X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplify.lhs;h=b30ed048e48f72607d4c88d4cd760c043423d874;hb=cb8efb737dae6e41f28d471883df67724a33120f;hp=2003c086c8dc2e55c43cdf83ccbb9e867530a59e;hpb=eba4dfc2e9cf3caae2cdb6e54558972745a121f7;p=ghc-hetmet.git diff --git a/compiler/simplCore/Simplify.lhs b/compiler/simplCore/Simplify.lhs index 2003c08..b30ed04 100644 --- a/compiler/simplCore/Simplify.lhs +++ b/compiler/simplCore/Simplify.lhs @@ -320,13 +320,7 @@ 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 +345,21 @@ 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 +367,21 @@ 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')]) } + + | 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 +{- 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. @@ -381,23 +398,6 @@ simplNonRecX env bndr new_rhs thing_inside -- NB: completeLazyBind uses postInlineUnconditionally; no need to do that here -} - - | otherwise - = simplBinder env bndr `thenSmpl` \ (env, bndr') -> - completeNonRecX env False {- Non-strict; pessimistic -} - bndr bndr' new_rhs thing_inside - -completeNonRecX env is_strict old_bndr new_bndr new_rhs thing_inside - = mkAtomicArgs is_strict - True {- OK to float unlifted -} - new_rhs `thenSmpl` \ (aux_binds, rhs2) -> - - -- Make the arguments atomic if necessary, - -- adding suitable bindings - addAtomicBindsE env (fromOL aux_binds) $ \ env -> - completeLazyBind env NotTopLevel - old_bndr new_bndr rhs2 `thenSmpl` \ (floats, env) -> - addFloats env floats thing_inside \end{code} @@ -596,6 +596,7 @@ 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 @@ -634,6 +635,7 @@ 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 @@ -1155,6 +1157,38 @@ 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 @@ -1201,25 +1235,6 @@ 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} @@ -1399,17 +1414,18 @@ 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} @@ -1679,8 +1695,9 @@ 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) @@ -1727,7 +1744,7 @@ knownCon env scrut con args bndr alts cont (DataAlt dc, bs, rhs) -> ASSERT( n_drop_tys + length bs == length args ) - bind_args env bs (drop n_drop_tys args) $ \ env -> + bind_args env dead_bndr bs (drop n_drop_tys args) $ \ env -> let -- It's useful to bind bndr to scrut, rather than to a fresh -- binding x = Con arg1 .. argn @@ -1746,21 +1763,29 @@ knownCon env scrut con args bndr alts cont simplNonRecX env bndr bndr_rhs $ \ env -> simplExprF env rhs cont where + dead_bndr = isDeadBinder bndr n_drop_tys | isVanillaDataCon dc = tyConArity (dataConTyCon dc) | otherwise = 0 -- Vanilla data constructors lack type arguments in the pattern -- Ugh! -bind_args env [] _ thing_inside = thing_inside env +bind_args env 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} @@ -1834,42 +1859,74 @@ mkDupableCont env (ApplyTo _ arg mb_se cont) ; (floats2, arg2) <- mkDupableArg env arg1 ; return (floats2, (ApplyTo OkToDup arg2 Nothing dup_cont, nondup_cont)) }} -mkDupableCont env cont@(Select _ case_bndr [_] se _) +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) - -- This case is just like the previous one. 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. - -- - -- NB: Originally I matched [(DEFAULT,_,_)], but in the common - -- case of Int, the alternative-filling-in code turned the outer case into - -- case (...) of y { I# _ -> MkT y } - -- and that doesn't match the DEFAULT! - -- Now I match on any single-alternative case. - -- I hope that is the right thing to do! + +{- 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 })