X-Git-Url: http://git.megacz.com/?p=ghc-hetmet.git;a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplify.lhs;h=dffdd75212206ead238a652ac81f1e75551ddc9c;hp=d8f9506b23c0c42fb20ca431ad52ea333fce8f85;hb=9da4639011348fb6c318e3cba4b08622f811d9c4;hpb=f2dcf256399e9a2de6343c625630b51f8abf4863 diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs index d8f9506..dffdd75 100644 --- a/compiler/simplCore/Simplify.lhs +++ b/compiler/simplCore/Simplify.lhs @@ -13,7 +13,7 @@ import DynFlags ( dopt, DynFlag(Opt_D_dump_inlinings), ) import SimplMonad import SimplEnv -import SimplUtils ( mkCase, mkLam, +import SimplUtils ( mkCase, mkLam, SimplCont(..), DupFlag(..), LetRhsFlag(..), mkRhsStop, mkBoringStop, mkLazyArgStop, pushContArgs, contResultType, countArgs, contIsDupable, contIsRhsOrArg, @@ -26,17 +26,14 @@ import Id ( Id, idType, idInfo, idArity, isDataConWorkId, idNewDemandInfo, setIdInfo, setIdOccInfo, zapLamIdInfo, setOneShotLambda ) -import MkId ( eRROR_ID ) -import Literal ( mkStringLit ) import IdInfo ( OccInfo(..), isLoopBreaker, setArityInfo, zapDemandInfo, setUnfoldingInfo, occInfo ) import NewDemand ( isStrictDmd ) -import Unify ( coreRefineTys, dataConCanMatch ) -import DataCon ( DataCon, dataConTyCon, dataConRepStrictness, isVanillaDataCon, - dataConInstArgTys, dataConTyVars ) +import TcGadt ( dataConCanMatch ) +import DataCon ( dataConTyCon, dataConRepStrictness ) import TyCon ( tyConArity, isAlgTyCon, isNewTyCon, tyConDataCons_maybe ) import CoreSyn import PprCore ( pprParendExpr, pprCoreExpr ) @@ -45,24 +42,24 @@ import CoreUtils ( exprIsDupable, exprIsTrivial, needsCaseBinding, exprIsConApp_maybe, mkPiTypes, findAlt, exprType, exprIsHNF, findDefault, mergeAlts, exprOkForSpeculation, exprArity, - mkCoerce, mkCoerce2, mkSCC, mkInlineMe, applyTypeToArg + mkCoerce, mkSCC, mkInlineMe, applyTypeToArg, + dataConRepInstPat ) import Rules ( lookupRule ) import BasicTypes ( isMarkedStrict ) import CostCentre ( currentCCS ) import Type ( TvSubstEnv, isUnLiftedType, seqType, tyConAppArgs, funArgTy, - splitFunTy_maybe, splitFunTy, coreEqType, splitTyConApp_maybe, - isTyVarTy, mkTyVarTys + coreEqType, splitTyConApp_maybe, + isTyVarTy, isFunTy, tcEqType ) -import Var ( tyVarKind, mkTyVar ) +import Coercion ( Coercion, coercionKind, + mkTransCoercion, mkSymCoercion, splitCoercionKind_maybe, decomposeCo ) import VarEnv ( elemVarEnv, emptyVarEnv ) import TysPrim ( realWorldStatePrimTy ) import PrelInfo ( realWorldPrimId ) import BasicTypes ( TopLevelFlag(..), isTopLevel, RecFlag(..), isNonRec ) -import Name ( mkSysTvName ) -import StaticFlags ( opt_PprStyle_Debug ) import OrdList import List ( nub ) import Maybes ( orElse ) @@ -320,13 +317,7 @@ simplNonRecBind' env bndr rhs rhs_se cont_ty thing_inside let (env2,bndr2) = addLetIdInfo env1 bndr bndr1 in - if needsCaseBinding bndr_ty rhs1 - then - thing_inside env2 `thenSmpl` \ (floats, body) -> - returnSmpl (emptyFloats env2, Case rhs1 bndr2 (exprType body) - [(DEFAULT, [], wrapFloats floats body)]) - else - completeNonRecX env2 True {- strict -} bndr bndr2 rhs1 thing_inside + completeNonRecX env2 True {- strict -} bndr bndr2 rhs1 thing_inside | otherwise -- Normal, lazy case = -- Don't use simplBinder because that doesn't keep @@ -351,7 +342,21 @@ simplNonRecX :: SimplEnv -> SimplM FloatsWithExpr simplNonRecX env bndr new_rhs thing_inside - | needsCaseBinding (idType bndr) new_rhs + = do { (env, bndr') <- simplBinder env bndr + ; completeNonRecX env False {- Non-strict; pessimistic -} + bndr bndr' new_rhs thing_inside } + + +completeNonRecX :: SimplEnv + -> Bool -- Strict binding + -> InId -- Old binder + -> OutId -- New binder + -> OutExpr -- Simplified RHS + -> (SimplEnv -> SimplM FloatsWithExpr) + -> SimplM FloatsWithExpr + +completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside + | needsCaseBinding (idType new_bndr) new_rhs -- Make this test *before* the preInlineUnconditionally -- Consider case I# (quotInt# x y) of -- I# v -> let w = J# v in ... @@ -359,12 +364,24 @@ simplNonRecX env bndr new_rhs thing_inside -- extra thunk: -- let w = J# (quotInt# x y) in ... -- because quotInt# can fail. - = simplBinder env bndr `thenSmpl` \ (env, bndr') -> - thing_inside env `thenSmpl` \ (floats, body) -> - let body' = wrapFloats floats body in - returnSmpl (emptyFloats env, Case new_rhs bndr' (exprType body') [(DEFAULT, [], body')]) + = do { (floats, body) <- thing_inside env + ; let body' = wrapFloats floats body + ; return (emptyFloats env, Case new_rhs new_bndr (exprType body) + [(DEFAULT, [], body')]) } - | preInlineUnconditionally env NotTopLevel bndr new_rhs + | otherwise + = -- Make the arguments atomic if necessary, + -- adding suitable bindings + -- pprTrace "completeNonRecX" (ppr new_bndr <+> ppr new_rhs) $ + mkAtomicArgsE env is_strict new_rhs $ \ env new_rhs -> + completeLazyBind env NotTopLevel + old_bndr new_bndr new_rhs `thenSmpl` \ (floats, env) -> + addFloats env floats thing_inside + +{- No, no, no! Do not try preInlineUnconditionally in completeNonRecX + Doing so risks exponential behaviour, because new_rhs has been simplified once already + In the cases described by the folowing commment, postInlineUnconditionally will + catch many of the relevant cases. -- 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 @@ -373,24 +390,11 @@ simplNonRecX env bndr new_rhs thing_inside -- 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. + | preInlineUnconditionally env NotTopLevel bndr new_rhs = thing_inside (extendIdSubst env bndr (DoneEx new_rhs)) - | otherwise - = simplBinder env bndr `thenSmpl` \ (env, bndr') -> - completeNonRecX env False {- Non-strict; pessimistic -} - bndr bndr' new_rhs thing_inside - -completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside - = mkAtomicArgs is_strict - True {- OK to float unlifted -} - new_rhs `thenSmpl` \ (aux_binds, rhs2) -> - - -- Make the arguments atomic if necessary, - -- adding suitable bindings - addAtomicBindsE env (fromOL aux_binds) $ \ env -> - completeLazyBind env NotTopLevel - old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) -> - addFloats env floats thing_inside + -- NB: completeLazyBind uses postInlineUnconditionally; no need to do that here +-} \end{code} @@ -530,8 +534,8 @@ simplLazyBind env top_lvl is_rec bndr bndr1 rhs rhs_se -- we only float if (a) arg' is a WHNF, or (b) it's going to top level -- and so there can't be any 'will be demanded' bindings in the floats. -- Hence the warning - ASSERT2( is_top_level || not (any demanded_float (floatBinds floats)), - ppr (filter demanded_float (floatBinds floats)) ) + WARN( not (is_top_level || not (any demanded_float (floatBinds floats))), + ppr (filter demanded_float (floatBinds floats)) ) tick LetFloatFromLet `thenSmpl_` ( addFloats env1 floats $ \ env2 -> @@ -589,6 +593,7 @@ completeLazyBind env top_lvl old_bndr new_bndr new_rhs | postInlineUnconditionally env top_lvl new_bndr occ_info new_rhs unfolding = -- Drop the binding tick (PostInlineUnconditionally old_bndr) `thenSmpl_` + -- pprTrace "Inline unconditionally" (ppr old_bndr <+> ppr new_bndr <+> ppr new_rhs) $ returnSmpl (emptyFloats env, extendIdSubst env old_bndr (DoneEx new_rhs)) -- Use the substitution to make quite, quite sure that the substitution -- will happen, since we are going to discard the binding @@ -603,7 +608,6 @@ completeLazyBind env top_lvl old_bndr new_bndr new_rhs -- means that we can avoid tests in exprIsConApp, for example. -- This is important: if exprIsConApp says 'yes' for a recursive -- thing, then we can get into an infinite loop - -- If the unfolding is a value, the demand info may -- go pear-shaped, so we nuke it. Example: -- let x = (a,b) in @@ -627,6 +631,7 @@ completeLazyBind env top_lvl old_bndr new_bndr new_rhs -- These seqs forces the Id, and hence its IdInfo, -- and hence any inner substitutions final_id `seq` + -- pprTrace "Binding" (ppr final_id <+> ppr unfolding) $ returnSmpl (unitFloat env final_id new_rhs, env) where @@ -706,7 +711,9 @@ 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 env (Cast body co) cont = simplCast env body co cont +simplExprF env (App fun arg) cont = simplExprF env fun + (ApplyTo NoDup arg (Just env) cont) simplExprF env (Type ty) cont = ASSERT( contIsRhsOrArg cont ) @@ -759,6 +766,69 @@ simplType env ty %************************************************************************ \begin{code} +simplCast :: SimplEnv -> InExpr -> Coercion -> SimplCont -> SimplM FloatsWithExpr +simplCast env body co cont + = let + addCoerce co cont + | (s1, k1) <- coercionKind co + , s1 `tcEqType` k1 = cont + addCoerce co1 (CoerceIt co2 cont) + | (s1, k1) <- coercionKind co1 + , (l1, t1) <- coercionKind co2 + -- 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 + , s1 `coreEqType` t1 = cont -- The coerces cancel out + | otherwise = CoerceIt (mkTransCoercion co1 co2) cont + + addCoerce co (ApplyTo dup arg arg_se cont) + | not (isTypeArg arg) -- This whole case only works for value args + -- Could upgrade to have equiv thing for type apps too + , Just (s1s2, t1t2) <- splitCoercionKind_maybe co + , isFunTy s1s2 + -- co : s1s2 :=: t1t2 + -- (coerce (T1->T2) (S1->S2) F) E + -- ===> + -- coerce T2 S2 (F (coerce S1 T1 E)) + -- + -- t1t2 must be a function type, T1->T2, because it's applied + -- to something but s1s2 might conceivably not be + -- + -- When we build the ApplyTo we can't mix the out-types + -- with the InExpr in the argument, so we simply substitute + -- to make it all consistent. It's a bit messy. + -- But it isn't a common case. + = result + where + -- we split coercion t1->t2 :=: s1->s2 into t1 :=: s1 and + -- t2 :=: s2 with left and right on the curried form: + -- (->) t1 t2 :=: (->) s1 s2 + [co1, co2] = decomposeCo 2 co + new_arg = mkCoerce (mkSymCoercion co1) arg' + arg' = case arg_se of + Nothing -> arg + Just arg_se -> substExpr (setInScope arg_se env) arg + result = ApplyTo dup new_arg (Just $ zapSubstEnv env) + (addCoerce co2 cont) + addCoerce co cont = CoerceIt co cont + in + simplType env co `thenSmpl` \ co' -> + simplExprF env body (addCoerce co' cont) +\end{code} + +%************************************************************************ +%* * +\subsection{Lambdas} +%* * +%************************************************************************ + +\begin{code} simplLam env fun cont = go env fun cont where @@ -766,25 +836,32 @@ simplLam env fun cont cont_ty = contResultType cont -- Type-beta reduction - go env (Lam bndr body) (ApplyTo _ (Type ty_arg) arg_se body_cont) + go env (Lam bndr body) (ApplyTo _ (Type ty_arg) mb_arg_se body_cont) = ASSERT( isTyVar bndr ) - tick (BetaReduction bndr) `thenSmpl_` - simplType (setInScope arg_se env) ty_arg `thenSmpl` \ ty_arg' -> - go (extendTvSubst env bndr ty_arg') body body_cont + do { tick (BetaReduction bndr) + ; ty_arg' <- case mb_arg_se of + Just arg_se -> simplType (setInScope arg_se env) ty_arg + Nothing -> return ty_arg + ; go (extendTvSubst env bndr ty_arg') body body_cont } -- Ordinary beta reduction - go env (Lam bndr body) cont@(ApplyTo _ arg arg_se body_cont) - = tick (BetaReduction bndr) `thenSmpl_` - simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env -> - go env body body_cont + go env (Lam bndr body) cont@(ApplyTo _ arg (Just arg_se) body_cont) + = do { tick (BetaReduction bndr) + ; simplNonRecBind env (zap_it bndr) arg arg_se cont_ty $ \ env -> + go env body body_cont } + + go env (Lam bndr body) cont@(ApplyTo _ arg Nothing body_cont) + = do { tick (BetaReduction bndr) + ; simplNonRecX env (zap_it bndr) arg $ \ env -> + go env body body_cont } -- Not enough args, so there are real lambdas left to put in the result go env lam@(Lam _ _) cont - = simplLamBndrs env bndrs `thenSmpl` \ (env, bndrs') -> - simplExpr env body `thenSmpl` \ body' -> - mkLam env bndrs' body' cont `thenSmpl` \ (floats, new_lam) -> - addFloats env floats $ \ env -> - rebuild env new_lam cont + = do { (env, bndrs') <- simplLamBndrs env bndrs + ; body' <- simplExpr env body + ; (floats, new_lam) <- mkLam env bndrs' body' cont + ; addFloats env floats $ \ env -> + rebuild env new_lam cont } where (bndrs,body) = collectBinders lam @@ -813,54 +890,6 @@ mkLamBndrZapper fun n_args %************************************************************************ \begin{code} -simplNote env (Coerce to from) body cont - = let - addCoerce s1 k1 cont -- Drop redundant coerces. This can happen if a polymoprhic - -- (coerce a b e) is instantiated with a=ty1 b=ty2 and the - -- two are the same. This happens a lot in Happy-generated parsers - | s1 `coreEqType` k1 = cont - - addCoerce s1 k1 (CoerceIt t1 cont) - -- coerce T1 S1 (coerce S1 K1 e) - -- ==> - -- e, if T1=K1 - -- coerce T1 K1 e, otherwise - -- - -- For example, in the initial form of a worker - -- we may find (coerce T (coerce S (\x.e))) y - -- and we'd like it to simplify to e[y/x] in one round - -- of simplification - | t1 `coreEqType` k1 = cont -- The coerces cancel out - | otherwise = CoerceIt t1 cont -- They don't cancel, but - -- the inner one is redundant - - addCoerce t1t2 s1s2 (ApplyTo dup arg arg_se cont) - | not (isTypeArg arg), -- This whole case only works for value args - -- Could upgrade to have equiv thing for type apps too - Just (s1, s2) <- splitFunTy_maybe s1s2 - -- (coerce (T1->T2) (S1->S2) F) E - -- ===> - -- coerce T2 S2 (F (coerce S1 T1 E)) - -- - -- t1t2 must be a function type, T1->T2, because it's applied to something - -- but s1s2 might conceivably not be - -- - -- When we build the ApplyTo we can't mix the out-types - -- with the InExpr in the argument, so we simply substitute - -- to make it all consistent. It's a bit messy. - -- But it isn't a common case. - = let - (t1,t2) = splitFunTy t1t2 - new_arg = mkCoerce2 s1 t1 (substExpr arg_env arg) - arg_env = setInScope arg_se env - in - ApplyTo dup new_arg (zapSubstEnv env) (addCoerce t2 s2 cont) - - addCoerce to' _ cont = CoerceIt to' cont - in - simplType env to `thenSmpl` \ to' -> - simplType env from `thenSmpl` \ from' -> - simplExprF env body (addCoerce to' from' cont) -- Hack: we only distinguish subsumed cost centre stacks for the purposes of @@ -991,7 +1020,7 @@ completeCall env var occ_info cont text "Cont: " <+> ppr call_cont]) else id) $ - makeThatCall env var unfolding args call_cont + simplExprF env unfolding (pushContArgs args call_cont) ; Nothing -> -- No inlining! @@ -999,43 +1028,7 @@ completeCall env var occ_info cont -- Done rebuild env (mkApps (Var var) args) call_cont }} - -makeThatCall :: SimplEnv - -> Id - -> InExpr -- Inlined function rhs - -> [OutExpr] -- Arguments, already simplified - -> SimplCont -- After the call - -> SimplM FloatsWithExpr --- Similar to simplLam, but this time --- the arguments are already simplified -makeThatCall orig_env var fun@(Lam _ _) args cont - = go orig_env fun args - where - zap_it = mkLamBndrZapper fun (length args) - - -- Type-beta reduction - go env (Lam bndr body) (Type ty_arg : args) - = ASSERT( isTyVar bndr ) - tick (BetaReduction bndr) `thenSmpl_` - go (extendTvSubst env bndr ty_arg) body args - - -- Ordinary beta reduction - go env (Lam bndr body) (arg : args) - = tick (BetaReduction bndr) `thenSmpl_` - simplNonRecX env (zap_it bndr) arg $ \ env -> - go env body args - - -- Not enough args, so there are real lambdas left to put in the result - go env fun args - = simplExprF env fun (pushContArgs orig_env args cont) - -- NB: orig_env; the correct environment to capture with - -- the arguments.... env has been augmented with substitutions - -- from the beta reductions. - -makeThatCall env var fun args cont - = simplExprF env fun (pushContArgs env args cont) -\end{code} - +\end{code} %************************************************************************ %* * @@ -1050,7 +1043,7 @@ makeThatCall env var fun args cont simplifyArgs :: SimplEnv -> OutType -- Type of the function -> Bool -- True if the fn has RULES - -> [(InExpr, SimplEnv, Bool)] -- Details of the arguments + -> [(InExpr, Maybe SimplEnv, Bool)] -- Details of the arguments -> OutType -- Type of the continuation -> (SimplEnv -> [OutExpr] -> SimplM FloatsWithExpr) -> SimplM FloatsWithExpr @@ -1088,11 +1081,14 @@ simplifyArgs env fn_ty has_rules args cont_ty thing_inside go env (applyTypeToArg fn_ty arg') args $ \ env args' -> thing_inside env (arg':args') -simplifyArg env fn_ty has_rules (Type ty_arg, se, _) cont_ty thing_inside +simplifyArg env fn_ty has_rules (arg, Nothing, _) cont_ty thing_inside + = thing_inside env arg -- Already simplified + +simplifyArg env fn_ty has_rules (Type ty_arg, Just se, _) cont_ty thing_inside = simplType (setInScope se env) ty_arg `thenSmpl` \ new_ty_arg -> thing_inside env (Type new_ty_arg) -simplifyArg env fn_ty has_rules (val_arg, arg_se, is_strict) cont_ty thing_inside +simplifyArg env fn_ty has_rules (val_arg, Just arg_se, is_strict) cont_ty thing_inside | is_strict = simplStrictArg AnArg env val_arg arg_se arg_ty cont_ty thing_inside @@ -1172,6 +1168,38 @@ a *strict* let, then it would be a good thing to do. Hence the context information. \begin{code} +mkAtomicArgsE :: SimplEnv + -> Bool -- A strict binding + -> OutExpr -- The rhs + -> (SimplEnv -> OutExpr -> SimplM FloatsWithExpr) + -> SimplM FloatsWithExpr + +mkAtomicArgsE env is_strict rhs thing_inside + | (Var fun, args) <- collectArgs rhs, -- It's an application + isDataConWorkId fun || valArgCount args < idArity fun -- And it's a constructor or PAP + = go env (Var fun) args + + | otherwise = thing_inside env rhs + + where + go env fun [] = thing_inside env fun + + go env fun (arg : args) + | exprIsTrivial arg -- Easy case + || no_float_arg -- Can't make it atomic + = go env (App fun arg) args + + | otherwise + = do { arg_id <- newId FSLIT("a") arg_ty + ; completeNonRecX env False {- pessimistic -} arg_id arg_id arg $ \env -> + go env (App fun (Var arg_id)) args } + where + arg_ty = exprType arg + no_float_arg = not is_strict && (isUnLiftedType arg_ty) && not (exprOkForSpeculation arg) + + +-- Old code: consider rewriting to be more like mkAtomicArgsE + mkAtomicArgs :: Bool -- A strict binding -> Bool -- OK to float unlifted args -> OutExpr @@ -1218,25 +1246,6 @@ addAtomicBinds :: SimplEnv -> [(OutId,OutExpr)] addAtomicBinds env [] thing_inside = thing_inside env addAtomicBinds env ((v,r):bs) thing_inside = addAuxiliaryBind env (NonRec v r) $ \ env -> addAtomicBinds env bs thing_inside - -addAtomicBindsE :: SimplEnv -> [(OutId,OutExpr)] - -> (SimplEnv -> SimplM FloatsWithExpr) - -> SimplM FloatsWithExpr --- Same again, but this time we're in an expression context, --- and may need to do some case bindings - -addAtomicBindsE env [] thing_inside - = thing_inside env -addAtomicBindsE env ((v,r):bs) thing_inside - | needsCaseBinding (idType v) r - = addAtomicBindsE (addNewInScopeIds env [v]) bs thing_inside `thenSmpl` \ (floats, expr) -> - WARN( exprIsTrivial expr, ppr v <+> pprCoreExpr expr ) - (let body = wrapFloats floats expr in - returnSmpl (emptyFloats env, Case r v (exprType body) [(DEFAULT,[],body)])) - - | otherwise - = addAuxiliaryBind env (NonRec v r) $ \ env -> - addAtomicBindsE env bs thing_inside \end{code} @@ -1251,13 +1260,17 @@ rebuild :: SimplEnv -> OutExpr -> SimplCont -> SimplM FloatsWithExpr rebuild env expr (Stop _ _ _) = rebuildDone env expr rebuild env expr (ArgOf _ _ _ cont_fn) = cont_fn env expr -rebuild env expr (CoerceIt to_ty cont) = rebuild env (mkCoerce to_ty expr) cont +rebuild env expr (CoerceIt co cont) = rebuild env (mkCoerce co 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 +rebuild env expr (ApplyTo _ arg mb_se cont) = rebuildApp env expr arg mb_se cont + +rebuildApp env fun arg mb_se cont + = do { arg' <- simplArg env arg mb_se + ; rebuild env (App fun arg') cont } -rebuildApp env fun arg cont - = simplExpr env arg `thenSmpl` \ arg' -> - rebuild env (App fun arg') cont +simplArg :: SimplEnv -> CoreExpr -> Maybe SimplEnv -> SimplM CoreExpr +simplArg env arg Nothing = return arg -- The arg is already simplified +simplArg env arg (Just arg_env) = simplExpr (setInScope arg_env env) arg rebuildDone env expr = returnSmpl (emptyFloats env, expr) \end{code} @@ -1286,11 +1299,11 @@ 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 + = knownCon env scrut (DataAlt con) args case_bndr alts cont | Lit lit <- scrut -- No need for same treatment as constructors -- because literals are inlined more vigorously - = knownCon env (LitAlt lit) [] case_bndr alts cont + = knownCon env scrut (LitAlt lit) [] case_bndr alts cont | otherwise = -- Prepare the continuation; @@ -1412,17 +1425,18 @@ simplCaseBinder env (Var v) case_bndr -- Failed try [see Note 2 above] -- not (isEvaldUnfolding (idUnfolding v)) - = simplBinder env (zap case_bndr) `thenSmpl` \ (env, case_bndr') -> + = simplBinder env (zapOccInfo case_bndr) `thenSmpl` \ (env, case_bndr') -> returnSmpl (modifyInScope env v case_bndr', case_bndr') -- We could extend the substitution instead, but it would be -- a hack because then the substitution wouldn't be idempotent -- any more (v is an OutId). And this does just as well. - where - zap b = b `setIdOccInfo` NoOccInfo simplCaseBinder env other_scrut case_bndr = simplBinder env case_bndr `thenSmpl` \ (env, case_bndr') -> returnSmpl (env, case_bndr') + +zapOccInfo :: InId -> InId +zapOccInfo b = b `setIdOccInfo` NoOccInfo \end{code} @@ -1502,6 +1516,7 @@ simplDefault :: SimplEnv simplDefault env case_bndr' imposs_cons cont Nothing = return [] -- No default branch + simplDefault env case_bndr' imposs_cons cont (Just rhs) | -- This branch handles the case where we are -- scrutinisng an algebraic data type @@ -1533,7 +1548,11 @@ simplDefault env case_bndr' imposs_cons cont (Just rhs) -- altogether if it can't match [con] -> -- It matches exactly one constructor, so fill it in - do { con_alt <- mkDataConAlt case_bndr' con inst_tys rhs + do { tick (FillInCaseDefault case_bndr') + ; us <- getUniquesSmpl + ; let (ex_tvs, co_tvs, arg_ids) = + dataConRepInstPat us con inst_tys + ; let con_alt = (DataAlt con, ex_tvs ++ co_tvs ++ arg_ids, rhs) ; Just (_, alt') <- simplAlt env [] case_bndr' cont con_alt -- The simplAlt must succeed with Just because we have -- already filtered out construtors that can't match @@ -1541,7 +1560,7 @@ simplDefault env case_bndr' imposs_cons cont (Just rhs) two_or_more -> simplify_default (map DataAlt gadt_imposs ++ imposs_cons) - | otherwise + | otherwise = simplify_default imposs_cons where cant_match tys data_con = not (dataConCanMatch data_con tys) @@ -1552,29 +1571,6 @@ simplDefault env case_bndr' imposs_cons cont (Just rhs) ; rhs' <- simplExprC env' rhs cont ; return [(DEFAULT, [], rhs')] } -mkDataConAlt :: Id -> DataCon -> [OutType] -> InExpr -> SimplM InAlt --- Make a data-constructor alternative to replace the DEFAULT case --- NB: there's something a bit bogus here, because we put OutTypes into an InAlt -mkDataConAlt case_bndr con tys rhs - = do { tick (FillInCaseDefault case_bndr) - ; args <- mk_args con tys - ; return (DataAlt con, args, rhs) } - where - mk_args con inst_tys - = do { (tv_bndrs, inst_tys') <- mk_tv_bndrs con inst_tys - ; let arg_tys = dataConInstArgTys con inst_tys' - ; arg_ids <- mapM (newId FSLIT("a")) arg_tys - ; returnSmpl (tv_bndrs ++ arg_ids) } - - mk_tv_bndrs con inst_tys - | isVanillaDataCon con - = return ([], inst_tys) - | otherwise - = do { tv_uniqs <- getUniquesSmpl - ; let new_tvs = zipWith mk tv_uniqs (dataConTyVars con) - mk uniq tv = mkTyVar (mkSysTvName uniq FSLIT("t")) (tyVarKind tv) - ; return (new_tvs, mkTyVarTys new_tvs) } - simplAlt :: SimplEnv -> [AltCon] -- These constructors can't be present when -- matching this alternative @@ -1609,7 +1605,6 @@ simplAlt env handled_cons case_bndr' cont' (LitAlt lit, bndrs, rhs) env' = mk_rhs_env env case_bndr' (mkUnfolding False (Lit lit)) simplAlt env handled_cons case_bndr' cont' (DataAlt con, vs, rhs) - | isVanillaDataCon con = -- Deal with the pattern-bound variables -- Mark the ones that are in ! positions in the data constructor -- as certainly-evaluated. @@ -1621,50 +1616,11 @@ simplAlt env handled_cons case_bndr' cont' (DataAlt con, vs, rhs) -- Bind the case-binder to (con args) let unf = mkUnfolding False (mkConApp con con_args) inst_tys' = tyConAppArgs (idType case_bndr') - con_args = map Type inst_tys' ++ map varToCoreExpr vs' + con_args = map Type inst_tys' ++ varsToCoreExprs vs' env' = mk_rhs_env env case_bndr' unf in simplExprC env' rhs cont' `thenSmpl` \ rhs' -> returnSmpl (Just (emptyVarEnv, (DataAlt con, vs', rhs'))) - - | otherwise -- GADT case - = let - (tvs,ids) = span isTyVar vs - in - simplBinders env tvs `thenSmpl` \ (env1, tvs') -> - case coreRefineTys con tvs' (idType case_bndr') of { - Nothing -- Inaccessible - | opt_PprStyle_Debug -- Hack: if debugging is on, generate an error case - -- so we can see it - -> let rhs' = mkApps (Var eRROR_ID) - [Type (substTy env (exprType rhs)), - Lit (mkStringLit "Impossible alternative (GADT)")] - in - simplBinders env1 ids `thenSmpl` \ (env2, ids') -> - returnSmpl (Just (emptyVarEnv, (DataAlt con, tvs' ++ ids', rhs'))) - - | otherwise -- Filter out the inaccessible branch - -> return Nothing ; - - Just refine@(tv_subst_env, _) -> -- The normal case - - let - env2 = refineSimplEnv env1 refine - -- Simplify the Ids in the refined environment, so their types - -- reflect the refinement. Usually this doesn't matter, but it helps - -- in mkDupableAlt, when we want to float a lambda that uses these binders - -- Furthermore, it means the binders contain maximal type information - in - simplBinders env2 (add_evals con ids) `thenSmpl` \ (env3, ids') -> - let unf = mkUnfolding False con_app - con_app = mkConApp con con_args - con_args = map varToCoreExpr vs' -- NB: no inst_tys' - env_w_unf = mk_rhs_env env3 case_bndr' unf - vs' = tvs' ++ ids' - in - simplExprC env_w_unf rhs cont' `thenSmpl` \ rhs' -> - returnSmpl (Just (tv_subst_env, (DataAlt con, vs', rhs'))) } - where -- add_evals records the evaluated-ness of the bound variables of -- a case pattern. This is *important*. Consider @@ -1692,8 +1648,9 @@ simplAlt env handled_cons case_bndr' cont' (DataAlt con, vs, rhs) -- If the case binder is alive, then we add the unfolding -- case_bndr = C vs -- to the envt; so vs are now very much alive + -- Note [Aug06] I can't see why this actually matters zap_occ_info | isDeadBinder case_bndr' = \id -> id - | otherwise = \id -> id `setIdOccInfo` NoOccInfo + | otherwise = zapOccInfo mk_rhs_env env case_bndr' case_bndr_unf = modifyInScope env case_bndr' (case_bndr' `setIdUnfolding` case_bndr_unf) @@ -1720,54 +1677,66 @@ and then All this should happen in one sweep. \begin{code} -knownCon :: SimplEnv -> AltCon -> [OutExpr] +knownCon :: SimplEnv -> OutExpr -> AltCon -> [OutExpr] -> InId -> [InAlt] -> SimplCont -> SimplM FloatsWithExpr -knownCon env con args bndr alts cont - = tick (KnownBranch bndr) `thenSmpl_` +knownCon env scrut 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 + -- This might give rise to a binding with non-atomic args + -- like x = Node (f x) (g x) + -- but simplNonRecX will atomic-ify it 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 -> + simplNonRecX env bndr scrut $ \ env -> simplExprF env rhs cont (DataAlt dc, bs, rhs) - -> ASSERT( n_drop_tys + length bs == length args ) - bind_args env bs (drop n_drop_tys args) $ \ env -> + -> -- ASSERT( n_drop_tys + length bs == length args ) + bind_args env dead_bndr bs (drop n_drop_tys args) $ \ env -> let - con_app = mkConApp dc (take n_drop_tys args ++ con_args) + -- It's useful to bind bndr to scrut, rather than to a fresh + -- binding x = Con arg1 .. argn + -- because very often the scrut is a variable, so we avoid + -- creating, and then subsequently eliminating, a let-binding + -- BUT, if scrut is a not a variable, we must be careful + -- about duplicating the arg redexes; in that case, make + -- a new con-app from the args + bndr_rhs = case scrut of + Var v -> scrut + other -> con_app + con_app = mkConApp dc (take n_drop_tys args ++ con_args) con_args = [substExpr env (varToCoreExpr b) | b <- bs] -- args are aready OutExprs, but bs are InIds in - simplNonRecX env bndr con_app $ \ env -> + simplNonRecX env bndr bndr_rhs $ \ env -> simplExprF env rhs cont where - n_drop_tys | isVanillaDataCon dc = tyConArity (dataConTyCon dc) - | otherwise = 0 - -- Vanilla data constructors lack type arguments in the pattern + dead_bndr = isDeadBinder bndr + n_drop_tys = tyConArity (dataConTyCon dc) -- Ugh! -bind_args env [] _ thing_inside = thing_inside env +bind_args env dead_bndr [] _ thing_inside = thing_inside env -bind_args env (b:bs) (Type ty : args) thing_inside +bind_args env dead_bndr (b:bs) (Type ty : args) thing_inside = ASSERT( isTyVar b ) - bind_args (extendTvSubst env b ty) bs args thing_inside + bind_args (extendTvSubst env b ty) dead_bndr bs args thing_inside -bind_args env (b:bs) (arg : args) thing_inside +bind_args env dead_bndr (b:bs) (arg : args) thing_inside = ASSERT( isId b ) - simplNonRecX env b arg $ \ env -> - bind_args env bs args thing_inside + let + b' = if dead_bndr then b else zapOccInfo b + -- Note that the binder might be "dead", because it doesn't occur + -- in the RHS; and simplNonRecX may therefore discard it via postInlineUnconditionally + -- Nevertheless we must keep it if the case-binder is alive, because it may + -- be used in teh con_app + in + simplNonRecX env b' arg $ \ env -> + bind_args env dead_bndr bs args thing_inside \end{code} @@ -1830,16 +1799,85 @@ mkDupableCont env cont@(ArgOf _ arg_ty _ _) -- let $j = \a -> ...strict-fn... -- in $j [...hole...] -mkDupableCont env (ApplyTo _ arg se cont) +mkDupableCont env (ApplyTo _ arg mb_se cont) = -- e.g. [...hole...] (...arg...) -- ==> -- let a = ...arg... -- in [...hole...] a do { (floats, (dup_cont, nondup_cont)) <- mkDupableCont env cont ; addFloats env floats $ \ env -> do - { arg1 <- simplExpr (setInScope se env) arg + { arg1 <- simplArg env arg mb_se ; (floats2, arg2) <- mkDupableArg env arg1 - ; return (floats2, (ApplyTo OkToDup arg2 (zapSubstEnv se) dup_cont, nondup_cont)) }} + ; return (floats2, (ApplyTo OkToDup arg2 Nothing dup_cont, nondup_cont)) }} + +mkDupableCont env cont@(Select _ case_bndr [(_,bs,rhs)] se case_cont) +-- | not (exprIsDupable rhs && contIsDupable case_cont) -- See notes below +-- | not (isDeadBinder case_bndr) + | all isDeadBinder bs + = returnSmpl (emptyFloats env, (mkBoringStop scrut_ty, cont)) + where + scrut_ty = substTy se (idType case_bndr) + +{- Note [Single-alternative cases] + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +This case is just like the ArgOf case. Here's an example: + data T a = MkT !a + ...(MkT (abs x))... +Then we get + case (case x of I# x' -> + case x' <# 0# of + True -> I# (negate# x') + False -> I# x') of y { + DEFAULT -> MkT y +Because the (case x) has only one alternative, we'll transform to + case x of I# x' -> + case (case x' <# 0# of + True -> I# (negate# x') + False -> I# x') of y { + DEFAULT -> MkT y +But now we do *NOT* want to make a join point etc, giving + case x of I# x' -> + let $j = \y -> MkT y + in case x' <# 0# of + True -> $j (I# (negate# x')) + False -> $j (I# x') +In this case the $j will inline again, but suppose there was a big +strict computation enclosing the orginal call to MkT. Then, it won't +"see" the MkT any more, because it's big and won't get duplicated. +And, what is worse, nothing was gained by the case-of-case transform. + +When should use this case of mkDupableCont? +However, matching on *any* single-alternative case is a *disaster*; + e.g. case (case ....) of (a,b) -> (# a,b #) + We must push the outer case into the inner one! +Other choices: + + * Match [(DEFAULT,_,_)], but in the common case of Int, + the alternative-filling-in code turned the outer case into + case (...) of y { I# _ -> MkT y } + + * Match on single alternative plus (not (isDeadBinder case_bndr)) + Rationale: pushing the case inwards won't eliminate the construction. + But there's a risk of + case (...) of y { (a,b) -> let z=(a,b) in ... } + Now y looks dead, but it'll come alive again. Still, this + seems like the best option at the moment. + + * Match on single alternative plus (all (isDeadBinder bndrs)) + Rationale: this is essentially seq. + + * Match when the rhs is *not* duplicable, and hence would lead to a + join point. This catches the disaster-case above. We can test + the *un-simplified* rhs, which is fine. It might get bigger or + smaller after simplification; if it gets smaller, this case might + fire next time round. NB also that we must test contIsDupable + case_cont *btoo, because case_cont might be big! + + HOWEVER: I found that this version doesn't work well, because + we can get let x = case (...) of { small } in ...case x... + When x is inlined into its full context, we find that it was a bad + idea to have pushed the outer case inside the (...) case. +-} mkDupableCont env (Select _ case_bndr alts se cont) = -- e.g. (case [...hole...] of { pi -> ei }) @@ -1976,7 +2014,7 @@ mkDupableAlt env case_bndr' cont alt then newId FSLIT("w") realWorldStatePrimTy `thenSmpl` \ rw_id -> returnSmpl ([rw_id], [Var realWorldPrimId]) else - returnSmpl (used_bndrs', map varToCoreExpr used_bndrs') + returnSmpl (used_bndrs', varsToCoreExprs used_bndrs') ) `thenSmpl` \ (final_bndrs', final_args) -> -- See comment about "$j" name above