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-// Copyright 2013 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef V8_EFFECTS_H_
-#define V8_EFFECTS_H_
-
-#include "src/ast/ast-types.h"
-
-namespace v8 {
-namespace internal {
-
-
-// A simple struct to represent (write) effects. A write is represented as a
-// modification of type bounds (e.g. of a variable).
-//
-// An effect can either be definite, if the write is known to have taken place,
-// or 'possible', if it was optional. The difference is relevant when composing
-// effects.
-//
-// There are two ways to compose effects: sequentially (they happen one after
-// the other) or alternatively (either one or the other happens). A definite
-// effect cancels out any previous effect upon sequencing. A possible effect
-// merges into a previous effect, i.e., type bounds are merged. Alternative
-// composition always merges bounds. It yields a possible effect if at least
-// one was only possible.
-struct Effect {
- enum Modality { POSSIBLE, DEFINITE };
-
- Modality modality;
- AstBounds bounds;
-
- Effect() : modality(DEFINITE) {}
- explicit Effect(AstBounds b, Modality m = DEFINITE)
- : modality(m), bounds(b) {}
-
- // The unknown effect.
- static Effect Unknown(Zone* zone) {
- return Effect(AstBounds::Unbounded(), POSSIBLE);
- }
-
- static Effect Forget(Zone* zone) {
- return Effect(AstBounds::Unbounded(), DEFINITE);
- }
-
- // Sequential composition, as in 'e1; e2'.
- static Effect Seq(Effect e1, Effect e2, Zone* zone) {
- if (e2.modality == DEFINITE) return e2;
- return Effect(AstBounds::Either(e1.bounds, e2.bounds, zone), e1.modality);
- }
-
- // Alternative composition, as in 'cond ? e1 : e2'.
- static Effect Alt(Effect e1, Effect e2, Zone* zone) {
- return Effect(AstBounds::Either(e1.bounds, e2.bounds, zone),
- e1.modality == POSSIBLE ? POSSIBLE : e2.modality);
- }
-};
-
-
-// Classes encapsulating sets of effects on variables.
-//
-// Effects maps variables to effects and supports sequential and alternative
-// composition.
-//
-// NestedEffects is an incremental representation that supports persistence
-// through functional extension. It represents the map as an adjoin of a list
-// of maps, whose tail can be shared.
-//
-// Both classes provide similar interfaces, implemented in parts through the
-// EffectsMixin below (using sandwich style, to work around the style guide's
-// MI restriction).
-//
-// We also (ab)use Effects/NestedEffects as a representation for abstract
-// store typings. In that case, only definite effects are of interest.
-
-template<class Var, class Base, class Effects>
-class EffectsMixin: public Base {
- public:
- explicit EffectsMixin(Zone* zone) : Base(zone) {}
-
- Effect Lookup(Var var) {
- Locator locator;
- return this->Find(var, &locator)
- ? locator.value() : Effect::Unknown(Base::zone());
- }
-
- AstBounds LookupBounds(Var var) {
- Effect effect = Lookup(var);
- return effect.modality == Effect::DEFINITE ? effect.bounds
- : AstBounds::Unbounded();
- }
-
- // Sequential composition.
- void Seq(Var var, Effect effect) {
- Locator locator;
- if (!this->Insert(var, &locator)) {
- effect = Effect::Seq(locator.value(), effect, Base::zone());
- }
- locator.set_value(effect);
- }
-
- void Seq(Effects that) {
- SeqMerger<EffectsMixin> merge = { *this };
- that.ForEach(&merge);
- }
-
- // Alternative composition.
- void Alt(Var var, Effect effect) {
- Locator locator;
- if (!this->Insert(var, &locator)) {
- effect = Effect::Alt(locator.value(), effect, Base::zone());
- }
- locator.set_value(effect);
- }
-
- void Alt(Effects that) {
- AltWeakener<EffectsMixin> weaken = { *this, that };
- this->ForEach(&weaken);
- AltMerger<EffectsMixin> merge = { *this };
- that.ForEach(&merge);
- }
-
- // Invalidation.
- void Forget() {
- Overrider override = {
- Effect::Forget(Base::zone()), Effects(Base::zone()) };
- this->ForEach(&override);
- Seq(override.effects);
- }
-
- protected:
- typedef typename Base::Locator Locator;
-
- template<class Self>
- struct SeqMerger {
- void Call(Var var, Effect effect) { self.Seq(var, effect); }
- Self self;
- };
-
- template<class Self>
- struct AltMerger {
- void Call(Var var, Effect effect) { self.Alt(var, effect); }
- Self self;
- };
-
- template<class Self>
- struct AltWeakener {
- void Call(Var var, Effect effect) {
- if (effect.modality == Effect::DEFINITE && !other.Contains(var)) {
- effect.modality = Effect::POSSIBLE;
- Locator locator;
- self.Insert(var, &locator);
- locator.set_value(effect);
- }
- }
- Self self;
- Effects other;
- };
-
- struct Overrider {
- void Call(Var var, Effect effect) { effects.Seq(var, new_effect); }
- Effect new_effect;
- Effects effects;
- };
-};
-
-
-template<class Var, Var kNoVar> class Effects;
-template<class Var, Var kNoVar> class NestedEffectsBase;
-
-template<class Var, Var kNoVar>
-class EffectsBase {
- public:
- explicit EffectsBase(Zone* zone) : map_(new(zone) Mapping(zone)) {}
-
- bool IsEmpty() { return map_->is_empty(); }
-
- protected:
- friend class NestedEffectsBase<Var, kNoVar>;
- friend class
- EffectsMixin<Var, NestedEffectsBase<Var, kNoVar>, Effects<Var, kNoVar> >;
-
- Zone* zone() { return map_->allocator().zone(); }
-
- struct SplayTreeConfig {
- typedef Var Key;
- typedef Effect Value;
- static const Var kNoKey = kNoVar;
- static Effect NoValue() { return Effect(); }
- static int Compare(int x, int y) { return y - x; }
- };
- typedef ZoneSplayTree<SplayTreeConfig> Mapping;
- typedef typename Mapping::Locator Locator;
-
- bool Contains(Var var) {
- DCHECK(var != kNoVar);
- return map_->Contains(var);
- }
- bool Find(Var var, Locator* locator) {
- DCHECK(var != kNoVar);
- return map_->Find(var, locator);
- }
- bool Insert(Var var, Locator* locator) {
- DCHECK(var != kNoVar);
- return map_->Insert(var, locator);
- }
-
- template<class Callback>
- void ForEach(Callback* callback) {
- return map_->ForEach(callback);
- }
-
- private:
- Mapping* map_;
-};
-
-template<class Var, Var kNoVar>
-const Var EffectsBase<Var, kNoVar>::SplayTreeConfig::kNoKey;
-
-template<class Var, Var kNoVar>
-class Effects: public
- EffectsMixin<Var, EffectsBase<Var, kNoVar>, Effects<Var, kNoVar> > {
- public:
- explicit Effects(Zone* zone)
- : EffectsMixin<Var, EffectsBase<Var, kNoVar>, Effects<Var, kNoVar> >(zone)
- {}
-};
-
-
-template<class Var, Var kNoVar>
-class NestedEffectsBase {
- public:
- explicit NestedEffectsBase(Zone* zone) : node_(new(zone) Node(zone)) {}
-
- template<class Callback>
- void ForEach(Callback* callback) {
- if (node_->previous) NestedEffectsBase(node_->previous).ForEach(callback);
- node_->effects.ForEach(callback);
- }
-
- Effects<Var, kNoVar> Top() { return node_->effects; }
-
- bool IsEmpty() {
- for (Node* node = node_; node != NULL; node = node->previous) {
- if (!node->effects.IsEmpty()) return false;
- }
- return true;
- }
-
- protected:
- typedef typename EffectsBase<Var, kNoVar>::Locator Locator;
-
- Zone* zone() { return node_->zone; }
-
- void push() { node_ = new(node_->zone) Node(node_->zone, node_); }
- void pop() { node_ = node_->previous; }
- bool is_empty() { return node_ == NULL; }
-
- bool Contains(Var var) {
- DCHECK(var != kNoVar);
- for (Node* node = node_; node != NULL; node = node->previous) {
- if (node->effects.Contains(var)) return true;
- }
- return false;
- }
-
- bool Find(Var var, Locator* locator) {
- DCHECK(var != kNoVar);
- for (Node* node = node_; node != NULL; node = node->previous) {
- if (node->effects.Find(var, locator)) return true;
- }
- return false;
- }
-
- bool Insert(Var var, Locator* locator);
-
- private:
- struct Node: ZoneObject {
- Zone* zone;
- Effects<Var, kNoVar> effects;
- Node* previous;
- explicit Node(Zone* zone, Node* previous = NULL)
- : zone(zone), effects(zone), previous(previous) {}
- };
-
- explicit NestedEffectsBase(Node* node) : node_(node) {}
-
- Node* node_;
-};
-
-
-template<class Var, Var kNoVar>
-bool NestedEffectsBase<Var, kNoVar>::Insert(Var var, Locator* locator) {
- DCHECK(var != kNoVar);
- if (!node_->effects.Insert(var, locator)) return false;
- Locator shadowed;
- for (Node* node = node_->previous; node != NULL; node = node->previous) {
- if (node->effects.Find(var, &shadowed)) {
- // Initialize with shadowed entry.
- locator->set_value(shadowed.value());
- return false;
- }
- }
- return true;
-}
-
-
-template<class Var, Var kNoVar>
-class NestedEffects: public
- EffectsMixin<Var, NestedEffectsBase<Var, kNoVar>, Effects<Var, kNoVar> > {
- public:
- explicit NestedEffects(Zone* zone) :
- EffectsMixin<Var, NestedEffectsBase<Var, kNoVar>, Effects<Var, kNoVar> >(
- zone) {}
-
- // Create an extension of the current effect set. The current set should not
- // be modified while the extension is in use.
- NestedEffects Push() {
- NestedEffects result = *this;
- result.push();
- return result;
- }
-
- NestedEffects Pop() {
- NestedEffects result = *this;
- result.pop();
- DCHECK(!this->is_empty());
- return result;
- }
-};
-
-} // namespace internal
-} // namespace v8
-
-#endif // V8_EFFECTS_H_