X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=ghc%2Fcompiler%2FsimplCore%2FSimplify.lhs;h=2bc7b8ba80fde18fc1b093e28bd91b83e707592a;hb=6858f7c15fcf9efe9e6fdf22de34d0791b0f0c08;hp=9dd953bac2beb6a9ccf1d37cbf65bb279e4afd17;hpb=9aa6d18bd696e8861fb8c3e065e49a989d2d67ac;p=ghc-hetmet.git diff --git a/ghc/compiler/simplCore/Simplify.lhs b/ghc/compiler/simplCore/Simplify.lhs index 9dd953b..2bc7b8b 100644 --- a/ghc/compiler/simplCore/Simplify.lhs +++ b/ghc/compiler/simplCore/Simplify.lhs @@ -8,65 +8,63 @@ module Simplify ( simplTopBinds, simplExpr ) where #include "HsVersions.h" -import CmdLineOpts ( switchIsOn, opt_SimplDoEtaReduction, - opt_SimplNoPreInlining, +import CmdLineOpts ( dopt, DynFlag(Opt_D_dump_inlinings), SimplifierSwitch(..) ) import SimplMonad -import SimplUtils ( mkCase, transformRhs, findAlt, - simplBinder, simplBinders, simplIds, findDefault, - SimplCont(..), DupFlag(..), mkStop, mkRhsStop, - contResultType, discardInline, countArgs, contIsDupable, +import SimplUtils ( mkCase, mkLam, newId, + simplBinder, simplLamBinders, simplBinders, simplRecIds, simplLetId, + SimplCont(..), DupFlag(..), LetRhsFlag(..), + mkStop, mkBoringStop, + contResultType, discardInline, countArgs, contIsDupable, contIsRhsOrArg, getContArgs, interestingCallContext, interestingArg, isStrictType ) -import Var ( mkSysTyVar, tyVarKind ) +import Var ( mustHaveLocalBinding ) import VarEnv -import VarSet ( elemVarSet ) -import Id ( Id, idType, idInfo, isDataConId, - idUnfolding, setIdUnfolding, isExportedId, isDeadBinder, - idDemandInfo, setIdInfo, - idOccInfo, setIdOccInfo, +import Id ( Id, idType, idInfo, idArity, isDataConId, + idUnfolding, setIdUnfolding, isDeadBinder, + idNewDemandInfo, setIdInfo, + setIdOccInfo, zapLamIdInfo, setOneShotLambda, ) -import IdInfo ( OccInfo(..), isDeadOcc, isLoopBreaker, - ArityInfo, setArityInfo, unknownArity, - setUnfoldingInfo, +import IdInfo ( OccInfo(..), isLoopBreaker, + setArityInfo, + setUnfoldingInfo, occInfo ) -import Demand ( Demand, isStrict ) -import DataCon ( dataConNumInstArgs, dataConRepStrictness, - dataConSig, dataConArgTys - ) +import NewDemand ( isStrictDmd ) +import DataCon ( dataConNumInstArgs, dataConRepStrictness ) import CoreSyn -import CoreFVs ( mustHaveLocalBinding, exprFreeVars ) -import CoreUnfold ( mkOtherCon, mkUnfolding, otherCons, - callSiteInline - ) -import CoreUtils ( cheapEqExpr, exprIsDupable, exprIsTrivial, exprIsConApp_maybe, - exprType, coreAltsType, exprIsValue, idAppIsCheap, - exprOkForSpeculation, etaReduceExpr, +import PprCore ( pprParendExpr, pprCoreExpr ) +import CoreUnfold ( mkOtherCon, mkUnfolding, otherCons, callSiteInline ) +import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding, + exprIsConApp_maybe, mkPiType, findAlt, findDefault, + exprType, coreAltsType, exprIsValue, + exprOkForSpeculation, exprArity, mkCoerce, mkSCC, mkInlineMe, mkAltExpr ) import Rules ( lookupRule ) +import BasicTypes ( isMarkedStrict ) import CostCentre ( currentCCS ) -import Type ( mkTyVarTys, isUnLiftedType, seqType, - mkFunTy, splitFunTy, splitTyConApp_maybe, - funResultTy +import Type ( isUnLiftedType, seqType, mkFunTy, tyConAppArgs, + funResultTy, splitFunTy_maybe, splitFunTy, eqType ) import Subst ( mkSubst, substTy, substExpr, - isInScope, lookupIdSubst, substIdInfo + isInScope, lookupIdSubst, simplIdInfo ) -import TyCon ( isDataTyCon, tyConDataConsIfAvailable ) import TysPrim ( realWorldStatePrimTy ) import PrelInfo ( realWorldPrimId ) -import Maybes ( maybeToBool ) -import Util ( zipWithEqual ) +import BasicTypes ( TopLevelFlag(..), isTopLevel, isNotTopLevel, + RecFlag(..), isNonRec + ) +import OrdList +import Maybe ( Maybe ) import Outputable \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. ----------------------------------------- @@ -77,6 +75,145 @@ 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. %************************************************************************ @@ -86,43 +223,360 @@ documented with simplifyArgs. %************************************************************************ \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. - simplIds (bindersOfBinds binds) $ \ bndrs' -> - simpl_binds binds bndrs' `thenSmpl` \ (binds', _) -> - freeTick SimplifierDone `thenSmpl_` - returnSmpl binds' + simplRecIds env (bindersOfBinds binds) `thenSmpl` \ (env, bndrs') -> + simpl_binds env binds bndrs' `thenSmpl` \ (floats, _) -> + freeTick SimplifierDone `thenSmpl_` + returnSmpl (floatBinds floats) where - -- We need to track the zapped top-level binders, because -- they should have their fragile IdInfo zapped (notably occurrence info) - simpl_binds [] bs = ASSERT( null bs ) returnSmpl ([], panic "simplTopBinds corner") - simpl_binds (NonRec bndr rhs : binds) (b:bs) = simplLazyBind True bndr b rhs (simpl_binds binds bs) - simpl_binds (Rec pairs : binds) bs = simplRecBind True pairs (take n bs) (simpl_binds binds (drop n bs)) - where - n = length pairs - -simplRecBind :: Bool -> [(InId, InExpr)] -> [OutId] - -> SimplM (OutStuff a) -> SimplM (OutStuff a) -simplRecBind top_lvl pairs bndrs' thing_inside - = go pairs bndrs' `thenSmpl` \ (binds', (binds'', res)) -> - returnSmpl (Rec (flattenBinds binds') : binds'', res) + -- 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 (NonRec b r) (b':_) = simplRecOrTopPair env TopLevel b b' r + simpl_bind 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 + +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 + +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 + | preInlineUnconditionally env NotTopLevel bndr + = tick (PreInlineUnconditionally bndr) `thenSmpl_` + thing_inside (extendSubst env bndr (ContEx (getSubstEnv rhs_se) rhs)) + + + | isStrictDmd (idNewDemandInfo bndr) || isStrictType (idType bndr) -- A strict let + = -- Don't use simplBinder because that doesn't keep + -- fragile occurrence in the substitution + simplLetId env bndr `thenSmpl` \ (env, bndr') -> + simplStrictArg env AnRhs rhs rhs_se cont_ty $ \ env rhs1 -> + + -- Make the arguments atomic if necessary, + -- adding suitable bindings + mkAtomicArgs True True rhs1 `thenSmpl` \ (aux_binds, rhs2) -> + addAtomicBindsE env aux_binds $ \ env -> + + -- Now complete the binding and simplify the body + completeNonRecX env bndr bndr' rhs2 thing_inside + + | otherwise -- Normal, lazy case + = -- Don't use simplBinder because that doesn't keep + -- fragile occurrence in the substitution + simplLetId env bndr `thenSmpl` \ (env, bndr') -> + simplLazyBind env NotTopLevel NonRecursive + bndr bndr' rhs rhs_se `thenSmpl` \ (floats, env) -> + addFloats env floats thing_inside +\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 + | preInlineUnconditionally env NotTopLevel 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 ... + -- + -- 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 (extendSubst env bndr (ContEx emptySubstEnv new_rhs)) + + | otherwise + = simplBinder env bndr `thenSmpl` \ (env, bndr') -> + completeNonRecX env bndr bndr' new_rhs thing_inside + +completeNonRecX env old_bndr new_bndr new_rhs thing_inside + | needsCaseBinding (idType new_bndr) new_rhs + = thing_inside env `thenSmpl` \ (floats, body) -> + returnSmpl (emptyFloats env, Case new_rhs new_bndr [(DEFAULT, [], wrapFloats floats body)]) + + | otherwise + = completeLazyBind env NotTopLevel + old_bndr new_bndr new_rhs `thenSmpl` \ (floats, env) -> + addFloats env floats thing_inside +\end{code} + + +%************************************************************************ +%* * +\subsection{Lazy bindings} +%* * +%************************************************************************ + +simplRecBind is used for + * recursive bindings only + +\begin{code} +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 [] _ = thing_inside `thenSmpl` \ stuff -> - returnSmpl ([], stuff) + go env [] _ = returnSmpl (emptyFloats env, env) - 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 + 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} + + +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 -- Check for unconditional inline + = tick (PreInlineUnconditionally bndr) `thenSmpl_` + returnSmpl (emptyFloats env, extendSubst env bndr (ContEx (getSubstEnv 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 bndr' rhs rhs_se + = -- Substitute IdInfo on binder, in the light of earlier + -- substitutions in this very letrec, and extend the + -- in-scope env, so that the IdInfo for this binder extends + -- over the RHS for the binder itself. + -- + -- 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: does no harm for non-recursive bindings + let + bndr_ty' = idType bndr' + bndr'' = simplIdInfo (getSubst rhs_se) (idInfo bndr) bndr' + env1 = modifyInScope env bndr'' bndr'' + rhs_env = setInScope rhs_se env1 + ok_float_unlifted = isNotTopLevel top_lvl && isNonRec is_rec + rhs_cont = mkStop bndr_ty' AnRhs + in + -- Simplify the RHS; note the mkStop, 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 bndr'' + (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 && null aux_binds then -- Shortcut a common case + completeLazyBind env1 top_lvl bndr bndr'' rhs2 + + -- 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. + -- exprIsValue definitely isn't right for that. + -- + -- BUT we can't use "exprIsCheap", 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 exprIsValue for the test, which ensures that the + -- thing is non-strict. I think. The WARN below tests for this + else if exprIsTrivial rhs2 || exprIsValue rhs2 then + -- 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 (floatBinds floats), + ppr (filter demanded_float (floatBinds floats)) ) + + tick LetFloatFromLet `thenSmpl_` ( + addFloats env1 floats $ \ env2 -> + addAtomicBinds env2 aux_binds $ \ env3 -> + completeLazyBind env3 top_lvl bndr bndr'' rhs2) + + else + completeLazyBind env1 top_lvl bndr bndr'' (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 new_bndr loop_breaker new_rhs + = -- Drop the binding + tick (PostInlineUnconditionally old_bndr) `thenSmpl_` + returnSmpl (emptyFloats env, extendSubst 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 + info_w_unf | loop_breaker = new_bndr_info + | otherwise = new_bndr_info `setUnfoldingInfo` unfolding + unfolding = mkUnfolding (isTopLevel top_lvl) new_rhs + + final_id = new_bndr `setIdInfo` info_w_unf + 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 + loop_breaker = isLoopBreaker occ_info + old_info = idInfo old_bndr + occ_info = occInfo old_info +\end{code} + + + %************************************************************************ %* * \subsection[Simplify-simplExpr]{The main function: simplExpr} @@ -168,195 +622,114 @@ might do the same again. \begin{code} -simplExpr :: CoreExpr -> SimplM CoreExpr -simplExpr expr = getSubst `thenSmpl` \ subst -> - simplExprC expr (mkStop (substTy subst (exprType 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 (getSubst 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 (Lit lit) (Select _ bndr alts se cont) - = knownCon (Lit lit) (LitAlt lit) [] bndr alts se 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 (Lit lit) cont - = rebuild (Lit lit) cont +simplExprF env (Type ty) cont + = ASSERT( contIsRhsOrArg cont ) + simplType env ty `thenSmpl` \ ty' -> + rebuild env (Type ty') cont -simplExprF (App fun arg) cont - = getSubstEnv `thenSmpl` \ se -> - simplExprF fun (ApplyTo NoDup arg se cont) +simplExprF env (Case scrut bndr alts) cont + | not (switchIsOn (getSwitchChecker env) NoCaseOfCase) + = -- Simplify the scrutinee with a Select continuation + simplExprF env scrut (Select NoDup bndr alts env cont) -simplExprF (Case scrut bndr alts) cont - = getSubstEnv `thenSmpl` \ subst_env -> - getSwitchChecker `thenSmpl` \ chkr -> - if not (switchIsOn chkr NoCaseOfCase) then - -- Simplify the scrutinee with a Select continuation - simplExprF scrut (Select NoDup bndr alts subst_env cont) - - else - -- If case-of-case is off, simply simplify the case expression + | otherwise + = -- If case-of-case is off, simply simplify the case expression -- in a vanilla Stop context, and rebuild the result around it - simplExprC scrut (Select NoDup bndr alts subst_env - (mkStop (contResultType cont))) `thenSmpl` \ case_expr' -> - rebuild case_expr' cont - + simplExprC env scrut case_cont `thenSmpl` \ case_expr' -> + rebuild env case_expr' cont + where + case_cont = Select NoDup bndr alts env (mkBoringStop (contResultType cont)) -simplExprF (Let (Rec pairs) body) cont - = simplIds (map fst pairs) $ \ bndrs' -> +simplExprF env (Let (Rec pairs) body) cont + = simplRecIds env (map fst pairs) `thenSmpl` \ (env, bndrs') -> -- NB: bndrs' don't have unfoldings or spec-envs -- We add them as we go down, using simplPrags - simplRecBind False 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 + simplRecBind env NotTopLevel pairs bndrs' `thenSmpl` \ (floats, env) -> + addFloats env floats $ \ env -> + simplExprF env body cont --- Comments about the Coerce case --- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ --- It's worth checking for a coerce in the continuation, --- in case we can cancel them. 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 +-- 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 -simplExprF (Note (Coerce to from) e) (CoerceIt outer_to cont) - = simplType from `thenSmpl` \ from' -> - if outer_to == from' then - -- The coerces cancel out - simplExprF e cont - else - -- They don't cancel, but the inner one is redundant - simplExprF e (CoerceIt outer_to cont) - -simplExprF (Note (Coerce to from) e) cont - = 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 (mkSCC 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 - setBlackList noInlineBlackList (simplExpr e) `thenSmpl` \ e' -> - rebuild (mkInlineMe 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 +--------------------------------- +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 (getSubst 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 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_` - simplTyArg ty_arg arg_se `thenSmpl` \ ty_arg' -> - extendSubst bndr (DoneTy ty_arg') - (go body body_cont) + tick (BetaReduction bndr) `thenSmpl_` + simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' -> + go (extendSubst env bndr (DoneTy 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 zapped_bndr arg arg_se cont_ty $ \ env -> + go env body body_cont where zapped_bndr = zap_it bndr - -- Not enough args - go lam@(Lam _ _) cont = completeLam [] lam cont + -- Not enough args, so there are real lambdas left to put in the result + go env lam@(Lam _ _) cont + = simplLamBinders 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 + (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, so there are real lambdas left to put in the result - --- We try for eta reduction here, but *only* if we get all the --- way to an exprIsTrivial expression. --- We don't want to remove extra lambdas unless we are going --- to avoid allocating this thing altogether - -completeLam rev_bndrs (Lam bndr body) cont - = simplBinder bndr $ \ bndr' -> - completeLam (bndr':rev_bndrs) body cont - -completeLam rev_bndrs body cont - = simplExpr body `thenSmpl` \ body' -> - case try_eta body' of - Just etad_lam -> tick (EtaReduction (head rev_bndrs)) `thenSmpl_` - rebuild etad_lam cont - - Nothing -> rebuild (foldl (flip Lam) body' rev_bndrs) cont - where - -- We don't use CoreUtils.etaReduceExpr, because we can be more - -- efficient here: (a) we already have the binders, (b) we can do - -- the triviality test before computing the free vars - try_eta body | not opt_SimplDoEtaReduction = Nothing - | otherwise = go rev_bndrs body - - go (b : bs) (App fun arg) | ok_arg b arg = go bs fun -- Loop round - go [] body | ok_body body = Just body -- Success! - go _ _ = Nothing -- Failure! - - ok_body body = exprIsTrivial body && not (any (`elemVarSet` exprFreeVars body) rev_bndrs) - ok_arg b arg = varToCoreExpr b `cheapEqExpr` arg + go env expr cont = simplExprF env expr cont mkLamBndrZapper :: CoreExpr -- Function -> SimplCont -- The context @@ -375,387 +748,94 @@ mkLamBndrZapper fun cont \end{code} ---------------------------------- -\begin{code} -simplType :: InType -> SimplM OutType -simplType ty - = getSubst `thenSmpl` \ subst -> - let - new_ty = substTy subst ty - in - seqType new_ty `seq` - returnSmpl new_ty -\end{code} - - -%************************************************************************ -%* * -\subsection{Binding} -%* * -%************************************************************************ - -@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 False {- not black listed -} bndr - = tick (PreInlineUnconditionally bndr) `thenSmpl_` - extendSubst bndr (ContEx rhs_se rhs) thing_inside - - | otherwise - = -- Simplify the RHS - simplBinder bndr $ \ bndr' -> - let - bndr_ty' = idType bndr' - is_strict = isStrict (idDemandInfo bndr) || isStrictType bndr_ty' - in - simplValArg bndr_ty' is_strict rhs rhs_se cont_ty $ \ rhs' -> - - -- Now complete the binding and simplify the body - if needsCaseBinding bndr_ty' rhs' then - addCaseBind bndr' rhs' thing_inside - else - completeBinding bndr bndr' False False rhs' thing_inside -\end{code} - - -\begin{code} -simplTyArg :: InType -> SubstEnv -> SimplM OutType -simplTyArg ty_arg se - = getInScope `thenSmpl` \ in_scope -> - let - ty_arg' = substTy (mkSubst in_scope se) ty_arg - in - seqType ty_arg' `seq` - returnSmpl ty_arg' - -simplValArg :: OutType -- rhs_ty: Type of arg; used only occasionally - -> Bool -- True <=> evaluate eagerly - -> InExpr -> SubstEnv - -> OutType -- cont_ty: Type of thing computed by the context - -> (OutExpr -> SimplM OutExprStuff) - -- Takes an expression of type rhs_ty, - -- returns an expression of type cont_ty - -> SimplM OutExprStuff -- An expression of type cont_ty - -simplValArg arg_ty is_strict arg arg_se cont_ty thing_inside - | is_strict - = getEnv `thenSmpl` \ env -> - setSubstEnv arg_se $ - simplExprF arg (ArgOf NoDup cont_ty $ \ rhs' -> - setAllExceptInScope env $ - thing_inside rhs') - - | otherwise - = simplRhs False {- Not top level -} - True {- OK to float unboxed -} - arg_ty arg arg_se - thing_inside -\end{code} - - -completeBinding - - deals only with Ids, not TyVars - - take an already-simplified RHS - -It does *not* attempt to do let-to-case. Why? Because they are 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} -completeBinding :: InId -- Binder - -> OutId -- New binder - -> Bool -- True <=> top level - -> Bool -- True <=> black-listed; don't inline - -> OutExpr -- Simplified RHS - -> SimplM (OutStuff a) -- Thing inside - -> SimplM (OutStuff a) - -completeBinding old_bndr new_bndr top_lvl black_listed new_rhs thing_inside - | isDeadOcc occ_info -- 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 - - | exprIsTrivial new_rhs - -- We're looking at a binding with a trivial RHS, so - -- perhaps we can discard it altogether! - -- - -- NB: a loop breaker never has postInlineUnconditionally True - -- and non-loop-breakers only have *forward* references - -- Hence, it's safe to discard the binding - -- - -- 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) - - -- Note that we do this unconditional inlining only for trival RHSs. - -- 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. - -- - -- NB: Even inline pragmas (e.g. 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 NOINLINEis 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. - = if must_keep_binding then -- Keep the binding - finally_bind_it unknownArity new_rhs - -- Arity doesn't really matter because for a trivial RHS - -- we will inline like crazy at call sites - -- If this turns out be false, we can easily compute arity - else -- Drop the binding - extendSubst 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 - tick (PostInlineUnconditionally old_bndr) `thenSmpl_` - thing_inside - - | Note coercion@(Coerce _ inner_ty) inner_rhs <- new_rhs - -- [NB inner_rhs is guaranteed non-trivial by now] - -- x = coerce t e ==> c = e; x = inline_me (coerce t c) - -- Now x can get inlined, which moves the coercion - -- to the usage site. This is a bit like worker/wrapper stuff, - -- but it's useful to do it very promptly, so that - -- x = coerce T (I# 3) - -- get's w/wd to - -- c = I# 3 - -- x = coerce T c - -- This in turn means that - -- case (coerce Int x) of ... - -- will inline x. - -- Also the full-blown w/w thing isn't set up for non-functions - -- - -- The inline_me note is so that the simplifier doesn't - -- just substitute c back inside x's rhs! (Typically, x will - -- get substituted away, but not if it's exported.) - = newId SLIT("c") inner_ty $ \ c_id -> - completeBinding c_id c_id top_lvl False inner_rhs $ - completeBinding old_bndr new_bndr top_lvl black_listed - (Note InlineMe (Note coercion (Var c_id))) $ - thing_inside - - - | otherwise - = transformRhs new_rhs finally_bind_it - - where - old_info = idInfo old_bndr - occ_info = occInfo old_info - loop_breaker = isLoopBreaker occ_info - trivial_rhs = exprIsTrivial new_rhs - must_keep_binding = black_listed || loop_breaker || isExportedId old_bndr - - finally_bind_it arity_info new_rhs - = getSubst `thenSmpl` \ subst -> - let - -- We make new IdInfo for the new binder by starting from the old binder, - -- doing appropriate substitutions. - -- Then we add arity and unfolding info to get the new binder - new_bndr_info = substIdInfo subst old_info (idInfo new_bndr) - `setArityInfo` arity_info - - -- 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 - info_w_unf | loop_breaker = new_bndr_info - | otherwise = new_bndr_info `setUnfoldingInfo` mkUnfolding top_lvl new_rhs - - final_id = new_bndr `setIdInfo` info_w_unf - in - -- These seqs forces the Id, and hence its IdInfo, - -- and hence any inner substitutions - final_id `seq` - addLetBind (NonRec final_id new_rhs) $ - modifyInScope new_bndr final_id thing_inside -\end{code} - - - %************************************************************************ %* * -\subsection{simplLazyBind} +\subsection{Notes} %* * %************************************************************************ -simplLazyBind basically just simplifies the RHS of a let(rec). -It does two important optimisations though: - - * It floats let(rec)s out of the RHS, even if they - are hidden by big lambdas - - * It does eta expansion - -\begin{code} -simplLazyBind :: Bool -- True <=> top level - -> 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 = black_list_fn bndr - in - - if preInlineUnconditionally black_listed bndr then - -- Inline unconditionally - 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 (conservative) -} - (idType bndr') - rhs rhs_se $ \ rhs' -> - - -- Now compete the binding and simplify the body - completeBinding bndr bndr' top_lvl black_listed rhs' thing_inside -\end{code} - - - \begin{code} -simplRhs :: Bool -- True <=> Top level - -> Bool -- True <=> OK to float unboxed (speculative) bindings - -- False for (a) recursive and (b) top-level bindings - -> OutType -- Type of RHS; used only occasionally - -> InExpr -> SubstEnv - -> (OutExpr -> SimplM (OutStuff a)) - -> SimplM (OutStuff a) -simplRhs top_lvl float_ubx rhs_ty rhs rhs_se thing_inside - = -- Simplify it - setSubstEnv rhs_se (simplExprF rhs (mkRhsStop rhs_ty)) `thenSmpl` \ (floats, (in_scope', rhs')) -> - - -- Float lets out of RHS - let - (floats_out, rhs'') = splitFloats float_ubx floats rhs' +simplNote env (Coerce to from) body cont + = let + in_scope = getInScope env + + 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 `eqType` 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) + | 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 + -- 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 = mkCoerce s1 t1 (substExpr (mkSubst in_scope (getSubstEnv arg_se)) arg) + in + ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont) + + addCoerce to' _ cont = CoerceIt to' cont in - if (top_lvl || wantToExpose 0 rhs') && -- Float lets if (a) we're at the top level - not (null floats_out) -- or (b) the resulting RHS is one we'd like to expose - 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 ) - addLetBinds floats_out $ - setInScope in_scope' $ - thing_inside rhs'' - -- in_scope' may be excessive, but that's OK; - -- it's a superset of what's in scope - else - -- Don't do the float - thing_inside (mkLets floats rhs') + simplType env to `thenSmpl` \ to' -> + simplType env from `thenSmpl` \ from' -> + simplExprF env body (addCoerce to' from' cont) --- 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) - -demanded_float (NonRec b r) = isStrict (idDemandInfo b) && not (isUnLiftedType (idType b)) - -- Unlifted-type (cheap-eagerness) lets may well have a demanded flag on them -demanded_float (Rec _) = False - --- If float_ubx is true we float all the bindings, otherwise --- we just float until we come across an unlifted one. --- Remember that the unlifted bindings in the floats are all for --- guaranteed-terminating non-exception-raising unlifted things, --- which we are happy to do speculatively. However, we may still --- not be able to float them out, because the context --- is either a Rec group, or the top level, neither of which --- can tolerate them. -splitFloats float_ubx floats rhs - | float_ubx = (floats, rhs) -- Float them all - | otherwise = 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') - - must_stay (Rec prs) = False -- No unlifted bindings in here - must_stay (NonRec b r) = isUnLiftedType (idType b) - -wantToExpose :: Int -> CoreExpr -> Bool --- True for expressions that we'd like to expose at the --- top level of an RHS. This includes partial applications --- even if the args aren't cheap; the next pass will let-bind the --- args and eta expand the partial application. So exprIsCheap won't do. --- Here's the motivating example: --- z = letrec g = \x y -> ...g... in g E --- Even though E is a redex we'd like to float the letrec to give --- g = \x y -> ...g... --- z = g E --- Now the next use of SimplUtils.tryEtaExpansion will give --- g = \x y -> ...g... --- z = let v = E in \w -> g v w --- And now we'll float the v to give --- g = \x y -> ...g... --- v = E --- z = \w -> g v w --- Which is what we want; chances are z will be inlined now. - -wantToExpose n (Var v) = idAppIsCheap v n -wantToExpose n (Lit l) = True -wantToExpose n (Lam _ e) = True -wantToExpose n (Note _ e) = wantToExpose n e -wantToExpose n (App f (Type _)) = wantToExpose n f -wantToExpose n (App f a) = wantToExpose (n+1) f -wantToExpose n other = False -- There won't be any lets + +-- 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 \end{code} - %************************************************************************ %* * -\subsection{Variables} +\subsection{Dealing with calls} %* * %************************************************************************ \begin{code} -simplVar var cont - = getSubst `thenSmpl` \ subst -> - case lookupIdSubst subst var of - DoneEx e -> zapSubstEnv (simplExprF e cont) - ContEx env1 e -> setSubstEnv env1 (simplExprF e cont) - DoneId var1 occ -> WARN( not (isInScope var1 subst) && mustHaveLocalBinding var1, +simplVar env var cont + = case lookupIdSubst (getSubst env) var of + DoneEx e -> simplExprF (zapSubstEnv env) e cont + ContEx se e -> simplExprF (setSubstEnv env se) e cont + DoneId var1 occ -> WARN( not (isInScope var1 (getSubst env)) && mustHaveLocalBinding var1, text "simplVar:" <+> ppr var ) - zapSubstEnv (completeCall var1 occ cont) + completeCall (zapSubstEnv env) var1 occ cont -- The template is already simplified, so don't re-substitute. -- This is VITAL. Consider -- let x = e in @@ -768,15 +848,16 @@ simplVar var cont --------------------------------------------------------- -- Dealing with a call -completeCall var occ cont - = getBlackList `thenSmpl` \ black_list_fn -> - getInScope `thenSmpl` \ in_scope -> - getContArgs var cont `thenSmpl` \ (args, call_cont, inline_call) -> - getDOptsSmpl `thenSmpl` \ dflags -> +completeCall env var occ_info cont + = getDOptsSmpl `thenSmpl` \ dflags -> let - black_listed = black_list_fn var - arg_infos = [ interestingArg in_scope arg subst - | (arg, subst, _) <- args, isValArg arg] + in_scope = getInScope env + chkr = getSwitchChecker env + + (args, call_cont, inline_call) = getContArgs chkr var cont + + arg_infos = [ interestingArg in_scope arg (getSubstEnv arg_env) + | (arg, arg_env, _) <- args, isValArg arg] interesting_cont = interestingCallContext (not (null args)) (not (null arg_infos)) @@ -785,20 +866,21 @@ completeCall var occ cont inline_cont | inline_call = discardInline cont | otherwise = cont - maybe_inline = callSiteInline dflags black_listed inline_call occ + active_inline = activeInline env var + maybe_inline = callSiteInline dflags active_inline inline_call occ_info var arg_infos interesting_cont in -- First, look for an inlining case maybe_inline of { Just unfolding -- There is an inlining! -> tick (UnfoldingDone var) `thenSmpl_` - simplExprF unfolding inline_cont + simplExprF env unfolding inline_cont ; Nothing -> -- No inlining! - simplifyArgs (isDataConId var) args (contResultType call_cont) $ \ args' -> + simplifyArgs env args (contResultType call_cont) $ \ env args' -> -- Next, look for rules or specialisations that match -- @@ -813,32 +895,61 @@ completeCall var occ cont -- But the black-listing mechanism means that inlining of the wrapper -- won't occur for things that have specialisations till a later phase, so -- it's ok to try for inlining 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 - getSwitchChecker `thenSmpl` \ chkr -> let - maybe_rule | switchIsOn chkr DontApplyRules = Nothing - | otherwise = lookupRule in_scope var args' + maybe_rule = case activeRule env of + Nothing -> Nothing -- No rules apply + Just act_fn -> lookupRule act_fn in_scope var args' in case maybe_rule of { Just (rule_name, rule_rhs) -> tick (RuleFired rule_name) `thenSmpl_` - simplExprF rule_rhs call_cont ; + (if dopt Opt_D_dump_inlinings dflags then + pprTrace "Rule fired" (vcat [ + text "Rule:" <+> ptext rule_name, + text "Before:" <+> ppr var <+> sep (map pprParendExpr args'), + text "After: " <+> pprCoreExpr rule_rhs]) + else + id) $ + simplExprF env rule_rhs call_cont ; Nothing -> -- No rules -- Done - rebuild (mkApps (Var var) args') call_cont + rebuild env (mkApps (Var var) args') call_cont }} +\end{code} + +%************************************************************************ +%* * +\subsection{Arguments} +%* * +%************************************************************************ +\begin{code} --------------------------------------------------------- -- Simplifying the arguments of a call -simplifyArgs :: Bool -- It's a data constructor - -> [(InExpr, SubstEnv, Bool)] -- Details of the arguments +simplifyArgs :: SimplEnv + -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments -> OutType -- Type of the continuation - -> ([OutExpr] -> SimplM OutExprStuff) - -> SimplM OutExprStuff + -> (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 @@ -863,236 +974,205 @@ simplifyArgs :: Bool -- It's a data constructor -- discard the entire application and replace it with (error "foo"). Getting -- all this at once is TOO HARD! -simplifyArgs is_data_con args cont_ty thing_inside - | not is_data_con - = go args thing_inside - - | otherwise -- It's a data constructor, so we want - -- to switch off inlining in the arguments - -- If we don't do this, consider: - -- let x = +# p q in C {x} - -- Even though x get's an occurrence of 'many', its RHS looks cheap, - -- and there's a good chance it'll get inlined back into C's RHS. Urgh! - = getBlackList `thenSmpl` \ old_bl -> - setBlackList noInlineBlackList $ - go args $ \ args' -> - setBlackList old_bl $ - thing_inside args' - +simplifyArgs env args cont_ty thing_inside + = go env args thing_inside where - go [] thing_inside = thing_inside [] - go (arg:args) thing_inside = simplifyArg is_data_con arg cont_ty $ \ arg' -> - go args $ \ args' -> - thing_inside (arg':args') - -simplifyArg is_data_con (Type ty_arg, se, _) cont_ty thing_inside - = simplTyArg ty_arg se `thenSmpl` \ new_ty_arg -> - thing_inside (Type new_ty_arg) - -simplifyArg is_data_con (val_arg, se, is_strict) cont_ty thing_inside - = getInScope `thenSmpl` \ in_scope -> - let - arg_ty = substTy (mkSubst in_scope se) (exprType val_arg) - in - if not is_data_con then - -- An ordinary function - simplValArg arg_ty is_strict val_arg se cont_ty thing_inside - else - -- A data constructor - -- simplifyArgs has already switched off inlining, so - -- all we have to do here is to let-bind any non-trivial argument - - -- It's not always the case that new_arg will be trivial - -- Consider f x - -- where, in one pass, f gets substituted by a constructor, - -- but x gets substituted by an expression (assume this is the - -- unique occurrence of x). It doesn't really matter -- it'll get - -- fixed up next pass. And it happens for dictionary construction, - -- which mentions the wrapper constructor to start with. - simplValArg arg_ty is_strict val_arg se cont_ty $ \ arg' -> - - if exprIsTrivial arg' then - thing_inside arg' - else - newId SLIT("a") (exprType arg') $ \ arg_id -> - addNonRecBind arg_id arg' $ - thing_inside (Var arg_id) -\end{code} - + go env [] thing_inside = thing_inside env [] + go env (arg:args) thing_inside = simplifyArg env arg cont_ty $ \ env arg' -> + go env args $ \ env args' -> + thing_inside env (arg':args') -%************************************************************************ -%* * -\subsection{Decisions about inlining} -%* * -%************************************************************************ - -NB: At one time I tried not pre/post-inlining top-level things, -even if they occur exactly once. Reason: - (a) some might appear as a function argument, so we simply - replace static allocation with dynamic allocation: - l = <...> - x = f x - becomes - x = f <...> - - (b) some top level things might be black listed - -HOWEVER, I found that some useful foldr/build fusion was lost (most -notably in spectral/hartel/parstof) because the foldr didn't see the build. +simplifyArg env (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) -Doing the dynamic allocation isn't a big deal, in fact, but losing the -fusion can be. +simplifyArg env (val_arg, arg_se, is_strict) cont_ty thing_inside + | is_strict + = simplStrictArg env AnArg val_arg arg_se cont_ty thing_inside -\begin{code} -preInlineUnconditionally :: Bool {- Black listed -} -> 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. - -preInlineUnconditionally black_listed bndr - | black_listed || opt_SimplNoPreInlining = False - | otherwise = case idOccInfo bndr of - OneOcc in_lam once -> not in_lam && once - -- Not inside a lambda, one occurrence ==> safe! - other -> False + | otherwise + = let + arg_env = setInScope arg_se env + in + simplType arg_env (exprType val_arg) `thenSmpl` \ arg_ty -> + simplExprF arg_env val_arg (mkStop arg_ty AnArg) `thenSmpl` \ (floats, arg1) -> + addFloats env floats $ \ env -> + thing_inside env arg1 + + +simplStrictArg :: SimplEnv -- The env of the call + -> LetRhsFlag + -> InExpr -> SimplEnv -- The arg plus its env + -> 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 call_env is_rhs arg arg_env cont_ty thing_inside + = simplExprF (setInScope arg_env call_env) arg + (ArgOf NoDup is_rhs 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{The main rebuilder} +\subsection{mkAtomicArgs} %* * %************************************************************************ -\begin{code} -------------------------------------------------------------------- --- Finish rebuilding -rebuild_done expr - = getInScope `thenSmpl` \ in_scope -> - returnSmpl ([], (in_scope, expr)) - ---------------------------------------------------------- -rebuild :: OutExpr -> SimplCont -> SimplM OutExprStuff - --- Stop continuation -rebuild expr (Stop _ _) = rebuild_done expr +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) --- ArgOf continuation -rebuild expr (ArgOf _ _ cont_fn) = cont_fn expr +There are three sorts of binding context, specified by the two +boolean arguments --- ApplyTo continuation -rebuild expr cont@(ApplyTo _ arg se cont') - = setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' -> - rebuild (App expr arg') cont' +Strict + OK-unlifted --- Coerce continuation -rebuild expr (CoerceIt to_ty cont) - = rebuild (mkCoerce to_ty (exprType expr) expr) cont +N N Top-level or recursive Only bind args of lifted type --- Inline continuation -rebuild expr (InlinePlease cont) - = rebuild (Note InlineCall expr) cont +N Y Non-top-level and non-recursive, Bind args of lifted type, or + but lazy unlifted-and-ok-for-speculation -rebuild scrut (Select _ bndr alts se cont) - = rebuild_case scrut bndr alts se cont -\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. +Y Y Non-top-level, non-recursive, Bind all args + and strict (demanded) + -We also make sure that we deal with this very common case: +For example, given - case e of - x -> ...x... + x = MkC (y div# z) -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) +there is no point in transforming to -Lastly, we generalise the transformation to handle this: + x = case (y div# z) of r -> MkC r - case e of ===> r - True -> r - False -> r +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. -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. +\begin{code} +mkAtomicArgs :: Bool -- A strict binding + -> Bool -- OK to float unlifted args + -> OutExpr + -> SimplM ([(OutId,OutExpr)], -- The floats (unusually) may include + OutExpr) -- things that need case-binding, + -- if the strict-binding flag is on + +mkAtomicArgs is_strict ok_float_unlifted rhs + = mk_atomic_args rhs `thenSmpl` \ maybe_stuff -> + case maybe_stuff of + Nothing -> returnSmpl ([], rhs) + Just (ol_binds, rhs') -> returnSmpl (fromOL ol_binds, rhs') -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. + where + mk_atomic_args :: OutExpr -> SimplM (Maybe (OrdList (Id,OutExpr), OutExpr)) + -- Nothing => no change + mk_atomic_args rhs + | (Var fun, args) <- collectArgs rhs, -- It's an application + isDataConId fun || valArgCount args < idArity fun -- And it's a constructor or PAP + = -- Worth a try + go nilOL [] args `thenSmpl` \ maybe_stuff -> + case maybe_stuff of + Nothing -> returnSmpl Nothing + Just (aux_binds, args') -> returnSmpl (Just (aux_binds, mkApps (Var fun) args')) + + | otherwise + = returnSmpl Nothing + + go binds rev_args [] + = returnSmpl (Just (binds, reverse rev_args)) + go binds rev_args (arg : args) + | exprIsTrivial arg -- Easy case + = go binds (arg:rev_args) args + + | not can_float_arg -- Can't make this arg atomic + = returnSmpl Nothing -- ... so give up + + | otherwise -- Don't forget to do it recursively + -- E.g. x = a:b:c:[] + = mk_atomic_args arg `thenSmpl` \ maybe_anf -> + case maybe_anf of { + Nothing -> returnSmpl Nothing ; + Just (arg_binds,arg') -> + + newId SLIT("a") arg_ty `thenSmpl` \ arg_id -> + go ((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 ) + returnSmpl (emptyFloats env, Case r v [(DEFAULT,[], wrapFloats floats expr)]) -So the case-elimination algorithm is: + | otherwise + = addAuxiliaryBind env (NonRec v r) $ \ env -> + addAtomicBindsE env bs thing_inside +\end{code} - 1. Eliminate alternatives which can't match - 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 +%************************************************************************ +%* * +\subsection{The main rebuilder} +%* * +%************************************************************************ - 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! +\begin{code} +rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr - or * [Prim cases] the scrutinee is a primitive variable +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 (exprType expr) 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 - 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.] +rebuildApp env fun arg cont + = simplExpr env arg `thenSmpl` \ arg' -> + rebuild env (App fun arg') cont +rebuildDone env expr = returnSmpl (emptyFloats env, expr) +\end{code} -If so, then we can replace the case with one of the rhss. +%************************************************************************ +%* * +\subsection{Functions dealing with a case} +%* * +%************************************************************************ Blob of helper functions for the "case-of-something-else" situation. @@ -1100,147 +1180,54 @@ Blob of helper functions for the "case-of-something-else" situation. --------------------------------------------------------- -- Eliminate the case if possible -rebuild_case scrut bndr alts se cont - | maybeToBool maybe_con_app - = knownCon scrut (DataAlt con) args bndr alts se cont +rebuildCase :: SimplEnv + -> OutExpr -- Scrutinee + -> InId -- Case binder + -> [InAlt] -- Alternatives + -> SimplCont + -> SimplM FloatsWithExpr - | canEliminateCase scrut bndr alts - = tick (CaseElim bndr) `thenSmpl_` ( - setSubstEnv se $ - simplBinder bndr $ \ bndr' -> - -- Remember to bind the case binder! - completeBinding bndr bndr' False False scrut $ - simplExprF (head (rhssOfAlts alts)) cont) +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 - | otherwise - = complete_case scrut bndr alts se cont - - where - maybe_con_app = exprIsConApp_maybe scrut - Just (con, args) = maybe_con_app - - -- See if we can get rid of the case altogether - -- See the extensive notes on case-elimination above -canEliminateCase scrut bndr alts - = -- 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 - ) + | Lit lit <- scrut -- No need for same treatment as constructors + -- because literals are inlined more vigorously + = knownCon env (LitAlt lit) [] case_bndr alts cont - where - (rhs1:other_rhss) = rhssOfAlts alts - binders_unused (_, bndrs, _) = all isDeadBinder bndrs - - var_demanded_later (Var v) = isStrict (idDemandInfo bndr) -- It's going to be evaluated later - var_demanded_later other = False - - ---------------------------------------------------------- --- Case of something else - -complete_case scrut case_bndr alts se cont + | otherwise = -- Prepare case alternatives - prepareCaseAlts case_bndr (splitTyConApp_maybe (idType case_bndr)) - impossible_cons alts `thenSmpl` \ better_alts -> - - -- Set the new subst-env in place (before dealing with the case binder) - setSubstEnv se $ + -- Filter out alternatives that can't possibly match + let + impossible_cons = case scrut of + Var v -> otherCons (idUnfolding v) + other -> [] + better_alts = case impossible_cons of + [] -> alts + other -> [alt | alt@(con,_,_) <- alts, + not (con `elem` impossible_cons)] + in -- Deal with the case binder, and prepare the continuation; -- The new subst_env is in place - prepareCaseCont better_alts cont $ \ cont' -> - + prepareCaseCont env better_alts cont `thenSmpl` \ (floats, cont') -> + addFloats env floats $ \ env -> -- Deal with variable scrutinee - ( - getSwitchChecker `thenSmpl` \ chkr -> - simplCaseBinder (switchIsOn chkr NoCaseOfCase) - scrut case_bndr $ \ case_bndr' zap_occ_info -> + simplCaseBinder env scrut case_bndr `thenSmpl` \ (alt_env, case_bndr', zap_occ_info) -> -- Deal with the case alternatives - simplAlts zap_occ_info impossible_cons - case_bndr' better_alts cont' `thenSmpl` \ alts' -> - - mkCase scrut case_bndr' alts' - ) `thenSmpl` \ case_expr -> - - -- 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 - impossible_cons = case scrut of - Var v -> otherCons (idUnfolding v) - other -> [] - - -knownCon :: OutExpr -> AltCon -> [OutExpr] - -> InId -> [InAlt] -> SubstEnv -> SimplCont - -> SimplM OutExprStuff - -knownCon expr con args bndr alts se cont - = tick (KnownBranch bndr) `thenSmpl_` - setSubstEnv se ( - simplBinder bndr $ \ bndr' -> - completeBinding bndr bndr' False 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! - case findAlt con alts of - (DEFAULT, bs, rhs) -> ASSERT( null bs ) - simplExprF rhs cont - - (LitAlt lit, bs, rhs) -> ASSERT( null bs ) - simplExprF rhs cont + simplAlts alt_env zap_occ_info impossible_cons + case_bndr' better_alts cont' `thenSmpl` \ alts' -> - (DataAlt dc, bs, rhs) -> ASSERT( length bs == length real_args ) - 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} + -- Put the case back together + mkCase scrut case_bndr' alts' `thenSmpl` \ case_expr -> -\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 = simplType (coreAltsType alts) `thenSmpl` \ alts_ty -> - mkDupableCont alts_ty cont thing_inside - -- At one time I passed in the un-simplified type, and simplified - -- it only if we needed to construct a join binder, but that - -- didn't work because we have to decompse function types - -- (using funResultTy) in mkDupableCont. + -- Notice that rebuildDone returns the in-scope set from env, not alt_env + -- The case binder *not* scope over the whole returned case-expression + rebuildDone env case_expr \end{code} simplCaseBinder checks whether the scrutinee is a variable, v. If so, @@ -1248,6 +1235,8 @@ 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: @@ -1256,13 +1245,52 @@ 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 no_case_of_case argument +Hence the check for NoCaseOfCase. + +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 .... } + +We'll perform the binder-swap for the outer case, giving + + case x of w1 { DEFAULT -> case w1 of w2 { A -> e1; B -> e2 } + ...other cases .... } + +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 + + case x of w1 { A -> let w2 = w1 in e1 + B -> let w2 = w1 in e2 + ...other cases .... } + +This is plain silly in the common case where w2 is dead. +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: -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: + data T = MkT !Int + + 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. + +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 }) @@ -1275,89 +1303,54 @@ Urk! b is alive! Reason: the scrutinee was a variable, and case elimination happened. Hence the zap_occ_info function returned by simplCaseBinder \begin{code} -simplCaseBinder no_case_of_case (Var v) case_bndr thing_inside - | not no_case_of_case - = simplBinder (zap case_bndr) $ \ case_bndr' -> - modifyInScope v case_bndr' $ +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', zap) -- We could extend the substitution instead, but it would be -- a hack because then the substitution wouldn't be idempotent -- any more (v is an OutId). And this just just as well. - thing_inside case_bndr' zap where zap b = b `setIdOccInfo` NoOccInfo -simplCaseBinder add_eval_info other_scrut case_bndr thing_inside - = simplBinder case_bndr $ \ case_bndr' -> - thing_inside case_bndr' (\ bndr -> bndr) -- NoOp on bndr +simplCaseBinder env other_scrut case_bndr + = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') -> + returnSmpl (env, case_bndr', \ bndr -> bndr) -- NoOp on 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) - arg_tys = dataConArgTys data_con - (inst_tys ++ mkTyVarTys ex_tyvars') - in - newIds SLIT("a") arg_tys $ \ bndrs -> - returnSmpl ((DataAlt data_con, ex_tyvars' ++ bndrs, rhs) : alts_no_deflt) - - other -> returnSmpl filtered_alts - 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)] - - missing_cons = [data_con | data_con <- tyConDataConsIfAvailable tycon, - not (data_con `elem` handled_data_cons)] - handled_data_cons = [data_con | DataAlt data_con <- scrut_cons] ++ - [data_con | (DataAlt data_con, _, _) <- filtered_alts] - --- The default case -prepareCaseAlts _ _ scrut_cons alts - = returnSmpl alts -- Functions - - ----------------------- -simplAlts zap_occ_info scrut_cons case_bndr' alts cont' +simplAlts :: SimplEnv + -> (InId -> InId) -- Occ-info zapper + -> [AltCon] -- Alternatives the scrutinee can't be + -> OutId -- Case binder + -> [InAlt] -> SimplCont + -> SimplM [OutAlt] -- Includes the continuation + +simplAlts env zap_occ_info impossible_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 + inst_tys' = tyConAppArgs (idType case_bndr') -- 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] + (con_alts,_) = findDefault alts + handled_cons = impossible_cons ++ [con | (con,_,_) <- con_alts] simpl_alt (DEFAULT, _, rhs) - = -- In the default case we record the constructors that the + = let + -- 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' (case_bndr' `setIdUnfolding` mkOtherCon handled_cons) $ - simplExprC rhs cont' `thenSmpl` \ rhs' -> + case_bndr_w_unf = case_bndr' `setIdUnfolding` mkOtherCon handled_cons + env_with_unf = modifyInScope env case_bndr' case_bndr_w_unf + in + simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' -> returnSmpl (DEFAULT, [], rhs') simpl_alt (con, vs, rhs) @@ -1367,14 +1360,14 @@ simplAlts zap_occ_info scrut_cons case_bndr' alts cont' -- 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 (add_evals con vs) $ \ vs' -> + simplBinders env (add_evals con vs) `thenSmpl` \ (env, vs') -> -- Bind the case-binder to (con args) let - unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys') + unfolding = mkUnfolding False (mkAltExpr con vs' inst_tys') + env_with_unf = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` unfolding) in - modifyInScope case_bndr' (case_bndr' `setIdUnfolding` unfolding) $ - simplExprC rhs cont' `thenSmpl` \ rhs' -> + simplExprC env_with_unf rhs cont' `thenSmpl` \ rhs' -> returnSmpl (con, vs', rhs') @@ -1392,11 +1385,77 @@ simplAlts zap_occ_info scrut_cons case_bndr' alts cont' 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 + | isTyVar v = v : cat_evals vs (str:strs) + | isMarkedStrict str = evald_v : cat_evals vs strs + | otherwise = zapped_v : cat_evals vs strs where - v' = zap_occ_info v + zapped_v = zap_occ_info v + evald_v = zapped_v `setIdUnfolding` mkOtherCon [] +\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( length bs + n_tys == length args ) + bind_args env bs (drop n_tys args) $ \ env -> + let + con_app = mkConApp dc (take n_tys args ++ con_args) + con_args = [substExpr (getSubst 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_tys = dataConNumInstArgs dc -- Non-existential type args +-- Ugh! +bind_args env [] _ thing_inside = thing_inside env + +bind_args env (b:bs) (Type ty : args) thing_inside + = bind_args (extendSubst env b (DoneTy ty)) bs args thing_inside + +bind_args env (b:bs) (arg : args) thing_inside + = simplNonRecX env b arg $ \ env -> + bind_args env bs args thing_inside \end{code} @@ -1407,94 +1466,141 @@ simplAlts zap_occ_info scrut_cons case_bndr' alts cont' %************************************************************************ \begin{code} -mkDupableCont :: OutType -- Type of the thing to be given to the continuation +prepareCaseCont :: SimplEnv + -> [InAlt] -> SimplCont + -> SimplM (FloatsWith SimplCont) -- Return a duplicatable continuation, + -- plus some extra bindings + +prepareCaseCont env [alt] cont = returnSmpl (emptyFloats env, cont) + -- No need to make it duplicatable if there's only one alternative + +prepareCaseCont env alts cont = simplType env (coreAltsType alts) `thenSmpl` \ alts_ty -> + mkDupableCont env alts_ty cont + -- At one time I passed in the un-simplified type, and simplified + -- it only if we needed to construct a join binder, but that + -- didn't work because we have to decompse function types + -- (using funResultTy) in mkDupableCont. +\end{code} + +\begin{code} +mkDupableCont :: SimplEnv + -> OutType -- Type of the thing to be given to the continuation -> SimplCont - -> (SimplCont -> SimplM (OutStuff a)) - -> SimplM (OutStuff a) -mkDupableCont ty cont thing_inside + -> SimplM (FloatsWith SimplCont) -- Return a duplicatable continuation, + -- plus some extra bindings + +mkDupableCont env ty 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 - newId SLIT("a") join_arg_ty ( \ arg_id -> - cont_fn (Var arg_id) `thenSmpl` \ (binds, (_, rhs)) -> - returnSmpl (Lam (setOneShotLambda arg_id) (mkLets binds rhs)) - ) `thenSmpl` \ join_rhs -> - + = returnSmpl (emptyFloats env, cont) + +mkDupableCont env _ (CoerceIt ty cont) + = mkDupableCont env ty cont `thenSmpl` \ (floats, cont') -> + returnSmpl (floats, CoerceIt ty cont') + +mkDupableCont env ty (InlinePlease cont) + = mkDupableCont env ty cont `thenSmpl` \ (floats, cont') -> + returnSmpl (floats, InlinePlease cont') + +mkDupableCont env join_arg_ty (ArgOf _ is_rhs cont_ty cont_fn) + = -- e.g. (...strict-fn...) [...hole...] + -- ==> + -- let $j = \a -> ...strict-fn... + -- in $j [...hole...] + -- Build the join Id and continuation -- We give it a "$j" name just so that for later amusement -- we can identify any join points that don't end up as let-no-escapes -- [NOTE: the type used to be exprType join_rhs, but this seems more elegant.] - newId SLIT("$j") (mkFunTy join_arg_ty cont_ty) $ \ join_id -> + newId SLIT("$j") (mkFunTy join_arg_ty cont_ty) `thenSmpl` \ join_id -> + newId SLIT("a") join_arg_ty `thenSmpl` \ arg_id -> + + cont_fn (addNewInScopeIds env [arg_id]) (Var arg_id) `thenSmpl` \ (floats, rhs) -> let - new_cont = ArgOf OkToDup cont_ty - (\arg' -> rebuild_done (App (Var join_id) arg')) + cont_fn env arg' = rebuildDone env (App (Var join_id) arg') + join_rhs = Lam (setOneShotLambda arg_id) (wrapFloats floats rhs) in tick (CaseOfCase join_id) `thenSmpl_` -- Want to tick here so that we go round again, -- and maybe copy or inline the code; -- not strictly CaseOf Case - addLetBind (NonRec join_id join_rhs) $ - thing_inside new_cont -mkDupableCont ty (ApplyTo _ arg se cont) thing_inside - = mkDupableCont (funResultTy ty) cont $ \ cont' -> - setSubstEnv se (simplExpr arg) `thenSmpl` \ arg' -> + returnSmpl (unitFloat env join_id join_rhs, + ArgOf OkToDup is_rhs cont_ty cont_fn) + +mkDupableCont env ty (ApplyTo _ arg se cont) + = -- e.g. [...hole...] (...arg...) + -- ==> + -- let a = ...arg... + -- in [...hole...] a + mkDupableCont env (funResultTy ty) cont `thenSmpl` \ (floats, cont') -> + addFloats env floats $ \ env -> + + simplExpr (setInScope se env) arg `thenSmpl` \ arg' -> if exprIsDupable arg' then - thing_inside (ApplyTo OkToDup arg' emptySubstEnv cont') + returnSmpl (emptyFloats env, ApplyTo OkToDup arg' (zapSubstEnv se) cont') else - newId SLIT("a") (exprType arg') $ \ bndr -> + newId SLIT("a") (exprType arg') `thenSmpl` \ arg_id -> - tick (CaseOfCase bndr) `thenSmpl_` + tick (CaseOfCase arg_id) `thenSmpl_` -- Want to tick here so that we go round again, - -- and maybe copy or inline the code; - -- not strictly CaseOf Case + -- and maybe copy or inline the code. + -- Not strictly CaseOfCase, but never mind - addLetBind (NonRec bndr arg') $ - -- But what if the arg should be case-bound? We can't use - -- addNonRecBind here because its type is too specific. + returnSmpl (unitFloat env arg_id arg', + ApplyTo OkToDup (Var arg_id) (zapSubstEnv se) 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. - thing_inside (ApplyTo OkToDup (Var bndr) emptySubstEnv cont') - -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') -> - - addAuxiliaryBinds 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 (mkStop (contResultType cont))) - -mkDupableAlt :: InId -> OutId -> SimplCont -> InAlt -> SimplM (OutStuff InAlt) -mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) - = simplBinders bndrs $ \ bndrs' -> - simplExprC rhs cont `thenSmpl` \ rhs' -> - - if (case cont of { Stop _ _ -> exprIsDupable rhs'; other -> False}) then +mkDupableCont env ty (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, dupable_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 dupable_cont `thenSmpl` \ (floats2, alts') -> + addFloats alt_env floats2 $ \ alt_env -> + returnSmpl (emptyFloats alt_env, Select OkToDup case_bndr' alts' (zapSubstEnv se) + (mkBoringStop (contResultType 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) + = mkDupableAlt env case_bndr' dupable_cont alt `thenSmpl` \ (floats1, alt') -> + addFloats env floats1 $ \ env -> + go env alts `thenSmpl` \ (floats2, alts') -> + returnSmpl (floats2, alt' : alts') + +mkDupableAlt env case_bndr' cont alt@(con, bndrs, rhs) + = simplBinders env bndrs `thenSmpl` \ (env, bndrs') -> + simplExprC env rhs cont `thenSmpl` \ rhs' -> + + if exprIsDupable rhs' then + returnSmpl (emptyFloats env, (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. @@ -1503,28 +1609,20 @@ mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) -- 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. - -- -- 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. + -- 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. - returnSmpl ([], alt) else let - rhs_ty' = exprType 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 (not . isDeadBinder) (case_bndr' : bndrs') + -- The deadness info on the new binders is unscathed 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 @@ -1542,28 +1640,55 @@ mkDupableAlt case_bndr case_bndr' cont alt@(con, bndrs, rhs) -- 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 + -- + -- 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 - then newId SLIT("w") realWorldStatePrimTy $ \ rw_id -> + ( if null used_bndrs' + then newId SLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id -> returnSmpl ([rw_id], [Var realWorldPrimId]) else - returnSmpl (used_bndrs', map varToCoreExpr used_bndrs) - ) - `thenSmpl` \ (final_bndrs', final_args) -> + returnSmpl (used_bndrs', map varToCoreExpr used_bndrs') + ) `thenSmpl` \ (final_bndrs', final_args) -> -- See comment about "$j" name above - newId SLIT("$j") (foldr (mkFunTy . idType) rhs_ty' final_bndrs') $ \ join_bndr -> - - -- Notice that we make the lambdas into one-shot-lambdas. The + newId SLIT("$j") (foldr mkPiType rhs_ty' final_bndrs') `thenSmpl` \ join_bndr -> + -- Notice the funky mkPiType. 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, (con, bndrs', join_call)) \end{code}