply
+ Just act_fn -> lookupRule act_fn in_scope rules var args
+ in
+ case maybe_rule of {
+ Just (rule_name, rule_rhs) ->
+ tick (RuleFired rule_name) `thenSmpl_`
+ (if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "Rule fired" (vcat [
+ text "Rule:" <+> ftext rule_name,
+ text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
+ text "After: " <+> pprCoreExpr rule_rhs,
+ text "Cont: " <+> ppr call_cont])
+ else
+ id) $
+ simplExprF env rule_rhs call_cont ;
+
+ Nothing -> -- No rules
-\begin{code}
-simplArg :: OutType -> Demand
- -> InExpr -> SubstEnv
- -> OutType -- Type of thing computed by the context
- -> (OutExpr -> SimplM OutExprStuff)
- -> SimplM OutExprStuff
-simplArg arg_ty demand arg arg_se cont_ty thing_inside
- | isStrict demand ||
- isUnLiftedType arg_ty ||
- (opt_DictsStrict && isDictTy arg_ty && isDataType arg_ty)
- -- Return true only for dictionary types where the dictionary
- -- has more than one component (else we risk poking on the component
- -- of a newtype dictionary)
- = getSubstEnv `thenSmpl` \ body_se ->
- transformRhs arg `thenSmpl` \ t_arg ->
- setSubstEnv arg_se (simplExprF t_arg (ArgOf NoDup cont_ty $ \ arg' ->
- setSubstEnv body_se (thing_inside arg')
- )) -- NB: we must restore body_se before carrying on with thing_inside!!
+ -- Next, look for an inlining
+ let
+ arg_infos = [ interestingArg arg | arg <- args, isValArg arg]
- | otherwise
- = simplRhs NotTopLevel True arg_ty arg arg_se thing_inside
-\end{code}
+ interesting_cont = interestingCallContext (notNull args)
+ (notNull arg_infos)
+ call_cont
+ active_inline = activeInline env var occ_info
+ maybe_inline = callSiteInline dflags active_inline inline_call occ_info
+ var arg_infos interesting_cont
+ in
+ case maybe_inline of {
+ Just unfolding -- There is an inlining!
+ -> tick (UnfoldingDone var) `thenSmpl_`
+ (if dopt Opt_D_dump_inlinings dflags then
+ pprTrace "Inlining done" (vcat [
+ text "Before:" <+> ppr var <+> sep (map pprParendExpr args),
+ text "Inlined fn: " <+> ppr unfolding,
+ text "Cont: " <+> ppr call_cont])
+ else
+ id) $
+ makeThatCall env var unfolding args call_cont
+
+ ;
+ Nothing -> -- No inlining!
+
+ -- Done
+ rebuild env (mkApps (Var var) args) call_cont
+ }}
+
+makeThatCall :: SimplEnv
+ -> Id
+ -> InExpr -- Inlined function rhs
+ -> [OutExpr] -- Arguments, already simplified
+ -> SimplCont -- After the call
+ -> SimplM FloatsWithExpr
+-- Similar to simplLam, but this time
+-- the arguments are already simplified
+makeThatCall orig_env var fun@(Lam _ _) args cont
+ = go orig_env fun args
+ where
+ zap_it = mkLamBndrZapper fun (length args)
-completeBinding
- - deals only with Ids, not TyVars
- - take an already-simplified RHS
+ -- Type-beta reduction
+ go env (Lam bndr body) (Type ty_arg : args)
+ = ASSERT( isTyVar bndr )
+ tick (BetaReduction bndr) `thenSmpl_`
+ go (extendTvSubst env bndr ty_arg) body args
-It does *not* attempt to do let-to-case. Why? Because they are used for
+ -- Ordinary beta reduction
+ go env (Lam bndr body) (arg : args)
+ = tick (BetaReduction bndr) `thenSmpl_`
+ simplNonRecX env (zap_it bndr) arg $ \ env ->
+ go env body args
+
+ -- Not enough args, so there are real lambdas left to put in the result
+ go env fun args
+ = simplExprF env fun (pushContArgs orig_env args cont)
+ -- NB: orig_env; the correct environment to capture with
+ -- the arguments.... env has been augmented with substitutions
+ -- from the beta reductions.
+
+makeThatCall env var fun args cont
+ = simplExprF env fun (pushContArgs env args cont)
+\end{code}
- - top-level bindings
- (when let-to-case is impossible)
- - many situations where the "rhs" is known to be a WHNF
- (so let-to-case is inappropriate).
+%************************************************************************
+%* *
+\subsection{Arguments}
+%* *
+%************************************************************************
\begin{code}
-completeBinding :: InId -- Binder
- -> OutId -- New binder
- -> Bool -- True <=> black-listed; don't inline
- -> OutExpr -- Simplified RHS
- -> SimplM (OutStuff a) -- Thing inside
- -> SimplM (OutStuff a)
-
-completeBinding old_bndr new_bndr black_listed new_rhs thing_inside
- | isDeadBinder old_bndr -- This happens; for example, the case_bndr during case of
- -- known constructor: case (a,b) of x { (p,q) -> ... }
- -- Here x isn't mentioned in the RHS, so we don't want to
- -- create the (dead) let-binding let x = (a,b) in ...
- = thing_inside
-
- | not black_listed && postInlineUnconditionally old_bndr new_rhs
- -- Maybe we don't need a let-binding! Maybe we can just
- -- inline it right away. Unlike the preInlineUnconditionally case
- -- we are allowed to look at the RHS.
- --
- -- NB: a loop breaker never has postInlineUnconditionally True
- -- and non-loop-breakers only have *forward* references
- -- Hence, it's safe to discard the binding
- = tick (PostInlineUnconditionally old_bndr) `thenSmpl_`
- extendSubst old_bndr (DoneEx new_rhs)
- thing_inside
-
- | otherwise
- = getSubst `thenSmpl` \ subst ->
- let
- -- We make new IdInfo for the new binder by starting from the old binder,
- -- doing appropriate substitutions,
- new_bndr_info = substIdInfo subst (idInfo old_bndr) (idInfo new_bndr)
- `setArityInfo` ArityAtLeast (exprArity new_rhs)
-
- -- At the *binding* site we use the new binder info
- binding_site_id = new_bndr `setIdInfo` new_bndr_info
-
- -- At the *occurrence* sites we want to know the unfolding
- -- We also want the occurrence info of the *original*
- occ_site_id = new_bndr `setIdInfo`
- (new_bndr_info `setUnfoldingInfo` mkUnfolding new_rhs
- `setInlinePragInfo` getInlinePragma old_bndr)
- in
- -- These seqs force the Ids, and hence the IdInfos, and hence any
- -- inner substitutions
- binding_site_id `seq`
- occ_site_id `seq`
-
- (modifyInScope occ_site_id thing_inside `thenSmpl` \ stuff ->
- returnSmpl (addBind (NonRec binding_site_id new_rhs) stuff))
-\end{code}
+---------------------------------------------------------
+-- Simplifying the arguments of a call
+
+simplifyArgs :: SimplEnv
+ -> OutType -- Type of the function
+ -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments
+ -> OutType -- Type of the continuation
+ -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr)
+ -> SimplM FloatsWithExpr
+
+-- [CPS-like because of strict arguments]
+
+-- Simplify the arguments to a call.
+-- This part of the simplifier may break the no-shadowing invariant
+-- Consider
+-- f (...(\a -> e)...) (case y of (a,b) -> e')
+-- where f is strict in its second arg
+-- If we simplify the innermost one first we get (...(\a -> e)...)
+-- Simplifying the second arg makes us float the case out, so we end up with
+-- case y of (a,b) -> f (...(\a -> e)...) e'
+-- So the output does not have the no-shadowing invariant. However, there is
+-- no danger of getting name-capture, because when the first arg was simplified
+-- we used an in-scope set that at least mentioned all the variables free in its
+-- static environment, and that is enough.
+--
+-- We can't just do innermost first, or we'd end up with a dual problem:
+-- case x of (a,b) -> f e (...(\a -> e')...)
+--
+-- I spent hours trying to recover the no-shadowing invariant, but I just could
+-- not think of an elegant way to do it. The simplifier is already knee-deep in
+-- continuations. We have to keep the right in-scope set around; AND we have
+-- to get the effect that finding (error "foo") in a strict arg position will
+-- discard the entire application and replace it with (error "foo"). Getting
+-- all this at once is TOO HARD!
+
+simplifyArgs env fn_ty args cont_ty thing_inside
+ = go env fn_ty args thing_inside
+ where
+ go env fn_ty [] thing_inside = thing_inside env []
+ go env fn_ty (arg:args) thing_inside = simplifyArg env fn_ty arg cont_ty $ \ env arg' ->
+ go env (applyTypeToArg fn_ty arg') args $ \ env args' ->
+ thing_inside env (arg':args')
+
+simplifyArg env fn_ty (Type ty_arg, se, _) cont_ty thing_inside
+ = simplType (setInScope se env) ty_arg `thenSmpl` \ new_ty_arg ->
+ thing_inside env (Type new_ty_arg)
+
+simplifyArg env fn_ty (val_arg, arg_se, is_strict) cont_ty thing_inside
+ | is_strict
+ = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside
+
+ | otherwise -- Lazy argument
+ -- DO NOT float anything outside, hence simplExprC
+ -- There is no benefit (unlike in a let-binding), and we'd
+ -- have to be very careful about bogus strictness through
+ -- floating a demanded let.
+ = simplExprC (setInScope arg_se env) val_arg
+ (mkBoringStop arg_ty) `thenSmpl` \ arg1 ->
+ thing_inside env arg1
+ where
+ arg_ty = funArgTy fn_ty
+
+
+simplStrictArg :: LetRhsFlag
+ -> SimplEnv -- The env of the call
+ -> InExpr -> SimplEnv -- The arg plus its env
+ -> OutType -- arg_ty: type of the argument
+ -> OutType -- cont_ty: Type of thing computed by the context
+ -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr)
+ -- Takes an expression of type rhs_ty,
+ -- returns an expression of type cont_ty
+ -- The env passed to this continuation is the
+ -- env of the call, plus any new in-scope variables
+ -> SimplM FloatsWithExpr -- An expression of type cont_ty
+
+simplStrictArg is_rhs call_env arg arg_env arg_ty cont_ty thing_inside
+ = simplExprF (setInScope arg_env call_env) arg
+ (ArgOf is_rhs arg_ty cont_ty (\ new_env -> thing_inside (setInScope call_env new_env)))
+ -- Notice the way we use arg_env (augmented with in-scope vars from call_env)
+ -- to simplify the argument
+ -- and call-env (augmented with in-scope vars from the arg) to pass to the continuation
+\end{code}
%************************************************************************
%* *
-\subsection{simplLazyBind}
+\subsection{mkAtomicArgs}
%* *
%************************************************************************
-simplLazyBind basically just simplifies the RHS of a let(rec).
-It does two important optimisations though:
+mkAtomicArgs takes a putative RHS, checks whether it's a PAP or
+constructor application and, if so, converts it to ANF, so that the
+resulting thing can be inlined more easily. Thus
+ x = (f a, g b)
+becomes
+ t1 = f a
+ t2 = g b
+ x = (t1,t2)
- * It floats let(rec)s out of the RHS, even if they
- are hidden by big lambdas
-
- * It does eta expansion
-
-\begin{code}
-simplLazyBind :: TopLevelFlag
- -> InId -> OutId
- -> InExpr -- The RHS
- -> SimplM (OutStuff a) -- The body of the binding
- -> SimplM (OutStuff a)
--- When called, the subst env is correct for the entire let-binding
--- and hence right for the RHS.
--- Also the binder has already been simplified, and hence is in scope
-
-simplLazyBind top_lvl bndr bndr' rhs thing_inside
- = getBlackList `thenSmpl` \ black_list_fn ->
- let
- black_listed = isTopLevel top_lvl && black_list_fn bndr
- -- Only top level things can be black listed, so the
- -- first test gets us 'False' without having to call
- -- the function, in the common case.
- in
- if not black_listed &&
- preInlineUnconditionally bndr &&
- not opt_SimplNoPreInlining
- then
- tick (PreInlineUnconditionally bndr) `thenSmpl_`
- getSubstEnv `thenSmpl` \ rhs_se ->
- (extendSubst bndr (ContEx rhs_se rhs) thing_inside)
-
- else -- Simplify the RHS
- getSubstEnv `thenSmpl` \ rhs_se ->
- simplRhs top_lvl False {- Not ok to float unboxed -}
- (idType bndr')
- rhs rhs_se $ \ rhs' ->
-
- -- Now compete the binding and simplify the body
- completeBinding bndr bndr' black_listed rhs' thing_inside
-\end{code}
+There are three sorts of binding context, specified by the two
+boolean arguments
+Strict
+ OK-unlifted
+N N Top-level or recursive Only bind args of lifted type
-\begin{code}
-simplRhs :: TopLevelFlag
- -> Bool -- True <=> OK to float unboxed (speculative) bindings
- -> OutType -> InExpr -> SubstEnv
- -> (OutExpr -> SimplM (OutStuff a))
- -> SimplM (OutStuff a)
-simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside
- = -- Swizzle the inner lets past the big lambda (if any)
- -- and try eta expansion
- transformRhs rhs `thenSmpl` \ t_rhs ->
-
- -- Simplify it
- setSubstEnv rhs_se (simplExprF t_rhs (Stop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) ->
-
- -- Float lets out of RHS
- let
- (floats_out, rhs'') | float_ubx = (floats, rhs')
- | otherwise = splitFloats floats rhs'
- in
- if (isTopLevel top_lvl || exprIsCheap rhs') && -- Float lets if (a) we're at the top level
- not (null floats_out) -- or (b) it exposes a cheap (i.e. duplicatable) expression
- then
- tickLetFloat floats_out `thenSmpl_`
- -- Do the float
- --
- -- There's a subtlety here. There may be a binding (x* = e) in the
- -- floats, where the '*' means 'will be demanded'. So is it safe
- -- to float it out? Answer no, but it won't matter because
- -- we only float if arg' is a WHNF,
- -- and so there can't be any 'will be demanded' bindings in the floats.
- -- Hence the assert
- WARN( any demanded_float floats_out, ppr floats_out )
- setInScope in_scope' (thing_inside rhs'') `thenSmpl` \ stuff ->
- -- in_scope' may be excessive, but that's OK;
- -- it's a superset of what's in scope
- returnSmpl (addBinds floats_out stuff)
- else
- -- Don't do the float
- thing_inside (mkLets floats rhs')
+N Y Non-top-level and non-recursive, Bind args of lifted type, or
+ but lazy unlifted-and-ok-for-speculation
--- In a let-from-let float, we just tick once, arbitrarily
--- choosing the first floated binder to identify it
-tickLetFloat (NonRec b r : fs) = tick (LetFloatFromLet b)
-tickLetFloat (Rec ((b,r):prs) : fs) = tick (LetFloatFromLet b)
+Y Y Non-top-level, non-recursive, Bind all args
+ and strict (demanded)
-demanded_float (NonRec b r) = isStrict (getIdDemandInfo b) && not (isUnLiftedType (idType b))
- -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them
-demanded_float (Rec _) = False
--- Don't float any unlifted bindings out, because the context
--- is either a Rec group, or the top level, neither of which
--- can tolerate them.
-splitFloats floats rhs
- = go floats
- where
- go [] = ([], rhs)
- go (f:fs) | must_stay f = ([], mkLets (f:fs) rhs)
- | otherwise = case go fs of
- (out, rhs') -> (f:out, rhs')
+For example, given
- must_stay (Rec prs) = False -- No unlifted bindings in here
- must_stay (NonRec b r) = isUnLiftedType (idType b)
-\end{code}
+ x = MkC (y div# z)
+there is no point in transforming to
+ x = case (y div# z) of r -> MkC r
-%************************************************************************
-%* *
-\subsection{Variables}
-%* *
-%************************************************************************
+because the (y div# z) can't float out of the let. But if it was
+a *strict* let, then it would be a good thing to do. Hence the
+context information.
\begin{code}
-simplVar var cont
- = getSubst `thenSmpl` \ subst ->
- case lookupSubst subst var of
- Just (DoneEx (Var v)) -> zapSubstEnv (simplVar v cont)
- Just (DoneEx e) -> zapSubstEnv (simplExprF e cont)
- Just (ContEx env' e) -> setSubstEnv env' (simplExprF e cont)
-
- Nothing -> let
- var' = case lookupInScope subst var of
- Just v' -> v'
- Nothing ->
-#ifdef DEBUG
- if isLocallyDefined var && not (idMustBeINLINEd var)
- -- The idMustBeINLINEd test accouunts for the fact
- -- that class dictionary constructors don't have top level
- -- bindings and hence aren't in scope.
- then
- -- Not in scope
- pprTrace "simplVar:" (ppr var) var
- else
-#endif
- var
- in
- getBlackList `thenSmpl` \ black_list ->
- getInScope `thenSmpl` \ in_scope ->
- completeCall black_list in_scope var var' cont
+mkAtomicArgs :: Bool -- A strict binding
+ -> Bool -- OK to float unlifted args
+ -> OutExpr
+ -> SimplM (OrdList (OutId,OutExpr), -- The floats (unusually) may include
+ OutExpr) -- things that need case-binding,
+ -- if the strict-binding flag is on
----------------------------------------------------------
--- Dealing with a call
-
-completeCall black_list_fn in_scope orig_var var cont
--- For reasons I'm not very clear about, it's important *not* to plug 'var',
--- which is replete with an inlining in its IdInfo, into the resulting expression
--- Doing so results in a significant space leak.
--- Instead we pass orig_var, which has no inlinings etc.
-
- -- Look for rules or specialisations that match
- -- Do this *before* trying inlining because some functions
- -- have specialisations *and* are strict; we don't want to
- -- inline the wrapper of the non-specialised thing... better
- -- to call the specialised thing instead.
- | maybeToBool maybe_rule_match
- = tick (RuleFired rule_name) `thenSmpl_`
- zapSubstEnv (simplExprF rule_rhs (pushArgs emptySubstEnv rule_args result_cont))
- -- See note below about zapping the substitution here
-
- -- Look for an unfolding. There's a binding for the
- -- thing, but perhaps we want to inline it anyway
- | maybeToBool maybe_inline
- = tick (UnfoldingDone var) `thenSmpl_`
- zapSubstEnv (completeInlining orig_var unf_template discard_inline_cont)
- -- The template is already simplified, so don't re-substitute.
- -- This is VITAL. Consider
- -- let x = e in
- -- let y = \z -> ...x... in
- -- \ x -> ...y...
- -- We'll clone the inner \x, adding x->x' in the id_subst
- -- Then when we inline y, we must *not* replace x by x' in
- -- the inlined copy!!
-
- | otherwise -- Neither rule nor inlining
- -- Use prepareArgs to use function strictness
- = prepareArgs (ppr var) (idType var) (get_str var) cont $ \ args' cont' ->
- rebuild (mkApps (Var orig_var) args') cont'
+mkAtomicArgs is_strict ok_float_unlifted rhs
+ | (Var fun, args) <- collectArgs rhs, -- It's an application
+ isDataConWorkId fun || valArgCount args < idArity fun -- And it's a constructor or PAP
+ = go fun nilOL [] args -- Have a go
+
+ | otherwise = bale_out -- Give up
where
- get_str var = case getIdStrictness var of
- NoStrictnessInfo -> (repeat wwLazy, False)
- StrictnessInfo demands result_bot -> (demands, result_bot)
-
-
- (args', result_cont) = contArgs in_scope cont
- val_args = filter isValArg args'
- arg_infos = map (interestingArg in_scope) val_args
- inline_call = contIsInline result_cont
- interesting_cont = contIsInteresting result_cont
- discard_inline_cont | inline_call = discardInline cont
- | otherwise = cont
-
- ---------- Unfolding stuff
- maybe_inline = callSiteInline black_listed inline_call
- var arg_infos interesting_cont
- Just unf_template = maybe_inline
- black_listed = black_list_fn var
-
- ---------- Specialisation stuff
- maybe_rule_match = lookupRule in_scope var args'
- Just (rule_name, rule_rhs, rule_args) = maybe_rule_match
-
-
-
--- 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.
-interestingArg in_scope (Type _) = False
-interestingArg in_scope (App fn (Type _)) = interestingArg in_scope fn
-interestingArg in_scope (Var v) = hasSomeUnfolding (getIdUnfolding v')
- where
- v' = case lookupVarSet in_scope v of
- Just v' -> v'
- other -> v
-interestingArg in_scope other = True
-
-
--- First a special case
--- Don't actually inline the scrutinee when we see
--- case x of y { .... }
--- and x has unfolding (C a b). Why not? Because
--- we get a silly binding y = C a b. If we don't
--- inline knownCon can directly substitute x for y instead.
-completeInlining var (Con con con_args) (Select _ bndr alts se cont)
- | conOkForAlt con
- = knownCon (Var var) con con_args bndr alts se cont
-
--- Now the normal case
-completeInlining var unfolding cont
- = simplExprF unfolding cont
-
------------ costCentreOk
--- costCentreOk checks that it's ok to inline this thing
--- The time it *isn't* is this:
---
--- f x = let y = E in
--- scc "foo" (...y...)
---
--- Here y has a "current cost centre", and we can't inline it inside "foo",
--- regardless of whether E is a WHNF or not.
-
-costCentreOk ccs_encl cc_rhs
- = not opt_SccProfilingOn
- || isSubsumedCCS ccs_encl -- can unfold anything into a subsumed scope
- || not (isEmptyCC cc_rhs) -- otherwise need a cc on the unfolding
-\end{code}
+ bale_out = returnSmpl (nilOL, rhs)
+ go fun binds rev_args []
+ = returnSmpl (binds, mkApps (Var fun) (reverse rev_args))
-\begin{code}
----------------------------------------------------------
--- Preparing arguments for a call
+ go fun binds rev_args (arg : args)
+ | exprIsTrivial arg -- Easy case
+ = go fun binds (arg:rev_args) args
-prepareArgs :: SDoc -- Error message info
- -> OutType -> ([Demand],Bool) -> SimplCont
- -> ([OutExpr] -> SimplCont -> SimplM OutExprStuff)
- -> SimplM OutExprStuff
+ | not can_float_arg -- Can't make this arg atomic
+ = bale_out -- ... so give up
-prepareArgs pp_fun orig_fun_ty (fun_demands, result_bot) orig_cont thing_inside
- = go [] demands orig_fun_ty orig_cont
- where
- not_enough_args = fun_demands `lengthExceeds` countValArgs orig_cont
- -- "No strictness info" is signalled by an infinite list of wwLazy
-
- demands | not_enough_args = repeat wwLazy -- Not enough args, or no strictness
- | result_bot = fun_demands -- Enough args, and function returns bottom
- | otherwise = fun_demands ++ repeat wwLazy -- Enough args and function does not return bottom
- -- NB: demands is finite iff enough args and result_bot is True
-
- -- Main game plan: loop through the arguments, simplifying
- -- each of them in turn. We carry with us a list of demands,
- -- and the type of the function-applied-to-earlier-args
-
- -- Type argument
- go acc ds fun_ty (ApplyTo _ arg@(Type ty_arg) se cont)
- = getInScope `thenSmpl` \ in_scope ->
- let
- ty_arg' = substTy (mkSubst in_scope se) ty_arg
- res_ty = applyTy fun_ty ty_arg'
- in
- seqType ty_arg' `seq`
- go (Type ty_arg' : acc) ds res_ty cont
-
- -- Value argument
- go acc (d:ds) fun_ty (ApplyTo _ val_arg se cont)
- = case splitFunTy_maybe fun_ty of {
- Nothing -> pprTrace "prepareArgs" (pp_fun $$ ppr orig_fun_ty $$ ppr orig_cont)
- (thing_inside (reverse acc) cont) ;
- Just (arg_ty, res_ty) ->
- simplArg arg_ty d val_arg se (contResultType cont) $ \ arg' ->
- go (arg':acc) ds res_ty cont }
-
- -- We've run out of demands, which only happens for functions
- -- we *know* now return bottom
- -- This deals with
- -- * case (error "hello") of { ... }
- -- * (error "Hello") arg
- -- * f (error "Hello") where f is strict
- -- etc
- go acc [] fun_ty cont = tick_case_of_error cont `thenSmpl_`
- thing_inside (reverse acc) (discardCont cont)
-
- -- We're run out of arguments
- go acc ds fun_ty cont = thing_inside (reverse acc) cont
-
--- Boring: we must only record a tick if there was an interesting
--- continuation to discard. If not, we tick forever.
-tick_case_of_error (Stop _) = returnSmpl ()
-tick_case_of_error (CoerceIt _ (Stop _)) = returnSmpl ()
-tick_case_of_error other = tick BottomFound
-\end{code}
-
-%************************************************************************
-%* *
-\subsection{Decisions about inlining}
-%* *
-%************************************************************************
+ | otherwise -- Don't forget to do it recursively
+ -- E.g. x = a:b:c:[]
+ = mkAtomicArgs is_strict ok_float_unlifted arg `thenSmpl` \ (arg_binds, arg') ->
+ newId FSLIT("a") arg_ty `thenSmpl` \ arg_id ->
+ go fun ((arg_binds `snocOL` (arg_id,arg')) `appOL` binds)
+ (Var arg_id : rev_args) args
+ where
+ arg_ty = exprType arg
+ can_float_arg = is_strict
+ || not (isUnLiftedType arg_ty)
+ || (ok_float_unlifted && exprOkForSpeculation arg)
+
+
+addAtomicBinds :: SimplEnv -> [(OutId,OutExpr)]
+ -> (SimplEnv -> SimplM (FloatsWith a))
+ -> SimplM (FloatsWith a)
+addAtomicBinds env [] thing_inside = thing_inside env
+addAtomicBinds env ((v,r):bs) thing_inside = addAuxiliaryBind env (NonRec v r) $ \ env ->
+ addAtomicBinds env bs thing_inside
+
+addAtomicBindsE :: SimplEnv -> [(OutId,OutExpr)]
+ -> (SimplEnv -> SimplM FloatsWithExpr)
+ -> SimplM FloatsWithExpr
+-- Same again, but this time we're in an expression context,
+-- and may need to do some case bindings
+
+addAtomicBindsE env [] thing_inside
+ = thing_inside env
+addAtomicBindsE env ((v,r):bs) thing_inside
+ | needsCaseBinding (idType v) r
+ = addAtomicBindsE (addNewInScopeIds env [v]) bs thing_inside `thenSmpl` \ (floats, expr) ->
+ WARN( exprIsTrivial expr, ppr v <+> pprCoreExpr expr )
+ (let body = wrapFloats floats expr in
+ returnSmpl (emptyFloats env, Case r v (exprType body) [(DEFAULT,[],body)]))
-\begin{code}
-preInlineUnconditionally :: InId -> Bool
- -- Examines a bndr to see if it is used just once in a
- -- completely safe way, so that it is safe to discard the binding
- -- inline its RHS at the (unique) usage site, REGARDLESS of how
- -- big the RHS might be. If this is the case we don't simplify
- -- the RHS first, but just inline it un-simplified.
- --
- -- This is much better than first simplifying a perhaps-huge RHS
- -- and then inlining and re-simplifying it.
- --
- -- NB: we don't even look at the RHS to see if it's trivial
- -- We might have
- -- x = y
- -- where x is used many times, but this is the unique occurrence
- -- of y. We should NOT inline x at all its uses, because then
- -- we'd do the same for y -- aargh! So we must base this
- -- pre-rhs-simplification decision solely on x's occurrences, not
- -- on its rhs.
- --
- -- Evne RHSs labelled InlineMe aren't caught here, because
- -- there might be no benefit from inlining at the call site.
- -- But things labelled 'IMustBeINLINEd' *are* caught. We use this
- -- for the trivial bindings introduced by SimplUtils.mkRhsTyLam
-preInlineUnconditionally bndr
- = case getInlinePragma bndr of
- IMustBeINLINEd -> True
- ICanSafelyBeINLINEd NotInsideLam True -> True -- Not inside a lambda,
- -- one occurrence ==> safe!
- other -> False
-
-
-postInlineUnconditionally :: InId -> OutExpr -> Bool
- -- Examines a (bndr = rhs) binding, AFTER the rhs has been simplified
- -- It returns True if it's ok to discard the binding and inline the
- -- RHS at every use site.
-
- -- NOTE: This isn't our last opportunity to inline.
- -- We're at the binding site right now, and
- -- we'll get another opportunity when we get to the ocurrence(s)
-
-postInlineUnconditionally bndr rhs
- | isExportedId bndr
- = False
| otherwise
- = case getInlinePragma bndr of
- IAmALoopBreaker -> False
-
- ICanSafelyBeINLINEd InsideLam one_branch -> exprIsTrivial rhs
- -- Don't inline even WHNFs inside lambdas; doing so may
- -- simply increase allocation when the function is called
- -- This isn't the last chance; see NOTE above.
-
- ICanSafelyBeINLINEd not_in_lam one_branch -> one_branch || exprIsTrivial rhs
- -- Was 'exprIsDupable' instead of 'exprIsTrivial' but the
- -- decision about duplicating code is best left to callSiteInline
-
- other -> exprIsTrivial rhs -- Duplicating is *free*
- -- NB: Even InlineMe and IMustBeINLINEd are ignored here
- -- Why? Because we don't even want to inline them into the
- -- RHS of constructor arguments. See NOTE above
- -- NB: Even IMustBeINLINEd is ignored here: if the rhs is trivial
- -- it's best to inline it anyway. We often get a=E; b=a
- -- from desugaring, with both a and b marked NOINLINE.
+ = addAuxiliaryBind env (NonRec v r) $ \ env ->
+ addAtomicBindsE env bs thing_inside
\end{code}
-
%************************************************************************
%* *
\subsection{The main rebuilder}
%************************************************************************
\begin{code}
--------------------------------------------------------------------
--- Finish rebuilding
-rebuild_done expr
- = getInScope `thenSmpl` \ in_scope ->
- returnSmpl ([], (in_scope, expr))
+rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr
----------------------------------------------------------
-rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff
-
--- Stop continuation
-rebuild expr (Stop _) = rebuild_done expr
-
--- ArgOf continuation
-rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr
-
--- ApplyTo continuation
-rebuild expr cont@(ApplyTo _ arg se cont')
- = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
- rebuild (App expr arg') cont'
-
--- Coerce continuation
-rebuild expr (CoerceIt to_ty cont)
- = rebuild (mkCoerce to_ty expr) cont
-
--- Inline continuation
-rebuild expr (InlinePlease cont)
- = rebuild (Note InlineCall expr) cont
+rebuild env expr (Stop _ _ _) = rebuildDone env expr
+rebuild env expr (ArgOf _ _ _ cont_fn) = cont_fn env expr
+rebuild env expr (CoerceIt to_ty cont) = rebuild env (mkCoerce to_ty expr) cont
+rebuild env expr (InlinePlease cont) = rebuild env (Note InlineCall expr) cont
+rebuild env expr (Select _ bndr alts se cont) = rebuildCase (setInScope se env) expr bndr alts cont
+rebuild env expr (ApplyTo _ arg se cont) = rebuildApp (setInScope se env) expr arg cont
--- Case of known constructor or literal
-rebuild expr@(Con con args) (Select _ bndr alts se cont)
- | conOkForAlt con -- Knocks out PrimOps and NoRepLits
- = knownCon expr con args bndr alts se cont
-
-
----------------------------------------------------------
--- The other Select cases
-
-rebuild scrut (Select _ bndr alts se cont)
- | -- Check that the RHSs are all the same, and
- -- don't use the binders in the alternatives
- -- This test succeeds rapidly in the common case of
- -- a single DEFAULT alternative
- all (cheapEqExpr rhs1) other_rhss && all binders_unused alts
-
- -- Check that the scrutinee can be let-bound instead of case-bound
- && ( exprOkForSpeculation scrut
- -- OK not to evaluate it
- -- This includes things like (==# a# b#)::Bool
- -- so that we simplify
- -- case ==# a# b# of { True -> x; False -> x }
- -- to just
- -- x
- -- This particular example shows up in default methods for
- -- comparision operations (e.g. in (>=) for Int.Int32)
- || exprIsValue scrut -- It's already evaluated
- || var_demanded_later scrut -- It'll be demanded later
-
--- || not opt_SimplPedanticBottoms) -- Or we don't care!
--- We used to allow improving termination by discarding cases, unless -fpedantic-bottoms was on,
--- but that breaks badly for the dataToTag# primop, which relies on a case to evaluate
--- its argument: case x of { y -> dataToTag# y }
--- Here we must *not* discard the case, because dataToTag# just fetches the tag from
--- the info pointer. So we'll be pedantic all the time, and see if that gives any
--- other problems
- )
-
--- && opt_SimplDoCaseElim
--- [June 99; don't test this flag. The code generator dies if it sees
--- case (\x.e) of f -> ...
--- so better to always do it
-
- -- Get rid of the case altogether
- -- See the extensive notes on case-elimination below
- -- Remember to bind the binder though!
- = tick (CaseElim bndr) `thenSmpl_` (
- setSubstEnv se $
- simplBinder bndr $ \ bndr' ->
- completeBinding bndr bndr' False scrut $
- simplExprF rhs1 cont)
-
- | otherwise
- = rebuild_case scrut bndr alts se cont
- where
- (rhs1:other_rhss) = [rhs | (_,_,rhs) <- alts]
- binders_unused (_, bndrs, _) = all isDeadBinder bndrs
+rebuildApp env fun arg cont
+ = simplExpr env arg `thenSmpl` \ arg' ->
+ rebuild env (App fun arg') cont
- var_demanded_later (Var v) = isStrict (getIdDemandInfo bndr) -- It's going to be evaluated later
- var_demanded_later other = False
+rebuildDone env expr = returnSmpl (emptyFloats env, expr)
\end{code}
-Case elimination [see the code above]
-~~~~~~~~~~~~~~~~
-Start with a simple situation:
-
- case x# of ===> e[x#/y#]
- y# -> e
-
-(when x#, y# are of primitive type, of course). We can't (in general)
-do this for algebraic cases, because we might turn bottom into
-non-bottom!
-
-Actually, we generalise this idea to look for a case where we're
-scrutinising a variable, and we know that only the default case can
-match. For example:
-\begin{verbatim}
- case x of
- 0# -> ...
- other -> ...(case x of
- 0# -> ...
- other -> ...) ...
-\end{code}
-Here the inner case can be eliminated. This really only shows up in
-eliminating error-checking code.
-We also make sure that we deal with this very common case:
+%************************************************************************
+%* *
+\subsection{Functions dealing with a case}
+%* *
+%************************************************************************
- case e of
- x -> ...x...
+Blob of helper functions for the "case-of-something-else" situation.
-Here we are using the case as a strict let; if x is used only once
-then we want to inline it. We have to be careful that this doesn't
-make the program terminate when it would have diverged before, so we
-check that
- - x is used strictly, or
- - e is already evaluated (it may so if e is a variable)
+\begin{code}
+---------------------------------------------------------
+-- Eliminate the case if possible
-Lastly, we generalise the transformation to handle this:
+rebuildCase :: SimplEnv
+ -> OutExpr -- Scrutinee
+ -> InId -- Case binder
+ -> [InAlt] -- Alternatives (inceasing order)
+ -> SimplCont
+ -> SimplM FloatsWithExpr
- case e of ===> r
- True -> r
- False -> r
+rebuildCase env scrut case_bndr alts cont
+ | Just (con,args) <- exprIsConApp_maybe scrut
+ -- Works when the scrutinee is a variable with a known unfolding
+ -- as well as when it's an explicit constructor application
+ = knownCon env (DataAlt con) args case_bndr alts cont
-We only do this for very cheaply compared r's (constructors, literals
-and variables). If pedantic bottoms is on, we only do it when the
-scrutinee is a PrimOp which can't fail.
+ | Lit lit <- scrut -- No need for same treatment as constructors
+ -- because literals are inlined more vigorously
+ = knownCon env (LitAlt lit) [] case_bndr alts cont
-We do it *here*, looking at un-simplified alternatives, because we
-have to check that r doesn't mention the variables bound by the
-pattern in each alternative, so the binder-info is rather useful.
+ | otherwise
+ = -- Prepare the alternatives.
+ prepareAlts scrut case_bndr alts `thenSmpl` \ (better_alts, handled_cons) ->
+
+ -- Prepare the continuation;
+ -- The new subst_env is in place
+ prepareCaseCont env better_alts cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ addFloats env floats $ \ env ->
-So the case-elimination algorithm is:
+ let
+ -- The case expression is annotated with the result type of the continuation
+ -- This may differ from the type originally on the case. For example
+ -- case(T) (case(Int#) a of { True -> 1#; False -> 0# }) of
+ -- a# -> <blob>
+ -- ===>
+ -- let j a# = <blob>
+ -- in case(T) a of { True -> j 1#; False -> j 0# }
+ -- Note that the case that scrutinises a now returns a T not an Int#
+ res_ty' = contResultType dup_cont
+ in
- 1. Eliminate alternatives which can't match
+ -- Deal with case binder
+ simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
- 2. Check whether all the remaining alternatives
- (a) do not mention in their rhs any of the variables bound in their pattern
- and (b) have equal rhss
+ -- Deal with the case alternatives
+ simplAlts alt_env handled_cons
+ case_bndr' better_alts dup_cont `thenSmpl` \ alts' ->
- 3. Check we can safely ditch the case:
- * PedanticBottoms is off,
- or * the scrutinee is an already-evaluated variable
- or * the scrutinee is a primop which is ok for speculation
- -- ie we want to preserve divide-by-zero errors, and
- -- calls to error itself!
+ -- Put the case back together
+ mkCase scrut case_bndr' res_ty' alts' `thenSmpl` \ case_expr ->
- or * [Prim cases] the scrutinee is a primitive variable
+ -- Notice that rebuildDone returns the in-scope set from env, not alt_env
+ -- The case binder *not* scope over the whole returned case-expression
+ rebuild env case_expr nondup_cont
+\end{code}
- or * [Alg cases] the scrutinee is a variable and
- either * the rhs is the same variable
- (eg case x of C a b -> x ===> x)
- or * there is only one alternative, the default alternative,
- and the binder is used strictly in its scope.
- [NB this is helped by the "use default binder where
- possible" transformation; see below.]
+simplCaseBinder checks whether the scrutinee is a variable, v. If so,
+try to eliminate uses of v in the RHSs in favour of case_bndr; that
+way, there's a chance that v will now only be used once, and hence
+inlined.
+Note 1
+~~~~~~
+There is a time we *don't* want to do that, namely when
+-fno-case-of-case is on. This happens in the first simplifier pass,
+and enhances full laziness. Here's the bad case:
+ f = \ y -> ...(case x of I# v -> ...(case x of ...) ... )
+If we eliminate the inner case, we trap it inside the I# v -> arm,
+which might prevent some full laziness happening. I've seen this
+in action in spectral/cichelli/Prog.hs:
+ [(m,n) | m <- [1..max], n <- [1..max]]
+Hence the check for NoCaseOfCase.
-If so, then we can replace the case with one of the rhss.
+Note 2
+~~~~~~
+There is another situation when we don't want to do it. If we have
+ case x of w1 { DEFAULT -> case x of w2 { A -> e1; B -> e2 }
+ ...other cases .... }
-Blob of helper functions for the "case-of-something-else" situation.
+We'll perform the binder-swap for the outer case, giving
-\begin{code}
----------------------------------------------------------
--- Case of something else
+ case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 }
+ ...other cases .... }
-rebuild_case scrut case_bndr alts se cont
- = -- Prepare case alternatives
- prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr))
- scrut_cons alts `thenSmpl` \ better_alts ->
-
- -- Set the new subst-env in place (before dealing with the case binder)
- setSubstEnv se $
+But there is no point in doing it for the inner case, because w1 can't
+be inlined anyway. Furthermore, doing the case-swapping involves
+zapping w2's occurrence info (see paragraphs that follow), and that
+forces us to bind w2 when doing case merging. So we get
- -- Deal with the case binder, and prepare the continuation;
- -- The new subst_env is in place
- prepareCaseCont better_alts cont $ \ cont' ->
-
+ case x of w1 { A -> let w2 = w1 in e1
+ B -> let w2 = w1 in e2
+ ...other cases .... }
- -- Deal with variable scrutinee
- ( simplBinder case_bndr $ \ case_bndr' ->
- substForVarScrut scrut case_bndr' $ \ zap_occ_info ->
- let
- case_bndr'' = zap_occ_info case_bndr'
- in
+This is plain silly in the common case where w2 is dead.
- -- Deal with the case alternaatives
- simplAlts zap_occ_info scrut_cons
- case_bndr'' better_alts cont' `thenSmpl` \ alts' ->
+Even so, I can't see a good way to implement this idea. I tried
+not doing the binder-swap if the scrutinee was already evaluated
+but that failed big-time:
- mkCase scrut case_bndr'' alts'
- ) `thenSmpl` \ case_expr ->
+ data T = MkT !Int
- -- Notice that the simplBinder, prepareCaseCont, etc, do *not* scope
- -- over the rebuild_done; rebuild_done returns the in-scope set, and
- -- that should not include these chaps!
- rebuild_done case_expr
- where
- -- scrut_cons tells what constructors the scrutinee can't possibly match
- scrut_cons = case scrut of
- Var v -> otherCons (getIdUnfolding v)
- other -> []
+ case v of w { MkT x ->
+ case x of x1 { I# y1 ->
+ case x of x2 { I# y2 -> ...
+Notice that because MkT is strict, x is marked "evaluated". But to
+eliminate the last case, we must either make sure that x (as well as
+x1) has unfolding MkT y1. THe straightforward thing to do is to do
+the binder-swap. So this whole note is a no-op.
-knownCon expr con args bndr alts se cont
- = tick (KnownBranch bndr) `thenSmpl_`
- setSubstEnv se (
- simplBinder bndr $ \ bndr' ->
- case findAlt con alts of
- (DEFAULT, bs, rhs) -> ASSERT( null bs )
- completeBinding bndr bndr' False expr $
- -- Don't use completeBeta here. The expr might be
- -- an unboxed literal, like 3, or a variable
- -- whose unfolding is an unboxed literal... and
- -- completeBeta will just construct another case
- -- expression!
- simplExprF rhs cont
-
- (Literal lit, bs, rhs) -> ASSERT( null bs )
- extendSubst bndr (DoneEx expr) $
- -- Unconditionally substitute, because expr must
- -- be a variable or a literal. It can't be a
- -- NoRep literal because they don't occur in
- -- case patterns.
- simplExprF rhs cont
-
- (DataCon dc, bs, rhs) -> ASSERT( length bs == length real_args )
- completeBinding bndr bndr' False expr $
- -- See note above
- extendSubstList bs (map mk real_args) $
- simplExprF rhs cont
- where
- real_args = drop (dataConNumInstArgs dc) args
- mk (Type ty) = DoneTy ty
- mk other = DoneEx other
- )
-\end{code}
-
-\begin{code}
-prepareCaseCont :: [InAlt] -> SimplCont
- -> (SimplCont -> SimplM (OutStuff a))
- -> SimplM (OutStuff a)
- -- Polymorphic recursion here!
-
-prepareCaseCont [alt] cont thing_inside = thing_inside cont
-prepareCaseCont alts cont thing_inside = mkDupableCont (coreAltsType alts) cont thing_inside
-\end{code}
-
-substForVarScrut checks whether the scrutinee is a variable, v.
-If so, try to eliminate uses of v in the RHSs in favour of case_bndr;
-that way, there's a chance that v will now only be used once, and hence inlined.
-
-If we do this, then we have to nuke any occurrence info (eg IAmDead)
-in the case binder, because the case-binder now effectively occurs
-whenever v does. AND we have to do the same for the pattern-bound
-variables! Example:
+Note 3
+~~~~~~
+If we replace the scrutinee, v, by tbe case binder, then we have to nuke
+any occurrence info (eg IAmDead) in the case binder, because the
+case-binder now effectively occurs whenever v does. AND we have to do
+the same for the pattern-bound variables! Example:
(case x of { (a,b) -> a }) (case x of { (p,q) -> q })
Here, b and p are dead. But when we move the argment inside the first
case RHS, and eliminate the second case, we get
- case x or { (a,b) -> a b }
+ case x of { (a,b) -> a b }
Urk! b is alive! Reason: the scrutinee was a variable, and case elimination
-happened. Hence the zap_occ_info function returned by substForVarScrut
+happened.
+
+Indeed, this can happen anytime the case binder isn't dead:
+ case <any> of x { (a,b) ->
+ case x of { (p,q) -> p } }
+Here (a,b) both look dead, but come alive after the inner case is eliminated.
+The point is that we bring into the envt a binding
+ let x = (a,b)
+after the outer case, and that makes (a,b) alive. At least we do unless
+the case binder is guaranteed dead.
\begin{code}
-substForVarScrut (Var v) case_bndr' thing_inside
- | isLocallyDefined v -- No point for imported things
- = modifyInScope (v `setIdUnfolding` mkUnfolding (Var case_bndr')
- `setInlinePragma` IMustBeINLINEd) $
+simplCaseBinder env (Var v) case_bndr
+ | not (switchIsOn (getSwitchChecker env) NoCaseOfCase)
+
+-- Failed try [see Note 2 above]
+-- not (isEvaldUnfolding (idUnfolding v))
+
+ = simplBinder env (zap case_bndr) `thenSmpl` \ (env, case_bndr') ->
+ returnSmpl (modifyInScope env v case_bndr', case_bndr')
-- We could extend the substitution instead, but it would be
-- a hack because then the substitution wouldn't be idempotent
- -- any more.
- thing_inside (\ bndr -> bndr `setInlinePragma` NoInlinePragInfo)
+ -- any more (v is an OutId). And this does just as well.
+ where
+ zap b = b `setIdOccInfo` NoOccInfo
-substForVarScrut other_scrut case_bndr' thing_inside
- = thing_inside (\ bndr -> bndr) -- NoOp on bndr
+simplCaseBinder env other_scrut case_bndr
+ = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') ->
+ returnSmpl (env, case_bndr')
\end{code}
-prepareCaseAlts does two things:
-1. Remove impossible alternatives
-
-2. If the DEFAULT alternative can match only one possible constructor,
- then make that constructor explicit.
- e.g.
- case e of x { DEFAULT -> rhs }
- ===>
- case e of x { (a,b) -> rhs }
- where the type is a single constructor type. This gives better code
- when rhs also scrutinises x or e.
\begin{code}
-prepareCaseAlts bndr (Just (tycon, inst_tys)) scrut_cons alts
- | isDataTyCon tycon
- = case (findDefault filtered_alts, missing_cons) of
-
- ((alts_no_deflt, Just rhs), [data_con]) -- Just one missing constructor!
- -> tick (FillInCaseDefault bndr) `thenSmpl_`
- let
- (_,_,ex_tyvars,_,_,_) = dataConSig data_con
- in
- getUniquesSmpl (length ex_tyvars) `thenSmpl` \ tv_uniqs ->
- let
- ex_tyvars' = zipWithEqual "simpl_alt" mk tv_uniqs ex_tyvars
- mk uniq tv = mkSysTyVar uniq (tyVarKind tv)
- in
- newIds (dataConArgTys
- data_con
- (inst_tys ++ mkTyVarTys ex_tyvars')) $ \ bndrs ->
- returnSmpl ((DataCon data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt)
-
- other -> returnSmpl filtered_alts
+simplAlts :: SimplEnv
+ -> [AltCon] -- Alternatives the scrutinee can't be
+ -- in the default case
+ -> OutId -- Case binder
+ -> [InAlt] -> SimplCont
+ -> SimplM [OutAlt] -- Includes the continuation
+
+simplAlts env handled_cons case_bndr' alts cont'
+ = do { mb_alts <- mapSmpl simpl_alt alts
+ ; return [alt' | Just (_, alt') <- mb_alts] }
+ -- Filter out the alternatives that are inaccessible
+ where
+ simpl_alt alt = simplAlt env handled_cons case_bndr' alt cont'
+
+simplAlt :: SimplEnv -> [AltCon] -> OutId -> InAlt -> SimplCont
+ -> SimplM (Maybe (TvSubstEnv, OutAlt))
+-- Simplify an alternative, returning the type refinement for the
+-- alternative, if the alternative does any refinement at all
+-- Nothing => the alternative is inaccessible
+
+simplAlt env handled_cons case_bndr' (DEFAULT, bndrs, rhs) cont'
+ = ASSERT( null bndrs )
+ simplExprC env' rhs cont' `thenSmpl` \ rhs' ->
+ returnSmpl (Just (emptyVarEnv, (DEFAULT, [], rhs')))
where
- -- Filter out alternatives that can't possibly match
- filtered_alts = case scrut_cons of
- [] -> alts
- other -> [alt | alt@(con,_,_) <- alts, not (con `elem` scrut_cons)]
+ env' = mk_rhs_env env case_bndr' (mkOtherCon handled_cons)
+ -- Record the constructors that the case-binder *can't* be.
- missing_cons = [data_con | data_con <- tyConDataCons tycon,
- not (data_con `elem` handled_data_cons)]
- handled_data_cons = [data_con | DataCon data_con <- scrut_cons] ++
- [data_con | (DataCon data_con, _, _) <- filtered_alts]
+simplAlt env handled_cons case_bndr' (LitAlt lit, bndrs, rhs) cont'
+ = ASSERT( null bndrs )
+ simplExprC env' rhs cont' `thenSmpl` \ rhs' ->
+ returnSmpl (Just (emptyVarEnv, (LitAlt lit, [], rhs')))
+ where
+ env' = mk_rhs_env env case_bndr' (mkUnfolding False (Lit lit))
+
+simplAlt env handled_cons case_bndr' (DataAlt con, vs, rhs) cont'
+ | isVanillaDataCon con
+ = -- Deal with the pattern-bound variables
+ -- Mark the ones that are in ! positions in the data constructor
+ -- as certainly-evaluated.
+ -- NB: it happens that simplBinders does *not* erase the OtherCon
+ -- form of unfolding, so it's ok to add this info before
+ -- doing simplBinders
+ simplBinders env (add_evals con vs) `thenSmpl` \ (env, vs') ->
+
+ -- Bind the case-binder to (con args)
+ let unf = mkUnfolding False (mkConApp con con_args)
+ inst_tys' = tyConAppArgs (idType case_bndr')
+ con_args = map Type inst_tys' ++ map varToCoreExpr vs'
+ env' = mk_rhs_env env case_bndr' unf
+ in
+ simplExprC env' rhs cont' `thenSmpl` \ rhs' ->
+ returnSmpl (Just (emptyVarEnv, (DataAlt con, vs', rhs')))
--- The default case
-prepareCaseAlts _ _ scrut_cons alts
- = returnSmpl alts -- Functions
+ | otherwise -- GADT case
+ = let
+ (tvs,ids) = span isTyVar vs
+ in
+ simplBinders env tvs `thenSmpl` \ (env1, tvs') ->
+ case coreRefineTys (getInScope env1) con tvs' (idType case_bndr') of {
+ Nothing -- Inaccessible
+ | opt_PprStyle_Debug -- Hack: if debugging is on, generate an error case
+ -- so we can see it
+ -> let rhs' = mkApps (Var eRROR_ID)
+ [Type (substTy env (exprType rhs)),
+ Lit (mkStringLit "Impossible alternative (GADT)")]
+ in
+ simplBinders env1 ids `thenSmpl` \ (env2, ids') ->
+ returnSmpl (Just (emptyVarEnv, (DataAlt con, tvs' ++ ids', rhs')))
+
+ | otherwise -- Filter out the inaccessible branch
+ -> return Nothing ;
+
+ Just refine@(tv_subst_env, _) -> -- The normal case
+ let
+ env2 = refineSimplEnv env1 refine
+ -- Simplify the Ids in the refined environment, so their types
+ -- reflect the refinement. Usually this doesn't matter, but it helps
+ -- in mkDupableAlt, when we want to float a lambda that uses these binders
+ -- Furthermore, it means the binders contain maximal type information
+ in
+ simplBinders env2 (add_evals con ids) `thenSmpl` \ (env3, ids') ->
+ let unf = mkUnfolding False con_app
+ con_app = mkConApp con con_args
+ con_args = map varToCoreExpr vs' -- NB: no inst_tys'
+ env_w_unf = mk_rhs_env env3 case_bndr' unf
+ vs' = tvs' ++ ids'
+ in
+ simplExprC env_w_unf rhs cont' `thenSmpl` \ rhs' ->
+ returnSmpl (Just (tv_subst_env, (DataAlt con, vs', rhs'))) }
-----------------------
-simplAlts zap_occ_info scrut_cons case_bndr'' alts cont'
- = mapSmpl simpl_alt alts
where
- inst_tys' = case splitTyConApp_maybe (idType case_bndr'') of
- Just (tycon, inst_tys) -> inst_tys
-
- -- handled_cons is all the constructors that are dealt
- -- with, either by being impossible, or by there being an alternative
- handled_cons = scrut_cons ++ [con | (con,_,_) <- alts, con /= DEFAULT]
-
- simpl_alt (DEFAULT, _, rhs)
- = -- In the default case we record the constructors that the
- -- case-binder *can't* be.
- -- We take advantage of any OtherCon info in the case scrutinee
- modifyInScope (case_bndr'' `setIdUnfolding` mkOtherCon handled_cons) $
- simplExprC rhs cont' `thenSmpl` \ rhs' ->
- returnSmpl (DEFAULT, [], rhs')
-
- simpl_alt (con, vs, rhs)
- = -- Deal with the pattern-bound variables
- -- Mark the ones that are in ! positions in the data constructor
- -- as certainly-evaluated
- simplBinders (add_evals con vs) $ \ vs' ->
-
- -- Bind the case-binder to (Con args)
- let
- con_app = Con con (map Type inst_tys' ++ map varToCoreExpr vs')
- in
- modifyInScope (case_bndr'' `setIdUnfolding` mkUnfolding con_app) $
- simplExprC rhs cont' `thenSmpl` \ rhs' ->
- returnSmpl (con, vs', rhs')
-
-
-- add_evals records the evaluated-ness of the bound variables of
-- a case pattern. This is *important*. Consider
-- data T = T !Int !Int
--
-- We really must record that b is already evaluated so that we don't
-- go and re-evaluate it when constructing the result.
+ add_evals dc vs = cat_evals dc vs (dataConRepStrictness dc)
- add_evals (DataCon dc) vs = cat_evals vs (dataConRepStrictness dc)
- add_evals other_con vs = vs
-
- cat_evals [] [] = []
- cat_evals (v:vs) (str:strs)
- | isTyVar v = v : cat_evals vs (str:strs)
- | isStrict str = (v' `setIdUnfolding` mkOtherCon []) : cat_evals vs strs
- | otherwise = v' : cat_evals vs strs
+ cat_evals dc vs strs
+ = go vs strs
where
- v' = zap_occ_info v
+ go [] [] = []
+ go (v:vs) strs | isTyVar v = v : go vs strs
+ go (v:vs) (str:strs)
+ | isMarkedStrict str = evald_v : go vs strs
+ | otherwise = zapped_v : go vs strs
+ where
+ zapped_v = zap_occ_info v
+ evald_v = zapped_v `setIdUnfolding` evaldUnfolding
+ go _ _ = pprPanic "cat_evals" (ppr dc $$ ppr vs $$ ppr strs)
+
+ -- If the case binder is alive, then we add the unfolding
+ -- case_bndr = C vs
+ -- to the envt; so vs are now very much alive
+ zap_occ_info | isDeadBinder case_bndr' = \id -> id
+ | otherwise = \id -> id `setIdOccInfo` NoOccInfo
+
+mk_rhs_env env case_bndr' case_bndr_unf
+ = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` case_bndr_unf)
+\end{code}
+
+
+%************************************************************************
+%* *
+\subsection{Known constructor}
+%* *
+%************************************************************************
+
+We are a bit careful with occurrence info. Here's an example
+
+ (\x* -> case x of (a*, b) -> f a) (h v, e)
+
+where the * means "occurs once". This effectively becomes
+ case (h v, e) of (a*, b) -> f a)
+and then
+ let a* = h v; b = e in f a
+and then
+ f (h v)
+
+All this should happen in one sweep.
+
+\begin{code}
+knownCon :: SimplEnv -> AltCon -> [OutExpr]
+ -> InId -> [InAlt] -> SimplCont
+ -> SimplM FloatsWithExpr
+
+knownCon env con args bndr alts cont
+ = tick (KnownBranch bndr) `thenSmpl_`
+ case findAlt con alts of
+ (DEFAULT, bs, rhs) -> ASSERT( null bs )
+ simplNonRecX env bndr scrut $ \ env ->
+ -- This might give rise to a binding with non-atomic args
+ -- like x = Node (f x) (g x)
+ -- but no harm will be done
+ simplExprF env rhs cont
+ where
+ scrut = case con of
+ LitAlt lit -> Lit lit
+ DataAlt dc -> mkConApp dc args
+
+ (LitAlt lit, bs, rhs) -> ASSERT( null bs )
+ simplNonRecX env bndr (Lit lit) $ \ env ->
+ simplExprF env rhs cont
+
+ (DataAlt dc, bs, rhs)
+ -> ASSERT( n_drop_tys + length bs == length args )
+ bind_args env bs (drop n_drop_tys args) $ \ env ->
+ let
+ con_app = mkConApp dc (take n_drop_tys args ++ con_args)
+ con_args = [substExpr env (varToCoreExpr b) | b <- bs]
+ -- args are aready OutExprs, but bs are InIds
+ in
+ simplNonRecX env bndr con_app $ \ env ->
+ simplExprF env rhs cont
+ where
+ n_drop_tys | isVanillaDataCon dc = tyConArity (dataConTyCon dc)
+ | otherwise = 0
+ -- Vanilla data constructors lack type arguments in the pattern
+
+-- Ugh!
+bind_args env [] _ thing_inside = thing_inside env
+
+bind_args env (b:bs) (Type ty : args) thing_inside
+ = ASSERT( isTyVar b )
+ bind_args (extendTvSubst env b ty) bs args thing_inside
+
+bind_args env (b:bs) (arg : args) thing_inside
+ = ASSERT( isId b )
+ simplNonRecX env b arg $ \ env ->
+ bind_args env bs args thing_inside
\end{code}
%************************************************************************
\begin{code}
-mkDupableCont :: InType -- Type of the thing to be given to the continuation
- -> SimplCont
- -> (SimplCont -> SimplM (OutStuff a))
- -> SimplM (OutStuff a)
-mkDupableCont ty cont thing_inside
+prepareCaseCont :: SimplEnv
+ -> [InAlt] -> SimplCont
+ -> SimplM (FloatsWith (SimplCont,SimplCont))
+ -- Return a duplicatable continuation, a non-duplicable part
+ -- plus some extra bindings
+
+ -- No need to make it duplicatable if there's only one alternative
+prepareCaseCont env [alt] cont = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
+prepareCaseCont env alts cont = mkDupableCont env cont
+\end{code}
+
+\begin{code}
+mkDupableCont :: SimplEnv -> SimplCont
+ -> SimplM (FloatsWith (SimplCont, SimplCont))
+
+mkDupableCont env cont
| contIsDupable cont
- = thing_inside cont
-
-mkDupableCont _ (CoerceIt ty cont) thing_inside
- = mkDupableCont ty cont $ \ cont' ->
- thing_inside (CoerceIt ty cont')
-
-mkDupableCont ty (InlinePlease cont) thing_inside
- = mkDupableCont ty cont $ \ cont' ->
- thing_inside (InlinePlease cont')
-
-mkDupableCont join_arg_ty (ArgOf _ cont_ty cont_fn) thing_inside
- = -- Build the RHS of the join point
- simplType join_arg_ty `thenSmpl` \ join_arg_ty' ->
- newId join_arg_ty' ( \ arg_id ->
- getSwitchChecker `thenSmpl` \ chkr ->
- cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) ->
- returnSmpl (Lam (setOneShotLambda arg_id) (mkLets binds rhs))
- ) `thenSmpl` \ join_rhs ->
-
- -- Build the join Id and continuation
- newId (coreExprType join_rhs) $ \ join_id ->
- let
- new_cont = ArgOf OkToDup cont_ty
- (\arg' -> rebuild_done (App (Var join_id) arg'))
- in
-
- -- Do the thing inside
- thing_inside new_cont `thenSmpl` \ res ->
- returnSmpl (addBind (NonRec join_id join_rhs) res)
+ = returnSmpl (emptyFloats env, (cont, mkBoringStop (contResultType cont)))
+
+mkDupableCont env (CoerceIt ty cont)
+ = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ returnSmpl (floats, (CoerceIt ty dup_cont, nondup_cont))
+
+mkDupableCont env (InlinePlease cont)
+ = mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ returnSmpl (floats, (InlinePlease dup_cont, nondup_cont))
+
+mkDupableCont env cont@(ArgOf _ arg_ty _ _)
+ = returnSmpl (emptyFloats env, (mkBoringStop arg_ty, cont))
+ -- Do *not* duplicate an ArgOf continuation
+ -- Because ArgOf continuations are opaque, we gain nothing by
+ -- propagating them into the expressions, and we do lose a lot.
+ -- Here's an example:
+ -- && (case x of { T -> F; F -> T }) E
+ -- Now, && is strict so we end up simplifying the case with
+ -- an ArgOf continuation. If we let-bind it, we get
+ --
+ -- let $j = \v -> && v E
+ -- in simplExpr (case x of { T -> F; F -> T })
+ -- (ArgOf (\r -> $j r)
+ -- And after simplifying more we get
+ --
+ -- let $j = \v -> && v E
+ -- in case of { T -> $j F; F -> $j T }
+ -- Which is a Very Bad Thing
+ --
+ -- The desire not to duplicate is the entire reason that
+ -- mkDupableCont returns a pair of continuations.
+ --
+ -- The original plan had:
+ -- e.g. (...strict-fn...) [...hole...]
+ -- ==>
+ -- let $j = \a -> ...strict-fn...
+ -- in $j [...hole...]
+
+mkDupableCont env (ApplyTo _ arg se cont)
+ = -- e.g. [...hole...] (...arg...)
+ -- ==>
+ -- let a = ...arg...
+ -- in [...hole...] a
+ simplExpr (setInScope se env) arg `thenSmpl` \ arg' ->
+
+ mkDupableCont env cont `thenSmpl` \ (floats, (dup_cont, nondup_cont)) ->
+ addFloats env floats $ \ env ->
-mkDupableCont ty (ApplyTo _ arg se cont) thing_inside
- = mkDupableCont (funResultTy ty) cont $ \ cont' ->
- setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' ->
if exprIsDupable arg' then
- thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont')
+ returnSmpl (emptyFloats env, (ApplyTo OkToDup arg' (zapSubstEnv se) dup_cont, nondup_cont))
else
- newId (coreExprType arg') $ \ bndr ->
- thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') `thenSmpl` \ res ->
- returnSmpl (addBind (NonRec bndr arg') res)
-
-mkDupableCont ty (Select _ case_bndr alts se cont) thing_inside
- = tick (CaseOfCase case_bndr) `thenSmpl_`
- setSubstEnv se (
- simplBinder case_bndr $ \ case_bndr' ->
- prepareCaseCont alts cont $ \ cont' ->
- mapAndUnzipSmpl (mkDupableAlt case_bndr case_bndr' cont') alts `thenSmpl` \ (alt_binds_s, alts') ->
- returnSmpl (concat alt_binds_s, alts')
- ) `thenSmpl` \ (alt_binds, alts') ->
-
- extendInScopes [b | NonRec b _ <- alt_binds] $
-
- -- NB that the new alternatives, alts', are still InAlts, using the original
- -- binders. That means we can keep the case_bndr intact. This is important
- -- because another case-of-case might strike, and so we want to keep the
- -- info that the case_bndr is dead (if it is, which is often the case).
- -- This is VITAL when the type of case_bndr is an unboxed pair (often the
- -- case in I/O rich code. We aren't allowed a lambda bound
- -- arg of unboxed tuple type, and indeed such a case_bndr is always dead
- thing_inside (Select OkToDup case_bndr alts' se (Stop (contResultType cont))) `thenSmpl` \ res ->
-
- returnSmpl (addBinds alt_binds res)
-
-
-mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt)
-mkDupableAlt case_bndr case_bndr' (Stop _) alt@(con, bndrs, rhs)
- | exprIsDupable rhs
- = -- It is worth checking for a small RHS because otherwise we
+ newId FSLIT("a") (exprType arg') `thenSmpl` \ arg_id ->
+
+ tick (CaseOfCase arg_id) `thenSmpl_`
+ -- Want to tick here so that we go round again,
+ -- and maybe copy or inline the code.
+ -- Not strictly CaseOfCase, but never mind
+
+ returnSmpl (unitFloat env arg_id arg',
+ (ApplyTo OkToDup (Var arg_id) (zapSubstEnv se) dup_cont,
+ nondup_cont))
+ -- But what if the arg should be case-bound?
+ -- This has been this way for a long time, so I'll leave it,
+ -- but I can't convince myself that it's right.
+
+mkDupableCont env (Select _ case_bndr alts se cont)
+ = -- e.g. (case [...hole...] of { pi -> ei })
+ -- ===>
+ -- let ji = \xij -> ei
+ -- in case [...hole...] of { pi -> ji xij }
+ tick (CaseOfCase case_bndr) `thenSmpl_`
+ let
+ alt_env = setInScope se env
+ in
+ prepareCaseCont alt_env alts cont `thenSmpl` \ (floats1, (dup_cont, nondup_cont)) ->
+ addFloats alt_env floats1 $ \ alt_env ->
+
+ simplBinder alt_env case_bndr `thenSmpl` \ (alt_env, case_bndr') ->
+ -- NB: simplBinder does not zap deadness occ-info, so
+ -- a dead case_bndr' will still advertise its deadness
+ -- This is really important because in
+ -- case e of b { (# a,b #) -> ... }
+ -- b is always dead, and indeed we are not allowed to bind b to (# a,b #),
+ -- which might happen if e was an explicit unboxed pair and b wasn't marked dead.
+ -- In the new alts we build, we have the new case binder, so it must retain
+ -- its deadness.
+
+ mkDupableAlts alt_env case_bndr' alts dup_cont `thenSmpl` \ (floats2, alts') ->
+ addFloats alt_env floats2 $ \ alt_env ->
+ returnSmpl (emptyFloats alt_env,
+ (Select OkToDup case_bndr' alts' (zapSubstEnv se)
+ (mkBoringStop (contResultType dup_cont)),
+ nondup_cont))
+
+mkDupableAlts :: SimplEnv -> OutId -> [InAlt] -> SimplCont
+ -> SimplM (FloatsWith [InAlt])
+-- Absorbs the continuation into the new alternatives
+
+mkDupableAlts env case_bndr' alts dupable_cont
+ = go env alts
+ where
+ go env [] = returnSmpl (emptyFloats env, [])
+ go env (alt:alts)
+ = do { (floats1, mb_alt') <- mkDupableAlt env case_bndr' dupable_cont alt
+ ; addFloats env floats1 $ \ env -> do
+ { (floats2, alts') <- go env alts
+ ; returnSmpl (floats2, case mb_alt' of
+ Just alt' -> alt' : alts'
+ Nothing -> alts'
+ )}}
+
+mkDupableAlt env case_bndr' cont alt
+ = simplAlt env [] case_bndr' alt cont `thenSmpl` \ mb_stuff ->
+ case mb_stuff of {
+ Nothing -> returnSmpl (emptyFloats env, Nothing) ;
+
+ Just (reft, (con, bndrs', rhs')) ->
+ -- Safe to say that there are no handled-cons for the DEFAULT case
+
+ if exprIsDupable rhs' then
+ returnSmpl (emptyFloats env, Just (con, bndrs', rhs'))
+ -- It is worth checking for a small RHS because otherwise we
-- get extra let bindings that may cause an extra iteration of the simplifier to
-- inline back in place. Quite often the rhs is just a variable or constructor.
-- The Ord instance of Maybe in PrelMaybe.lhs, for example, took several extra
-- inlined, but after the join points had been inlined it looked smaller, and so
-- was inlined.
--
- -- But since the continuation is absorbed into the rhs, we only do this
- -- for a Stop continuation.
- returnSmpl ([], alt)
+ -- NB: we have to check the size of rhs', not rhs.
+ -- Duplicating a small InAlt might invalidate occurrence information
+ -- However, if it *is* dupable, we return the *un* simplified alternative,
+ -- because otherwise we'd need to pair it up with an empty subst-env....
+ -- but we only have one env shared between all the alts.
+ -- (Remember we must zap the subst-env before re-simplifying something).
+ -- Rather than do this we simply agree to re-simplify the original (small) thing later.
-mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs)
- | otherwise
- = -- Not worth checking whether the rhs is small; the
- -- inliner will inline it if so.
- simplBinders bndrs $ \ bndrs' ->
- simplExprC rhs cont `thenSmpl` \ rhs' ->
+ else
let
- rhs_ty' = coreExprType rhs'
- (used_bndrs, used_bndrs')
- = unzip [pr | pr@(bndr,bndr') <- zip (case_bndr : bndrs)
- (case_bndr' : bndrs'),
- not (isDeadBinder bndr)]
- -- The new binders have lost their occurrence info,
- -- so we have to extract it from the old ones
+ rhs_ty' = exprType rhs'
+ used_bndrs' = filter abstract_over (case_bndr' : bndrs')
+ abstract_over bndr
+ | isTyVar bndr = not (bndr `elemVarEnv` reft)
+ -- Don't abstract over tyvar binders which are refined away
+ -- See Note [Refinement] below
+ | otherwise = not (isDeadBinder bndr)
+ -- The deadness info on the new Ids is preserved by simplBinders
in
- ( if null used_bndrs'
-- If we try to lift a primitive-typed something out
-- for let-binding-purposes, we will *caseify* it (!),
-- with potentially-disastrous strictness results. So
-- Consider: let j = if .. then I# 3 else I# 4
-- in case .. of { A -> j; B -> j; C -> ... }
--
- -- Now CPR should not w/w j because it's a thunk, so
+ -- Now CPR doesn't w/w j because it's a thunk, so
-- that means that the enclosing function can't w/w either,
-- which is a lose. Here's the example that happened in practice:
-- kgmod :: Int -> Int -> Int
-- kgmod x y = if x > 0 && y < 0 || x < 0 && y > 0
-- then 78
-- else 5
-
- then newId realWorldStatePrimTy $ \ rw_id ->
+ --
+ -- I have seen a case alternative like this:
+ -- True -> \v -> ...
+ -- It's a bit silly to add the realWorld dummy arg in this case, making
+ -- $j = \s v -> ...
+ -- True -> $j s
+ -- (the \v alone is enough to make CPR happy) but I think it's rare
+
+ ( if not (any isId used_bndrs')
+ then newId FSLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id ->
returnSmpl ([rw_id], [Var realWorldPrimId])
else
- returnSmpl (used_bndrs', map varToCoreExpr used_bndrs)
- )
- `thenSmpl` \ (final_bndrs', final_args) ->
-
- newId (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr ->
-
- -- Notice that we make the lambdas into one-shot-lambdas. The
+ returnSmpl (used_bndrs', map varToCoreExpr used_bndrs')
+ ) `thenSmpl` \ (final_bndrs', final_args) ->
+
+ -- See comment about "$j" name above
+ newId FSLIT("$j") (mkPiTypes final_bndrs' rhs_ty') `thenSmpl` \ join_bndr ->
+ -- Notice the funky mkPiTypes. If the contructor has existentials
+ -- it's possible that the join point will be abstracted over
+ -- type varaibles as well as term variables.
+ -- Example: Suppose we have
+ -- data T = forall t. C [t]
+ -- Then faced with
+ -- case (case e of ...) of
+ -- C t xs::[t] -> rhs
+ -- We get the join point
+ -- let j :: forall t. [t] -> ...
+ -- j = /\t \xs::[t] -> rhs
+ -- in
+ -- case (case e of ...) of
+ -- C t xs::[t] -> j t xs
+ let
+ -- We make the lambdas into one-shot-lambdas. The
-- join point is sure to be applied at most once, and doing so
-- prevents the body of the join point being floated out by
-- the full laziness pass
- returnSmpl ([NonRec join_bndr (mkLams (map setOneShotLambda final_bndrs') rhs')],
- (con, bndrs, mkApps (Var join_bndr) final_args))
+ really_final_bndrs = map one_shot final_bndrs'
+ one_shot v | isId v = setOneShotLambda v
+ | otherwise = v
+ join_rhs = mkLams really_final_bndrs rhs'
+ join_call = mkApps (Var join_bndr) final_args
+ in
+ returnSmpl (unitFloat env join_bndr join_rhs, Just (con, bndrs', join_call)) }
\end{code}
+
+Note [Refinement]
+~~~~~~~~~~~~~~~~~
+Consider
+ data T a where
+ MkT :: a -> b -> T a
+
+ f = /\a. \(w::a).
+ case (case ...) of
+ MkT a' b (p::a') (q::b) -> [p,w]
+
+The danger is that we'll make a join point
+
+ j a' p = [p,w]
+
+and that's ill-typed, because (p::a') but (w::a).
+
+Solution so far: don't abstract over a', because the type refinement
+maps [a' -> a] . Ultimately that won't work when real refinement goes on.
+
+Then we must abstract over any refined free variables. Hmm. Maybe we
+could just abstract over *all* free variables, thereby lambda-lifting
+the join point? We should try this.
projects / ghc-hetmet.git / blobdiff