First implementation of HUnique<T> and HUniqueSet<T>, which is supposed to replace UniqueValueId.

src/unique.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_HYDROGEN_UNIQUE_H_
+#define V8_HYDROGEN_UNIQUE_H_
+
+#include "handles.h"
+#include "utils.h"
+#include "zone.h"
+
+namespace v8 {
+namespace internal {
+
+
+template <typename T>
+class UniqueSet;
+
+
+// Represents a handle to an object on the heap, but with the additional
+// ability of checking for equality and hashing without accessing the heap.
+//
+// Creating a Unique<T> requires first dereferencing the handle to obtain
+// the address of the object, which is used as the hashcode and the basis for
+// comparison. The object can be moved later by the GC, but comparison
+// and hashing use the old address of the object, without dereferencing it.
+//
+// Careful! Comparison of two Uniques is only correct if both were created
+// in the same "era" of GC or if at least one is a non-movable object.
+template <typename T>
+class Unique V8_FINAL {
+ public:
+  // TODO(titzer): make private and introduce some builder/owner class.
+  explicit Unique(Handle<T> handle) {
+    if (handle.is_null()) {
+      raw_address_ = NULL;
+    } else {
+      raw_address_ = reinterpret_cast<Address>(*handle);
+      ASSERT_NE(raw_address_, NULL);
+    }
+    handle_ = handle;
+  }
+
+  // Constructor for handling automatic up casting.
+  // Ex. Unique<JSFunction> can be passed when Unique<Object> is expected.
+  template <class S> Unique(Unique<S> uniq) {
+#ifdef DEBUG
+    T* a = NULL;
+    S* b = NULL;
+    a = b;  // Fake assignment to enforce type checks.
+    USE(a);
+#endif
+    raw_address_ = uniq.raw_address_;
+    handle_ = uniq.handle_;  // Creates a new handle sharing the same location.
+  }
+
+  template <typename U>
+  bool operator==(const Unique<U>& other) const {
+    return raw_address_ == other.raw_address_;
+  }
+
+  template <typename U>
+  bool operator!=(const Unique<U>& other) const {
+    return raw_address_ != other.raw_address_;
+  }
+
+  intptr_t Hashcode() const {
+    return reinterpret_cast<intptr_t>(raw_address_);
+  }
+
+  bool IsNull() {
+    return raw_address_ == NULL;
+  }
+
+  // Don't do this unless you have access to the heap!
+  // No, seriously! You can compare and hash and set-ify uniques that were
+  // all created at the same time; please don't dereference.
+  Handle<T> handle() {
+    return handle_;
+  }
+
+  friend class UniqueSet<T>;  // Uses internal details for speed.
+  template <class U>
+  friend class Unique;  // For comparing raw_address values.
+
+ private:
+  Address raw_address_;
+  Handle<T> handle_;
+};
+
+
+template <typename T>
+class UniqueSet V8_FINAL : public ZoneObject {
+ public:
+  // Constructor. A new set will be empty.
+  UniqueSet() : size_(0), capacity_(0), array_(NULL) { }
+
+  // Add a new element to this unique set. Mutates this set. O(|this|).
+  void Add(Unique<T> uniq, Zone* zone) {
+    // Keep the set sorted by the {raw_address} of the unique elements.
+    for (int i = 0; i < size_; i++) {
+      if (array_[i] == uniq) return;
+      if (array_[i].raw_address_ > uniq.raw_address_) {
+        // Insert in the middle.
+        Grow(size_ + 1, zone);
+        for (int j = size_ - 1; j >= i; j--) array_[j + 1] = array_[j];
+        array_[i] = uniq;
+        size_++;
+        return;
+      }
+    }
+    // Append the element to the the end.
+    Grow(size_ + 1, zone);
+    array_[size_++] = uniq;
+  }
+
+  // Compare this set against another set. O(|this|).
+  bool Equals(UniqueSet<T>* that) {
+    if (that->size_ != this->size_) return false;
+    for (int i = 0; i < this->size_; i++) {
+      if (this->array_[i] != that->array_[i]) return false;
+    }
+    return true;
+  }
+
+  // Check if this set is a subset of the given set. O(|this| + |that|).
+  bool IsSubset(UniqueSet<T>* that) {
+    if (that->size_ < this->size_) return false;
+    int j = 0;
+    for (int i = 0; i < this->size_; i++) {
+      Unique<T> sought = this->array_[i];
+      while (true) {
+        if (sought == that->array_[j++]) break;
+        // Fail whenever there are more elements in {this} than {that}.
+        if ((this->size_ - i) > (that->size_ - j)) return false;
+      }
+    }
+    return true;
+  }
+
+  // Returns a new set representing the intersection of this set and the other.
+  // O(|this| + |that|).
+  UniqueSet<T>* Intersect(UniqueSet<T>* that, Zone* zone) {
+    if (that->size_ == 0 || this->size_ == 0) return new(zone) UniqueSet<T>();
+
+    UniqueSet<T>* out = new(zone) UniqueSet<T>();
+    out->Grow(Min(this->size_, that->size_), zone);
+
+    int i = 0, j = 0, k = 0;
+    while (i < this->size_ && j < that->size_) {
+      Unique<T> a = this->array_[i];
+      Unique<T> b = that->array_[j];
+      if (a == b) {
+        out->array_[k++] = a;
+        i++;
+        j++;
+      } else if (a.raw_address_ < b.raw_address_) {
+        i++;
+      } else {
+        j++;
+      }
+    }
+
+    out->size_ = k;
+    return out;
+  }
+
+  // Returns a new set representing the union of this set and the other.
+  // O(|this| + |that|).
+  UniqueSet<T>* Union(UniqueSet<T>* that, Zone* zone) {
+    if (that->size_ == 0) return this->Copy(zone);
+    if (this->size_ == 0) return that->Copy(zone);
+
+    UniqueSet<T>* out = new(zone) UniqueSet<T>();
+    out->Grow(this->size_ + that->size_, zone);
+
+    int i = 0, j = 0, k = 0;
+    while (i < this->size_ && j < that->size_) {
+      Unique<T> a = this->array_[i];
+      Unique<T> b = that->array_[j];
+      if (a == b) {
+        out->array_[k++] = a;
+        i++;
+        j++;
+      } else if (a.raw_address_ < b.raw_address_) {
+        out->array_[k++] = a;
+        i++;
+      } else {
+        out->array_[k++] = b;
+        j++;
+      }
+    }
+
+    while (i < this->size_) out->array_[k++] = this->array_[i++];
+    while (j < that->size_) out->array_[k++] = that->array_[j++];
+
+    out->size_ = k;
+    return out;
+  }
+
+  // Makes an exact copy of this set. O(|this| + |that|).
+  UniqueSet<T>* Copy(Zone* zone) {
+    UniqueSet<T>* copy = new(zone) UniqueSet<T>();
+    copy->size_ = this->size_;
+    copy->capacity_ = this->size_;
+    copy->array_ = zone->NewArray<Unique<T> >(this->size_);
+    memcpy(copy->array_, this->array_, this->size_ * sizeof(Unique<T>));
+    return copy;
+  }
+
+  inline int size() {
+    return size_;
+  }
+
+ private:
+  // These sets should be small, since operations are implemented with simple
+  // linear algorithms. Enforce a maximum size.
+  static const int kMaxCapacity = 65535;
+
+  uint16_t size_;
+  uint16_t capacity_;
+  Unique<T>* array_;
+
+  // Grow the size of internal storage to be at least {size} elements.
+  void Grow(int size, Zone* zone) {
+    CHECK(size < kMaxCapacity);  // Enforce maximum size.
+    if (capacity_ < size) {
+      int new_capacity = 2 * capacity_ + size;
+      if (new_capacity > kMaxCapacity) new_capacity = kMaxCapacity;
+      Unique<T>* new_array = zone->NewArray<Unique<T> >(new_capacity);
+      if (size_ > 0) {
+        memcpy(new_array, array_, size_ * sizeof(Unique<T>));
+      }
+      capacity_ = new_capacity;
+      array_ = new_array;
+    }
+  }
+};
+
+
+} }  // namespace v8::internal
+
+#endif  // V8_HYDROGEN_UNIQUE_H_