Revert "Implement simple effect typing for variables" and "Handle switch effects".

src/effects.h

-// Copyright 2013 the V8 project authors. All rights reserved.
-// Redistribution and use in source and binary forms, with or without
-// modification, are permitted provided that the following conditions are
-// met:
-//
-//     * Redistributions of source code must retain the above copyright
-//       notice, this list of conditions and the following disclaimer.
-//     * Redistributions in binary form must reproduce the above
-//       copyright notice, this list of conditions and the following
-//       disclaimer in the documentation and/or other materials provided
-//       with the distribution.
-//     * Neither the name of Google Inc. nor the names of its
-//       contributors may be used to endorse or promote products derived
-//       from this software without specific prior written permission.
-//
-// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
-// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
-// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
-// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
-// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
-// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
-// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
-// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
-// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
-// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
-// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-
-#ifndef V8_EFFECTS_H_
-#define V8_EFFECTS_H_
-
-#include "v8.h"
-
-#include "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() {}
-  Effect(Bounds b, Modality m = DEFINITE) : modality(m), bounds(b) {}
-
-  // The unknown effect.
-  static Effect Unknown(Isolate* isolate) {
-    return Effect(Bounds::Unbounded(isolate), POSSIBLE);
-  }
-
-  static Effect Forget(Isolate* isolate) {
-    return Effect(Bounds::Unbounded(isolate), DEFINITE);
-  }
-
-  // Sequential composition, as in 'e1; e2'.
-  static Effect Seq(Effect e1, Effect e2, Isolate* isolate) {
-    if (e2.modality == DEFINITE) return e2;
-    return Effect(Bounds::Either(e1.bounds, e2.bounds, isolate), e1.modality);
-  }
-
-  // Alternative composition, as in 'cond ? e1 : e2'.
-  static Effect Alt(Effect e1, Effect e2, Isolate* isolate) {
-    return Effect(
-        Bounds::Either(e1.bounds, e2.bounds, isolate),
-        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 Find(var, &locator)
-        ? locator.value() : Effect::Unknown(Base::isolate());
-  }
-
-  Bounds LookupBounds(Var var) {
-    Effect effect = Lookup(var);
-    return effect.modality == Effect::DEFINITE
-        ? effect.bounds : Bounds::Unbounded(Base::isolate());
-  }
-
-  // Sequential composition.
-  void Seq(Var var, Effect effect) {
-    Locator locator;
-    if (!Insert(var, &locator)) {
-      effect = Effect::Seq(locator.value(), effect, Base::isolate());
-    }
-    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 (!Insert(var, &locator)) {
-      effect = Effect::Alt(locator.value(), effect, Base::isolate());
-    }
-    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::isolate()), 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(); }
-  Isolate* isolate() { return zone()->isolate(); }
-
-  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) {
-    ASSERT(var != kNoVar);
-    return map_->Contains(var);
-  }
-  bool Find(Var var, Locator* locator) {
-    ASSERT(var != kNoVar);
-    return map_->Find(var, locator);
-  }
-  bool Insert(Var var, Locator* locator) {
-    ASSERT(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; }
-  Isolate* isolate() { return zone()->isolate(); }
-
-  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) {
-    ASSERT(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) {
-    ASSERT(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) {
-  ASSERT(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();
-    ASSERT(!this->is_empty());
-    return result;
-  }
-};
-
-} }  // namespace v8::internal
-
-#endif  // V8_EFFECTS_H_