X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=compiler%2FsimplCore%2FSimplUtils.lhs;h=693644f258096743b55c8022ad9da8508c4f0fae;hb=088962101d8ad4ba5455e295258df009c72315f2;hp=1e510421e72a1c94632f5c100e6faadc5557f97f;hpb=f2dcf256399e9a2de6343c625630b51f8abf4863;p=ghc-hetmet.git diff --git a/compiler/simplCore/SimplUtils.lhs b/compiler/simplCore/SimplUtils.lhs index 1e51042..693644f 100644 --- a/compiler/simplCore/SimplUtils.lhs +++ b/compiler/simplCore/SimplUtils.lhs @@ -25,7 +25,7 @@ module SimplUtils ( import SimplEnv import DynFlags ( SimplifierSwitch(..), SimplifierMode(..), - DynFlag(..), dopt ) + DynFlags, DynFlag(..), dopt ) import StaticFlags ( opt_UF_UpdateInPlace, opt_SimplNoPreInlining, opt_RulesOff ) import CoreSyn @@ -79,8 +79,10 @@ data SimplCont -- Strict contexts SimplCont | ApplyTo DupFlag - InExpr SimplEnv -- The argument, as yet unsimplified, - SimplCont -- and its environment + CoreExpr -- The argument + (Maybe SimplEnv) -- (Just se) => the arg is un-simplified and this is its subst-env + -- Nothing => the arg is already simplified; don't repeatedly simplify it! + SimplCont -- and its environment | Select DupFlag InId [InAlt] SimplEnv -- The case binder, alts, and subst-env @@ -181,18 +183,18 @@ countArgs (ApplyTo _ arg se cont) = 1 + countArgs cont countArgs other = 0 ------------------- -pushContArgs :: SimplEnv -> [OutArg] -> SimplCont -> SimplCont +pushContArgs ::[OutArg] -> SimplCont -> SimplCont -- Pushes args with the specified environment -pushContArgs env [] cont = cont -pushContArgs env (arg : args) cont = ApplyTo NoDup arg env (pushContArgs env args cont) +pushContArgs [] cont = cont +pushContArgs (arg : args) cont = ApplyTo NoDup arg Nothing (pushContArgs args cont) \end{code} \begin{code} getContArgs :: SwitchChecker -> OutId -> SimplCont - -> ([(InExpr, SimplEnv, Bool)], -- Arguments; the Bool is true for strict args - SimplCont) -- Remaining continuation + -> ([(InExpr, Maybe SimplEnv, Bool)], -- Arguments; the Bool is true for strict args + SimplCont) -- Remaining continuation -- getContArgs id k = (args, k', inl) -- args are the leading ApplyTo items in k -- (i.e. outermost comes first) @@ -374,12 +376,12 @@ interestingCallContext :: Bool -- False <=> no args at all interestingCallContext some_args some_val_args cont = interesting cont where - interesting (Select _ _ _ _ _) = some_args - interesting (ApplyTo _ _ _ _) = True -- Can happen if we have (coerce t (f x)) y + interesting (Select {}) = some_args + interesting (ApplyTo {}) = True -- Can happen if we have (coerce t (f x)) y -- Perhaps True is a bit over-keen, but I've -- seen (coerce f) x, where f has an INLINE prag, -- So we have to give some motivaiton for inlining it - interesting (ArgOf _ _ _ _) = some_val_args + interesting (ArgOf {}) = some_val_args interesting (Stop ty _ interesting) = some_val_args && interesting interesting (CoerceIt _ cont) = interesting cont -- If this call is the arg of a strict function, the context @@ -695,7 +697,13 @@ our new view that inlining is like a RULE, so I'm sticking to the 'active' story for now. \begin{code} -postInlineUnconditionally :: SimplEnv -> TopLevelFlag -> OutId -> OccInfo -> OutExpr -> Unfolding -> Bool +postInlineUnconditionally + :: SimplEnv -> TopLevelFlag + -> InId -- The binder (an OutId would be fine too) + -> OccInfo -- From the InId + -> OutExpr + -> Unfolding + -> Bool postInlineUnconditionally env top_lvl bndr occ_info rhs unfolding | not active = False | isLoopBreaker occ_info = False @@ -703,19 +711,28 @@ postInlineUnconditionally env top_lvl bndr occ_info rhs unfolding | exprIsTrivial rhs = True | otherwise = case occ_info of - OneOcc in_lam one_br int_cxt - -> (one_br || smallEnoughToInline unfolding) -- Small enough to dup + -- The point of examining occ_info here is that for *non-values* + -- that occur outside a lambda, the call-site inliner won't have + -- a chance (becuase it doesn't know that the thing + -- only occurs once). The pre-inliner won't have gotten + -- it either, if the thing occurs in more than one branch + -- So the main target is things like + -- let x = f y in + -- case v of + -- True -> case x of ... + -- False -> case x of ... + -- I'm not sure how important this is in practice + OneOcc in_lam one_br int_cxt -- OneOcc => no work-duplication issue + -> smallEnoughToInline unfolding -- Small enough to dup -- ToDo: consider discount on smallEnoughToInline if int_cxt is true -- - -- NB: Do we want to inline arbitrarily big things becuase - -- one_br is True? that can lead to inline cascades. But - -- preInlineUnconditionlly has dealt with all the common cases - -- so perhaps it's worth the risk. Here's an example - -- let f = if b then Left (\x.BIG) else Right (\y.BIG) - -- in \y. ....f.... - -- We can't preInlineUnconditionally because that woud invalidate - -- the occ info for b. Yet f is used just once, and duplicating - -- the case work is fine (exprIsCheap). + -- NB: Do NOT inline arbitrarily big things, even if one_br is True + -- Reason: doing so risks exponential behaviour. We simplify a big + -- expression, inline it, and simplify it again. But if the + -- very same thing happens in the big expression, we get + -- exponential cost! + -- PRINCIPLE: when we've already simplified an expression once, + -- make sure that we only inline it if it's reasonably small. && ((isNotTopLevel top_lvl && not in_lam) || -- But outside a lambda, we want to be reasonably aggressive @@ -731,18 +748,25 @@ postInlineUnconditionally env top_lvl bndr occ_info rhs unfolding -- int_cxt to prevent us inlining inside a lambda without some -- good reason. See the notes on int_cxt in preInlineUnconditionally + IAmDead -> True -- 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 ... + other -> False - -- The point here is that for *non-values* that occur - -- outside a lambda, the call-site inliner won't have - -- a chance (becuase it doesn't know that the thing - -- only occurs once). The pre-inliner won't have gotten - -- it either, if the thing occurs in more than one branch - -- So the main target is things like - -- let x = f y in - -- case v of - -- True -> case x of ... - -- False -> case x of ... - -- I'm not sure how important this is in practice + +-- Here's an example that we don't handle well: +-- let f = if b then Left (\x.BIG) else Right (\y.BIG) +-- in \y. ....case f of {...} .... +-- Here f is used just once, and duplicating the case work is fine (exprIsCheap). +-- But +-- * We can't preInlineUnconditionally because that woud invalidate +-- the occ info for b. +-- * We can't postInlineUnconditionally because the RHS is big, and +-- that risks exponential behaviour +-- * We can't call-site inline, because the rhs is big +-- Alas! + where active = case getMode env of SimplGently -> isAlwaysActive prag @@ -818,7 +842,7 @@ mkLam env bndrs body cont | dopt Opt_DoLambdaEtaExpansion dflags, any isRuntimeVar bndrs - = tryEtaExpansion body `thenSmpl` \ body' -> + = tryEtaExpansion dflags body `thenSmpl` \ body' -> returnSmpl (emptyFloats env, mkLams bndrs body') {- Sept 01: I'm experimenting with getting the @@ -901,13 +925,13 @@ when computing arity; and etaExpand adds the coerces as necessary when actually computing the expansion. \begin{code} -tryEtaExpansion :: OutExpr -> SimplM OutExpr +tryEtaExpansion :: DynFlags -> OutExpr -> SimplM OutExpr -- There is at least one runtime binder in the binders -tryEtaExpansion body +tryEtaExpansion dflags body = getUniquesSmpl `thenSmpl` \ us -> returnSmpl (etaExpand fun_arity us body (exprType body)) where - fun_arity = exprEtaExpandArity body + fun_arity = exprEtaExpandArity dflags body \end{code}