deps/v8/src/effects.h
// 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/v8.h"
#include "src/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;
Bounds bounds;
Effect() : modality(DEFINITE) {}
explicit Effect(Bounds b, Modality m = DEFINITE) : modality(m), bounds(b) {}
// The unknown effect.
static Effect Unknown(Zone* zone) {
return Effect(Bounds::Unbounded(zone), POSSIBLE);
}
static Effect Forget(Zone* zone) {
return Effect(Bounds::Unbounded(zone), DEFINITE);
}
// Sequential composition, as in 'e1; e2'.
static Effect Seq(Effect e1, Effect e2, Zone* zone) {
if (e2.modality == DEFINITE) return e2;
return Effect(Bounds::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(
Bounds::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());
}
Bounds LookupBounds(Var var) {
Effect effect = Lookup(var);
return effect.modality == Effect::DEFINITE
? effect.bounds : Bounds::Unbounded(Base::zone());
}
// 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 v8::internal
#endif // V8_EFFECTS_H_