src/type-feedback-vector.h

// Copyright 2014 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_TYPE_FEEDBACK_VECTOR_H_
#define V8_TYPE_FEEDBACK_VECTOR_H_

#include "src/checks.h"
#include "src/elements-kind.h"
#include "src/heap/heap.h"
#include "src/isolate.h"
#include "src/objects.h"

namespace v8 {
namespace internal {

// The shape of the TypeFeedbackVector is an array with:
// 0: first_ic_slot_index (== length() if no ic slots are present)
// 1: ics_with_types
// 2: ics_with_generic_info
// 3: first feedback slot
// ...
// [<first_ic_slot_index>: feedback slot]
// ...to length() - 1
//
class TypeFeedbackVector : public FixedArray {
 public:
  // Casting.
  static TypeFeedbackVector* cast(Object* obj) {
    DCHECK(obj->IsTypeFeedbackVector());
    return reinterpret_cast<TypeFeedbackVector*>(obj);
  }

  static const int kReservedIndexCount = 3;
  static const int kFirstICSlotIndex = 0;
  static const int kWithTypesIndex = 1;
  static const int kGenericCountIndex = 2;

  int first_ic_slot_index() {
    DCHECK(length() >= kReservedIndexCount);
    return Smi::cast(get(kFirstICSlotIndex))->value();
  }

  int ic_with_type_info_count() {
    return length() > 0 ? Smi::cast(get(kWithTypesIndex))->value() : 0;
  }

  void change_ic_with_type_info_count(int delta) {
    if (delta == 0) return;
    int value = ic_with_type_info_count() + delta;
    // Could go negative because of the debugger.
    if (value >= 0) {
      set(kWithTypesIndex, Smi::FromInt(value));
    }
  }

  int ic_generic_count() {
    return length() > 0 ? Smi::cast(get(kGenericCountIndex))->value() : 0;
  }

  void change_ic_generic_count(int delta) {
    if (delta == 0) return;
    int value = ic_generic_count() + delta;
    if (value >= 0) {
      set(kGenericCountIndex, Smi::FromInt(value));
    }
  }

  int Slots() {
    if (length() == 0) return 0;
    return Max(0, first_ic_slot_index() - kReservedIndexCount);
  }

  int ICSlots() {
    if (length() == 0) return 0;
    return length() - first_ic_slot_index();
  }

  // Conversion from a slot or ic slot to an integer index to the underlying
  // array.
  int GetIndex(FeedbackVectorSlot slot) {
    return kReservedIndexCount + slot.ToInt();
  }

  int GetIndex(FeedbackVectorICSlot slot) {
    int first_ic_slot = first_ic_slot_index();
    DCHECK(slot.ToInt() < ICSlots());
    return first_ic_slot + slot.ToInt();
  }


  // Conversion from an integer index to either a slot or an ic slot. The caller
  // should know what kind she expects.
  FeedbackVectorSlot ToSlot(int index) {
    DCHECK(index >= kReservedIndexCount && index < first_ic_slot_index());
    return FeedbackVectorSlot(index - kReservedIndexCount);
  }

  FeedbackVectorICSlot ToICSlot(int index) {
    DCHECK(index >= first_ic_slot_index() && index < length());
    return FeedbackVectorICSlot(index - first_ic_slot_index());
  }

  Object* Get(FeedbackVectorSlot slot) { return get(GetIndex(slot)); }
  void Set(FeedbackVectorSlot slot, Object* value,
           WriteBarrierMode mode = UPDATE_WRITE_BARRIER) {
    set(GetIndex(slot), value, mode);
  }

  Object* Get(FeedbackVectorICSlot slot) { return get(GetIndex(slot)); }
  void Set(FeedbackVectorICSlot slot, Object* value,
           WriteBarrierMode mode = UPDATE_WRITE_BARRIER) {
    set(GetIndex(slot), value, mode);
  }


  static Handle<TypeFeedbackVector> Allocate(Isolate* isolate, int slot_count,
                                             int ic_slot_count);

  static Handle<TypeFeedbackVector> Copy(Isolate* isolate,
                                         Handle<TypeFeedbackVector> vector);

  // Clears the vector slots and the vector ic slots.
  void ClearSlots(SharedFunctionInfo* shared);

  // The object that indicates an uninitialized cache.
  static inline Handle<Object> UninitializedSentinel(Isolate* isolate);

  // The object that indicates a megamorphic state.
  static inline Handle<Object> MegamorphicSentinel(Isolate* isolate);

  // The object that indicates a premonomorphic state.
  static inline Handle<Object> PremonomorphicSentinel(Isolate* isolate);

  // The object that indicates a generic state.
  static inline Handle<Object> GenericSentinel(Isolate* isolate);

  // The object that indicates a monomorphic state of Array with
  // ElementsKind
  static inline Handle<Object> MonomorphicArraySentinel(
      Isolate* isolate, ElementsKind elements_kind);

  // A raw version of the uninitialized sentinel that's safe to read during
  // garbage collection (e.g., for patching the cache).
  static inline Object* RawUninitializedSentinel(Heap* heap);

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(TypeFeedbackVector);
};
}
}  // namespace v8::internal

#endif  // V8_TRANSITIONS_H_