Implement simple effect typing for variables

src/effects.h

Index: src/effects.h
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+// 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_